A shale full pore size distribution and connectivity quantitative characterization method

Abstract

This invention relates to a method for quantitative characterization of the full pore size distribution and connectivity of shale. The method includes the following steps: (1) measuring the two-dimensional nuclear magnetic resonance (NMR) T1-T2 spectrum and NMR T2 spectrum of dry core samples and saturated oil core samples respectively; conducting high-pressure mercury intrusion testing on parallel core samples; completing the calibration of T2 and pore throat radius; and determining the distribution of connected pores in the core; (2) splitting the core into sheets along the foliation; measuring the two-dimensional NMR T1-T2 spectrum of sheet-like dry core samples; comparing it with the T1-T2 spectrum of dry core samples; and calculating the distribution of disconnected pores in the core; (3) grinding the core into 200-mesh particles; measuring the two-dimensional NMR T1-T2 spectrum of granular dry core samples; comparing it with the T1-T2 spectrum of sheet-like dry core samples; and calculating the distribution of disconnected pores in the core; and (4) calculating the full pore size distribution and connectivity of shale. This method achieves quantitative characterization of the full pore size distribution and connectivity of different reservoir spaces of shale by conducting NMR tests on shale in different states and morphologies.

Description

Technical Field

[0001] This invention relates to the field of shale oil and gas reservoir evaluation and development technology, specifically to a method for quantitative characterization of the full pore size distribution and connectivity of shale. Background Technology

[0002] As my country's oil and gas industry accelerates its upgrading and transformation, and oil and gas exploration and development technologies mature, unconventional oil and gas resources such as shale oil are showing enormous development potential and are gradually becoming the main force for increasing reserves and production in my country's petrochemical energy sector. Before shale oil development, accurate characterization of reservoir micropore size distribution and connectivity is fundamental to reservoir evaluation and development plan design. Pore size distribution and connectivity directly affect the occurrence state, flow capacity, and fracturing effect of reservoir fluids. Characterization of pore size distribution and connectivity serves as a "geological navigator" for efficient shale oil development. It not only provides quantitative basis for optimizing reservoir stimulation parameters and selecting sweet spots, but also directly determines single-well production and ultimate recovery rate.

[0003] Currently, while techniques such as high-pressure mercury intrusion porosimetry (HS-MP), nuclear magnetic resonance (NMR), CT scanning, and digital core analysis are widely used for characterizing shale pore structure and depicting natural fractures, they have significant limitations. H-MP-MP relies on destructive manipulation, indirectly reflecting pore structure characteristics using mercury intrusion pressure differences, and is only suitable for characterizing connected pores. CT scanning has limited accuracy and struggles to identify nanoscale matrix pores in shale. Furthermore, pore size distribution and connectivity evaluation results based on digital core simulations lack core experimental data support, resulting in low accuracy. Existing pore structure characterization methods based on NMR testing can only determine the pore size distribution of connected pores across the entire shale scale, failing to characterize non-connected pores and the connectivity of shale pores.

[0004] In summary, existing methods for characterizing shale pore size distribution and connectivity have many shortcomings, with significant limitations in applicability and accuracy. Therefore, there is an urgent need to establish a quantitative method for characterizing the full pore size distribution and connectivity of shale that can consider the multi-scale pore structure characteristics. Summary of the Invention

[0005] To address the problems existing in the background technology, this invention proposes a novel method for quantitatively characterizing the full-pore size distribution and connectivity of shale. This method determines the total porosity, connected porosity, and disconnected porosity distribution of shale by conducting two-dimensional nuclear magnetic resonance (NMR) tests on shale cores in different states and morphologies, thereby achieving a quantitative characterization of the full-pore size distribution and the connectivity of different reservoir spaces. The proposed method for quantitatively characterizing the full-pore size distribution and connectivity of shale will provide a powerful tool for shale oil reservoir evaluation.

