Method for obtaining in-situ nuclear magnetic resonance t2 spectrum of oil-based mud invasion into high-wax crude oil formation

Abstract

The application discloses an oil-based mud invasion high-wax crude oil formation in-situ nuclear magnetic resonance T2 spectrum acquisition method, which comprises the following steps: S1, constructing a nuclear magnetic resonance T2 spectrum model of saturated single-phase fluid through numerical simulation, and setting model parameters; S2, constructing a nuclear magnetic resonance T2 spectrum model of two-phase fluid with different oil-based mud saturations under the oil-based mud environment based on the nuclear magnetic resonance T2 spectrum model; S3, taking a core on a reservoir site, making a rock sample and performing a physical experiment, and measuring a nuclear magnetic resonance T2 spectrum of the rock sample; and S4, comparing and analyzing the nuclear magnetic resonance T2 spectrum obtained through the physical experiment with the two-phase fluid nuclear magnetic resonance T2 spectrum model obtained through numerical simulation, and obtaining a nuclear magnetic resonance logging response characteristic law of the oil-based mud invasion high-wax oil layer. The method has high calculation speed and excellent data processing capacity, can significantly improve the measurement precision and reliability of the magnetic resonance logging under the oil-based mud invasion, and is widely applicable to the fields of oil exploration and geological survey.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of nuclear magnetic resonance logging (NMR), and particularly relates to a method for obtaining in-situ nuclear magnetic resonance T2 spectrum of oil-based mud invasion into a high-wax-content crude oil formation. BACKGROUND

[0002] With the continuous deepening of oil and gas exploration and development, more and more complex reservoirs are discovered and developed. In some areas, the crude oil has a high wax content and special fluid characteristics. In particular, in the high-wax-content crude oil formation, the physical properties of the crude oil are significantly different from those of the conventional crude oil. When oil-based mud drilling is used, the influence of oil-based mud invasion on the formation is more complex. The nuclear magnetic resonance logging (NMR) method based on the physical phenomenon of nuclear magnetic resonance has been widely used in the evaluation of oil and gas reservoirs. In particular, in the measurement of porosity, oil and gas saturation, and fluid identification, the NMR technology has become an important tool for reservoir logging evaluation due to its high sensitivity. At present, the NMR logging technology is mainly applied in two main aspects. On the one hand, there are many types of indoor nuclear magnetic resonance measurement instruments, such as the MesoMR12-060H-I nuclear magnetic resonance measurement equipment of Suzhou Nuomi, which are mainly used for core analysis measurement, reservoir parameter evaluation, unconventional energy and oil and gas reservoir development evaluation, etc. On the other hand, there are nuclear magnetic logging series in boreholes, mainly nuclear magnetic logging instruments produced by foreign logging companies and domestic manufacturers, which are mainly used to better apply NMR technology to the interpretation and evaluation of complex oil and gas reservoirs.

[0003] At present, there is little work on the influence of oil-based mud invasion on the T2 spectrum of NMR measurement. However, the related researches are mainly concentrated in conventional reservoirs or conventional crude oil. There is currently a lack of targeted research on the T2 spectrum of NMR measurement after oil-based mud invasion in high-wax-content crude oil formations, as well as targeted analysis and summary of the T2 spectrum response characteristics, which causes the T2 spectrum response characteristics in high-wax-content crude oil formations to be unclear and seriously affects the application of T2 spectrum in reservoir evaluation. High-wax-content crude oil usually exists in a liquid state in underground reservoirs, but due to changes in temperature and pressure, the wax substances in the crude oil may precipitate or crystallize to form solid wax crystals, which makes the physical properties of this type of crude oil reservoir different from those of ordinary crude oil reservoirs, especially the T2 spectrum of NMR measurement. SUMMARY

[0004] In view of the above deficiencies in the prior art, the method for obtaining the T2 spectrum response characteristics of in-situ nuclear magnetic resonance of oil-based mud invasion into a high-wax-content crude oil formation provided by the present application solves the problem that there is currently a lack of targeted research on the T2 spectrum of NMR measurement after oil-based mud invasion in high-wax-content crude oil formations, which causes the T2 spectrum response characteristics to be unclear and seriously affects the application of T2 spectrum in reservoir evaluation.

