Shale semi-permeable membrane efficiency measurement experiment and characterization method based on rock strength

Abstract

The application discloses a shale semi-permeable membrane efficiency experiment and characterization method based on rock strength and relates to the technical field of petroleum engineering.The application prepares multiple shale samples, carries out wetting saturation treatment on the shale samples, carries out drilling fluid immersion experiments on the shale samples after grouping, obtains rock strength of the shale samples after drilling fluid immersion and mass change of the shale samples before and after immersion, and thus determines a shale semi-permeable membrane efficiency characterization formula based on rock strength based on a chemical permeation pressure calculation formula and a water content change calculation formula of the shale samples, so as to accurately characterize shale semi-permeable membrane efficiency.The application effectively avoids the problems of long time consumption and high requirements in traditional pressure transmission experiments and provides a basis for effective characterization of wellbore stability.

Description

Technical Field

[0001] This invention relates to the field of petroleum engineering technology, specifically to an experimental and characterization method for the efficiency of shale semi-permeable membranes based on rock strength. Background Technology

[0002] Shale oil and gas, as an important component of unconventional energy, will become a crucial pathway to solving the energy crisis and achieving sustainable development. Due to the semi-permeable membrane properties of shale, an ideal semi-permeable membrane allows only the solvent to pass through while completely preventing solute migration (i.e., the membrane efficiency of an ideal semi-permeable membrane is 1), while shale semi-permeable membranes are non-ideal, with efficiencies ranging from 0 to 1. The higher the membrane efficiency, the stronger its ability to confine solutes, and the more significant its impact on clay hydration, pore pressure transmission, and wellbore stability. Therefore, membrane efficiency is a key parameter for analyzing the properties of shale semi-permeable membranes and a crucial foundation for establishing chemical-flow-mechanical coupled wellbore stability models.

[0003] However, current research on the efficiency of shale semi-permeable membranes still has many shortcomings: First, testing the efficiency of shale semi-permeable membranes is quite difficult; traditional pressure transmission experiments take a very long time, which seriously affects the efficiency of practical engineering applications. In addition, the experiment requires the detection of small changes in pressure, and sample disturbance will significantly affect the experimental results of traditional pressure transmission experiments.

[0004] Second, research on the efficiency of shale semi-permeable membranes mainly focuses on chemical seepage at the microscopic level. The macroscopic rock mechanics scale is obtained through finite element simulation calculations, which cannot effectively characterize the efficiency of shale membranes at the macroscopic rock mechanics scale.

[0005] Third, the influence of the water content and activity of shale itself cannot be ignored when studying the efficiency of shale semi-permeable membranes, which has not been addressed in previous studies on shale membrane efficiency.

[0006] Therefore, it is urgent to propose an experimental and characterization method for shale semi-permeable membrane efficiency based on rock strength, which fully considers the influence of the initial water content and activity of shale on membrane efficiency, so as to achieve accurate characterization of shale semi-permeable membrane efficiency. Summary of the Invention

[0007] This invention aims to solve the above-mentioned problems and proposes an experimental and characterization method for shale semi-permeable membrane efficiency based on rock strength. It fully considers the influence of the initial water content and activity of shale itself on the efficiency of shale semi-permeable membrane, and realizes accurate characterization of shale semi-permeable membrane efficiency. It effectively avoids the problems of long time consumption and high requirements in traditional pressure transmission experiments. It can analyze the relationship between shale semi-permeable membrane efficiency and water content and rock strength from a macroscopic perspective, and accurately reflect the changes in shale pore pressure, providing a basis for effectively characterizing wellbore stability.

[0008] The present invention adopts the following technical solution: An experiment to characterize the efficiency of a shale semi-permeable membrane based on rock strength includes the following steps: Step 1: Prepare multiple cylindrical shale samples, dry them, and weigh them; Step 2: Based on the humidification saturation method, each shale sample is humidified in the core humidification device using a saturated salt solution until the weight of the shale sample remains constant. Then, the initial saturation, initial activity, and initial weight of each shale sample are measured to obtain the change in water content of each shale sample before and after humidification saturation treatment. Step 3: Divide the shale samples into multiple experimental groups for immersion in different types of drilling fluids. In the same experimental group, select a portion of the shale samples to be wrapped with an artificial semi-permeable membrane and another portion of the shale samples to be unwrapped. Set different types of drilling fluids for each experimental group and immerse each shale sample in the corresponding drilling fluid for a specified time to conduct the drilling fluid immersion experiment. Step 4: After soaking in drilling fluid, obtain the changes in water content of each shale sample, and conduct rock mechanics experiments on each shale sample after soaking in drilling fluid to obtain the rock strength of each shale sample and obtain the experimental results of each experimental group. Step 5: Based on the experimental results of each experimental group, obtain the rock strength of shale samples wrapped with artificial semi-permeable membranes and shale samples without artificial semi-permeable membranes under different types of drilling fluids and under the same type of drilling fluid and different drilling fluid activity conditions. This is used to characterize the efficiency of shale semi-permeable membranes.

