A method and apparatus for characterizing pore connectivity

Abstract

The application discloses a pore connectivity characterization method and device. According to the corresponding relationship between porosity and nuclear magnetic signal intensity obtained by nuclear magnetic experiments on multiple standard rock samples in advance, a nuclear magnetic resonance T2 spectrum of a core saturated with prepared formation water is converted into a relaxation spectrum with the horizontal coordinate being relaxation time and the vertical coordinate being porosity component, a first porosity component cumulative value of the relaxation time being not less than a set segmentation value and a second porosity component cumulative value of the relaxation time being less than the segmentation value are determined, and a first characterization parameter of pore connectivity is obtained; a nuclear magnetic resonance T2 spectrum of the core after centrifugation is converted into a relaxation spectrum, a third porosity component cumulative value of the relaxation time being not less than the segmentation value is determined, and a ratio of the first and third porosity component cumulative values is taken as a second characterization parameter of pore connectivity; and a comprehensive characterization parameter of pore connectivity is determined according to the first and second characterization parameters. The two factors of the proportion of mesopores and macropores and the proportion of pore movable fluid can be comprehensively considered to characterize the pore connectivity.

Description

Technical Field

[0001] This invention relates to the field of reservoir evaluation technology in petroleum exploration, and in particular to a method and apparatus for characterizing pore connectivity. Background Technology

[0002] Pore ​​connectivity is a fundamental parameter characterizing pore permeability. The most basic parameter characterizing pore connectivity is reservoir permeability, which is generally expressed as the ability of gases and liquids to pass through a sample. However, for highly heterogeneous and dense reservoirs, characterizing reservoir connectivity solely through permeability is relatively simplistic. Moreover, dense reservoirs differ from conventional reservoirs in their permeation mechanisms. The permeation of dense reservoirs does not conform to Darcy's law, and its permeation process is relatively complex and subject to initiation pressure. Therefore, the permeability of dense reservoirs cannot accurately reflect the differences in sample connectivity.

[0003] Another method for characterizing reservoir connectivity is to use capillary pressure curves to reflect the pore structure characteristics of the sample, obtaining parameters reflecting reservoir connectivity and reservoir capacity. Parameters reflecting reservoir capacity mainly include maximum mercury saturation and maximum connecting pore throat radius, while parameters reflecting connectivity mainly include mercury removal efficiency and displacement pressure. Mercury removal efficiency is achieved by injecting mercury into the pores until maximum saturation is reached, then removing the mercury. The proportion of mercury removed is the mercury removal efficiency; the mercury that can be removed is considered to have been injected into the connecting pore throat. A higher mercury removal efficiency indicates better sample connectivity. Displacement pressure refers to the injection pressure at which mercury begins to enter the pore throat; the better the pore throat connectivity, the lower the displacement pressure value.

[0004] Capillary pressure curve testing is an important method for determining pore connectivity. However, during capillary pressure curve testing, the injection pressure of mercury increases with increasing mercury saturation. For tight reservoirs, a very high injection pressure is required to ensure a significant amount of mercury is injected. This high injection pressure causes corresponding changes in the pore structure of the sample, and the capillary pore connectivity changes compared to testing at lower pressures. Furthermore, rock samples used for capillary pressure curve testing cannot be used for other reservoir experiments due to mercury injection, resulting in sample waste. Summary of the Invention

[0005] In view of the above problems, the present invention is proposed to provide a pore connectivity characterization method and apparatus that overcomes or at least partially solves the above problems, and can characterize pore connectivity by comprehensively considering two factors: the proportion of medium and large pores and the proportion of movable fluid in the pores.

[0006] In a first aspect, embodiments of the present invention provide a method for characterizing pore connectivity, comprising:

[0007] Based on the relationship between porosity and NMR signal intensity obtained from NMR experiments on multiple standard rock samples, the NMR T2 spectrum of the saturated formation water core is converted into a first relaxation spectrum with relaxation time on the horizontal axis and porosity component on the vertical axis. Based on the first relaxation spectrum, the cumulative value of the first porosity component with a relaxation time not less than a set relaxation time segment value and the cumulative value of the second porosity component with a relaxation time less than the segment value are determined. The ratio of the cumulative value of the first porosity component to the cumulative value of the second porosity component is used as the first characterization parameter of pore connectivity.

