Diagenetic Effects on Reservoir Properties in a Carbonate Debris Deposit: Case Study in the Berai Limestone, “M” Field, Makassar Strait, Indonesia

Abstract

After the drilling of four wells that successfully found gas, an unexpected dry well (NW-1) was encountered on what was thought to be the same trend in the “M” field, Paternoster Platform, Southeast Kalimantan – Indonesia. The “M” field is developed in carbonate slope debris reservoirs with gas accumulations within the Oligocene - Early Miocene Berai limestone (primary objective). The dry NW-1 well was a surprise as a previous study indicated that this was a favourable location to drill and the wireline from the well indicated a similar carbonate host. This study has shown that the Berai limestone has a complex depositional and stratigraphic framework and that it has experienced a multistage diagenetic and tectonic evolution. In order to reduce the risk in any future exploration drilling, this integrated study was done, using data from all the existing wells in the “M” Field, including the NW-1 well. This study incorporated all cores and developed a new understanding of the controls on the reservoir development based on the integration of petrography, stable isotope, and wireline log data. The dry NW-1 well was cemented earlier in its burial due to pervasive marine cementation, as evidence by the integration of thin section and isotopic data. In contrast, another well (M-4), containing a siginificant gas accumulation, experienced a longer diagenetic history a phase of later deeper burial leaching that significantly enhanced the reservoir quality of the Berai limestone in this well. This study defines a previously unrecognized non-meteoric origin for porosity development in down-slope Miocene carbonates. This creates a “greenfields” opportunity for exploration in similar settings locally and elsewhere in Indonesia and the Southeast Asia.