Geochemical Characteristics And Resource Potential Evaluation Of The Hydrocarbon Source Rocks In Jurassic In Puguang Region

The Puguang region lies in the northeast of SichuanBasin, and the size of its exploratory area is about 1116 square kilometer. Tectonically, it is bounded on the north by the front fault-fold belt in DabaMountain over-thrust nappe tectonic zone, and the south by the gentle fold belt in central SichuanBasin. There develop the Qianfoya Formation and the Ziliujing Formation two sets of hydrocarbon source rock in the middle and lower Jurassic series in this region. Presently, the researches on the characteristics of distribution, evolution, generation and expulsion of the hydrocarbon source rock, and the recognization of resource potential, as well as the evolutive history of hydrocarbon generation are not profound, especially on the main period, scale, size of generation and expulsion.Based on the systematic researches of the sedimentral and structural background in this region, using seismic and drilled date, and coupled with the experienced tectonic stages after the deposition in Triassic, the tectonic activity characteristics in different stages and its influence on hydrocarbon source rock transformation and petroleum entrapment are analyzed, the recovery of the erosion thickness in the sedimentary discontinuity is carried out. Taking advantage of the analysis on abundance, type, maturity of the organic carbon, and the chemistical methods of pyrolytic analysis, microscopic examination of the kerogen, the foundmental geochemical characteristic of hydrocarbon source rock in the middle and lower Jurassic in Puguang region is studied. The results show that the content of organic carbon in the hydrocarbon source rock in Qianfoya Formation is 0.4 percent to 2.89 percent, with an average of 0.88 percent, and the medium and the fine occupy 50 percent; the content of chloroform asphalt "A" is 0.0011 percent to 0.0274 percent, with an average of 0.0066 percent, the total hydrocarbon content has an average of 7.21 parts per million. The two sets of hydrocarbon source rock mainly develop the “III” type organic matter, and partly the “II” type. The average percent of the “Ro” is around 1.9, already reaching high mature to over-mature stage. In the recovery result of the erosion thickness, the erosion thickness in YanMountain stage and Xi Mountain stage is huge, lying between 2295 meter and 3654 meter. In plane, the erosion thickness is huge in upheaval tectonic zone and thin in depression.Different index are clarified after summarizing test date and consulting literature date. The amount and stage of hydrocarbon generation and expulsion in the middle and lower Jurassic in Puguang region is analog computed with the help of software Petromod in basin simulation. Result shows that the source rocks in Ziliujing Formation enter the hydrocarbon generation threshold in the middle of Middle Jurassic, and its “Ro” value reach 1.3 percent(high mature stage) in the late of Early Cretaceous; The source rocks in Qianfoya Formation enter the hydrocarbon generation threshold in the late of Late Jurassic, and its “Ro” value reach 1.3 percent(high mature stage) in the late of Early Cretaceous. Total quantity of gas resource in the hydrocarbon source rocks in Jurassic is 65.333 billion stere, including 28.704 billion stere in the Ziliujing Formation and 36.629 billion stere in the Qianfoya Formation.Research shows that the distribution of the organic carbon content in the two sets of hydrocarbon source rock is uneven, belonging to medium and fine hydrocarbon source rock, but the better source rock develop locally. The type of kerogen in source rock is mainly the “III” type, and the maturity all get into mature to over-mature stage, bearing gas wholly; Integrated the geochemical characteristic, the simulation of heat evolution with the resource computational result in the two sets of hydrocarbon rock, this region is of huge resource potential and high developmental potential.