[0008] Based on the relationship between porosity and NMR signal intensity, the NMR T2 spectrum of the core after centrifugation according to the set rules is converted into a second relaxation spectrum with relaxation time on the horizontal axis and porosity component on the vertical axis. Based on the second relaxation spectrum, a third porosity component cumulative value with relaxation time not less than the segmentation value is determined. The ratio of the first porosity component cumulative value to the third porosity component cumulative value is used as the second characterization parameter of pore connectivity.

[0009] The comprehensive characterization parameters of pore connectivity are determined based on the first characterization parameter and the second characterization parameter.

[0010] In a second aspect, embodiments of the present invention provide a pore connectivity characterization device, comprising:

[0011] The first characterization parameter determination device is used to convert the nuclear magnetic resonance T2 spectrum of the saturated formation water core into a first relaxation spectrum with relaxation time as the horizontal axis and porosity component as the vertical axis, based on the correspondence between porosity and nuclear magnetic resonance signal intensity obtained in advance through nuclear magnetic resonance experiments of multiple standard rock samples. Based on the first relaxation spectrum, it determines the cumulative value of the first porosity component with a relaxation time not less than a set relaxation time segment value and the cumulative value of the second porosity component with a relaxation time less than the segment value. The ratio of the cumulative value of the first porosity component to the cumulative value of the second porosity component is used as the first characterization parameter of pore connectivity.

[0012] The second characterization parameter determination device is used to convert the nuclear magnetic resonance T2 spectrum of the core after centrifugation according to a set rule into a second relaxation spectrum with relaxation time on the horizontal axis and porosity component on the vertical axis, based on the correspondence between porosity and nuclear magnetic resonance signal intensity, and to determine a third porosity component cumulative value with relaxation time not less than the segmentation value based on the second relaxation spectrum, and to use the ratio of the first porosity component cumulative value to the third porosity component cumulative value as the second characterization parameter of pore connectivity.

[0013] A comprehensive characterization parameter determination device is used to determine comprehensive characterization parameters of pore connectivity based on the first characterization parameter and the second characterization parameter.

[0014] Thirdly, embodiments of the present invention provide a computer program product with a porosity connectivity characterization function, including a computer program / instruction, wherein the computer program / instruction implements the above-mentioned porosity connectivity characterization method when executed by a processor.

[0015] The beneficial effects of the above-described technical solutions provided in the embodiments of the present invention include at least the following:

[0016] The pore connectivity characterization method provided in this invention, based on the correspondence between porosity and NMR signal intensity obtained from NMR experiments on multiple standard rock samples, converts the NMR T2 spectrum of a saturated formation water core into a first relaxation spectrum with relaxation time on the horizontal axis and porosity component on the vertical axis. It then determines the cumulative value of the first porosity component with a relaxation time not less than a set segmentation value and the cumulative value of the second porosity component with a relaxation time less than the segmentation value, thus obtaining a first characterization parameter for pore connectivity. A larger relaxation time indicates a larger pore size; therefore, this first characterization parameter can characterize the proportion of larger pores in the rock sample. The proportion is determined by converting the nuclear magnetic resonance T2 spectrum of the centrifuged core into a second relaxation spectrum, and determining the cumulative value of the third porosity component with a relaxation time not less than the segmentation value. The ratio of the cumulative values ​​of the first and third porosity components is used as the second characterization parameter of pore connectivity. After centrifugation, the mobile water in the pores is driven out, so the second characterization parameter reflects the proportion of connected pores in the rock sample. Based on the first and second characterization parameters, a comprehensive characterization parameter of pore connectivity is determined. The comprehensive characterization parameter can combine the proportion of macropores and the proportion of connected pores, and more comprehensively and reasonably characterize the pore connectivity.

[0017] (2) The pore connectivity characterization method provided in the embodiments of the present invention has a wide range of applications and can be applied to the pore connectivity characterization of various types of reservoirs such as tight reservoirs, and the experimental process is non-destructive to rock samples.

[0018] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0019] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings:

[0020] Figure 1 This is a flowchart of the pore connectivity characterization method in an embodiment of the present invention;

[0021] Figure 2 This is an example diagram illustrating the determination of relaxation spectrum and first and second characterization parameters in an embodiment of the present invention;

[0022] Figure 3 This is an example diagram of the capillary pressure curve of the sample in an embodiment of the present invention;

[0023] Figure 4 The NMR relaxation spectra of saturated samples and the proportion of NMR porosity components in pores of different scales;

[0024] Figure 5 The nuclear magnetic resonance relaxation spectra before and after centrifugation;

[0025] Figure 6 This is a schematic diagram of the pore connectivity characterization device in an embodiment of the present invention. Detailed Implementation

[0026] Exemplary embodiments of the present disclosure will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.

