Enhancing Oil Recovery in a Brown Oilfield of Offshore South China

Located in offshore South China, XJ oil field entered the mature development phase after more than 20 years of production, with the water cut of the field increasing to 93%. A new strategy was executed starting in 2018 that targeted the remaining oil column, which was being squeezed by a strong bottomwater. One of the biggest challenges was the high uncertainty of the oil/water contacts in the current reservoir state. After reviewing the technical and geological challenges encountered, we will describe the successful approach taken to optimize the remaining reserves recovery using innovative horizontal well placement strategies. Using a few case studies, we will illustrate how we executed this innovative well placement strategy. This includes landing the horizontal wells at the upper part of the reservoir with low incident angle, drilling the horizontal sections close to the top of target zones using a reservoir boundary detection tool, and using a continuous packer for the well completion to reduce the water cut. In addition, we will describe how the team evaluated and selected logging technologies in the planning phase for proper well placement. The two cases discussed in this paper are based on horizontal wells completed using the following new strategy: maintaining a long lateral section in the upper layer of a predefined target, following the undulating structure while mapping the thin sandstone, keeping the trajectory in the target zone, etc. To ensure that each horizontal well could meet the target productivity index planned, real-time data were used in reservoir modeling to determine the required lateral length of each horizonal well. With the purpose of controlling water cut and improving oil recovery in these laterals, a new completion assembly, including a perforated liner with special completion material that prevented water from entering the liners, were installed in selected intervals according the logging data interpretation. Several observations will be highlighted, including: Real-time logging data can effectively evaluate the reservoir properties and structural changes along the lateral Optimum well placement in the lateral section is critical for draining the remaining oil column An optimized completion design based on real-time reservoir evaluation. The performance of the wells drilled to date shows that the production increased from 1,000 to 3,000 BOPD with zero to very low water cut. A reversing production trend from a declining trend to a growth trend is recorded. The successful implementation of the new strategy and the application of fit-for-purpose technologies in mature oil fields lead to improved production and increased oil recovery.