Publications

The Early Miocene Baturaja Formation is one of the principal reservoirs in the "X" Field. These carbonate rocks show complex facies, porosity and permeability. The objectives of this research are to work out diagenetic processes and depositional environments, and to discern the interconnection between diagenesis and porosity development of carbonate rocks of the Baturaja Formation. A detailed diagenetic and porosity development study was carried out from 143 thin sections of cuttings, 6 thin sections of core using a polarization microscope, detailed core description, well logging data analysis, and carbon and oxygen isotopes. The Baturaja Formation has undergone complex diagenetic processes, which include microbial micritization, dissolution, neomorphism, dolomitization, compaction, dedolomitization, autigenic quartz cementation, and hydrocarbon filling. The diagenetic history of Baturaja Formation can be divided into five stages: marine phreatic, mixing zone, fresh water vadose, fresh water phreatic and deep burial environments. Porosity of the Baturaja Formation in "X-1" well is mostly secondary : vuggy, moldic, intercrystalline and fracture porosity. Porosity tends to be significantly lower below 2546m, at the boundary between the Upper Baturaja (2438-2546m) and Lower Baturaja (2546-2719m). The Upper Baturaja is more porous, with a total porosity of 5-22%, whereas the Lower Baturaja porosity is 1-13%. Dissolution formed vuggy and moldic porosity, developed more intensively in Upper Baturaja than in Lower Baturaja. The original porosity, as defined by depositional texture, is highly modified by multiple diagenetic processes.