TAYLOR, IONE L., LEE E. McRAE, and GREGORY O. SMITH, Amoco Production Research, Tulsa, OK

ABSTRACT: Sedimentology and Diagensis of Tertiary Sandstones from the Chindwin Basin, Myanmar (Burman): A Case Study for Predicting Reservoir Quality from Outcrop

An intense hydrocarbon exploration effort was recently conducted in the Chindwin basin, located in the remote mountainous jungles of northern Myanmar (Burma). Multidisciplinary geologic/geophysical studies, combining both extensive field investigation and subsequent analytical work, were undertaken to assess various exploration risks inherent in frontier basins such as the Chindwin. This paper addresses a timely and challenging question in

remote exploration areas--that of reservoir prediction where no subsurface data exists available control is only from outcrop.

The Chindwin basin is a sub-basin to the larger, primarily compressional, forearc basin--the inner Burman Tertiary trough. This trough contains sedimentary section from the post-Cretaceous accretionary continental margin which developed in response to subductive convergence of the Indian and Asian plates. Chindwin basin-fill consists of 15,000+ m of Upper Cretaceous to Pleistocene clastic strata. Depositional environments for this sequence range from slope, shelf and marginal marine in the Mesozoic to pre-middle Eocene, to entirely nonmarine interbedded sandstones and finer-grained clastics in the post-middle Eocene to Pleistocene section.

Petrologic evaluation of these feldspathic litharenites found primary effects controlling reservoir quality to include provenance, as it dictates brittle versus ductile grain distribution; and transport and deposition, as they control grain size and sorting.

Mineralogically identical samples can range in reservoir quality fromexcellent (24% porosity, 890 md permeability) to poor (8% porosity, 0.6 md permeability). The low porosity/permeability samples contain ductile volcanic lithics that compactionally deform to occlude porosity. High porosity/permeability samples contain rigid plutonic lithics that preserve intergranular porosity with burial.

Diagenetic trends persist across an area in excess of 150 km. A vertical zonation in cement type occurs which appears to follow a vertical thermal profile. Despite thick accumulations, the rocks show no diagnostic evidence of deep burial. Understanding the inter-relationship between sediment provenance and burial history has proven critical in locating the most favorable reservoir rock in this basin.

AAPG Search and Discovery Article #90987©1993 AAPG Annual Convention, New Orleans, Louisiana, April 25-28, 1993.