[0027] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0028] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0029] In the description of this invention, it should be noted that the terms "comprising," "including," "having," "containing," etc., are all open-ended terms, meaning that they include but are not limited to. Furthermore, the terms "first," "second," and "third," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0030] To address the issues in existing technologies where the permeability of tight reservoirs cannot accurately reflect the pore connectivity of samples, and where capillary pressure curve testing methods for analyzing pore connectivity have significant errors and damage the samples, this invention provides a method and apparatus for characterizing pore connectivity. This method can characterize pore connectivity by comprehensively considering two factors: the proportion of mesopores and macropores, and the proportion of movable fluid in the pores. Furthermore, the experimental process is non-destructive to the rock samples.

[0031] This invention is a method for determining pore connectivity based on nuclear magnetic resonance (NMR) rock sample testing. The theoretical basis is that hydrogen nuclei in a sample undergo NMR in a stable magnetic field. After the stable magnetic field is removed, the orientation of the hydrogen nuclei in the rock sample returns to its original disordered distribution. There is a change in the orientation of the hydrogen nuclei from the application of the fixed magnetic field to its removal; the time for this change is called the relaxation time. The distribution characteristics of the relaxation time during this process can reflect the fluid and pore distribution characteristics within the pores. Since the relaxation time is positively correlated with the pore throat scale after the pores are saturated with fluid, and also positively correlated with the proportion of movable fluid, it is assumed that movable fluid is mainly located in the connected pore throats. Therefore, the connectivity of the rock sample can be reflected by the proportion of movable fluid and the relaxation spectrum characteristics of the rock sample.

[0032] Example

[0033] This invention provides a method for characterizing pore connectivity, the process of which is as follows: Figure 1 As shown, it includes the following steps:

[0034] Step S11: Based on the correspondence between porosity and NMR signal intensity obtained from NMR experiments on multiple standard rock samples, the NMR T2 spectrum of the saturated formation water core is converted into the first relaxation spectrum with relaxation time on the horizontal axis and porosity component on the vertical axis.

[0035] Specifically, the aforementioned core samples can be obtained through the following steps:

[0036] After the core oil is washed and dried, formation water is prepared by saturating it using a vacuum pressurized water saturation device.

[0037] Furthermore, the core sample selected can be a core drill plunger (plunger length 3-5cm, diameter 2.5cm), or alternatively, the core sample can be of other shapes or sizes.

[0038] The core is washed with a solution made of kerosene and benzene for 5 to 7 days until the solution becomes transparent. The core is then removed and dried.

[0039] Based on the analysis results of the formation water sample ion concentration, a formation water solution was prepared. The dried core was placed in a vacuum pressurization saturation device, and after being evacuated for 8 hours, the formation water was saturated at a pressure of 20 MPa for 72 hours.

[0040] The relationship between porosity and NMR signal intensity can be predetermined through the following steps:

[0041] The nuclear magnetic resonance (NMR) signal intensity of multiple rock samples with known porosity and saturated formation water was tested in advance to obtain the correspondence between porosity and NMR signal intensity.

[0042] This involves testing the NMR signal intensity of at least 3-5 samples with known porosity, and establishing a correlation between porosity and NMR signal intensity based on the test results. Samples with known porosity are used as standard calibration samples.

[0043] Based on the obtained correspondence between porosity and NMR signal intensity, the standard calibrated sample is used for calibration (with consistent NMR test parameters). The signal intensity in the T2 spectrum is converted into porosity, resulting in the first relaxation spectrum with relaxation time (which can be the logarithm of relaxation time) on the horizontal axis and porosity component on the vertical axis.

[0044] Step S12: Determine the cumulative value of the first porosity component with a relaxation time not less than the set relaxation time segment value and the cumulative value of the second porosity component with a relaxation time less than the segment value based on the first relaxation spectrum. Use the ratio of the cumulative value of the first porosity component to the cumulative value of the second porosity component as the first characterization parameter of pore connectivity.