[0006] The technical solution provided by this invention is: a method for quantitative characterization of the full-pore size distribution and connectivity of shale, comprising the following steps:

[0007] 1. Shale cores and their parallel samples were dried to constant weight at 110℃, and the two-dimensional nuclear magnetic resonance (NMR) T1-T2 spectra of the cores were measured. d and nuclear magnetic resonance T2 spectrum P d2 High-pressure mercury intrusion testing was conducted on parallel core samples to determine the distribution of the connecting pore throat radius S. e ;

[0008] 2. Saturate the core with n-decane and determine the two-dimensional nuclear magnetic resonance T1-T2 spectrum of the saturated oil core. o and nuclear magnetic resonance T2 spectrum P o2 ;

[0009] 3. The core was dried to constant weight at 110℃, then split into sheets along the foliation. The two-dimensional nuclear magnetic resonance (NMR) T1-T2 spectra of the sheet cores were measured. s ;

[0010] 4. Grind the flaky core into 200-mesh particles, dry the granular core at 110℃ to constant weight, and measure the two-dimensional nuclear magnetic resonance (NMR) T1-T2 spectrum of the granular core. b ;

[0011] 5. Based on the results of two-dimensional nuclear magnetic resonance T1-T2 spectrum measurements of cores in different states and morphologies, the full pore size distribution and connectivity of shale were calculated. The specific calculation method is as follows:

[0012] ①According to P d2 P o2 and S e Determine the conversion relationship TS between the oil's transverse relaxation time (T2) and the core pore throat radius (r);

[0013] ②Based on the interpretation of the two-dimensional nuclear magnetic resonance pattern, by TS, P d Determine the hydrocarbon distribution in clay interlayer pores, organic matter pores, and inorganic matter pores of different sizes in dry core samples. d ;

[0014] ③ Based on the interpretation of the two-dimensional nuclear magnetic resonance (NMR) chart, from TS and P o Determine the hydrocarbon distribution in clay interlayer pores, organic matter pores, and inorganic matter pores of different sizes in saturated oil cores. o ;

[0015] ④S o Subtract S d Determine the distribution of connecting holes S fe ;

[0016] ⑤ Based on the interpretation of the two-dimensional nuclear magnetic resonance pattern, from TS, P s Determine the hydrocarbon distribution in clay interlayer pores, organic matter pores, and inorganic matter pores of different sizes in sheet-like dry core samples. s ;

[0017] ⑥S d Subtract S s Determine the distribution of non-connected seams S fif ;

[0018] ⑦ Based on the interpretation of the two-dimensional nuclear magnetic resonance pattern, from TS, P b Determine the hydrocarbon distribution in clay interlayer pores, organic matter pores, and inorganic matter pores of different sizes in granular dry core samples. b ;

[0019] ⑧S s Subtract S b Determine the distribution of non-connected holes S fip ;

[0020] ⑨ S fe S fif S fip The total pore size distribution S is obtained by adding the two samples together. fa ;

[0021] ⑩ Calculate the ratio of the porosity of interconnected pores to the total porosity in clay interlayer pores, organic matter pores, and inorganic matter pores of different sizes to obtain the connectivity of different types of pores.

[0022] The beneficial effects of this invention are as follows: Based on the principle that only hydrocarbons in connected pores can escape from the rock core through heating, this invention innovatively proposes a quantitative characterization method for the full-scale pore size distribution and connectivity of shale. This solves the problem that existing reservoir rock pore structure characterization methods cannot accurately determine the full-scale distribution of disconnected pores and the connectivity of pore throats of different sizes in shale. This invention clarifies the distribution of connected pores and fractures based on the interpretation results of the two-dimensional nuclear magnetic resonance (NMR) T1-T2 spectra of saturated oil in shale. By splitting the core along the foliation into sheets, previously unconnected fractures within the core are connected. After drying, hydrocarbons escape from the core. Comparison of the interpretation results of the two-dimensional NMR T1-T2 spectra of dry core samples and sheet-like dry core samples clarifies the distribution of unconnected fractures. Further grinding the sheet-like core into granules connects previously unconnected pores. After drying, hydrocarbons escape from the core. Comparison of the interpretation results of the two-dimensional NMR T1-T2 spectra of dry core samples and granular dry core samples clarifies the distribution of unconnected pores. Finally, the full-scale distribution of connected pores and fractures, unconnected pores and fractures, total pore size and fracture density, and connectivity in shale are determined. The quantitative characterization method for the full-scale pore size distribution and connectivity of shale proposed in this invention provides a novel scientific approach for shale oil reservoir evaluation. Attached Figure Description

