ABSTRACT: Geochemistry of gasses in the Malay Basin

Waples, Douglas¹, Mahadir Ramly², and Meor Shahrin Mahmood²
(1) N/A, Denver, CO 
(2) N/A, Kuala Lumpur, Malaysia

Three end-member gas types have been identified in the Malay Basin: biogenic, thermal and basement gas. The thermal gas has been divided into two subgroups: "normal" thermal gas originating at relatively shallow depths and "deep" thermal gas from more-mature source rocks.

Most gas samples studied composed of mixtures of two or all three of the end members. Gases with a significant biogenic component are limited to the northeast corner of the basin and are not associated with large accumulations. The biogenic gas was probably generated locally and does not appear to offer an important exploration.

Gases dominated by CO₂ are predominantly sourced from the basement. These gases have migrated vertically from the basement where they dominate only where extensive fault systems extend all the way to the basement. Although some accumulations are very large, targets are at risk of being dominated by CO₂.

Area in the north central part of the basin contains gas that appears to be mainly of "normal" thermal origin. Accumulations are of moderate size. Lack of contamination by basement gas and "deep" thermal gas in this area suggests a lack of deep faults where this will limit the volume of hydrocarbon gas in this area.

Much of the basin contains gas that is a mixture of "normal" thermal, "deep" thermal and CO₂ from the basement in varying proportions. "Deep" thermal gas seems to dominate over "normal" thermal gas in the large accumulations. This suggests that the key to exploring for large gas reserves is to find areas where vertical faults are adequate, but there is also evidence that these faults do not extend all the way to the basement.

AAPG Search and Discovery Article #90913©2000 AAPG International Conference and Exhibition, Bali, Indonesia