[0045] Specifically, the relaxation time segment value can be determined through the following steps:

[0046] The minimum throat radius of mesopores is determined according to the pore classification standard. Based on the correspondence between relaxation time and throat radius, the relaxation time corresponding to the minimum throat radius is determined as the set relaxation time segment value. Since the relaxation time is positively correlated with the pore radius, the relaxation time segment value can be used to segment pores with larger radii (mesopores and above) and pores with smaller radii (pores below mesopores, including micropores and pores below micropores).

[0047] The first relaxation spectrum uses the porosity component as the ordinate, where the porosity component specifically refers to the ratio of the pore volume to the rock sample volume corresponding to the pore radius at the given relaxation time. Therefore, the envelope area of ​​the relaxation spectrum, i.e., the area enclosed by the spectrum curve and the relaxation time axis, reflects the magnitude of the total porosity.

[0048] Specifically, in some embodiments, the execution of step S12 may include:

[0049] Determine the envelope region enclosed by the relaxation spectral line and the relaxation time axis in the first relaxation spectrum; determine the area of ​​the envelope region to the right of the set relaxation time division value as the cumulative value of the first porosity component, and determine the area of ​​the envelope region to the left of the division value as the cumulative value of the second porosity component.

[0050] See Figure 2 As shown, the envelope region enclosed by the relaxation spectral lines and the relaxation time axis in the first relaxation spectrum is located to the right of the set relaxation time division value, as follows: Figure 2 The right-hand filling region is shown in the image; the envelope region enclosed by the relaxation spectral line and the relaxation time axis is the part to the left of the set relaxation time division value, as shown in the image. Figure 2 The left-hand filling area is shown in the diagram.

[0051] Step S13: Based on the correspondence between porosity and NMR signal intensity, the NMR T2 spectrum of the core after centrifugation according to the set rules is converted into a second relaxation spectrum with relaxation time on the horizontal axis and porosity component on the vertical axis.

[0052] Centrifuging the core according to a set rule can specifically include:

[0053] After centrifuging the core at the currently set centrifugation speed, obtain the nuclear magnetic resonance T2 spectrum after centrifugation until the current obtained nuclear magnetic resonance T2 spectrum matches the most recently obtained nuclear magnetic resonance T2 spectrum to meet the set conditions, and the current set centrifugation speed is greater than the set centrifugation speed of the most recently obtained centrifugation.

[0054] The obtained nuclear magnetic resonance T2 spectrum no longer changed, indicating that the centrifugation was relatively thorough and the mobile water had been basically expelled.

[0055] Step S14: Determine the cumulative value of the third porosity component with a relaxation time not less than the segmentation value based on the second relaxation spectrum, and use the ratio of the cumulative value of the first porosity component to the cumulative value of the third porosity component as the second characterization parameter of pore connectivity.

[0056] Determine the envelope region enclosed by the relaxation spectral line and the relaxation time axis in the second relaxation spectrum; determine the area of ​​this envelope region to the right of the segmentation value as the cumulative value of the third porosity component.

[0057] Step S15: Determine the comprehensive characterization parameters of pore connectivity based on the first characterization parameter and the second characterization parameter.

[0058] In some embodiments, the square root of the product of the first characterization parameter and the second characterization parameter can be determined as the comprehensive characterization parameter of pore connectivity.

[0059] The pore connectivity of rock samples was analyzed based on the first characterization parameter, the second characterization parameter, and the comprehensive characterization parameter. The larger the first characterization parameter, the higher the proportion of mesopores and above in the rock sample. The larger the second characterization parameter, the higher the proportion of connected pores in the rock sample. The larger the comprehensive characterization parameter, the better the pore connectivity of the rock sample.

[0060] The pore connectivity characterization method provided in this invention, based on the correspondence between porosity and NMR signal intensity obtained from NMR experiments on multiple standard rock samples, converts the NMR T2 spectrum of a saturated formation water core into a first relaxation spectrum with relaxation time on the horizontal axis and porosity component on the vertical axis. It then determines the cumulative value of the first porosity component with a relaxation time not less than a set segmentation value and the cumulative value of the second porosity component with a relaxation time less than the segmentation value, thus obtaining a first characterization parameter for pore connectivity. A larger relaxation time indicates a larger pore size; therefore, this first characterization parameter can characterize the proportion of larger pores in the rock sample. The proportion is determined by converting the nuclear magnetic resonance T2 spectrum of the centrifuged core into a second relaxation spectrum, and determining the cumulative value of the third porosity component with a relaxation time not less than the segmentation value. The ratio of the cumulative values ​​of the first and third porosity components is used as the second characterization parameter of pore connectivity. After centrifugation, the mobile water in the pores is driven out, so the second characterization parameter reflects the proportion of connected pores in the rock sample. Based on the first and second characterization parameters, a comprehensive characterization parameter of pore connectivity is determined. The comprehensive characterization parameter can combine the proportion of macropores and the proportion of connected pores, and more comprehensively and reasonably characterize the pore connectivity.

