A method for evaluating a well logging fracture development index

Abstract

This invention discloses a method for evaluating the fracture development index in well logging, belonging to the field of oil and gas field exploration and development technology. Its features include the following steps: a) calculating the measured fracture development index FI. 实测 b. By determining the objective function, using the non-negative least squares method, and combining it with the crack development index FI calculated in step a. 实测 The crack development index model is obtained by solving for the acoustic time difference weighting coefficient W1 and the resistivity weighting coefficient W2 respectively; c. The crack development index FI is calculated using the crack development index model and verified by actual measurement of the crack development index FI. 实测 The following steps are performed: d) Verification is conducted; then, other fracture development indices FI are calculated using the fracture development index model, and the fracture development index is evaluated. This invention can effectively evaluate the development index of microscopic fractures that can be identified in thin sections, thereby improving exploration and development efficiency and reducing exploration and development costs.

Description

Technical Field

[0001] This invention relates to the field of oil and gas field exploration and development technology, and in particular to a method for evaluating the well logging fracture development index. Background Technology

[0002] Currently, fracture identification mainly relies on direct observation through field outcrops and core samples, as well as indirect observation through imaging-based special logging. However, existing methods are largely costly, yield limited data, and provide incomplete observations. Conventional logging can mostly only identify low-angle macroscopic fractures, and is primarily qualitative. Currently, fracture evaluation in well logging is mainly divided into quantitative and qualitative evaluation. Quantitative evaluation mainly involves imaging logging and fracture identification logging, but these special logging curves are unavailable in most areas. Qualitative evaluation mainly involves qualitative and semi-quantitative evaluation using sonic logging and resistivity logging of low-angle fractures.

[0003] Chinese patent document with publication number CN110276827A and publication date of September 24, 2019 discloses a method for evaluating the effectiveness of shale reservoirs. The method is characterized by establishing a shale reservoir space model for the target formation based on the fact that the effectiveness of shale reservoirs is controlled by the characteristics of shale reservoirs, such as oil generation, storage, preservation, modifiability, and mobility.

[0004] The method includes the following steps:

[0005] S1: Sequence stratigraphy is divided and correlated using core samples, well logs and well logging data. Within the sequence stratigraphic framework, a sedimentary model of "vertical stratification and planar partitioning" under the control of climate cycles is established to determine the sedimentary environment of organic-rich mudstone and shale.

[0006] S2: The facies of mudstone and shale were divided by a combination of macroscopic structure and three-end-member analysis of four rock components to determine the genesis and distribution of mudstone and shale facies.

[0007] S3: Using thin sections and field emission scanning electron microscopy, we identified diagenetic events in mudstone and shale, determined the diagenetic sequence and diagenetic stage, and selected organic-rich mudstone and shale for thermal simulation experiments using autoclave equipment to establish a diagenetic evolution model for organic-rich mudstone and shale.

[0008] S4: The reservoir space type of mudstone and shale was identified using core, thin section, field emission scanning electron microscopy and energy dispersive spectroscopy; the reservoir space composition was obtained using high pressure mercury intrusion, N2 and CO2 adsorption methods;

[0009] Environmental scanning electron microscopy was used to observe the occurrence and location of oil and gas in actual mudstone and shale samples and thermal simulation experimental samples, to determine the favorable reservoir space types and summarize their characteristics to determine their genesis; for organic matter pores, Avizo digital core modeling software and focused ion beam scanning electron microscopy were used to establish a three-dimensional model of organic matter pores to determine their spatial structure characteristics.

[0010] S5: Based on the study of shale sedimentary environment, lithofacies characteristics, diagenesis, reservoir space and fluid characteristics, comprehensively analyze the "generation, storage, capping, migration, enclosure and preservation" characteristics of shale oil reservoirs, and establish a shale oil reservoir model;

[0011] Based on this, the corresponding fuzzy mathematical method is selected to finally determine the mudstone and shale reservoir type;

[0012] The specific steps of S5 are as follows:

[0013] S51: Select reasonable evaluation parameters based on the analysis of influencing factors of various evaluation contents of shale reservoir effectiveness;

[0014] S52: Combine the Analytic Hierarchy Process (AHP) and the Entropy Weight Method to evaluate parameter weights;

[0015] S53: Couple fuzzy and grey evaluation methods to perform grey fuzzy comprehensive evaluation;

[0016] S54: Based on the results, the mudstone and shale reservoir type is determined.

