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

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 Zxij, wherein the standardized geological parameter for the j-th geological parameter is denoted as Pj, and a formula of the standardization processing is as follows:
• Z
• ⁢
• x
• i
• ⁢
• j
• =
• x
• ι
• ˙
• ⁢
• j
• -
• min
• ⁢
• {
• x
• 1
• ⁢
• j
• ,
• x
• 2
• ⁢
• j
• ,
• …
• ,
• x
• nj
• ,
• }
• max
• ⁢
• {
• x
• 1
• ⁢
• j
• ,
• x
• 2
• ⁢
• j
• ,
• …
• ,
• x
• nj
• ,
• }
• -
• min
• ⁢
• {
• x
• 1
• ⁢
• j
• ,
• x
• 2
• ⁢
• j
• ,
• …
• ,
• x
• nj
• ,
• }
• ,
• where xij is a value of an i-th sample of a j-th geological parameter before the standardization processing;
• Zxij is a value of the i-th sample of the j-th geological parameter after the standardization processing;
• min {x1j, x2j, . . . , xnj} is a minimum value of all sample data of the j-th geological parameter, max {x1j, x2j, . . . , xnj} 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 ωj′ of each of the five geological parameters to obtain five weight coefficients respectively corresponding to the five geological parameters, where ωj′=tj;
• S4, sorting the five weight coefficients in descending order to obtain an ordered sequence:
• t1>t2>t3>t4>t5, wherein a standardized geological parameter corresponding to the weight coefficient t1 is P1, a standardized geological parameter corresponding to the weight coefficient t2 is P2, a standardized geological parameter corresponding to the weight coefficient t3 is P3, a standardized geological parameter corresponding to the weight coefficient t4 is P4, and a standardized geological parameter corresponding to the weight coefficient t5 is P5;
• 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
• ×
• P
• 4
• 2
• +
• t
• 5
• ×
• P
• 5
• 3
• ;
• 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
• =
• ∑
• i
• =
• 1
• n
• ⁢
• (
• Q
• t
• ˙
• -
• Q
• _
• )
• ⁢
• (
• S
• i
• -
• S
• _
• )
• ∑
• i
• =
• 1
• n
• ⁢
• (
• Q
• i
• -
• Q
• _
• )
• 2
• ,
• b
• =
• S
• ¯
• -
• a
• ⁢
• Q
• _
• ,
• where Qi 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, Si 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.