Recent Step-out Exploration in the Greater Sirikit East Area, Sirikit Oil field, Onshore Thailand, a Model for Overlooked Area

Abstract

Greater Sirikit East (GSE) Field represents recent step-out exploration success in the east of Sirikit Main Field. Sirikit Main was discovered in 1981 and remains the largest field in the basin, with surrounding smaller fields: Sirikit West (northwest, 1983), Thap Raet (north, 1988), Sirikit East (northeast, 1992) and Nong Jig (southwest, 1999). GSE comprises of multiple blocks defined by structural and stratigraphic closures. It shares common reservoir and source rock with Sirikit Main. Some of the trap types and seals are also common. However, some trap types and seal elements are not typical in Sirikit Main. More detailed subsurface evaluations were conducted to explore all the working petroleum systems. This is the key and challenge to the GSE that had been overlooked in the past due to the absence of considerable structural closure in the key horizon maps. Aggressive step-out exploration in GSE started in 2006. More than 12 exploration/delineation wells have been drilled to date testing multiple blocks and plays. The exploration concepts have been continuously developed by taking the feedback from the well post drill evaluation. The new developed or refined concepts were then applied to the subsequent exploration/delineation drilling. This cycle allows better risk mitigation as well as more accurate well targeting. To minimize exploration cost, time and risk, following strategies have been adopted whenever feasible: To use existing drilling surface location, to combine multiple targets and to provide back-up side-track target. Utilizing existing surface location made significant time and cost saving by avoiding costly land acquisition, access road building and time-consuming environmental impact assessment. Continuous exploration and delineation drilling in 5 years has changed the GSE area. The previously overlooked large area that looks like a monocline in main marker maps turned out to hold multiple hydrocarbon accumulations involving both stratigraphic and structural traps. Introduction Greater Sirikit East Field is located just to the east of the Sirikit Field in the S1 concession, Phitsanulok Basin (Figure 1), Central Plain Onshore Thailand, approximately 400 kilometers north of Bangkok. The concession is 100% owned and operated by PTT Exploration and Production. Sirikit Field was discovered in 1981 and remains the largest field in the basin. Up to 2000, 5 adjacent smaller fields have been discovered. Sirikit West Field in the northwest was discovered in 1983. Thap Raet Field in the north, discovered in 1988, Sirikit East in the Northeast, discovered in 1992, Nong Jig oil in the southwest, discovered in 1999, and Nong Pluang gas in the south-southwest, discovered in 2000. The first-discovered Sirikit Field is normally called as Sirikit Main Field in order to distinguish it from the neighboring fields bearing 'Sirikit' name.