[0017] The patent document discloses an evaluation method for the effectiveness of shale reservoirs. Based on the characteristics of shale oil reservoirs, lithofacies is determined as the basic evaluation unit. Oil generation potential, reservoir capacity, potential for alteration, and flowability are selected as evaluation criteria. A systematic analysis of influencing factors is then conducted, prioritizing organic carbon content and hydrocarbon generation potential, fracture type and development intensity, pore type and porosity, diagenesis, relative brittleness coefficient and brittleness index, and critical flow pore size as evaluation parameters. A grey fuzzy mathematics method is used to derive the shale reservoir type. However, it still cannot effectively evaluate the development index of micro-fractures that can be identified in thin sections. Summary of the Invention

[0018] In order to overcome the shortcomings of the prior art, the present invention provides a method for evaluating the development index of well logging fractures. The present invention can effectively evaluate the development index of micro-fractures that can be identified by thin sections, thereby improving exploration and development efficiency and reducing exploration and development costs.

[0019] This invention is achieved through the following technical solution:

[0020] A method for evaluating the fracture development index in well logging, characterized by comprising the following steps:

[0021] a. First, obtain the lower limit of measured fracture density and measured fracture density from core samples, thin sections, and imaging logs of the calibration well. Then, calculate the measured fracture development index FI using Equation 3. 实测 ;

[0022] FI 实测 =f(1-FVDC / FVDC0) Equation 3

[0023] in:

[0024] FI 实测 —Measured crack development index, dimensionless;

[0025] f() — Normalization function, with a value of 0-1, dimensionless;

[0026] FVDC—Measured crack density, meters per crack;

[0027] FVDC0—Lower limit of measured crack density, meter / crack;

[0028] b. By determining the objective function, using the non-negative least squares method, and combining it with the crack development index FI calculated in step a. 实测 The crack development index model is obtained by solving the acoustic time difference weighting coefficient W1 and the resistivity weighting coefficient W2 respectively.

[0029] c. Calculate the crack development index FI using the crack development index model, and verify the measured crack development index FI. 实测 Conduct an inspection;

[0030] d. Then, using the crack development index model, calculate other crack development indices FI and evaluate the crack development indices.

[0031] In step b, determining the objective function means determining the norm using Equation 4;

[0032] ||FI-FI 实测 ||→1 / (+∞) Equation 4

[0033] in:

[0034] FI—Crack Development Index, dimensionless;

[0035] FI 实测 —Measured crack development index, dimensionless.

[0036] In step b, solving for the acoustic time difference weighting coefficient W1 and resistivity weighting coefficient W2 means calculating them using Equation 2.

[0037] W1+W2=1 Equation 2

[0038] in:

[0039] W1 — Weighting coefficient for acoustic time difference, dimensionless;

[0040] W2 — resistivity weighting coefficient, dimensionless.

[0041] In step c, calculating the crack development index FI specifically refers to calculating it according to Equation 1.

[0042] FI=(f(1-AC0 / AC)W1+f(1-RT / RT0)W2)×f(1-GR / GR0)Equation 1

[0043] in:

[0044] FI—Crack Development Index, dimensionless;

[0045] f() — Normalization function, with a value of 0-1, dimensionless;

[0046] AC0 – Skeleton acoustic wave time difference, ms / ft;

[0047] AC – Measured sound wave time difference, ms / ft;

[0048] W1 — Weighting coefficient for acoustic time difference, dimensionless;

[0049] RT—Measured deep lateral resistivity, in Ω·m;

[0050] RT0—Lateral resistivity of the compact layer, in Ω·m;

[0051] W2 — resistivity weighting coefficient, dimensionless;

[0052] GR – Measured natural gamma value, API;

[0053] GR0 – Natural gamma value of mudstone, API.

