A shale conductivity calculation method

Abstract

The application discloses a shale conductivity calculation method, and belongs to the technical field of shale oil and gas development.The method comprises the following steps: carrying out a proppant embedding test on a shale sample under different closing pressure conditions to calculate a shale conductivity value; carrying out a mineral content determination experiment to obtain the quartz and clay mineral content of the sample; carrying out a porosity determination experiment to obtain the porosity value of the shale sample; carrying out a particle density determination experiment to obtain the particle density value of the shale sample; carrying out a rock scratch experiment to obtain the compressive strength value of the shale sample; taking the shale conductivity as a dependent variable, taking the quartz content, clay content, particle density, porosity and compressive strength as independent variables, and adopting a multiple linear regression method to establish a shale conductivity calculation model.The method is simple, economical, practical, scientific and effective, and can guide the evaluation of the fracturing effect of a shale oil and gas reservoir on site by optimizing a plurality of shale conductivity sensitive parameters and adopting the multiple linear regression method to establish the shale conductivity calculation model.

Description

Technical Field

[0001] The present invention belongs to the technical field of shale oil and gas development, and particularly relates to a method for calculating shale conductivity. Background Art

[0002] Shale oil and gas reservoirs are characterized by low porosity and dense density, making them highly unfavorable for oil and gas migration and extremely difficult to extract. In recent years, breakthroughs have been made in shale oil and gas development, thanks to advances in large-scale hydraulic fracturing technology. Shale oil and gas recovery rates are significantly influenced by the effectiveness of shale fracturing, which can be evaluated by measuring the conductivity of the shale after fracturing.

[0003] The invention patent with authorization publication number CN109426673 B discloses a method and device for determining the conductivity of an oblique support area in a shale reservoir. The method obtains the conductivity of the oblique support area by multiplying the permeability of the target oblique support area by the corresponding fracture width. The invention patent with authorization publication number CN 113029898 B provides a device and method for testing the dynamic conductivity of fractures and the gas supply capacity of bedrock. The device includes a core holder, a gas supply device, a liquid supply device, a back pressure device, and a flow detection device. It can not only be used to measure the gas supply capacity of bedrock, but also provide experimental support for the study of the impact of fracture conductivity on productivity evaluation during shale gas development. The invention patent with application publication number CN116029107 A provides a method for evaluating the conductivity of shale reservoir fractures. The method determines the conductivity of each position within each fracture in the fracture network of the target shale reservoir based on the uneven distribution of proppant in the fracture network of the target shale reservoir.

[0004] While the above methods provide qualitative evaluation and quantitative calculation of shale conductivity under various specific conditions, they do not provide a calculation method for shale conductivity under different closure pressures. During shale reservoir fracturing, proppant injection is required to ensure the effective preservation of the formed fractures. However, under the influence of formation closure pressure, proppant embeds itself into the reservoir to varying degrees, causing fracture closure and impairing the reservoir stimulation effect. Therefore, it is necessary to study shale conductivity under different closure pressures. Summary of the Invention

[0005] In order to solve the above problems, the present invention proposes a method for calculating shale conductivity, comprising the following steps:

[0006] S1. Conduct proppant embedment tests on shale samples under different closure pressure conditions and calculate the shale conductivity value;

[0007] S2. Conduct mineral content determination experiments on shale samples to obtain the quartz and clay mineral contents of the samples;

[0008] S3. Conducting a porosity measurement experiment on the shale sample to obtain a porosity value of the shale sample;

[0009] S4. Conducting a particle density measurement experiment on the shale sample to obtain a particle density value of the shale sample;

[0010] S5. Perform a rock scratch test on the shale sample to obtain the compressive strength value of the shale sample;

[0011] S6. A shale conductivity calculation model was established using the multivariate linear regression method, with shale conductivity as the dependent variable and quartz content, clay content, particle density, porosity, and compressive strength as independent variables.

[0012] Furthermore, in step S1, the proppant-embedded test material includes fluid, rock plate, proppant and vulcanized silicone adhesive.