[0061] The pore connectivity characterization method provided in this invention has a wide range of applications and can be used to characterize the pore connectivity of various types of reservoirs, such as tight reservoirs, and the experimental process is non-destructive to rock samples.

[0062] Taking a core sample of lacustrine carbonate rock as an example, the above method is illustrated. The sample is characterized by the following features: it is mainly composed of calcite, dolomite, and a small amount of detrital particles and gypsum and other salt minerals. The lithology is mainly argillaceous / marl (cloud) rock, gypsum-bearing lime (cloud) rock, algal lime (cloud) rock, and granular lime (cloud) rock. According to the pore scanning of the cast thin section, the observation of the scanning electron microscope, and the mercury porosimetry analysis of the sample, the sample has developed pores and fractures of various sizes. The pores are divided into nano- to micron-scale dolomite intercrystalline pores and intercrystalline dissolution pores (sample C9), micron- to millimeter-scale carbonate rock dissolution pores (sample C20), and micron- to millimeter-scale interlayer fractures, fracture formations, and interconnected fractures (sample S27).

[0063] See Figure 3 The results of mercury intrusion porosimetry for samples S27, C20, and C9 are shown in Table 1. These include mercury intrusion and withdrawal curves (the relationship between mercury saturation and capillary pressure) and the relationship between pore throat radius and frequency. Based on these results, the pore structure parameters of each sample are shown in Table 1. Samples S27 and C20 have relatively coarse pore asymmetry and large median pore radius. These two types of samples have a higher proportion of coarse pore throats. Sample C9 has a higher median mercury intrusion pressure, indicating a poorer pore structure.

[0064] Table 1 Pore structure parameters of experimental samples

[0065] S27 9.48 1.63 0.35 2.93 0.28 1.48 0.50 1.19 90.41 18.84 C20 6.82 0.32 0.44 1.65 0.16 1.45 0.51 0.17 90.78 20.97 C9 7.29 0.17 -0.19 2.28 0.17 20.19 0.04 0.61 88.86 45.67

[0066] Existing technologies generally determine pore connectivity based on parameters such as permeability, displacement pressure, and mercury removal efficiency. However, according to physical properties and mercury intrusion porosimetry results, samples with higher permeability have lower mercury removal efficiency. It is generally believed that samples with better connectivity have higher permeability and correspondingly higher mercury removal efficiency, but current test results cannot determine the connectivity of samples.

[0067] Since there are contradictions in the results of physical property testing and mercury porosimetry in determining connectivity, this embodiment adopts the method of nuclear magnetic resonance testing to determine pore connectivity.

[0068] First, based on the NMR test results of the samples after saturation with fluid, the pore type and the relative proportion of pores at different scales were analyzed according to the NMR relaxation spectra. NMR tests were performed on the three samples after saturation with formation water. The final relaxation spectra (T2 spectra) and the proportion of NMR porosity components at different pore scales for each sample are shown in [reference needed]. Figure 4 As shown, the cumulative porosity component includes the porosity component with a relaxation time of less than 10ms (micropores, small pores), the cumulative porosity component with a relaxation time in the interval [10ms, 100ms] (medium pores), and the cumulative porosity component with a relaxation time of more than 100ms (large pores, super-large pores). The results of NMR experiments on multiple samples showed that: the NMR relaxation spectrum of the sample with micron-millimeter scale interlayer fractures, tectonic fractures, and interconnected pores (sample S27) after saturation with fluid exhibited a single-peak distribution, with the peak value distributed between 1 and 10 ms. This sample developed intercrystalline pores and interlayer fractures connected to intercrystalline pores, with micropores and mesopores accounting for a relatively high proportion of porosity components. The NMR relaxation spectrum of the carbonate rock with micron-millimeter scale karst pores (sample C20) exhibited a bimodal distribution, with the peak values ​​concentrated in two intervals: 0.1–1 ms and 10–1000 ms. The porosity component of macropores accounted for a relatively high proportion. This type of sample developed mesopores and larger dissolution pores. The NMR relaxation spectrum of the dolomite with nano-micron scale intercrystalline pores and intercrystalline dissolution pores (sample C9) exhibited a single-peak distribution, with the peak value distributed between 0.01 and 10 ms, with intercrystalline pores being the dominant feature.

