Quantitative characterization method and device for oil-water micro-distribution in low-permeability oil reservoirs

Abstract

The specification relates to the technical field of low-permeability reservoir development, and particularly discloses a method and device for quantitatively characterizing oil-water micro-distribution in a low-permeability reservoir. The method comprises: vacuumizing and pressurizing a first core to saturate water, performing nuclear magnetic resonance (NMR) testing to obtain a saturated water NMR T2 spectrum; performing constant-rate mercury injection testing on a second core to obtain constant-rate mercury injection testing data; drying the first core, vacuumizing and pressurizing the first core to saturate deuterium water, then saturating formation crude oil by using a displacement method, performing NMR testing to obtain a saturated oil NMR T2 spectrum; displacing the first core with deuterium water, and performing NMR testing on the displaced first core to obtain a residual oil NMR T2 spectrum; and determining oil-water micro-distribution characteristics of a target reservoir based on the constant-rate mercury injection testing data, the saturated water NMR T2 spectrum, the saturated oil NMR T2 spectrum and the residual oil NMR T2 spectrum. The above scheme realizes quantitative characterization of oil-water micro-distribution in a low-permeability reservoir.

Description

TECHNICAL FIELD

[0001] The present specification relates to the technical field of low-permeability reservoir development, and in particular, to a method and device for quantitatively characterizing oil-water micro-distribution in a low-permeability reservoir. BACKGROUND

[0002] In the development of a low-permeability reservoir, the micro-distribution of oil and water in the porous medium is extremely important. On the one hand, the micro-distribution of oil and water is a manifestation of its macro-distribution and the basis for determining the macro-distribution of oil and water. The accumulation of crude oil and the distribution of residual oil are affected by the micro-distribution of oil and water. On the other hand, the micro-distribution of oil and water has a close influence on the seepage law of oil and water and the water flooding efficiency in the water flooding process. Therefore, in the low-permeability reservoir, from well placement to the development of technical policies and the tertiary oil recovery stage, the micro-distribution of oil and water is an important factor to be considered.

[0003] However, the micro-distribution of oil and water in a low-permeability reservoir cannot be accurately quantitatively characterized in the prior art.

[0004] At present, no effective solution has been proposed for the above problem. SUMMARY

[0005] The embodiments of the present specification provide a method and device for quantitatively characterizing the micro-distribution of oil and water in a low-permeability reservoir, to solve the problem that the micro-distribution of oil and water in a low-permeability reservoir cannot be accurately quantitatively characterized in the prior art.

[0006] The embodiments of the present specification provide a method for quantitatively characterizing the micro-distribution of oil and water in a low-permeability reservoir, comprising: vacuumizing and pressurizing a first core to saturate water, performing nuclear magnetic resonance testing to obtain a saturated water nuclear magnetic resonance T2 spectrum; performing a constant-speed mercury injection experiment on a second core to obtain constant-speed mercury injection experiment data; wherein the first core and the second core are cores of a target reservoir of a low-permeability reservoir; drying the first core, vacuumizing and pressurizing to saturate deuterium water, then saturating the formation crude oil by displacement, performing nuclear magnetic resonance testing to obtain a saturated oil nuclear magnetic resonance T2 spectrum; displacing the first core with deuterium water, and performing nuclear magnetic resonance testing on the displaced first core to obtain a residual oil nuclear magnetic resonance T2 spectrum; determining the micro-distribution characteristics of oil and water in the target reservoir based on the constant-speed mercury injection experiment data, the saturated water nuclear magnetic resonance T2 spectrum, the saturated oil nuclear magnetic resonance T2 spectrum, and the residual oil nuclear magnetic resonance T2 spectrum.

[0007] The embodiment of the present specification further provides a method for quantitatively characterizing oil-water micro-distribution of a low-permeability oil reservoir, comprising: obtaining a saturated water nuclear magnetic resonance T2 spectrum, a saturated oil nuclear magnetic resonance T2 spectrum and a residual oil nuclear magnetic resonance T2 spectrum of a first core; obtaining constant-rate mercury injection experiment data of a second core, wherein the first core and the second core are cores in a target reservoir of the low-permeability oil reservoir; and determining an oil-water micro-distribution characteristic of the target reservoir based on the constant-rate mercury injection experiment data, the saturated water nuclear magnetic resonance T2 spectrum, the saturated oil nuclear magnetic resonance T2 spectrum and the residual oil nuclear magnetic resonance T2 spectrum.

[0008] The embodiment of the present specification further provides a device for quantitatively characterizing oil-water micro-distribution of a low-permeability oil reservoir, comprising: a first obtaining module configured to obtain a saturated water nuclear magnetic resonance T2 spectrum, a saturated oil nuclear magnetic resonance T2 spectrum and a residual oil nuclear magnetic resonance T2 spectrum of a first core; a second obtaining module configured to obtain constant-rate mercury injection experiment data of a second core, wherein the first core and the second core are cores in a target reservoir of the low-permeability oil reservoir; and a determining module configured to determine an oil-water micro-distribution characteristic of the target reservoir based on the constant-rate mercury injection experiment data, the saturated water nuclear magnetic resonance T2 spectrum, the saturated oil nuclear magnetic resonance T2 spectrum and the residual oil nuclear magnetic resonance T2 spectrum.

[0009] The embodiment of the present specification further provides a computer device, comprising a processor and a memory for storing processor-executable instructions, wherein the processor executes the instructions to implement the steps of the method for quantitatively characterizing oil-water micro-distribution of a low-permeability oil reservoir according to any of the above embodiments.

[0010] The embodiment of the present specification further provides a computer-readable storage medium having computer instructions stored thereon, wherein the instructions are executed to implement the steps of the method for quantitatively characterizing oil-water micro-distribution of a low-permeability oil reservoir according to any of the above embodiments.

[0011] In the embodiment of the present application, a method for quantitatively characterizing oil-water micro-distribution in a low-permeability oil reservoir is provided. A first core is subjected to vacuumization and pressurization to saturate water, and a nuclear magnetic resonance test is performed to obtain a nuclear magnetic resonance T2 spectrum of the saturated water. A second core is subjected to a constant-rate mercury injection experiment to obtain constant-rate mercury injection experiment data. The first core and the second core are cores of a target reservoir of the low-permeability oil reservoir. The first core is dried, vacuumized, pressurized to saturate deuterium water, and then saturated with formation crude oil by displacement. A nuclear magnetic resonance test is performed to obtain a nuclear magnetic resonance T2 spectrum of the saturated oil. The first core is displaced with deuterium water, and a nuclear magnetic resonance test is performed on the displaced first core to obtain a nuclear magnetic resonance T2 spectrum of the residual oil. Based on the constant-rate mercury injection experiment data, the nuclear magnetic resonance T2 spectrum of the saturated water, the nuclear magnetic resonance T2 spectrum of the saturated oil, and the nuclear magnetic resonance T2 spectrum of the residual oil, the oil-water micro-distribution characteristics of the target reservoir are determined. In the above scheme, the oil-water micro-distribution characteristics in the original saturated oil state and the oil-water micro-distribution characteristics in the residual oil state after water displacement are jointly characterized by combining the constant-rate mercury injection and the nuclear magnetic resonance experiment. The problem that the oil-water distribution in the low-permeability oil reservoir during development is difficult to quantitatively characterize is solved. The quantitative characterization of the oil-water distribution in the initial saturated oil state and the oil-water distribution in the residual oil state is achieved. A solid and reliable reference basis is provided for formulating well placement schemes, development parameters, and remaining oil tapping schemes to achieve efficient development of the low-permeability oil reservoir. The method has very important significance for enhancing the recovery of the low-permeability oil reservoir. In addition, the above method has low operation cost, convenient calculation, high accuracy, strong applicability, and is convenient for wide application in various low-permeability oil fields. BRIEF DESCRIPTION OF DRAWINGS

[0012] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the present application and together with the description, serve to explain the principles of the present application. In the drawings:

[0013] Figure 1 A sampling position diagram of an experimental sample in an embodiment of the present application;

[0014] Figure 2 A nuclear magnetic resonance T2 spectrum of saturated water in an embodiment of the present application;

[0015] Figure 3 A pore throat radius distribution curve in an embodiment of the present application;

[0016] Figure 4 Nuclear magnetic resonance T2 spectra of saturated oil and residual oil in an embodiment of the present application;

[0017] Figure 5 A schematic diagram for calibrating relaxation rates based on a quasi-full-pore distribution curve and a nuclear magnetic resonance T2 spectrum in an embodiment of the present application;

[0018] Figure 6Figure 1 is a full pore distribution curve graph in an embodiment of the present specification and a pore throat size and distribution frequency curve graph;

[0019] Figure 7 Figure 1 is a full pore distribution curve graph in an embodiment of the present specification and a pore throat size and distribution frequency curve graph;

[0020] Figure 8 Figure 1 is a full pore distribution curve graph in an embodiment of the present specification and a pore throat size and distribution frequency curve graph;

[0021] Figure 9 Figure 1 is a full pore distribution curve graph in an embodiment of the present specification and a pore throat size and distribution frequency curve graph;

