The Coal Reservoir Characteristics And The Prediction Of Favorable Development Blocksin Zhengzhuang.Block Of Qinshui Basin

The study area,Zhengzhuang block,is located in the southern end of Qinshui synclinorium,The main coal seam of the study area is the No.3 coal of Shanxi Formation.Based on well logging and 2-D seismic data,the fine geological structure was interpretated.Using seismic interpretation,3D structure model of research area was established.Structural situation,structural feature and structural evolution were analyzed,and the tectonic and structural controls on coalbed methane(CBM)accumulation were summarized.The 2D seismic data in the study area are converted to 3D seismic data.Sparse pulse wave impedance inversion was made to analyze the reservoir physical properties including the thickness and gas content of the coal seam.Establishing the comprehensive evaluation system through the method of multi level fuzzy mathematics,we can make comprehensive evaluation of the study area,and select the favorable development block.I n study area,the stratum trend is tilted to the northwest from the southeast.The structure type is mainly a series of wide and gentle folds,which mainly extend to NNE and SN.The faults,whose distribution is relatively concentrated,are less in this study area.The Yanshan movement in the study area is the most severe,and Yanshan period was the main reservoir forming stage with a huge quantity of CBM.The axial part of syncline with the largest gas content,is the favorable area for CBM enrichment.Near the fault zone,the reservoir pressure is reduced,which gives rise to desorption of CBM and coalbed methane desorbs seriously.Sparse pulse wave impedance inversion was made to convert seismic profile to lithological profile.Then the reservoir physical properties including the thickness and gas content of coal seam were analyzed.The average thickness of coal seam is 5.5 m,while the average gas content of the study block reaches to 20 m3/t.Porosity distribution is uniform,the range of 0.65-10.54%,averaged 4.68%.The buried depth of coal seam,coal thickness,the overlying mudstone thickness,coal quality is also important to the enrichment of CBM.With the increase of buried depth,coal reservoir pressure increased,which result inthe gas conten of coal seam increased.The mudstone caprock of coal seam roof has played an important role in the preservation process of coalbed gas.If the overlying mudstone is too thin,CBM is easy to escape.Higher ash content in coal seam,coal seam gas adsorption ability is poor,and the gas content is lower.With the multi-level fuzzy comprehensive evaluation method,we make comprehensive evaluation and prediction of the favorable development block of coal seam gas in the area.The selected parameters are independent of each other,and do not influence each other.According to the prediction of overall evaluation,comprehensive evaluation parameter is up to 0.7 above in the study area.Favorable zone I(2000 m3/d<daily output)mainly distributed in the north in the study area.