Construction method of shale oil content recovery coefficient

Abstract

The invention relates to a method for constructing a shale oil content recovery coefficient, and belongs to the field of unconventional oil-gas exploration and developing.A pressure-maintaining coring shale sample is adopted for research, and a two-dimensional nuclear magnetic resonance experiment is utilized for obtaining the oil content of a stratum in an in-situ state; then, the sample is smashed and divided into two parts, one part is subjected to oil washing and drying to remove heavy oil, and the oil content difference of the other part of the sample without oil washing and the oil washing sample in the pyrolysis experiment has comparability; finally, by comparing the difference between the original oil content measured by two-dimensional nuclear magnetic resonance and the pyrolysis S1 measured value, a recovery coefficient is established, and quantitative recovery of the oil content is achieved. According to the method, the problem that the oil content is obviously underestimated due to volatilization of light components generally existing in the process of measuring the oil content of the medium-high maturity shale is solved, the oil content can directly reflect the actual oil content level of the shale under the in-situ condition, and the technical bottleneck that the in-situ oil content is difficult to accurately obtain through traditional conventional coring is broken through.

Description

TECHNICAL FIELD

[0001] The application relates to a shale oil-bearing rate recovery coefficient construction method, in particular to a shale oil-bearing rate recovery coefficient construction method for medium-high maturity shale, and belongs to the technical field of unconventional oil and gas exploration and development. BACKGROUND

[0002] The oil-bearing rate is a key parameter in shale oil resource potential evaluation, and its accuracy directly determines the reliability of the resource quantity calculation result. However, during a series of processes such as coring, transportation, storage and pre-experiment treatment of the core, the loss of light hydrocarbon is common, which leads to the fact that the measured oil-bearing rate is significantly lower than the true value under the in-situ formation condition. This problem is particularly prominent in medium-high maturity shale, and the main reason is that the proportion of light components in the hydrocarbon contained in the shale is relatively high. Once the core is exposed to the low-pressure environment on the surface, the light components are easily volatilized and dispersed, thereby causing the systematic low measured oil-bearing rate.

[0003] Under the current background technology condition, the steps for determining the oil-bearing rate of medium-high maturity shale are as follows: firstly, pyrolysis experiments are carried out on the conventional coring sample to obtain the pyrolysis S1 value, and then the original oil-bearing rate is obtained according to the recovery coefficient. The common methods for determining the light component recovery coefficient of medium-high maturity shale at present include: (1) pyrolysis comparison method; (2) crude oil component method; (3) component hydrocarbon generation kinetics method; and (4) empirical formula method. The common feature of the above methods is that the original in-situ oil-bearing rate is recovered by indirect calculation or empirical correction on the premise that the sample has been lost light components to different degrees, and the results are restricted by the sample preservation condition, experimental hypothesis and model reliability.

[0004] Although some scholars have tried to use pressure-maintaining coring samples to carry out shale light component recovery coefficient research in recent years, the current experimental procedures are not uniform, and the key steps such as the acquisition of the original in-situ oil-bearing rate, the subsequent oil washing-drying-pyrolysis parameter setting and the data comparison method still lack systematic technical solutions and operable standard specifications. The existing work is mostly at the exploratory stage, and the repeatability and comparability are insufficient, so it is difficult to form a widely applicable recovery coefficient determination system. Therefore, it is urgent to construct a scientific, verifiable and generalizable light component recovery coefficient experimental method. SUMMARY

[0005] In view of the deficiencies of the prior art, the present application proposes a shale oil content recovery coefficient construction method, aiming to solve the problem of significant underestimation of oil content caused by volatilization of light components in the process of determining oil content of medium-high maturity shale, the present application uses pressure-maintained coring shale samples to carry out research, and uses two-dimensional nuclear magnetic resonance experiment to obtain in-situ oil content data of the formation; then, the sample is crushed and divided into two parts, one part is washed and dried to remove heavy oil in the shale pores, and the other part is not washed, so that the oil content difference between the unwashed sample and the washed sample in the pyrolysis experiment is comparable. Finally, by comparing the difference between the original oil content measured by two-dimensional nuclear magnetic resonance and the measured value of pyrolysis S1, a recovery coefficient suitable for medium-high mature shale is established, and the quantitative recovery of oil content is realized.