[0013] Furthermore, the fluid is a 2% concentration potassium chloride solution, and the prepared potassium chloride solution is no more than 12 hours old;

[0014] The rock plate is made of the core of the target fracturing layer, and the size of the rock plate matches the test equipment;

[0015] Proppants include quartz sand, coated quartz sand, ceramsite and coated ceramsite;

[0016] The temperature resistance of the vulcanized silicone adhesive reaches 200°C and above, and the curing time at room temperature does not exceed 24 hours.

[0017] Furthermore, in step S2, the shale sample is pretreated before the mineral content determination experiment, and the process is as follows:

[0018] S21, washing the shale sample with chloroform as the organic solvent, and treating the sample until the fluorescence level is below level 4;

[0019] S22, drying the oil-washed shale sample in a constant temperature drying oven at 50°C for 24 hours;

[0020] S23. Grind the oil-washed and dried shale sample into 100-mesh powder using an agate mortar.

[0021] Furthermore, in step S3, the porosity measurement experiment adopts a gas method, the measuring medium is helium, the measuring pressure is 0.7 MPa, and the confining pressure is 1.2 MPa.

[0022] Furthermore, in step S4, the shale volume and weight are measured and the shale particle density is calculated according to the density formula.

[0023] Furthermore, in step S5, the rock scratch test process is as follows: a driving device under computer control drives the scratching tool to scratch the rock surface at a constant rate and constant depth, and the computer collects and records the displacement and force data information of the scratching tool in real time, and substitutes the measured force data into the scratching test theoretical model to calculate the compressive strength of the rock.

[0024] Furthermore, in step S5, before the rock scratch test officially begins, the core surface is pre-scratched, and the blade is repeatedly scratched several times to ensure uniform contact between the blade and the core surface.

[0025] The present invention has the following advantages: Traditional methods for calculating shale conductivity rely on proppant embedment tests, which are time-consuming and labor-intensive. The method provided by the present invention optimizes multiple shale conductivity-sensitive parameters and uses a multivariate linear regression method to establish a shale conductivity calculation model. This method is simple, economical, practical, and scientifically effective. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 Cross-plot of shale conductivity calculated by the model of the present invention and shale conductivity calculated by proppant embedment test. DETAILED DESCRIPTION

[0027] In order to make the technical means and objectives of the present invention easier to understand, the present invention is further described below in conjunction with specific embodiments. A method for calculating shale conductivity is provided.

[0028] Reference Figure 1 , this specific embodiment adopts the following technical solution: a method for calculating shale conductivity, comprising the following steps:

[0029] S1. Conduct proppant embedment tests on shale samples under different closure pressure conditions and calculate the shale conductivity value;

[0030] S2. Conduct mineral content determination experiments on shale samples to obtain the quartz and clay mineral contents of the samples;

[0031] S3. Conducting a porosity measurement experiment on the shale sample to obtain a porosity value of the shale sample;

[0032] S4. Conducting a particle density measurement experiment on the shale sample to obtain a particle density value of the shale sample;

[0033] S5. Perform a rock scratch test on the shale sample to obtain the compressive strength value of the shale sample;

[0034] S6. A shale conductivity calculation model was established using the multivariate linear regression method, with shale conductivity as the dependent variable and quartz content, clay content, particle density, porosity, and compressive strength as independent variables.

[0035] Step S1: Conduct proppant embedment tests on shale samples under different closure pressure conditions to calculate the shale conductivity value

[0036] The shale samples used in the examples of the present invention were taken from the Longmaxi Formation in the Zigong area in the southeastern Sichuan Basin;

[0037] The experimental instrument is a fracture conductivity test system developed by Jiangsu Haian Petroleum Research Instrument Co., Ltd.

[0038] Main technical indicators of the instrument: Experimental temperature: room temperature - 180 ° C; Closing pressure: 0 ~ 120 MPa; Conductivity: 0 ~ 2000 μm 2 ·cm; Permeability: 0-4000mD; Working medium: acid, gas, liquid, etc.;

[0039] The proppant embedment test materials include fluid, rock plate, proppant and vulcanized silicone adhesive. The specific requirements are:

[0040] (1) Fluid: 2% potassium chloride solution, the prepared potassium chloride solution should not exceed 12 hours;

[0041] (2) Rock plate: Made from the core of the target fracture layer, the size of the rock plate matches the test equipment;

[0042] (3) Proppant: including quartz sand, coated quartz sand, ceramsite and coated ceramsite;

[0043] (4) Vulcanized silicone adhesive: temperature resistance of 200°C and above, and curing time at room temperature not exceeding 24 hours.

