Reservoir Characteration Study Of The Pre-salt Carbonates In Rozhkovsky Field,F Block,Pre-Caspian Basin,Kazakhstan

Pre-Caspian Bain is mainly located in Western Kazakhstan.During the geological time,huge succestion of sediments were deposited in the bains,which was divided into three strata(pre-salt,salt,post-salt)by salts deposition.F block is locted in the North Sidewall Zone of Pre-Casipan Baisn,while R structure,as an anticline,is in the northern part.Duirng the Carboniferous period,huge succession of carbonate sediments were deposited in Pre-Caspian Basin.The carbonate sediments are organized by the open plarform and plarform margin marked at the thin silisiclastic interbedding.In spite of previous work,there is a general lacking of systemic approaches on petrographic and geochemical attributes of the carbonate comples,especially in Rozhkovsky field in north Pre-Caspian Basin,with respect to the burial and tectonic history.The effect of diagenetic process on quality and spatial distribution of hydrocarbon reservoirs in the pre-salt carboante strata in F block,northern Pre-Caspian Basin needs to be addressed.This study is based on analysis of 6 cored wells,petrography(cathodoluminescence and SEM),sequence stratigraphy,and stable isotopes,aiming to construct the pore-system evolution in the reservoirs during the eustacy environment.Based on the obtained petrography and equence stratigraphy,these sediments areinterpreted as: grainstone(bioclast-,intraclast-,oncoilit-);packstone-grainstone;packstone;wacke-packstone,wacke-mudstone;siltsone and dolomitica limestone,which mainly produced mainly in plarform margin and open platform facies duringgeneral transgressive system with total 4 second order sequences and 8 third ordersequences in Tournasian stage lower Carbonifecous.The residual interparticle porescontribute the main oil and gas storage spaces in carbonate reservoir which are richedin grain-supported stone distributing in platform margin shoals and open platforminner shoals and are preserved by micro-fine crystalline calcite as a coat around theparticles formed duirng early sea-water diagenesis process,which keep the particlesand pore shape in compaction.The fractuers and stylolites are formed in laterdiagenesis process as fluid pathway to connect the different pores and increasereservoir porosity and permeability.