[0006] The present application adopts the following technical scheme:

[0007] A shale oil content recovery coefficient construction method, comprising the following steps:

[0008] S1, under well site conditions, a core sample is obtained by using pressure-maintained coring technology, and is immediately transferred to a Dewar flask containing liquid nitrogen for-196℃ cryopreservation, and is transported to the laboratory under-196℃ cryopreservation conditions to maximize the inhibition of volatilization loss of light hydrocarbon components;

[0009] S2, the core sample is taken out from the Dewar flask in the laboratory, and a cube-shaped core sample of a specified size is cut and prepared under-196℃ conditions, to obtain a test sample, which is re-placed in a liquid nitrogen container for cryopreservation, to ensure the in-situ preservation state of the crude oil components in the sample;

[0010] S3, before nuclear magnetic resonance testing, the test sample is taken out from the liquid nitrogen container, and is naturally thawed to the best thawing time, and then two-dimensional nuclear magnetic resonance T1-T2 testing is immediately performed, the corresponding nuclear magnetic T2 signal of the extracted crude oil is obtained, including free oil signal and adsorbed oil signal, based on the calibration relationship between nuclear magnetic T2 signal and crude oil quality, the corresponding crude oil quality in the test sample is obtained, and then the oil content m is obtained o The oil content can truly reflect the occurrence state of crude oil in shale under in-situ conditions;

[0011] S4, after completing the nuclear magnetic resonance test, the test sample is crushed and divided into two parts, one part is directly subjected to rock pyrolysis experiment to obtain pyrolysis S1 and pyrolysis S2 before oil washing, and the other part is subjected to oil washing and then rock pyrolysis experiment to obtain pyrolysis and pyrolysis after oil washing; The pyrolysis experiment can use a Rock-Eval 6 type pyrolysis instrument.

[0012] S5, based on the crude oil occurrence morphology in shale pores and the characteristics of light component loss under different experimental conditions, this invention proposes two types of oil content recovery coefficients: one is the total oil content recovery coefficient C. t The first is used to characterize the overall recovery degree of in-situ oil content in shale relative to conventional pyrolysis test results; the second is the light-to-medium quality oil content recovery coefficient C. l This is used to quantitatively characterize the compensation relationship of light and medium crude oil components lost during core sampling, storage, and testing. Total oil content recovery coefficient C t and the recovery coefficient C of light and medium quality oil l The calculation formula is as follows:

[0013] (1)

[0014] (2).

[0015] This invention utilizes the aforementioned comparative experiments to determine the degree of loss of light components in pyrolysis S1, thereby establishing a repeatable and quantifiable recovery coefficient system. The recovery coefficients constructed using this method can provide quantitative evidence for obtaining in-situ oil content in long-stored and conventionally cored shale samples, significantly improving the accuracy and reliability of oil content evaluation in medium-to-high maturity shale oil.

[0016] Preferably, in step S2, after the core sample is taken out of the liquid nitrogen in the Dewar bottle, it is placed in a safety shield and the core sample is kept at a low temperature of -196°C by continuously spraying liquid nitrogen, while the core is cut.

[0017] The safety shield is made of polycarbonate, which is a common material.

[0018] Preferably, in step S3, the optimal thawing time is determined as follows:

[0019] The test sample was weighed immediately after being removed from the liquid nitrogen container. Because water vapor condenses easily on the sample surface at low temperatures, the sample surface needed to be wiped before weighing to avoid mass errors caused by condensation and interference with the NMR signal. The test sample was then placed in a quartz glass tube, which was sealed with a cork. One-dimensional NMR T2 testing was performed inside the quartz glass tube, with each measurement lasting less than one minute. As the test sample gradually thawed, the crude oil in the pores changed from a frozen state to a liquid state. Hydrogen protons underwent resonant transitions in the radio frequency magnetic field, and the total signal value of the one-dimensional T2 spectrum continuously increased during the thawing process. When the total signal value reached its maximum value with increasing time and began to show a downward trend, the corresponding thawing time was determined to be the optimal thawing time.