[0054] In step c, the crack development index FI is measured. 实测 The inspection specifically refers to the inspection of crack density measured by electrical imaging, crack density measured by core samples, and crack density measured by thin sections.

[0055] The measured fracture density using electro-imaging refers to the quantitative identification of the number and density of fractures by applying electro-imaging logging and utilizing the low resistivity characteristics of fractures.

[0056] The measured crack density in the core refers to the crack density actually measured on the core through observation.

[0057] The measured crack density of the thin section refers to the crack density measured through a thin section of a rock casting.

[0058] In step d, calculating other fracture development indices FI specifically refers to obtaining fracture development indices through measured natural gamma, measured sonic transit time, and measured deep lateral resistivity in conventional well logging.

[0059] In step d, evaluating the crack development index specifically means that the higher the crack development index, the more developed the cracks are. The crack development index ranges from 0 to 1.

[0060] The beneficial effects of this invention are mainly reflected in the following aspects:

[0061] 1. In this invention, a) firstly, the lower limit of the measured fracture density and the measured fracture density of the core, thin section and imaging logging of the calibration well are obtained, and the measured fracture development index FI is calculated by Equation 3. 实测 b. By determining the objective function, using the non-negative least squares method, and combining it with the crack development index FI calculated in step a. 实测 The crack development index model is obtained by solving for the acoustic time difference weighting coefficient W1 and the resistivity weighting coefficient W2 respectively; c. The crack development index FI is calculated using the crack development index model and verified by actual measurement of the crack development index FI. 实测 d. Then, using the fracture development index model, calculate other fracture development indices FI and evaluate the fracture development index. As a complete technical solution, compared with existing technologies, it can effectively evaluate the development index of micro-fractures that can be identified in thin sections, thereby improving exploration and development efficiency and reducing exploration and development costs.

[0062] 2. In step c of this invention, the crack development index FI is measured. 实测 The inspection specifically refers to the inspection of crack density measured by electrical imaging, crack density measured by core, and crack density measured by thin section. By organically combining the crack density measured by electrical imaging, crack density measured by core, and crack density measured by thin section, the objectivity and accuracy of subsequent crack development index evaluation can be ensured.

[0063] 3. The present invention, the measured fracture density by electro-imaging, refers to the quantitative identification of the number and density of fractures by applying electro-imaging logging through the low resistivity characteristics of fractures, and can identify fractures larger than centimeters; the resolution is higher than that of conventional logging and seismic prediction, and the observation range and continuity are higher than those of thin section identification and core observation.

[0064] 4. The core measured crack density of this invention refers to the actual measurement of crack density on the core through observation, which can identify cracks larger than millimeters, with high resolution and accuracy.

[0065] 5. The present invention refers to the measurement of crack density in thin sections, which is achieved by measuring crack density in thin sections of rock castings and can identify cracks ranging from micrometers to centimeters in size.

[0066] 6. The present invention is simple and practical to operate, and has good reliability.

[0067] 7. This invention utilizes a wealth of conventional logging curves, including natural gamma ray, sonic transit time, and deep lateral resistivity curves, to evaluate fracture development. This allows the fracture development index to be applied over a wide range of applications, avoiding the difficulties caused by high coring costs, limited coring, small core samples, and scarce cast sections, which prevent the fracture development index from being widely used. This makes the operation more convenient. Attached Figure Description

[0068] The present invention will now be further described in detail with reference to the accompanying drawings and specific embodiments:

[0069] Figure 1 This is a flowchart of the present invention. Detailed Implementation

[0070] Example 1

[0071] See Figure 1 A method for evaluating the fracture development index in well logging includes the following steps:

[0072] a. First, obtain the lower limit of measured fracture density and measured fracture density from core samples, thin sections, and imaging logs of the calibration well. Then, calculate the measured fracture development index FI using Equation 3. 实测 ;

[0073] FI 实测 =f(1-FVDC / FVDC0) Equation 3

[0074] in:

[0075] FI 实测 —Measured crack development index, dimensionless;

[0076] f() — Normalization function, with a value of 0-1, dimensionless;

[0077] FVDC—Measured crack density, meters per crack;

[0078] FVDC0—Lower limit of measured crack density, meter / crack;

[0079] b. By determining the objective function, using the non-negative least squares method, and combining it with the crack development index FI calculated in step a. 实测 The crack development index model is obtained by solving the acoustic time difference weighting coefficient W1 and the resistivity weighting coefficient W2 respectively.

