Method for quantitative evaluation of self-sealing property of organic-rich shale

Abstract

A method for quantitative evaluation of self-sealing property of organic-rich shale includes: S1, selecting geological parameters for evaluating the self-sealing property of the organic-rich shale; S2, taking organic-rich shale samples, and measuring the geological parameters of each sample; S3, calculating a weight coefficient w; of each geological parameter; S4, calculating a self-sealing evaluation coefficient S, and correcting the S to obtain a corrected self-sealing evaluation coefficient S; S5, establishing a self-sealing evaluation standard of the organic-rich shale according to the S, wherein if S0.6, the self-sealing grade is excellent, if 0.45S<0.6, the self-sealing grade is good, if 0.3S<0.45, the self-sealing grade is medium, and if S<0.3, the self-sealing grade is poor. According to the method, the self-sealing property of the shale is quantitatively evaluated, and the preservation condition of the shale gas in the shale formation can be more accurately predicted.

Claims

1. A method for quantitative evaluation of self-sealing property of organic-rich shale, comprising: S1, selecting geological parameters for evaluating the self-sealing property of the organic-rich shale, wherein the geological parameters comprise five geological parameters of adsorption gas content, overlying pressure, connectivity difference A, connectivity difference B and bound water content; wherein the connectivity difference A is a difference between connectivity of shale itself and connectivity of roof strata; wherein the connectivity difference B is a difference between the connectivity of the shale itself and connectivity of floor strata; S2, taking a plurality of organic-rich shale samples, measuring the adsorption gas content, the overlying pressure, the connectivity difference A, the connectivity difference B and the bound water content of each of the plurality of organic-rich shale samples, and then carrying out standardization processing on each of the five geological parameters to obtain standardized geological parameters Zx.sub.ij, wherein the standardized geological parameter for the j-th geological parameter is denoted as P.sub.j, and a formula of the standardization processing is as follows: $Z{x}_{ij}=\frac{x_{\stackrel{}{\mathrm{.Math.}}j}-\min \left\{x_{1j},x_{2j},.Math.,x_{\mathrm{nj}},\right\}}{\max \left\{x_{1j},x_{2j},.Math.,x_{\mathrm{nj}},\right\}-\min \left\{x_{1j},x_{2j},.Math.,x_{\mathrm{nj}},\right\}},$ where x.sub.ij is a value of an i-th sample of a j-th geological parameter before the standardization processing; Zx.sub.ij is a value of the i-th sample of the j-th geological parameter after the standardization processing; min {x.sub.1j, x.sub.2j, . . . , x.sub.nj} is a minimum value of all sample data of the j-th geological parameter, max {x.sub.1j, x.sub.2j, . . . , x.sub.nj} is a maximum value in all sample data of the j-th geological parameter; and j=1, 2, 3, 4, 5; S3, calculating a weight coefficient .sub.j of each of the five geological parameters to obtain five weight coefficients respectively corresponding to the five geological parameters, where .sub.j=t.sub.j; S4, sorting the five weight coefficients in descending order to obtain an ordered sequence: t.sub.1>t.sub.2>t.sub.3>t.sub.4>t.sub.5, wherein a standardized geological parameter corresponding to the weight coefficient t.sub.1 is P.sub.1, a standardized geological parameter corresponding to the weight coefficient t.sub.2 is P.sub.2, a standardized geological parameter corresponding to the weight coefficient t.sub.3 is P.sub.3, a standardized geological parameter corresponding to the weight coefficient t.sub.4 is P.sub.4, and a standardized geological parameter corresponding to the weight coefficient t.sub.5 is P.sub.5; S5, calculating a self-sealing evaluation coefficient S, wherein a formula of the self-sealing evaluation coefficient S is as follows: $S=t_1{P}_1^3+t_2{P}_2^2+t_3{P}_3+t_4\sqrt[2]{P_4}+t_5\sqrt[3]{P_5};$ S6, correcting the self-sealing evaluation coefficient S by taking a measured total gas content Q corresponding to different samples as a constraint, and establishing a functional relation between the self-sealing evaluation coefficient S and the measured total gas content Q by taking the self-sealing evaluation coefficient S as a dependent variable and the measured total gas content Q as an independent variable using a least square method, namely, a correction formula of the self-sealing evaluation coefficient S as follows:
S=aQ+b, where S is a corrected self-sealing evaluation coefficient, a is a slope, and b is an intercept; and calculation formulas of the a and the b are as follows: $a=\frac{{.Math.}_{i=1}^n\left(Q_{\stackrel{}{t}}-\stackrel{\_}{Q}\right)\left(S_i-\stackrel{\_}{S}\right)}{{.Math.}_{i=1}^n{\left(Q_i-\stackrel{\_}{Q}\right)}^2},$ $b=\stackrel{}{S}-a\stackrel{\_}{Q},$ where Q.sub.i is a measured total gas content corresponding to the i-th sample, Q is an average value of the measured total gas content of all samples, S.sub.i is a self-sealing evaluation coefficient of the i-th sample before correction, and S is an average value of the self-sealing evaluation coefficients of all samples before correction; S7, substituting the measured total gas content Q corresponding to the different samples into the correction formula established in the step S6 to obtain the corrected self-sealing evaluation coefficient S, and establishing, according to the corrected self-sealing evaluation coefficient S, a self-sealing evaluation standard of the organic-rich shale comprising four grades as follows: an excellent self-sealing grade in response to the corrected self-sealing evaluation coefficient S greater than or equal to 0.6; a good self-sealing grade in response to the corrected self-sealing evaluation coefficient S greater than or equal to 0.45 and less than 0.6; a medium self-sealing grade in response to the corrected self-sealing evaluation coefficient S greater than or equal to 0.3 and less than 0.45; a poor self-sealing grade in response to the corrected self-sealing evaluation coefficient S less than 0.3.

