Shale flow conductivity calculation method

Abstract

A shale flow conductivity calculation method belongs to the technical field of shale oil and gas development, and comprises the following steps: carrying out proppant embedding tests on a shale sample under different closing pressure conditions, and calculating a shale flow conductivity value; carrying out a mineral content determination experiment to obtain the contents of quartz and clay minerals in 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 a shale sample particle density value; carrying out a rock scratch experiment to obtain a compressive strength value of the shale sample; the shale flow conductivity is used as a dependent variable, the quartz content, the clay content, the particle density, the porosity and the compressive strength are used as independent variables, and a multiple linear regression method is adopted to establish a shale flow conductivity calculation model. According to the method, multiple shale flow conductivity sensitive parameters are optimized, the multiple linear regression method is adopted, the shale flow conductivity calculation model is established, on-site shale oil and gas reservoir fracturing effect evaluation is guided, and the method is simple, economical, practical, scientific and effective.

Description

Technical Field

[0001] The 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 density, which are very unfavorable for oil and gas migration, resulting in great difficulty in exploitation. In recent years, thanks to the advancement of large-scale hydraulic fracturing technology, shale oil and gas development has made breakthrough progress. Shale oil and gas recovery is largely affected by the effect of shale fracturing transformation, which can be evaluated by measuring the shale conductivity after fracturing transformation.

[0003] The invention patent with the authorization announcement 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 the authorization announcement number CN 113029898 B provides a testing device and method for 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, which can not only be used to measure the gas supply capacity of bedrock, but also provide experimental support for the study of the influence of fracture conductivity on production capacity evaluation during shale gas development; the invention patent with the application publication number CN116029107 A provides a method for evaluating the conductivity of shale reservoir fractures. The method determines the conductivity of each position in each fracture in the fracture network of the target shale reservoir based on the non-uniform distribution of proppant in the fracture network of the target shale reservoir.

[0004] Although the above methods provide qualitative evaluation and quantitative calculation of shale conductivity under a variety of specific conditions, they do not provide a calculation method for shale conductivity under different closure pressure conditions. During the fracturing process of shale reservoirs, in order to ensure that the formed fractures can be effectively preserved, proppants need to be injected into them. However, under the action of formation closure pressure, the proppants will be embedded in the reservoir to varying degrees, resulting in fracture closure and poor reservoir transformation effect. Therefore, it is necessary to study the shale conductivity under different closure pressure conditions. 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. Carry out proppant embedding test 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. Conduct a particle density measurement experiment on the shale sample to obtain a particle density value of the shale sample;

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

[0011] S6. Taking 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 was used to establish a shale conductivity calculation model.

[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% 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 to a fluorescence level below level 4;

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

[0020] S23. Grind the shale sample after washing and drying 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 density of shale particles is calculated according to a 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 formally begins, the surface of the core is pre-scratched, and the blade is made to contact the surface of the core evenly by repeated scratching.

[0025] The beneficial effects of the present invention are as follows: the traditional method for calculating shale conductivity needs to rely on proppant embedding test, which has the disadvantages of being time-consuming and laborious. The method provided by the present invention optimizes multiple shale conductivity sensitive parameters, adopts a multivariate linear regression method, and establishes a shale conductivity calculation model, which has the advantages of being simple, economical, practical, scientific and 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 embedding test. DETAILED DESCRIPTION

[0027] In order to make the technical means and objectives of the present invention easy to understand, the present invention is further described below in combination with specific implementation methods, a method for calculating shale conductivity,

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

[0029] S1. Carry out proppant embedding test 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. Conduct a particle density measurement experiment on the shale sample to obtain a particle density value of the shale sample;

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

[0034] S6. Taking 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 was used to establish a shale conductivity calculation model.

[0035] Step S1: Carry out proppant embedding 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 part of the 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 ℃; Closing pressure: 0 ~ 120MPa; Flow conductivity: 0 ~ 2000μm 2 ·cm; Permeability: 0-4000mD; Working medium: acid, gas, liquid, etc.;

[0039] The proppant embedding 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 fracturing 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, the sample needs to be subjected to a closure pressure for a sufficient period of time to allow the proppant filling layer to reach a semi-steady state. The liquid is allowed to flow through the proppant filling layer under a certain closure pressure. When the liquid flows through the proppant filling layer under different closure pressure conditions, the proppant filling seam width, pressure difference and flow rate are measured. The conductivity and permeability of the proppant filling layer are 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 and room temperature conditions, there must be no non-Darcy flow or inertial effects;

[0048] After three flow tests at one closure pressure are completed, the closure pressure value can be increased to another value, and a certain period of time is allowed for the proppant packing layer to reach a semi-steady state. Then, three different flow tests are performed again to obtain the required data and determine the conductivity of the proppant packing layer under this condition.

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

[0053] (1) Wash the shale sample with chloroform as the organic solvent and treat it to a fluorescence level below level 4;

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

[0055] (3) Use an agate mortar to grind the shale sample after washing and drying into a 100-mesh powder.

[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 was used to determine the porosity of shale samples, with helium as the measuring medium;

[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 determination experiment includes the following steps:

[0062] (1) Measure rock volume using 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 scoring surface and ensure that the burial direction of the rock sample is consistent with the scoring direction, and use a splint to securely fix the core;

[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 scratching depth, and officially start the scratching test. The computer collects and records the 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: Taking 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 embedding 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 density of shale particles, 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;

[0082] Table 2

[0083]

[0084]

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

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

[0087] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical solutions and concepts of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A method for calculating shale conductivity, characterized in that: The steps include: S1. Carry out proppant embedding test 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. Conduct a particle density measurement experiment on the shale sample to obtain a particle density value of the shale sample; S5. Perform rock scratch test on the shale sample to obtain the compressive strength value of the shale sample; S6. Taking 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 was used to establish a shale conductivity calculation model.

2. The method for calculating shale conductivity according to claim 1, characterized in that: In the step S1, the proppant embedding test material includes fluid, rock plate, proppant and vulcanized silicone adhesive.

3. The method for calculating shale conductivity 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 method for calculating shale conductivity 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 to a fluorescence level below level 4; S22, drying the shale sample after oil washing in a constant temperature drying oven at a temperature of 50°C for 24 hours; S23. Grind the shale sample after washing and drying into 100 mesh powder using an agate mortar.

5. The method for calculating shale conductivity 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 method for calculating shale conductivity according to claim 1, characterized in that: In step S4, the shale volume and weight are measured and the density of 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 make it contact evenly with the surface of the rock core.

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