[0022] Figure 10 Figure 1 is a full pore distribution curve graph in an embodiment of the present specification and a pore throat size and distribution frequency curve graph;

[0023] Figure 11 Figure 1 is a full pore distribution curve graph in an embodiment of the present specification and a pore throat size and distribution frequency curve graph;

[0024] Figure 12 Figure 1 is a full pore distribution curve graph in an embodiment of the present specification and a pore throat size and distribution frequency curve graph;

[0025] Figure 13 Figure 1 is a full pore distribution curve graph in an embodiment of the present specification and a pore throat size and distribution frequency curve graph;

[0026] Figure 14 Figure 1 is a full pore distribution curve graph in an embodiment of the present specification and a pore throat size and distribution frequency curve graph;

[0027] Figure 15 Figure 1 is a full pore distribution curve graph in an embodiment of the present specification and a pore throat size and distribution frequency curve graph;

[0028] Figure 16 Figure 1 is a full pore distribution curve graph in an embodiment of the present specification and a pore throat size and distribution frequency curve graph;

[0029] Figure 17 Figure 1 is a full pore distribution curve graph in an embodiment of the present specification and a pore throat size and distribution frequency curve graph;

[0030] Figure 18 Figure 1 is a full pore distribution curve graph in an embodiment of the present specification and a pore throat size and distribution frequency curve graph;

[0031] Figure 19 Figure 1 is a full pore distribution curve graph in an embodiment of the present specification and a pore throat size and distribution frequency curve graph; DETAILED DESCRIPTION

[0032] The principles and spirit of the present specification will be described below with reference to several exemplary embodiments. It should be understood that these embodiments are given only so that those skilled in the art can better understand and implement the present specification, and do not limit the scope of the present specification in any way. On the contrary, these embodiments are provided so that the present specification disclosure is more thorough and complete, and the scope of the present disclosure is fully conveyed to those skilled in the art.

[0033] Those skilled in the art understand that the embodiments of the present specification can be implemented as a system, device, apparatus, method or computer program product. Therefore, the present specification disclosure can be specifically implemented in the following forms: complete hardware, complete software (including firmware, resident software, microcode, etc.), or a combination of hardware and software.

[0034] The main means for studying oil-water micro-distribution at present are as follows: CT imaging technology, oil-bearing thin section identification, nuclear magnetic resonance technology and numerical simulation method. Among them, CT imaging technology can quickly, accurately and non-destructively obtain high-resolution images representing the pore structure of the rock. In recent years, this technology has also been used in the visualization research of multiphase flow and reaction flow in porous media. With the help of micro-CT imaging equipment, the occurrence position, distribution characteristics and saturation distribution of each phase fluid of three fluids (water, benzyl alcohol and alkane) in the pore space are obtained, which provides a new research approach for studying micro-residual oil distribution and flow characteristics. However, CT imaging technology has the problems of high experimental cost and inability to quantitatively characterize, so it is difficult to carry out large-scale application. Oil-bearing thin section identification uses a low-viscosity and high-strength adhesive to make a core that is not contaminated and can truly reflect the distribution of underground fluids into an oil-bearing thin section. The biggest advantage of this method is that it basically maintains the distribution of fluids in the underground pore space, and the occurrence form of residual oil can be easily observed. However, the thin section preparation process is difficult, the image resolution is low, and it is usually used for simple qualitative evaluation. Nuclear magnetic resonance technology can distinguish oil and water signals by adding water-soluble paramagnetic ions to obtain oil-water distribution images. This method is used to observe the flow of oil and water in the pore space of the core and quantitatively study the saturation distribution characteristics of oil and water. However, due to the poor image quality, the analysis error is large. Numerical simulation method is an intermediate simulation method between macro and micro, which is mainly used to study the thermodynamic properties and migration mechanism of fluids, flow simulation at micro scale, and flow of complex fluids in porous media. Numerical simulation method has the characteristics of simple calculation, low cost and repeatability, and has carried out a lot of research on micro seepage and residual oil distribution. However, due to the characteristics of real core, such as pore structure and complexity, and the roughness of rock surface, the results of numerical simulation cannot represent the real distribution and migration characteristics of fluids in the rock.

[0035] Based on the above problems, the embodiment of the present specification provides a low-permeability oil reservoir oil-water micro-distribution quantitative characterization method. In the embodiment, the low-permeability oil reservoir oil-water micro-distribution quantitative characterization method can include the following steps.

[0036] First step: prepare a long 4.5 cm to 7.5 cm long and 2.5 cm wide reservoir core in a low-permeability oil reservoir, wash the core with oil, dry it, and cut a short core with a length of 0.5 cm and a width of 2.5 cm from one side of the core, as shown in Figure 1 . Figure 1 In the embodiment, the No. 1 core is a long core, and the No. 2 core is a short core. The porosity and permeability of the two cores are measured respectively, and the measurement results are shown in Table 1 below.

[0037] Table 1

[0038]

[0039] After obtaining the measurement results, it is determined whether the porosity and permeability of the long core and the short core are close. If yes, the subsequent step is performed. Otherwise, the core is prepared again. In an embodiment, it can be determined whether the difference between the permeability of the long core and the short core is within a preset range. If yes, it is determined whether the difference between the porosity of the long core and the short core is within a preset range. If yes, the subsequent step is performed. The preset range can be set according to actual conditions.

[0040] Second step: vacuum and pressurize the No. 1 core to saturate water, and the pressure added is 17 MPa. The nuclear magnetic resonance test parameters are: the radio frequency distribution range is 1-30 MHz, the control accuracy is 0.1 MHz, the echo time is set to 0.12 ms, the waiting measurement time is 1.125 s, and the scanning number is 64 times. After the nuclear magnetic resonance detection, the saturated water nuclear magnetic resonance T2 spectrum can be obtained, as shown in Figure 2 . The No. 2 core is used for constant-speed mercury injection experiment, and the constant-speed mercury injection experiment equipment model is ASPPE-730, and the mercury injection speed is 6×10 - 5 mL / min. The constant-speed mercury injection can obtain the pore throat size and distribution frequency, that is, the pore radius distribution frequency curve (or referred to as the pore size and distribution frequency curve, or referred to as the pore size distribution curve) and the throat radius distribution frequency curve (or referred to as the throat size and distribution frequency curve, or referred to as the throat size distribution curve), as shown in Figure 3 .

[0041] Step 3: Core No. 1 was dried at 105℃ for 10 hours, cooled, and then re-vacuumed and pressurized (17MPa) with 99.99% pure deuterium water. Subsequently, the formation crude oil was saturated using the displacement method at a displacement pressure of 17MPa, a displacement pressure differential of 2MPa, and a confining pressure of 19MPa, until water production ceased at the outlet for 30 consecutive minutes. The core was then aged at 52℃ and 17MPa for 600 hours. After aging, NMR testing was performed again to obtain the saturated oil NMR T2 spectrum of the crude oil, as shown below. Figure 4 The solid line in the figure shows that, since hydrogen atom signals cannot be detected in the deuterium-saturated water in the core before the oil saturation process, the NMR detects hydrogen signals in the oil after the oil saturation process.

[0042] Step 4: Under conditions of 52℃, displacement pressure 17MPa, displacement pressure differential 2MPa, and confining pressure 19MPa, core No. 1 was displaced with deuterium water until oil production ceased at the outlet for 30 consecutive minutes. Nuclear magnetic resonance (NMR) testing was then performed again. The NMR T2 spectrum of the residual oil was obtained at this point, as shown below. Figure 4 The dashed line in the figure shows the residual oil. The residual oil's nuclear magnetic resonance T2 spectrum reflects its resonance signal.

[0043] Step 5: Characterize the total porosity distribution curve of saturated water using data from constant-rate mercury intrusion porosimetry experiments and the T2 NMR spectrum of saturated water. First, establish the relationship between relaxation time and pore throat size to determine the relaxation rate. According to the NMR mechanism, since the relaxation time of water in porous media mainly reflects the surface relaxation characteristics of water, i.e., the strength of the interaction force between water and the pore surface of the porous medium, the stronger the liquid-solid interaction force, the shorter the liquid relaxation time, and vice versa. The transverse relaxation time of atoms within a single pore of saturated water in a uniform magnetic field can be approximated as:

[0044]

[0045] Where T2 is the atomic transverse relaxation time, c represents the shape factor (pore shape factor is 3, throat shape factor is 2), and V represents the pore volume in μm. 3 S represents surface area, in μm. 2 ρ is the relaxation rate, in μm / ms, and r is the pore radius, in μm.

[0046] Please refer to Figure 5 This diagram illustrates a schematic representation of an embodiment of this specification, showing the calibration of relaxation rate based on a quasi-total porosity distribution curve and an NMR T2 spectrum. The throat size and distribution frequency curve obtained by constant-rate mercury intrusion can be superimposed with the pore size and distribution frequency curve to obtain the quasi-total porosity distribution curve. For example... Figure 5As shown, the quasi-total porosity distribution curve and the total porosity distribution obtained from NMR both exhibit a bimodal shape. The two peaks in the quasi-total porosity distribution curve represent the throat distribution and the pore distribution, respectively. Figure 5 It can be seen that the quasi-total porosity distribution curve and the full porosity distribution curve have a high degree of similarity in the shape of the left peak, which meets the conditions for NMR relaxation rate calibration. Therefore, the T2 spectrum is calibrated using the left peak of the quasi-total porosity distribution curve to determine the relaxation rate. The abscissa of the left peak of the quasi-total porosity distribution curve is 0.4 μm, and the abscissa of the left peak of the full porosity distribution curve is 0.63 ms. Here, there is a small throat, and the shape factor c is 2. Substituting the above three data into Formula 1, the relaxation rate ρ is calculated to be 0.317 μm / ms.

