CHARACTERISTICS OF DOLOMITIZED LIMESTONE OF PRUPUH FORMATION BASED ON PETROGRAPHY ANALYSIS IN SENDANG AGUNG, EAST JAVA

Abstract

The East Java Basin is a large hydrocarbon producing basin in Java. From the drilling wells in this
region it is known that the reservoir comes from carbonate rocks. The Prupuh Formation acts as a
reservoir because of its high porosity value, not only primary porosity but also secondary porosity.
The study of limestone characteristics of Prupuh Formation in Sendang Agung Village, Paciran
District, Lamongan Regency, East Java Province is a combination of field and laboratory activities.
Field activities include collecting data through detailed measurements, making measured
stratigraphic cross sections with systematic rocks sampling. Laboratory activities are petrographic
analysis through thin sections. The purpose of this study is to increase the knowledge about
Prupuh limestone which acts as a reservoir in the East Java Basin oil and gas system. Based on the
results of the field activity, a measured stratigraphic section with a thickness of 32.5 meters was
made, the lower and middle sections were composed of dolomite, then at the top there were
bioclastic limestones as reported by Pringgoprawiro, 1983. A total of 6 (six) rock samples were
chosen for petrographic analysis of thin sections. Results of the analysis obtained 32 meters is a
crystalline dolomite with a very bad porosity system. Dolomite which is found is the result of
dolomitization of the wackestone bioclastics limestone. So it was concluded that the carbonate
rocks the Prupuh Formation in research area had very bad potential to become reservoir rocks.