The Relationship Between Fracture Characteristics And Hydrocarbon Accumulation Of The Carboniferous—permian In Hashan Region

Hashan region, the northwestern margin of junggar basin, has good petroleum geological conditions and exploration prospects. Currently, oil and gas exploration direction of Hashan region has been converted from shallow clastic sequence to deep complex volcanic strata, the carboniferous and Permian volcanic rock reservoirs gradually become the focus of the oil and gas exploration. Because Hashan region has undergone multiphase tectonic movement intensely, overthrust fault and associated fracture extensive development in carboniferous and Permian. Different types of tectonic fracture have great differences in hydrocarbon accumulation activity.Therefore, to identify tectonic fracture development characteristics and the relationship between hydrocarbon accumulation of the carboniferous and Permian of Hashan region has great theoretical and practical significance for volcanic rock reservoir exploration and development.This thesis mainly research on the Carboniferous and Permianof Hashan region in the northwestern maigin of jungger basin.The petrological characteristics of the Carboniferous and Permian was studied in detail. This thesis was guided by the research of Hashan region tectonic evolution. By using drilling core, cast sections, imaging logging, seismic data interpretation rock machanics tests and geochemical of fluids comprehensive analysis technology, this thesis studied the fracture characteristics, divided its stages and established the relationship between fracture stages and hydrocarbon accumulation, discussed the mechanism of effective fracture formation and predicted the distribution of effective fracture. Finally, this thesis has made on certain achievements and knowledge as follows:(1)The rock types is diversity in Hashan region and the reservoir lithology was controlled by volcanic lithofaces. The fracture’ development of reservoir is controlled by tectonic activity, and the quality of pyroclastic reserviors is the best.(2)By observing the drilling core, it is found that the carboniferous and the Permian in Hashan region mainly develop high angle fracture and accompanied by low angle fracture,vertical fractureor mesh fracture. The fracture of imaging logging data statistical result shows that reservoir mainly develops high angle fracture which is toward northwest, and the density of high conductivefracture is significantly higher than resistivefracture, which illustrates that the reservoir structural cracks of carboniferous and the Permian have ideal fluid channel capacity and effective ability for gas accumulation.(3)Through stable isotopic geochemical analysis on the strontium, carbon and oxygen of the filled carbonate mineral in fracture,a result can be concluded that there are three formation mechanism of carbonate mineral:①mantle source or deep fluid origin,②atmospheric fresh water transformation origin,③hydrocarbon contamination or transformation origin.(4)The fluorescence characteristics and uniform temperature of fluid inclusion in fracture filling mineral show that multiphase active fluid exists in carboniferous system and Permian system fracture, of which the fluid temperature includes four main range: <50℃, 60~85℃, 90~130℃, >130℃, however, the hydrocarbon inclusions mainly exist in the three higher range.(5)The results of rock mechanics test shows that the carboniferous and Permian mudstone has maximum comprehensive strength, however, the basalt is minimum. Theoretically, when the tectonic stress field is under the same intensity, the structure development degree of the lithology in stratum from high to law is: basalt > volcanic breccias>tuff>mudstone. This thesis considers that the intensive development section of tectonic fracture in carboniferous system and Permian system are primarily controlled by the tectonic position in carboniferous system and Permian system which the lithology located through the analysis of the controlling factors of the rock.(6)By analyzing tectonic evolution of Hashan region, and the relationship between time of faulting activity and characteristic of its associated fracture, this thesis argues that the fracture of Carboniferous and Permian mainly formed in indosinian. which can be divided into two classes and four periods.The first class(filled fracture):①low angle fracture in the End-Permian tended to southeast,②netted fracture in the End-Permian.The second class(opened fracture):③high angle fracture in Early-Middle Triassic tended to northwest,④low angle fracture in Early-Middle Triassic tended to southeast or north west.(7)The research of fluid geochemistry shows hydrocarbon injection of Carboniferous and Permian experienced three periods including late Permian,late Triassic and late Cretaceous.The periods of hydrocarbon injection was well matched with the opened fracture formation time. Therefore, the latest two periods opened fracture is great significance for hydrocarbon migration and accumulation and belong to effective facture.(8)The effective fracture mainly distributed in the scope of F3, F4 fault and the area of Carboniferous volcanic rock influenced by F3,F4 fault.