[0044] During the experiment, a closure pressure is applied to the sample for a sufficient period of time to allow the proppant layer to reach a semi-steady state. Liquid is then allowed to flow through the proppant layer under a certain closure pressure. The proppant gap width, pressure differential, and flow rate are measured under different closure pressure conditions. The conductivity and permeability of the proppant layer are then calculated.

[0045] The closing pressures are 10MPa, 20MPa, 30MPa, 40MPa, 50MPa, 60MPa and 70MPa;

[0046] Three flow tests can be performed at each closing pressure, and the test results are the average of the three flow tests;

[0047] At the required flow rate and room temperature conditions, there must be no non-Darcy flow or inertial effects;

[0048] After completing three flow rate tests at one closure pressure, the closure pressure can be increased to another value, and a certain amount of time can be allowed for the proppant pack to reach a semi-steady state. Then, three more tests can be conducted at different flow rates to obtain the required data and determine the conductivity of the proppant pack under these conditions.

[0049] Repeat this procedure until all experiments with the designed closing pressure and flow rate have been completed.

[0050] Step S2: Conduct mineral content determination experiments on shale samples to obtain the quartz and clay mineral contents of the samples

[0051] The experimental instrument for the determination of mineral content is a D8 DISCOVER X-ray diffractometer;

[0052] Shale samples need to be pretreated before the mineral content determination experiment. The specific process is as follows:

[0053] (1) The shale samples were washed with chloroform as an organic solvent until the fluorescence level was below level 4;

[0054] (2) The shale samples after oil washing were dried in a constant temperature drying oven at 50°C for 24 hours;

[0055] (3) The shale sample after washing and drying was ground into 100 mesh powder using an agate mortar.

[0056] Step S3: Conduct a porosity measurement experiment on the shale sample to obtain the porosity value of the shale sample

[0057] The gas method is used to determine the porosity of shale samples, and the measuring medium is helium;

[0058] The experimental instrument is HKXD-C helium porosity automatic measuring instrument;

[0059] The experimental temperature was 25 °C, the measured pressure was 0.7 MPa, and the confining pressure was 1.2 MPa.

[0060] Step S4: Conduct a particle density measurement experiment on the shale sample to obtain the particle density value of the shale sample

[0061] The shale particle density measurement experiment includes the following steps:

[0062] (1) Measure rock volume using the HKXD-C helium porosity automatic measuring instrument;

[0063] (2) Measure the weight of shale using a DX-100E high-precision balance with a measurement accuracy of 0.0001 g;

[0064] (3) Calculate the density of shale particles according to the density formula;

[0065] Step S5: Perform rock scratch test on shale samples to obtain the compressive strength value of shale samples

[0066] The instrument used in the rock scratch test is a full-scale core strength continuous scratch test system;

[0067] The system mainly includes: ① scoring drive device; ② load measuring instrument; ③ depth measuring instrument; ④ horizontal displacement measuring instrument; ⑤ scoring knife; ⑥ rock sample fixing device; ⑦ computer acquisition and control system.

[0068] The specific operation process of the rock scratch test is as follows:

[0069] (1) Rock sample assembly: Select the carving surface and ensure that the burial direction of the rock sample is consistent with the carving direction, and use the splint to fix the core firmly;

[0070] (2) Before the formal start of the scoring, the core surface needs to be pre-scored, and the blade and the core surface need to be evenly contacted by repeated scoring;

[0071] (3) Evaluate the strength of the rock sample to determine the scratching rate and depth, and officially start the scratching test. The computer collects and records data such as the horizontal tangential force and vertical force exerted on the blade in real time;

[0072] (4) Keep the scratching starting point, scratching surface, scratching depth and scratching rate unchanged, and repeat the scratching test twice;

[0073] (5) After the scratch test is completed, take the average of the three scratch data and record the data.

[0074] Step S6: Using shale conductivity as the dependent variable and quartz content, clay content, particle density, porosity and compressive strength as independent variables, a multivariate linear regression method is used to establish a shale conductivity calculation model.

