Publications

The Walio Field, located in the southern Kepala Burung PSC, remains the largest oil producer in the region, with estimated original oil in place (OOIP) of 537 MMSTB (cumulative production: 218 MMSTB), primarily from the Kais Formation (OOIP: 471 MMSTB, Np: 211 MMSTB) and marginally from the Post Kais interval (OOIP: 66 MMSTB, Np: 7 MMSTB). As production from the Kais Formation declines due to water breakthrough, reservoir characterization of the underdeveloped Post Kais interval (Textularia-II and U-Marker) becomes critical to sustaining field productivity.

Integrated analysis of 55 feet of core data (3 wells), 47 core plugs (porosity-permeability), XRD/SEM, and thin sections reveals that the Post Kais interval comprises mudstone interbedded with argillaceous bioclastic limestone (wackestone to packstone), deposited in a low- to medium-energy inner-to-mid shelf environment. The lithology is dominated by 70–85% limestone, with 5–10% dolomite and 2–10% clay minerals (illite-smectite dominant). Despite moderate porosity (5–22%, mouldic type), permeability is low (0.01–72 mD) due to micrite cementation and argillaceous content, resulting in marginal production rates. Reservoir drive mechanisms include depletion drive with localized gas cap or water influx.

Given the subeconomic viability of dedicated Post Kais wells, strategies such as reperforation of depleted Kais wells, matrix acidizing, hydraulic fracturing, or horizontal drilling are proposed to enhance recovery. This study underscores the potential of the Post Kais interval as a secondary target to extend field life, contingent on improved reservoir connectivity.