Reservoir Genesis And Geochemical Characteristics Of The Carbonate Rocks Of Callovian-Oxfordian Formation, Turkmenistan

Based on the sedimentary facies,genesis and evolution characteristics of the carbonate rocks of Callovian-Oxfordian Formation,the reservoir genesis and geochemical characterist ics were studied by petrology analysis and geochemical characteristics including carbon, oxygen isotopes, fluid inclusions, cathodeluiminescence on the basis of the latest achievements of the domestic and foreign relevant research. The conclusions and new recognitions as fol lows :Reservoir main developed in limestones and grainstones which distributed in the facies of platform margin reefs and shoals. Source-reservoir-cap assemblage provided favourable condition for gas pool forming. The reservoir type was defined as fissure-pore type,pore–fissure type andfracture reservoirs.Based on the study of well core observation,thin section identification and reservoir properties.The constructive diagenetic processes are mainly dolomitization, recrystallization, dissolution and fracturing, which effectively improve the reservoir porosity and permeability and constitute the basic characteristics of the reservoir that has the combination of a variety of primary secondary porosity types such as organicvisceral pores ,intergranular pores, intragranular pores, moldic pores, intercrystal pores, superlarge dissolved pores, dissolved caverns and fracturesBased on the detailed the geochemical characteristics researches including carbon, oxygen isotopes, the depositional environment,genesis and evolution characteristics were analyzed. We got the following conclusions: Using the samples of well representativeness of the original water, we established the evolution curves of the carbon in the Oxfordian. The shape of the stratum curve of the Carbon i sotope resembles that in geological time, reef-bank facies developed in the period of sustained transgression ,our research provides another reliable example of the global transgression and reef building in Late Jurassic. Oxygen isotope composition of carbonate rocks obviously corresponds to diagenetic environments and their evolution. Diagenetic alteration of microcrystalline limestone, grainstone is slightly which demonstrate the limited influence of non-marine fluid during post-s edimentation. Burial dolomitization and calcite precipitation in caverns and cracks were all the same product from the interaction between the same diagenetic fluid and the rocks in different diagenetic phases ,and the diagenetic process occurred in diagenetic thermal fluid systems which were relatively euxinic, lack of the continental fresh water and controlled mainly by temperaturThe key element controlled reservoir is summarized: the early deposit ional and diagenetic environment which controlled the early porosities; tectonics and formaion pressures which formed the fractures and dissolutions;and fluid rock interact ions that influenced the deep burial dissolution and the preservation of the porosities.