[0069] Based on the statistical results of porosity components within different pore throat radius ranges, the ratio of porosity components of mesopores and larger to those of micropores (parameter a) was calculated. The results show that the parameter a value is 0.2 for samples with interconnected interlayer fractures, tectonic fractures, and cracks at the micron to millimeter scale (sample S27); the parameter a value is 0.45 for carbonate karst cavities at the micron to millimeter scale (sample C20); and the parameter a value is 0.04 for dolomite intercrystalline pores and intercrystalline dissolution pores at the nanometer to micron scale (sample C9).

[0070] Next, the sample was subjected to multiple centrifugations and NMR tests until the NMR relaxation spectrum before and after the final centrifugation no longer changed. The changes in the NMR relaxation spectrum of the sample before centrifugation and after the final centrifugation were compared to obtain the desired results. Figure 5 The NMR relaxation spectra before and after centrifugation and the cumulative curves of NMR porosity components obtained from them are shown. The envelope area of ​​the relaxation spectrum represents the porosity occupied by the fluid in the pores. The greater the change in the envelope area of ​​the spectrum before and after centrifugation, the higher the proportion of mobile fluid discharged during centrifugation, and the better the sample connectivity. The calculated parameter b (the ratio of the cumulative value of the porosity components of the mesopores and above before centrifugation to the cumulative value of the porosity components of the mesopores and above after the last centrifugation) shows that: the parameter b value of the sample with micron-millimeter scale interlayer fractures, tectonic fractures and cracks (sample S27) is 2.28; the parameter b value of the sample with micron-millimeter scale carbonate karst pores (sample C20) is 1.81; and the parameter b value of the sample with nano-micron scale dolomite intercrystalline pores and intercrystalline dissolution pores (sample C9) is 1.05.

[0071] The parameter b mentioned above can be calculated not only using the envelope area method introduced earlier, but also through... Figure 5 Calculate based on the right-hand diagram, according to Figure 5 The cumulative curves of nuclear magnetic resonance porosity components before and after centrifugation are used to determine the porosity component values ​​before and after centrifugation at the relaxation time segment (e.g., 10 ms), and the ratio between the two is calculated as parameter b.

[0072] The pore connectivity discrimination parameter (c) is calculated according to the formula determined by this method. The pore connectivity discrimination parameters for three types of samples were calculated separately. The discrimination parameter c-value for samples with interconnected interlayer fractures, tectonic fractures, and cracks at the micrometer to millimeter scale (sample S27) was 0.67; the discrimination parameter c-value for carbonate karst pores at the micrometer to millimeter scale (sample C20) was 0.90; and the discrimination parameter c-value for dolomite intercrystalline pores and intercrystalline dissolution pores at the nanometer to micrometer scale (sample C9) was 0.20. According to the pore connectivity discrimination method, the samples with interconnected carbonate karst pores had the best pore connectivity. Although the samples with interconnected interlayer fractures, tectonic fractures, and cracks had a higher proportion of mobile fluid in the pores, the samples with cracks had poor pore connectivity except for cracks, and the overall connectivity was not as good as the samples with interconnected dissolution pores. The discrimination results are more consistent with the pore development characteristics of the samples themselves.

[0073] Based on the inventive concept of this invention, embodiments of this invention also provide a pore connectivity characterization device, the structure of which is as follows: Figure 6 As shown, it includes:

[0074] The first characterization parameter determination device 61 is used to convert the nuclear magnetic resonance T2 spectrum of the saturated formation water core into a first relaxation spectrum with relaxation time as the horizontal axis and porosity component as the vertical axis, based on the correspondence between porosity and nuclear magnetic signal intensity obtained in advance through nuclear magnetic resonance experiments of multiple standard rock samples. Based on the first relaxation spectrum, it determines the cumulative value of the first porosity component with a relaxation time not less than a set relaxation time segment value and the cumulative value of the second porosity component with a relaxation time less than the segment value. The ratio of the cumulative value of the first porosity component to the cumulative value of the second porosity component is used as the first characterization parameter of pore connectivity.

