A shale pore water free volume prediction method based on component weighting

Abstract

The application discloses a shale pore water free amount prediction method based on component weighting, and relates to the field of shale detection.The method comprises the following steps: performing centrifugal experiments on each core column under multiple different centrifugal pressure difference conditions, and obtaining the mass of the core column after each centrifugal experiment; calculating the cumulative movable water amount after the centrifugal experiment under each centrifugal pressure difference condition according to the initial mass of the core column and the mass of the core column after the centrifugal experiment under each centrifugal pressure difference condition; determining the pore water free amount of the core column according to each centrifugal pressure difference of each core column and the cumulative movable water amount corresponding to each centrifugal pressure difference; establishing a relationship between the shale components and the pore water free amount of each core column in a linear weighting manner according to the shale components of each core column; determining the coefficient in the relationship according to the relationship corresponding to multiple core columns; and predicting the pore water free amount of the shale to be predicted according to the relationship with the determined coefficient.The application improves the prediction efficiency of the shale pore water free amount.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of shale pore water detection, in particular to a shale pore water free volume prediction method based on component weighting. BACKGROUND

[0002] With the continuous progress of shale gas exploration and development in China, some new problems have emerged in the process of shale gas development, which restrict the efficient exploitation of shale gas. Among them, the determination of shale matrix pore water mobility has been highly valued by the industry. In the process of shale gas accumulation and evolution, although it has experienced hydrocarbon generation drainage, vaporization liquid carrying and other water consumption historical activities, a part of water (referred to as shale matrix pore water) is still left in the shale matrix pore. Shale matrix pore water includes adsorbed water and free water, and free water is the main movable part in the process of pore water discharge. Shale gas exploration practice shows that the discharge of pore water affects the production and mining efficiency of shale gas. In addition, the shale formation flowback water has high salinity, toxic substances such as heavy metals, and risks of polluting groundwater and surface water. Therefore, evaluating the free volume of shale pore water not only helps to reasonably predict the shale gas well flowback rule, but also provides a scientific basis for the green and sustainable development of China's shale gas. At present, the detection efficiency of shale pore water free volume needs to be improved. SUMMARY

[0003] The purpose of the present application is to provide a shale pore water free volume prediction method based on component weighting, which improves the prediction efficiency of shale pore water free volume.

[0004] To achieve the above purpose, the present application provides the following scheme:

[0005] A shale pore water free volume prediction method based on component weighting, comprising:

[0006] Obtaining a core sample, and obtaining a plurality of core columns from the core sample;

[0007] Obtaining the initial mass of each core column;

[0008] Performing a centrifugal experiment on each core column under a plurality of different centrifugal pressure difference conditions, and obtaining the mass of the core column after each centrifugal experiment;

[0009] Drying the core column after all centrifugal experiments to obtain the mass of the dried core column;

[0010] For each core column, calculating the cumulative movable water volume after the centrifugal experiment under each centrifugal pressure difference condition according to the initial mass of the core column and the mass of the core column after the centrifugal experiment under each centrifugal pressure difference condition;

[0011] determining the free water content of the core column according to each centrifugal pressure difference of each core column and the cumulative mobile water amount corresponding to each centrifugal pressure difference;

[0012] establishing a relationship between the shale component and the free water content of each core column in a linear weighted manner according to the shale component of each core column, denoted as a free water content prediction model;

[0013] determining the coefficient in the free water content prediction model according to the free water content prediction model corresponding to the plurality of core columns;

[0014] predicting the free water content of the shale to be predicted according to the free water content prediction model with the determined coefficient.

[0015] Optionally, for each core column, the cumulative mobile water amount after the centrifugal experiment under each centrifugal pressure difference condition is calculated according to the initial mass of the core column and the mass of the core column after the centrifugal experiment under each centrifugal pressure difference condition, and specifically includes:

[0016] According to the formula the cumulative mobile water amount after the centrifugal experiment under the xth centrifugal pressure difference condition is calculated.

[0017] wherein Q m is the cumulative mobile water amount after the centrifugal experiment under the xth centrifugal pressure difference condition, m1 represents the initial mass of the core column, m0 represents the mass of the core column after drying, and mx represents the mass of the core column after the centrifugal experiment under the xth centrifugal pressure difference condition. x

[0018] Optionally, the free water content of the core column is determined according to each centrifugal pressure difference of each core column and the cumulative mobile water amount corresponding to each centrifugal pressure difference, and specifically includes:

[0019] According to the formula the free water content of the core column is determined;

[0020] wherein Q m represents the cumulative mobile water amount, ΔP represents the centrifugal pressure difference, ΔP L is the centrifugal pressure difference corresponding to the cumulative mobile water amount reaching half of the free water content, Q f is the free water content.

