Petrophysical rock typing (PRT) and evaluation of Cenomanian–Santonian lithostratigraphic units in southwest of Iran

Abstract

Southern Iran is one of the most significant parts of the world in terms of economic aggregation of hydrocarbons. In this paper, reservoir quality of the Cenomanian–Santonian deposits has been evaluated in southwestern Iran. According to the reservoir qualification, five particular rock types have been classified based on log responses through K-nearest neighbors (KNN) method. 1–5 are representing poor, weak, moderate, superior and non-reservoir types of rock, respectively. Rock types 3 and 4 are determined as the best types which can play a suitable reservoir role in hydrocarbon accumulation. The mentioned groups generally consist of porous limestones with low level of clay content. Rock types number 1 and 2 indicate the low porosity tight limestones and rock type 5 belongs to clays and shaly layers with high gamma radiations. Lithology of these intervals is specified using Rhomaa–Umaa and NPHI–RHOB crossplots which displayed calcite mineral is the main mineral formed both formations. SEM analysis and Th–K crossplot confirmed that Illite, Montmorillonite and Kaolinite are major clay minerals settled in these intervals that may have impact on reservoir characteristics. Interparticle and micro-porosities are considered as dominant kinds of porosities based on velocity deviation log (VDL) and it is proved by SEM results. Rock types 3 and 4 have been considered as the most productive zones which can be the best target for future perforating operation. According to petrophysical evaluation results, Ilam (Santonian) reservoir quality is enhanced toward northeast and southwest (Maximum abundance of rock type 4) of the studied area in comparison to central part. The Sarvak (Cenomanian–Turonian) Formation is in the highest level of reservoir quality in the southwest of the studied area (abundance of rock types 4 and 3).