Experimental and modeling research on heated rock fracture seepage

In the underground storage of oil and gas and the geological treatment of high radioactive waste,the tempera-ture of rocks and the seepage pressure of fractures significantly influence the seepage characteristics of rock fractures. When the seepage pressure gradient increases gradually,the seepage flow increases accordingly and the Darcy flow be-comes nonlinear seepage flow. In order to study the basic seepage law of high-temperature induced rock fractures,a self-developed test apparatus for coupling temperature-stress-seepage flow was used to conduct seepage tests under dif-ferent permeability pressures on rock samples after high-temperature heating. The test system consists of three sets of independent loading parts:confining pressure unit,axial pressure unit and water pressure unit. Under the 1 MPa confi-ning pressure,the evolution law of seepage flow rate and pressure gradient was studied. The three-dimensional CT scanning was adopted to obtain the aperture distribution of rock fractures after the seepage test,and the statistical anal-ysis of fracture aperture and the statistical distribution of rock layer-by-layer porosity were obtained. The network structure of rock internal cracks could be clearly observed,which provides a basis for studying rock multi-fracture seepage. The relationship between seepage flow rate and seepage pressure gradient was described by the Forchheimer equation. The seepage process was divided into Darcy flow and nonlinear seepage flow. A nonlinear factor E was introduced to solve the threshold value of the critical Darcy flow and critical Reynolds number. As for actual rock engineering,E = 0． 1 was defined as the boundary point between linear flow and nonlinear flow. In order to study the relative loss rate of momentum under different seepage pressures,the Euler number was used to calculate the momentum loss rate of rock fissure seepage. Results show that with the increase of seepage pressure,the relative loss rate of momentum tends to de-crease first and then increase. Under a certain seepage pressure,the Euler number reaches a minimum value,indica-ting that the rate of fluid flow change under its pressure is the smallest. The results can provide a guidance for studying the seepage process of rock fracture induced by high-temperature.