[0020] Preferably, in step S3, through experimental verification, the present invention determines that the optimal thawing time for this type of shale sample is 2 minutes.

[0021] Preferably, in step S3, the calibration relationship between the crude oil NMR signal and the crude oil quality is obtained through the following method:

[0022] One-dimensional nuclear magnetic resonance T2 tests were directly performed on crude oil samples produced from the well. The T2 signals of crude oil samples of different qualities were obtained sequentially. Based on linear regression, the calibration relationship between crude oil T2 signals and crude oil quality was established.

[0023] Preferably, both one-dimensional NMR T2 and two-dimensional NMR T1-T2 tests are performed using a high-precision benchtop NMR analyzer, model MR Cores-xx. The parameters for the two-dimensional NMR T1-T2 test are as follows: magnetic field strength is 0.5T, magnetic resonance frequency is 22 MHz, probe diameter is 30 mm, echo time (TE) is 0.07 ms, waiting time (TW) is 1000 ms, number of echoes (NECH) is 4000, and number of scans (NS) is 16.

[0024] Preferably, in step S4, the sample is pulverized to 60-80 mesh and the pulverized test sample, which is divided into two equal parts, is placed for more than 10 days to simulate the storage state of conventional core samples.

[0025] The oil washing process is as follows: the powder sample is wrapped in filter paper and placed in a Soxhlet extractor. Dichloromethane is used as the extraction solvent and the extraction is carried out continuously for 5-7 days to fully remove the mobile hydrocarbon fluids in the shale pores. After the oil washing is completed, the sample is dried at 110℃ for 5 hours.

[0026] Preferably, steps S1 to S5 are performed on core samples of different maturity levels to calculate the total oil content recovery coefficient C of the core samples of different maturity levels. t and the recovery coefficient C of light and medium quality oil l Establish the relationship between maturity and total oil content recovery coefficient C. t and the recovery coefficient C of light and medium quality oil l In relation to the relationship between shale well sections where pressure-maintaining coring has not been carried out, the total oil content recovery coefficient C can be obtained simply by obtaining the maturity of the shale samples. t and the recovery coefficient C of light and medium quality oil l .

[0027] Preferably, the maturity and total oil content recovery coefficient C is established. t and the recovery coefficient C of light and medium quality oil l When considering the relationship, select core samples of more than 5 different maturity levels for experiments.

[0028] Preferably, for shale well sections where pressure-maintaining coring has not been carried out, conventional pyrolysis experiments are conducted to obtain pyrolysis S1, and the total oil content recovery coefficient C is... tand the recovery coefficient C of light and medium quality oil l Multiplying these values ​​by the pyrolysis S1 yields the total in-situ oil content and the light to medium oil content of the shale.

[0029] Because the loss of light hydrocarbons is unavoidable during core sampling, transportation, storage, and sample pretreatment, existing pyrolysis experiments yield pyrolysis S1, and the resulting oil content is insufficient to reflect the true in-situ oil content of the formation, leading to significant biases in resource assessment. Furthermore, while two-dimensional nuclear magnetic resonance (NMR) experiments can partially characterize in-situ oil content, the lack of a quantitative correlation between NMR and pyrolysis results limits their application in oil content correction.

[0030] This invention constructs an experimental system capable of obtaining near-in-situ oil-bearing conditions and establishes a method for recovering light components applicable to medium- to high-maturity shale by comparing the results of two-dimensional nuclear magnetic resonance experiments with measured pyrolysis S1 values. By setting two experimental conditions—washed and unwashed—after sample crushing, this invention can quantify the impact of different treatment methods on oil content, thereby obtaining the recovery coefficients for total oil content and light to medium-quality oil content. This solves the problems of existing technologies being unable to effectively recover light hydrocarbon losses and lacking unified recovery standards.

[0031] For any details not covered in this invention, please refer to the prior art.