2. The method for the quantitative evaluation of the self-sealing property of the organic-rich shale as claimed in claim 1, wherein in the step S3, the calculating a weight coefficient .sub.j of each of the five geological parameters comprises: S31, calculating a proportion of the value of the i-th sample of the j-th geological parameter after the standardization processing in the j-th geological parameter as follows: $Q_{ij}=\frac{Z{x}_{\mathrm{ij}}}{{.Math.}_{i=1}^{n}Z{x}_{\mathrm{ij}}},$ where Zx.sub.ij is the value of the i-th sample of the j-th geological parameter after the standardization processing; i=1, . . . , n; n is a number of samples; S32, calculating an entropy value of the j-th geological parameter after the standardization processing as follows: $E_j=-k{.Math.}_{j=0}^n{Q}_{\mathrm{ij}}\mathrm{In}\left(Q_{\mathrm{ij}}\right),$ where k is a constant, $k=\frac{1}{\ln \left(n\right)};$ S33, calculating a weight of the j-th geological parameter after the standardization processing as follows:
j=1E.sub.j; S34, normalizing the weights to ensure that a sum of all the weights is 1 as follows: ${}_{j^{}}=\frac{{}_j}{{.Math.}_j^m{}_j},$ where m=5.

3. The method for the quantitative evaluation of the self-sealing property of the organic-rich shale as claimed in claim 1, wherein in the step S2, the adsorption gas content is measured by an isothermal adsorption experiment.

4. The method for the quantitative evaluation of the self-sealing property of the organic-rich shale as claimed in claim 1, wherein in the step S2, the overlying pressure is calculated based on gravity-logging data.

5. The method for the quantitative evaluation of the self-sealing property of the organic-rich shale as claimed in claim 1, wherein in the step S2, the connectivity of the shale itself, the connectivity of the roof strata, and the connectivity of the floor strata are all measured by a spontaneous dialysis experiment.

6. The method for the quantitative evaluation of the self-sealing property of the organic-rich shale as claimed in claim 1, wherein in the step S2, the bound water content is measured by a nuclear magnetic resonance experiment.

Description

DETAILED DESCRIPTION OF EMBODIMENTS

(1) Hereinafter, the illustrated embodiments of the disclosure will be described, and it should be understood that the illustrated embodiments described herein are only used to illustrate and explain the disclosure, and are not used to limit the disclosure.

(2) Specifically, a method for quantitative evaluation of self-sealing property of organic-rich shale includes the following detailed steps.