[0080] c. Calculate the crack development index FI using the crack development index model, and verify the measured crack development index FI. 实测 Conduct an inspection;

[0081] d. Then, using the crack development index model, calculate other crack development indices FI and evaluate the crack development indices.

[0082] This embodiment is the most basic implementation method, which can effectively evaluate the development index of micro-cracks that can be identified in thin sections, thereby improving exploration and development efficiency and reducing exploration and development costs.

[0083] Example 2

[0084] See Figure 1 A method for evaluating the fracture development index in well logging includes the following steps:

[0085] a. First, obtain the lower limit of measured fracture density and measured fracture density from core samples, thin sections, and imaging logs of the calibration well. Then, calculate the measured fracture development index FI using Equation 3. 实测 ;

[0086] FI 实测 =f(1-FVDC / FVDC0) Equation 3

[0087] in:

[0088] FI 实测 —Measured crack development index, dimensionless;

[0089] f() — Normalization function, with a value of 0-1, dimensionless;

[0090] FVDC—Measured crack density, meters per crack;

[0091] FVDC0—Lower limit of measured crack density, meter / crack;

[0092] b. By determining the objective function, using the non-negative least squares method, and combining it with the crack development index FI calculated in step a. 实测 The crack development index model is obtained by solving the acoustic time difference weighting coefficient W1 and the resistivity weighting coefficient W2 respectively.

[0093] c. Calculate the crack development index FI using the crack development index model, and verify the measured crack development index FI. 实测 Conduct an inspection;

[0094] d. Then, using the crack development index model, calculate other crack development indices FI and evaluate the crack development indices.

[0095] In step b, determining the objective function means determining the norm using Equation 4;

[0096] ||FI-FI 实测 ||→1 / (+∞) Equation 4

[0097] in:

[0098] FI—Crack Development Index, dimensionless;

[0099] FI 实测 —Measured crack development index, dimensionless.

[0100] In step b, solving for the acoustic time difference weighting coefficient W1 and resistivity weighting coefficient W2 means calculating them using Equation 2.

[0101] W1+W2=1 Equation 2

[0102] in:

[0103] W1 — Weighting coefficient for acoustic time difference, dimensionless;

[0104] W2 — resistivity weighting coefficient, dimensionless.

[0105] In step c, calculating the crack development index FI specifically refers to calculating it according to Equation 1.

[0106] FI=(f(1-AC0 / AC)W1+f(1-RT / RT0)W2)×f(1-GR / GR0) Equation 1

[0107] in:

[0108] FI—Crack Development Index, dimensionless;

[0109] f() — Normalization function, with a value of 0-1, dimensionless;

[0110] AC0 – Skeleton acoustic wave time difference, ms / ft;

[0111] AC – Measured sound wave time difference, ms / ft;

[0112] W1 — Weighting coefficient for acoustic time difference, dimensionless;

[0113] RT—Measured deep lateral resistivity, in Ω·m;

[0114] RT0—Lateral resistivity of the compact layer, in Ω·m;

[0115] W2 — resistivity weighting coefficient, dimensionless;

[0116] GR – Measured natural gamma value, API;

[0117] GR0 – Natural gamma value of mudstone, API.

[0118] Furthermore, in step c, the crack development index FI is measured. 实测 The inspection specifically refers to the inspection of crack density measured by electrical imaging, crack density measured by core samples, and crack density measured by thin sections.

[0119] This embodiment is a preferred implementation. In step c, the crack development index FI is measured. 实测 The inspection specifically refers to the inspection of crack density measured by electrical imaging, crack density measured by core, and crack density measured by thin section. By organically combining the crack density measured by electrical imaging, crack density measured by core, and crack density measured by thin section, the objectivity and accuracy of subsequent crack development index evaluation can be ensured.

