Research On Reservoir Characteristics And Sweet Spot Prediction Technology Of Shale Gas Of Wufeng-Longmaxi Formation In Jiaoshiba And Dingshan Area

Taking Jiaoshiba and Dingshan Area as the target area, research on reservoir characteristics and sweet spot prediction technology of shale gas of Wufeng-Longmaxi Formation in Jiaoshiba and Dingshan Area is carried out. In terms of the research progress for reservoir prediction on sweet spot and the exploration & development situation of shale gas reservoirs home and abroad, combining with the geologic conditions and the focus & difficulty in the shale gas exploration & development in Jiaoshiba area, the research workflow is determined. Firstly, based on the thorough analysis on regional geological data, the main logging-seismic sequences in the target intervals are identified using logging and seismic data, and the shale gas reservoirs are classified. Combining with the case study on shale gas in Jiaoshiba area and neighboring area, the accumulation controllingling conditions of sweet spots of shale gas are analyzed. Secondly, in terms of the rock physical analysis and rock sampling test results, the logging responses of sweet spot are analyzed using single- and multi-well analysis. According to the vertical and horizontal distribution of reservoir we establish some shale gas sweet spot geological models, and choose the forward modeling and seismic analysis technology to analyze the seismic response characteristics of shale gas sweet spot, and as well as the lithology and physical, reservoir space types and distribution, electrical characteristics and gas content features. According to reservoir characteristics, shale gas rich integration controlling factors analysis, exploration and development situation of shale gas, we determine the main controlling factors in this area. Finally, for the main controlling factors we make a study in shale gas sweet spot reservoir seismic prediction technology, we carry out the comprehensive evaluation analysis for shale gas sweet spot reservoir in best shale section to predict favorable shale gas reservoir distribution, which is combined with the geological condition.Through structure analysis we realize that the Jiaoshiba structure formation is flat, strata angle is about 5-10 degrees, structural trend is in NE-SW, and structural fracture is not developed, but the micro-fracture is developed in this structure, strata depth is 500-3500 meters, which is suitable for shale gas enrichment. Dingshan structure is relatively steep, strata dip angle can reach 30 degrees, structural fracture is not developed in the structure, but the structure is relatively smaller, and it is greatly influenced by the marginal faults, strata depth is relatively big.Combined with shale logging-seismic sequence and reservoir classification through the analysis of geological and sedimentary facies, we confirm that deep-water shelf and shallow shelf stratum in Wufeng-longmaxi group is the main strata, which is the main reservoir located in the bottom of the target reservoir section. Through the sedimentary facies division and analysis, we confirm that the target reservoir is corresponding to the deep silicon shale shelf, deep sand shale shelf, deep mixing product shelf sedimentary microfacies, the carbon-rich and high silicon shale(or carbonaceous shale, black shale, gray black shale, etc.) deposit in the deep silicon shale shelf microfacies is the best quality shale, and is also the major gas section.The shale gas sweet spot reservoir deposit in deep shelf of Wufeng-Longmaxi group in this area can be divided into three sections in vertical, and the first section reservoir(the lower part of about 38 meters, JY1 well) is the high quality reservoir section, and according to the shale gas exploration and development, we know that about 10 meters’ shale at the bottom is the best shale reservoir. The logging response characteristics for the high quality reservoir section is high gamma ray, low resistance, high acoustic time, high porosity, low density characteristics, and is layered structure. Seismic responses of the high quality reservoir are strong reflection at the top and bottom of the reservoir, and as the thickness of reservoir is bigger or gas content is higher, the trough of the waveform at the top will be wider(or longer affected by many sets of reservoir, or affected by sandstone interbedded the single trough will be changed to two troughs with a peak), bottom margin slightly drop-down features.Through the integrated controlling factors analysis, we confirm that the main controlling factors that affect the shale gas sweet spot in this area are gas content characteristics, the preservation conditions(pressure, buried depth, fault condition, roof and floor lithology, etc.), the TOC content, shale distribution characteristics, pore and permeability and brittle, among them the pressure condition can directly reflect the shale gas production, is the most direct controlling factor of shale gas sweet spot reservoir in this area, high pressure and high gas production.According to the logging response characteristics and seismic response characteristics of reservoir in this area, in view of the shale gas reservoir rich integration main controlling factors, we carry out the shale gas sweet spot seismic prediction technology research, which includes pressure prediction technology, organic carbon(TOC) prediction technology, shale distribution prediction technology, porosity prediction technology, micro-fracture prediction technology, brittleness prediction technology, through the study we form a shale gas sweet spot prediction technology series, which include Fillippone pressure prediction technology based on imitate acoustic seismic inversion speed, TOC prediction method based on logging and rock sample analysis, brittleness index prediction method based on rock physics analysis(at the same time, the brittle shale rock physical quantities is established), porosity prediction method based on multi variate statistical analysis, etc. At the same time, we carry out sweet spot gas content prediction technology research, mainly to use prestack inversion method, frequency property analysis methods to predict shale gas reservoir of gas content. For the micro-fracture(or joint) that affect the pore and permeability of reservoir, we carry out the study of ant tracking technology, azimuth anisotropy fracture detection technology, the curvature entropy prediction technology, structure and stress field analysis technology and so on, which based on prestack and poststack seismic data, and predict the micro-fracture distribution in JSD-JSB and JSD-DS tectonic belt.On the basis of parameters result of shale gas integrated controlling factors, according to the geology conditions of Jiaoshiba and Dingshan area and the present situation of shale gas exploration and development, we carry out the comprehensive evaluation analysis, which mainly use the method of multi-attribute analysis and weighting coefficient method, combined with the geology condition of shale gas reservoir(including structural condition, sedimentary condition, etc.) to predict the best shale gas sweet spot enrichment region located at the bottom of Wufeng-Longmaxi group. According to the research results we get a deepening understanding of sweet spot in geology of Jiaoshiba and Dingshan area, and also put forward to the concept of sweet spot in the area.