Geochemical characteristics and diagenetic fluid of the Callovian-Oxfordian carbonate reservoirs in Amu Darya basin.
阿姆河盆地卡洛夫-牛津阶碳酸盐岩储层地球化学特征和成岩流体分析

The Callovian-Oxfordian carbonate rocks are the most important gas reservoirs in Amu Darya basin,Turkmenistan.Based on the reservoir petrology,the geochemical characteristics such as trace elements of Fe,Mn and Sr,isotopes of C,O and Sr and fluid inclusions,the genesis and diagenetic fluids of different carbonate reservoirs were analyzed.We got the following conclusions:(1) The rudists were calibrated at the age of 157.2Ma according to the global strontium isotope stratigraphy curve,and the reservoirs were at the age of Callovian-Oxfordian.(2) The Callovian-Oxfordian carbonates were a sustained transgressive-regressive cycle.The reef-bank facies well developed in the sustained transgression,while the regional dense caprocks developed in the sustained regression.(3) High concerntration of Fe and Sr,low concerntration of Mn,little changed δ13C and negative deviated δ18O with increased diagenesis implied that the diagenesis occurred in a closed and euxinic system which was devoid of meteoric water and were mainly controlled by temperature.(4) Combined with geochemical characteristicsof stable isotopes,fluid inclusions and the vitrinite reflectance,it was believed that the Callovian-Oxfordian carbonates are still at the stage of the middle diagenesis.(5) The dissolution of reef-bank limestones,burial dolomitization and calcites filling in fractures and vugs were all products from the interaction between the fluid and the rocks in different diagenetic phases.The diagenetic fluid was 87Sr-rich hot brine from the deep strata.