マレーシア•サラワク沖における炭化水素鉱床中の二酸化炭素の起源：マイグレーションモデリングをもちいた簡便な手法による検討からの示唆

Abstract

： In petroleum exploration, it is crucial to understand the origin of CO 2 in petroleum reservoirs to avoid CO 2 -rich reservoirs. The gas isotopic signature is a clue to its origin; however, it is not uncommon that such geochemical data are lacking or limited. This is the case with offshore Sarawak, Malaysia, where the origin of CO 2 cannot be determined as mantle-or carbonate-origin because of lack of helium isotope data. In this study, the CO 2 origin in the area was examined using a simpli ed migration modeling approach that considered the CO 2 source areas for mantle-and carbonate-origin scenarios and migration pathways after basin geometry. There were remarkable differences between the CO 2 -charged areas, as indicated by the two scenarios. The mantle-origin scenario, which assumed that CO 2 was sourced from an area of crustal thinning, suggested that CO 2 was mainly charged to the North Luconica, West Luconia, and Baram Delta provinces, as well as the areas along the West Balingian and West Baram Lines. The carbonate-origin scenario, assuming CO 2 sourced from the deeply buried thick-shelf carbonates, implied high CO 2 concentrations in Central Luconia, Balingian, southeastern North Luconia, the western margin of the Baram Delta, and the southeastern margin of the Tatau provinces. The modeling results from the carbonate-origin scenario suggest that the deeply buried thick-shelf carbonates alone cannot explain the entire CO 2 distribution in the study area. In contrast, the mantle-origin scenario showed better consistency between the modeling results and measured CO 2 concentrations in the reservoirs. The scenario can be an additional or even alternative explanation to the CO 2 distribution offshore Sarawak. Although this simpli ed methodology cannot provide conclusive results, it is an effective way to assess CO 2 charge scenarios in sedimentary basins where gas isotope data are lacking or limited.Keywords： Carbon dioxide, mantle, carbonate, migration modeling, basin modeling, Sarawak, Malaysia ＊ 令和 4 年 6 月 8 日，令和 4 年度石油技術協会春季講演会地質・探 鉱部門シンポジウム「上流事業の強靭化・脱炭素化 -地質・探 鉱技術適用の取り組み-」 This article is based on the presentation at the JAPT symposium titled "Application of geology and exploration technology to make the oil and gas upstream business more resilient and decarbonized" on June 8th, 2022.