Deep Marine Reservoir Analog From Semilir Formation Outcrop Data in Ngoro-Oro Area, Gunungkidul, Indonesia

A deep marine reservoir is unique since it has complex lithology that affects the reservoir quality. The turbidite deposit, which is one of deep marine reservoir, is a fascinating research subject. It is commonly found in the subsurface as petroleum reservoirs. As a reservoir, it is essential to understand the character of the turbidite deposits qualitatively and quantitatively. The Miocene Semilir Formation is a magnificent model of an epiclastic deep marine sequence outcropped in the southern mountain area of Yogyakarta. This study aims to build the analogy model and characterize the epiclastic turbidite deposits as reservoir rock based on petrology and petrography data. Generally, the Early Miocene Semilir Formation in the study area is characterized by sandstone, tuff, shale, and breccia which are recognized as classical turbidite facies in the form of Ta, Tb, Tc, Td (Bouma, 1962) and coarse-grained turbidite facies in the form of R1, R2, R3, S1, S2 (Lowe, 1982). Based on porosity calculation, R1 and Ta facies have good porosity hence it may have high potential as hydrocarbon reservoirs. Directional fallout sedimentation mechanism and low tuff percentage are the main controlling factors in deep marine reservoir properties.