Decline Curve Analysis For Composite Reservoirs
Authors: Issaka M.B. , Ambastha A.K. 
Published: March 2010

Abstract
Analysis of production decline curves presents a useful tool in forecasting the future production from a well or reservoir. A knowledge of the future production is an important factor in the economic analysis of exploration and production expenditures. Decline curve analysis can be used to estimate the production performance of a stimulated well due to acidizing. A comparison of the production decline before and after acid treatment will enable a determination of the technical and economic success of the treatment.
Decline curve analysis for homogeneous reservoirs has been discussed extensively in the literature. However, the conventional homogeneous decline type curves are not appropriate for composite reservoirs. While production decline curves for radial, composite reservoirs have been presented, the same is not the case for composite reservoirs in elliptical, linear and spherical flow geometries.
This study presents a comparison of the production performances of two-region, composite reservoirs in radial, elliptical, linear and spherical flow geometries. Transient rate and cumulative production responses for both infinite and closed, finite reservoirs for the various flow geometries are discussed. Normalizing factors are presented to enable comparison of production rate and cumulative production responses for the various composite reservoirs. A detailed investigation of the effects of mobility and storativity ratios, and also, the reservoir size on the production rate and cumulative production responses from radial and linear, composite reservoirs are presented.
Results from this study show that the mobility-storativity product, MF, is not a correlating parameter for transient rate and cumulative production responses from finite, linear, composite reservoirs, unlike the case for infinitely large, linear, composite reservoirs. Some type curves for decline curve analysis of radial and linear composite reservoirs are presented.

Introduction
Analysis of production decline curves presents a useful tool in forecasting the future production from a well or reservoir. A knowledge of the future production is an important factor in the economic analysis of exploration and production expenditures. Decline curve analysis can be used to estimate the production performance of a stimulated well due to acidizing. A comparison of the production decline curves before and after acid treatment will enable a determination of the technical and economic success of the treatment.
For homogeneous reservoirs, Fetkovich(1) presented an extensive discussion of decline curve analysis using type curves. He showed, among other things, how to use production decline type curves to estimate the formation flow capacity (kh) and the porosity- compressibility (Φct). For composite reservoirs, however, Olarewaju and Lee(2) have argued that the conventional homogeneous decline type curves are not appropriate. Olarewaju and Lee(2–4) have presented production decline curves for the analysis of transient rate data from radial, composite reservoirs with a damaged or stimulated well. Turki et al.(5) presented rate decline and rate decline derivative type curves for constant-pressure production in a two-region, radial, composite reservoir. They conducted a parametric study of the effects of mobility ratio, storativity ratio and distance to the discontinuity on the rate decline and rate decline derivative for both infinite and finite composite reservoirs.