Carbonate Microporosity of Middle Miocene Jonggrangan Formation


Microporosity of carbonate rocks provide critical information towards fluid properties, log response, and ultimate recovery o f
hydrocarbon reservoir. The existence of water bound inside and around micro and macro-pore systems will significantly affect
saturation water signature from wireline log, thus detail identification of this feature is essential and can be used to reduce
uncertainty in formation evaluation.
This study emphasizes on the occurrence of microporosity, variation, and diagenesis of carbonate rocks of Jonggrangan
Formation in Central Java. Moreover, this study attempts to serve as an analog for Middle Miocene carbonate reservoir in the
South Central Java offshore, that has confirmed the presence of thick carbonate successions based on past exploration wells.
Both allochthonous and autochthonous carbonate facies have been identified and categorized based on texture and
grain composition: (1) Coral Floatstone; (2) Wackestone with micrite and microspar matrix; and (3) Boundstone microfacies
associations. Qualitative porosity measurement based on thin section analysis was conducted utilizing point-counting technique
in order to investigate variation in microporosity. These including: (1) microporous grains; (2) spar grain (3)microporous matrix;
(4) microspar matrix (5) microporous of fibrous to bladed cement (MFBC); and (6) microporosity of equant cement (MEC). Our
study indicates that the presence of microporosity is primarily controlled by diagenetic, environment of deposition (EOD),
carbonate grains and mineralogy, as well as organism behavior. In addition, over a period of time, it can be inferred that
diagenesishistory holds important role to shape development of microporosity in carbonate rocks.