[0023] Appendix Figure 1 This is a picture of a shale core sample.

[0024] Appendix Figure 2 This is a graph showing the results of two-dimensional nuclear magnetic resonance T1-T2 spectrum testing of a dry shale core sample.

[0025] Appendix Figure 3 This is a diagram showing the results of two-dimensional nuclear magnetic resonance T1-T2 spectrum testing of shale core samples after they were saturated with oil.

[0026] Appendix Figure 4 This is a diagram showing the results of two-dimensional nuclear magnetic resonance T1-T2 spectrum testing of a shale core sample after it was split into flakes and dried.

[0027] Appendix Figure 5 This is a graph showing the results of two-dimensional nuclear magnetic resonance T1-T2 spectrum testing of a shale core sample after it has been ground into granules and dried.

[0028] Appendix Figure 6 This is a graph showing the T2 NMR spectrum of a dry shale core sample.

[0029] Appendix Figure 7 This is a graph showing the T2 NMR spectrum of a shale core sample after it has been saturated with oil.

[0030] Appendix Figure 8 This is a diagram showing the T2-r calibration results of shale core samples. Detailed Implementation

[0031] To enable those skilled in the art to better understand the technical solutions in this application, the technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this application.

[0032] The specific embodiments of the present invention will be further described in detail below with reference to examples. Example

[0033] One shale sample from the Qingyi Formation of the Songliao Basin was selected. The sample was 6.78 cm long and 2.47 cm in diameter. Quantitative characterization of its full-pore size distribution and connectivity was performed. See Appendix for the experimental shale sample. Figure 1 .

[0034] (1) The core and its parallel samples were dried at 110℃. The mass of the core and its parallel samples was measured every 24 hours. When the mass of the core and its parallel samples remained constant for 48 consecutive hours, the drying was stopped and the core and its parallel samples were taken out. According to the standard "SY / T 6490-2023 Laboratory Measurement Specification for Nuclear Magnetic Resonance Parameters of Rock Samples", the two-dimensional nuclear magnetic resonance T1-T2 spectrum and nuclear magnetic resonance T2 spectrum of the dried core sample were tested to obtain the two-dimensional nuclear magnetic resonance T1-T2 spectrum P of the dried core sample. d (See attached) Figure 2 ) and nuclear magnetic resonance T2 spectrum Pd2 (See attached) Figure 6 According to the standard GB / T 21650.1-2008 "Determination of Pore Size Distribution and Porosity of Solid Materials by Mercury Intrusion Porosimetry and Gas Adsorption Methods - Part 1: Mercury Intrusion Porosimetry", high-pressure mercury intrusion porosimetry was performed on the dried parallel samples to obtain the pore throat distribution S of the parallel samples. e (See attached) Figure 8 );

[0035] (2) According to the standard GB / T 29172-2012 Core Analysis Methods, the core saturated with n-decane was analyzed. According to the standard SY / T 6490-2023 Laboratory Measurement Specification for Nuclear Magnetic Resonance Parameters of Rock Samples, two-dimensional nuclear magnetic resonance T1-T2 spectra and nuclear magnetic resonance T2 spectra of the saturated oil core were tested. The two-dimensional nuclear magnetic resonance T1-T2 spectra of the saturated oil core were obtained. o (See attached) Figure 3 ) and nuclear magnetic resonance T2 spectrum P o2 (See attached) Figure 7 );