[0009] Preferably, in the drilling fluid soaking experiment, at least two drilling fluid activities are set for the same type of drilling fluid to obtain shale samples soaked under the same type of drilling fluid and different drilling fluid activity conditions.

[0010] Preferably, the molecular weight cutoff of the artificial semipermeable membrane is 100 Daltons.

[0011] Preferably, in step 2, the change in water content of the shale sample is determined by weighing the shale sample before and after the humidification and saturation treatment or by obtaining the nuclear magnetic resonance T2 spectrum area of ​​the shale sample before and after the humidification and saturation treatment. In step 4, the change in water content of the shale sample is determined by weighing the shale sample before and after soaking in drilling fluid or by obtaining the nuclear magnetic resonance T2 spectrum area of ​​the shale sample before and after soaking in drilling fluid.

[0012] A method for characterizing the efficiency of shale semi-permeable membranes based on rock strength, comprising the following steps: Based on the rock strength of shale samples coated with artificial semi-permeable membranes and shale samples without artificial semi-permeable membranes under different drilling fluid activity conditions and the same type of drilling fluid as described above, the method for determining the efficiency of shale semi-permeable membranes based on rock strength is used to determine the efficiency of shale semi-permeable membranes based on rock strength. Step 1: Select three shale samples that have been soaked in the same type of drilling fluid, namely the first shale sample, the second shale sample and the third shale sample. The first and second shale samples are both shale samples wrapped with artificial semi-permeable membranes and the drilling fluid activities of the two samples are different. The third shale sample is a shale sample that has not been wrapped with artificial semi-permeable membranes. Step 2: Based on the chemical osmotic pressure and water content changes of the first and second rock samples, determine the chemical osmotic transport coefficient and equivalent adsorption capacity of the shale sample, and calculate the semi-permeable membrane efficiency of the shale sample by combining the water content change of the third rock sample before and after soaking in drilling fluid. Step 3: Obtain the water content of each shale sample in the shale semi-permeable membrane efficiency characterization experiment. The water content is the difference between the mass of the shale sample after soaking in drilling fluid and the mass when dried. Combined with the rock strength of each shale sample, the relationship between rock strength and water content is fitted to determine the formula for calculating shale water content. Step 4: Based on the shale water content calculation formula, redetermine the calculation formula for the water content change of the shale sample, determine the characterization form of the water content change based on rock strength, and substitute it into the chemical osmotic pressure calculation formula of the shale sample to obtain the characterization formula for the shale semi-permeable membrane efficiency based on rock strength. The formula for characterizing the efficiency of the shale semi-permeable membrane based on rock strength is as follows: ; In the formula, For semi-permeable membrane efficiency; Let be the molar volume of water; It is the ideal gas constant; Absolute temperature; Drilling fluid activity; Shale activity; The chemical osmotic transport coefficient; This is the equivalent adsorption capacity; , , All are fitting coefficients; It is the natural logarithm function; The rock strength of the shale after soaking in drilling fluid; This represents the rock strength of the shale before it is soaked in drilling fluid.

[0013] Preferably, in step 2, the chemical osmotic pressure of the shale sample is calculated using the following formula: ; In the formula, Chemical osmotic pressure, unit: ; is the ideal gas constant, with a value of 8.314. ; Absolute temperature, unit: ; This is the molar volume of water, in units of . ; The semi-permeable membrane efficiency is dimensionless. It refers to the efficiency of a semi-permeable membrane when the core sample is encased in an artificial semi-permeable membrane. The value is 1; Drilling fluid activity, dimensionless; Shale activity, dimensionless; It is the natural logarithm function; The formula for calculating the change in water content of the shale sample is as follows: ; In the formula, This represents the change in water content, in units of... ; This is the chemical osmotic transport coefficient, in units of... ; The chemical osmotic pressure of shale; Equivalent adsorption capacity, in units of .

[0014] Preferably, in step 2, since both the first and second rock samples are wrapped with artificial semi-permeable membranes, the efficiency of the semi-permeable membranes for the first and second rock samples is determined. The chemical osmotic pressure of the first and second rock samples is calculated using the chemical osmotic pressure calculation formula. Combined with the mass of the first and second rock samples before and after soaking in drilling fluid, the change in water content of the first and second rock samples is determined. According to the formula for calculating the change in water content, we get: ; ; Solving the simultaneous equations, we obtain the chemical permeability transport coefficient of the shale sample. and equivalent adsorption capacity The calculation formula is: ; ; In the formula, This represents the change in water content of the first rock sample, in units of... ; This represents the change in water content of the second rock sample, in units of... ; The chemical osmotic pressure of the first rock sample is given in units of . ; The chemical osmotic pressure of the second rock sample is given in units of... ; Determine the chemical permeability transport coefficient of shale samples and equivalent adsorption capacity Subsequently, because the third rock sample was not encased in an artificial semi-permeable membrane, the chemical permeability transport coefficient of the shale sample was... and equivalent adsorption capacity Substituting these values ​​into the formula for calculating water content change, and considering the water content change before and after soaking the third rock sample in drilling fluid... The chemical osmotic pressure of the third rock sample was calculated. for ; Based on the chemical osmotic pressure calculation formula and the activity of the drilling fluid soaked in the third rock sample, the semi-permeable membrane efficiency of the shale sample was determined as follows: .