[0047] Secondly, the calibrated relaxation rate is used to convert the saturated water NMR T2 spectrum into a pore and throat radius distribution curve, which is called the total pore distribution curve. Figure 6 As shown.

[0048] Next, subtract the distribution frequency of the throat size and distribution curve from the distribution frequency of the total pore size distribution curve to obtain the pore size and distribution frequency. Then, multiply the pore radius by the scaling factor (3 / 2) from tubular to spherical pore volume to obtain the total pore size distribution curves for tubular throats and spherical pore volumes. This represents all the pore size and distribution curves and throat size and distribution curves in the core sample. Figure 7 As shown.

[0049] Regarding the scaling factor from tubular to spherical, the tubular shape represents the throat, and the spherical shape represents the pore. In formula (1), the shape factor of the pore is 3, and the shape factor of the throat is 2. Since... Figure 5 The relaxation rate is calibrated using the throat. This relaxation rate is only suitable for the throat. Therefore, for pores, it is necessary to multiply by the tubular to spherical scaling factor to convert the relaxation rate calibrated for the throat into the relaxation rate calibrated for the pore.

[0050] Step 6: Use the relaxation rate to... Figure 4 The T2 NMR spectrum of saturated oil was converted into a curve showing the size distribution of crude oil droplets within the entire pore structure of saturated oil, also known as the pore and throat crude oil size and distribution frequency curve. The results are shown in […]. Figure 8 The solid curve in the figure is shown. The shape factor is 2, and the relaxation rate is 0.317 μm / ms.

[0051] For example, with an oil saturation of 77.5%, it is approximated that the oil content in the throat accounts for 77.5% of the throat volume. The ordinate of the throat size distribution curve under saturated water conditions can be multiplied by 0.775 to obtain the crude oil size and distribution frequency curve in the throat under saturated oil conditions (i.e., the crude oil droplet size distribution curve within the throat, or the size and distribution frequency of crude oil within the throat). The results are shown in […]. Figure 8 The dashed curve in the figure is shown.

[0052] Figure 6 shows the pore and throat residual oil droplet size and distribution frequency curves in the residual oil state. Figure 8 Figure 7 shows the pore and throat residual oil droplet size and distribution frequency curves in the residual oil state. Figure 8 Figure 8 shows the pore and throat residual oil droplet size and distribution frequency curves in the residual oil state. Figure 9 Figure 9 shows the pore and throat residual oil droplet size and distribution frequency curves in the residual oil state. Figure 9 Figure 10 shows the pore and throat residual oil droplet size and distribution frequency curves in the residual oil state. Figure 9 As shown in Figure 10, the residual oil droplet or film radius in the throat is 0.04 μm to 1.5 μm, and the most numerous oil droplet corresponds to a radius of 0.4 μm. The residual oil droplet or film radius in the pore is 0.15 μm to 603 μm, and the most numerous oil droplet corresponds to a radius of 25.4 μm, which accounts for 2.78% of the total pore volume. Since the pore is the main storage space for oil in a low permeability reservoir, and the throat is the flow space for oil, the oil and water distribution in the pore is analyzed. Figure 10 Figure 11 shows the pore and throat residual oil droplet size and distribution frequency curves in the residual oil state. Figure 10 As shown in Figure 11, the oil distribution frequency is less than the pore distribution frequency in the range of a radius greater than 40 μm, indicating that the pore is not completely filled with oil, and the remaining space is occupied by water. Therefore, the oil signal in the large pore and the oil signal in the small and medium pores are superimposed, causing the oil frequency to be greater than the pore frequency in the range of a radius less than 40 μm. Figure 10 Figure 12 shows the pore and throat residual oil droplet size and distribution frequency curves in the residual oil state. Figure 14 Figure 13 shows the pore and throat residual oil droplet size and distribution frequency curves in the residual oil state.

[0053] Step 7: Convert the residual oil NMR T2 spectrum in Figure 6 to the pore and throat radius size and distribution frequency curves using the relaxation rate, i.e., the residual oil droplet size distribution curve in the residual oil state in the full pore, which can also be referred to as the pore and throat residual oil size and distribution frequency. The results are shown by the solid curve in Figure 7. The shape factor is 2, and the relaxation rate is 0.317 μm / ms. Figure 4 Figure 11 As an example, the residual oil saturation is 44.9%, so it is approximately considered that the oil content in the throat accounts for 44.9% of the throat volume. The vertical coordinate of the throat size and distribution frequency curve in Figure 6 (i.e., the throat size distribution curve in the water-saturated state) can be multiplied by 0.449 to obtain the residual oil droplet size distribution curve in the throat, and the results are shown by the dashed curve in Figure 7 (i.e., the throat residual oil size and distribution frequency in Figure 6).

[0054] As an example, the residual oil saturation is 44.9%, so it is approximately considered that the oil content in the throat accounts for 44.9% of the throat volume. The vertical coordinate of the throat size and distribution frequency curve in Figure 6 (i.e., the throat size distribution curve in the water-saturated state) can be multiplied by 0.449 to obtain the residual oil droplet size distribution curve in the throat, and the results are shown by the dashed curve in Figure 7 (i.e., the throat residual oil size and distribution frequency in Figure 6). Figure 7 Figure 11 As an example, the residual oil saturation is 44.9%, so it is approximately considered that the oil content in the throat accounts for 44.9% of the throat volume. The vertical coordinate of the throat size and distribution frequency curve in Figure 6 (i.e., the throat size distribution curve in the water-saturated state) can be multiplied by 0.449 to obtain the residual oil droplet size distribution curve in the throat, and the results are shown by the dashed curve in Figure 7 (i.e., the throat residual oil size and distribution frequency in Figure 6). Figure 11 As an example, the residual oil saturation is 44.9%, so it is approximately considered that the oil content in the throat accounts for 44.9% of the throat volume. The vertical coordinate of the throat size and distribution frequency curve in Figure 6 (i.e., the throat size distribution curve in the water-saturated state) can be multiplied by 0.449 to obtain the residual oil droplet size distribution curve in the throat, and the results are shown by the dashed curve in Figure 7 (i.e., the throat residual oil size and distribution frequency in Figure 6).

[0055] As an example, the residual oil saturation is 44.9%, so it is approximately considered that the oil content in the throat accounts for 44.9% of the throat volume. The vertical coordinate of the throat size and distribution frequency curve in Figure 6 (i.e., the throat size distribution curve in the water-saturated state) can be multiplied by 0.449 to obtain the residual oil droplet size distribution curve in the throat, and the results are shown by the dashed curve in Figure 7 (i.e., the throat residual oil size and distribution frequency in Figure 6).​​Figure 11 The residual oil size and distribution frequency in the pores and throats under the residual oil state are subtracted from the residual oil size and distribution frequency in the throats, and the resulting curve is multiplied by 3 / 2 to convert it into a residual oil droplet size distribution curve within the pores. Figure 12 The solid line in the middle (i.e. Figure 12 The size and distribution frequency of residual oil in the pores are shown in the figure. Figure 12 The size and distribution frequency of residual oil in the throat are also shown. Figure 12 It can be seen that the radius of residual oil droplets or oil films in the throat ranges from 0.04 μm to 1.5 μm, with the most numerous oil droplets corresponding to a radius of 0.4 μm, accounting for 0.42% of the total pore volume; the radius of crude oil droplets or oil films in the pores ranges from 0.15 μm to 318 μm, with the most numerous oil droplets corresponding to a radius of 11.29 μm, accounting for 1.58% of the total pore volume. Comparing the distribution of crude oil in the saturated oil state, the radius of the largest oil droplet decreased from 603 μm to 318 μm, indicating that after water flooding, the large oil droplets were completely or partially displaced from the core, and the remaining part became smaller oil droplets that remained in the core. Figure 13 The diagram shows the porosity and the size and distribution frequency of residual oil droplets within the pores under residual oil conditions. Figure 13 It can be seen that the radius and distribution frequency of the residual oil droplets both decreased, especially for oil droplets with a radius greater than 20 μm, which showed a larger decrease, indicating that the water drive mainly displaced the large oil droplets in the pores. Figure 15 This is a local viewpoint of the residual oil state, and... Figure 13 The combination allows for quantitative characterization of residual oil size and distribution.

[0056] For example, Figure 15 The residual oil distribution morphology is mainly due to large oil droplet residues caused by the Jamin effect and small blind-end oil droplet residues caused by the pore structure. Figure 13 Analysis shows that the residual oil is mainly composed of oil with a radius greater than 10μm, which is mainly large oil droplets remaining in the pores. Therefore, during the tertiary oil recovery period, emulsification should be the main method to drive out the large oil droplets in the pores.

