| CPC E21B 47/005 (2020.05) | 1 Claim |
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1. A quantitative evaluation method for integrity and damage evolution of a cement sheath in an oil-gas well, comprising:
preparing experimental samples in order to perform quantitative evaluation of the integrity and the damage evolution of the cement sheath, comprising:
utilizing a wellbore configuration and a cement slurry system to simulate actual temperature and pressure to prepare casing-cement sheath-formation combinations;
defining an outer wall of a casing in contact with the cement sheath as a target surface, and defining an inner wall of the cement sheath in contact with the casing as a contact surface;
dividing the prepared casing-cement sheath-formation combinations into a blank group and a conditional control group, the blank group being used for quantitatively evaluating the integrity of the cement sheath without an alternating load and the conditional control group being used for quantitatively evaluating of a regularity of the damage evolution of the cement sheath with the alternating load;
separating the cement sheath and the casing of the blank group, and using the cement sheath and the casing of the blank group to prepare a mechanical property test sample, a three-dimensional contour scanning sample of the target surface and the contact surface, a scanning electron microscope (SEM) scanning sample, and a mercury intrusion test sample; and
separating the cement sheath and the casing of the conditional control group, and using the cement sheath and the casing of the conditional control group to prepare a mechanical property test sample, a three-dimensional contour scanning sample of the target surface and the contact surface, a SEM scanning sample, and a mercury intrusion test sample;
testing macroscopic mechanical properties of the cement sheath with the alternating load, and testing macroscopic mechanical properties of the cement sheath without the alternating load, comprising:
performing interface mechanical property tests to obtain a radial cementing strength SBR of a casing-cement sheath interface of the blank group;
performing mechanical property tests to obtain a tensile strength QBL and a compressive strength QBC of the cement sheath of the blank group;
performing mechanical property tests to obtain obtaining a tensile strength QEL and a compressive strength QEC of the cement sheath of the conditional control group; and
performing interface mechanical property tests to obtain a radial cementing strength SER of a casing-cement sheath interface of the conditional control group;
measuring and evaluating fractal dimensions of casing-cement sheath interface morphology with the alternating load, and measuring and evaluating fractal dimensions of the casing-cement sheath interface morphology without the alternating load, comprising:
utilizing an optical diffraction instrument to perform three-dimensional scans on the three-dimensional contour scanning sample of the target surface and the contact surface of the blank group and perform three-dimensional scans on the three-dimensional contour scanning sample of the target surface and the contact surface of the conditional control group, obtaining three-dimensional contour images of the target surfaces and the contact surfaces, and obtaining heights H of measurement points under different measurement sizes τTF and τCF, where τTF represents a measurement size of the target surface and τCF represents a measurement size of the contact surface;
utilizing a structural-function-based fractal model LgS(τTF)=lgCTF+(4-2DTFθ)LgτTF to draw the measurement size τTF of the target surface and a corresponding structural measurement function S(τTF) on a double logarithmic coordinate system, S(τTF) represents the corresponding structural measurement function of the target surface, S(τTF)=[H(Z+τTF, θ)−H(Z, θ)]2, where Z represents a coordinate of measurement point data on the target surface along an axial direction of the casing, θ represents an angel of an angel coordinate of the measurement point data on the target surface along a circumferential direction of the casing, τTF represents the measurement size of the target surface, H(Z+τTF, θ) represents a height of a measurement point (Z+τTF, θ) in the three-dimensional contour image of the target surface; H(Z, θ) represents a height of a measurement point (Z, θ) in the three-dimensional contour image of the target surface; CTF represents a size coefficient of the target surface; and DTF represents a fractal dimension of the target surface with the angle θ;
