Triassic Oil And Gas In Western Sichuan Fog Zhongshan - Lotus Mountain Region Forming Conditions

With the guidance of petroleum system theory and by applying the principles of petroleum geology, structural geology, sedimentology, geophysics, geochemistry and reservoir geology, this study focuses on the conditions of pool formation in the Upper Triassic Xujiahe Formation in Wuzhongshan-Lianhuashan area, western Sichuan basin. Based on a large quantity of analytical data from gas, gas condensate and core samples from discovered Upper Triassic reservoirs and wells with oil and gas shows, reservoir geochemistry studies, such as source rock evaluation, gas provenance analysis, gas pay zone/water zone discrimination and mode of hydrocarbon migration-accumulation, have been carried out. In the meantime, stresses have also been laid on the study of distribution of reservoir bitumen and reservoir facies, reservoir rock correlation and trap assessment, with the help of field observation, well log correlation and new techniques of seismic tracing. Comprehensive analyses of the success and failure of previous exploration and the factors controlling oil and gas enrichment have been done; efforts have been made to reveal the regularity of oil/gas migration and accumulation; a mode of pool formation within the Xujiahe Formation in Wuzhongshan-Lianhuashan area, in accordance with the geologic character, has been established; a systematical evaluation of conditions of pool formation in the area under study, has been carried out, and favorable exploratory targets have been proposed. The improved Understanding gained from the above work provides a basis for the scientific decision making in well site selection in future exploration planning.Through the present study the following results are obtained:1. Characteristics of sedimentology and reservoir rock distribution are systematically analyzed and described, and have been proven by exploration.2. Through comprehensive correlation and analyses of gas composition, carbon isotope, gas condensate and reservoir bitumen on samples from more than ten wells penetrating various zones of the Xujiahe Formation, it is found that relatively distinctive criteria exist for the three source beds (Xu-1, Xu-3 and Xu-5), and thus the origin and main source bed for the individual gas pay zones of the Upper Triassic are determined.3. After anatomizing the Xu-2 oil reservoir on the Huojing structure, it is concluded that the oil found in the reservoir is the leftover of a previous gas condensate accumulation, with the free gases having escaped. This new realization and point-of-view is of significance in guiding future gas exploration in the area under study.4. A comprehensive Anatomy of the regularity of pool formation in the southern area in western Sichuan was carried out, the major controlling factors of pool formation were systematically summarized, and a mode of pool formation consistent with the geological character of the area has been established.5. On the basis of comprehensive studies on the major factors controlling the pool formation, predictions on favorable reservoir zones and traps have been made. As a result of drilling target optimization, three drilling sites are proposed.