[0120] Example 3

[0121] See Figure 1 A method for evaluating the fracture development index in well logging includes the following steps:

[0122] a. First, obtain the lower limit of measured fracture density and measured fracture density from core samples, thin sections, and imaging logs of the calibration well. Then, calculate the measured fracture development index FI using Equation 3. 实测 ;

[0123] FI 实测 =f(1-FVDC / FVDC0) Equation 3

[0124] in:

[0125] FI 实测 —Measured crack development index, dimensionless;

[0126] f() — Normalization function, with a value of 0-1, dimensionless;

[0127] FVDC—Measured crack density, meters per crack;

[0128] FVDC0—Lower limit of measured crack density, meter / crack;

[0129] b. By determining the objective function, using the non-negative least squares method, and combining it with the crack development index FI calculated in step a. 实测 The crack development index model is obtained by solving the acoustic time difference weighting coefficient W1 and the resistivity weighting coefficient W2 respectively.

[0130] c. Calculate the crack development index FI using the crack development index model, and verify the measured crack development index FI. 实测 Conduct an inspection;

[0131] d. Then, using the crack development index model, calculate other crack development indices FI and evaluate the crack development indices.

[0132] In step b, determining the objective function means determining the norm using Equation 4;

[0133] ||FI-FI 实测 ||→1 / (+∞) Equation 4

[0134] in:

[0135] FI—Crack Development Index, dimensionless;

[0136] FI 实测 —Measured crack development index, dimensionless.

[0137] In step b, solving for the acoustic time difference weighting coefficient W1 and resistivity weighting coefficient W2 means calculating them using Equation 2.

[0138] W1+W2=1 Equation 2

[0139] in:

[0140] W1 — Weighting coefficient for acoustic time difference, dimensionless;

[0141] W2 — resistivity weighting coefficient, dimensionless.

[0142] In step c, calculating the crack development index FI specifically refers to calculating it according to Equation 1.

[0143] FI=(f(1-AC0 / AC)W1+f(1-RT / RT0)W2)×f(1-GR / GR0)Equation 1

[0144] in:

[0145] FI—Crack Development Index, dimensionless;

[0146] f() — Normalization function, with a value of 0-1, dimensionless;

[0147] AC0 – Skeleton acoustic wave time difference, ms / ft;

[0148] AC – Measured sound wave time difference, ms / ft;

[0149] W1 — Weighting coefficient for acoustic time difference, dimensionless;

[0150] RT—Measured deep lateral resistivity, in Ω·m;

[0151] RT0—Lateral resistivity of the compact layer, in Ω·m;

[0152] W2 — resistivity weighting coefficient, dimensionless;

[0153] GR – Measured natural gamma value, API;

[0154] GR0 – Natural gamma value of mudstone, API.

[0155] In step c, the crack development index FI is measured. 实测 The inspection specifically refers to the inspection of crack density measured by electrical imaging, crack density measured by core samples, and crack density measured by thin sections.

[0156] The measured fracture density using electro-imaging refers to the quantitative identification of the number and density of fractures by applying electro-imaging logging and utilizing the low resistivity characteristics of fractures.

[0157] The measured crack density in the core refers to the crack density actually measured on the core through observation.

[0158] The measured crack density of the thin section refers to the crack density measured through a thin section of a rock casting.

[0159] This embodiment is another preferred implementation. Electro-imaging measured fracture density refers to the quantitative identification of the number and density of fractures by applying electro-imaging logging through the low resistivity characteristics of fractures. It can identify fractures larger than centimeters. The resolution is higher than that of conventional logging and seismic prediction, and the observation range and continuity are higher than those of thin section identification and core observation.

[0160] Core-measured fracture density refers to the actual measurement of fracture density on the core through observation. It can identify fractures larger than millimeters, with high resolution and accuracy.

[0161] Thin-section measured crack density refers to the measurement of crack density through thin sections of rock castings, which can identify cracks ranging from micrometers to centimeters in size.

