Carbonate Conduit System And Its Relation With Hydrocarbon Distribution In Tahe Oilfield

Tahe oil field is the largest marine carbonate oil & gas field both in the Tarim basin and in China.Oil and gas exploration and exploitation are strongly restricted by the complex hydrocarbon migration and accumulation in this area.The study on the carbonate conduit system and its relation with hydrocarbon distribution has great theoretical and practical significance to the reasonable recognition on hydrocarbon distribution,the prospecting on the favorable areas and the popularization of conduit system controlling on hydrocarbon.The faults and fractures formed during the period of the early Hercynian and the late Hercynian are the important conduit type for the hydrocarbon vertical migration. The development of faults and fractures has the feature of zonation.Laterally, hydrocarbon reservoirs distribute along the faults as a beaded shape;vertically,the reservoirs that faults reach have the relation with faults more or less.According to the analysis on the conduit validity based on the performance data of reservoir development,the conduit effect in the north is better than that in the south,the central area better than the east and west,the vertical faults better than the lateral ones.According to the lateral comparison between wells,the oil-bearing formations development has close relationship with the unconformity and is directly controlled by the space distribution of unconformity.Hydrocarbon distributes mainly between the 60 to 150m below the unconformity.The top surfaces of Yijianfang Formation and the Yingshang Formaiton have a favorable oil & gas show,and the upper formations have a week oil&gas show.The traceability of the oil & gas profile and the oil&water profile proves that there exist important conduit effects of unconformity on the hydrocarbon lateral migration.Karst holes or fracture(including suture) develop greatly in the Tahe oil field and have the same distribution features as the faults.The vertical zonation of them can be verified by the logging information of oil&gas wells.The karst development models can be concluded into stageⅠand stageⅡ.The oil & gas show in suture(especially the one in the Lower Ordovician) and the data between wells prove that the suture is important conduit pathway for hydrocarbon in the karst holes or fractures.Laterally, oil&gas develop greatly in the areas where karst holes or fractures intensive develop; vertically,the strong heterogeneity results in the complex direction of hydrocarbon migration and the weak regularity.Fault(fractures),unconformities and karst holes or fracture(including suture) overlap,cross and connect to each other,forming the 3-D conduit system of "layer-surface-net" and the conduit effect is sectional.Fault,unconformity and karst holes or fracture are the main conduit type in the main body area which is relatively complex;Fault and unconformity are the main conduit type in the surrounding areas, which is simpler.2 different conduit system models are established for the main body area and the surrounding areas.Finally,the south area of Block 7 and the northwest area of Block 2 are the favorable areas for future exploration and the fluid potential can prove the prospecting.