[0021] Optionally, the free water content prediction model is represented as:

[0022]

[0023] wherein Q f is the free water content, n represents the number of shale components, and a​i Ci represents the coefficient of the i-th shale component, i Ci represents the mass percentage of the i-th shale component, F1 is an intercept.

[0024] Optionally, the coefficients in the free pore water content prediction model corresponding to the plurality of core columns are determined according to the free pore water content prediction model, and specifically, the method comprises the following steps:

[0025] The coefficients in the free pore water content prediction model are determined according to the free pore water content prediction model corresponding to the plurality of core columns by using the least square method.

[0026] Optionally, the core column is subjected to centrifugal experiments under a plurality of different centrifugal pressure difference conditions, and the mass of the core column after each centrifugal experiment is obtained, and specifically, the method comprises the following steps:

[0027] The core column is subjected to centrifugal experiments under at least 7 different centrifugal pressure difference conditions, and the mass of the core column after each centrifugal experiment is obtained.

[0028] Optionally, the core column after all centrifugal experiments is dried to obtain the mass of the dried core column, and specifically, the method comprises the following steps:

[0029] The core column after all centrifugal experiments is placed in a vacuum drying oven and dried at a temperature of 110 DEG C for more than 24 hours to obtain the mass of the dried core column.

[0030] Optionally, the shale component includes total organic carbon content and inorganic mineral composition.

[0031] According to the specific embodiments provided by the present application, the following technical effects are disclosed:

[0032] The present application quantitatively evaluates the free pore water content of shale through centrifugal experiments, and establishes a weighted model based on shale components, i.e., a free pore water content prediction model. According to the relationship, the free pore water content of known shale components is predicted. The method is simple and easy to operate, time-saving and labor-saving, and has high operability and practicability, and improves the prediction efficiency of the free pore water content of shale. BRIEF DESCRIPTION OF DRAWINGS

[0033] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed in the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0034] Figure 1A flowchart of a shale pore water free amount prediction method based on component weighting according to the present application is shown in the figure.

[0035] Figure 2 A core column cumulative movable water amount change graph under each centrifugal pressure difference condition according to the present application is shown in the figure.

[0036] Figure 3 A centrifugal pressure difference reciprocal-movable water amount reciprocal relationship graph according to the present application is shown in the figure.

[0037] Figure 4 A simplified volume model graph for predicting shale pore water free amount according to the present application is shown in the figure.

[0038] Figure 5 A shale pore water free amount test result-model prediction result relationship graph according to the present application is shown in the figure.

[0039] Figure 6 A shale pore water free amount test result-model prediction result comparison graph according to the present application is shown in the figure. DETAILED DESCRIPTION

[0040] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the scope of protection of the present application.

[0041] The purpose of the present application is to provide a shale pore water free amount prediction method based on component weighting, which improves the prediction efficiency of shale pore water free amount.

[0042] In order to make the above-mentioned purposes, features and advantages of the present application more obvious and easy to understand, the present application will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0043] The presence of water in the pores of shale matrix is ​​intrinsically linked to the composition of shale and its pore-throat system (reservoir space). This is because the rock skeleton, pore-throat system, and pore water are genetically interrelated: various organic and inorganic minerals form the rock skeleton, within which the pore-throat system develops, and pore water is contained within these pores. The complex composition of shale (organic and inorganic matter) and the varying hydrophilicity of its components lead to significant differences in the water-bearing characteristics of organic matter pores and inorganic mineral pores. Generally, inorganic mineral surfaces are considered to be strongly hydrophilic, especially clay minerals. However, whether organic matter pores contain water remains controversial, as moisture content may be controlled by factors such as kerogen type, maturity, and functional groups. Organic matter pores formed during hydrocarbon generation are generally considered to have oil-wet characteristics and are almost water-free. However, some studies have shown that the functional group structure within kerogen pores gives them a certain degree of hydrophilicity, allowing water molecules to adsorb onto the surface of these functional groups and distribute within the pores of shale organic matter. Therefore, clarifying which types of pore spaces / spaces pore water stores in shale and understanding the coupling relationship between pore water and shale components is crucial. Since free water is stored within the interior of pore spaces, and the free water content is closely related to the pore volume that holds it, pore volumes of the same size within different shale components contribute equally to the free water content.

[0044] Example 1

[0045] like Figure 1 As shown, the present invention provides a method for predicting the free pore water content in shale based on component weighting, comprising the following steps:

[0046] Step 101: Obtain core samples and obtain multiple core columns from the core samples.