[0162] Example 4

[0163] See Figure 1 A method for evaluating the fracture development index in well logging includes the following steps:

[0164] a. First, obtain the lower limit of measured fracture density and measured fracture density from core samples, thin sections, and imaging logs of the calibration well. Then, calculate the measured fracture development index FI using Equation 3. 实测 ;

[0165] FI 实测 =f(1-FVDC / FVDC0) Equation 3

[0166] in:

[0167] FI 实测 —Measured crack development index, dimensionless;

[0168] f() — Normalization function, with a value of 0-1, dimensionless;

[0169] FVDC—Measured crack density, meters per crack;

[0170] FVDC0—Lower limit of measured crack density, meter / crack;

[0171] b. By determining the objective function, using the non-negative least squares method, and combining it with the crack development index FI calculated in step a. 实测 The crack development index model is obtained by solving the acoustic time difference weighting coefficient W1 and the resistivity weighting coefficient W2 respectively.

[0172] c. Calculate the crack development index FI using the crack development index model, and verify the measured crack development index FI. 实测 Conduct an inspection;

[0173] d. Then, using the crack development index model, calculate other crack development indices FI and evaluate the crack development indices.

[0174] In step b, determining the objective function means determining the norm using Equation 4;

[0175] ||FI-FI 实测 ||→1 / (+∞) Equation 4

[0176] in:

[0177] FI—Crack Development Index, dimensionless;

[0178] FI 实测 —Measured crack development index, dimensionless.

[0179] In step b, solving for the acoustic time difference weighting coefficient W1 and resistivity weighting coefficient W2 means calculating them using Equation 2.

[0180] W1+W2=1 Equation 2

[0181] in:

[0182] W1 — Weighting coefficient for acoustic time difference, dimensionless;

[0183] W2 — resistivity weighting coefficient, dimensionless.

[0184] In step c, calculating the crack development index FI specifically refers to calculating it according to Equation 1.

[0185] FI=(f(1-AC0 / AC)W1+f(1-RT / RT0)W2)×f(1-GR / GR0) Equation 1

[0186] in:

[0187] FI—Crack Development Index, dimensionless;

[0188] f() — Normalization function, with a value of 0-1, dimensionless;

[0189] AC0 – Skeleton acoustic wave time difference, ms / ft;

[0190] AC – Measured sound wave time difference, ms / ft;

[0191] W1 — Weighting coefficient for acoustic time difference, dimensionless;

[0192] RT—Measured deep lateral resistivity, in Ω·m;

[0193] RT0—Lateral resistivity of the compact layer, in Ω·m;

[0194] W2 — resistivity weighting coefficient, dimensionless;

[0195] GR – Measured natural gamma value, API;

[0196] GR0 – Natural gamma value of mudstone, API.

[0197] In step c, the crack development index FI is measured. 实测 The inspection specifically refers to the inspection of crack density measured by electrical imaging, crack density measured by core samples, and crack density measured by thin sections.

[0198] Furthermore, the measured fracture density using electrical imaging refers to the quantitative identification of the number and density of fractures by applying electrical imaging logging and utilizing the low resistivity characteristics of fractures.

[0199] Furthermore, the measured crack density in the core refers to the crack density actually measured on the core through observation.

[0200] Furthermore, the measured crack density of the thin section refers to the crack density measured through a thin section of a rock casting.

[0201] Furthermore, in step d, calculating other fracture development indices FI specifically refers to obtaining fracture development indices through measured natural gamma, measured sonic transit time, and measured deep lateral resistivity in conventional well logging.

[0202] This embodiment is another preferred implementation method. The whole method is simple to operate and practical, and has good reliability.

[0203] Example 5

[0204] See Figure 1 A method for evaluating the fracture development index in well logging includes the following steps:

[0205] a. First, obtain the lower limit of measured fracture density and measured fracture density from core samples, thin sections, and imaging logs of the calibration well. Then, calculate the measured fracture development index FI using Equation 3. 实测 ;

[0206] FI 实测 =f(1-FVDC / FVDC0) Equation 3

[0207] in:

[0208] FI 实测 —Measured crack development index, dimensionless;

[0209] f() — Normalization function, with a value of 0-1, dimensionless;

[0210] FVDC—Measured crack density, meters per crack;

[0211] FVDC0—Lower limit of measured crack density, meter / crack;

[0212] b. By determining the objective function, using the non-negative least squares method, and combining it with the crack development index FI calculated in step a. 实测 The crack development index model is obtained by solving the acoustic time difference weighting coefficient W1 and the resistivity weighting coefficient W2 respectively.