(3) (1) Geological parameters are selected to evaluate the self-sealing property of the organic-rich shale. Adsorption gas content reflects the strength of shale adsorption capacity. Methane molecules adhere to pores on the surface of organic matter and minerals by adsorption, forming an adsorption gas layer, which hinders the free flow of gas, thus enhancing the self-sealing property of shale. Therefore, the higher the adsorption gas content, the stronger the self-sealing property of shale. The increase of overlying pressure can close the micro-nano throat in shale, thus forming a higher breakthrough pressure and enhancing the sealing capacity of shale. Therefore, the greater the overlying pressure, the stronger the self-sealing capacity of shale. Organic-rich shale itself has good connectivity, but its roof and floor strata connectivity is poor, which can minimize the escape of gas, while maintaining the accumulation of internal gas, thus conducive to the preservation and enrichment of shale gas. Therefore, the greater the difference in connectivity between shale itself and roof and floor strata, the better the self-sealing property of shale. Most of the micro-nano pores in shale are occupied by water molecules, and the water film and capillary water formed by these water molecules can effectively seal pore channels and prevent gas dispersion, thus enhancing the self-sealing property of shale. Therefore, the higher the bound water content, the stronger the self-sealing property of shale. In this situation, the disclosure selects the adsorption gas content, the overlying pressure, the difference between the connectivity of organic-rich shale itself and the connectivity of the roof strata, the difference between the connectivity of organic-rich shale itself and the connectivity of the floor strata, and the bound water content as evaluation parameters, which can well reflect the strength of the self-sealing property of organic-rich shale. Among them, the adsorption gas content is measured by isothermal adsorption experiment, the overlying pressure is calculated by gravity-logging data, the connectivity is measured by spontaneous dialysis experiment, and the bound water content is measured by NMR experiment. In this embodiment, the selected organic-rich shale samples and the test results of geological parameters of each sample are shown in Table 1.

(4) TABLE-US-00001 TABLE 1 riginal data of evaluation parameters Bound Gas Adsorption Overlying water content Sample gas content pressure Connectivity Connectivity content Q Well Stratum number (m.sup.3/t) (MPa) difference A difference B (%) (m.sup.3/t) A1 L1 1 1.76 92.42 0.17 0.25 12.3 10.2 L2 2 2.31 84.68 0.23 0.31 8.4 11.1 L3 3 0.92 77.17 0.29 0.19 5.6 3.3 A2 L1 4 1.23 90.72 0.15 0.21 14.4 7.3 L2 5 1.65 85.23 0.27 0.28 21.5 12.1 L3 6 2.54 78.92 0.25 0.21 19.1 8.2 A3 L1 7 0.78 93.16 0.18 0.27 9.8 6.6 L2 8 2.01 83.89 0.19 0.33 13.7 10.6 L3 9 1.34 76.59 0.27 0.17 16.4 4.9 A4 L1 10 1.59 92.87 0.2 0.24 7.5 7.7 L2 11 2.11 85.98 0.25 0.35 23 13.2 L3 12 0.83 78.56 0.33 0.18 21.2 7.5 A5 L1 13 1.47 91.35 0.19 0.21 18.3 8.3 L2 14 2.82 83.75 0.2 0.32 10.1 9.8 L3 15 1.75 77.69 0.31 0.23 7.9 6.5

(5) (2) The measured geological parameters are performed with standardization processing to make them in the same comparison scale. The formula for the standardization processing is as follows:

(6) $\begin{array}{cc}{\mathrm{Zx}}_{\mathrm{ij}}=\frac{x_{\mathrm{ij}}-\min \left\{x_{1j},x_{2j},.Math.,x_{nj},\right\}}{\max \left\{x_{1j},x_{2j},.Math.x_{\mathrm{nj}},\right\}-\min \left\{x_{1j},x_{2j},.Math.,x_{nj},\right\}}.& \left(1\right)\end{array}$

(7) In the formula, x.sub.ij is a value of an i-th sample of a j-th geological parameter before the standardization processing; Zx.sub.ij is a value of the i-th sample of the j-th geological parameter after the standardization processing; min {x.sub.1j, x.sub.2j, . . . , x.sub.nj} is a minimum value of all sample data of the j-th geological parameter; max {x.sub.1j, x.sub.2j, . . . , x.sub.nj} is a maximum value in all sample data of the j-th geological parameter.

(8) The data of each geological parameter after standardization are shown in Table 2.

(9) TABLE-US-00002 TABLE 2 Data of each parameter after standardization Sample Adsorption gas Overlying Connectivity Connectivity Bound water Well Stratum number content pressure difference A difference B content A1 L1 1 0.48 0.96 0.11 0.44 0.39 L2 2 0.75 0.49 0.44 0.78 0.16 L3 3 0.07 0.04 0.78 0.11 0.00 A2 L1 4 0.22 0.85 0.00 0.22 0.51 L2 5 0.43 0.52 0.67 0.61 0.91 L3 6 0.86 0.14 0.56 0.22 0.78 A3 L1 7 0.00 1.00 0.17 0.56 0.24 L2 8 0.60 0.44 0.22 0.89 0.47 L3 9 0.27 0.00 0.67 0.00 0.62 A4 L1 10 0.40 0.98 0.28 0.39 0.11 L2 11 0.65 0.57 0.56 1.00 1.00 L3 12 0.02 0.12 1.00 0.06 0.90 A5 L1 13 0.34 0.89 0.22 0.22 0.73 L2 14 1.00 0.43 0.28 0.83 0.26 L3 15 0.48 0.07 0.89 0.33 0.13

(10) (3) The weight coefficients of geological parameters for evaluation of the self-sealing property of organic-rich shale are determined, including the following steps.

