Publications

Krisna Field is located in the western part of the offshore Southeast Sumatra (SES) Block, in the Sunda Basin. The field, which is managed by the Central Business Unit, SES Block, produces oil from carbonate reservoirs within the Baturaja Formation, with the main production coming from the upper interval (UBR). Production plots and water injection data show that there are problems associated with reservoir heterogenity and conectivity. It therefore became essential to undertake the task of reservoir charactertization in order to address these problems and gain an understanding and establish a rationale for forward direction to achieve maximum recovery efficiency. It is the objective of this study to identify lithofacies and facies associations and characterize the distributions of rock type, porosity and permeability. Thin section petrographic analysis of core samples from Krisna D-04 and Krisna E-02 wells show that there are five lithofacies: foraminifera shale, planktonic foraminifera packstone, skeletal wackestone, skeletal packstone, and benthic foraminifera packstone. The carbonate reservoir was previously interpreted as a reef complex. However, lithofacies and seismic attribute (mean amplitude) analysis indicate two facies associations are present, skeletal mound and slope to basin. Rock type (RT) identification using Pore Geometry Structure was used as an indicator of reservoir heterogeneity. This resulted in the identification of six RT’s, each with specific porosity and permeability trends, unrelated to lithofacies, but correlated to pore types and sizes. The six rock types are: RT1 associated with interparticle-moldic micropores, RT2 associated with interparticle mesopores, RT3 associated with interparticle-moldic mesopores, RT4 associated with interparticle-moldic macropores, RT5 associated with vuggy-moldic macropores, and RT6 associated with vuggy-channeling. Using a stochastic methodolgy it was possible to show that rock type distribution in the skeletal mound facies association controlled porosity and permeability distribution. The study determined that rock type, porosity, and permeability distribution are the main factors controlling heterogenity and conectivity in the UBR reservoir. The study results will be used as the main input to a dynamic simulation for water injection and further development planning in Krisna Field.