[0075] The second characterization parameter determination device 62 is used to convert the nuclear magnetic resonance T2 spectrum of the core after centrifugation according to a set rule into a second relaxation spectrum with relaxation time on the horizontal axis and porosity component on the vertical axis, based on the correspondence between porosity and nuclear magnetic resonance signal intensity, and to determine a third porosity component cumulative value with relaxation time not less than the segmentation value based on the second relaxation spectrum, and to use the ratio of the first porosity component cumulative value to the third porosity component cumulative value as the second characterization parameter of pore connectivity.

[0076] The comprehensive characterization parameter determination device 63 is used to determine the comprehensive characterization parameter of pore connectivity based on the first characterization parameter and the second characterization parameter.

[0077] In some embodiments, the comprehensive characterization parameter determination device 63 is specifically used for:

[0078] The square root of the product of the first characterization parameter and the second characterization parameter is determined as the comprehensive characterization parameter of pore connectivity.

[0079] Regarding the apparatus in the above embodiments, the specific manner in which each module performs its operation has been described in detail in the embodiments related to the method, and will not be elaborated upon here.

[0080] Based on the inventive concept of the present invention, embodiments of the present invention also provide a computer program product with a porosity connectivity characterization function, including a computer program / instruction, wherein the computer program / instruction implements the above-mentioned porosity connectivity characterization method when executed by a processor.

[0081] It should be understood that the specific order or hierarchy of steps in the disclosed process is an example of an exemplary method. Based on design preferences, it should be understood that the specific order or hierarchy of steps in the process may be rearranged without departing from the scope of this disclosure. The appended method claims provide elements of various steps in an exemplary order and are not intended to limit the scope to the specific order or hierarchy described.

[0082] In the detailed description above, various features are combined together in a single embodiment to simplify this disclosure. This approach to disclosure should not be construed as reflecting an intention that embodiments of the claimed subject matter require more features than are explicitly stated in each claim. Rather, as reflected in the appended claims, the invention is presented with fewer features than all of the features in a single disclosed embodiment. Therefore, the appended claims are hereby explicitly incorporated into the detailed description, with each claim representing a separate preferred embodiment of the invention.

[0083] The foregoing description includes examples of one or more embodiments. It is certainly impossible to describe all possible combinations of components or methods in order to describe the above embodiments, but those skilled in the art will recognize that further combinations and arrangements of the various embodiments are possible. Therefore, the embodiments described herein are intended to cover all such changes, modifications, and variations that fall within the scope of the appended claims. Furthermore, the term "comprising" as used in the specification or claims is interpreted in a manner similar to the term "including," as interpreted when used as a conjunction in the claims. Additionally, the use of any term "or" in the specification of the claims is intended to mean "non-exclusive or."

Claims

1. A method for characterizing pore connectivity, characterized in that, include: Based on the relationship between porosity and NMR signal intensity obtained from NMR experiments on multiple standard rock samples, the NMR T2 spectrum of the saturated formation water core is converted into a first relaxation spectrum with relaxation time on the horizontal axis and porosity component on the vertical axis. Based on the first relaxation spectrum, the cumulative value of the first porosity component with a relaxation time not less than a set relaxation time segment value and the cumulative value of the second porosity component with a relaxation time less than the set relaxation time segment value are determined. The ratio of the cumulative value of the first porosity component to the cumulative value of the second porosity component is used as the first characterization parameter of pore connectivity. Based on the relationship between porosity and NMR signal intensity, the NMR T2 spectrum of the core after centrifugation according to the set rules is converted into a second relaxation spectrum with relaxation time on the horizontal axis and porosity component on the vertical axis. Based on the second relaxation spectrum, a third porosity component cumulative value with a relaxation time not less than the set relaxation time segment value is determined. The ratio of the first porosity component cumulative value to the third porosity component cumulative value is used as the second characterization parameter of pore connectivity. The comprehensive characterization parameter of pore connectivity is determined based on the first characterization parameter and the second characterization parameter. The core is centrifuged according to a set rule, specifically including: after centrifuging the core at the current set centrifugation speed, the nuclear magnetic resonance T2 spectrum after the current centrifugation is obtained until the currently obtained nuclear magnetic resonance T2 spectrum is the same as the most recently obtained nuclear magnetic resonance T2 spectrum, wherein the current set centrifugation speed is greater than the set centrifugation speed of the most recently centrifuged centrifugation. The set relaxation time segment value is determined by the following steps: determining the minimum throat radius of the mesopore according to the pore classification standard; and determining the relaxation time corresponding to the minimum throat radius as the set relaxation time segment value based on the correspondence between relaxation time and throat radius.

