The Research On Fault Control Of Hydrocarbon Accumulation And Preservation In The Thrust Belt Of Southern Junggar Foreland Basin

The southern Junggar foreland basin is an important oil and gas exploration field for the foreland basins in central and western China. In view of the problem that the relation of fracture, hydrocarbon accumulation and preservation is not clear at present, under the guide of fault-related folding theory and fault control hydrocarbon theory , the relationship of faults and the formation and evolution of traps, hydrocarbon migration and preservation had been studied detailly in this paper, and the models of reservoir migration and accumulation in the southern Junggar foreland basin wrere established.The active period of foreland thrust belt in southern Junggar foreland basin were divided into four stages: (1)normal fault-phase formation period of Carboniferous passive continental margin stage;(2) thrust fault formation period of Late Carboniferous-Permian peripheral foreland basin stage ;(3)faults'activities period of Cretaceous tectonic compression stage;(4) thrust fault formation period in renewable foreland basin since the late Tertiary. According to the fault active period and the layer broken by the fault, the faults were divided into two major type,basement-involved faults and detachment faults with detachment surfaces formed by three sets of detachment layers. According to the theory of fault related fold and the seismic profile, the formation and development process of basement-involved style and caprock detachment is analyzed, the features of partition and zone of tectonic style is defined.Oil and gas were characterized as multi-period accumulation and mainly formed in late period in thrust belt of Southern Junggar foreland basin, early paths of hydrocarbon migration were mainly sand bodies and unconformity surfaces, oil and gas migrated laterally to ancient uplift. In the period of regenerated foreland basin, the main paths of hydrocarbon migration were faults, oil and gas mainly migrated in vertical direction. The period of regenerated foreland basin missed the period of abundant hydrocarbon generation and expulsion from main source rock, the process of adjusting and damaging early reservoir by faults begins, and then secondary reservoir was formed. With respect to the formation time, spatial distribution, migration and accumulation process, reservoir and seal conditions of trap, the effectiveness of various traps was analyzed, it's considered that the drilling target in the thrust belt was the trap with all four aspects mentioned above, indicating the four types of favorable target models are: (1) trap in tectonic layers in thin-thin superimposed style formed in the Neogene; (2) the tectonic style of basement-involved structural style restricted by caprock generally involve better content of gas and oil, where formation of interest assembles in the mid-lower structure layers; (3) the lower tectonic layer traps in the thick-thin superimposed structure style may be favorable mode, if located in hydrocarbon migration path, the mid-lower structure of hydrocarbon-bearing layer is good; (4) the low part of tectonic layers in the basement-involved structural styles of inherited development, oil and gas accumulated in the early time ,while trap's integrity not undermined in late time.The internal structure and sealing mechanism in southern Junggar foreland basin was analyzed, the type of fault sealing and the evaluation method of fault sealing suitable to the Central and Western Areas of foreland basin is established. Also the fault sealing of Anjihai anticline, Kayindike anticline and West-Lake anticline is evaluated. It's considered that the main type of the fracture were sealed by clay smear and phyllosilicate /framework fault rock. The sealing ability of fault vary greatly for the same fault of different l formation as well as the same formation of different location .The main control factors of hydrocarbon accumulation in the thrust belt of Southern Junggar foreland basin: effective hydrocarbon controlled distribution of oil and gas; paleohigh control the early direction of hydrocarbon migration and distribution; oil sources faults control the distribution of late hydrocarbon; high-quality caprock becomes a critical factor for charging and preservation of oil and gas,fault sealing control the accumulation layer of oil and gas. Using the slippage area of faults and inclination reflecting transporting ability of oil and gas, the quantitative evaluation to fault transporting ability in the thrust belt of southern Junggar foreland basin was made. By proposing the method of evaluating the sealing ability of caprock to hydrocarbon allowing for fault vertical sealing and caprock quality, the comprehensive evaluation to the sealing ability of caprock to hydrocarbons, which were in the period of each renewable foreland basins, was made. According effective hydrocarbon, and efficient transporting and favorable preservation conditions, favorable enrichment region mainly distribute in the second and the third tectonic zone in the thrust belt of southern Junggar foreland basin is forecasted.