[0005] In order to achieve the above-mentioned purposes, the technical scheme adopted by the present application is as follows: an oil-based mud invasion high-wax crude oil formation in-situ nuclear magnetic resonance T2 spectrum acquisition method, comprising the following steps:

[0006] S1, constructing a nuclear magnetic resonance T2 spectrum model of saturated single-phase fluid through numerical simulation, and setting model parameters;

[0007] S2, constructing a nuclear magnetic resonance T2 spectrum model of two-phase fluid under different oil-based mud saturation degrees in an oil-based mud environment based on the nuclear magnetic resonance T2 spectrum model of saturated single-phase fluid;

[0008] S3, taking a core on site, making a piston-like indoor nuclear magnetic resonance experimental rock sample, and performing a physical experiment to measure the nuclear magnetic resonance T2 spectrum of the rock sample;

[0009] S4, comparing and analyzing the nuclear magnetic resonance T2 spectrum obtained through the physical experiment with the nuclear magnetic resonance T2 spectrum model of two-phase fluid obtained through numerical simulation to obtain the nuclear magnetic resonance logging response characteristic law of oil-based mud invasion high-wax oil layer.

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

[0011] Further, in the step S1, a nuclear magnetic resonance T2 spectrum of 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 through the following formula:

[0012]

[0013] In the formula, T2 represents the rock nuclear magnetic resonance transverse relaxation time, T 2B represents the pore fluid volume relaxation time, 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 pore characteristic size.

[0014] Further, the model parameters 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] Further, in the step S2, the expression of the nuclear magnetic resonance T2 spectrum model of two-phase fluid under different oil-based mud invasion saturation degrees is as follows:

[0017]

[0018] In the formula, Echo(t) represents the magnetization, S represents the proportion of the jth pore component, S w S represents the water saturation, I HO S represents the hydrogen index of oil, T 2w S represents the volume relaxation time of water, ρ w S represents the surface relaxation intensity of water, S j and V j S represents the surface area and volume of the jth pore, S o S represents the oil saturation, T 2o S represents the volume relaxation time of oil, t represents the acquisition time, and m represents the number of echoes.

[0019] Further, the step S3 comprises the following sub-steps:

[0020] S31, drilling sampling is performed on the reservoir to prepare rock samples for piston-like indoor nuclear magnetic resonance experiments;

[0021] S32, the rock samples are grouped and numbered;

[0022] S33, the rock samples in each group are respectively saturated with water, formation crude oil and oil-based mud under vacuum and pressure;

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

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

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

[0026] Further, in the step S4, the nuclear magnetic resonance logging response characteristic law of the oil-based mud invading the high-wax oil layer includes static characteristic law and dynamic characteristic law;

[0027] The static characteristic law is that, when saturated with formation water, the nuclear magnetic resonance T2 spectrum mainly has a single peak or a double peak, and the relaxation time is generally within 1000 ms; when saturated with oil-based mud, compared with the water saturation, the right side spectrum peak corresponds to a large relaxation time, and the amplitude is also greater than the right side peak amplitude of the water saturation nuclear magnetic resonance T2 spectrum;

[0028] The dynamic characteristic law is that, after the oil-based mud invades the high-wax crude oil formation, the nuclear magnetic resonance T2 spectrum shows that the right side large pore spectrum peak is right-shifted, and the spectrum amplitude is increased, while the left side small pore changes little.

