Tapping Moveable Oil Rim in Challenging Matured Oil Field Through the Synergy Geosteering Approach

ABC field is located in offshore Peninsula Malaysia where recently a redevelopment project was undertaken to target the unswept oil via drilling horizontal wells. Offset well’s performance suggested highly dynamic fluid contact movement with reservoir sweep being non-uniform. Fluid types were expected to have low resistivity low contrast and vertical depth uncertainty of structure adding the complexity in landing and horizontal section drilling. A multi-disciplinary approach with synergy geosteering was vital to optimize horizontal well placement. A workflow was developed which synergized subsurface and drilling scope to mitigate risks associated with the uncertainties. Geosteering pre-job model was built with multiple offset wells’ properties and range of expected fluid contacts. Post pilot hole drilling the model was updated by incorporating the actual fluid contacts and structure for an optimum drilling strategy. The structure uncertainty was further reduced with the advantage of deterministic inversion of high-definition reservoir mapping technology while drilling. Due to observed non-uniform fluid contacts away from the landing point, real-time inversion in combination with open hole logs was used in horizontal section to maintain desired stand off from both oil and gas. The high-definition reservoir scale mapping with deterministic inversion method was utilized to identify low resistivity low contrast boundaries of oil from transition zone which was challenging to be achieved by a conventional geosteering tool. The top of reservoirs mapped by geosteering were incorporated with the seismic amplitude analysis to assist in real time decision making. It was essential to ensure smooth landing point for good borehole tortuosity since the landing and horizontal section were drilled in one section. The tool clearly revealed the transition zone and Oil Water Contact (OWC) at 10-20m TVD below the bit with higher confidence compared to standard tool in horizontal section. In the lateral section, OWC and dip angle were mapped concurrently which allowed the team to achieve the required production length while maintaining standoff from the swept zone. The success of integrated subsurface workflow with synergy of geosteering proven as the ultimate solution to overcome the challenges of horizontal well placement in this field. All wells with geosteering accomplished landing at an optimum depth and planned horizontal length despite tight True Vertical Depth (TVD) window. Ultimately, wells completed and unloaded, delivering higher than the expected rates with close to zero water cut (WC).