Shale Gas Reservoir Evaluation Of Da’anzhai Member In Ziliujing Formation Of Lower Jurassic In Eastern Sichuan Basin

Shale gas using had made a great success in North America and other European countries with to broaden the space of energy exploration and provided a new vision for us.With the shortage of energy,unconventional energy which represented by shale gas had attracted attention.The previously exploration of shale gas in North American had proved that the organic carbon content,organic matter maturity,and mineral composition would control the shale gas.The exploration of shale gas need to adopt advanced technology such as horizontal drilling and large pieces of fracturing,and also requires in rich water resources.In addition,the problem of pollution is an important reason in limiting shale gas exploration.Nonetheless,shale gas exploration is very important for our country which has a huge shortage of energy,in 2011,China’s ministry of land and resources assessment of China’s shale gas recoverable resources about 25×10¹² m³,in recent year shale gas exploration has made significant progress,but overall still belongs to the early stage.Since 1953s,the Sichuan basin start drilling exploration,to build up five oil and gas fields,proven geological reserves of 81.1836million tons,among them the top village segments accounted for 93%.Thus,including shale gas,it is a fact that Dan an walled section is rich in oil and gas reservoir,but the particularity of reservoir in Dan an village section make it hard to objective evaluation,and the same problem in other shale gas reservoirs have been met.As a typical unconventional oil and gas resources,the core issue of shale gas is different from to find traps as the main target of conventional oil and gas exploration,as the main target,but looking for reservoir and reservoir space of the shale reservoir recognition and quantitative analysis,classification,connectivity or holes,seams and controlling factor analysis has been plagued reservoir study of the technical difficulties.The paper based on the field profile observation and indoor thin section identification,application of argon ion polishing),field emission scanning electron microscopy technology,X-ray diffraction,physical property data and rock mechanics analysis and so on,to explore Da an village of shale gas reservoir fracture and the development of nanoscale pore characteristics,on the basis of the screening evaluation parameters,establish the Da an village section of shale gas of reservoir evaluation standard.In the northwestern Sichuan basin tectonic unit belonging to Yangtze massif,the west respectively the LongMen mountain thrust nappe belt and Songpan ganzi fold belt,the north close to the Qin Ling tectonic belt MiCangShan-Daba mountain thrust nappe belt.Scope of the basin in the LongMen mountain fault,for the west side,seven step fault in the east side,and mount Emei-clay fracture for the south side southward,where fracture for the north side.On the basis of the field profile observation and indoor thin section identification,combined with logging,think the top village for a full assault-lake sedimentary cycle.Plane,around the center of the lake basin subsidence and sedimentation centers,the development has in turn ring zonal distribution of semi deep lake,shallow lake and lakeside sedimentary subcaches,the shallow lake subcaches according to the characteristics of sediment can be divided into carbonate shallow lake and erogenous clastic shallow lake 2 types,sedimentary fancies and logging response model is set up and model.Application of argon ion polishing and field emission scanning electron microscopy technology in east Sichuan region Da’anzhai Section of shale gas reservoir pore types and their characteristics are studied,determine the six types of pore development in reservoir:（1）organic matter scattered on the surface of nm level pore,poor connectivity;（2）the hole in the granules,mainly pyrite strawberry hexagonal hole,poor connectivity;（3）fossil clastic inner hole,connectivity is poor;（4）amid hole between clay minerals content layer,better connectivity;（5）clay interlayer nm level-um solution pores,good connectivity;More than 6 micro fracture,development in organic matter and mineral edge brittle,also for nm level-um,good connectivity.（4）,（5）,（6）kinds of pore as the main reservoir space.By cryogenic liquid nitrogen adsorption method and BET equation and calculation of Da an village section of the shale reservoir pore size distribution is given priority to with 10 nm-25 nm in the hole,100 nm to 150 nm of microporous also occupies a large proportion,and<5 nm holes is less.Specific surface area of the shale reservoir was positively correlation with entrance,confirmed that the aperture is given priority to with hole in nanoscale.The specific surface area of shale reservoirs separately with clay minerals and organic carbon content and vitrine reflectance of the correlation analysis,the results show that the content of clay minerals in shale reservoir control the most obvious of the development of nanoscale pore organic matter maturity has a certain influence to its,and its content of pore development control is limited.Through the work area around nine section and the crack observation Wells in work area 1 description,measurement and statistics,determine the cause of the fracture types include the seam between the layers,digenetic contraction joints and construction joints,the development of the cracks are mainly affected by the lithology and thickness of strata,sedimentary-the more times of diagenesis and tectonic stress superposition compound control,which is produced by tectonic action is the main factor of regional tectonic fracture,Dan an walled section since the depositional digenetic mainly experienced three sub-regions tectonic setting,of late Yan mountain respectively from south to north east to west and from north to south of extrusion stress,the early Himalayan period in the south east to north west of compressive principal stress,and the late Himalayan period north-south west to the east of principal stress.Based on the research of nanoscale pore and fracture characteristics,combined with the U.S.shale gas exploration success experience,screening of organic carbon content and maturity,hydrocarbon content,shale thickness,mineral composition and mechanical characteristics,reservoir space and reservoir physical property,such as the seven key geological factors to try to top village segments of sophomore and shale reservoir evaluation.The hole reservoir belongs to low-density of low permeability reservoir,the organic carbon content relative to the United States five shale gas reservoir is slightly low,just no village itself for sophomore and the period of hydrocarbon generation potential of the largest,the measured average air content is0.71 m³/t,obviously lower than 0.41 m³/t;A sophomore of the organic matter maturity is moderate,the minimum is 1.1%,the maximum was 1.46%,the average of1.2%.In a large amount of hydrocarbon generation stage and satisfy the conditions needed for the development of shale gas;A sophomore of the rich organic matter dark shale cumulative thickness of 30 m and 50 m,brittleness mineral content is higher in mineral composition and longitudinal brittle mineral content have decreased with increasing depth change tendency;Clay pore development between flocks,better connectivity,micro and ultra-cracks are relatively developed,the organic matter edge joints and rigid mineral edge joints and organic matter in the sophomore year period and the period of the upper more development,and in the second period of the lower part is less development;Rock mechanics experiments showed that under the condition of the same under pressure,with argillaceous shell limestone and calcareous shale containing scale than single shell limestone and shale are more likely to fracture,the experimental results show a sophomore of the lithological combination is easier to form cracks.According to the above evaluation standards,in Eastern Sichuan Basin Da’anzhai Section and has the value of shale gas exploration and development,and a sophomore and upper should be taken seriously.