Unlocking Untapped Potential of By-Passed Hydrocarbons to Extend Field Life in the Southern Gulf of Thailand

Abstract The Southern Gulf of Thailand has been one of major gas-producing region since 2002, with development historically focused on hydrocarbon reservoirs below the Mid Miocene Unconformity (MMU). As the field matures, these deep intervals are increasingly depleted, with marginal remaining volumes and rising development costs. This study explores the potential of by-passed hydrocarbons in intermediate sections as a viable alternative to sustain production and extend the field's life, particularly in the underdeveloped northern area of the existing operating field. In 2022, a delineation well was drilled in the northern part of the field to evaluate future development for the proposed targeted platform. While the primary target showed limited potential, the well encountered significant hydrocarbon pay above the MMU. Notably, a reservoir at 2,500 ft TVDss revealed a significant volume of gas in place across a conservative 1,000-acre AOI. Analog production data from similar hydrocarbon reservoirs suggest performance significantly exceeds volumetric estimates. Additional shallow reservoirs, ranging from −1,900 to 4,600 ft TVDss, were identified but fall below seismic resolution. These zones, supported by analog-based estimation, offer further upside volume. The findings have sparked renewed interest in the northern area, raising the question of whether these untapped hydrocarbon volume could become the next development focus. Developing these shallow reservoirs poses several technical challenges, including well trajectory constraints, drillability, stability, sand production risk, and facility limitations. To address these, a cross-functional team conducted a comprehensive evaluation covering subsurface, well design, economic feasibility, and platform development. This collaborative effort aimed to justify reserve booking and secure project approval. The technical assessment confirmed that the by-passed hydrocarbon zones in the northern area of the Southern Gulf of Thailand are both economically viable and technically feasible for development. These findings enabled the inclusion of this opportunity in the region's development inventory. Furthermore, the approach has been successfully extended to nearby discoveries, enhancing the value of marginal prospects and contributing to the long-term sustainability of future development projects. This study highlights the strategic value of shallow by-passed hydrocarbons (below −2,000 ft TVDss to MMU) in mature fields. Benefits include lower CO2 content, higher gas rate due to better sand quality in shallower section, and reduced facility life requirements. This enables cost savings and potential reuse of infrastructure. The insights gained can be applied to similar fields, offering a replicable model for maximizing remaining hydrocarbon volume and prolonging field life, by-passed potential in other areas as well as shorter facility life and able to transfer the usage for other areas plus cost saving associated.