[0032] The beneficial effects of this invention are as follows:

[0033] 1. This invention addresses the issue of easy volatility and loss of light components in medium-to-high maturity shale oil by establishing a sample pretreatment process based on pressure-controlled coring, combined with rapid cryopreservation with liquid nitrogen and core cutting under low-temperature conditions. By immediately transferring the pressure-controlled coring core cylinder to a liquid nitrogen environment at the well site and maintaining the core in a completely cryogenic state in the laboratory for cutting and sample preparation, the in-situ state of crude oil in the shale pores is preserved to the maximum extent. This effectively suppresses the volatilization and escape of light and medium-quality crude oil during coring, transportation, and sample preparation, avoiding the systematic underestimation of crude oil content under conventional atmospheric pressure coring or room temperature treatment conditions. It provides a near-in-situ sample basis for subsequent quantitative nuclear magnetic resonance analysis, significantly improving the reliability of shale oil content evaluation results.

[0034] 2. This invention proposes a quantitative thawing control method based on the stability of the total signal in the one-dimensional nuclear magnetic resonance (NMR) T2 spectrum. By monitoring the change of the NMR signal over time during thawing, the critical moment when the core sample transitions from a frozen state to a fully liquid state is accurately determined, and two-dimensional NMR T1–T2 measurements are then performed based on this. Simultaneously, a crude oil NMR signal-mass calibration equation is established in conjunction with actual shale oil production, achieving a quantitative conversion of NMR signal to crude oil quality. This method avoids the problems of limited fluid movement due to insufficient thawing or further loss of light components due to over-thawing, enabling two-dimensional NMR testing to accurately characterize the in-situ occurrence characteristics of free and adsorbed oil in shale pores. The resulting oil content directly reflects the actual oil content level of shale under in-situ conditions, overcoming the technical bottleneck of traditional NMR or pyrolysis methods in accurately obtaining in-situ oil content.

[0035] 3. To address the issue of easy loss of light and medium crude oil components during sampling and testing in conventional Rock-Eval pyrolysis testing, this invention, based on in-situ NMR oil content testing results, introduces a comparative analysis of pyrolysis parameters before and after oil washing, proposing two types of oil content recovery coefficient models: one is the total oil content recovery coefficient, used to quantitatively characterize the overall underestimation of oil content by conventional pyrolysis results relative to in-situ; the other is the light and medium oil content recovery coefficient, used to specifically characterize the loss compensation relationship of light and medium crude oil components. This invention establishes a comparable relationship between the two experimental systems by comparing and correlating the in-situ oil content measured by NMR with the values ​​obtained from pyrolysis experiments. Through the introduction of the above recovery coefficients, the results of traditional pyrolysis testing can be quantitatively corrected, significantly improving the accuracy and comparability of oil content evaluation for medium-to-high maturity shale oil. This method not only reveals the loss patterns of crude oil in different occurrence states during testing but also provides a reliable parameter basis for shale oil mobility evaluation and precise resource calculation, possessing good engineering application value and promising prospects for promotion. Attached Figure Description

[0036] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments of this application and their descriptions are used to explain this application and do not constitute an undue limitation of this application.

[0037] Figure 1 This is a flowchart illustrating the method for constructing the shale oil content recovery coefficient according to the present invention.

[0038] Figure 2 This is a schematic diagram showing the trend of nuclear magnetic resonance (NMR) signal intensity of shale samples as a function of thawing time.

[0039] Figure 3 Two-dimensional nuclear magnetic resonance T1-T2 spectra of shale samples taken under pressure;

[0040] Figure 4Comparison of pyrolysis spectra of shale samples before and after oil washing;

[0041] Figure 5 This is a graph showing the relationship between the oil content recovery coefficient of medium-to-high maturity shale. Detailed Implementation

[0042] To enable those skilled in the art to better understand the technical solutions in this specification, the technical solutions in the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. However, this is not the only description; all aspects not described in detail herein are based on conventional techniques in the art.

[0043] Example 1

[0044] A method for constructing the oil content recovery coefficient of shale is presented. This embodiment uses core samples from high-maturity shale oil layers in the Qingshankou Formation of the Gulong Depression in the Songliao Basin, my country, as the research object. The method for establishing the oil content recovery coefficient of light components is systematically constructed and described. Figure 1 As shown, it includes the following steps:

[0045] S1, under the well site conditions, core samples were obtained using pressure-holding coring technology and immediately transferred to a Dewar flask containing liquid nitrogen for -196℃ cryopreservation. The samples were then transported to the laboratory under -196℃ cryopreservation conditions to minimize the volatilization loss of light hydrocarbon components.

