Diagenetic history and porosity evolution of an Early Miocene carbonate buildup (Upper Burman Limestone), Yadana gas field, offshore Myanmar

Abstract

Abstract The Miocene Yadana carbonate platform is a major offshore gas reservoir located in the Andaman Sea (offshore Myanmar). The integration of petrographic analysis of carbonate rocks, stable isotope measurements and seismic interpretation provided new insights into the diagenetic history of the Upper Burman Limestone reservoir. The high (28%) average porosity of the reservoir is dominantly related to strong development of microporosity, moldic and vuggy porosity. Mud-supported, coral-rich sediments record significant early marine dissolution of aragonite and early lithification of matrix that has led to the development of dense layers. Stable isotope and petrographic data from the top of the reservoir suggest that the long-term depositional hiatus (middle to late Miocene) was related to platform drowning and non-deposition in a deep marine setting. Moderate dolomitization has affected the top and flanks of the platform during the depositional hiatus. Microporosity development and sparry calcite cementation mainly occurred in marine to marine shallow burial environments. A major decrease in porosity, averaging 10%, below the gas-water contact suggests a major phase of porosity evolution during and/or after the hydrocarbon emplacement which is mainly related to 1) increased moldic and vuggy porosity development within the gas zone, 2) microporosity preservation in loosely-packed, subrounded micrites within the gas zone, and 3) microporosity reduction by calcite precipitation within the water zone leading to the development of densely-packed, euhedral micrites.