[0075] As shown in Table 1: the shale conductivity of the proppant embedment test under different closure pressure conditions and the corresponding quartz mineral content, clay mineral content, shale particle density, porosity and compressive strength calculation results;

[0076] Table 1

[0077]

[0078] The calculation model of shale conductivity can be expressed by formula (1):

[0079] Conductivity = a × Q UA +b×C LA +c×D EN +d×P oro +e×U CS +f(1)

[0080] Where: Q UA is the quartz mineral content, %; C LA is the clay mineral content, %; D EN is the shale particle density, cm 3 / g;P oro is the shale porosity value, %; U CS is the compressive strength value, ksi; a, b, c, d, e are the formula fitting coefficients, and f is a constant, dimensionless.

[0081] As shown in Table 2, the fitting coefficients and constant f values ​​in formula (1) under different closing pressure conditions are shown;

[0082] Table 2

[0083]

[0084]

[0085] like Figure 1 Shown is a cross-plot of the shale conductivity calculated by the model and the shale conductivity calculated by the proppant embedding test;

[0086] There is a good correlation between the two, and all data points fall near Y=X, indicating that the calculation model provided by the example of the present invention has high accuracy.

[0087] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed in the present invention, who makes equivalent replacements or changes based on the technical solutions and concepts of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A method for calculating shale conductivity, characterized in that: The steps include: S1. Conduct proppant embedment tests on shale samples under different closure pressure conditions and calculate the shale conductivity value; S2. Conduct mineral content determination experiments on shale samples to obtain the quartz and clay mineral contents of the samples; S3. Conducting a porosity measurement experiment on the shale sample to obtain a porosity value of the shale sample; S4. Conducting a particle density measurement experiment on the shale sample to obtain a particle density value of the shale sample; S5. Perform a rock scratch test on the shale sample to obtain the compressive strength value of the shale sample; S6. A shale conductivity calculation model was established using the multivariate linear regression method, with shale conductivity as the dependent variable and quartz content, clay content, particle density, porosity, and compressive strength as independent variables.

2. The shale conductivity calculation method according to claim 1, characterized in that: In step S1, the proppant-embedded test material includes fluid, rock plate, proppant and vulcanized organosilicon adhesive.

3. The shale conductivity calculation method according to claim 2, characterized in that: The fluid is a 2% potassium chloride solution, and the prepared potassium chloride solution is no more than 12 hours old; The rock plate is made of the core of the target fracturing layer, and the size of the rock plate matches the test equipment; Proppants include quartz sand, coated quartz sand, ceramsite and coated ceramsite; The temperature resistance of the vulcanized silicone adhesive reaches 200°C and above, and the curing time at room temperature does not exceed 24 hours.

4. The shale conductivity calculation method according to claim 1, characterized in that: In step S2, the shale sample is pretreated before the mineral content determination experiment, and the process is as follows: S21, washing the shale sample with chloroform as the organic solvent, and treating the sample until the fluorescence level is below level 4; S22, drying the oil-washed shale sample in a constant temperature drying oven at 50°C for 24 hours; S23. Grind the oil-washed and dried shale sample into 100-mesh powder using an agate mortar.

5. The shale conductivity calculation method according to claim 1, characterized in that: In step S3, the porosity measurement experiment adopts a gas method, the measuring medium is helium, the measuring pressure is 0.7 MPa, and the confining pressure is 1.2 MPa.

6. The shale conductivity calculation method according to claim 1, characterized in that: In step S4, the volume and weight of the shale are measured and the density of the shale particles is calculated according to the density formula.

7. The method for calculating shale conductivity according to claim 1, characterized in that: In step S5, the rock scratch test process is as follows: a driving device under computer control drives the scratching tool to scratch the rock surface at a constant rate and constant depth, and the computer collects and records the displacement and force data information of the scratching tool in real time, and substitutes the measured force data into the scratching test theoretical model to calculate the compressive strength of the rock.

8. The method for calculating shale conductivity according to claim 1, characterized in that: In step S5, before the rock scratch test officially begins, the surface of the rock core is pre-scratched, and the blade is repeatedly scratched several times to ensure uniform contact between the blade and the surface of the rock core.

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