[0046] S2. Core samples are taken out from the Dewar bottle in the laboratory and cut into cube core samples of specified size at a low temperature of -196℃ to obtain test samples. The test samples are then placed back into liquid nitrogen containers for cryopreservation to ensure the in-situ preservation of crude oil components in the samples.

[0047] S3. Before the NMR test, the test sample is removed from the liquid nitrogen container and allowed to thaw naturally to the optimal thawing time. Immediately afterward, a two-dimensional NMR T1-T2 test is performed to extract the NMR T2 signal corresponding to the crude oil in the pores of the test sample, including the free oil signal (e.g., ...). Figure 3 Region B) and adsorbed oil signals (such as Figure 3 Region C) consists of two parts. Based on the calibration relationship between the NMR T2 signal and crude oil quality, the corresponding crude oil quality in the test sample is obtained, and then the oil content m is obtained. o This oil content can truly reflect the occurrence state of crude oil in shale under in-situ conditions;

[0048] S4, after completing the nuclear magnetic resonance test, the test sample was crushed and divided into two equal parts. One part was directly subjected to rock pyrolysis experiment to obtain the pyrolysis S1 and S2 before washing the oil. The other part was first washed with oil and then subjected to rock pyrolysis experiment to obtain the pyrolysis after washing the oil. and pyrolysis The pyrolysis experiment can be conducted using a Rock-Eval 6 pyrolysis apparatus, and the results are as follows: Figure 4 As shown. The pyrolysis S1 sample before washing exhibited a high FID signal (FID signal is the electrical signal generated by the hydrogen flame ionization detector) below 300℃, reflecting the presence of a large amount of volatile or easily desorbable light and medium hydrocarbons in the shale pores. After washing, the FID signal of the pyrolysis S1 sample (300℃) significantly decreased and approached zero, indicating that free and elutable light and medium crude oil had been effectively removed. For pyrolysis S2, there was still a significant response in the pyrolysis spectrum before and after washing, the difference mainly stemming from heavy oil and asphaltenes in the shale pores. These hydrocarbon components exist in an adsorbed state or bound to organic matter and mineral matrix, requiring release through thermal decomposition at higher temperatures. Their content can be measured by the difference in S2 signal before and after washing (…). The adsorbed heavy oil content in shale was characterized and used to quantitatively calculate the adsorbed heavy oil content in shale.

[0049] S5, based on the crude oil occurrence morphology in shale pores and the characteristics of light component loss under different experimental conditions, this invention proposes two types of oil content recovery coefficients: one is the total oil content recovery coefficient C. t The first is used to characterize the overall recovery degree of in-situ oil content in shale relative to conventional pyrolysis test results; the second is the light-to-medium quality oil content recovery coefficient C. l This is used to quantitatively characterize the compensation relationship of light and medium crude oil components lost during core sampling, storage, and testing. Total oil content recovery coefficient C t and the recovery coefficient C of light and medium quality oil l The calculation formula is as follows:

[0050] (1)

[0051] (2).

[0052] This invention utilizes the aforementioned comparative experiments to determine the degree of loss of light components in pyrolysis S1, thereby establishing a repeatable and quantifiable recovery coefficient system. The recovery coefficients constructed using this method can provide quantitative evidence for obtaining in-situ oil content in long-stored and conventionally cored shale samples, significantly improving the accuracy and reliability of oil content evaluation in medium-to-high maturity shale oil.

[0053] The method for constructing the oil content recovery coefficient proposed in this embodiment is simple in process and clear in concept. By directly comparing the oil content of the same sample under in-situ conditions and under leached conditions, the recovery coefficient is quantitatively determined, effectively reducing the uncertainty introduced into the experimental process. Compared with the prior art, this invention has significant advantages in terms of data intuitiveness, in-situ representativeness, and result reliability.