utilizing a structural-function-based fractal model LgS(τCF)=lgCCF+(4-2DCFα)LgτCF to draw the measurement size τCF of the contact surface and a corresponding structural measurement function S(τCF) on the double logarithmic coordinate system, S(τCF) represents the corresponding structural measurement function of the contact surface, S(τCF)=[H(Y+τCF, α)−H(Z, α)]2, where Y represents a coordinate of measurement point data on the contact surface along an axial direction of the cement sheath, α represents an angel of an angel coordinate of the measurement point data on the contact surface along a circumferential direction of the cement sheath, τCF represents the measurement size of the contact surface, H(Z+τCF, α) represents a height of a measurement point (Y+τCF, α) in the three-dimensional contour image of the contact surface; H(Y, α) represents a height of a measurement point (Y, α) in the three-dimensional contour image of the contact surface; CCF represents a size coefficient of the contact surface; DCFα represents a fractal dimension of the contact surface with the angel α;
calculating a fractal dimension of each of the target surfaces of the blank group and the conditional control group along directions of 0°, 90°, 180°, and 270° through a curve slope of the fractal model LgS(τTF)=lgCTF+(4-2DTFθ)LgτTF, taking an average value of DTF0, DTF90, DTF180, and DTF270 as the fractal dimension of the target surface; defining DBTF as the fractal dimension of the target surface of the blank group, and defining DETF as the fractal dimension of the target surface of the conditional control group; and
calculating a fractal dimension of each of the contact surfaces of the blank group and the conditional control group along directions of 0°, 90°, 180°, and 270° through a curve slope of the fractal model LgS(τCF)=lgCCF+(4-2DCFα)LgτCF, taking an average value of DCF0, DCF90, DCF180, and DCF270 as the fractal dimension of the contact surface, defining DBCF as the fractal dimension of the contact surface of the blank group, and defining DECF as the fractal dimension of the contact surface of the conditional control group;
measuring and evaluating a fractal dimension of cement sheath pore morphology with the alternating load, and measuring and evaluating a fractal dimension of the cement sheath pore morphology without the alternating load, comprising:
utilizing a mercury intrusion method to perform mercury intrusion tests on the mercury intrusion test sample of the blank group and perform mercury intrusion tests on the mercury intrusion test sample of the conditional control group, obtaining true porosities φ of the blank group and the conditional control group, obtaining total volumes VPi of mercury entering cement sheath pores under different injection pressures Pi of the blank group and the conditional control group, and obtaining pore diameters 2Ri under the different injection pressures Pi of the blank group and the conditional control group;
utilizing a pore volume fractal model Lg(|dVPi/dRi|)=(2−DP)LgRi+CP to draw an absolute value of an incremental ratio |dVPi/dRi| between one of the total volumes VPi and a pore radius on the double logarithmic coordinate system, where Ri represents the pore radius of the mercury intrusion test samples of the blank group and the conditional control group under a corresponding one of the different injection pressures Pi; DP represents the fractal dimension of the cement sheath pore morphology in the mercury intrusion test sample; CP represents a fractal model constant of the cement sheath pores of the mercury intrusion test sample; and
calculating the fractal dimensions of the cement sheath pore morphology of the blank group and the conditional control group through a curve slope of Lg(|dVPi/dRi|)=(2−DP)LgRi+CP, defining DBP as the fractal dimension of the cement sheath pore morphology of the blank group and defining DEP as the fractal dimension of the cement sheath pore morphology of the conditional control group;
measuring and evaluating a fractal dimension of cement sheath particle morphology with the alternating load, and measuring and evaluating a fractal dimension of the cement sheath particle morphology without the alternating load, comprising:
utilizing a scanning electron microscope to perform surface scanning on the SEM scanning samples of the blank group and the conditional control group prepared in the step 1, thereby obtaining SEM images of the cement sheaths of the blank group and control group at different magnifications;
utilizing a program based on Python+OpenCV to binarize the SEM images, thereby obtaining binary images at different thresholds, white areas in the binary images representing microscopic particles, and black areas in the binary images representing microscopic pores;
