| Gujiao Mining Area locate at the northwest of Qinshui basin,more than 30 km from Taiyuan City,Shanxi province.The exploration and development of coalbed methane(CBM)in this area is in its primary stage.The main production seams for CBM include the No.2 coal seam in Shanxi formation,and the Nos.8 and 9 coal seam in Taiyuan formation.Based on the exploration and production data of CBM well in Malan,Tunlan,and Dongqu mines in the Gujiao Mining Area,a prediction model of gas content in coal reservoir is established,which can analyse the gas distribution characteristics of coal seam.Then the thesis discusses the gas content property and its geological controls.Finally,the thesis analyses the productivity of CBM wells and concludes some suggestions for the development of CBM in the study area.The research are theoretical and in practical significant for exploration and development of CBM in this area.Firstly,by analyzing the relationship between compensation density logging,natural gamma logging,apparent resistivity logging,natural potential logging,caliper logging of coal reservoir and gas content,the thesis establishes a multi-linear regression model to forecast gas content.The model is evaluated and verified by in-situ gas content data of several exploration wells.Results show that absolute error of the calculated values ranges from 0.02 cm3/g to 3.82 cm3/g(average is 1.39 cm3/g).The relative error of calculated values ranges from 0.24% to 37.85%,with an average value of 17.68%.Thus,the established model has certain feasibility in the prediction of gas content in the study area.Then the thesis analyses the gas content characteristics of CBM reservoirs.Regionally,gas content and methane concentration in the southwest of Malan Mine are relatively low because of air oxidation.The high gas content area of the three coal seams are in the northern part of the Lijiashe fault.Vertically,No.8 coal seam in the study area would has the highest gas content and methane concentration,followed by No.9 coal seam and No.2 coal seam.Grey-correlation analysis was applied to study the controlling factors of gas content.It was found that as for as the importance for gas content control,it is the order of geological structure>burial depth>roofproperty>coal petrologic features.Finally,the thesis analyses the production data of CBM wells.According to the characteristics of gas production curves,it is divided into five types: descending type,smooth type,multi-box type,rising type and multi-peak type.From the aspect of geological conditions,hydraulic fracturing effect and the way of development,the thesis explains the reasons for the difference in productivity,and puts forward some suggestions for CBM development: 1)in the western syncline control area,it is preferred to select the inverted trapezoidal well pattern arrangement,and appropriately increase the drainage intensity in the low position of the structure.2)In the eastern fault control area,it is preferred to select the plum blossom well pattern arrangement in Lijiashe-Tounanmao graben subarea.At the same time,direct or indirect hydraulic fracturing methods are suggested for CBM development,in consideration of the geological characteristics of the coal bearing strata.3)In the choice of development method,single coalbed development should be selected as much as possible.If a multi-coalbed development method is chosen,then it is necessary to analyse the reservoir characteristic and formulate the matching production system ahead of the development. |
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