Characteristics, Mechanism of Faults and Impact on the Trap in Bachu Area of Tarim Basin, NW China
Yi Wang; Zhongpei Zhang
Most structural deformations in Bachu area of Tarim Basin were previously misinterpreted to be some kind structural attitude with an uplift occurring between two high-angle reverse faults. Latest field research and reintegration of seismic data by using the structural analysis method based on the theory of the maximum effective moment criterion(MEMC) show that there are actually conjugate kink zones on its both side limbs. The most angles between the zones is about 110°, and the anticlines or uplifts in between are of box shape. This range covers all the observations available from nature and experiments. The conjugate kink-band under the control of the MEMC is a common type of structural deformation in the area. Some structural styles in anisotropic rocks that were previously misinterpreted to be high angle reverse faults are more possibly of hinge zones of kinks. Based on the study results and exploration practices, we comprehensively analyzed kink-band geometry , formation mechanism and interpretation of seismic data. It is believed that the large kink-bands and conjugate kink-bands in the area are the dominant styles of structural deformations in the abdomen of the cratonic basin under the condition of compression. It is verified that there are a series of structure fractures with interspace dilatation, which is beneficial to hydrocarbon accumulation in the traps - kink-band related traps, and established the kink-band related trap model.
The identification features to distinguish between kink-band and fault zone on the seismic section have been established through a series of the seismic-geologic fine interpretation of seismic data and geophysical forward modeling. Focus on the analysis of the characteristics of the high Angle kink-band and low Angle thrust fault, interlayer fault and their relationship, can we learned that a series of large kink-bands and low Angle fracture zone of Bachu Area formed in Himalayan orogeny period make up the complicated structure style of the area, which are the results of coexist structures formed in different deformation stage under the background of continuous compression in the period.
The study indicates that the tectonic attribute of Bachu Uplift belong to the kind of large kink-band type anticline structure, overall structure style dominated in large basement involved kink-band in the deep layer and dominated in small and medium-sized kink-bands and thin-skinned thrust fault structures in the shallow level. The evolution of Bachu Uplift went through the stages of embryonic form of knee fold type ancient uplift occured in Tarim internal craton in the late Paleozoic, of uplift and denudation of the stratum in the Mesozoic, of significantly large kink-band type uplift structure and thrust faulting in the Cenozoic powered from kunlun orogenic belt system on the southwest margin of Tarim massif. There are two kinds of structure slope: one for kink-band itself (steep inclined slope belt), one for the gentle slope area in the periphery of the kink-band belt.
Accurate identification and discrimination of kink-bands from faulted structures by using geophysical data and in combination with field observation of geological structures is a new idea for searching for new type of structural traps. By the controlling of the large kink-bands tectonism occurred at the Himalayan orogeny, the two types of structural slope belt may control different types of reservoirs.
The kink-band belt (steep inclined slope) area is the favorable area to prospect for kink-band related reservoir in Ordovician, Silurian, Devonian and Carboniferous, and Selibuya - Mazhatage structural zone is as a representative of this kind.
Gentle dip slope belt area, take Maigaiti slop area as typical example of relative stable structure hinge region of experiencing seesaw movement along north-south that occured in the early and late two phases. The gentle dip slope zones formed at the late Caledonian and late Hercynian orogeny is the favorable area for prospecting the protogenetic reservoir formed in late Hercynian.
AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013