Abstract

The Sirikit field is a large field developed in a complex tilted fault block. The relatively simple stratigraphy on the tilted fault block flank becomes difficult to trace onto the tilted fault block crest. A recent reinterpretation of the reprocessed three dimensional seismic reflection data revealed that the difficulties of correlating reservoirs toward the crest are caused by features associated with degradation of the footwall, particularly (1) the prevalence of low-angle detachment faulting and (2) the development of discordant stratigraphic sections resulting from multiple episodes of erosion at the tilted fault block crest, followed by the eastward onlap of the section onto the eroded footwall surface. The main characteristic of this structure is the preservation of the onlapping sections through periodic propagation of the main bounding fault toward the hanging wall, which resulted in the accretion of former hanging-wall rocks to the footwall. This propagation sequence appears to be atypical for most degraded footwalls described in the literature. The degraded footwall model replaced earlier splaying bounding fault models used for development planning. Implementing this new structural model opened up new appraisal opportunities as the compartmentalization and reservoir distribution pictures changed. Appraisal of the reservoir now present above the hydrocarbon-water contacts following the new structural model led to a 15% increase in recoverable hydrocarbon volumes.

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