[0047] Step 101 specifically includes: obtaining fresh core samples through drilling. The fresh core samples are promptly wrapped in plastic wrap and sealed with wax, and then stored at low temperature to reduce pore water loss.

[0048] A core column with a diameter of 2.5 cm and a certain length was drilled along the bedding direction parallel to the fresh core sample using wire cutting.

[0049] Step 102: Obtain the initial mass of each core column.

[0050] Step 103: Perform centrifugation experiments on each core column under multiple different centrifugation pressure difference conditions, and obtain the mass of the core column after each centrifugation experiment.

[0051] Step 103 specifically includes:

[0052] At a certain experimental temperature and normal pressure, centrifugal experiments are performed on each of the core columns under at least 7 different centrifugal pressure difference conditions, and the mass of the core column after each centrifugal experiment is obtained.

[0053] The centrifugal experiment under each centrifugal pressure difference condition lasts at least 4 hours. After the centrifugal experiment under each centrifugal pressure difference condition is completed, the core column is taken out and weighed to obtain the mass of the core column, denoted as m x .

[0054] Step 104: drying the core column after all centrifugal experiments to obtain the mass of the dried core column.

[0055] Step 104 specifically includes:

[0056] For each core column, the core column after all centrifugal experiments is placed in a vacuum drying oven and dried at a temperature of 110°C for more than 24 hours to obtain the mass of the dried core column.

[0057] Step 105: for each of the core columns, calculating the cumulative mobile water amount after the centrifugal experiment under each centrifugal pressure difference condition according to the initial mass of the core column and the mass of the core column after the centrifugal experiment under each centrifugal pressure difference condition.

[0058] Step 105 specifically includes:

[0059] The cumulative mobile water amount after the centrifugal experiment under the xth centrifugal pressure difference condition is calculated according to the formula .

[0060] Wherein, Q m is the cumulative mobile water amount after the centrifugal experiment under the xth centrifugal pressure difference condition, mg / g; m1 represents the initial mass of the core column, m0 represents the mass of the dried core column, g; mx represents the mass of the core column after the centrifugal experiment under the xth centrifugal pressure difference condition, g. x .

[0061] Step 106: determining the free pore water content of the core column according to each centrifugal pressure difference of each of the core columns and the corresponding cumulative mobile water amount of each centrifugal pressure difference.

[0062] Step 106 specifically includes: after obtaining the mobile water amount under different centrifugal pressure difference conditions, the free pore water content can be calculated according to the relationship between the mobile water amount and the centrifugal pressure difference, i.e.

[0063] The free pore water content of the core column is determined according to the formula .

[0064] Wherein, Q mΔP represents the cumulative movable water volume after centrifugation under the x-th centrifugation pressure difference condition, where ΔP is the centrifugation pressure difference in MPa. L Q is the centrifugal pressure difference (MPa) corresponding to the accumulation of movable water reaching half of the free pore water. f This represents the amount of free pore water, in mg / g.

[0065] The movable water volume Q under different centrifugal pressure differences m The corresponding data were fitted to determine the amount of free pore water in the core column.

[0066] Step 107: Based on the shale composition of each core column, establish the relationship between the shale composition and the amount of free pore water in each core column using a linear weighted method, denoted as the pore water free amount prediction model.

[0067] The shale composition includes total organic carbon (TOC) and inorganic mineral composition, which includes quartz, plagioclase, barite, ferroalloy, calcite, pyrite, and total clay content.

[0068]

[0069] The prediction model for pore water free quantity is expressed as follows:

[0070]

[0071] Among them, Q f ρ represents the amount of pore water released; n represents the quantity of shale components; a i The coefficient representing the i-th shale component, mg / (g·%); C i F1 represents the mass percentage of the i-th shale component; F1 is the intercept, mg / g.

[0072] The coefficients in the pore water free volume prediction model include the coefficients and intercepts of the i-th shale component.

[0073] Step 108: Determine the coefficients in the pore water free volume prediction model based on the prediction model for the pore water free volume corresponding to the multiple core columns.

[0074] Step 108 specifically includes:

[0075] The least squares method was used to fit data to the pore water free volume prediction model corresponding to multiple core columns, and the coefficients in the pore water free volume prediction model were determined.

[0076] Step 109: Predict the amount of pore water free in the shale to be predicted based on the pore water free volume prediction model with determined coefficients.

