Publications

The Ngimbang Clastics is a syn-rift succession filling several NE-SW trending Paleogene half-grabens in the East Java Basin. It consists of thick (c. 90 m), but laterally-restricted fluvio-deltaic deposits and thinner (c. 60 m), but more extensive glauconitic shallow-marine sandstones. The succession records an initial period of lowstand incision and fluvio-deltaic deposition, followed by an overall and regionally-extensive phase of transgressive deposition. However, in detail the geometry and depositional controls on the platform are poorly understood. In addition, although this play has been proven (since 1985), it remains under-explored: (1) the Pagerungan Field has produced 1.5 TCF gas from this play, (2) only 3.5% of exploration wells drilled in the basin target this play, and (3) it is estimated that there is about 1000 MMBOE of yet-to-find resources. This study is focused on a play fairway analysis with emphasis on reservoir distribution on the North Madura Platform. Well data, including biostratigraphy, petrography, and wireline logs, together with 3D seismic have been used to provide an integrated analysis of reservoir facies, depositional environments and rock properties. Optical stacks of seismic attributes have provided new insight into the seismic geomorphology of the Ngimbang Clastics, most notably with regards to reservoir presence and geometry. It is shown that pre-existing basement structure (thrust-fold belt) and regional dip strongly controlled the orientation of the depositional system. Incised and unincised valley systems have been clearly identified. The depositional history was initiated by regionally extensive emergence and lowstand fluvial incision, followed by a prolonged period of transgression, when shallow-marine sand filled the previously exposed areas. The transgression reached its maximum when widespread shallow-marine carbonates were deposited, which then acted as a seal. This paper documents (1) the paleogeographic evolution of the Ngimbang Clastics play, and (2) CRS maps of reservoir, seal and charge. Exploration implications are discussed.