--> Combination Traps In Jasmine And Ban Yen Fields, Gulf Of Thailand: Identification, Recognition And Development Strategy

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Combination Traps In Jasmine And Ban Yen Fields, Gulf Of Thailand: Identification, Recognition And Development Strategy


The Jasmine and Ban Yen Fields are comprised of more than 175 individual oil accumulation segments. In terms of hydrocarbon trap category, most of these segments are pure structural traps, where the geological structure alone forms the trap geometry and is responsible for the oil accumulation. However, in some segments, the observed oil accumulations require combination traps to work. The trap geometry is a result of combining the geological structure and reservoir sandstones distribution. Most of the early exploration and development wells were optimized based on geological structure. Seismic attributes were utilized to ensure reservoir presence and quality but within the structural trap. The presence of combination traps was initially identified through integrated evaluation of the well logs, formation pore-pressures, oil production and seismic data in the later stage of field development. In the post-rift fluvial reservoir interval of Jasmine and Ban Yen Fields, it is well known that typical hydrocarbon columns are small, this being the result of one or more of the following factors: i) limited vertical relief of the structural trap, ii) the vertical or lateral sealing capacity, or iii) the limited volume of hydrocarbon that migrated into the trap. However, pressure-derived fluid contact and or production data in some segments suggests an oil column beyond the structural closure or spill point. Integration with seismic attribute analysis revealed the working combination trap responsible for oil accumulation beyond structural closure. More challenging combination traps to identify in the field are those for which reservoirs are not present in the crestal part of the structure where most of the wells are located. In a three-way dip closure structure where the crest of the structure is coincident with trapping fault(s), the development wells are often structurally optimized and always located very close to the fault plane(s). A channel sand might be present down-dip away from the fault(s) with a geometry that forms a hydrocarbon trap and hence not penetrated by any well. Seismic attributes may help the identification process where the seismic image is sufficient. In some cases, there is not enough isolation or shale thickness over and under to image the reservoir and well data become an important part of the evaluation. Integrated evaluation of the combination traps has led to a revision of the development strategy, as well as further appraisal of potential hydrocarbon accumulations. Three dimensional geological modeling and reservoir simulation were performed to better optimize the hydrocarbon development. In a structural trap with stacked reservoirs, it is geometrically straight forward to combine multiple reservoirs in a deviated development well. Additional effort is required to optimize the development of hydrocarbon that are not purely structurally trapped. Dedicated development wells are sometimes the only (or preferred) option. Downdip, off structure exploration/appraisal wells were drilled to unlock the potential from the combination traps.