Method for acquiring in-situ nuclear magnetic resonance T2 spectrum of high-wax-content crude oil stratum invaded by foundation mud

Abstract

The invention discloses a method for acquiring an in-situ nuclear magnetic resonance T2 spectrum of a high-wax-content crude oil stratum invaded by foundation mud, which comprises the following steps of: S1, constructing a nuclear magnetic resonance T2 spectrum model of a saturated single-phase fluid through numerical simulation, and setting model parameters; s2, based on the nuclear magnetic resonance T2 spectrum model, constructing a two-phase fluid nuclear magnetic resonance T2 spectrum model of different oil-based mud saturations in the oil-based mud environment; s3, performing on-site coring on the reservoir, preparing a rock sample, performing a physical experiment, and measuring to obtain a nuclear magnetic resonance T2 spectrum of the rock sample; s4, the nuclear magnetic resonance T2 spectrum obtained through the physical experiment and the two-phase fluid nuclear magnetic resonance T2 spectrum model obtained through numerical simulation are compared and analyzed, and the nuclear magnetic resonance logging response characteristic rule of the oil-based mud invading high-wax-content oil layer is obtained. The method has high calculation speed and excellent data processing capability, can remarkably improve the measurement precision and reliability of magnetic resonance logging under the invasion of the oil-based mud, and is widely applied to the fields of oil exploration, geological survey and the like.

Description

Technical Field

[0001] The invention belongs to the technical field of nuclear magnetic resonance logging (NMR), and in particular relates to a method for obtaining an in-situ nuclear magnetic resonance T2 spectrum of base mud invading a high-wax crude oil formation. Background Art

[0002] With the continuous deepening of oil and gas exploration and development, more and more complex reservoirs have been discovered and developed. Crude oil in some areas has a high wax content and special fluid properties. Especially in high-wax crude oil formations, the physical properties of crude oil are significantly different from those of conventional crude oil. When drilling with oil-based mud, the impact of oil-based mud invasion on the formation is more complicated. The nuclear magnetic resonance logging (NMR) method based on the physical phenomenon of nuclear magnetic resonance has been widely used in oil and gas reservoir evaluation. Especially in measuring porosity, oil and gas saturation, and fluid identification, NMR technology has become an important tool for reservoir logging evaluation due to its high sensitivity. At present, NMR logging technology is mainly used in two main aspects. On the one hand, it is indoor nuclear magnetic resonance measurement. There are many types of instruments. The domestic ones mainly include Suzhou Newmai nuclear magnetic resonance measurement equipment (MesoMR12-060H-I), etc., which are mainly used in core analysis and measurement, reservoir parameter evaluation, unconventional energy and oil and gas reservoir development evaluation, etc.; on the other hand, it is the borehole nuclear magnetic logging series, which are mainly nuclear magnetic logging instruments produced by foreign logging companies and domestic manufacturers. It mainly applies NMR technology to better interpret and evaluate complex oil and gas reservoirs.

[0003] At present, there are a few studies on the impact of oil-based mud invading the formation on the T2 spectrum measured by NMR, but the related research is mainly focused on conventional reservoirs or conventional crude oil. There is a lack of targeted research on the T2 spectrum measured by NMR after the invasion of oil-based mud in high-wax crude oil formations, as well as targeted analysis and summary of the T2 spectrum response characteristics, which makes the T2 spectrum response characteristics of NMR measurements in high-wax crude oil formations unclear and seriously affects the application of T2 spectrum in reservoir evaluation. High-wax crude oil usually exists in liquid form in underground reservoirs, but due to changes in temperature and pressure, waxy substances in crude oil may precipitate or crystallize to form solid wax crystals, which makes this type of crude oil reservoir different from ordinary crude oil reservoirs in physical properties, especially the T2 spectrum measured by NMR. Summary of the invention

[0004] In view of the above-mentioned deficiencies in the prior art, the method for acquiring the in-situ nuclear magnetic resonance T2 spectrum response characteristics of oil-based mud invading high-wax crude oil formations provided by the present invention solves the problem in the current methods that there is a lack of targeted research on the T2 spectrum measured by NMR after the oil-based mud invades the high-wax crude oil formation, which makes the T2 spectrum response characteristics of the NMR measurement unclear and seriously affects the application of T2 spectrum in reservoir evaluation.

