ABSTRACT: Explanation of regional thermal maturity and CO₂ variations, offshore Myanmar

Matthews, Martin D.¹, Michael A. Kowalski², and David B. Ephraim²
(1) Exploration Technologies, Inc, Sugar Land, TX 
(2) Texaco Exploration, Bellaire, TX

Heat flow in the Northeastern Gulf of Martaban varies spatially and temporally. These variations are significant to hydrocarbon and CO₂ generation. There are four thermal events associated with rifting: 1) Sag, then cooling; 2) Renewed subsidence and faulting, 6 to 2 ma; 3) Northern platform heating, 2 to 1 ma; and 4) Southern platform heating.

The Miocene kerogen, within the deep basin, entered the "oil window" 8 to 5.5 ma, the "gas window" 6.5 to 5 ma and the "dry gas window" 6 to 4.5 ma. This kerogen ceased generating significant hydrocarbon quantites when the source reached the depth of dry-gas production. Recent production of gas is from non-expelled heavier hydrocarbons. Subsequently, maturation has progressed shoreward.

The Miocene kerogen, within the shallow platform, entered the "oil window" in the last 0.6 million years. In areas of lower heat flow, the source is immature. Generation that transitions these two areas is gradual in the absence of let-out faults. The upper zone is currently undergoing active generation whereas the deeper zones had done so earlier. Where a let-out fault is present, in the zone landward of the fault, the kerogen is usually less than 70% transformed.

The probability of CO₂ generation should be greatest in, and adjacent to, regions of highest heat flow. Current heat flow is divided into low and high levels. The difference appears to be related to basement rifting and later intrusions. The free-air gravity was used to interpret the distribution of the rifts and different heat flow regimes.

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