Paradigm Shift to Unlock Opportunities in Mature Oil Field: Integrated Multilevel Contact Modeling for Sweet-Spot Mapping in Handil Main Zone

Abstract Handil is a mature oil field located in Mahakam Delta characterized by multi-layer fluvio-deltaic sandstone reservoirs. Producing since 1975 and facing decline throughout the years, aggressive infill drilling campaign has emerged as primary solution to address the issue. Field mature condition possesses challenges like complex fluid contact evolution and uncertain un-swept oil distribution, hence making it difficult to map the sweet-spot and locate new infill wells. Previous sweet-spot mapping method of single fluid contact has become less preferable due to reservoir complexity meanwhile resource-intensive reservoir simulation is inapplicable. This paper shares sweet-spot mapping methodology using new paradigm: multilevel contact model, providing valuable and practical insights for new infill well placement. Fluid contact evolutions were observed in medium aquifer supported Handil Main Zone reservoirs. Opposed to previous method of single fluid contact, the oil-water contact rise occurred with high variation across the field, even within single reservoir unit. Some recently drilled wells results showed water-bearing wells more likely occurred near producer wells, while oil-bearing wells likely occurred at certain distance from producer wells, despite being at structurally lower area within the same reservoir. This phenomenon indicated that producer wells only drained hydrocarbon to certain extent, called drainage radius. Multilevel contact modelling was introduced by integrating multilevel contact surface into the 3D static model. The contact surfaces were created in each reservoir unit by incorporating drainage radius of each producer wells as lateral limit and perforation depth of each producer wells as top vertical limit. Historical production data were utilized to generate drainage radius for each well. A detailed 3D static reservoir model was first constructed to visualize the reservoir distribution, consisting of over 300 reservoirs from over 50 layers in Handil Main Zone. Multilevel Contact surfaces of each reservoir unit were then integrated into the model in all layers, resulting in producible net-pay map and its volumetric figure as the representation of remaining oil undrained by existing producers. Rigorous QCs and blind test were carried out to ensure model reliability, showing good correlation between predicted and realized values of reservoir properties. Following blind test satisfying result, stacking producible net-pay map of every layer in Handil Main Zone were utilized as the basis of future well placements. Despite Handil 50 years of production, the application of this approach had led to identification of a substantial number of potential recovery opportunities, including 19 wells of newly proposed Plan of Development. This paper presents a novel and robust approach in sweet-spot mapping for mature oil fields where reservoir simulation is inapplicable. The practicality of this method suits the most for fields with fast growing data, enabling immediate update from new wells into the workflow.