(11) a. The proportion Q.sub.ij of the value of the i-th sample of the j-th geological parameter after the standardization processing in the j-th geological parameter is calculated as follows:

(12) $\begin{array}{cc}{Q}_{ij}=\frac{Z{x}_{ij}}{{.Math.}_{i=1}^n{\mathrm{Zx}}_{ij}}.& \left(2\right)\end{array}$

(13) In the formula, Zx.sub.ij is the value of the i-th sample of the j-th geological parameter after the standardization processing; i=1, . . . , n; j=1, . . . , m; n is a number of samples; and m is a number of geological parameters. In this embodiment, n=15 and m=5. The calculation results are shown in Table 3.

(14) TABLE-US-00003 TABLE 3 Q.sub.ij values of different sample values of parameters Sample Adsorption Overlying Connectivity Connectivity Bound water Well Stratum number gas content pressure difference A difference B content A1 L1 1 0.07 0.13 0.02 0.07 0.05 L2 2 0.11 0.07 0.07 0.12 0.02 L3 3 0.01 0.00 0.11 0.02 0.00 A2 L1 4 0.03 0.11 0.00 0.03 0.07 L2 5 0.06 0.07 0.10 0.09 0.13 L3 6 0.13 0.02 0.08 0.03 0.11 A3 L1 7 0.00 0.13 0.02 0.08 0.03 L2 8 0.09 0.06 0.03 0.13 0.06 L3 9 0.04 0.00 0.10 0.00 0.09 A4 L1 10 0.06 0.13 0.04 0.06 0.02 L2 11 0.10 0.08 0.08 0.15 0.14 L3 12 0.00 0.02 0.15 0.01 0.12 A5 L1 13 0.05 0.12 0.03 0.03 0.10 L2 14 0.15 0.06 0.04 0.13 0.04 L3 15 0.07 0.01 0.13 0.05 0.02

(15) b. An entropy value of the j-th geological parameter after the standardization processing is calculated, and the formula is as follows:

(16) 0$\begin{array}{cc}{E}_j=-k{.Math.}_{i=0}^n{Q}_{\mathrm{ij}}\mathrm{In}\left(Q_{\mathrm{ij}}\right).& \left(3\right)\end{array}$

(17) In the formula, k is a constant,

(18) $k=\frac{1}{\ln \left(n\right)}=\frac{1}{\ln \left(15\right)}=0.3693.$

(19) The calculation results are shown in Table 4.

(20) TABLE-US-00004 TABLE 4 Entropy values of evaluation parameters Adsorption Bound gas Overlying Connectivity Connectivity water content pressure difference A difference B content E.sub.1 E.sub.2 E.sub.3 E.sub.4 E.sub.5 0.9028 0.8847 0.9138 0.8989 0.9067

(21) c. A weight w; of the j-th geological parameter after the standardization processing is calculated as follows, and the formula is as follows:
.sub.j=1E.sub.j(4).

(22) The calculation results are shown in Table 5.

(23) TABLE-US-00005 TABLE 5 Weights of evaluation parameters Adsorption Bound gas Overlying Connectivity Connectivity water content pressure difference A difference B content .sub.1 .sub.2 3 .sub.4 .sub.5 0.9028 0.8847 0.9138 0.8989 0.9067

(24) d. The weights are normalized according to the formula (5) to ensure that the sum of all weights is 1, and the calculation results are shown in Table 6.

(25) $\begin{array}{cc}{}_{j^{}}=\frac{{}_j}{{.Math.}_j^m{}_j}.& \left(5\right)\end{array}$

(26) TABLE-US-00006 TABLE 6 Normalized weight coefficient of each evaluation parameter Adsorption Bound gas Overlying Connectivity Connectivity water content pressure difference A difference B content .sub.1 .sub.2 .sub.3 .sub.4 .sub.5 0.1971 0.2339 0.1748 0.2050 0.1892

(27) (4) Making .sub.j=t, the five weight coefficients t are sorted according to a sequence from large to small: t.sub.1>t.sub.2>t.sub.3>t.sub.4>t.sub.5. The maximum weight coefficient t.sub.1=0.2339, the corresponding geological parameter is overlying pressure, and the normalized overlying pressure is P.sub.1. The second largest weight coefficient t.sub.2=0.2050, the corresponding geological parameter is connectivity difference B, and the normalized connectivity difference B is P.sub.2. The third largest weight coefficient t.sub.3=0.1971, the corresponding geological parameter is adsorption gas content, and the normalized adsorption gas content is P.sub.3. The fourth largest weight coefficient t.sub.4=0.1892, the corresponding geological parameter is bound water content, and the normalized bound water content is P.sub.4. The minimum weight coefficient t.sub.5=0.1748, the corresponding geological parameter is connectivity difference A, and the normalized connectivity difference A is P.sub.5.

