Application of Decline Analysis in Fractured Reservoirs, Field Case Studies

Abstract

Decline curve analysis has some advantages over transient well test analysis in which it is not required to shut-in the well and also wellbore storage effects do not exist. Few studies have been done on decline curve analysis of naturally fractured reservoirs but there are even some limitations with available models. On the other hand well test could be expensive and in some operational conditions shutting the well to obtain reservoir parameters is almost impossible. Therefore, investigating the applicability of homogenous reservoir decline models for production data analysis of naturally fractured reservoirs is necessary. In this paper the most important decline models have been used to evaluate reservoir parameters in three Iranian naturally fractured reservoirs and the results have been compared to transient well test analysis. A useful and applicable procedure is also introduced to correct the initial production data when they do not have necessary conditions. The results show that Agarwal-Gardner and Blasingame type curves predict acceptable values for permeability compared to transient well test analysis while Fetkovich type curve cannot predict accurate values. Determined skin values in all wells of the three studied reservoirs are negative. Negative values can be considered to be affected by existing fracture networks in the vicinity of producing wells and also periodic well stimulations. The results also show that Neglecting produced condensates of gas condensate reservoirs with Liquid-Gas Ratio (LGR) less than 100 bbl/MMscf cannot significantly affect decline curve analysis results.