[0005] In order to achieve the above-mentioned purpose of the invention, the technical solution adopted by the present invention is: a method for obtaining an in-situ nuclear magnetic resonance T2 spectrum of a base mud invading a high-waxy crude oil formation, comprising the following steps:

[0006] S1. Construct a nuclear magnetic resonance T2 spectrum model of a saturated single-phase fluid through numerical simulation and set the model parameters;

[0007] S2, based on the NMR T2 spectrum model of saturated single-phase fluid, a two-phase fluid NMR T2 spectrum model with different oil-based mud saturations is constructed in an oil-based mud environment;

[0008] S3, taking cores from the reservoir on site, making plunger-shaped rock samples for indoor nuclear magnetic resonance experiments, and conducting physical experiments to measure and obtain the nuclear magnetic resonance T2 spectrum of the rock samples;

[0009] S4. Compare and analyze the NMR T2 spectrum obtained from physical experiments with the two-phase fluid NMR T2 spectrum model obtained from numerical simulation to obtain the NMR logging response characteristics of oil-based mud invading high-wax oil layers.

[0010] Furthermore, in step S1, the single-phase fluid includes formation water, formation crude oil and oil-based mud; and the formation crude oil has a high wax content.

[0011] Furthermore, in step S1, a nuclear magnetic resonance image of a saturated single-phase fluid is constructed with relaxation time as the horizontal coordinate and signal intensity as the vertical coordinate. Spectrum, and construct the NMR T2 spectrum model by the following formula;

[0012]

[0013] In the formula, represents the rock NMR transverse relaxation time, represents the pore fluid volume relaxation time, represents the solid-liquid interface relaxation rate or surface relaxation intensity, represents the pore surface area, represents the pore volume, and S / V represents the characteristic pore size.

[0014] Furthermore, the model parameters that are set include:

[0015] The surface relaxation intensity of water is 20 mm / ms, the surface relaxation intensity of oil is 10 mm / ms, and the echo interval is 1 ms.

[0016] Furthermore, in step S2, the two-phase fluid nuclear magnetic resonance T2 spectrum model expression of different oil-based mud invasion saturations is:

[0017]

[0018] In the formula, represents the magnetization intensity, represents the proportion of the jth pore component, represents water saturation, Indicates the hydrogen index of oil. is the volume relaxation time of water, represents the surface relaxation strength of water, and denote the surface area and volume of the jth pore, respectively. Indicates oil saturation, represents the volume relaxation time of oil, t represents the acquisition time, and m represents the number of echoes.

[0019] Furthermore, the step S3 includes the following sub-steps:

[0020] S31, drilling and sampling the reservoir to prepare a plunger-shaped rock sample for indoor nuclear magnetic resonance experiment;

[0021] S32, grouping and numbering the rock samples;

[0022] S33, vacuum pressurizing each group of rock samples to saturate with water, formation crude oil and oil-based mud;

[0023] S34, measuring the nuclear magnetic resonance T2 spectrum of saturated water and formation crude oil on rock samples;

[0024] S35. Under high temperature conditions, oil-based mud is used to displace saturated water and formation crude oil, and the nuclear magnetic resonance T2 spectrum of the rock samples is measured.

[0025] Furthermore, in step S35, oil-based mud is used to displace saturated water and formation crude oil under high temperature conditions through fully sealed multi-heat source high-temperature and high-pressure auxiliary equipment.

[0026] Furthermore, in step S4, the NMR logging response characteristic law of oil-based mud invading a high wax content oil layer includes a static characteristic law and a dynamic characteristic law;

[0027] The static characteristic law is: when saturated with formation water, NMR The spectrum is mainly single-peak or double-peak, and the relaxation time is generally within 1000ms. When the oil-based mud is saturated, the NMR Compared with the saturated water spectrum, the right peak corresponds to a larger relaxation time and a larger amplitude than the saturated water NMR spectrum. The peak amplitude on the right side of the spectrum;

[0028] The dynamic characteristic law is: after the oil-based mud invades the high waxy crude oil formation, the nuclear magnetic resonance The spectrum shows that the spectrum peak of the large hole on the right shifts to the right and the spectrum amplitude increases, while the small hole on the left changes slightly.