[0015] Preferably, in step 3, by fitting the water content and rock strength of all shale samples, the relationship between rock strength and water content is obtained as follows: ; In the formula, Moisture content, unit: ; It is a natural constant; Rock strength, unit: ; , , All are fitting coefficients; Taking the logarithm of both sides, the formula for calculating shale water content is: ; In the formula, It is the natural logarithm function.

[0016] Preferably, in step 4, since the change in shale water content is the change in the mass of the shale itself before and after soaking in drilling fluid, the form of characterizing the change in water content based on rock strength is determined according to the shale water content calculation formula: ; In the formula, This represents the change in water content, in units of... ; The water content of the shale after soaking in drilling fluid; This represents the water content of the shale before it is soaked in drilling fluid. The rock strength of the shale after soaking in drilling fluid; The rock strength of shale before it is soaked in drilling fluid; Substituting these values ​​into the chemical osmotic pressure calculation formula for shale samples, we obtain the following formula for characterizing the efficiency of shale semi-permeable membranes based on rock strength: ; In the formula, The efficiency of the semipermeable membrane is dimensionless. This is the molar volume of water, in units of . ; It is the ideal gas constant; Absolute temperature, unit: ; Drilling fluid activity, dimensionless; Shale activity, dimensionless; This is the chemical osmotic transport coefficient, in units of... ; This is the equivalent adsorption capacity, in units of ; , , All are fitting coefficients; It is the natural logarithm function; The rock strength of the shale after soaking in drilling fluid; This represents the rock strength of the shale before it is soaked in drilling fluid.

[0017] The present invention has the following beneficial effects: This invention proposes an experimental and characterization method for shale semi-permeable membrane efficiency based on rock strength. This method fully considers the influence of the initial water content and activity of shale on the shale semi-permeable membrane efficiency. By utilizing drilling fluid activity, shale activity, and the rock strength of shale before and after drilling fluid soaking, it achieves accurate calculation of the rock strength semi-permeable membrane efficiency. This effectively solves the problems of time-consuming, demanding, and inaccurate methods using traditional pressure transmission experiments to determine rock strength semi-permeable membrane efficiency. Furthermore, this invention can obtain the relationship between shale semi-permeable membrane efficiency and shale water content and rock strength from a macroscopic perspective, and can also accurately obtain the changes in pore pressure in shale reservoirs. It achieves accurate characterization of shale semi-permeable membrane efficiency on a macroscopic scale of rock mechanics, providing a basis for effectively characterizing wellbore stability. Attached Figure Description

[0018] Figure 1 This is a flowchart of an experiment to characterize the efficiency of a shale semi-permeable membrane based on rock strength, according to the present invention.

[0019] Figure 2 This is a schematic diagram of the core humidification device of the present invention; in the figure, 1 is a shale sample, 2 is the core humidification device, 3 is a constant temperature chamber, 4 is a sieve, and 5 is a saturated salt solution.

[0020] Figure 3 This is a flowchart of a method for characterizing the efficiency of shale semi-permeable membranes based on rock strength, according to the present invention. Detailed Implementation

[0021] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings.

[0022] Example 1 This embodiment discloses an experiment for characterizing the efficiency of shale semi-permeable membranes based on rock strength. This is used to obtain the rock strength of shale samples with an external artificial semi-permeable membrane and shale samples without an external artificial semi-permeable membrane under different types of drilling fluids, as well as under different drilling fluid activity conditions with the same type of drilling fluid. Figure 1 As shown, the specific steps include: Step 1: Prepare multiple cylindrical shale samples, dry them, and weigh them.

[0023] In this embodiment, the obtained shale is cut, polished, and processed into cylindrical specimens with a diameter of 25 mm and a height of 50 mm to obtain multiple shale samples. After drying, the samples are weighed to obtain the dry weight of each shale sample, that is, the weight of the shale sample without water.

[0024] Step 2: Based on the humidification saturation method, each shale sample is humidified using a saturated salt solution in a core humidification device to obtain the initial saturation, initial activity, and initial weight of each shale sample. The change in water content of the shale sample is determined by weighing the shale sample before and after humidification saturation treatment or by obtaining the nuclear magnetic resonance T2 spectrum area of ​​the shale sample before and after humidification saturation treatment.