[0029] The present application has the following beneficial effects:

[0030] (1) The method of the present application is to clarify the NMR T2 spectrum response characteristic change of the high-wax-content crude oil formation before and after the invasion of oil-based mud, to obtain the T2 spectrum change characteristics of the high-wax-content crude oil formation by using a laboratory nuclear magnetic resonance instrument (MesoMR12-060H-I) and numerical simulation, and to accurately capture the T2 spectrum response characteristics after the invasion of oil-based mud, which is of great significance for accurately evaluating the properties of fluids and the pore structure of the formation and optimizing the development plan of oil and gas fields.

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

[0032] Figure 1 The method flow chart for obtaining in-situ nuclear magnetic resonance T2 spectrum of high-wax-content crude oil formation invaded by oil-based mud is provided.

[0033] Figure 2 The structure diagram of high-temperature and high-pressure auxiliary accessories is provided.

[0034] Figure 3 The nuclear magnetic T2 spectrum of saturated single-phase fluid rock sample is provided.

[0035] Figure 4 The T2 spectrum characteristics of oil-based mud invaded oil-saturated rock sample are provided. DETAILED DESCRIPTION

[0036] The specific embodiments of the present application are described below to facilitate the understanding of the present application by those skilled in the art, but it should be clear that the present application is not limited to the scope of the specific embodiments, and for those skilled in the art, it is obvious that various changes are within the spirit and scope of the present application defined and determined by the appended claims, and all the inventions utilizing the concept of the present application are within the scope of protection.

[0037] The embodiment of the present application provides a method for obtaining in-situ nuclear magnetic resonance T2 spectrum of high-wax-content crude oil formation invaded by oil-based mud, as shown in Figure 1 The method comprises the following steps:

[0038] S1, constructing a nuclear magnetic resonance T2 spectrum model of saturated single-phase fluid by numerical simulation, and setting model parameters;

[0039] S2, constructing a nuclear magnetic resonance T2 spectrum model of two-phase fluid under different oil-based mud saturation in an oil-based mud environment based on the nuclear magnetic resonance T2 spectrum model of saturated single-phase fluid;

[0040] S3, coring the reservoir, making a piston-like indoor nuclear magnetic resonance experimental rock sample and performing a physical experiment, and measuring a nuclear magnetic resonance T2 spectrum of the rock sample;

[0041] S4, comparing and analyzing the nuclear magnetic resonance T2 spectrum obtained by the physical experiment with a two-phase fluid nuclear magnetic resonance T2 spectrum model obtained by numerical simulation, and obtaining a nuclear magnetic resonance logging response characteristic law of oil-based mud invasion into a high-wax oil layer.

[0042] In step S1 of the embodiment of the application, the single-phase fluid includes formation water, formation crude oil and oil-based mud; wherein the formation crude oil is high in wax.

[0043] Specifically, when the nuclear magnetic resonance T2 spectrum model of the single-phase fluid is constructed, the nuclear magnetic resonance T2 spectrum of the saturated single-phase fluid is taken as the relaxation time as the horizontal coordinate and the signal intensity as the vertical coordinate, and the nuclear magnetic resonance T2 spectrum model is constructed through the following formula:

[0044]

[0045] In the formula, T2 represents the rock nuclear magnetic resonance transverse relaxation time, T 2B represents the pore fluid volume relaxation time, p represents the solid-liquid interface relaxation rate or surface relaxation strength, S represents the pore surface area, V represents the pore volume, and S / V represents the pore characteristic size.

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

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

[0048]

[0049] In the formula, Echo(t) is the magnetization strength of the jth group of pores; is the proportion of the jth group of pores; t is the acquisition time; S j and V j are the surface area and volume of the jth pore respectively; S w is the water saturation; S o is the oil saturation; T 2w is the volume relaxation time of water; T 2o is the volume relaxation time of oil; p w is the surface relaxation strength of water; I Hw is the hydrogen index of water; I HO is the hydrogen index of oil; and m is the echo number; in the above formula, the hydrogen index I HwThe value is 1.