[0057] The method described in the above embodiments, by combining constant-rate mercury injection and nuclear magnetic resonance experiments, jointly characterized the size and distribution of oil droplets in the initial saturated oil state and the size and distribution of residual oil droplets in the residual oil state after waterflooding. This solves the problem of quantitatively characterizing oil-water distribution during the development of low-permeability reservoirs, achieving quantitative characterization of oil-water distribution in both the initial and residual oil states. It provides a solid and reliable reference for formulating well placement plans, development parameters, and residual oil tapping schemes for efficient development in low-permeability reservoirs, and is of great significance for improving oil recovery in these reservoirs. Furthermore, this method has low operating costs, is computationally convenient, highly accurate, and widely applicable, making it suitable for large-scale application in various low-permeability oilfields.

[0058] The embodiment of the present specification also provides a method for quantitatively characterizing oil-water micro-distribution in a low-permeability oil reservoir. Please refer to Figure 16 , a flow chart of the method for quantitatively characterizing oil-water micro-distribution in a low-permeability oil reservoir in an embodiment of the present specification is shown. As Figure 16 indicated, the method for quantitatively characterizing oil-water micro-distribution in a low-permeability oil reservoir provided by an embodiment of the present specification can include the following steps.

[0059] In step S161, the first core is vacuumized and pressurized to be saturated with water, and a nuclear magnetic resonance test is performed to obtain a saturated water nuclear magnetic resonance T2 spectrum; the second core is subjected to a constant-rate mercury injection experiment to obtain constant-rate mercury injection experiment data; wherein the first core and the second core are cores of a target reservoir of a low-permeability oil reservoir.

[0060] Specifically, the first core and the second core are cores in a target reservoir of a low-permeability oil reservoir. The first core is used for a nuclear magnetic resonance test, and the second core is used for a constant-rate mercury injection experiment. Due to the experimental requirements of the nuclear magnetic resonance test and the constant-rate mercury injection experiment, generally, the length of the first core is greater than the length of the second core. For example, the length of the first core can be greater than 5 cm, and the length of the second core can be 0.5 cm to 1 cm. For another example, a reservoir core with a length of 4.5 cm to 7.5 cm and a width of 2.5 cm can be prepared, the core is washed with oil, dried, and a short core with a length of 0.5 cm and a width of 2.5 cm is cut from one side of the core, and a long core is left. The long core is the first core, and the short core is the second core.

[0061] In an embodiment, the first core can be vacuumized and pressurized to be saturated with water, and the pressure applied is 17 MPa. The nuclear magnetic resonance test parameters are as follows: the radio frequency distribution range is 1-30 MHz, the control accuracy is 0.1 MHz, the echo time is set to 0.12 ms, the waiting measurement time is 1.125 s, and the scanning number is 64. The nuclear magnetic resonance test obtains a saturated water nuclear magnetic resonance T2 spectrum. The second core can be used for a constant-rate mercury injection experiment, and the constant-rate mercury injection experiment equipment model is ASPPE-730, and the mercury injection rate is 6×10 -5 mL / min. The constant-rate mercury injection experiment obtains constant-rate mercury injection experiment data. The constant-rate mercury injection experiment data can include a pore size distribution frequency curve and a throat size distribution frequency curve in a saturated water state.

[0062] In step S162, the first core is dried, vacuumized, pressurized to be saturated with deuterium water, and then saturated with formation crude oil by displacement, and a nuclear magnetic resonance test is performed to obtain a saturated oil nuclear magnetic resonance T2 spectrum.

[0063] Specifically, the first core can be dried at 105 DEG C for 10 hours, and after cooling, re-vacuumized and pressurized (17 MPa) to saturate deuterium water with a purity of 99.99%. Then, the core is saturated with formation crude oil by displacement method, with a displacement pressure of 17 MPa, a displacement pressure difference of 2 MPa, and a confining pressure of 19 MPa, until no water is produced at the outlet end in 30 consecutive minutes, and the core is aged at 52 DEG C and a pressure of 17 MPa for 600 hours. After aging, nuclear magnetic resonance test is performed again to obtain a saturated oil nuclear magnetic resonance T2 spectrum. Since no hydrogen signal can be detected in the deuterium water saturated in the core before the saturated oil process, the hydrogen signal in the oil is detected after the nuclear magnetic resonance test.

[0064] In step S163, deuterium water is used to displace the first core, and nuclear magnetic resonance test is performed on the first core after displacement to obtain a residual oil nuclear magnetic resonance T2 spectrum.

[0065] Specifically, the No. 1 core can be displaced with deuterium water under the conditions of 52 DEG C, a displacement pressure of 17 MPa, a displacement pressure difference of 2 MPa, and a confining pressure of 19 MPa, until no oil is produced at the outlet end in 30 consecutive minutes, and nuclear magnetic resonance test is performed again to obtain a residual oil nuclear magnetic resonance T2 spectrum. At this time, the T2 spectrum obtained by nuclear magnetic resonance test reflects the resonance signal of residual oil.

[0066] In step S164, based on the constant-rate mercury injection experiment data, the saturated water nuclear magnetic resonance T2 spectrum, the saturated oil nuclear magnetic resonance T2 spectrum, and the residual oil nuclear magnetic resonance T2 spectrum, the oil-water micro-distribution characteristics of the target reservoir are determined.

[0067] After obtaining the constant-rate mercury injection experiment data, the saturated water nuclear magnetic resonance T2 spectrum, the saturated oil nuclear magnetic resonance T2 spectrum, and the residual oil nuclear magnetic resonance T2 spectrum, the oil-water micro-distribution characteristics of the target reservoir can be determined based on these data. The oil-water micro-distribution characteristics can include oil-water micro-distribution characteristic data of the reservoir in the saturated oil state and the residual oil state.

[0068] In the above embodiment, the constant-rate mercury injection and nuclear magnetic resonance experiments are combined to jointly represent the oil-water micro-distribution characteristics in the original saturated oil state and the oil-water micro-distribution characteristics in the residual oil state after water displacement, solving the problem that the oil-water distribution in the development process of low-permeability reservoirs is difficult to quantitatively represent, and realizing the quantitative representation of the oil-water distribution in the initial saturated oil state and the oil-water distribution in the residual oil state, which provides a solid and reliable reference for formulating well arrangement schemes, development parameters, and remaining oil tapping schemes for high-efficiency development of low-permeability reservoirs, and has great significance for enhancing the recovery of low-permeability reservoirs. In addition, the above method has low operation cost, convenient calculation, high accuracy, and strong applicability, and is convenient for wide application in low-permeability oilfields.

[0069] In some embodiments of the present disclosure, after determining the oil-water microscopic distribution characteristics of the target reservoir, the method further includes: determining the development parameters of the target reservoir based on the oil-water microscopic distribution characteristics. In this way, the reservoir development efficiency can be improved.

[0070] In some embodiments of the present disclosure, based on the constant-rate mercury injection experiment data, the saturated water nuclear magnetic resonance T2 spectrum, the saturated oil nuclear magnetic resonance T2 spectrum and the residual oil nuclear magnetic resonance T2 spectrum, the oil-water microscopic distribution characteristics of the target reservoir are determined, which can include: determining the relaxation rate parameter based on the constant-rate mercury injection experiment data and the saturated water nuclear magnetic resonance T2 spectrum; determining the full pore size distribution curve under the saturated water state according to the constant-rate mercury injection experiment data, the relaxation rate parameter and the saturated water nuclear magnetic resonance T2 spectrum; determining the oil droplet size distribution curve under the saturated oil state according to the constant-rate mercury injection experiment data, the relaxation rate parameter and the saturated oil nuclear magnetic resonance T2 spectrum; determining the oil droplet size distribution curve under the residual oil state according to the constant-rate mercury injection experiment data, the relaxation rate parameter and the residual oil nuclear magnetic resonance T2 spectrum. In this way, the oil droplet size distribution curve under the original saturated oil state and the oil droplet size distribution curve under the residual oil state after water flooding can be determined based on the constant-rate mercury injection experiment data and the nuclear magnetic resonance T2 spectrum.

[0071] In some embodiments of the present disclosure, the constant-rate mercury injection experiment data can include a pore size distribution curve and a throat size distribution curve; accordingly, based on the constant-rate mercury injection experiment data and the saturated water nuclear magnetic resonance T2 spectrum, the relaxation rate parameter is determined, which can include: superimposing the pore size distribution curve and the throat size distribution curve to obtain a quasi-full pore size distribution curve; and using the left peak of the quasi-full pore size distribution curve to calibrate the saturated water nuclear magnetic resonance T2 spectrum to determine the relaxation rate parameter. In this way, the relaxation rate can be calibrated using the constant-rate mercury injection experiment data and the saturated water nuclear magnetic resonance T2 spectrum.