[0036] (3) The core was dried at 110℃, and the core mass was measured every 24 hours. When the core mass remained constant for 48 consecutive hours, drying was stopped and the core was removed. The core was split into sheets along the foliation and dried at 110℃. The sheet core mass was measured every 24 hours. When the sheet core mass remained constant for 48 consecutive hours, drying was stopped and the sheet core was removed. Two-dimensional nuclear magnetic resonance (NMR) T1-T2 spectrum tests were performed on the sheet core according to the standard "SY / T 6490-2023 Laboratory Measurement Specification for Nuclear Magnetic Resonance Parameters of Rock Samples". The P-value of the two-dimensional nuclear magnetic resonance (NMR) T1-T2 spectrum of the sheet core was measured. s (See attached) Figure 4 );

[0037] (4) Grind the flaky core into 200-mesh particles and dry the granular core at 110℃. Measure the mass of the granular core every 24 hours. When the mass of the granular core remains constant for 48 consecutive hours, stop drying and remove the granular core. Perform two-dimensional nuclear magnetic resonance (NMR) T1-T2 spectrum testing on the granular core according to the standard "SY / T 6490-2023 Laboratory Measurement Specification for Nuclear Magnetic Resonance Parameters of Rock Samples". Measure the P-value of the two-dimensional NMR T1-T2 spectrum of the granular core. b (See attached) Figure 5 );

[0038] (5) The full pore size distribution and connectivity of shale were calculated based on the T1-T2 spectra of two-dimensional nuclear magnetic resonance cores in different states and morphologies. The specific calculation method is as follows:

[0039] ①P o2 Subtract P d2 The nuclear magnetic resonance T2 spectrum of the saturated oil was obtained (see appendix). Figure 8 ), and compare the nuclear magnetic resonance T2 spectrum of saturated oil with S e Relative to the standard, the conversion relationship (TS) between the oil's transverse relaxation time (T2) and the core pore throat radius (r) is obtained as T2 = 51.37r. 0.83 ;

[0040] ②Based on the interpretation chart of two-dimensional nuclear magnetic resonance, from P d The T2 value ranges and hydrocarbon distributions in clay interlayer pores, organic matter pores, small to medium-sized inorganic matter pores, and large inorganic matter pores in the dry core sample were determined. The T2 value ranges for each type of pore were converted into radius value ranges using TS, yielding the hydrocarbon distribution S in clay interlayer pores, organic matter pores, and inorganic matter pores of different sizes in the dry core sample. d (See Appendix 1);

[0041] ③ Based on the interpretation of the two-dimensional nuclear magnetic resonance pattern, from P o The hydrocarbon distribution in clay interlayer pores, organic matter pores, small and medium-sized inorganic matter pores, and large inorganic matter pores in saturated oil cores was determined. Combined with the radius ranges of various pore types determined in step ②, the hydrocarbon distribution S in clay interlayer pores, organic matter pores, and inorganic matter pores of different sizes in saturated oil cores was obtained. o (See Appendix 1);

[0042] ④S o Subtract S d The distribution of connected pores S is obtained. fe (See Appendix 1);

[0043] ⑤ Based on the interpretation of the two-dimensional nuclear magnetic resonance pattern, from P s The hydrocarbon distribution in clay interlayer pores, organic matter pores, small to medium-sized inorganic matter pores, and large inorganic matter pores in sheet-like dry core samples was determined. Combined with the radius ranges of various pore types determined in step ②, the hydrocarbon distribution S in clay interlayer pores, organic matter pores, and inorganic matter pores of different sizes in sheet-like dry core samples was obtained. s (See Appendix 1);

[0044] ⑥S d Subtract S s The distribution of discontinuous seams S is obtained. fif (See Appendix 1);

[0045] ⑦ Based on the interpretation of the two-dimensional nuclear magnetic resonance plate, by P b The hydrocarbon distribution in clay interlayer pores, organic matter pores, small and medium-sized inorganic matter pores, and large inorganic matter pores in granular core samples was determined. Combined with the radius ranges of various pore types determined in step ②, the hydrocarbon distribution S in clay interlayer pores, organic matter pores, and inorganic matter pores of different sizes in the dry granular core sample was obtained. b (See Appendix 1);