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

[0051] S31. Drill and sample the reservoir to prepare a plunger-shaped rock sample for indoor nuclear magnetic resonance experiments;

[0052] Among them, the formation crude oil obtained on site was high wax crude oil, which was solidified at room temperature, had poor fluidity and high viscosity;

[0053] S32. Group and number the rock samples;

[0054] S33. Vacuum pressurize each group of rock samples with saturated water, formation crude oil, and oil-based mud, respectively.

[0055] S34. Measure the nuclear magnetic resonance T2 spectra of saturated water and formation crude oil in rock samples;

[0056] Among them, the nuclear magnetic resonance T2 spectra of saturated water and formation crude oil exhibit the nuclear magnetic resonance 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 nuclear magnetic resonance T2 spectra are measured on rock samples; among them, the displacement T2 spectra of oil-based mud displacing saturated water or crude oil are manifested as the nuclear magnetic resonance dynamic response characteristics of oil-based mud intruding into formations with different saturation levels.

[0058] Specifically, in this embodiment, because the selected formation crude oil has a high wax content and poor fluidity, the experiment needs to be conducted at a high temperature to ensure that the experimental results are not affected by the physical state of the crude oil. Figure 2 As shown, by using a 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 effect of pressurization, saturation, and displacement of formation crude oil, and reducing the decomposition of crude oil at high temperatures.

[0059] In step S4 of this embodiment of the invention, the nuclear magnetic resonance logging response characteristics of oil-based mud invading high wax-containing oil layers include static characteristics and dynamic characteristics.

[0060] Among them, the static characteristic rules are as follows: Figure 3 As shown, when formation water is saturated, the T2 nuclear magnetic resonance spectrum mainly exhibits a single peak or a double peak (e.g., Figure 3 As shown), the relaxation time is generally within 1000 ms; for saturated oil-based mud, compared with water-saturated mud, the right-hand peak of the NMR T2 spectrum corresponds to a larger relaxation time, and the amplitude is also greater than that of the right-hand peak of the water-saturated NMR T2 spectrum; in Figure 3 In the diagram, (a) represents saturated formation water, (b) represents saturated crude oil, and (c) represents saturated oil-based mud.

[0061] The state characteristic law is as shown in the following table: Figure 4 As shown in the table, after the oil-based mud invades the high-wax-content crude oil formation, the nuclear magnetic resonance T2 spectrum shows that the large-pore spectrum peak on the right side moves to the right (tail phenomenon), and the spectrum amplitude increases, while the small-pore on the left side changes less. Figure 4 In the table, (a) is numerical simulation, and (b) is experiment.

[0062] The principles and implementation manners of the present application are described by using specific examples in the present application, and the above examples are only used to help understand the method of the present application and its core idea; meanwhile, for the ordinary skilled in the art, according to the idea of the present application, the specific implementation manners and application ranges can be changed, and the above description should not be understood as the limitation of the present application.

[0063] The person skilled in the art will understand that the examples described herein are used to help the reader understand the principles of the present application, and should be understood as the protection scope of the present application not being limited to such specific statements and examples. The person skilled in the art can make various other specific modifications and combinations according to the technical inspirations disclosed in the present application without departing from the essence of the present application, and these modifications and combinations are still within the protection scope of the present application.

