Study On The Main Factors Of Natural Gas Accumulation And The Exploration Direction Around The Baxian Sag In Baxian Depression

Source rock of Shahejie Formation in Baxian Depression generated abundant oil and gas, which is the key point of Huabei Oilfield's exploration in recent years. But the natural gas resources potential, especially the accumulation effect are not clear in this area. In this thesis, we have studied the occurrence and evolution of Shahejie Formation's source rock, we also evaluate the oil and gas generation ability, the migration and accumulation rules are studied systematically through the petroleum geology,geochemical and geophysical datas and the previous studies.There are several positions of source rock in Baxian Depression. Through the results of our evaluation, we conclude that the middle and lower Es3 and upper Es4 are the main source rock, and the resource of mature gas and high-mature gas is very rich. Mature and high-mature source rock mainly distribute in Baxian sag where is the center of hydrocarbon generation. All gas and oil in structural belts that around the Baxian sag come from Baxian sag, low-mature gas of Chaheji-Gaojiabao region comes from the underlied middle and lower Es3's source rock; the source of the low-lift region's oil and gas is Es3 which belongs to the downthrow block of Niudong fault, hydrocarbon in Wenan slop comes from the source rock of Es3 that inner the sag, hydrocarbon of the upper slop mixs with the oil and gas that come from the lower Es1.Different structural belts around the Baxian sag have different features of faults and associations of reservoir and cap. In view of different structural belts, we analyze the features of the faults and the affection to the accumulation of oil and gas, evaluate the reservoir and associations of reservoir and cap. We find that Shale Gouge Ratio(SGR) is a effective parameter for the evaluation of closure property of faults: SGR>0.6 sealing off the oil reservoir, SGR>0.7 sealing off the gas reservoir; the distinction of displacement pressure(ΔPd) of reservoir and cap:ΔPd>3,2~3,1~2,<1 are good,preferable moderate,bad associations of reservoir and cap respectively; establishing the standards of logging evaluation of carbonate reservoir.Dissecting the typical oil and gas reservoirs on every structural belt around the Baxian sag, analyzing the main factors of accumulation of oil and gas, establishing 4 patterns of accumulation of oil and gas: the pattern of differential oil and gas accumulation lower and upper of the Wenan slope,the pattern of oil and gas lost early and accumulate later accumulation on low-lift,the pattern of high-mature oil and gas accumulation in deep block buried hill and the pattern of low-mature oil and gas accumulation in rolling anticline of Chaheji and Gaojiabao. Combining the patterns of accumulation and the conditions of accumulation in different structural belts, pointing out that the buried hill around the Baxian sag and the lithologic trap in the area of sag are the target areas of next exploration. The buried hill around the Baxian sag consist of low-lift buried hill,Niudong step-fault buried hill and buried hill inside of the Wenan slope. Optimising the Niudong step-fault buried hill and buried hill lower of the Wenan slope, analyzing the exploration prospectives of the lithologic hydrocarbon reservoir in the area of sag.