Determination of the Formation Permeability and Skin Factor From a Variable Flow Rate Drawdown Test

Abstract

At present, the flow rate variation during a drawdown test is usually treated as a sequence of discrete constant rates and the principle of superposition is used. Below a more general method of analyzing data of variable flow rate drawdown (VFRD) tests is presented. The flow rate q(t) is considered as a continuous function of time (t). It is assumed that the function q(t) can be approximated by a polynomial of some degree. The pressure response for the VFRD test is obtained by the direct integration of the Duhamel integral. A Cartesian plot and a linear regression computer program are used to process test data and to provide an estimate of the values of skin factor and formation permeability. An example of calculations for a field test is presented.