Assessing vertical compartmentalization within the KHM field, southwest of Iran: An integrated approach

Abstract

KHM field is a recently discovered gas reservoir with an oil-rim which hosts an enormous hydrocarbon in Permian-Triassic reservoirs. Five Drill Stem tests have been done in this field, four of which tested gas and one tested unexpected oil in lowermost part of Upper Permian Strata. However, understanding the nature of fluid accumulations and vertical continuity within the reservoir was a perplexing issue in this reservoir. Five gases and their associated liquids were subjected to gas-chromatography, molecular and isotopic analyses and then combined with well test and engineering data to investigate compartmentalization and fluid phase in the reservoir. Molecular and isotopic data indicated that the fluids tested in Middle Permian lower Dalan were different and separated from the Upper Permian Upper Dalan reservoirs via good sealing efficiency of anhydritic Nar member. In upper Dalan reservoir, the gas-chromatography data indicated two different geochemical traits, suggesting that the oil is separated from the overlying gas reservoir. However, the similar gas isotopic data together with pressure and PVT data indicated that the separation in geochemical fingerprint is due to phase separation in reservoir, and the tested intervals are actually connected two-phase critical fluids which are in equilibrium with each other. This study indicated that the gas-chromatogram fingerprinting is sensitive to both pressure continuity and phase separation, whereas, gas isotopic composition is mainly controlled by pressure continuity.