Impact of the Petroleum System Approach to Exploration and Appraisal Efficiency in the Mahakam Delta

Abstract Oil production in the Mahakam Delta area started a century ago. In the late 60's, exploration was resumed in the swampy delta and offshore area and led to the discovery of several giant oil and gas fields. At that time, drilling was focused on structural plays. By the mid 80's, when production started to decline, a global requestioning was undertaken through a regional synthesis, based on the reinterpretation of existing seismic and well data. One of the tools of choice used during this study was sequence stratigraphy. A new petroleum system model was defined, and allowed to revitalize exploration and identify targets linked to stratigraphic concepts within or near the identified kitchens. Some of these targets were successfully drilled, and one of them, Peciko, was quickly recognized as a new giant gas and condensate field. Understanding the trapping model, and particularly its hydrodynamic component was a key factor for fast and successful delineation. Sedimentological studies (including field observations on similar sand bars of the modern delta) combined with systematic pressure measurements, greatly contributed to the field model. The thin sand reservoirs were found to be more continuous than expected; and, thus were organized into more manageable thicker flow-units. The Peciko model was in turn applied to the previously discovered Tunu field, leading to spectacular new reserve additions. The creaming curves at both basin and field scales clearly reflect the level of maturity for oil and gas in the Mahakam. Improved exploration and appraisal efficiency has resulted in rapid increases in production.