Effective Hydraulic Fracture Length and the Determination of Productivity Index

Abstract

ABSTRACT This paper presents a new technique for analyzing the performance of hydraulically fractured vertical wells in bounded reservoirs. The main objective is to present a new set of practical equations, based on the recently introduced concepts in well testing, for evaluating the effective length of the hydraulic fracture contributing to unrestricted production. It is determined that the performance of a hydraulically fractured vertical well with mechanical skin and fracture half length Xf1 can be substituted by the performance of a fractured half-length Xf2 with no skin. New equations presented in this paper can be used to determine pseudo skin factor, effective fracture half-length, mechanical skin factor, shape factor, and productivity index of fractured vertical wells. The new equations and guidelines given in this paper can be used to determine the magnitude of formation damage around hydraulically fractured vertical wells and to evaluate the success of the stimulation treatment. An example based on simulated well test data is presented to illustrate the application of the new technique. The problems associated with the use of the finite-conductivity fracture model are discussed and it is recommended that the pressure transient data obtained on fractured vertical wells be analyzed with effective hydraulic fracture length concept, in preference to the finite-conductivity fracture model.