[0072] In some embodiments of the present disclosure, based on the constant-rate mercury injection experiment data, the relaxation rate parameter and the saturated water nuclear magnetic resonance T2 spectrum, the full pore size distribution curve under the saturated water state is determined, which can include: converting the saturated water nuclear magnetic resonance T2 spectrum into the full pore size distribution curve under the saturated water state using the relaxation rate parameter; subtracting the distribution frequency of the throat size distribution curve from the distribution frequency of the full pore size distribution curve to obtain the pore size distribution curve in the full pore size distribution curve; and multiplying the pore size distribution curve in the full pore size distribution curve by a tubular-to-spherical ratio factor to obtain the pore size distribution curve under the tubular throat and spherical pore volume. In this way, the pore size distribution curve under the tubular throat and spherical pore volume can be determined.

[0073] In some embodiments of the present disclosure, determining the oil droplet size distribution curve in the saturated oil state according to the constant-rate mercury injection experiment data, the relaxation rate parameter, and the saturated oil nuclear magnetic resonance T2 spectrum can include: generating a full-pore residual oil droplet size distribution curve in the saturated oil state according to the relaxation rate and the saturated oil nuclear magnetic resonance T2 spectrum; multiplying the throat size distribution curve by the residual oil saturation to obtain a residual oil droplet size distribution curve in the throat in the saturated oil state; and obtaining a pore residual oil size distribution curve in the saturated oil state based on the full-pore residual oil droplet size distribution curve in the saturated oil state and the residual oil droplet size distribution curve in the throat in the saturated oil state. According to the pore residual oil size distribution curve in the saturated oil state and the residual oil local view graph of the first core, the oil droplet size distribution curve in the residual oil state is determined. In this way, the oil droplet size distribution curve in the saturated oil state, i.e., the oil-water micro-distribution characteristics in the saturated oil state, can be obtained.

[0074] In some embodiments of the present disclosure, determining the oil droplet size distribution curve in the residual oil state according to the constant-rate mercury injection experiment data, the relaxation rate parameter, and the residual oil nuclear magnetic resonance T2 spectrum can include: generating a full-pore residual oil droplet size distribution curve in the residual oil state according to the relaxation rate and the residual oil nuclear magnetic resonance T2 spectrum; multiplying the throat size distribution curve by the residual oil saturation to obtain a residual oil droplet size distribution curve in the throat in the residual oil state; and obtaining a pore residual oil size distribution curve in the residual oil state based on the full-pore residual oil droplet size distribution curve in the residual oil state and the residual oil droplet size distribution curve in the throat in the residual oil state. According to the pore residual oil size distribution curve in the residual oil state and the residual oil local view graph of the first core, the oil droplet size distribution curve in the residual oil state is determined.

[0075] In some embodiments of the present specification, the first core is subjected to vacuumized pressurized saturated water, and nuclear magnetic resonance test is performed to obtain a saturated water nuclear magnetic resonance T2 spectrum; the second core is subjected to constant-speed mercury injection experiment to obtain constant-speed mercury injection experiment data, which can include: measuring a first porosity and a first permeability of the first core; measuring a second porosity and a second permeability of the second core; determining whether a difference between the first porosity and the second porosity is within a first preset range; in a case where it is determined that the difference between the first porosity and the second porosity is within the first preset range, determining whether a difference between the first permeability and the second permeability is within a second preset range; in a case where it is determined that the difference between the first permeability and the second permeability is within the second preset range, performing vacuumized pressurized saturated water on the first core, and performing nuclear magnetic resonance test to obtain a saturated water nuclear magnetic resonance T2 spectrum; performing constant-speed mercury injection experiment on the second core to obtain constant-speed mercury injection experiment data. In this way, the above method is only performed when the porosities and permeabilities of the first core and the second core are close, which can improve the accuracy of the determined oil-water micro-distribution characteristics, and further improve the efficiency of reservoir development based on the oil-water micro-distribution characteristics.

[0076] Each of the embodiments in the present specification is described in a progressive manner, and the same or similar parts between the embodiments can be referred to each other. Each embodiment mainly describes the difference from other embodiments. For specific description, refer to the description of the related processing embodiments described above, which will not be repeated here.

[0077] The above describes specific embodiments of the present specification. Other embodiments are within the scope of the appended claims. In some cases, the acts or steps recited in the claims can be performed in an order other than that described in the embodiments and still achieve desirable results. In addition, the processes depicted in the figures do not necessarily require the particular order shown or sequential order to achieve the desired results. In some embodiments, multitasking and parallel processing are possible or advantageous.

[0078] The embodiment of the present specification also provides a low-permeability oil reservoir oil-water micro-distribution quantitative characterization method. Although the present specification provides the method operation steps or device structures as shown in the following embodiments or drawings, more or fewer operation steps or module units can be included in the method or device based on conventional or non-inventive labor. In steps or structures that do not have necessary causality in logic, the execution order of these steps or the module structure of the device is not limited to the execution order or module structure shown in the embodiment description and the drawings of the present specification. When the method or module structure is applied to the actual device or terminal product, it can be sequentially executed or executed in parallel (for example, parallel processor or multi-thread processing environment, even distributed processing environment) according to the method or module structure shown in the embodiment or drawing.

[0079] Specifically, Figure 17 A flowchart of a low-permeability oil reservoir oil-water micro-distribution quantitative characterization method in an embodiment of the present specification is shown. As shown in Figure 17 The low-permeability oil reservoir oil-water micro-distribution quantitative characterization method provided by an embodiment of the present specification can include the following steps:

[0080] In step S171, the saturated water nuclear magnetic resonance T2 spectrum, the saturated oil nuclear magnetic resonance T2 spectrum, and the residual oil nuclear magnetic resonance T2 spectrum of the first core are obtained.

[0081] In step S172, the constant-rate mercury injection experiment data of the second core are obtained, wherein the first core and the second core are cores in a target reservoir of a low-permeability oil reservoir.

[0082] The method in the embodiment can be applied to a computer device. The computer device can obtain the saturated water nuclear magnetic resonance T2 spectrum, the saturated oil nuclear magnetic resonance T2 spectrum, and the residual oil nuclear magnetic resonance T2 spectrum of the first core. The computer device can also obtain the constant-rate mercury injection experiment data of the second core.

[0083] In one embodiment, the saturated water nuclear magnetic resonance T2 spectrum, the saturated oil nuclear magnetic resonance T2 spectrum, and the residual oil nuclear magnetic resonance T2 spectrum of the first core and the constant-rate mercury injection experiment data of the second core can be obtained by a user through an input device.

[0084] In another embodiment, after the nuclear magnetic resonance device obtains the saturated water nuclear magnetic resonance T2 spectrum, the saturated oil nuclear magnetic resonance T2 spectrum, and the residual oil nuclear magnetic resonance T2 spectrum of the first core, the saturated water nuclear magnetic resonance T2 spectrum, the saturated oil nuclear magnetic resonance T2 spectrum, and the residual oil nuclear magnetic resonance T2 spectrum of the first core can be automatically sent to the computer device.

[0085] The first core and the second core are cores in a target reservoir of a low-permeability oil reservoir. The first core is used for a nuclear magnetic resonance test, and the second core is used for a constant-rate mercury injection experiment. Due to the experimental requirements of the nuclear magnetic resonance test and the constant-rate mercury injection experiment, the length of the first core is generally greater than the length of the second core. For example, the length of the first core can be greater than 5 cm, and the length of the second core can be 0.5 cm to 1 cm. For another example, a reservoir core with a length of 4.5 cm to 7.5 cm and a width of 2.5 cm can be prepared, the core is washed with oil, dried, and a short core with a length of 0.5 cm and a width of 2.5 cm is cut from one side of the core, and a long core is left. The long core is the first core, and the short core is the second core.

[0086] In one embodiment, the first core can be vacuumized and saturated with water under pressure, and the pressure added is 17 MPa. The nuclear magnetic resonance test parameters are as follows: the radio frequency distribution range is 1-30 MHz, the control accuracy is 0.1 MHz, the echo time is set to 0.12 ms, the waiting measurement time is 1.125 s, and the scanning number is 64. The nuclear magnetic resonance T2 spectrum of the saturated water is obtained by the nuclear magnetic resonance. The second core can be used for a constant-rate mercury injection experiment. The constant-rate mercury injection experiment equipment model is ASPPE-730, and the mercury injection rate is 6×10 -5 mL / min. The constant-rate mercury injection experiment data are obtained by the constant-rate mercury injection. The constant-rate mercury injection experiment data can include the pore size distribution frequency curve and the throat size distribution frequency curve under the saturated water state.

[0087] In one embodiment, the first core can be dried at 105°C for 10 hours, and after cooling, the core is vacuumized and saturated with deuterium water with a purity of 99.99% under pressure (17 MPa). Then, the core is saturated with formation crude oil by displacement, the displacement pressure is 17 MPa, the displacement pressure difference is 2 MPa, the confining pressure is 19 MPa, until no water is produced at the outlet end in 30 consecutive minutes, and the core is aged at 52°C and under a pressure of 17 MPa for 600 hours. After aging, the nuclear magnetic test is performed again to obtain the nuclear magnetic resonance T2 spectrum of the saturated oil. Since the hydrogen atom signal of the deuterium water saturated in the core before the saturated oil process cannot be detected, the hydrogen signal in the oil is detected by the nuclear magnetic test after the saturated oil.