Claims

1. A method for obtaining in situ NMR T2 spectra of oil-based mud invaded high-wax crude oil formations, characterized in that, The method comprises the following steps: S1, constructing a nuclear magnetic resonance T2 spectrum model of saturated single-phase fluid by numerical simulation, and setting model parameters; S2, constructing a nuclear magnetic resonance T2 spectrum model of two-phase fluid with different oil-based mud saturation under the oil-based mud environment based on the nuclear magnetic resonance T2 spectrum model of saturated single-phase fluid; S3, taking a core from a reservoir, making a piston-like indoor nuclear magnetic resonance experimental rock sample, and performing a physical experiment to measure the nuclear magnetic resonance T2 spectrum of the rock sample; S4, comparing and analyzing the nuclear magnetic resonance T2 spectrum of the rock sample obtained by the physical experiment with the nuclear magnetic resonance T2 spectrum model of two-phase fluid obtained by numerical simulation to obtain the nuclear magnetic resonance logging response characteristic law of oil-based mud invasion into a high-wax oil layer; In the step S1, the single-phase fluid includes formation water, formation crude oil and oil-based mud; the formation crude oil is high in wax content; In the step S1, a nuclear magnetic resonance T2 spectrum of a saturated single-phase fluid is constructed with a relaxation time as an abscissa and a signal intensity as an ordinate and a nuclear magnetic resonance T2 spectrum model of the single-phase fluid is constructed by the following formula; ； wherein T2 represents the rock's nuclear magnetic resonance transverse relaxation time, T2f represents the pore fluid volume relaxation time, Sf represents the solid-liquid interface relaxation rate or surface relaxation strength, S represents the pore surface area, V represents the pore volume, and S / V represents the pore characteristic dimension.

2. The method for obtaining in situ NMR T2 profile of oil-based mud invaded high- waxy crude oil formation according to claim 1, characterized in that, 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.

3. The method for obtaining in situ NMR T2 profile of oil-based mud invaded high- waxy crude oil reservoirs according to claim 1, characterized in that, In the step S2, the expression of the nuclear magnetic resonance T2 spectrum model of two-phase fluid with different oil-based mud saturation is: ； wherein Mz represents the magnetization, φj represents the proportion of the jth pore component, Sw represents the water saturation, Hj represents the hydrogen index of oil, T2w represents the volume relaxation time of water, S2w represents the surface relaxation intensity of water, and Sj and Vj represent the surface area and volume of the jth pore, respectively, So represents the oil saturation, T2o represents the volume relaxation time of oil, t represents the acquisition time, and m represents the number of echoes.

4. The method for obtaining in situ NMR T2 profile of oil-based mud invaded high- waxy crude oil reservoirs according to claim 1, characterized in that, The step S3 comprises the following sub-steps: S31, taking a sample from a reservoir by drilling to make a piston-like indoor nuclear magnetic resonance experimental rock sample; S32, grouping and numbering the rock samples; S33, respectively vacuum-pressurizing and saturating the rock samples with water, formation crude oil and oil-based mud; S34, measuring the nuclear magnetic resonance T2 spectrum of the rock samples saturated with water and formation crude oil; S35, displacing the water and formation crude oil saturated in the rock samples with oil-based mud under high-temperature conditions, and measuring the nuclear magnetic resonance T2 spectrum of the rock samples.

5. The method for obtaining in situ NMR T2 profile of oil-based mud invaded high- waxy crude oil formation according to claim 4, characterized in that, In the step S35, the water and formation crude oil saturated in the rock samples are displaced with oil-based mud under high-temperature conditions by using a full-sealing multi-heat-source high-temperature high-pressure auxiliary device.

6. The method for obtaining in situ NMR T2 profile of oil-based mud invaded high- waxy crude oil reservoirs according to claim 1, characterized in that, In the step S4, the nuclear magnetic resonance logging response characteristic law of oil-based mud invasion into a high-wax oil layer includes static characteristic law and dynamic characteristic law; The static characteristic law is that when the formation water is saturated, the nuclear magnetic resonance spectrum is single peak or double peak, and the relaxation time is within 1000 ms; when the oil-based mud is saturated, the nuclear magnetic resonance spectrum is single peak or double peak, and the relaxation time is within 1000 ms; when the oil-based mud is saturated, the nuclear magnetic resonance spectrum is single peak or double peak, and the relaxation time is within 1000 ms; when the oil-based mud is saturated, the nuclear magnetic resonance The dynamic characteristic law is that after the oil-based mud invades the high-wax crude oil formation, the nuclear magnetic resonance spectrum shows that the right side macropore spectrum peak moves right, and the spectrum amplitude increases, while the left side micropore changes less.

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