Cost-Effective Produced Residual Oil in Mature Reservoirs: A High-Definition Reservoir Mapping and Maximizing Reservoir Contact Technology Approach

Abstract This study addresses the challenge of improving residual oil recovery in a mature reservoir with a recovery factor of 75% in the South China Sea. Traditional infill well methods were deemed cost-ineffective due to low production expectations, leading to the adoption of an integrated approach combining high-definition reservoir mapping with a Deep Azimuthal Resistivity tool and Maximized Reservoir Contact (MRC) technology. The strategy involved sidetracking an existing well near the reservoir top to reduce construction costs. The separation from the original well was achieved by adjusting the hole azimuth, and the horizontal section was extended to target remaining oil-rich zones. Deep azimuthal resistivity mapping provided a detailed visualization of reservoir structures up to 9 meters from the wellbore, enabling precise well placement and safe monitoring of the oil-water contact (OWC). Early detection of boundary changes allowed for trajectory adjustments, reducing well tortuosity while maintaining optimal positioning within the reservoir. Customized completion intervals were designed based on reservoir properties and thickness to delay water breakthrough, extend reservoir lifespan, and enhance sweep efficiency. The sidetracked well was successfully drilled 4.5 meters above the reservoir, achieving the maximum allowable dogleg severity and intersecting the target zone after 29 meters, with a 5-meter separation from the original wellbore. Using deep azimuthal resistivity inversion, the well trajectory was controlled within 0.5 meters of the formation top, maintaining Geo-stop until the oil column thinned to 3 meters. The horizontal section reached 428 meters, double the field average for infill wells. Reservoir mapping guided the completion strategy, isolating the first 100 meters from bottom water intrusion. This approach doubled daily production rates and demonstrated the operational and economic feasibility of enhanced residual oil recovery in mature reservoirs. This integrated solution offers a cost-effective alternative for residual oil recovery in mature reservoirs, achieving production rates comparable to traditional infill wells while reducing total investment by 50%. The success of this approach highlights its potential for broader application in similar fields.