[0029] The beneficial effects of the present invention are:

[0030] (1) The method of the present invention is to clarify the change of NMR T2 spectrum response characteristics of high waxy crude oil formations before and after oil-based mud invasion. The method combines an indoor nuclear magnetic resonance instrument (MesoMR12-060H-I) and numerical simulation to obtain the change characteristics of T2 spectrum of high waxy crude oil formations, and accurately captures the T2 spectrum response characteristics after oil-based mud invasion. It is of great significance for accurately evaluating the properties of fluids and the pore structure of formations, optimizing oil and gas field development plans, etc.

[0031] (2) The method of the present invention has a high computing speed and excellent data processing capability, and can significantly improve the measurement accuracy and reliability of magnetic resonance logging under oil-based mud invasion, and is widely applicable to fields such as petroleum exploration and geological survey. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 The present invention provides a flow chart of the method for obtaining an in-situ nuclear magnetic resonance T2 spectrum of base mud invading a high-waxy crude oil formation.

[0033] Figure 2 This is a structural diagram of the high-temperature and high-pressure auxiliary accessories provided by the present invention.

[0034] Figure 3 The present invention provides a nuclear magnetic T2 spectrum of a saturated single-phase fluid rock sample.

[0035] Figure 4 The invention provides T2 spectrum characteristics of oil-based mud invading a saturated crude oil rock sample. DETAILED DESCRIPTION

[0036] The specific implementation modes of the present invention are described below so that those skilled in the art can understand the present invention. However, it should be clear that the present invention is not limited to the scope of the specific implementation modes. For those of ordinary skill in the art, as long as various changes are within the spirit and scope of the present invention as defined and determined by the attached claims, these changes are obvious, and all inventions and creations utilizing the concept of the present invention are protected.

[0037] The embodiment of the present invention provides a method for obtaining an in-situ nuclear magnetic resonance T2 spectrum of a base mud invading a high waxy crude oil formation, such as Figure 1 As shown, the following steps are included:

[0038] S1. Construct a nuclear magnetic resonance T2 spectrum model of a saturated single-phase fluid through numerical simulation and set the model parameters;

[0039] S2, based on the NMR T2 spectrum model of saturated single-phase fluid, a two-phase fluid NMR T2 spectrum model with different oil-based mud saturations is constructed in an oil-based mud environment;

[0040] S3, taking cores from the reservoir on site, making plunger-shaped rock samples for indoor nuclear magnetic resonance experiments, and conducting physical experiments to measure and obtain the nuclear magnetic resonance T2 spectrum of the rock samples;

[0041] S4. Compare and analyze the NMR T2 spectrum obtained from physical experiments with the two-phase fluid NMR T2 spectrum model obtained from numerical simulation to obtain the NMR logging response characteristics of oil-based mud invading high-wax oil layers.

[0042] In step S1 of the embodiment of the present invention, the single-phase fluid includes formation water, formation crude oil and oil-based mud; wherein the formation crude oil has a high wax content.

[0043] Specifically, when constructing the NMR T2 spectrum model of a single-phase fluid, the NMR spectrum of the saturated single-phase fluid with relaxation time as the horizontal coordinate and signal intensity as the vertical coordinate is Spectrum, and construct the NMR T2 spectrum model by the following formula;

[0044]

[0045] In the formula, represents the rock NMR transverse relaxation time, represents the pore fluid volume relaxation time, represents the solid-liquid interface relaxation rate or surface relaxation intensity, represents the pore surface area, represents the pore volume, and S / V represents the characteristic pore size.

[0046] In this embodiment, the set model parameters include: the surface relaxation intensity of water is 20 mm / ms, the surface relaxation intensity of oil is 10 mm / ms, and the echo interval is 1 ms.

[0047] In step S2 of the embodiment of the present invention, the expression of the two-phase fluid nuclear magnetic resonance T2 spectrum model with different oil-based mud invasion saturations is constructed in the oil-based mud environment:

[0048]

[0049] Where, Echo(t) is the magnetization intensity; is the proportion of the pore components in the jth group; t is the acquisition time; and are the surface area and volume of the jth pore, respectively; is water saturation; is the oil saturation; is the volume relaxation time of water; is the volume relaxation time of the oil; is the surface relaxation strength of water; is the hydrogen index of water; is the hydrogen index of oil; m is the number of echoes; in the above formula, the hydrogen index of water The value is 1.

