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The Research of Hydrocarbon Accumulation Regularity of the Sandy Conglomerate in Haiwaihe Nearshore Submerged Fan


The nearshore submerged fan is developed in the steep slope belt of a fault depressed lake which is characterized by the rapid sediment and frequent facies changes. Reservoir heterogeneity is strong, and effective reservoir prediction is very difficult. Oil and gas accumulation controlling factors are complex,and exploration success rate is low. Haiwaihe tectonic belt is a nose structure controlled by Haiwaihe-Hainan fault in the western central rise of Liaohe Depression in the Bohai Bay Basin. The sandy conglomerates in the nearshore submerged fan are deposited rapidly in the 3rd member of the Oligocene Shahejie Formation (E3s3) controlled by the continuously active boundary fault. Several exploratory wells were drilled as the high positions of structural reservoirs and did not produce commercial oil flow. Haiwaihe-Hainan fault is divided into 3 segments including southern, central and northern parts, and the difference in segment motions of faults controls depositional effects. There are three major sedimentary fans which are controlled by three ancient valleys, by researches of palaeo-geomorphology in the sedimentary period of the sand conglomerate. Further use of facies-controlled inversion, various attributes of dip formation, analysis of compression attributes and so on, the nearshore submerged fan is divided into fan-root, fan-middle and fan-front. We subdivided 5 developing stages of fans, predicted the thickness of sandy conglomerate, and hydrocarbon detection is also implemented. Based on analyzing of configuration between the fans and oil-gas systems and experiences of area nearby, it is considered that reservoirs in fan-middle with proper burial depth are of good physical property, and contacts hydrocarbon source rocks directly with good sealing ability of fan-root, which is highly full of oil and gas enrichment, on the contrary, structural high part is low enrichment. Through the researches above, advantaged objectives are evaluated with changed exploration ideas. New exploratory well is drilled through thick sandy conglomerate of fan-middle in Haiwaihe fan which produces over hundreds of tons industrial oil flow per day and confirms large-scale reserves.