低渗致密砂岩气体滑脱流动机理研究

以苏里格气田盒8段低渗致密砂岩为研究对象,开展了常规条件下(出口端为大气压)和回压条件下的气体滑脱流动实验。结果表明:无回压条件下,相对高渗岩样的气测渗透率与平均压力倒数关系符合Klinkenberg模型,对于相对低渗且孔隙半径更小的岩样,则需要采用二次曲线模型描述;当施加回压时,气体滑脱随回压的增大而减弱,达到临界回压时,气测渗透率趋于稳定,但该临界值随岩样渗透率的减小而增大。分析认为,Knudsen数(Kn数)能综合反映渗透率(平均孔隙半径)和气体压力(回压)对气体滑脱程度的影响。高压压汞表明,研究区块渗透率越低的岩样,具有更小的孔隙半径,从而具有更大的Kn数,产生更强的气体滑脱;增大回压有助于减小分子平均自由程,从而减小Kn数,弱化甚至消除气体滑脱效应。

Laboratory investigation of gas slippage mechanism in low-tight sandstones

Taking the He 8 low-tight sandstones of Sulige gas field as research subjects,gas slippage flow experiments with/without back pressure were conducted.The results show that on no back pressure conditions,samples with high permeability comply with the Klinkenberg model,while samples with low permeability and small pore radius fit well with the quadratic model.When the back pressure is exerted,the gas slippage effect becomes weaker with the growth of back pressure,and the gas permeability keeps stable if the critical back pressure is approached.Knudsen number (Kn) can reflect the influences of permeability(pore radius) and gas pressure(back pressure) on slippage.The high pressure mercury injection results indicate that samples with lower permeability have smaller pore radius,bigger Kn and stronger gas slippage effect,resulting in great gas slippage.Increasing the back pressure can reduce the molecular average free path,and then reduce the Kn so as to weaken the gas slippage.