[0054] Example 2

[0055] A method for constructing the shale oil content recovery coefficient, as described in Example 1, differs in that, in step S2, after the core sample is taken out of the Dewar bottle containing liquid nitrogen, it is placed in a safety shield, and the core sample is kept at a low temperature of -196℃ by continuously spraying liquid nitrogen, while the core is cut.

[0056] The safety shield is made of polycarbonate, which is a common material.

[0057] Example 3

[0058] A method for constructing the shale oil content recovery coefficient, as described in Example 2, differs in that the optimal thawing time is determined in step S3 as follows:

[0059] The test sample was weighed immediately after being removed from the liquid nitrogen container. Because water vapor condenses easily on the sample surface at low temperatures, the sample surface needed to be wiped before weighing to avoid mass errors caused by condensation and interference with the NMR signal. The test sample was then placed in a quartz glass tube, which was sealed with a cork. One-dimensional NMR T2 testing was performed inside the quartz glass tube, with each measurement lasting less than one minute. As the test sample gradually thawed, the crude oil in the pores changed from a frozen state to a liquid state. Hydrogen protons underwent resonant transitions in the radio frequency magnetic field, and the total signal value of the one-dimensional T2 spectrum continuously increased during the thawing process. When the total signal value reached its maximum value with increasing time and began to show a downward trend, the corresponding thawing time was determined to be the optimal thawing time.

[0060] In this embodiment, before conducting the NMR experiment, the shale sample preserved in liquid nitrogen was thawed, causing the crude oil in the sample pores to return from a solid to a liquid state. This ensured that the fluid molecules possessed the necessary mobility to obtain a stable and reliable T1-T2 relaxation signal. This thawing process effectively eliminates the influence of low-temperature freezing conditions on NMR relaxation characteristics, allowing the test results to accurately reflect the fluid state within the shale pores and improving the accuracy and repeatability of the experimental data. To obtain a universally applicable optimal thawing time, this embodiment used cored samples numbered 1 to 4 under pressure. By continuously measuring the NMR signal intensity of the samples under different thawing time conditions, the variation of the NMR signal intensity with thawing time was analyzed to determine the optimal thawing time for the samples. Figure 2 The diagram shows the trend of nuclear magnetic resonance (NMR) signal intensity of samples 1 to 4 as a function of thawing time. When the NMR signal intensity reaches its maximum value and begins to decline with increasing thawing time, the corresponding thawing time is determined to be the optimal thawing time.

[0061] Experiments have shown that the optimal thawing time for this type of shale sample is 2 minutes.

[0062] Example 4

[0063] A method for constructing a shale oil content recovery coefficient, as described in Example 3, differs in that, in step S3, the calibration relationship between crude oil NMR signal and crude oil quality is obtained through the following method:

[0064] One-dimensional nuclear magnetic resonance T2 tests were directly performed on crude oil samples produced from the well. The T2 signals of crude oil samples of different qualities were obtained sequentially. Based on linear regression, the calibration relationship between crude oil T2 signals and crude oil quality was established.

[0065] One-dimensional NMR T2 and two-dimensional NMR T1-T2 tests were performed using a high-precision benchtop NMR analyzer, model MR Cores-xx. The parameters for the two-dimensional NMR T1-T2 test were as follows: magnetic field strength 0.5T, magnetic resonance frequency 22 MHz, probe diameter 30 mm, echo time (TE) 0.07 ms, waiting time (TW) 1000 ms, number of echoes (NECH) 4000, and number of scans (NS) 16.

[0066] Figure 3 To obtain the two-dimensional nuclear magnetic resonance (NMR) T1-T2 spectra of the pressure-controlled cored shale samples, the blocky samples were removed from the liquid nitrogen environment and thawed for 2 minutes before undergoing T1-T2 NMR testing to preserve the in-situ state of the crude oil within the samples as much as possible. In the T1-T2 spectra shown, different signal regions correspond to different types of hydrogen nuclei responses: region A represents the NMR signal of solid organic matter, region B represents the signal of adsorbed oil and heavy oil, region C represents the signal of free oil, region D represents the signal of hydroxyl water and adsorbed water, and region E represents the signal of free water. By extracting the crude oil-related signals from regions B and C of the spectra and combining this with the calibration relationship between the crude oil NMR signal and mass, the oil content of the sample can be quantitatively calculated. This oil content characterizes the oil content of the shale under in-situ conditions.

