[Seminar] The occurrence and origin of anomalously high CO2 gas reservoirs in the Pattani Trough, the Gulf of Thailand

Tomonari MINEZAKI (Mitsui Oil Exploration Co., Ltd)

25 October 2016 | 1pm – 2 pm | Room 333 Geology Building

Abstract: This presentaion discusses the distribution of anomalously high carbon dioxide (CO2) in gas reservoirs of the Platong gas field in the Pattani Trough. Stable carbon isotopic data and a structural model are presented to discuss the origin of the CO2-rich gases. The Pattani Trough is an elongated N-S trending Cenozoic rift basin with high heat flows, located in the Gulf of Thailand. Hydrocarbons (gas, condensate and to a lesser degree oil) are trapped in Miocene fluvial sandstones within highly faulted graben systems.

The CO2 contents of most gases in the Pattani Basin show an overall increase with depth from a few percent to near 25%. These gases largely originated from the thermal decomposition of land-plant organic matter during maturation. Some wells in the Platong and Erawan fields however encountered gas reservoirs containing CO2 above 60% and as high as over 90%. At the Platong “G” Platform, the vertical and lateral distribution of high CO2 forms a large plume, related with a structural nose above a local high of basement rocks. Carbon isotopic analyses suggest that these anomalously high CO2 occurrences are of inorganic origin. Geological and geophysical data suggest that these gases were generated by the thermal decomposition and/or dissolution of the Paleozoic basement carbonates; they migrated upward through deep-seated bounding faults which provided the fluid conduits. The structural complexity at the Platong “G” nose facilitated fluid migrations vertically and laterally, resulting in the mixture of normal (5-25%) and anomalously high (60 to over 90%) CO2 gases.

Tomonari Minezaki has over 30 years of worldwide exploration and development experience in oil industry. He graduated from Niigata University, Japan with a bachelor’s degree in geology, and joined Japan China Oil Development Corp. (JCODC) in 1984. During JCODC, he has worked as a project geologist for three oil fields in Bohai Bay, and also studied deltaic and turbidite sandstone reservoirs for three years at JNOC Technology Reserach Center. He joined Mitsui Oil Exploration Co., Ltd. (MOECO) in 1994, and worked many worldwide projects particulary Southeast Asia and Latin America. During MOECO from 1998 to 2000, he has seconded at Unocal Thailand in Bangkok as a project geologist. He is currently assigned as Chief Geologist of MOECO Tokyo headquater, and is also a senior graduate student at Tsukuba University. You may contact Tomonari Minezaki by e-mail at tomonari.minezaki@moeco.com .