Influence Of Temperature On The Seepage Characteristics Of Shale

Shale permeability is one of the key parameters that affect shale gas extractionefficiency. The seepage channel is changed in correspondence with the change ofsubstrate thermal expansion volume resulting from the difference in ground temperatureduring shale gas extraction process. At the same time, the shale clay minerals andorganic matter in thermal expansion coefficient difference is very big. The temperaturechange, the difference of the volume expansion makes the shale internal structurechange, the seepage velocity of the gas will change, eventually lead to shalepermeability change. So a research into the rule of shale seepage under the effect of heatflow fluid-solid coupling is of great significance to an efficient extraction of shale gas.By combining the theoretical analysis with experiment, this paper firstly analyzedthe variation of internal friction of methane under different temperature, the strain ofshale skeleton, the shrink effect of matrix and their law of function to methane’sseepage velocity. Secondly, it analyzed the influence of the third thermal stress oninfluent and found the solution of displacement under the effect of the third thermalstress by using thermo elasticity to get the corresponding amendment permeability.Thirdly, it analyzed the research results by experiment. Here follows the main researchfindings:①Temperature increment can increase the decelerating effect of methane’s internalfriction which is harmful to the influent of shale gas; The compression of thermal stresson shale skeleton and matrix thermal expansion’s making the matrix crack smaller areboth unfavorable to the influent of shale gas; Temperature increment leads to anincrease in the desorption of the adsorbed layer and matrix shrinkage effect can slightlychange the influent gallery, both of which have little influence on the seepage of shalegas.②Shale seepage experiment showed that the higher the temperature, the smallerthe methane seepage velocity. That’s mean, the effect of temperature on methane andshale solid is greater than the adsorption desorption effect. The main factor oftemperature’s influence on permeability is the effect of thermal expansion and thermalstress on shale skeleton. The permeability of shale is decline with temperatureincrement.③Main composition of clay minerals and organic matter in shale thermal expansion when temperature rise, which changed the shale pore structure, produce the third type of thermal stress, thermal stress of the third kind, permeability reduction, in line with the effective stress principle, the calculation model is as follows.④Shale deformation is caused by crustal stress and thermal stress, thermal strain can change seepage channel and affect permeability; we got the confirmed solution of displacement of the third type of thermal strain by differential equation of heat coupling stress equilibrium, and worked out the correction factor of permeability. The modified permeability is in consistent with the permeability of experiment, the lower the permeability, the higher the correction accuracy of permeability.