[0067] Example 5

[0068] A method for constructing the oil content recovery coefficient of shale, as described in Example 4, except that in step S4, the sample is crushed to 60-80 mesh and the crushed test sample, which is divided into two equal parts, is placed for more than 10 days to simulate the storage state of conventional core samples.

[0069] The oil washing process is as follows: the powder sample is wrapped in filter paper and placed in a Soxhlet extractor. Dichloromethane is used as the extraction solvent and the extraction is carried out continuously for 5-7 days to fully remove the mobile hydrocarbon fluids that exist in the form of free and weakly adsorbed states. After the oil washing is completed, the sample is dried at 110℃ for 5 hours.

[0070] Example 6

[0071] A method for constructing the shale oil content recovery coefficient, as described in Example 5, differs in that it is applied to six different maturity levels R. o =0.90%, R o =1.20%, R o =1.32%, R o =1.33%, R o =1.42%, R o The core sample with a content of 1.55% was subjected to steps S1 to S5 to obtain the total oil content recovery coefficient C. t and the recovery coefficient C of light and medium quality oil l Maturity R is established through exponential fitting. o With the total oil content recovery coefficient C t and the recovery coefficient C of light and medium quality oil l The curve, the result is as follows Figure 5 As shown, for shale well sections where pressure-maintaining coring has not been carried out, it is only necessary to obtain the shale sample maturity R. o The total oil content recovery coefficient C can be obtained by querying the corresponding parameters of the curve. t and the recovery coefficient C of light and medium quality oil l .

[0072] For shale well sections where pressure-maintaining coring was not carried out, conventional pyrolysis experiments were conducted to obtain pyrolysis S1 and the total oil content recovery coefficient C. t and the recovery coefficient C of light and medium quality oil l Multiplying these values ​​by the pyrolysis S1 yields the in-situ total oil content and light-to-medium quality oil content of the shale. This method avoids the complex experimental procedures under pressure-maintaining coring conditions, significantly improving the efficiency and applicability of shale oil content evaluation.

[0073] In practical applications, for shale well sections where pressure-maintaining coring has not been carried out, this invention only requires obtaining sample maturity and conducting conventional pyrolysis experiments to determine the appropriate parameters. Figure 5 The relationship between maturity and recovery coefficient in shale is used to obtain the corresponding recovery coefficient, which is then used to correct the oil content measured by pyrolysis, thereby quickly estimating the total in-situ oil content and light to medium oil content of shale.

[0074] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for constructing a shale oil content recovery coefficient, characterized in that, Includes the following steps: S1, under the well site conditions, core samples were obtained using pressure-holding coring technology and immediately transferred to a Dewar bottle containing liquid nitrogen for -196℃ freezing and storage, and then transported to the laboratory under -196℃ freezing and storage conditions. S2, in the laboratory, the core sample is taken out from the Dewar bottle and cut into a cube core sample of the specified size at -196℃ to obtain the test sample. The test sample is then placed back into the liquid nitrogen container for cryopreservation. S3. Before the NMR test, the test sample is removed from the liquid nitrogen container and allowed to thaw naturally to the optimal thawing time. Immediately afterward, a two-dimensional NMR T1-T2 test is performed to extract the NMR T2 signal corresponding to the produced crude oil. Based on the calibration relationship between the NMR T2 signal and the crude oil mass, the corresponding crude oil mass in the test sample is obtained, and thus the oil content m is calculated. o ; S4, after completing the nuclear magnetic resonance test, the test sample was crushed and divided into two equal parts. One part was directly subjected to rock pyrolysis experiment to obtain the pyrolysis S1 and S2 before washing the oil. The other part was first washed with oil and then subjected to rock pyrolysis experiment to obtain the pyrolysis after washing the oil. and pyrolysis ; S5, Calculate the total oil content recovery coefficient C t and the recovery coefficient C of light and medium quality oil l The calculation formula is as follows: （1） （2）。 2. The method for constructing the shale oil content recovery coefficient according to claim 1, characterized in that, In step S2, after the core sample is taken out of the Dewar bottle containing liquid nitrogen, it is placed in a safety shield and the core sample is kept at -196°C by continuously spraying liquid nitrogen. At the same time, the core is cut.