(28) (5) Comprehensively considering the adsorption gas content, the overlying pressure, the difference between the connectivity of organic-rich shale and the connectivity of the roof strata, the difference between the connectivity of organic-rich shale and the connectivity of the floor strata, and the bound water content, the self-sealing evaluation coefficient S of organic-rich shale is calculated as follows:

(29) $S=t_1{P}_1^3+t_2{P}_2^2+t_3{P}_3+t_4\sqrt[2]{P_4}+t_5\sqrt[3]{P_5}).$

(30) In this embodiment:

(31) $S=0.2339\mathrm{overlying}{\mathrm{pressure}}^3+0.2050\mathrm{connectivity}\mathrm{difference}{B}^2+0.1971\mathrm{adsorption}\mathrm{gas}\mathrm{content}+0.1892\sqrt[2]{\mathrm{bound}\mathrm{water}\mathrm{content}}+t_5\sqrt[3]{\mathrm{connectivity}\mathrm{difference}A}.$

(32) (6) The self-sealing evaluation coefficient S is corrected by taking a measured total gas content Q corresponding to different samples as a constraint, and a functional relation between the self-sealing evaluation coefficient S and the measured total gas content Q is established by taking the self-sealing evaluation coefficient S as a dependent variable and the measured total gas content Q as an independent variable using a least square method, namely, a correction formula of the self-sealing evaluation coefficient S as follows:
S=aQ+b.

(33) In the formula, S is a corrected self-sealing evaluation coefficient, a is a slope, and b is an intercept; and calculation formulas of the a and the b are as follows:

(34) $\begin{array}{c}a=\frac{{.Math.}_{i=1}^n\left(Q_i-\stackrel{\_}{Q}\right)\left(S_{i-}\stackrel{\_}{S}\right)}{{.Math.}_{i=1}^n{\left(Q_i-\stackrel{\_}{Q}\right)}^2},\\ b=\stackrel{}{S}-a\stackrel{\_}{Q}.\end{array}$

(35) In the formula, Q.sub.i is a measured total gas content corresponding to the i-th sample, Q is an average value of the measured total gas content of all samples, S.sub.i is a self-sealing evaluation coefficient of the i-th sample before correction, and S is an average value of the self-sealing evaluation coefficients of all samples before correction.

(36) In this embodiment,

(37) $a=\frac{{.Math.}_{i=1}^n\left(Q_i-\stackrel{\_}{Q}\right)\left(S_i-\stackrel{\_}{S}\right)}{{.Math.}_{i=1}^n{\left(Q_i-\stackrel{\_}{Q}\right)}^2}=0.0412,$
b=SaQ=0.115, namely, S=0.0412Q+0.115.

(38) (7) The measured total gas content Q corresponding to different samples is substituted into the formula S=0.0412Q+0.115 to obtain the corrected self-sealing evaluation coefficient S of different samples.

(39) (8) Based on the corrected self-sealing evaluation coefficient S of different samples and the established self-sealing evaluation standard of organic-rich shale, each sample is evaluated, and the evaluation results are shown in Table 7.

(40) TABLE-US-00007 TABLE 7 Self-sealing evaluation results of organic-rich shale Corrected self-sealing Sample evaluation Self-sealing Well Stratum number coefficient S grade A1 L1 1 0.54 good L2 2 0.57 good L3 3 0.25 poor A2 L1 4 0.42 medium L2 5 0.61 excellent L3 6 0.45 good A3 L1 7 0.39 medium L2 8 0.55 good L3 9 0.32 medium A4 L1 10 0.43 medium L2 11 0.66 excellent L3 12 0.42 medium A5 L1 13 0.46 good L2 14 0.52 good L3 15 0.38 medium

(41) The above is only the illustrated embodiment of the disclosure, and it does not limit the disclosure in any form. Although the disclosure has been disclosed in the illustrated embodiment, it is not used to limit the disclosure. Any person skilled in the art, within the scope of the technical solution of the disclosure, when using the above disclosed technical content to make some changes or modification for equivalent changes in the equivalent embodiment, but not out of the content of the technical solution of the disclosure, according to the technical substance of the disclosure of the above embodiment of any simple modifications, equivalent changes and modifications, are still within the scope of the technical solution of the disclosure.