原位气体渗透率测量试验公式推导及分析

Deduction of in-situ gas permeability test equation

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。

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 boundaryrout 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 isrout. 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.