[0088] In one embodiment, the first core can be dried at 105°C for 10 hours, and after cooling, the core is vacuumized and saturated with deuterium water with a purity of 99.99% under pressure (17 MPa). Then, the core is saturated with formation crude oil by displacement, the displacement pressure is 17 MPa, the displacement pressure difference is 2 MPa, the confining pressure is 19 MPa, until no water is produced at the outlet end in 30 consecutive minutes, and the core is aged at 52°C and under a pressure of 17 MPa for 600 hours. After aging, the nuclear magnetic test is performed again to obtain the nuclear magnetic resonance T2 spectrum of the saturated oil. Since the hydrogen atom signal of the deuterium water saturated in the core before the saturated oil process cannot be detected, the hydrogen signal in the oil is detected by the nuclear magnetic test after the saturated oil.

[0089] Step S173, based on the constant-rate mercury injection experiment data, the saturated water nuclear magnetic resonance T2 spectrum, the saturated oil nuclear magnetic resonance T2 spectrum and the residual oil nuclear magnetic resonance T2 spectrum, determine the oil-water micro-distribution characteristics of the target reservoir.

[0090] After obtaining the constant-rate mercury injection experiment data, the saturated water nuclear magnetic resonance T2 spectrum, the saturated oil nuclear magnetic resonance T2 spectrum and the residual oil nuclear magnetic resonance T2 spectrum, the oil-water micro-distribution characteristics of the target reservoir can be determined based on these data. Among them, the oil-water micro-distribution characteristics can include oil-water micro-distribution characteristic data of the reservoir in the saturated oil state and the residual oil state.

[0091] In the above embodiment, the constant-rate mercury injection and nuclear magnetic resonance experiments are combined to jointly represent the oil-water micro-distribution characteristics in the original saturated oil state and the oil-water micro-distribution characteristics in the residual oil state after water flooding, solving the problem that the oil-water distribution in the development process of low-permeability reservoirs is difficult to quantitatively characterize, and realizing the quantitative characterization of the oil-water distribution in the initial saturated oil state and the oil-water distribution in the residual oil state. It provides a solid and reliable reference for formulating well deployment schemes, development parameters and remaining oil tapping schemes for efficient development of low-permeability reservoirs, which has great significance for enhancing the recovery of low-permeability reservoirs. In addition, the above method has low operation cost, convenient calculation, high accuracy and strong applicability, and is convenient for wide application in various low-permeability oilfields.

[0092] In some embodiments of the present specification, based on the constant-rate mercury injection experiment data, the saturated water nuclear magnetic resonance T2 spectrum, the saturated oil nuclear magnetic resonance T2 spectrum and the residual oil nuclear magnetic resonance T2 spectrum, determining the oil-water micro-distribution characteristics of the target reservoir can include: determining the relaxation rate parameter based on the constant-rate mercury injection experiment data and the saturated water nuclear magnetic resonance T2 spectrum; determining the full pore size distribution curve in the saturated water state according to the constant-rate mercury injection experiment data, the relaxation rate parameter and the saturated water nuclear magnetic resonance T2 spectrum; determining the oil droplet size distribution curve in the saturated oil state according to the constant-rate mercury injection experiment data, the relaxation rate parameter and the saturated oil nuclear magnetic resonance T2 spectrum; determining the oil droplet size distribution curve in the residual oil state according to the constant-rate mercury injection experiment data, the relaxation rate parameter and the residual oil nuclear magnetic resonance T2 spectrum.

[0093] In some embodiments of the present specification, the constant-rate mercury injection experiment data includes a pore size distribution curve and a throat size distribution curve; accordingly, based on the constant-rate mercury injection experiment data and the saturated water nuclear magnetic resonance T2 spectrum, determining the relaxation rate parameter can include: superimposing the pore size distribution curve and the throat size distribution curve to obtain a quasi-full pore size distribution curve; and using the left peak of the quasi-full pore size distribution curve to calibrate the saturated water nuclear magnetic resonance T2 spectrum to determine the relaxation rate parameter.

[0094] In some embodiments of the present disclosure, determining the full pore size distribution curve under the saturated water state according to the constant-rate mercury injection experiment data, the relaxation parameter and the saturated water nuclear magnetic resonance T2 spectrum can include: converting the saturated water nuclear magnetic resonance T2 spectrum into the full pore size distribution curve under the saturated water state by using the relaxation parameter; subtracting the distribution frequency of the throat size distribution curve from the distribution frequency of the full pore size distribution curve to obtain a pore size distribution curve in the full pore size distribution curve; and multiplying the pore size distribution curve in the full pore size distribution curve by a tubular-to-spherical scaling factor to obtain a pore size distribution curve under the volume of tubular throat and spherical pore.

[0095] In some embodiments of the present disclosure, determining the oil droplet size distribution curve under the saturated oil state according to the constant-rate mercury injection experiment data, the relaxation parameter and the saturated oil nuclear magnetic resonance T2 spectrum can include: generating a full pore-in-oil droplet size distribution curve under the saturated oil state according to the relaxation parameter and the saturated oil nuclear magnetic resonance T2 spectrum; multiplying the throat size distribution curve by the oil saturation to obtain an oil-in-throat size distribution curve under the saturated oil state; obtaining a pore-in-oil size distribution curve under the saturated oil state based on the full pore-in-oil droplet size distribution curve under the saturated oil state and the oil-in-throat size distribution curve under the saturated oil state; and determining the oil droplet size distribution curve under the saturated oil state according to the pore-in-oil size distribution curve under the saturated oil state and the local visibility map of the first core under the saturated oil state.

[0096] In some embodiments of the present disclosure, determining the oil droplet size distribution curve under the residual oil state according to the constant-rate mercury injection experiment data, the relaxation parameter and the residual oil nuclear magnetic resonance T2 spectrum can include: generating a full pore-in-oil droplet size distribution curve under the residual oil state according to the relaxation parameter and the residual oil nuclear magnetic resonance T2 spectrum; multiplying the throat size distribution curve by the residual oil saturation to obtain a residual oil-in-throat size distribution curve under the residual oil state; obtaining a pore-in-oil size distribution curve under the residual oil state based on the full pore-in-oil droplet size distribution curve under the residual oil state and the residual oil-in-throat size distribution curve under the residual oil state; and determining the oil droplet size distribution curve under the residual oil state according to the pore-in-oil size distribution curve under the residual oil state and the local visibility map of the first core under the residual oil state.

[0097] In some embodiments of the present specification, the obtaining the saturated water nuclear magnetic resonance T2 spectrum, the saturated oil nuclear magnetic resonance T2 spectrum and the residual oil nuclear magnetic resonance T2 spectrum of the first core can include: obtaining a first porosity and a first permeability of the first core; obtaining a second porosity and a second permeability of the second core; determining whether the difference between the first porosity and the second porosity is within a first preset range; in a case where it is determined that the difference between the first porosity and the second porosity is within the first preset range, determining whether the difference between the first permeability and the second permeability is within a second preset range; in a case where it is determined that the difference between the first permeability and the second permeability is within the second preset range, obtaining the saturated water nuclear magnetic resonance T2 spectrum, the saturated oil nuclear magnetic resonance T2 spectrum and the residual oil nuclear magnetic resonance T2 spectrum of the first core.

[0098] Each of the embodiments in the present specification is described in a progressive manner, and the same or similar parts between the embodiments can be referred to each other. Each of the embodiments focuses on the difference from other embodiments. For details, refer to the description of the related processing embodiments described above, which will not be repeated here.

[0099] The above describes specific embodiments of the present specification. Other embodiments are within the scope of the appended claims. In some cases, the actions or steps recited in the claims can be performed in an order different than the order in the embodiments and still achieve the desired result. In addition, the processes depicted in the figures do not necessarily require the particular order shown or sequential order to achieve the desired results. In certain implementations, multitasking and parallel processing are also possible or advantageous.

[0100] Based on the same inventive concept, the present specification also provides a device for quantitatively characterizing oil-water micro-distribution in a low-permeability oil reservoir, as described in the following embodiments. Since the device for quantitatively characterizing oil-water micro-distribution in a low-permeability oil reservoir solves the problem by the same principle as the method for quantitatively characterizing oil-water micro-distribution in a low-permeability oil reservoir, the implementation of the device for quantitatively characterizing oil-water micro-distribution in a low-permeability oil reservoir can refer to the implementation of the method for quantitatively characterizing oil-water micro-distribution in a low-permeability oil reservoir, and the repeated parts will not be repeated. The term "unit" or "module" used below can be a combination of software and / or hardware that implements a predetermined function. Although the device described in the following embodiments is preferably implemented in software, hardware, or a combination of software and hardware is also possible and contemplated. Figure 18 is a structural block diagram of the device for quantitatively characterizing oil-water micro-distribution in a low-permeability oil reservoir according to an embodiment of the present specification, as shown in Figure 18 The structure is described below.

[0101] The first obtaining module 181 is configured to obtain a saturated water nuclear magnetic resonance T2 spectrum, a saturated oil nuclear magnetic resonance T2 spectrum and a residual oil nuclear magnetic resonance T2 spectrum of a first core.

