Integrated Trap Description And Assessment Of Prospects In Xianhe 3D Block Liaohe Western Depression

Xianhe block is located in the shallow water area of Bohai Bay with an area of 100 km2. Geologically, it lies on the footwall of Hainan No.l Fault within Liaohe Western Depression. Two exploratory wells, LHl-1-1 and Shi-1, have been drilled and there are oil and gas shows in Sha-1, Sha-2 and Sha-3 segments in Shi-1 well, which actually is drilled on the Xianhe Structure. However, reservoirs and traps has been the main concerns in the exploration of hydrocarbons in this area. This paper uses the 3D visualization technique and all geological and geophysical information available to characterize traps and perform prospect evaluation.Several normal faults within the Hainan Fault Zone constitute a fault-step zone and form a narrow and steep zone, which controlled the development and distribution of depositional systems in this area. Near shore sub-aqueous fans, fan delta and delta occurred on the footwall of the Hainan Marginal Fault, whereas turbidity fans developed in the deep water area and the footwall of the Hainan No.2 Fault.As mentioned before Shi-1 well on the Xianhe Structure has showed good indication of oil and gas, especially in the Sha-3 segment. Observation from 3D visualization technology indicates that although Shi-1 well has not penetrated the main part of a turbidity, it did encounter the margin of the turbidity sand body. That demonstrates area around Shi-1 well is one of the potential areas, which are likely accumulating oil and gas.All Sha-1 and Sha-2 segments are characterized by over-pressure, indicating that the preservation conditions within Sha-1 and Sha-2 segments are good and hydrocarbon accumulations within them are likely formed and contained. Since over-pressure strata can prevent hydrocarbon in the underlying strata from dispersing, they can be considered as effective seals. The Sha-1 and Sha-2 segments in the Middle Step area are favorable for the accumulation and preservation of hydrocarbon reservoirs in Sha-3 segment. Therefore, prospects in Sha-3 segment should be considered as the favorite targets for finding bigger reservoirs and the Middle Step area should be selected to make abreakthrough in Sha-3 segment.In sum, since Xianhe block is located in the area between Hainan and Qingshui depressions, it has the exclusive advantage of getting hydrocarbons from the two depressions. Hydrocarbons in Sha-3 segment have been well preserved due to the development of over-pressure seals. Sha-1 and Sha-2 segments have potential in the Lower Step area. All indicate that Xianhe block has the conditions for forming medium size oil and gas field and therefore has great potential of finding oil and gas reservoirs.