based on the true porosities φ obtained by using the mercury intrusion method, taking the true porosities φ as a control factor and using a threshold segmentation algorithm based on an edge strength to adaptively adjust thresholds of the binary images, and selecting target binary images which have same true porosities with the SEM scanning samples of the blank group and the conditional control group;
utilizing a Matlab program to calculate areas and perimeters of white areas in the target binary images;
utilizing an area-perimeter fractal model Lg(AGi)=DG*Lg(PGi)+CG to draw the areas and perimeters of the white areas in the target binary images on the double logarithmic coordinate system, where PGi represents an equivalent perimeter of a white geometric figure in the target binary images, AGi represents an equivalent area of the white geometric figure with the equivalent perimeter PGi in the target binary images, DG represents the fractal dimension of the cement sheath particle morphology, and CG represents a fractal model constant of cement sheath particles; and
calculating the fractal dimension of the cement sheath particle morphology of each of the blank group and the conditional control group through a curve slope of Lg(AGi)=DG*Lg(PGi)+CG, defining DBG as the fractal dimension of the cement sheath particle morphology of the blank group and defining DEG as the fractal dimension of the cement sheath particle morphology of the conditional control group;
measuring and evaluating a fractal dimension of cement sheath crack morphology after actions of the alternating load, comprising:
utilizing the scanning electron microscopy to perform surface scanning on the SEM scanning sample of the conditional control group, thereby obtaining SEM images of the cement sheath of the conditional control group at different magnifications;
obtaining target binary images of cement sheath cracks;
utilizing a Matlab program to calculate a total number N(δFi) of square boxes with a side length δFi covering the target binary images of the cement sheath cracks;
utilizing a box model LgN(δFi)=DEF*LgδFi+CF to draw the side length δFi and the total number N(δFi) of the square boxes on the double logarithmic coordinate system, where DEF represents the fractal dimension of the cement sheath crack morphology; CEF represents a fractal model constant of the cement sheath crack morphology; and
calculating the fractal dimension DEF of cement sheath crack morphology of the conditional control group through a curve slope of LgN(δFi)=DEF*LgδFi+CEF;
building functional relationships FB1(SBR, DBTF) and FB2(SBR, DBCF) between the radial cementing strength of the casing-cement sheath interface of the blank group and the fractal dimensions of the casing-cement sheath interface morphology of the blank group;
building functional relationships FB3(QBL, DBP) and FB4(QBC, DBP) between the macroscopic mechanical properties of the cement sheath of the blank group and the fractal dimension of the cement sheath pore morphology of the blank group;
building functional relationships FB5(QBL, DBG) and FB6(QBC, DBG) between the macroscopic mechanical properties of the cement sheath of the blank group and the fractal dimension of the cement sheath particle morphology of the blank group;
building functional relationships FE1(SER, DETF) and FE2(SER, DECF) between the radial cementing strength of the casing-cement sheath interface of the conditional control group and the fractal dimensions of the casing-cement sheath interface morphology of the conditional control group;
building functional relationships FE3(QEL, DEP) and FE4(QEC, DEP) between the macroscopic mechanical properties of the cement sheath of the conditional control group and the fractal dimension of the cement sheath pore morphology of the conditional control group;
building functional relationships FE5(QEL, DEG) and FE6(QEC, DEG) between the macroscopic mechanical properties of the cement sheath of the conditional control group and the fractal dimension of the cement sheath particle morphology of the conditional control group;
building functional relationships FE7(QEL, DEF) and FE8(QEC, DEF) between the macroscopic mechanical properties of the cement sheath of the conditional control group and the fractal dimension of the cement sheath crack morphology;
utilizing the fractal dimensions DBTF, DBCF, DBP, DBG and the functional relationships FB1(SBR, DBTF), FB2(SBR, DBCF), FB3(QBL, DBP), FB4(QBC, DBP), FB5(QBL, DBG) and FB6(QBC, DBG) to quantitatively evaluate the integrity of the cement sheath of the blank group; and
utilizing the fractal dimensions DETF, DECF, DEP, DEG, DEF and functional relationships FE1(SER, DETF), FE2(SER, DECF) FE3(QEL, DEP), FE4(QEC, DEP), FE5(QEL, DEG), FE6(QEC, DEG), FE7(QEL, DEF) and FE8(QEC, DEF) to quantitatively evaluate the regularity of the damage evolution of the cement sheath of the conditional control group.
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