Stratigraphic Traps in Distal Lacustrine Delta, a Case History from Greater Sirikit East Field, Phitsanulok Basin, Central Plain, Thailand

Abstract

Greater Sirikit East oil and gas field is located just to the east of the Sirikit Main field in the S1 concession, Phitsanulok Basin, Thailand. The main reservoirs are fluvio-deltaic Lan Krabu formation members of K, L and M that interfinger with the open lacustrine Chumsaeng formation. Hydrocarbon traps in the field can be grouped into structural and stratigraphic traps. Numerous small structural closures have been proven to be hydrocarbon bearing. Delineation and development well drillings have also proven the working stratigraphic trap system in the absence of structural trap. In some structural closure, observed hydrocarbon column heights from well data exceed their relevant structural spill point, invoking the larger working stratigraphic trap system responsible for the hydrocarbon accumulation.Various examples of proven stratigraphic traps in the field will be presented in this paper. Structural maps, well correlation, pore-pressure plot, production data and existing internal studies on sequence stratigraphy and reservoir facies were incorporated in this evaluation. Reservoir characterization from seismic data is not considered feasible due to resolution limit. Most of stratigraphic traps are within the distal sub-members of Lan Krabu Formation such as M, L2, K4, K2 and K1 which are dominated by mouthbar facies. The trapping is formed by combination of deposition and structure geometries. The structure is East-Northeast dipping, while the depositional direction is from the Northwest to Southeast direction. A trap system is hence formed where reservoir sand pinch-out to the southeast direction that is structurally up-dip, bounded by north-south trending fault in the west.