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Well che89, located in the Chepaizi area in the northwest margin of Junggar basin, acquires high production industrial oil flow, which is an important breakthrough in the exploration of the south foreland slope area of Junggar basin. The Chepaizi area is near two hydrocarbon generation depressions of Sikeshu and Shawan, which have sets of hydrocarbon source rock of Carboniferous to Jurassic as well as Upper Tertiary. Geological and geochemical parameters are proper for the accumulation of mixed source crude oil. Carbon isotope, group composition and biomarkers of crude oil in Upper Tertiary of well Che89 show that the features of crude oil in Upper Tertiary Shawan Formation are between that of Permian and Jurassic, some of them are similar to these two, and some are of difference, they should be the mixed source of Permian and Jurassic. Geochemical analysis and geological study show that sand extract of Lower Tertiary Wulunguhe Formation has the same source as the crude oil and sand extract of Upper Tertiary Shawan Formation, but they are not charged in the same period. Oil/gas of Wulunguhe Formation is charged before Upper Tertiary sedimentation, and suffered serious biodegradation and oxidation and rinsing, which provide a proof in another aspect that the crude oil of Upper Tertiary Shawan Formation of well Che89 is not from hydrocarbon source rock of Lower Tertiary.

Overpressure is widespread in the southern margin of the Junggar Basin, northwestern China. Pressure measurements in drillstem tests and repeated formation tests and estimates from wire-line logs indicate contrasting overpressure values between permeable sandstones and adjacent low-permeability mudrocks. In addition, excess pressure differs among anticlines with similar depth, lithologies, and geologic age, indicating significant lateral changes of overpressure. Major factors controlling overpressure generation and distribution include rapid sediment deposition, pressure compartmentalization by thick mudrocks, tectonic stress, faulting, and folding. Clay transformation and hydrocarbon generation are believed to be insignificant in overpressure generation in the southern Junggar Basin. Numerical modeling of pressure generation and evolution suggests that faulting and stratal tilting associated with folding are the most significant factors in the overpressure generation of a permeable sandstone. The extremely high overpressure (pressure coefficient up to 2.43) may have been caused by hydraulic adjustment within permeable sandstones associated with structural deformation caused by post-Miocene intense tectonic activities.

As proved by the analysis of growth strata and regional study, the intense tectonism of the Cenozoic in the northern margin of Tianshan Orogenic Belt initiated at about 10–7 Ma BP and associated with intense tectonic deformation, led to the formation of three thrust belts at the northern margin of Tianshan Orogenic Belt. The time of intense deformation is much younger than that of the southern Tianshan, which suggests that the tectonic deformation propagated from the southern Tianshan to the northern Tianshan due to the India-Asia collision. The intense deformation of the Late Cenozoic resulted in relatively gentle deformation in the western Uromuqi-Qigu anticline and widespread tectonic deformation transporting and retrogressing from the south to the north. The differential tectonic deformation indicates that the front of thrust belt is beneficial to hydrocarbon accumulating. Moreover, for the intense denudation and uplifting along the structure belt of foreland, structures with gentle deformation are advantageous to the preservation of oil and gas accumulating during the early phase.

On the basis of the pressure data ob- tained from the southern margin of the Junggar Basin, Northwestern China, the distribution and evolution of overpressures in high permeable sandy and in low-permeability shale formations are characterized. The evolution of overpressures in various structural processes, especially in erosion and mechanical de- formation, is quantified by numerical modeling stud- ies. The modeling results show that anomalies of high pressure observed in boreholes are likely a combination of several effects, i.e. 1) the compaction caused by overloading, 2) the compaction caused by lateral tectonic stressing, 3) lateral transmission of hydraulic pressure associated with fold formation, and 4) vertical hydraulic connection caused by opening faults crossing formations with different initial excessive pressures. The main mechanisms of overpressures and their distributions are defined.