A TRANSIENT PRESSURE STUDY ON THE INFLUENCE OF BLOCK SIZE FOR DRAWDOWN TESTS IN NATURALLY FRACTURED RESERVOIRS

Abstract

Block size has been concluded to be one of the main parameters of a naturally fractured reservoir. In one-phase flow, it controls the transition from the early fracture dominated stages of production to asymptotic composite (fracture plus matrix) behavior. Classical well test analysis in terms of a semilogarithmic graph of pressure vs time, has shown that drawdown pressures are not sensitive enough to the variation of block size method. This work presents the results of a study aimed at characterizing the naturally fractured reservoir by means of the transition period behavior of the pressure derivative function . Based on the numerical Laplace inversion results, it was observed that the pressure derivative function for the different block sizes can be correlated through a horizontal displacement of the axis, when multiplied by the ratio , where and are two block sizes satisfying > . A discussion of previous results by Braester analyzed by means of the radial flow semilog graph of pressure vs time is also included.