[0102] The second obtaining module 182 is configured to obtain constant-rate mercury injection experiment data of a second core, where the first core and the second core are cores in a target reservoir of a low-permeability oil reservoir.

[0103] The determining module 183 is configured to determine an oil-water micro-distribution characteristic of the target reservoir based on the constant-rate mercury injection experiment data, the saturated water nuclear magnetic resonance T2 spectrum, the saturated oil nuclear magnetic resonance T2 spectrum and the residual oil nuclear magnetic resonance T2 spectrum.

[0104] From the above description, it can be seen that the embodiments of the present specification achieve the following technical effects: combining constant-rate mercury injection and nuclear magnetic resonance experiments, jointly representing oil-water micro-distribution characteristics in an original saturated oil state and oil-water micro-distribution characteristics in a residual oil state after water flooding, solving the problem that oil-water distribution in a low-permeability oil reservoir development process is difficult to quantitatively represent, realizing quantitative representation of oil-water distribution in an initial saturated oil state and oil-water distribution in a residual oil state, providing a solid and reliable reference basis for formulating well arrangement schemes, development parameters and remaining oil tapping schemes for efficient development of low-permeability oil reservoirs, and having very important significance for enhancing oil recovery of low-permeability oil reservoirs. In addition, the above method has low operation cost, convenient calculation, high accuracy and strong applicability, and is convenient for wide application in various low-permeability oil fields.

[0105] The present specification also provides a computer device, which can specifically refer to Figure 19 The computer device provided in the present specification can specifically include an input device 191, a processor 192 and a memory 193. The memory 193 is configured to store processor-executable instructions. The processor 192 executes the instructions to implement the steps of the low-permeability oil reservoir oil-water micro-distribution quantitative representation method described in any of the above embodiments.

[0106] In the embodiment, the input device can be specifically one of main devices for information exchange between the user and the computer system. The input device can include a keyboard, a mouse, a camera, a scanner, a light pen, a handwriting input board, a voice input device, etc.; the input device is used to input raw data and programs for processing the data into the computer. The input device can also acquire data transmitted by other modules, units, devices. The processor can be implemented in any appropriate manner. For example, the processor can take the form of a microprocessor or a processor and a computer readable medium storing computer readable program code (such as software or firmware) executable by the (micro)processor, logic gates, switches, application specific integrated circuits (ASIC), programmable logic controllers, and embedded microcontrollers, etc. The memory can be specifically a memory device for saving information in modern information technology. The memory can include multiple levels, and in a digital system, as long as it can save binary data, it can be a memory; in an integrated circuit, a circuit without a physical form and with a storage function is also called a memory, such as RAM, FIFO, etc.; in a system, a storage device with a physical form is also called a memory, such as a memory stick, a TF card, etc.

[0107] In the embodiment, the functions and effects realized by the computer device can be explained in comparison with other embodiments, and will not be repeated here.

[0108] The embodiment of the present specification also provides a computer storage medium based on a low-permeability oil reservoir oil-water micro-distribution quantitative characterization method, the computer storage medium stores computer program instructions, and when the computer program instructions are executed, the steps of the low-permeability oil reservoir oil-water micro-distribution quantitative characterization method described in any of the above embodiments are realized.

[0109] In the embodiment, the storage medium includes but is not limited to random access memory (RAM), read-only memory (ROM), cache, hard disk drive (HDD), or memory card. The memory can be used to store computer program instructions. The network communication unit can be an interface set according to the standard of the communication protocol, used for network connection communication.

[0110] In the embodiment, the functions and effects realized by the program instructions stored in the computer storage medium can be explained in comparison with other embodiments, and will not be repeated here.

[0111] Obviously, those skilled in the art should understand that each module or each step of the above-mentioned embodiments of the present description can be realized by a general computing device, which can be centralized on a single computing device or distributed on a network composed of multiple computing devices, and optionally, each module or each step can be realized by program codes executable by a computing device, so that each module or each step can be stored in a storage device and executed by a computing device, and in some cases, the steps shown or described can be executed in different order, or each module or step can be manufactured into an individual integrated circuit module, or multiple modules or steps can be manufactured into a single integrated circuit module. Thus, the embodiments of the present description are not limited to any specific combination of hardware and software.

[0112] It is to be understood that the above description is intended to be illustrative and not restrictive. Many embodiments and applications other than the examples provided would be apparent to those of skill in the art upon reading the above description. The scope of the description should be determined, not with reference to the above description, but should instead be determined with reference to the appended claims, along with the full range of equivalents to which such claims are entitled. In this regard, the description contemplates that the components and / or steps recited in the claims can be combined in a number of ways to yield desired structures and / or methodologies. Thus, the description is not limited to the specific arrangements or mixtures of components or steps recited.

[0113] The above description is merely illustrative of the exemplary embodiments of the present description, and is not intended to limit the present description. The embodiments of the present description can have various modifications and changes, and all modifications, equivalent replacements, improvements, etc. within the spirit and principles of the present description should be included in the protection scope of the present description.

Claims

1. A method for quantitative characterizing the microscopic distribution of oil and water in low-permeability reservoirs, characterized in that, include: The first core was vacuum-pressurized with saturated water and subjected to nuclear magnetic resonance (NMR) testing to obtain the saturated water NMR T2 spectrum. A constant-rate mercury intrusion (MRI) experiment was performed on the second core to obtain the MRI data. The first and second cores represent cores from the target reservoir in a low-permeability oil reservoir. The MRI data includes pore size distribution curves and throat size distribution curves. The first core was dried, vacuumed, and pressurized with deuterium-saturated water. Then, the formation crude oil was saturated by displacement method, and nuclear magnetic resonance (NMR) testing was performed to obtain the saturated oil NMR T2 spectrum. The first core was then displaced with deuterium-saturated water, and the first core after displacement was subjected to NMR testing to obtain the residual oil NMR T2 spectrum. Based on the constant-rate mercury injection experiment data, the saturated water NMR T2 spectrum, the saturated oil NMR T2 spectrum, and the residual oil NMR T2 spectrum, the oil-water microstructure distribution characteristics of the target reservoir are determined. The determination of the oil-water microstructure distribution characteristics of the target reservoir based on the constant-rate mercury intrusion porosimetry (MRP) experimental data, the saturated water NMR T2 spectrum, the saturated oil NMR T2 spectrum, and the residual oil NMR T2 spectrum includes: determining the relaxation rate parameter based on the constant-rate mercury intrusion porosimetry (MRP) experimental data and the saturated water NMR T2 spectrum; determining the total pore size distribution curve under saturated water conditions based on the constant-rate mercury intrusion porosimetry (MRP) experimental data, the relaxation rate parameter, and the saturated water NMR T2 spectrum; determining the oil droplet size distribution curve under saturated oil conditions based on the constant-rate mercury intrusion porosimetry (MRP) experimental data, the relaxation rate parameter, and the saturated oil NMR T2 spectrum; and determining the oil droplet size distribution curve under residual oil conditions based on the constant-rate mercury intrusion porosimetry (MRP) experimental data, the relaxation rate parameter, and the residual oil NMR T2 spectrum. The determination of the oil droplet size distribution curve in the saturated oil state, based on the constant-rate mercury intrusion porosimetry experimental data, the relaxation rate parameter, and the saturated oil NMR T2 spectrum, includes: generating the crude oil droplet size distribution curve within the entire pore under saturated oil conditions based on the relaxation rate parameter and the saturated oil NMR T2 spectrum; multiplying the throat size distribution curve by the oil saturation to obtain the crude oil droplet size distribution curve within the throat under saturated oil conditions; obtaining the crude oil size distribution curve within the pores under saturated oil conditions based on the crude oil droplet size distribution curve within the entire pore under saturated oil conditions and the crude oil droplet size distribution curve within the throat under saturated oil conditions; and determining the oil droplet size distribution curve under saturated oil conditions based on the crude oil size distribution curve within the pores under saturated oil conditions and the saturated oil local field-view diagram of the first core, to quantitatively characterize the size and distribution frequency of oil droplets; the saturated oil local field-view diagram is obtained by observing the core slices under a microscope under saturated oil conditions. The determination of the oil droplet size distribution curve in the residual oil state, based on the constant-rate mercury intrusion porosimetry experimental data, the relaxation rate parameter, and the residual oil NMR T2 spectrum, includes: generating a residual oil droplet size distribution curve in the entire pore under the residual oil state based on the relaxation rate and the residual oil NMR T2 spectrum; multiplying the throat size distribution curve by the residual oil saturation to obtain the residual oil droplet size distribution curve in the throat under the residual oil state; obtaining the crude oil size distribution curve in the pores under the residual oil state based on the residual oil droplet size distribution curve in the entire pore under the residual oil state and the residual oil droplet size distribution curve in the throat under the residual oil state; and determining the oil droplet size distribution curve in the residual oil state based on the crude oil size distribution curve in the pores under the residual oil state and the local field-of-view map of the residual oil in the first core.

2. The method according to claim 1, characterized in that, Based on the constant-rate mercury injection experimental data and the saturated water nuclear magnetic resonance T2 spectrum, the relaxation rate parameters were determined, including: The pore size distribution curve and the throat size distribution curve are superimposed to obtain the quasi-full pore size distribution curve; The T2 nuclear magnetic resonance spectrum of the saturated water was calibrated using the left peak of the quasi-full pore size distribution curve to determine the relaxation rate parameter.