2. The method as described in claim 1, characterized in that, The determination of the comprehensive characterization parameters of pore connectivity based on the first characterization parameter and the second characterization parameter specifically includes: The square root of the product of the first characterization parameter and the second characterization parameter is determined as the comprehensive characterization parameter of pore connectivity.

3. The method as described in claim 1, characterized in that, Also includes: The pore connectivity of the rock sample is analyzed based on the first characterization parameter, the second characterization parameter, and the comprehensive characterization parameter. The larger the first characterization parameter, the higher the proportion of mesopores and above in the rock sample. The larger the second characterization parameter, the higher the proportion of connected pores in the rock sample. The larger the comprehensive characterization parameter, the better the pore connectivity of the rock sample.

4. The method as described in claim 1, characterized in that, The step of determining the cumulative value of the first porosity component with a relaxation time not less than a set relaxation time segment value and the cumulative value of the second porosity component with a relaxation time less than the set relaxation time segment value based on the first relaxation spectrum specifically includes: Determine the envelope region enclosed by the relaxation spectral lines and the relaxation time axis in the first relaxation spectrum; The area of ​​the envelope region to the right of the set relaxation time division value is determined as the cumulative value of the first porosity component, and the area of ​​the envelope region to the left of the set relaxation time division value is determined as the cumulative value of the second porosity component; correspondingly, The step of determining the cumulative value of the third porosity component, whose relaxation time is not less than the set relaxation time segment value, based on the second relaxation spectrum specifically includes: Determine the envelope region enclosed by the relaxation spectral lines and the relaxation time axis in the second relaxation spectrum; The area to the right of the set relaxation time division value of the envelope region is determined as the cumulative value of the third porosity component.

5. The method according to any one of claims 1 to 4, characterized in that, The core was obtained through the following steps: After the core oil is washed and dried, formation water is prepared by saturating it using a vacuum pressurized water saturation device.

6. The method as described in claim 5, characterized in that, The preparation of formation water by vacuum pressurization and saturation using a saturation device specifically includes: The formation water was saturated and prepared for 72 hours under a pressure of 20 MPa using a vacuum pressurization saturation device.

7. A device for characterizing pore connectivity, characterized in that, The apparatus is used to perform the pore connectivity characterization method according to claim 1, the apparatus comprising: The first characterization parameter determination device is used to convert the nuclear magnetic resonance T2 spectrum of the saturated formation water core into a first relaxation spectrum with relaxation time as the horizontal axis and porosity component as the vertical axis, based on the correspondence between porosity and nuclear magnetic resonance signal intensity obtained in advance through nuclear magnetic resonance experiments of multiple standard rock samples. Based on the first relaxation spectrum, it determines the cumulative value of a first porosity component with a relaxation time not less than a set relaxation time segment value and the cumulative value of a second porosity component with a relaxation time less than the set relaxation time segment value. The ratio of the cumulative value of the first porosity component to the cumulative value of the second porosity component is used as the first characterization parameter of pore connectivity. The second characterization parameter determination device is used to convert the nuclear magnetic resonance T2 spectrum of the core after centrifugation according to a set rule into a second relaxation spectrum with relaxation time on the horizontal axis and porosity component on the vertical axis, based on the correspondence between porosity and nuclear magnetic resonance signal intensity; determine a third cumulative value of porosity component with relaxation time not less than the set relaxation time segment value based on the second relaxation spectrum; and use the ratio of the first cumulative value of porosity component to the third cumulative value of porosity component as a second characterization parameter of pore connectivity. The centrifugation of the core according to the set rule specifically includes: centrifuging the core at a currently set centrifugation speed, obtaining the current centrifuged nuclear magnetic resonance T2 spectrum, until the currently obtained nuclear magnetic resonance T2 spectrum is the same as the most recently obtained nuclear magnetic resonance T2 spectrum. A comprehensive characterization parameter determination device is used to determine comprehensive characterization parameters of pore connectivity based on the first characterization parameter and the second characterization parameter.

8. A computer program product with porosity connectivity characterization function, comprising a computer program / instructions, wherein, When the computer program / instruction is executed by the processor, it implements the porosity connectivity characterization method according to any one of claims 1 to 6.

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