Abstract: In recent years, great exploratory achievement has been made by the discovery of a billion ton scale conglomerate oil field in Triassic Baikouquan Formation in the Mahu depression, Junggar Basin. From 3D fine structural interpretation of the Baikouquan Formation (located to the east of the Manas Lake) based on new 3D seismic data surrounding the Mahu depression, we found that the middle and deep sections of the area can be divided into four main structural layers. The Baikouquan Formation possesses well developed multiple fault systems which show strong regularity in horizontal fault distribution for various fault types. Faults not only control the development and distribution of deep and shallow structures, but also are closely associated with oil and gas reservoirs. Overall, five types of fault developed in the study area, where the thrust deep fault, formed under the strong extrusion stress of the Hercynian period and developed in the Indosinian period, controls the formation and development of the main bulge and nose structures in the Mahu depression. At the same time, these faults are important transport channels for oil and gas migration across formation from source to the Baikouquan Formation. Daily oil production, therefore, significantly inversely correlates with the distance to the thrust deep fault; traps near the fault have a higher probability achieving high production. Moreover, en echelon strike-slip fault developed along the EW direction, extending long distance horizontally and plugging oil and gas channels from above. Finally, The fault distribution correlates well with the distribution of reservoir developing areas.

Key words: Junggar Basin, Mahu depression, Baikouquan Formation, fault, reservoir control