3. The method according to claim 2, characterized in that, Based on the constant-rate mercury intrusion porosimetry experimental data, the relaxation rate parameter, and the saturated water NMR T2 spectrum, the total pore size distribution curve under saturated water conditions is determined, including: The relaxation rate parameter is used to convert the saturated water nuclear magnetic resonance T2 spectrum into a full pore size distribution curve under saturated water conditions. Subtracting the distribution frequency of the throat size distribution curve from the distribution frequency of the total pore size distribution curve yields the pore size distribution curve within the total pore size distribution curve. Multiply the pore size distribution curve in the total pore size distribution curve by the scaling factor from tubular to spherical to obtain the pore size distribution curves for tubular throats and spherical pore volumes.

4. The method according to claim 1, characterized in that, The first core was vacuum-pressurized with saturated water, and nuclear magnetic resonance (NMR) tests were performed to obtain the T2 NMR spectrum of the saturated water. A constant-rate mercury intrusion porosimetry (CPI) experiment was conducted on the second core, yielding the following data: Measure the first porosity and first permeability of the first core sample; measure the second porosity and second permeability of the second core sample. Determine whether the difference between the first porosity and the second porosity is within a first preset range; If the difference between the first porosity and the second porosity is determined to be within a first preset range, it is then determined whether the difference between the first permeability and the second permeability is within a second preset range. If the difference between the first permeability and the second permeability is determined to be within a second preset range, the first core is vacuum-pressurized with saturated water and subjected to nuclear magnetic resonance (NMR) testing to obtain the saturated water NMR T2 spectrum; a constant-rate mercury intrusion test is performed on the second core to obtain constant-rate mercury intrusion test data.

5. A method for quantitative characterization of the microscopic distribution of oil and water in low-permeability reservoirs, characterized in that, include: The saturated water T2 NMR spectrum, saturated oil T2 NMR spectrum, and residual oil T2 NMR spectrum of the first core were obtained. Obtain constant-rate mercury intrusion porosimetry (CRI) data from the second core sample, wherein the first and second core samples are cores from the target reservoir of a low-permeability oil reservoir; the CRI data include pore size distribution curves and throat size distribution curves. Based on the constant-rate mercury injection experiment data, the saturated water NMR T2 spectrum, the saturated oil NMR T2 spectrum, and the residual oil NMR T2 spectrum, the oil-water microstructure distribution characteristics of the target reservoir are determined. The determination of the oil-water microstructure distribution characteristics of the target reservoir based on the constant-rate mercury intrusion porosimetry (MRP) experimental data, the saturated water NMR T2 spectrum, the saturated oil NMR T2 spectrum, and the residual oil NMR T2 spectrum includes: determining the relaxation rate parameter based on the constant-rate mercury intrusion porosimetry (MRP) experimental data and the saturated water NMR T2 spectrum; determining the total pore size distribution curve under saturated water conditions based on the constant-rate mercury intrusion porosimetry (MRP) experimental data, the relaxation rate parameter, and the saturated water NMR T2 spectrum; determining the oil droplet size distribution curve under saturated oil conditions based on the constant-rate mercury intrusion porosimetry (MRP) experimental data, the relaxation rate parameter, and the saturated oil NMR T2 spectrum; and determining the oil droplet size distribution curve under residual oil conditions based on the constant-rate mercury intrusion porosimetry (MRP) experimental data, the relaxation rate parameter, and the residual oil NMR T2 spectrum. The determination of the oil droplet size distribution curve in the saturated oil state, based on the constant-rate mercury intrusion porosimetry experimental data, the relaxation rate parameter, and the saturated oil NMR T2 spectrum, includes: generating the crude oil droplet size distribution curve within the entire pore under saturated oil conditions based on the relaxation rate parameter and the saturated oil NMR T2 spectrum; multiplying the throat size distribution curve by the oil saturation to obtain the crude oil droplet size distribution curve within the throat under saturated oil conditions; obtaining the crude oil size distribution curve within the pores under saturated oil conditions based on the crude oil droplet size distribution curve within the entire pore under saturated oil conditions and the crude oil droplet size distribution curve within the throat under saturated oil conditions; and determining the oil droplet size distribution curve under saturated oil conditions based on the crude oil size distribution curve within the pores under saturated oil conditions and the saturated oil local field-view diagram of the first core, to quantitatively characterize the size and distribution frequency of oil droplets; the saturated oil local field-view diagram is obtained by observing the core slices under a microscope under saturated oil conditions. The determination of the oil droplet size distribution curve in the residual oil state, based on the constant-rate mercury intrusion porosimetry experimental data, the relaxation rate parameter, and the residual oil NMR T2 spectrum, includes: generating a residual oil droplet size distribution curve in the entire pore under the residual oil state based on the relaxation rate and the residual oil NMR T2 spectrum; multiplying the throat size distribution curve by the residual oil saturation to obtain the residual oil droplet size distribution curve in the throat under the residual oil state; obtaining the crude oil size distribution curve in the pores under the residual oil state based on the residual oil droplet size distribution curve in the entire pore under the residual oil state and the residual oil droplet size distribution curve in the throat under the residual oil state; and determining the oil droplet size distribution curve in the residual oil state based on the crude oil size distribution curve in the pores under the residual oil state and the local field-of-view map of the residual oil in the first core.

6. A device for quantitative characterizing the microscopic distribution of oil and water in low-permeability reservoirs, characterized in that, include: The first acquisition module is used to acquire the saturated water nuclear magnetic resonance T2 spectrum, the saturated oil nuclear magnetic resonance T2 spectrum, and the residual oil nuclear magnetic resonance T2 spectrum of the first core. The second acquisition module is used to acquire constant rate mercury intrusion porosimetry (CPI) data from the second core, wherein the first core and the second core are cores from the target reservoir of a low-permeability oil reservoir; the constant rate mercury intrusion porosimetry (CPI) data includes pore size distribution curves and throat size distribution curves; The determination module is used to determine the oil-water microstructure distribution characteristics of the target reservoir based on the constant-rate mercury injection experiment data, the saturated water NMR T2 spectrum, the saturated oil NMR T2 spectrum, and the residual oil NMR T2 spectrum. Specifically, the determining module is used to: determine the relaxation rate parameter based on the constant-rate mercury intrusion porosimetry experimental data and the saturated water NMR T2 spectrum; determine the total pore size distribution curve in the saturated water state based on the constant-rate mercury intrusion porosimetry experimental data, the relaxation rate parameter, and the saturated water NMR T2 spectrum; determine the oil droplet size distribution curve in the saturated oil state based on the constant-rate mercury intrusion porosimetry experimental data, the relaxation rate parameter, and the saturated oil NMR T2 spectrum; and determine the oil droplet size distribution curve in the residual oil state based on the constant-rate mercury intrusion porosimetry experimental data, the relaxation rate parameter, and the residual oil NMR T2 spectrum. The process of determining the oil droplet size distribution curve in the saturated oil state based on the constant-rate mercury intrusion test data, the relaxation rate parameter, and the saturated oil NMR T2 spectrum includes: generating the crude oil droplet size distribution curve within the entire pores of the saturated oil state based on the relaxation rate parameter and the saturated oil NMR T2 spectrum; multiplying the throat size distribution curve by the oil saturation to obtain the crude oil droplet size distribution curve within the throat of the saturated oil state; and obtaining the saturated oil state based on the crude oil droplet size distribution curve within the entire pores of the saturated oil state and the crude oil droplet size distribution curve within the throat of the saturated oil state. The crude oil size distribution curve in the pores under saturated oil conditions; based on the crude oil size distribution curve in the pores under saturated oil conditions and the local field-of-view diagram of the saturated oil in the first core, the oil droplet size distribution curve under saturated oil conditions is determined to quantitatively characterize the size and frequency of oil droplet distribution; the local field-of-view diagram of the saturated oil is obtained by observing the core slices under a microscope under saturated oil conditions; wherein, based on the constant-rate mercury intrusion porosimetry experimental data, the relaxation rate parameter, and the residual oil nuclear magnetic resonance T2 spectrum, the oil droplet size distribution curve under residual oil conditions is determined, including: based on the relaxation rate and the residual oil nuclear magnetic resonance T2 spectrum. The residual oil droplet size distribution curve in the entire pore under residual oil conditions is generated by multiplying the throat size distribution curve by the residual oil saturation to obtain the residual oil droplet size distribution curve in the throat under residual oil conditions. Based on the residual oil droplet size distribution curve in the entire pore under residual oil conditions and the residual oil droplet size distribution curve in the throat under residual oil conditions, the crude oil size distribution curve in the pores under residual oil conditions is obtained. According to the crude oil size distribution curve in the pores under residual oil conditions and the local field of view of residual oil in the first core, the droplet size distribution curve under residual oil conditions is determined.

7. A computer device, characterized in that, It includes a processor and a memory for storing processor-executable instructions, wherein the processor, when executing the instructions, implements the steps of the method of claim 5.

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