| Zhongguai Uplift,rich in oil and gas resources,is located in the western Junggar Basin,close to three hydrocarbon-generating depressions,named depression in the West of Pen-1-Well,Shawan Depression,and Mahu Depression.Faults and unconformities are very developed,showing favorable hydrocarbon accumulation conditions.In this uplift,there are oil and gas discoveries in different layers from the Jurassic to the Carboniferous.However,the exploration degree of the Carboniferous is relatively low compared to above strata.In addition,there are many different kinds of volcanic lithologies and numerous tectonic movements,resulting in a complicated hydrocarbon accumulation condition.In view of the lack of research on the reservoir formation models and controlling factors for hydrocarbon accumulation,it is necessary to systematically study the characteristics of volcanic reservoirs,summarize the controlling factors of hydrocarbon accumulation,and establish a reservoir-forming model in this area.Based on the identification data of thin slices,drilling,well logging and core description data,concluding that the Carboniferous volcanic reservoirs in Zhongguai are mainly lavas and volcaniclastic rocks.The reservoirs mainly include pores,micro-cracks and erosion hole.The reservoir shows low porosity and low permeability as a whole,which can be divided into four categories according to porosity and permeability and pore structure.Lithologic lithofacies,fault structures and weathering and leaching can control the reservoir porosity and permeability by affecting the formation and subsequent alteration of pore seams,thereby controlling the reservoir's reservoir capacity.At the top of Zhonggua uplift,the mudstone or sandstone interbedded of the third member of Permian Wuerhe Formation,the second member of Wuerhe Formation and the Triassic Karamay Formation can be used as cap rock.Through typical reservoir anatomy,the Carboniferous reservoirs in the Zhongguai area have fault blocks,fault noses,lithology and fault-lithologic oil and gas reservoirs.Most of the crude oils show high density and high viscosity and belong to medium and heavy crude oils.The distribution range of crude oil solidification points is large,but most of them are neutral oils.The oil and gas along the plane are distributed along the fracture surface,and oil and gas are distributed in the vertical direction within 75 m from the unconformity surface.The oil source comparison results show that the source rocks of the Wuerhe Formation,Fengcheng Formation and Jiamuhe Formation of the Permian all contributed to the crude oil in the central depression,and the source of the Wuerhe Formation was dominant.The Carboniferous volcanic reservoirs in the Zhongguai uplift are controlled by lithologic lithofacies,faults,and unconformity structures.The reservoirs with good physical properties are the eruptive facies represented by volcanic breccia and the overflow facies represented by dacite and andesite;the three types of fracture systems,such as strike-slip,boundary,and secondary,are developed in the study area.In fact,the strike-slip faults provide oil source migration channels for the Carboniferous hydrocarbon reservoirs in this area.The secondary faults control the distribution of oil and gas reservoirs;the top boundary of the Carboniferous system develops a wide range of unconformities,and the type of transport is mainly macro-overlapping.The integration of lateral and lateral + vertical conductances combined with micro coarse-coarse and fine-coarse provides channel conditions for hydrocarbon migration.The study shows that the reservoirs in this area have the characteristics of new-generation paleo-reservoir,near-source hydrocarbon supply,fracture,unconformity transport,and multi-source hydrocarbon supply.Crude oil undergoes two phases of reservoir formation and one-stage adjustment to form the current distribution pattern. |
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