[0046] ⑧S s Subtract Sb The distribution of unconnected holes S is obtained. fip (See Appendix 1);

[0047] ⑨ S fe S fif S fip The total pore size distribution S is obtained by adding the two samples together. fa (See Appendix 1);

[0048] ⑩ Calculate the ratio of the porosity of interconnected pores in clay interlayer pores, organic matter pores and inorganic matter pores of different sizes to their total porosity to obtain the connectivity of different types of pores (see Appendix Table 1).

[0049] Appendix Table 1 Quantitative Characterization Results of Full Pore Size Distribution and Connectivity of Core Samples

[0050]

[0051] Although the invention has been described with reference to embodiments, various modifications can be made thereto and equivalent steps can be substituted without departing from the scope of the invention. The invention is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A method for quantitatively characterizing the full-aperture distribution and connectivity of shale, comprising the following steps: (1) The shale core and its parallel samples were dried at 110℃ to constant weight, and the two-dimensional nuclear magnetic resonance T1-T2 spectrum of the dried core was measured. d and nuclear magnetic resonance T2 spectrum P d2 High-pressure mercury intrusion testing was conducted on parallel core samples after drying to determine the distribution of the connecting pore throat radius S. e ; (2) The core was saturated with n-decane, and the two-dimensional nuclear magnetic resonance T1-T2 spectrum of the saturated oil core was measured. o and nuclear magnetic resonance T2 spectrum P o2 ; (3) The core was dried to constant weight at 110℃, and then split along the foliation into sheets that connected the previously unconnected fractures. The two-dimensional nuclear magnetic resonance (T1-T2) spectra of the sheet cores were measured. s ; (4) Grind the flaky core into 200-mesh particles, dry the granular core at 110℃ to constant weight, and measure the two-dimensional nuclear magnetic resonance T1-T2 spectrum of the granular core. b ; (5) Calculate the full pore size distribution and connectivity of shale based on the T1-T2 spectrum measurement results of two-dimensional nuclear magnetic resonance cores in different states and morphologies; The specific calculation method for step (5) is as follows: ①According to P d2 P o2 and S e Determine the conversion relationship TS between the oil's transverse relaxation time (T2) and the core pore throat radius (r); ②Based on the interpretation of the two-dimensional nuclear magnetic resonance pattern, by TS, P d Determine the hydrocarbon distribution in clay interlayer pores, organic matter pores, and inorganic matter pores of different sizes in dry core samples. d ; ③ Based on the interpretation of the two-dimensional nuclear magnetic resonance (NMR) chart, from TS and P o Determine the hydrocarbon distribution in clay interlayer pores, organic matter pores, and inorganic matter pores of different sizes in saturated oil cores. o ; ④S o Subtract S d Determine the distribution of connecting holes S fe ; ⑤ Based on the interpretation of the two-dimensional nuclear magnetic resonance pattern, from TS, P s Determine the hydrocarbon distribution in clay interlayer pores, organic matter pores, and inorganic matter pores of different sizes in sheet-like dry core samples. s ; ⑥S d Subtract S s Determine the distribution of non-connected seams S fif ; ⑦ Based on the interpretation of the two-dimensional nuclear magnetic resonance pattern, from TS, P b Determine the hydrocarbon distribution in clay interlayer pores, organic matter pores, and inorganic matter pores of different sizes in granular dry core samples. b ; ⑧S s Subtract S b Determine the distribution of non-connected holes S fip ; ⑨ S fe S fif S fip The total pore size distribution S is obtained by adding the two samples together. fa ; ⑩ Calculate the ratio of the porosity of interconnected pores to the total porosity in clay interlayer pores, organic matter pores, and inorganic matter pores of different sizes to obtain the connectivity of different types of pores.

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