Test method for gas permeability in time-dependent deformation of low-permeability rocks under gas-thermal-mechanical coupling

Abstract

The invention belongs to the field of deep high-temperature and high-pressure oil and gas exploitation rock mechanical testing, and particularly relates to a gas permeation testing method in low-permeability rock time-dependent deformation under the action of thermal-gas-mecha-nical coupling. The method includes the following steps that a rock core test piece is installed into a clamp holder, and the leakproofness of gas permeation testing is checked; the confining pressure, the temperature, the air pressure and the axial pressure are sequentially applied to a triaxial cell to predetermined values; the pressure of a high air pressure tank is increased instantaneously, the gas permeation parameters in the time state are calculated, and accordingly the rock gas permeation rate existing when the numerical value of a low air pressure tank is equal to the numerical value of the high air pressure tank is calculated; the gas pressure is adjusted to an initial value, the gas permeation rates at other moments are determined, and the gas permeation rates are given to a computer for drawing output. By the adoption of the method, the gas permeability of low-permeability rock under different time-dependent scales can be determined, the relation among the permeability parameter, the temperature parameter, the time parameter, the stress parameter and the strain parameter can be drawn automatically through a computer program, data result errors caused by not taking multi-field coupling and time-dependent factors into account in an existing device are avoided, and measurement accuracy is improved.

Description

technical field [0001] The invention belongs to the field of rock mechanics testing in deep oil and gas exploitation, and in particular relates to a gas permeation test method in the aging deformation process of low-permeability rocks under the action of gas-thermal-mechanical coupling, which is suitable for the development of oil-gas fields under the action of deep high temperature and high pressure and the action of gas-thermal-mechanical coupling Research and determination of gas permeability coefficient during long-term deformation of low-permeability rock materials in nuclear waste underground storage projects. Background technique [0002] Temperature, stress, and gas permeability are the main factors affecting the geological environment of low-permeability oil and gas reservoirs. The three are interrelated, affect each other, and restrict each other, forming a rock-gas thermal multi-field coupling problem. And the rock has obvious time-dependent deformation characteri...

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Problems solved by technology

[0004] Pan Weiyi and Lun Zengmin et al. provided a device and method for rock gas permeability measurement under high pressure in the patent "A device and method for gas permeability measurement of rock under high pressure" (application number 201010520289.1); but this device only considers If the effect of confining pressure is not considered, it is impossible to simulate the state of unequal three-dimensional stress in the actual formation and study the influence of different axial stresses and different aging effects on rock gas permeability

Rock permeability is closely related to load and time. The patent applicant and Xu Weiya et al. wrote "Experimental Research on Rheological Properties and Seepage Evolution Mechanism of Clastic Rocks Under the Coupling Action of Seepage-Stress" (Journal of Rock Mechanics and Engineering, 33(8): 1613-1625, 2014.), it is believed that loading and aging effects will cause rock permeability to change by 2-5 orders of magnitude, and it has strong directionality; in addition, this device calculates the rock gas permeability coefficient based on Darcy’s law; but Due to the high density of deep rocks, low permeability, fine channels for the flow of oil, gas and water, and high seepage resistance, the interaction force at the liquid-solid interface is significant, and there is an obvious start-up pressure for seepage, resulting in classic Darcy linear seepage. The relationship is not applicable, so this device is not suitable for gas permeability testing of deep low-permeability rocks;

[0005] Chen Yifeng and Hu Shaohua proposed a low-permeability rock transient pressure pulse permeability measurement device and measurement method in the patent "Low-permeability Rock Transient Pressure Pulse Permeability Measurement Device and Measurement Method" (application number 201310207056.X). The pressure pulse method tests the gas permeability of low-permeability rocks, but does not consider the state of three-dimensional stress in the actual formation and the influence of temperature and aging effects on the gas permeability characteristics of rocks. The gas permeability test is also not applicable during the rock aging deformation process under stress state;

[0006] Xu Weiya and Wang Wei et al. proposed in the patent "A Device and Method for Measuring Rock Gas Permeability" (Application No. 201210590766.0) to calculate the rock gas permeability by recording the axial pressure difference between the two ends of the rock sample material at different times. The device and method, the calculation method of this device is similar to the pressure pulse method, but it still does not consider the state of the actual formation three-dimensional stress and the influence of temperature and aging effect on the permeability characteristics of rock gas; As the depth increases, the temperature increases, the thermal expansion of rock skeleton particles, and the deterioration of mechanical properties. Combined with the long-term effects of gas penetration and aging, the structure will be significantly damaged, and it is easy to expand or even disintegrate, resulting in the collapse of the pore structure of tight rock reservoirs and The strength is greatly reduced, so the influence of temperature and aging is an important factor to be considered in the study of rock gas permeability

[0007] On the basis of referring to relevant domestic materials, it is believed that the original rock gas permeation testing technology has certain limitations, such as the inability to consider different stress paths, the temperature cannot be controlled, the sealing of the test device is not good, the effect of aging deformation is not considered, and data processing is not considered. Defects such as complete manualization; the inventor combined the multi-field coupling rock test method with the gas permeability measurement method and the data processing visualization method to invent a gas permeability test method in the aging deformation process of low-permeability rock under the coupling of gas and heat. The method has high accuracy, can accurately set environmental parameters such as stress, temperature and air seepage pressure, realizes data transmission and automatic processing, and outputs data and curves at the same time, improves the efficiency of data collection and processing, and ensures accuracy. The technology is the first at home and abroad, with good practicability and forward-looking

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