[0025] In existing technologies, testing the mechanical properties of rock using core samples soaked in drilling fluid is a common method for analyzing the stability of drilling fluid and wellbore. However, conventional methods of soaking core samples in drilling fluid for rock mechanics analysis do not consider the influence of water content in the core. The presence of formation water in shale creates pore pressure, affecting drilling fluid intrusion. Furthermore, the difference in activity between the formation water in the core and the drilling fluid creates a chemical potential that further influences water intrusion. Additionally, conventional core saturation methods require immersing the core sample in formation water and applying pressure to obtain a water-saturated core sample, a process that significantly impacts the rock strength. Therefore, to accurately obtain the rock strength of shale samples, this invention employs a wet saturation method to saturate the shale samples.

[0026] The core wetting device used in this embodiment is as follows: Figure 2As shown, the core humidification device 2 has a sieve 4 inside for placing the shale sample 1. A saturated salt solution 5 is placed below the sieve 4. The core humidification device is placed in a constant temperature chamber 3, allowing the saturated salt solution to evaporate and reach equilibrium with the condensation of water molecules in the sealed space. A humidity measuring instrument inside the core humidification device is used for observation. After the humidity inside the core humidification device reaches a stable state, the shale sample is placed above the sieve of the core humidification device, allowing the shale sample to absorb moisture from the air in the sealed space. Considering the extremely low permeability of shale, a sufficiently long time is required during the humidification saturation process to ensure that the shale sample completes the water vapor exchange with the environment. In this embodiment, after 15 days of humidification saturation treatment, the mass of each shale sample needs to be measured daily using a high-precision balance. If the results of multiple consecutive measurements are consistent, the shale sample is considered to have completed the humidification saturation treatment. At this point, the hydrochemical potential of the shale sample reaches equilibrium with the water potential corresponding to the humidity environment.

[0027] Compared to traditional core sample saturation methods, the core sample wetting method used in this embodiment has less impact on the rock strength of the core sample. The pretreated shale sample has initial saturation and shale activity, which is beneficial for the accurate determination of the efficiency of the shale semi-permeable membrane.

[0028] Step 3: Divide the shale samples into multiple experimental groups for immersion in different types of drilling fluids. Within the same experimental group, select a portion of the shale samples to be wrapped with an artificial semi-permeable membrane, and select another portion of the shale samples to be unwrapped. Set different types of drilling fluids for each experimental group, and set at least two drilling fluid activities for the same type of drilling fluid. Immerse each shale sample in the corresponding drilling fluid for a specified time to conduct a drilling fluid immersion experiment.

[0029] To investigate the properties of shale semi-permeable membranes, this embodiment uses an artificial semi-permeable membrane to encapsulate shale samples for comparison with non-ideal shale semi-permeable membranes. Currently, reverse osmosis membranes are the semi-permeable membranes that can remove salt ions to the greatest extent and are commonly used in wastewater treatment and water purification. Because reverse osmosis membranes allow a small molecular weight to pass through, a certain pressure is required in practical applications to allow water molecules to pass through. The artificial semi-permeable membrane used in this embodiment has a molecular weight cutoff of 100 Daltons. This type of semi-permeable membrane is semi-permeable, seamless, and stable, and can block components with molecular weights greater than 100 Daltons to a certain extent, effectively blocking large molecular components in drilling fluids, such as KCl and CaCl2. + Cl - Ca 2+ In drilling fluids, it does not exist as a single ion, but rather as a hydrated ion, with potassium ions (K) being a key component. + The common radius is 0.331 nm, and the chloride ion Cl... -The common radius is 0.332 nm, and the calcium ion Ca... 2+ The common radius is 0.412 nm, potassium ion K + The coordination number of the first hydrated layer is approximately 6-7, and the chloride ion Cl... - The coordination number of the first hydration layer is approximately 5-6, and the calcium ion Ca... 2+ The coordination number of the first hydration layer is approximately 6-8. At this point, the molecular weight of the hydrated ions is greater than 100 Da, and the artificial semi-permeable membrane can effectively block the propagation of hydrated ions. However, the artificial semi-permeable membrane cannot be considered an ideal semi-permeable membrane; it mainly serves to hinder ion transfer and delay ion propagation, but cannot completely intercept ions. Therefore, in this embodiment, the artificial semi-permeable membrane is used as a benchmark to determine the properties of the shale semi-permeable membrane.

[0030] Step 4: After soaking in drilling fluid, the water content change of each shale sample is obtained by weighing the shale samples before and after soaking in drilling fluid or by obtaining the nuclear magnetic resonance T2 spectrum area of ​​the shale samples before and after soaking in drilling fluid. Rock mechanics experiments are then conducted on each shale sample after soaking in drilling fluid to obtain the rock strength of each shale sample and obtain the experimental results of each experimental group.