3. The method for constructing the shale oil content recovery coefficient according to claim 2, characterized in that, In step S3, the optimal thawing time is determined as follows: After removing the test sample from the liquid nitrogen container, the sample is wiped clean and weighed immediately. The sample is then placed in a quartz glass tube, which is sealed with a cork. One-dimensional nuclear magnetic resonance (NMR) T2 testing is performed inside the tube, with each measurement lasting less than one minute. As the sample thaws, the crude oil in the pores changes from a solid to a liquid state. Hydrogen protons undergo resonant transitions in the radio frequency magnetic field, and the total signal value of the one-dimensional T2 spectrum continuously increases with the thawing process. When the total signal value reaches its maximum value with increasing time and begins to decline, the corresponding thawing time is determined to be the optimal thawing time.

4. The method for constructing the shale oil content recovery coefficient according to claim 3, characterized in that, In step S3, the optimal defrosting time is 2 minutes.

5. The method for constructing the shale oil content recovery coefficient according to claim 4, characterized in that, In step S3, the calibration relationship between the crude oil NMR signal and the crude oil quality is obtained through the following method: One-dimensional nuclear magnetic resonance T2 tests were directly performed on crude oil samples actually produced from shale oil wells to obtain the nuclear magnetic T2 signals of crude oil samples of different qualities in sequence. Based on linear regression, a calibration relationship between crude oil nuclear magnetic T2 signals and crude oil quality was established.

6. The method for constructing the shale oil content recovery coefficient according to claim 5, characterized in that, Both one-dimensional NMR T2 and two-dimensional NMR T1-T2 tests were performed using a high-precision benchtop NMR analyzer. The parameters for the two-dimensional NMR T1-T2 test were as follows: magnetic field strength of 0.5T, magnetic resonance frequency of 22 MHz, probe diameter of 30 mm, echo time of 0.07 ms, waiting time of 1000 ms, number of echoes of 4000, and number of scans of 16.

7. The method for constructing the shale oil content recovery coefficient according to claim 6, characterized in that, In step S4, the sample is pulverized to 60-80 mesh and the pulverized test sample, which is divided into two equal parts, is placed for more than 10 days to simulate the storage state of conventional core samples. The oil washing process is as follows: the powder sample is wrapped in filter paper and placed in a Soxhlet extractor. Dichloromethane is used as the extraction solvent and the extraction is carried out continuously for 5-7 days to fully remove the mobile hydrocarbon fluids in the shale pores. After the oil washing is completed, the sample is dried at 110℃ for 5 hours.

8. The method for constructing the shale oil content recovery coefficient according to claim 7, characterized in that, Steps S1 to S5 were performed on core samples of different maturity levels to calculate the total oil content recovery coefficient C for core samples of different maturity levels. t and the recovery coefficient C of light and medium quality oil l Establish the relationship between maturity and total oil content recovery coefficient C. t and the recovery coefficient C of light and medium quality oil l In relation to the relationship between shale well sections where pressure-maintaining coring has not been carried out, the total oil content recovery coefficient C can be obtained simply by obtaining the maturity of the shale samples. t and the recovery coefficient C of light and medium quality oil l .

9. The method for constructing the shale oil content recovery coefficient according to claim 8, characterized in that, Establish the maturity and total oil content recovery coefficient C t and the recovery coefficient C of light and medium quality oil l When considering the relationship, select core samples of more than 5 different maturity levels for experiments.

10. The method for constructing the shale oil content recovery coefficient according to claim 8, characterized in that, For shale well sections where pressure-maintaining coring was not carried out, conventional pyrolysis experiments were conducted to obtain pyrolysis S1 and the total oil content recovery coefficient C. t and the recovery coefficient C of light and medium quality oil l Multiplying these values ​​by the pyrolysis S1 yields the total in-situ oil content and the light to medium oil content of the shale.

Images