Fluid inclusion characteristics and hydrocarbons accumulation of the cretaceous reservoirs in Kuqa foreland thrust belt, Tarim Basin, Northwest China

According to the sample analysis of fluid inclusion, combined with the diagenesis, burial history, hydrocarbon generation history and tectonic evolution history, hydrocarbon accumulation periods and process in the Cretaceous reservoirs of Kuqa foreland thrust belt are studied in this paper. It is proposed that Kuqa thrust belt has experienced three stages of hydrocarbon charges, which results in different hydrocarbon accumulation in different anticline traps of the study area. A small amount of crude oil and high-mature oil-gas was charged into part of the geological structures in early-middle Kangcun period (16.3-11 Ma), as well as late Kangcun and early-middle Kuqa period(11-3 Ma)respectively. However, massive natural gas was strongly charged in late Kuqa-Quaternary(3-0 Ma) to form all the gas reservoirs. The research results show that fluid inclusion of the Cretaceous reservoirs are mainly gas inclusion distributed in the whole region and liquid-hydrocarbon and hydrocarbon inclusion found in certain structural traps. Characteristics of fluid inclusion under microscope and UV fluorescence suggest that liquid-hydrocarbon inclusion are light yellow to yellow green and hydrocarbon inclusion are light blue to blue-white. Homogeneous temperature test of coeval aqueous inclusion indicates that the number of main peak and peak values vary in the different structural traps. Two peak temperature values(80-90 ℃, 110-120 ℃) are found in Kela gas field, while three peak temperature values(90-110 ℃, 120-130 ℃, 140-150 ℃) are found in Dabei gas field, and one peak temperature value(140-150 ℃) is found in Keshen gas field, among which the first peak value becomes higher from north to south. Tectonic evolution further reveals the charging difference in different structural locations controlled by multiple episodes of fault activities and trap forming periods. As a result, it is speculated that dry gas reservoirs formed in Late Kuqa-Quaternary can still be discovered by successive explorations toward south. © 2015, China University of Mining and Technology. All right reserved.