Successful Development of the Deepest Oligocene Syn-Rift Sediment in the Malaysia-Thailand Joint Development Area: Is the Deeper Zone Our Future?

Abstract

Field X, located in the offshore Malaysia-Thailand Joint Development Area (MTJDA), comprises multiple stack gas reservoirs with a combination of trap styles. This paper highlights the challenges and lessons learned in successfully developing the deepest Oligocene syn-rift sediment in the MTJDA, which was initially discovered by the one appraisal well drilled in 2010. A further comprehensive evaluation was performed to justify the deepening of development drilling in 2019 (as appraisal cum to development) and 2021-2022 (as infill wells) with promising results. The discovery of hydrocarbon resources in the deepest Oligocene syn-rift sediment at MTJDA was part of an appraisal program by deepening the development well. The two wells discovered and proved the presence of multi-stack gas sands in this deepest section (3800-4000 mTVDSS). The clastic sediment deposits in a fluvio-deltaic system. The reservoir properties of this syn-rift sediment are better than the early post-rift sediment (early Miocene). The production test confirmed the initial gas flow rate of about 15 MMscfd. A comprehensive analysis was performed to evaluate a sizeable volume before more development wells were proposed for this deepest sediment. The initial understanding of Late Oligocene syn-rift sediment was very minimal at the beginning of the project. One of the neighbouring well information suggests lacustrine delta environments based on core data. However, a fair-quality seismic amplitude shows a broader channel belt (over 3km width) which usually exists in the braided stream. In view of the two appraisals cum to development wells' successful discovery, more than five wells were proposed to penetrate this zone as a deepening target from the existing discovered zone. The fit for purpose well designed with a monobore concept, was selected. Upon completing the development drilling with denser well spacing, it suggests the discontinuity of blocky sand presence with multiple fluid contact (stratigraphic compartmentalization), which is usually found in narrower channel reservoirs at the deltaic system rather than the braided stream. The good reservoir properties observe from the open hole log, formation tester, and production test. The success story of these wells opens future opportunities to plan more deep well to develop Oligocene sediment, which prove to be a good hydrocarbon producer. This paper updates the previous understanding of geology, such as the depositional environment, and the understanding of reservoir productivity of the Oligocene sediment in MTJDA. It also proved sizable reservoir quality with extensive lateral presence and good productivity. Hence, the company foresee a promising future from this deep reservoir to prolong its long-term development plan.