[0077] The present application obtains the movable water amount of fresh shale core under different centrifugal force conditions, calculates the shale pore water free amount, and establishes the coupling relationship between the shale component and the pore water free amount, to obtain a weighted model based on the shale component. According to the mathematical model, the pore water free amount of shale with other known material composition can be predicted.

[0078] Example 2

[0079] Step a: Taking a shale gas well in Weiyuan block of Sichuan Basin as an example, 6 fresh core samples are obtained by drilling coring. The fresh core is wrapped with preservative film and sealed with wax in time, and is stored in low temperature refrigerator to minimize the loss of pore water.

[0080] Step b: A core column with a diameter of 2.5 cm and a certain length is drilled along the parallel bedding direction of the fresh core sample by wire cutting, and a total of 21 core columns are drilled. The mass of each core column is weighed and recorded as m1.

[0081] Step c: Under the conditions of 30℃ experimental temperature and normal pressure, centrifugal experiments under more than 7 centrifugal pressure difference conditions are carried out for each core column. The centrifugal pressure difference size is adjusted by setting the centrifuge speed. The centrifuge speed is set to 3000r / min, 4000r / min, 5000r / min, 6000r / min, 7000r / min, 8000r / min, 9000r / min and 10000r / min. The centrifugal experiment duration under each centrifugal pressure difference condition is at least 4 hours. After the centrifugal experiment under each centrifugal pressure difference condition is completed, the core column is taken out and weighed, and the mass of the core column is recorded as m x .

[0082] Step d: After the centrifugal experiment is completed, the core column is placed in a vacuum drying oven and dried at 110℃ for more than 24 hours. Then the core column is taken out and the mass of the core under dry condition is weighed and recorded as m0.

[0083] Step e: The total amount of pore water can be calculated according to the data obtained in steps b and d (see Table 1), and the calculation formula is:

[0084]

[0085] In the formula, Q t is the total amount of pore water, mg / g; m1 is the mass of fresh core column, g; m0 is the mass of dry core column, g.

[0086] Table 1: Shale pore water content and shale component results determined by experiment

[0087]

[0088]

[0089] Based on the data obtained in steps b, c and d, the cumulative mobile water content of the core column under each centrifugal pressure difference condition can be calculated (see Figure 2 ), and the calculation formula is as follows:

[0090]

[0091] In the formula, Q is the cumulative mobile water content, mg / g; m x is the mass of the core column after the centrifugal experiment under each centrifugal pressure difference condition, g.

[0092] Step f: After obtaining the mobile water content under different centrifugal pressure difference conditions, the free water content in the pore water can be calculated according to the relationship between the mobile water content and the centrifugal pressure difference, and the calculation formula is as follows:

[0093]

[0094] In the formula, ΔP is the centrifugal pressure difference, MPa; ΔP L is the median pressure difference, that is, the centrifugal pressure difference corresponding to the mobile water content reaching half of the free water content, MPa; Q f is the free water content in the pore water, mg / g.

[0095] As shown in Figure 3 , the mathematical formula (3) can well describe the experimental data, and the intercept of the fitting line in the figure is 1 / Q f , from which the free water content can be inversely calculated. The analysis results of the 21 core columns are shown in Table 1.

[0096] Step g: After completing the test of the pore water parameters, the percentage contents of the organic components and inorganic components of all the core columns are tested by using the general Chinese national standard (GB / T 19145-2003) and the industry standard (SY / T 5163-2010), and the components include: total organic carbon content (TOC) and inorganic mineral composition (see Table 1). The shale is simplified as a volume model as shown in Figure 4 , and the percentage contents of the total organic carbon content (TOC) C1 and the inorganic mineral composition (quartz C2, plagioclase C3, barite C4, ferrodolomite C5, calcite C6, pyrite C7, and total amount of clay C8) satisfy the following relationship:

[0097]

[0098] In the formula, C iMass percentage of component i (i = 1, TOC; i = 2, quartz; i = 3, plagioclase; i = 4, barite; i = 5, ankerite; i = 6, calcite; i = 7, pyrite; i = 8, total clay), wt. %.

[0099] Step h: Based on the data obtained in steps f and g, a linear weighted relationship between shale components and free water content was established:

[0100]

[0101] where a i is the fitting coefficient, mg / (g·%) and F1 is the intercept, mg / g.

[0102] Step i: The parameters described in step h were obtained by the least square method (see Table 2). The free water content of shale pore water calculated by equations (4) and (5) was very close to the test value Figure 5 and Figure 6 . This indicates that the mathematical model based on component weighting can be used to predict the free water content of shale pore water with other known compositions.

