The Characteristics Of Zhangwu Fault Depression And Its Oil-gas Distribution

Songnan area in recent years has shown a good momentum of exploration.At present in many rift found a good oil and gas shows, submit the proved reserves of nearly100million tons in its neighboring area. In201150000000tons to forecast reserves in Zhangwu fault, Last year, Sinopec northeast oil and gas company actualized Zhangwu1wells found the flow of oil in Shahai formation, and Zhangwu2wells obtained industrial oil flow in Jiufotang formation, achieved a major breakthrough in oil and gas exploration in this area.In recent years, China petroleum and Sinopec concentrate superior power, through the seismic, logging, geological exploration and so many kinds of research methods and carry out large-scale exploration and research work for many fault depression in southern Songliao Basin, they learned a further information about the distribution characteristics, sedimentary background, hydrocarbon generation condition and the reservoir rock characteristics of Songnan area. Petroleum geologists are aware of Songnan area not only Lujiapu fault depression has greater potential for exploration, the eastern Zhangwu fault depression also have same potential for exploration. The output industrial oil flow of Zhangwu1wells and2wells, confirmed the good oil and gas exploration prospect.The comprehensive application of drilling, well logging, core, outcrop and seismic data, researching on the characteristic of Zhangwu fault depression stratigraphic. On the base of research of the stratigraphic characteristics, through the interpretation of2D seismic data fine structure in the stratum of Zhangwu, clarified the structural features and evolution characteristics of Zhangwu fault depression; Combining with the sedimentary core, single well and well facies, subfacies and microfacies study, determined the basin filling evolution model;Through the integrated use of geochemical data, reservoir physical property data and reservoir description data,we determined the faulted reservoir geological conditions, and on this basis, summarized the characteristic of the distribution of oil and gas. Through careful research, we conclude that:1、Zhangwu depression was formed in the early Cretaceous, located in the southwest of Songliao Basin. From the basin formation characteristics of the early Early Cretaceous, it represented magmatism and hot mantle upwelling, extensive volcano eruption along the fracture zone, the accumulation of the Yixian Formation of a volcano rock interbedded sedimentary rocks. With the extension of crust and faulted strengthen, it deposited Jiufotang formation, Shahai formation and Fuxin formation. In the middle and late Fuxin formation deposition, because of dissipated in mantle heat, weakened in crustal extension, crustal uplifted and then denudated.The evolution of Zhangwu rift ended.2、Controlled by the old tectonic and sedimentary characteristics of tectonic movement, Sedimentary characteristics of the fault depression is near source rapid accumulation. Zhangwu fault depression mainly developed volcano facies. alluvial fan facies, fan delta facies and lacustrine facies. Yixian formation is the volcano petrographic; the facies of lower Jiufotang formation are shallow lake and deep lake facies, delta front; the facies of upper Jiufotang formation are shallow lake facies and fan delta front. Shahai formation mainly deposited alluvial fan facies, fan delta and shore-shallow lake facies; Fuxin formation mainly developed fluvial flood plain.3、Jiufotang formation developed dark mudstone in Zhangwu fault depression, to be the mian hydrocarbon source rocks, the lower Jiufotang formation developed good hydrocarbon source rock, it has large thickness, high abundance, good types, but relatively low maturity, the hydrocarbon source rock of Jiufotang formation of Zhangwu2well and Zhangwu3well in the mature, while Zhangwul well in the immature stage. Jiufotang formation hydrocarbon source rocks were deposited in a deep lake environment, The source of parent material mainly from the lower aquatic plants, mixed some terrestrial higher plants. From the rift deep depression to the high position of slope,the more close to the edge of the basin, the more mixed terrestrial higher plant, This leads from the rift deep depression to the edge slope, the Jiufotang hydrocarbon source rock organic matter type becomes gradually worse. It also reflects the transition trend of organic development of rift deep depression in reduction environment gradually becomes weak oxidable and weak reductive environment to the edge slope.4、It is mainly the clastic reservoir in Zhangwu fault depression, the reservoir lithology of Shahai Fm. is mainly lithic sandstone, with low compositional maturity, medium-sorting, grain-supported structure, and mainly pore cementation. In the aspect of physical properties, the average porosity of Shahai formation is17.6%and the average permeability is106.9md, which belongs to medium porosity and medium-low permeability reservoir; The reservoir lithology of Jiufotang formation, is mainly feldspathic sandstone, with low compositional maturity, medium-sorting, grain-supported structure, and mainly pore cementation. In the aspect of physical properties, the average porosity of Jiufotang formation, is11.2%and the average permeability is11.7md, which belongs to medium-low porosity and medium-low permeability reservoir. 5、The Zhangwu fault depression has a complete source-reservoir-cap combination: it has a set of hydrocarbon source rocks, that is dark mudstone of Jiufotang formation, it develops three sets of reservoir, that is the lower segment thin sand body of Jiufotang formation, the upper and lower segment fan delta and lower Shahai formation fan delta reservoir. From the longitudinal and transverse, we distinguish three types of effective reservoir combination:self-generation and self-reservoiring type, lower-generation and upper-reservoiring type, upper-generation and lower-reservoiring type.6、Oil and gas reservoir in Zhangwu fault depression has the characteristic with the Jiufotang formation reservoir monolayer thin(less than3m) and many layers in vertical; while with the Shahai formation reservoir shallow buried depth, distribution of concentration.7、In terms of oil-gas distribution pattern:near the oil source is a prerequisite for oil and gas accumulation, favorable sedimentary facies belt is the foundation for the oil and gas bearing traps; fault, at least broken away from the larger fault less developed, is the main geological factors in reservoiring of Jiufotang formation in Zhangwu fault depression.Possibly, the steep slope zone is favorable for hydrocarbon migration and accumulation. Thin sand body of lower segment in Jiufotang formation may also be favorable exploration target.