Characteristics of Siltstone and Carbonates within the Gas Chimney at the South Makassar Basin

This study made observations on mineralogy, petrological, and petrographic textures related to diagenesis and traces of methane presence in cuttings samples in sedimentary rock in well XS-01, Makassar Strait, Indonesia. The research methods carried out included a description of the cuttings sample, XRD, and petrography aimed at obtaining information on mineralogy, petrology, and diagenesis aspects of rocks, as well as documenting petrographic texture of the presence of methane in samples that prove the presence of methane in the recent past. The results showed that the identified mineralogy are calcite, quartz, amorphous silica, kaolinite, and montmorillonite. The rock types include claystone, siltstone, wackestone, packstone, and crystalline limestone. There are three (3) petrographic textures related to diagenesis: fracturing, calcite cementation, and silicification. Cement is drusy calcite and amorphous silica, representing the diagenesis stage of mesogenesis. The micrite petrographic texture shows as clotted peloidal micrite in wackestone, which was interpreted as a product of microbial activity during carbonate mineral precipitation stimulated by the Anaerobic Oxidation of Methane (AOM) process. This texture indicates the remnant of methane that characterizes the biogenic gas from the chimney gas zone. The gas chimney is common geological structures within the subsurface realm, which is recorded on the seismic sections.very easy to see or easily distinguished from other geologic features on the seismic section. However, the characterization of mineralogy, petrology, and petrographic textures is still rarely found in the literature due to limited accessibility to the interior of gas chimneystill quite rare. In this study, observations were made on mineralogy, petrological, and petrographic textures related to diagenesis and traces of methane gas presence in cuttings samples in sedimentary rock in well XS-01, Makassar Strait, Indonesia. The research methods carried out included a description of the cuttings sample, XRD test, and thin-section petrography aimed at obtaining information on mineralogy, petrology, and diagenesis aspects of rocks, as well as document-ing petrographic textures of traces of the presence of methane gas in samples that prove the presence of methane gas in the recent past. The results showed that the identified mineralogy are calcite, quartz, amorphous silica, kaolinite, and montmorillonite. The rock types include claystone, siltstone, wackestone, packstone, and crystalline limestone. There are three (3) petrographic textures related to diagenesis, namely fracturing, calcite cementation, and silicification. Cements are, with the types of cement including drusy calcite and amorphous silica which represent the diagenesis stage of mesogenesis. The micrite petrographic texture shows as clotted peloidal micrite in wackestone which were interpreted as a product of microbial activity during carbonate mineral precipitation stimulated by the Anaerobic Oxidation of Methane process. This texture is an indicator of remnant of methane that characterizes the biogenic gas from the chimney gas zone.