Decline Curve Analysis for Double-Porosity Systems

Abstract

ABSTRACT A type curve matching method for analyzing constant pressure testing in a double-porosity system is presented. Both infinite systems and closed outer boundary systems are considered. Rate responses of constant pressure wells with and without wellbore skin are described. Five type curves are presented for the rate response of the constant pressure active well. The first four curves describe: (1) An infinite system without wellbore skin, (2) a closed outer boundary system without wellbore skin, (3) an infinite system with wellbore skin, and (4) a closed outer boundary system with wellbore skin. In the fifth type curve, the first four type curves are assembled into one. A log-log type curve matching method is presented, where the parameters λ, ω, reD, and S are estimated. The parameters λ and ω describe interporosity flow and relative fracture storativity respectively, and τeD and S are the dimensionless size of the system and the wellbore skin respectively. This paper considers only the estimation of these four parameters. The estimations of permeabilities and storativities have been described in the past, hence, are not described in this paper. It is observed that the presence of wellbore skin has an important effect on the rate response of the double-porosity system. It is essential for the success of the analysis, especially in the determination of λ and reD, to include wellbore skin. The presented analysis method is valid for transient interporosity flow with fracture skin greater than 0.33, with slab-shaped matrix. Three type curve matching examples are presented along with a discussion of the applicability and practicality of the analysis method.