Abstract:

Maxi fault is the eastern boundary fault of Maxi trough, and is also an important oil-controlling fault. Based on the interpretation of a series of seismic profiles and the analysis of deformation characterisitcs along the fault, as well as the influence on the deposition, the fault can be divided into three parts or segments,i.e. the strike-slip part in the north, the major uplifting and subsiding part in the middle, and the splays in the south. The middle segment is located between Houliugusi and Nanmazhuang with an extension of about 11 km, the strike of the fault turns from nearly NS in the south to NNW in the north.It can be seen from the section that the fault plane is flat and straight,and steeply dipping to the west with an angle of about 60?. The fault movement has been strongest in the Paleogene and formed the Maxi trough in the footwall. The southern segment of the fault is located to the south of Liugusi and to the north of Hejian with an extension of about 12 km. A series of subsidiary faults that are dispersing to the south and the middle segment of the major fault formed a typical brush structural system. The throw and the dip angle of those faults decrease with depth, and finally flock together to a nearly horizontal detachment surface in the basment rock. It is kind of end effect commonly seen in the strike-slip and tenso-shear faults. The strike-slip fault segment in the north is located to the north of Nanmazhuang, and extends through the eastern side of Mozhou buried hill to Gaojiazhuang area in Baxian sag, with an extension of about 30 km. The fault became a strike-slip fault to the north of Ren 105 well. The plane is steeply dipping to the west and nearly erecting, and reflect as a straight line in seismic profile,and is characterized by narrow crushed zone in the basement and dispersing upward in the overlying rocks as flower-like structure, which is apparently the result of the strike-slip fault in later period. Maxi fault is actually a thrust fault zone developed in front of a large detached structure in the pre-Paleogene Fuping metamorphic complex.In Paleogene,a strong extensional rift formed under the effect of regional dextral shear and extensional stresses with Maxi trough to be in the thrown wall. Maxi fault underwent sinistral and dextral strike-slip movements at the end of both Paleogene and Neogene,which formed many associated structures, such as an echelon faults, diapiric structures, brush structures, flower-like structures,compressional anticlines, and pull-apart depression. The steeply dipping of Maxi fault and quickly subsiding of the footwall result in the Maxi trough to be rich in hydrocarbon source rocks, as well as to have the richest resources in Raoyang sag. Maxi fault also controlled the distribution of petroleum. Firstly, many traps have been formed along the fault through the multiple activities; secondly, faults become ideal pathways for oil and gas migration;thirdly,sandstones develop along the fault. Therefore,Maxi fault has not only controlled the source rocks but also controlled the distribution of oil and gas.

Key words: fault segment, associated structure, oil and gas, Paleogene, Maxi fault, Raoyang sag