[0031] Step 5: Based on the experimental results of each experimental group, obtain the rock strength of shale samples wrapped with artificial semi-permeable membranes and shale samples without artificial semi-permeable membranes under different types of drilling fluids and under the same type of drilling fluid and different drilling fluid activity conditions. This is used to characterize the efficiency of shale semi-permeable membranes.

[0032] This embodiment also proposes a method for characterizing the efficiency of shale semi-permeable membranes based on rock strength, such as... Figure 3 As shown, the rock strength of shale samples coated with artificial semi-permeable membranes and shale samples without artificial semi-permeable membranes, determined by the above-mentioned rock strength-based shale semi-permeable membrane efficiency experiment based on rock strength, is used to determine the efficiency of shale semi-permeable membranes. This process includes the following steps: Step 1: Select three shale samples that have been soaked in the same type of drilling fluid, namely the first shale sample, the second shale sample, and the third shale sample. The first and second shale samples are both shale samples wrapped with artificial semi-permeable membranes and the drilling fluids soaked in them have different activities. The third shale sample is a shale sample that has not been wrapped with artificial semi-permeable membranes.

[0033] Step 2: Based on the chemical osmotic pressure and water content changes of the first and second rock samples, determine the chemical permeation transport coefficient and equivalent adsorption capacity of the shale sample. Combined with the water content change of the third rock sample before and after soaking in drilling fluid, calculate the semi-permeable membrane efficiency of the shale sample.

[0034] Step 3: Obtain the water content of each shale sample in the shale semi-permeable membrane efficiency characterization experiment. The water content is the difference between the mass of the shale sample after soaking in drilling fluid and the mass when dried. Combined with the rock strength of each shale sample, the relationship between rock strength and water content is fitted to determine the formula for calculating shale water content.

[0035] Step 4: Based on the shale water content calculation formula, redetermine the calculation formula for the water content change of the shale sample, determine the characterization form of the water content change based on rock strength, and substitute it into the chemical osmotic pressure calculation formula of the shale sample to obtain the characterization formula for the shale semi-permeable membrane efficiency based on rock strength.

[0036] The specific process for characterizing the efficiency of the shale semi-permeable membrane is as follows: Three shale samples were selected and treated with the same type of drilling fluid. These were designated as the first, second, and third shale samples. The first and second shale samples were encased in an artificial semi-permeable membrane, and the drilling fluids used to encapsulate them had different activities. The third shale sample was not encased in an artificial semi-permeable membrane.

[0037] Because the first and second rock samples are wrapped with an artificial semi-permeable membrane, the semi-permeable membrane efficiency of the first and second rock samples is... The value is set to 1, and the chemical osmotic pressure of the first rock sample is calculated using the chemical osmotic pressure calculation formula for shale samples. Chemical osmotic pressure of the second rock sample .

[0038] In this embodiment, the chemical osmotic pressure calculation formula for the shale sample is as follows: ; In the formula, Chemical osmotic pressure, unit: ; is the ideal gas constant, with a value of 8.314. ; Absolute temperature, unit: ; This is the molar volume of water, in units of . ; The efficiency of the semipermeable membrane is dimensionless. Drilling fluid activity, dimensionless; Shale activity, dimensionless; It is the natural logarithm function.

[0039] The change in water content of the first rock sample is then calculated using the formula for calculating the change in water content of shale samples. Change in water content of the second rock sample .

[0040] In this embodiment, the formula for calculating the change in water content of the shale sample is as follows: ; In the formula, This represents the change in water content, in units of... ; This is the chemical osmotic transport coefficient, in units of... ; The chemical osmotic pressure of shale; This is the equivalent adsorption capacity, in units of .

[0041] Based on the formula for calculating water content change, and considering the masses of the first and second rock samples before and after soaking in drilling fluid, the water content change of each sample is determined, resulting in: ; ; Solving the simultaneous equations, we obtain the chemical permeability transport coefficient of the shale sample. and equivalent adsorption capacity The calculation formula is: ; ; In the formula, This represents the change in water content of the first rock sample, in units of... ; This represents the change in water content of the second rock sample, in units of... ; The chemical osmotic pressure of the first rock sample is given in units of . ; The chemical osmotic pressure of the second rock sample is given in units of... .

[0042] Determine the chemical permeability transport coefficient of shale samples and equivalent adsorption capacity Subsequently, because the third rock sample was not encased in an artificial semi-permeable membrane, the chemical permeability transport coefficient of the shale sample was... and equivalent adsorption capacity Substituting these values ​​into the formula for calculating water content change, and considering the water content change before and after soaking the third rock sample in drilling fluid... The chemical osmotic pressure of the third rock sample was calculated. for .

[0043] Based on the chemical osmotic pressure calculation formula and the activity of the drilling fluid soaked in the third rock sample, the semi-permeable membrane efficiency of the shale sample was determined as follows: .

