Application of Morphology and Elemental Distribution of Gamma-Ray Log in Consideration of Environmental Conditions and Sequence Stratigraphy of Asmari Formation, Karun Field

The Oligo–Miocene Asmari Formation is the most important reservoir rocks of the Dezful embayment oil fields. This study interpret sedimentary environments and sequence stratigraphy of the Asmari Formation in Karun oil field based on changes in facies, gamma-ray log morphology and change in concentration of thorium, potassium and uranium elements of the natural gamma- ray spectrometry. In this regard, 1 evaporate, 9 carbonate facies and 1 mixed facies were recognized. The thorium to uranium ratio used to analyze the oxidation, reduction condition. Based on the vertical distribution of the facies in the sequence stratigraphy framework, three 3rd order sequences were determined. Changing the trend of logs in time reflects the decreasing trend of gamma- ray in the sequence boundary and increasing trend at maximum flooding surface. Five main morphologies including left Box Car shape, Right Box Car shape, Serrated Bell shape, Serrated Funnel shape and serrated shape have been recognized. The conformity of this morphologies with the sequence stratigraphy leads to the relationship between the Left Box Car shape with Low stand system tract, Serrated Bell shape and Right Box Car shape with Transgressive system tract and Serrated Funnel shape with High system tract.