Reservoir Characterisation and Evaluation of Micaceous sandstone of Geleki Field,Upper Assam, India - An Integrated Study

摘要

Tipam sandstone, the main hydrocarbon-producingrnreservoir of Geleki Field located in Upper Assam,rnIndia, is of highly complex nature containing goodrnamount of mica (Muscovite) in addition to quartz,rnfeldspar and montmorillonite as inferred fromrnsedimentological studies. Mica complicates logrnanalysis as most lithology indicators reflect it asrnhigh-density shale, resulting in pessimistic reservoirrnevaluation.rnMica is often misinterpreted as shale by commonrnclay indicators used in conventional deterministicrninterpretation models based upon Density-Neutron-GRrnlogs. However, mica should be considered asrnstructural part of the rock not affecting porosity andrnpermeability. Surface of mica is altered byrndiagenesis and acquires surface conductancernleading to reduced resistivity of the formation evenrnat constant porosity. Therefore, if mica is notrnincluded in lithological model the evaluation can bernmisleading. Further, high computed shale volumernwill make good reservoirs either appear worthlessrnor with reduced potential.In the present paper, the influence of mica onrnvarious log responses has been analysed, basedrnupon which a highly micaceous sandstone facie hasrnbeen identified in the upper portion of the reservoir.rnHowever, presence of mica and feldspar inrnmoderate proportions is inferred throughout thernformation. Multi-mineral interpretation model basedrnupon statistical inverse modeling technique hasrnbeen successfully used for realistic evaluation ofrnreservoir parameters leading to identification of newrnhydrocarbon bearing layers.rnOil production from a well tested on the basis of thernpresent integrated study has confirmed the efficacyrnof the suggested model. Extension of the model tornother similar reservoirs can lead to better reservoirrncharacterization and delineation of by-passedrnhydrocarbons.