[0044] By fitting the water content and rock strength of all shale samples in the shale semi-permeable membrane efficiency experiment, the relationship between rock strength and water content was obtained as follows: ; In the formula, Moisture content, unit: ; It is a natural constant; Rock strength, unit: ; , , All are fitting coefficients.

[0045] Taking the logarithm of both sides, the formula for calculating shale water content is: ; In the formula, It is the natural logarithm function.

[0046] Since the change in shale water content is the change in the mass of the shale itself before and after soaking in drilling fluid, based on the shale water content calculation formula, the form for representing the change in water content based on rock strength is determined as follows: ; In the formula, This represents the change in water content, in units of... ; The water content of the shale after soaking in drilling fluid; This represents the water content of the shale before it is soaked in drilling fluid. The rock strength of the shale after soaking in drilling fluid; This represents the rock strength of the shale before it is soaked in drilling fluid.

[0047] Substituting the characterization form of water content change based on rock strength into the chemical osmotic pressure calculation formula for shale samples, the characterization formula for shale semi-permeable membrane efficiency based on rock strength is obtained as follows: ; In the formula, The efficiency of the semipermeable membrane is dimensionless. This is the molar volume of water, in units of 1000 m³ / s. ; is the ideal gas constant, with a value of 8.314. ; Absolute temperature, unit: ; Drilling fluid activity, dimensionless; Shale activity, dimensionless; This is the chemical osmotic transport coefficient, in units of... ; Equivalent adsorption capacity, in units of ; , , All are fitting coefficients; It is the natural logarithm function; The rock strength of the shale after soaking in drilling fluid; This represents the rock strength of the shale before it is soaked in drilling fluid.

[0048] Example 2 In this embodiment, three shale samples were prepared. The shale semi-permeable membrane efficiency characterization experiment based on rock strength, as described in Example 1, was conducted. In all three experiments, the shale samples were immersed in the same type of drilling fluid for the same duration. The first and second shale samples were wrapped with an artificial semi-permeable membrane, while the third shale sample was not. The drilling fluid activity of the first shale sample was 0.885, the second shale sample's activity was 0.87, and the third shale sample's activity was 0.885. After the shale semi-permeable membrane efficiency characterization experiment, the change in water content of the first shale sample was measured to be 0.175. The change in water content of the second shale sample was 0.082. The change in water content of the third shale sample was 0.331. .

[0049] Based on the drilling fluid activity and shale activity, the chemical osmotic pressure of the first shale sample was calculated using the chemical osmotic pressure calculation formula for shale samples. -9.76 Chemical osmotic pressure of the second shale sample -12.11 .

[0050] Furthermore, using the formula for calculating the change in water content to represent the change in water content for the first and second shale samples, we obtain: ; ; Solve simultaneously, taking into account the chemical osmotic pressure of the first shale sample. -9.76 Chemical osmotic pressure of the second shale sample -12.11 Changes in water content of the first shale sample It is 0.175 Changes in water content of the second shale sample It is 0.082 The chemical permeability transport coefficient of the shale sample was calculated. It is 0.0395 Equivalent adsorption capacity It is 0.561 .

[0051] Determine the chemical permeability transport coefficient of shale samples and equivalent adsorption capacity Then, using the formula The chemical osmotic pressure of the third shale sample was calculated. -5.811 Using the formula The semi-permeable membrane efficiency of the third shale sample was calculated to be 0.595.

[0052] By fitting the water content and rock strength of the first, second, and third shale samples, the relationship between rock strength and water content was obtained as follows: ; In the formula, Moisture content, unit: ; It is a natural constant; Rock strength, unit: .

[0053] Taking the logarithm of both sides, the formula for calculating shale water content is: .

[0054] Therefore, the representation of water content change based on rock strength in this embodiment is determined as follows: ; In the formula, This represents the change in water content, in units of... ; The water content of the shale after soaking in drilling fluid; This represents the water content of the shale before it is soaked in drilling fluid. The rock strength of the shale after soaking in drilling fluid; This represents the rock strength of the shale before it is soaked in drilling fluid.

[0055] Due to the rock strength of the third shale sample when it was not soaked in drilling fluid 59.88 Rock strength of shale after soaking in drilling fluid It is 24.28 The change in water content of the third shale sample was calculated. It is 0.328 Then, based on the shale semi-permeable membrane efficiency characterization formula based on rock strength, the shale semi-permeable membrane efficiency of the shale sample in this embodiment is calculated. The value is 0.603, which is very close to the shale semi-permeable membrane efficiency of 0.595 calculated from the change in water content of the third shale sample.

