Structural Evolution And Good Exploration Target Appraisal Of Qigu Fault-Fold Belts

There is abundant of oil and gas seedings in the south of Junggar Basin, as a result, the region attracts many of petroleum geologists. But the region is next to the north of Mount Tianshan, influenced by squeezing action because of Mount Tianshan uplift, structural form of this region has diversity and complexity and structural form of Qigu fault-folded belts is the most complicated.Aimed at diversity and complexity of Qigu fault-folded belts, based on surveying evolution of mountain, formation development of region, water system change, seismic data explanation, petroleum geological conditions assessment, directed by swell and shrink of earth, theoretical geology, combining geology data, key seismic profile explanation fruit, drilling and formation testing data, standard strata profile of Toutunhe Formation, Qigu structure data, the main structural characteristic of Qigu fault-folded belts is studied in this paper, including tectonic flexible plait, sturcture layering in vertical, surface feature of tear fault, tectonic slippage face characteristic, detachment mechanism, unconformity, molasse formation, source characteristic and stream terrace which is ignored by petroleum geologist. The research result of tear fault provides reliable theoretical basis to explain forming of Changji anticline, the analysis of detachment mechanism make us know the cause of Qigu faul-folded belts. Unconformity and stream terrace characteristic study help us recognize that moutain evaluation has some influence to Qigu fault-folded belts.We have clear recognization about typical structural phenomenon of the region by studying strucrual characteristic of Qigu fault-folded belts, in order to understand structural evolution characteristic we use the theory of swell and shrink of earth to divide Mount Tianshan evolution process into four stages, as follows:uplift stage in later Miocene, lateral extrusion fold stage in early Pleistocene, large fault-folded belts sliding nappe stage in middle Pleistocene, uplift and adjust stage in late Pleistocene. Combining divided result of Mount Tianshan uplift stage in late period, based on angular unconformity of Dushanzi Formation in key seismic profile(N8626) and Toutunhe-Haojiagou standard strata profile, the structural evolution process of Qigu fault-folded belts is divided into four stage:tilt stage in late Miocene(about5.332Ma), fault-folded stage in early Miocene(about2.590～0.781Ma), detachment stage(about0.126Ma), wedge stage(about0.0117Ma). These four stages are corresponding with Mount Tianshan evolution stages.The research fruit of structural evolution is finally used to guide oil and gas exploration, abundant of oil and gas seedings of Qigu fault-fold belts in the south of Junggar Basin and exploration and development practice have already proved that the south of Junggar Basin has whole oiliness characteristic. Based on the investigation of petroleum geology condition and other data, every factor of hydrocarbon accumulation is analyzed in this paper. Accumulation model of three structural zones in the south of Junggar Basin are analyzed and compared. The analyzed result is that the hydrocarbon accumulation condition of Qigu fault-fold belts is good and it has certain condition to form large scale reservoir. At the same time, because structural evolution patterns of three structural zones are different, hydrocarbon accumulation model is very different, but they have the same characteristic(many resource, many stage, complexity). Aiming at this complexity, we use theory geology age divide hydrocarbon accumulation process, construct the relationship between climate and hydrocarbon accumulation function, obtain the new cogntion.