原位气体渗透率测量试验公式推导及分析

原位气体渗透率测量试验能够较真实地给出孔隙介质原位渗透率,克服了实验室试验对试样孔隙结构强度要求高、试样尺寸代表性小的不足。根据径向一维稳态气体渗流方程推导出原位试验公式,并用二维轴对称模型分析了试验区域的压力场分布,进而给出公式中径向外边界rout取试验段长度与单根胶塞长度1/2和,以及有效测量范围为半径rout球形区域的结论。同时推导出试验符合达西定律的判断方法:从小到大至少进行3次不同流量的试验,在以流量为横轴,压力平方差为纵轴的坐标系中,试验数据点能够近似拟合成一条过原点的直线。

Deduction of in-situ gas permeability test equation

The gas permeability of porous medium can be estimated by in-situ tests, which can avoid the defects of laboratory tests, that is, the pore structure of samples must be steady, and the sample size is small. The equation used in-situ tests is derived from 1-dimensional radial gas seepage model, and then the pressure field is given based on analysis of 2-dimensional axially symmetric model. The radial outer boundary r_out in the in-situ test equation is the sum of test length and half packer length, and the effective region is the sphere of which the radius is r_out. The judgment of whether or not the tests obey the Darcy's law is deduced: the tests are conducted under at least three different fluxes. Taking the flux as abscissa and the difference of pressure square as ordinate, the test points can be curve-fitted as a straight line which crosses origin.