マレーシアサラワク沖セントラルルコニア海域における炭酸塩岩ビルドアップヘのガス移動・集積システム

Abstract

A Miocene carbonate platform, named Central Luconia carbonate platform, is widely extended in offshore. Sarawak, Malaysia. There are some 200 of Miocene-Pliocene carbonate build-ups are developed on the carbonate platform, and some 70 of them have been tested so far, of which around 40 have been proved to be gas-bearing and the rest were water-bearing.Through the exploration activity over the Central Luconia area by Nippon Oil Exploration Co. Ltd. since 1987, it was found that five main geological factors, i.e. (a) Cycle I/II gas focal structure, (b) Upper Cycle V thief beds, (c) crest/flank faults, (d) the balance between seal collapsing critical pressure and build-up formation pressure, and (e) gas chimney, can be utilized for gas prospect screening and gas column height prediction.Through the several carbonate studies, a probable theory of gas migration and accumulation system has been led; 1) gas migration and focusing in Cycle II focal structure, 2) gas leakage from the crest of the Cycle II focal structure due to pressure unbalance, 3) vertical migration through fractures in Cycle III shale sections, 4) gas accumulation in Cycle IV/V carbonate build-ups which are located just above the crest of the Cycle II focal structures, 5) gas leakage from the crest of Cycle IV/V carbonate build-ups due to pressure unbalance (gas chimney). Four mega-sized high structures were found in the study area as the location where such a series of gas migration and accumulation system is under performing.