[0103] Table 2 Coefficients of the free water content prediction model based on component weighting

[0104] [a1] [a2] [a3] [a4] [a5] [a6] [a7] [a8] F1 1.000 0.898 0.856 0.876 0.875 0.895 0.885 0.902 -0.900

[0105] The various embodiments in the specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0106] The principles and implementation modes of the present application are described by using specific examples in this specification. The above description of the embodiments is only used to help understand the method of the present application and its core idea; at the same time, for those skilled in the art, according to the idea of the present application, the specific implementation mode and application range will be changed. In summary, the content of the specification should not be understood as a limitation of the present application.

Claims

1. A method for predicting the amount of free pore water in shale based on component weighting, characterized in that, The method comprises the following steps: obtaining core samples, and obtaining a plurality of core columns from the core samples, specifically comprising: wrapping and wax-sealing the removed core samples by preservative film, and storing them in low-temperature refrigeration; obtaining the initial mass of each core column; performing centrifugal experiments on each core column under a plurality of different centrifugal pressure difference conditions, and obtaining the mass of each core column after each centrifugal experiment; drying the core columns after all centrifugal experiments, and obtaining the mass of the dried core columns; for each core column, calculating the cumulative mobile water amount after the centrifugal experiment under each centrifugal pressure difference condition according to the initial mass of the core column and the mass of the core column after the centrifugal experiment under each centrifugal pressure difference condition; determining the free water content of each core column according to each centrifugal pressure difference of each core column and the corresponding cumulative mobile water amount; establishing a relationship between the shale composition and the free water content of each core column by linear weighting according to the shale composition of each core column, and recording the relationship as a free water content prediction model; determining the coefficient in the free water content prediction model according to the free water content prediction model corresponding to each core column; predicting the free water content of a to-be-predicted shale according to the free water content prediction model with the determined coefficient; the free water content prediction model is expressed as: where Q f is the free pore water content, n indicates the number of shale fractions, a i indicates the coefficient of the i-th shale fraction, C i indicates the mass percentage content of the i-th shale fraction, F1 is the intercept.

2. The component-weighted-based shale free-pore water fraction prediction method of claim 1, wherein, for each core column, calculating the cumulative mobile water amount after the centrifugal experiment under each centrifugal pressure difference condition according to the initial mass of the core column and the mass of the core column after the centrifugal experiment under each centrifugal pressure difference condition, specifically comprising: The cumulative mobile water amount after centrifugal experiment under the xthcentrifugal pressure difference condition is calculated according to the formula The cumulative mobile water amount after centrifugal experiment under the xthcentrifugal pressure difference condition is calculated according to the formula wherein Q m is the cumulative mobile water amount after the xth centrifugal experiment under the centrifugal pressure difference condition, m1 represents the initial mass of the core column, m0 represents the mass of the core column after drying, and m x represents the mass of the core column after the xth centrifugal experiment under the centrifugal pressure difference condition.

3. The component-weighted-based prediction method of shale free fluid pore volume according to claim 1, wherein, determining the free water content of each core column according to each centrifugal pressure difference of each core column and the corresponding cumulative mobile water amount, specifically comprising: According to the formula determining the free pore water content of the core column; wherein Q m represents the cumulative mobile water amount, ΔP is the centrifugal pressure difference, ΔP L is the centrifugal pressure difference corresponding to the cumulative mobile water amount reaching half of the free water porosity, Q f is the free water porosity.

4. The component-weighted-based shale free fluid porosity prediction method of claim 1, wherein, determining the coefficient in the free water content prediction model according to the free water content prediction model corresponding to each core column, specifically comprising: determining the coefficient in the free water content prediction model according to the free water content prediction model corresponding to each core column by the least square method.

5. The component-weighted-based shale free-pore water fraction prediction method of claim 1, wherein, performing centrifugal experiments on each core column under a plurality of different centrifugal pressure difference conditions, and obtaining the mass of each core column after each centrifugal experiment, specifically comprising: performing centrifugal experiments on each core column under at least 7 different centrifugal pressure difference conditions, and obtaining the mass of each core column after each centrifugal experiment.

6. The component-weighted-based shale free-pore water fraction prediction method of claim 1, wherein, drying the core columns after all centrifugal experiments, and obtaining the mass of the dried core columns, specifically comprising: placing the core columns after all centrifugal experiments in a vacuum drying oven, drying them at a temperature of 110 DEG C for more than 24 hours, and obtaining the mass of the dried core columns.

7. The component-weighted-based shale free-pore water fraction prediction method of claim 1, wherein, the shale composition comprises total organic carbon content and inorganic mineral composition.

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