[0056] To further verify the accuracy of the method for calculating the shale semi-permeable membrane efficiency of the present invention, based on the experimental results of different types of drilling fluid immersion experiments, shale samples coated with artificial semi-permeable membranes under different drilling fluid activities were selected as benchmarks for each type of drilling fluid. The shale semi-permeable membrane efficiency of the shale sample coated with artificial semi-permeable membranes under a third type of drilling fluid activity was calculated. The calculated result was 0.99, which is very close to the expected value of 1. This verifies that the method of the present invention can accurately obtain the shale semi-permeable membrane efficiency, and the calculation process is simple and convenient. It fully considers the influence of drilling fluid activity, formation water activity, and rock strength on the shale semi-permeable membrane efficiency, avoiding the problems of long time consumption and high requirements in traditional pressure transmission experiments.

[0057] Of course, the above description is not intended to limit the present invention, and the present invention is not limited to the examples given above. Any changes, modifications, additions or substitutions made by those skilled in the art within the scope of the present invention should also fall within the protection scope of the present invention.

Claims

1. An experiment for characterizing the efficiency of a shale semi-permeable membrane based on rock strength, characterized in that, Includes the following steps: Step 1: Prepare multiple cylindrical shale samples, dry them, and weigh them; Step 2: Based on the humidification saturation method, each shale sample is humidified in the core humidification device using a saturated salt solution until the weight of the shale sample remains constant. Then, the initial saturation, initial activity, and initial weight of each shale sample are measured to obtain the change in water content of each shale sample before and after humidification saturation treatment. Step 3: Divide the shale samples into multiple experimental groups for immersion in different types of drilling fluids. In the same experimental group, select a portion of the shale samples to be wrapped with an artificial semi-permeable membrane and another portion of the shale samples to be unwrapped. Set different types of drilling fluids for each experimental group and immerse each shale sample in the corresponding drilling fluid for a specified time to conduct the drilling fluid immersion experiment. Step 4: After soaking in drilling fluid, obtain the changes in water content of each shale sample, and conduct rock mechanics experiments on each shale sample after soaking in drilling fluid to obtain the rock strength of each shale sample and obtain the experimental results of each experimental group. Step 5: Based on the experimental results of each experimental group, obtain the rock strength of shale samples wrapped with artificial semi-permeable membranes and shale samples without artificial semi-permeable membranes under different types of drilling fluids and under the same type of drilling fluid and different drilling fluid activity conditions. This is used to characterize the efficiency of shale semi-permeable membranes.

2. The shale semi-permeable membrane efficiency characterization experiment based on rock strength according to claim 1, characterized in that, In the drilling fluid immersion experiment, at least two drilling fluid activities were set for the same type of drilling fluid to obtain shale samples immersed under the same type of drilling fluid and different drilling fluid activities.

3. The shale semi-permeable membrane efficiency characterization experiment based on rock strength according to claim 1, characterized in that, The artificial semipermeable membrane has a molecular weight cutoff of 100 Daltons.

4. The shale semi-permeable membrane efficiency characterization experiment based on rock strength according to claim 1, characterized in that, In step 2, the change in water content of the shale sample is determined by weighing the shale sample before and after the humidification and saturation treatment or by obtaining the nuclear magnetic resonance T2 spectrum area of ​​the shale sample before and after the humidification and saturation treatment. In step 4, the change in water content of the shale sample is determined by weighing the shale sample before and after soaking in drilling fluid or by obtaining the nuclear magnetic resonance T2 spectrum area of ​​the shale sample before and after soaking in drilling fluid.

5. A method for characterizing the efficiency of shale semi-permeable membranes based on rock strength, characterized in that, The rock strength of shale samples coated with artificial semi-permeable membranes and shale samples without artificial semi-permeable membranes, determined by the experimental method for shale semi-permeable membrane efficiency based on rock strength according to any one of claims 1 to 4, is used to determine the efficiency of shale semi-permeable membranes based on rock strength, comprising the following steps: Step 1: Select three shale samples that have been soaked in the same type of drilling fluid, namely the first shale sample, the second shale sample and the third shale sample. The first and second shale samples are both shale samples wrapped with artificial semi-permeable membranes and the drilling fluid activities of the two samples are different. The third shale sample is a shale sample that has not been wrapped with artificial semi-permeable membranes. Step 2: Based on the chemical osmotic pressure and water content changes of the first and second rock samples, determine the chemical osmotic transport coefficient and equivalent adsorption capacity of the shale sample, and calculate the semi-permeable membrane efficiency of the shale sample by combining the water content change of the third rock sample before and after soaking in drilling fluid. Step 3: Obtain the water content of each shale sample in the shale semi-permeable membrane efficiency characterization experiment. The water content is the difference between the mass of the shale sample after soaking in drilling fluid and the mass when dried. Combined with the rock strength of each shale sample, the relationship between rock strength and water content is fitted to determine the formula for calculating shale water content. Step 4: Based on the shale water content calculation formula, redetermine the calculation formula for the water content change of the shale sample, determine the characterization form of the water content change based on rock strength, and substitute it into the chemical osmotic pressure calculation formula of the shale sample to obtain the characterization formula for the shale semi-permeable membrane efficiency based on rock strength. The formula for characterizing the efficiency of the shale semi-permeable membrane based on rock strength is as follows: ； In the formula, For semi-permeable membrane efficiency; Let be the molar volume of water; It is the ideal gas constant; Absolute temperature; Drilling fluid activity; Shale activity; The chemical osmotic transport coefficient; This is the equivalent adsorption capacity; , , All are fitting coefficients; It is the natural logarithm function; The rock strength of the shale after soaking in drilling fluid; This represents the rock strength of the shale before it is soaked in drilling fluid.

