Rembang Zone Petroleum Play, Stratigraphic and Petrographic Analysis of Ngrayong Formation as Reservoir, Jamprong Area, Tuban, East Java

Abstract

The following research took place in the Jamprong area, Tuban Regency, East Java Province within a study area of 2 km2. Physiographically, the study area is situated in the anticlinorium of the Rembang Zone. This research aims to define the reservoir potential of outcrop samples from the Ngrayong Formation as an analogue for the subsurface. In addition, the depositional environment and the age of the rock in the research area was determined. The Ngrayong Formation is regarded as a potential reservoir in the North East Java Basin. The accumulated data consists of stratigraphy, petrographic analysisand paleontological analysis of rock samples, and geological mapping has been carried out to determine the distribution of rocks. Facies were determined based on outcrop observations and comprise predominantly arkose sandstone facies with fine – coarse grained, moderately sorted and with cross-bedding, herringbone, and lamination, and another facies namely massive carbonate grainstone. Based on these facies, the interpreted depositional environment is the transition of tidal flat to shallow marine carbonate platform with relative biostratigraphic age of Middle Miocene, Langhian to Serravallian (M6-M8 planktonic foraminiferal biozones). Rocks in the study area have porosity >20% or very good and permeability >130 or fair based on petrographic observations, and this supports the interpretation of the Ngrayong Formations as a potential reservoir of hydrocarbons.