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The K Gas Field located in the onshore Central Kalimantan province is a unique field due to its tight, very low permeability, very thick and over-pressured reservoir. The Upper Berai is a carbonate rock build-up deposited on basement or horst heights and is generally comprise interlayered pack-grainstones and mud-wackestones and leached framestones, characterized by secondary porosity development in form of intracrystalline, vuggy, moldic, and framework porosity. At the very top consist of coral, and deeper the number of corals decreases and is replaced by the dominance of red algae, echinoderms and small forams. Considered as complex and heterogeneous, the reservoir is generally tight with porosity around 2-16 % (avg. 4%), and permeability around 0.01-15 mD (avg. 0.05 mD). The thickness varies from 269 to 294 m with calculated net pay for Western and Eastern structure between 116 m and 160 m, respectively.

In the Lower Berai carbonate reservoir, which is Lower Oligocene, thin gas content was also found. However, the property showed that the quality was not very good, which is likely due to the facies being deposited in a sea area with low-medium energy, resulting in finer-grained carbonates. The early diagenesis process causes primary porosity and permeability to be filled with replacement minerals. Just like Upper Berai, Lower Berai has also never experienced subaerial exposure or diagenesis by fresh water, which causes the process of dissolving biota shells and replacement minerals not to run well.

Based on seismic analysis and well data, the depositional system of this field is classified as a semi-isolated carbonate platform (Subekti et al., 2015). This carbonate platform has a character like an isolated platform, but still in its carbonate it still has sediment influx from mainland. The following are the facies found within K Field depositional system: Lagoon, Platform Interior, Reef Complex, Forereef, Open Marine, and Patch Reef.