6. The method for characterizing the efficiency of shale semi-permeable membranes based on rock strength according to claim 5, characterized in that, In step 2, the formula for calculating the chemical osmotic pressure of the shale sample is: ； In the formula, Chemical osmotic pressure, unit: ; is the ideal gas constant, with a value of 8.

314. ; Absolute temperature, unit: ; This is the molar volume of water, in units of . ; The semi-permeable membrane efficiency is dimensionless. It refers to the efficiency of a semi-permeable membrane when the core sample is encased in an artificial semi-permeable membrane. The value is 1; Drilling fluid activity, dimensionless; Shale activity, dimensionless; It is the natural logarithm function; The formula for calculating the change in water content of the shale sample is as follows: ； In the formula, This represents the change in water content, in units of... ; This is the chemical osmotic transport coefficient, in units of... ; The chemical osmotic pressure of shale; Equivalent adsorption capacity, in units of .

7. The method for characterizing the efficiency of shale semi-permeable membranes based on rock strength according to claim 6, characterized in that, In step 2, since both the first and second rock samples are wrapped with artificial semi-permeable membranes, the efficiency of the semi-permeable membranes for the first and second rock samples is determined. The chemical osmotic pressure of the first and second rock samples is calculated using the chemical osmotic pressure calculation formula. Combined with the mass of the first and second rock samples before and after soaking in drilling fluid, the change in water content of the first and second rock samples is determined. According to the formula for calculating the change in water content, we get: ； ； Solving the simultaneous equations, we obtain the chemical permeability transport coefficient of the shale sample. and equivalent adsorption capacity The calculation formula is: ； ； In the formula, This represents the change in water content of the first rock sample, in units of... ; This represents the change in water content of the second rock sample, in units of... ; The chemical osmotic pressure of the first rock sample is given in units of . ; The chemical osmotic pressure of the second rock sample is given in units of... ; Determine the chemical permeability transport coefficient of shale samples and equivalent adsorption capacity Subsequently, because the third rock sample was not encased in an artificial semi-permeable membrane, the chemical permeability transport coefficient of the shale sample was... and equivalent adsorption capacity Substituting these values ​​into the formula for calculating water content change, and considering the water content change before and after soaking the third rock sample in drilling fluid... The chemical osmotic pressure of the third rock sample was calculated. for ; Based on the chemical osmotic pressure calculation formula and the activity of the drilling fluid soaked in the third rock sample, the semi-permeable membrane efficiency of the shale sample was determined as follows: .

8. The method for characterizing the efficiency of shale semi-permeable membranes based on rock strength according to claim 5, characterized in that, In step 3, by fitting the water content and rock strength of all shale samples, the relationship between rock strength and water content is obtained as follows: ； In the formula, Moisture content, unit: ; It is a natural constant; Rock strength, unit: ; , , All are fitting coefficients; Taking the logarithm of both sides, the formula for calculating shale water content is: ； In the formula, It is the natural logarithm function.

9. The method for characterizing the efficiency of shale semi-permeable membranes based on rock strength according to claim 8, characterized in that, In step 4, since the change in shale water content is the change in the mass of the shale itself before and after soaking in drilling fluid, the form for representing the change in water content based on rock strength is determined according to the shale water content calculation formula: ； In the formula, This represents the change in water content, in units of... ; The water content of the shale after soaking in drilling fluid; This represents the water content of the shale before it is soaked in drilling fluid. The rock strength of the shale after soaking in drilling fluid; The rock strength of shale before it is soaked in drilling fluid; Substituting these values ​​into the chemical osmotic pressure calculation formula for shale samples, we obtain the following formula for characterizing the efficiency of shale semi-permeable membranes based on rock strength: ； In the formula, The efficiency of the semipermeable membrane is dimensionless. This is the molar volume of water, in units of . ; It is the ideal gas constant; Absolute temperature, unit: ; Drilling fluid activity, dimensionless; Shale activity, dimensionless; This is the chemical osmotic transport coefficient, in units of... ; Equivalent adsorption capacity, in units of ; , , All are fitting coefficients; It is the natural logarithm function; The rock strength of the shale after soaking in drilling fluid; This represents the rock strength of the shale before it is soaked in drilling fluid.

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