The Research Of Reservoiring Pattern And Main Controlling Factors Of Natrual Gas In Heidimiao Oil Layer In The South Of Daqing Placanticline

The two local structures of the south of Daqing placanticline' main part are Putaohua structure and Aobaota structure,which the northeastern Puxi nose develops in.The nose which is cut by the northwesten fault forms some northwesten noses.Successive development is the character of three local structures,whose area gradually increased,with gradual reduction of the amplitude of structure. Putaohua and Aobaota structures are asymmetric anticlines which gradually steep from east to west. The range and amplitude of the two structures are controled by the efflorescent dense fracture zone.There are three modes of tectonic inversion: fault reversal structure, fold reversal structure and hybrid reversal structure.Underwater is the sedimentary main period of nen-3 member and nen-4 member, the sedimentary environment of which is delta front subfacies and prodelta subfacies,except for delta plain facies.The direction of sand body genereral distribution is north-south.The central area is banding sand body.The sand thickness of study area gradually thin out from north to south.The east and west sand body is thinner.There are three sources of natrual gas:thermogenic natrual gas from Qingshankou group has the same source of Putaohua oil layer, bionatrual gas from Nenjiang group and mixture natrual gas made by deep carbon dioxide.The main channels of natrual gas migration from Heidimiao oil layer are fractures and sand bodys. The evaluation grade of H11 and H12 sub layers' cap rock mainly is middle, the sealing ability of other sub layers becomes better and better from up to down.The main control factors of natrual gas accumulation are source-faulting, cap rock and trap.The main period of natrual gas accumulation in Heidimiao oil layer is Mingshui member and Paleogene, when massive natrual gas which has been expulsed by the source rocks of nen-1 member and nen-2 member is transformed into Heidimiao oil layer by the source-faults in the active period ,then the natrual gas is formed reservoirs by accumulation.The natrual gas which is generated and excreted from nen-1 member and nen-2 member underlying source rocks upward migrates into Heidimiao oil layer by buoyancy along source-faults which pass T1 and T06 reflecting horizon;and lateraly migrates for a short distance, then comes into traps whose type may be block fault, fault barrier, fault-lithology or anticlinal trap for forming reservoirs by multidisciplinary analysis of natrual gas accumulated reservoir' conditions.The comprehensive evaluation of oil-natrual gas possibility of traps shows that Puxi-2, Puxi-3 and Xinzhao-3 sub oil layers in H1 oil group and Puxi-3, Puxi-2 and Xinzhao-2 sub oil layers in H2 oil group are the favorable areas for the next natrual gas exploration.