Publications

The presence of oil and gas fields in the North Madura Platform is attributed the existence of long-distance near lateral migration from two kitchen areas, the Central Deep and the Madura Basin. However, the complex hydrocarbon distributions on multiple reservoir levels within the known traps are not well understood. This paper presents a model of hydrocarbon charging history to the platform. The key to this model is the recognition of the mechanics of hydrocarbon migration and hydrocarbon fluid behaviours. The model was simulated using an invasion percolation algorithm for secondary migration which says that migration occurs in a state of capillary equilibrium in a flow regime dominated by buoyancy (driving) and capillary (restrictive) forces. The model was then calibrated to known reservoir accumulations on the platform. In the Bukit Tua and Jenggolo Field complex, the oil is mostly trapped at the lowest part of the North Madura Platform in Ngimbang Formation and CD Carbonate. As the charging of oil continued and the reservoir became saturated, the top seal was breached and the oil filled the overlying Kujung II clastics and carbonates which are sealed by intra-formational shales. Due to the gentle nature of the Kujung II structure, the trapped oil column could not generate enough buoyancy pressure to breach the seal’s capillary entry pressure, preventing the oil from migrating any further. Later generation of lighter hydrocarbons (gas) reached the platform in the Ngimbang Formation and CD carbonate that were saturated with oil, bypassed, continued up to Kujung II formation to be trapped and mixed with oil. Being lighter, the gas was able to breach the Kujung II gentle traps to migrate further up to Kujung I where it was permanently trapped and sealed by the thick Rancak Formation. Kujung I carbonate platform reservoirs are all filled by gas. Charging and entrapment modeling in the North Madura Platform helps to understand the hydrocarbon filling history in Bukit Tua field. Maturity modeling of the Central Deep kitchen area indicated effective expulsion and charging to Bukit Tua field. 3D high resolution, facies-based, charge modeling was further conducted to observe the hydrocarbon entrapment behaviours.