Evaluation of in situ hydraulic properties of formations at great depth : K. Hayashi, T. Ito & H. Abe, Geothermal Science & Technology, 4(3), 1995, pp 145–157

Abstract

The pressure decay process during the so-called pressure pulse test is analysed for evaluating in situ hydraulic properties of a formation at great depth. The present analysis takes the following factors into account, i.e., the compliance of the tubular connecting the straddle packer to the pump on the surface and anisotropy of a formation. Both of these factors have been ignored in the conventional approach, resulting in less reliable results of evaluation. Furthermore, an automatic and objective method is developed for the evaluation, instead of the manual type-curve-fitting process which has been used in the conventional method. The new method utilises a two-dimensional optimisation, where the objective function is defined as a weighted residual sum of squares of the deviation between an experimentally observed pressure decay and a reference curve of the pressure decay, i.e., a type curve, which is theoretically prepared in advance for a given set of hydraulic properties. The method was applied to pressure decay data of pressure pulse tests performed in a field test. The application result was satisfactory. Hydraulic properties would vary depending on fluid pressure in a reservoir or a formation. The present paper also discusses a method for estimating the dependence of hydraulic properties on pressure