The Comprehensive Research On Carboniferous Volcanic Rock Reservoir Of Zhongguai Uplift In Northwestern Margin Of Junggar Basin

Volcanic reservoir has been a new field of oil-gas exploration in recent years, and the comprehensive research on volcanic reservoir has important theoretical value and practical guiding significance. This paper takes volcanic of carboniferous system in the uplifting area with middle inflexion at the northwestern edge of Junggar Basin as the object of study, it conducts systematic research on the features lithology and lithofacies and distribution, features of fracture and law of development, reservoir feature and cause, main controlling factor of reservoir and others of the volcanic reservoir in the uplifting area with middle inflexion by using the materials including geology, well logging, well drilling, and experimental measurement. It will optimizes and establishes the comprehensive evaluation index of volcanic reservoir and implement classification and comprehensive evaluation on the reservoir. And it finally confirms the beneficial goal of oil-gas exploration by combing with oil-gas reservoir-forming regularity and practical production. This paper has mainly achieved results as below:(1) Based on the comparison and optimization through lithology identification technology on volcanic, it proposes the method to identify the lithology of volcanic rocks by genetic BP neural network technique based on calibrating conventional well logging parameters with core(slice). It applies samples of core(slice) to calibrate the conventional well logging parameters, uses genetic BP neural network technique to training the sample parameters, and establish mapping relation between the conventional well logging parameters and lithology. This method has high rate of identification of lithology, and is quite applicable for the identification and explanation of lithology, and it’s also the important premise and basis of the research on division of volcanic lithofacies and reservoir.(2) The volcanic reservoir of carboniferous system mainly contains volcanic lava(andesite and basalt) and pyroclastic rock(volcanic breccia and volcanic tuff). The lithofacies includes facies of extravasation and explosion; The explosive volcanic breccia and andesite of extravasation belong to the most beneficial lithofacies, which are mainly distributed in the central of the uplifting area with middle inflexion and Wuba area of the area with middle inflexion.(3) The fracture development of volcanic of carboniferous system will mostly form causative high-angle fracture and upright fracture, and the density of fracture is small with relatively close appearance and high filling degree. The fracture develop the most along the NE(50°±15°) and EW(85°±10°). There are four phases of the development of fracture. The development of fracture is largely affected by lithology and construction. The development of fractures in volcanic breccia and andesite is the most complete and the development of fractures near the horizontally upward fracture zone and area near the vertically upward weathering front is the most complete.(4) Through the fracture prediction and research on evaluation, it further develops and improves the technology of comprehensive prediction and evaluation on fracture of volcanic rocks. Firstly, by using the geological analogy, degree of rock failure theory, and extraction of seismic attribute, it forecasts the distribution of fracture development of volcanic rocks, and confirms the weight coefficients of results of fracture predictions by different methods, and then it conducts comprehensive prediction and evaluation of fracture with weight theory; with the reference of research results of effectiveness of fractures, it defines the distribution range of effective fracture development, overcome the limitation of fracture prediction by single method, and efficiently improves the precision of fracture prediction.(5) The volcanic reservoir has features of both fracture and pore, the reserving space mostly contains secondary pores and fractures. secondary pores are caused by weathering, leaching and dissolution during burial stage. Fractures are caused by tectonic movement. The thin pore structure(Type Ⅱ) is the main structure; the development of reservoir has experiences 3 diageneses and 5 evolutionary phases. The development of reservoir will be affected by lithology and lithofacies, tectonic movement, weathering and leaching, and diagenesis. The lithology and lithofacies decide the basic functions of accumulation and storage and pore type, and is the basis of later evolution of reserving space; The weathering and leaching can effectively improve the development degree of secondary pore, which is helpful for forming of effective reserving layers; The tectonic movement will strengthen the fracture development and improve reservoir physical property; The diagenesis determines the storage of primary pore and formation of secondary pore. And especially the weathering during supergene period and leaching and dissolution during burial stage both have important influence on the improvement of reservoir stratum.(6) Establish the comprehensive assessment index system aim at the volcanic reservoir stratum of Northwest Margin of Junggar Basin. According to the research of reservoir stratum main controlling factor, choose the qualitative parameter and quantitative parameter that control the development of the reservoir stratum to build the comprehensive assessment index system of the volcanic reservoir stratum, then classify and assessment the volcanic reservoir stratum. The results of the classification and assessment show that, reservoir stratum of Type I mainly developes near the apex of shell of the crust of weathering that next to fault zone longitudinally, and on the plane, it mainly distributes at high positions in paleostructure, and in the volcanic breccia of explosive facies and andesite of extravasation facies in the fracture development zone; The reservoir stratum of Type II is relatively far from the crust of weathering in the vertically upward direction, and on the plane, it largely develops at high positions in paleostructure, and in the andesite of extravasation facies and volcanic tuff of explosive facies which are relatively far from the fracture zone; The reservoir stratum of Type III primarily develops in the basalt and granite, and has the worst performance and little economic value.(7) Carboniferous system volcanic oil-gas distribution is mainly distributed along the three zones(close to fault zone, structural high part zone, beneficial lithofacies development zone), one side(near the plane of unconformity), integrate with reservoir stratum comprehensive assessment result and actual exploration, and confirm the next favorable exploration target area, the research result is significant for the exploration and development of volcanic oil-gas in the study area.