[0050] Step S3 of the embodiment of the present invention includes the following sub-steps:

[0051] S31, drilling and sampling the reservoir to prepare a plunger-shaped rock sample for indoor nuclear magnetic resonance experiment;

[0052] Among them, the formation crude oil obtained on site is highly waxy crude oil, which is solidified, has poor fluidity and high viscosity at room temperature;

[0053] S32, grouping and numbering the rock samples;

[0054] S33, vacuum pressurizing each group of rock samples to saturate with water, formation crude oil and oil-based mud;

[0055] S34, measuring the nuclear magnetic resonance T2 spectrum of saturated water and formation crude oil on rock samples;

[0056] Among them, the NMR T2 spectra of saturated water and formation crude oil show the NMR response characteristics of saturated single-phase fluids;

[0057] S35. Under high temperature conditions, oil-based mud is used to displace saturated water and formation crude oil, and the nuclear magnetic resonance T2 spectrum of the rock samples is measured; among which, the displacement T2 spectrum of the oil-based mud displacing saturated water or crude oil is manifested as the nuclear magnetic resonance dynamic response characteristics of the oil-based mud invading formations with different saturations.

[0058] Specifically, in this embodiment, since the selected formation crude oil has a high wax content and poor fluidity, in order to ensure that the experimental results are not affected by the physical state of the crude oil, the experiment needs to be carried out at a high temperature, such as Figure 2 As shown, through fully sealed multi-heat source high-temperature and high-pressure auxiliary equipment, oil-based mud is used to displace saturated water and formation crude oil under high temperature conditions, ensuring the effects of pressurization, saturation, and displacement of formation crude oil, and reducing the decomposition of crude oil at high temperature.

[0059] In step S4 of the embodiment of the present invention, the NMR logging response characteristic law of oil-based mud invading a high wax content oil layer includes a static characteristic law and a dynamic characteristic law;

[0060] Among them, the static characteristic law is: Figure 3 As shown, when saturated with formation water, NMR The spectral morphology is mainly single-peak or double-peak (such as Figure 3As shown in Figure 2), the relaxation time is generally within 1000ms; when saturated with oil-based mud, NMR Compared with the saturated water spectrum, the right peak corresponds to a larger relaxation time and a larger amplitude than the saturated water NMR spectrum. The peak amplitude on the right side of the spectrum; Figure 3 In the figure, (a) is saturated formation water, (b) is saturated crude oil, and (c) is saturated oil-based mud.

[0061] The characteristic law of state is: Figure 4 As shown in the figure, after the oil-based mud invades the high waxy crude oil formation, the nuclear magnetic resonance The spectrum shows that the spectrum peak of the large hole on the right shifts to the right (tailing phenomenon), and the spectrum amplitude increases, while the small hole on the left changes slightly; Figure 4 In the figure, (a) is the numerical simulation and (b) is the experiment.

[0062] The present invention uses specific embodiments to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core idea. At the same time, for those skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as a limitation on the present invention.

[0063] Those skilled in the art will appreciate that the embodiments described herein are intended to help readers understand the principles of the present invention, and should be understood that the protection scope of the present invention is not limited to such specific statements and embodiments. Those skilled in the art can make various other specific variations and combinations that do not deviate from the essence of the present invention based on the technical revelations disclosed by the present invention, and these variations and combinations are still within the protection scope of the present invention.

Claims

1. A method for obtaining an in-situ nuclear magnetic resonance T2 spectrum of a base mud invading a high waxy crude oil formation, characterized in that: The following steps are involved: S1. Construct a nuclear magnetic resonance T2 spectrum model of a saturated single-phase fluid through numerical simulation and set the model parameters; S2, based on the NMR T2 spectrum model of saturated single-phase fluid, a two-phase fluid NMR T2 spectrum model with different oil-based mud saturations is constructed in an oil-based mud environment; S3, taking cores from the reservoir on site, making plunger-shaped rock samples for indoor nuclear magnetic resonance experiments, and conducting physical experiments to measure and obtain the nuclear magnetic resonance T2 spectrum of the rock samples; S4. Compare and analyze the NMR T2 spectrum obtained from physical experiments with the two-phase fluid NMR T2 spectrum model obtained from numerical simulation to obtain the NMR logging response characteristics of oil-based mud invading high-wax oil layers.

