Fracture Development Characteristics And Reservoir-Controlling Effects Of Longmaxi Formation Shale In Yongshan-Daguan Area,Northeast Yunnan

The Yongshan-Daguan Area is located in the northwest of the North Yunnan-Guizhou Depression.Affected by complex tectonic environment,in the area,the fractures of Wufeng-Longmaxi Formation shale are usually developed and there are few researches on shale reservoir fractures.The research of fracture development and its control on hydrocarbon accumulation about shale reservoir in the study area not only refines the characterization of shale gas reservoirs in this area,but also enriches the theories of shale gas enrichment about fractured reservoirs in complex structural areas.In this thesis,based on field survey,experimental analysis,and numerical simulation,combined with the data of drilling and logging,the analytical methods of structural geology and reservoir geology are used to study the development,formation time,influencing factors and spatial distribution of fractures in organic-rich shale of Wufeng-Longmaxi Formation in Yongshan-Daguan Area and the influence and control of fracture development on shale gas enrichment.The following key insights are gained:（1）In the shale reservoir of Wufeng Formation-Lower Longmaxi Formation in the study area,the type of kerogen isⅠ,the average TOC is higher in the north where it is more than 1%with lower in the south,and the degree of thermal evolution is high to over mature stage.The average brittle mineral content is 67.86%,the average pore volume is 0.0405 cm³/g,with microporous contributed the most,and the average specific surface area is 19.3503 m²/g,which is basically contributed by mesoporous and microporous.With an average porosity of 2.979%and permeability of 0.01105×10^-3μm²,it is an ultra-low porosity and ultra-low permeability reservoir.The thickness of organic-rich shale section is between 10～160 m,which is thick in the north and thin in the south.The shale gas accumulation conditions in the northern part of the area are better.（2）The fractures in the shale reservoir of the study area are mainly bedding fractures and high-angle structural fractures,with the development of slip fractures,abnormally high-pressure fractures and shrinkage fractures.The fractures are widely developed in the area and a complex network of fractures of various scales is formed.The formation of fractures is greatly influenced by the tectonic movement of Yanshan period.Fluid charging can be divided into four phases,and the salinity of fluid shows a trend of"down-up-down"with the decrease of homogenization temperature,while the sealing property of reservoir gradually deteriorates.The fracture development in the area is controlled by structural factors,such as period and magnitude of tectonic stress,and is influnced by non-structural factors,such as organic matter content,brittle mineral content.（3）The three types of logging curves,such as gamma ray,resistivity and sonic time difference,are well responsive to fractures.Based on the vertical prediction model of fractures constructed by R/S analysis method and AHP,it is considered that the boundary between Wufeng Formation and Longmaxi Formation,the lower and middle-upper part of Lower Longmaxi Formation are the strata with good fracture development.After analyzing the fracture development in the Himalayan period by numerical simulation of stress field,it is concluded that the target layer fractures formed during the Himalayan period are well developed in the northeast,southeast and middle of the study area,and their distribution is affected by tectonic morphology.（4）The development of fractures enhances the porosity and permeability of reservoir,and promotes the development of macropores under certain conditions.It has a dual effect on the gas bearing capacity of the reservoir.When the reservoir structure is simple and stable with sealing property well,the development of fractures promotes the enrichment of shale gas.There are four types of fracture and tectonic pattern assemblage patterns in the area,including wide-slow syncline,tight syncline,large fault and denudation anticline.Only in the wide-slow syncline type,fracture development promotes shale gas enrichment.Fracture development time affects reservoir gas content.The development of fractures whose formation time was coupled with the hydrocarbon generation time of reservoir,is conducive to the enrichment of shale gas,such as contraction fractures and abnormal high pressure fractures.The fractures,such as tectonic fractures,which are formed during uplift and destroy reservoir sealing,promote the escape of shale gas.In this thesis,there are 67 figures,13 tables and 160 references.