[0213] c. Calculate the crack development index FI using the crack development index model, and verify the measured crack development index FI. 实测 Conduct an inspection;

[0214] d. Then, using the crack development index model, calculate other crack development indices FI and evaluate the crack development indices.

[0215] In step b, determining the objective function means determining the norm using Equation 4;

[0216] ||FI-FI 实测 ||→1 / (+∞) Equation 4

[0217] in:

[0218] FI—Crack Development Index, dimensionless;

[0219] FI 实测 —Measured crack development index, dimensionless.

[0220] In step b, solving for the acoustic time difference weighting coefficient W1 and resistivity weighting coefficient W2 means calculating them using Equation 2.

[0221] W1+W2=1 Equation 2

[0222] in:

[0223] W1 — Weighting coefficient for acoustic time difference, dimensionless;

[0224] W2 — resistivity weighting coefficient, dimensionless.

[0225] In step c, calculating the crack development index FI specifically refers to calculating it according to Equation 1.

[0226] FI=(f(1-AC0 / AC)W1+f(1-RT / RT0)W2)×f(1-GR / GR0) Equation 1

[0227] in:

[0228] FI—Crack Development Index, dimensionless;

[0229] f() — Normalization function, with a value of 0-1, dimensionless;

[0230] AC0 – Skeleton acoustic wave time difference, ms / ft;

[0231] AC – Measured sound wave time difference, ms / ft;

[0232] W1 — Weighting coefficient for acoustic time difference, dimensionless;

[0233] RT—Measured deep lateral resistivity, in Ω·m;

[0234] RT0—Lateral resistivity of the compact layer, in Ω·m;

[0235] W2 — resistivity weighting coefficient, dimensionless;

[0236] GR – Measured natural gamma value, API;

[0237] GR0 – Natural gamma value of mudstone, API.

[0238] In step c, the crack development index FI is measured. 实测 The inspection specifically refers to the inspection of crack density measured by electrical imaging, crack density measured by core samples, and crack density measured by thin sections.

[0239] The measured fracture density using electro-imaging refers to the quantitative identification of the number and density of fractures by applying electro-imaging logging and utilizing the low resistivity characteristics of fractures.

[0240] The measured crack density in the core refers to the crack density actually measured on the core through observation.

[0241] The measured crack density of the thin section refers to the crack density measured through a thin section of a rock casting.

[0242] In step d, calculating other fracture development indices FI specifically refers to obtaining fracture development indices through measured natural gamma, measured sonic transit time, and measured deep lateral resistivity in conventional well logging.

[0243] In step d, evaluating the crack development index specifically means that the higher the crack development index, the more developed the cracks are. The crack development index ranges from 0 to 1.

[0244] This embodiment represents the optimal implementation method. It utilizes a wealth of conventional logging curves, including natural gamma ray, sonic transit time, and deep lateral resistivity curves, to evaluate fracture development. This allows the fracture development index to be applied over a wide range of applications, avoiding the difficulties caused by high coring costs, limited coring, small core samples, and scarce cast sections, which prevent the fracture development index from being widely used. This makes the operation more convenient.

[0245] The following section specifically evaluates the fractures in the tight oil reservoirs of the Sha-1 and Liang-Shang sections of the Sichuan Basin's central Sichuan oil and gas field:

[0246] Step 1: First, obtain the lower limit of measured fracture density and measured fracture density from core samples, thin sections, and imaging logging of the calibration well. Then, calculate the measured fracture development index FI using Equation 3. 实测 ;

[0247] Step 2: By determining the objective function, using the non-negative least squares method, and combining Equations 1, 2, 4 and Step 1, the weight coefficients W1 and W2 are obtained. The solution analysis yields W1 = 0.7 and W2 = 0.3, thus obtaining the crack development index model.

[0248] Step 3: Calculate the crack development index FI using the crack development index model, and verify the measured crack development index FI. 实测 Conduct an inspection;

[0249] Step 4: Calculate other crack development indices FI using the crack development index model, and evaluate the crack development indices.