2. The method for obtaining in-situ nuclear magnetic resonance T2 spectrum of base mud invading high waxy crude oil formation according to claim 1, characterized in that: In step S1, the single-phase fluid includes formation water, formation crude oil and oil-based mud; the formation crude oil has a high wax content.

3. The method for obtaining in-situ nuclear magnetic resonance T2 spectrum of base mud invading high waxy crude oil formation according to claim 2, characterized in that: In the step S1, a nuclear magnetic resonance T2 spectrum of a saturated single-phase fluid is constructed with relaxation time as the horizontal coordinate and signal intensity as the vertical coordinate, and a nuclear magnetic resonance T2 spectrum model is constructed by the following formula: Where T2 represents the transverse relaxation time of rock NMR, T 2B represents the volume relaxation time of pore fluid, ρ represents the solid-liquid interface relaxation rate or surface relaxation intensity, S represents the pore surface area, V represents the pore volume, and S / V represents the characteristic pore size.

4. The method for obtaining in-situ nuclear magnetic resonance T2 spectrum of base mud invading high waxy crude oil formation according to claim 3, characterized in that: The model parameters that are set include: The surface relaxation intensity of water is 20 mm / ms, the surface relaxation intensity of oil is 10 mm / ms, and the echo interval is 1 ms.

5. The method for obtaining in-situ nuclear magnetic resonance T2 spectrum of base mud invading high waxy crude oil formation according to claim 1, characterized in that: In step S2, the two-phase fluid nuclear magnetic resonance T2 spectrum model expression of different oil-based mud invasion saturations is: Where Echo(t) represents the magnetization intensity, represents the proportion of the jth pore component, S w Indicates water saturation, I HO Indicates the hydrogen index of oil, T 2w represents the volume relaxation time of water, ρ w represents the surface relaxation strength of water, S j and V j represent the surface area and volume of the jth pore, S o Indicates oil saturation, T 2o represents the volume relaxation time of oil, t represents the acquisition time, and m represents the number of echoes.

6. The method for obtaining in-situ nuclear magnetic resonance T2 spectrum of base mud invading high waxy crude oil formation according to claim 1, characterized in that: The step S3 comprises the following sub-steps: S31, drilling and sampling the reservoir to prepare a plunger-shaped rock sample for indoor nuclear magnetic resonance experiment; S32, grouping and numbering the rock samples; S33, vacuum pressurizing each group of rock samples to saturate with water, formation crude oil and oil-based mud; S34, measuring the nuclear magnetic resonance T2 spectrum of saturated water and formation crude oil on rock samples; S35. Under high temperature conditions, oil-based mud is used to displace saturated water and formation crude oil, and the nuclear magnetic resonance T2 spectrum of the rock samples is measured.

7. The method for obtaining in-situ nuclear magnetic resonance T2 spectrum of base mud invading high waxy crude oil formation according to claim 6, characterized in that: In step S35, oil-based mud is used to displace saturated water and formation crude oil under high temperature conditions through fully sealed multi-heat source high-temperature and high-pressure auxiliary equipment.

8. The method for obtaining in-situ nuclear magnetic resonance T2 spectrum of base mud invading high waxy crude oil formation according to claim 1, characterized in that: In the step S4, the NMR logging response characteristic law of oil-based mud invading a high wax-containing oil layer includes a static characteristic law and a dynamic characteristic law; The static characteristic law is: when saturated with formation water, the nuclear magnetic resonance T2 spectrum is mainly single-peak or double-peak, and the relaxation time is generally within 1000ms; when saturated with oil-based mud, compared with saturated water, the relaxation time corresponding to the right spectrum peak of the nuclear magnetic resonance T2 spectrum is larger, and the amplitude is also greater than the right peak amplitude of the saturated water nuclear magnetic resonance T2 spectrum; The dynamic characteristic law is: after the oil-based mud invades the high wax crude oil formation, the nuclear magnetic resonance T2 spectrum shows that the spectrum peak of the large pores on the right shifts to the right and the spectrum amplitude increases, while the small pores on the left change slightly.

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