Abstract:

The AmuDarya right bank area is one of the important overseas cooperative areas of the China National Petroleum Corporation. The structural feature of the Lowermiddle Jurassic series in this area is not understood well currently, which restricts the next exploration activity. In this paper, making full use of existing geological and drilling data as well as latecollective 3D seismic data, we investigate the structural feature of the Lowermiddle Jurassic series in the middle of the AmuDarya right bank area by tracing and matching of the strata surfaces, and further analyze the style of the structural trapping and their effectiveness in the formation of hydrocarbon reservoirs. The investigation indicates that four groups of faults develop in the Lowermiddle Jurassic series in this area with their strike being NWSE, nearly EW,NEESWW and NESW direction respectively, and there are obvious differences among their formation time, kinetic characteristics, evolutionary process and spatial distribution. Similarly, in this area develop three groups of fold structures with their strikes being NWSE, NESW and NNESWW, respectively. Under the influence of the structural development, the main type of structural trapping is anticline trap, which is often cut by faults and is remolded to form faultanticline composite trap. According to the main controlling factors of the trap development, the anticline traps could be classified into the anticline trap (Type A)that develops on the palaeohigh of the basement rock, and the compressive anticline trap(Type B) that develops in the Neogene era and is independent of the palaeohigh of the basement rock. The type A is drape fold in the early period and is reformed during the subsequent compressional movement, with being formalized in the Neogene era. There are obvious differences in the effectiveness of the formation of hydrocarbon reservoirs between various types of structural traps. The type A develops on the palaeohigh of the basement rock so that the reservoir of the Lowermiddle Jurassic series develops well. Contrarily, the type B is mainly located at the east of the research area, where the depositional water was so deep in the Earlymiddle Jurassic that the reservoir of the Lowermiddle Jurassic series develops badly. According to reconstruction extent of the subsequent compressional movement, the type A could be further divided into type A1 and type A2. The type A1 was reconstructed weakly during the after compressional movement, so the reactivity of the faults being located at the edge of the palaeohigh of the basement rock in the early stage couldnt destroy the primary oil gas pools of the Lowermiddle Jurassic series that were formed before Neogene completely with some native reservoirs saved. The type A2 was remolded so intensely during the after compressional movement that the reactivity of the existing faults or neogenic faults activity almost eliminate the primary oil gas pools of the Lowermiddle Jurassic series. As a whole, the effectiveness in the formation of hydrocarbon reservoirs in the Lowermiddle Jurassic series of the type A1 is better than that of the type A2, which is better than the type B.

Key words: AmuDarya right bank area, the Lowermiddle Jurassic series, structural feature, structural trap, the effectiveness in the formation of hydrocarbon reservoir