[0250] Based on the logging response characteristics of fractures, conventional logging information that is relatively sensitive to fractures includes sonic transit time and resistivity; while the factor affecting fracture identification is the lithological clay content, the fractures identified by special logging methods such as electrical imaging and fracture identification are equivalent to the macroscopic fractures observed in core samples. Combining this with microscopic fractures observed in thin sections, the measured fracture index can be determined. The method of this invention can accurately evaluate the fracture development index.

Claims

1. A method for evaluating the fracture development index in well logging, characterized in that, Includes the following steps: a. First, obtain the lower limit of measured fracture density and measured fracture density from core samples, thin sections, and imaging logs of the calibration well. Then, calculate the measured fracture development index FI using Equation 3. 实测 ; FI 实测 =f(1-FVDC / FVDC0)Equation 3 in: FI 实测 —Measured crack development index, dimensionless; f() — Normalization function, with a value of 0-1, dimensionless; FVDC—Measured crack density, meters per crack; FVDC0—Lower limit of measured crack density, meter / crack; b. By determining the objective function, using the non-negative least squares method, and combining it with the crack development index FI calculated in step a. 实测 The crack development index model is obtained by solving the acoustic time difference weighting coefficient W1 and the resistivity weighting coefficient W2 respectively. c. Calculate the crack development index FI using the crack development index model, and verify the measured crack development index FI. 实测 Conduct an inspection; d. Then, using the crack development index model, calculate other crack development indices FI. And evaluate the crack development index; In step b, determining the objective function means determining the norm using Equation 4; ‖FI-FI 实测 ‖→1 / (+∞) Equation 4 in: FI—Crack Development Index, dimensionless; FI 实测 —Measured crack development index, dimensionless; In step b, solving for the acoustic time difference weighting coefficient W1 and resistivity weighting coefficient W2 means calculating them using Equation 2. W1 + W2 = 1 (Equation 2) in: W1 — Acoustic wave time difference weighting coefficient, dimensionless; W2 — resistivity weighting coefficient, dimensionless; In step c, calculating the crack development index FI specifically refers to calculating it according to Equation 1. FI=(f(1-AC0 / AC)W1+f(1-RT / RT0)W2)×f(1-GR / GR0) Equation 1 in: FI—Crack Development Index, dimensionless; f() — Normalization function, with a value of 0-1, dimensionless; AC0 – Skeleton acoustic wave time difference, ms / ft; AC – Measured sound wave time difference, ms / ft; W1 — Acoustic wave time difference weighting coefficient, dimensionless; RT—Measured deep lateral resistivity, in Ω·m; RT0—Lateral resistivity of the compact layer, in Ω·m; W2 — resistivity weighting coefficient, dimensionless; GR – Measured natural gamma value, API; GR0 – Natural gamma value of mudstone, API; In step d, other crack development indices FI are calculated. Specifically, it refers to obtaining the fracture development index by measuring natural gamma, sonic transit time, and deep lateral resistivity in conventional well logging.

2. The method for evaluating the fracture development index in well logging according to claim 1, characterized in that: In step c, the crack development index FI is measured. 实测 The inspection specifically refers to the inspection of crack density measured by electrical imaging, crack density measured by core samples, and crack density measured by thin sections.

3. The method for evaluating the fracture development index in well logging according to claim 2, characterized in that: The measured fracture density using electro-imaging refers to the quantitative identification of the number and density of fractures by applying electro-imaging logging and utilizing the low resistivity characteristics of fractures.

4. The method for evaluating the fracture development index in well logging according to claim 2, characterized in that: The measured crack density in the core refers to the crack density actually measured on the core through observation.

5. The method for evaluating the fracture development index in well logging according to claim 2, characterized in that: The measured crack density of the thin section refers to the crack density measured through a thin section of a rock casting.

6. The method for evaluating the fracture development index in well logging according to claim 1, characterized in that: In step d, evaluating the crack development index specifically means that the higher the crack development index, the more developed the cracks are. The crack development index ranges from 0 to 1.

Images