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Subsurface Controls on Hydrocarbon Flow During Production and Their Impact on Recovery: Lessons Learned From the Central Luconia Gas Fields, Sarawak, Malaysia

Abstract

Carbonate fields in Central Luconia have been delivering gas for about 30 years and petroleum engineers have been collecting large amounts of static & dynamic data by exploring, appraising and producing these Miocene platforms hosting the gas. The knowledge acquired is presently used to optimize existing field recovery, develop new fields without production data and reduce geohazards for drilling operations. It also provides an outstanding data set that can be extrapolated to understand the role of reservoir heterogeneities and hydrocarbon properties on production behavior and recovery in similar fields with less data outside Luconia. Based on this rich data set, reservoir heterogeneities that have a large impact on production and recovery are faults and fractures, karst, argillaceous flooding layers, and carbonate depositional facies and their diagenetic overprint. These heterogeneities, and their relative position with respect to the GWC, control water ingress during production and hence the recovery mechanism that prevails (depletion versus natural water drive). The impact on recovery and sweep patterns that this has is important for locating bypassed hydrocarbons and selecting enhanced recovery methods. Bounding faults, long-lived reef margins, and karsts are found to be vertical conduits for aquifer inflow. By comparison, argillaceous flooding layers can act as effective baffles, holding back water rise during production or even form horizontal pressure compartments which can be hazardous for infill wells. The recovery and production behavior is further strongly dependent on the hydrocarbon-column height and the shape of the build-up, which can be captured by the ratio of column height to reservoir area: a given hydrocarbon volume trapped in a narrow pinnacle with a long column will yield higher recoveries than a short column distributed over a platform with large areal extent. These two reservoir types (long-column pinnacle vs short-column platform) also call for different development strategies (vertical vs horizontal wells). Also of importance is the strength & size of connected aquifers. Field examples of these behaviors based on production data, 3D, & 4D seismic surveys will be shown and conclusions drawn for fields in similar settings. The results can be utilized to predict the behavior of green fields with similar properties in order to decide on development strategies, optimize well count, type & placement, as well as completion designs.