The Study Of Coalbed Methane Prospective Zone Optimizatoin And Development Strategy In The Dacheng Area

Based on coal reservoir geology and coalbed methane surface mining in the Dacheng area of Jizhong depression,the North China Basin,this dissertation analyzes the geological characteristics of coalbed methane and the engineering test status in the study area.Firstly,the geological characteristics in the study area were carried out.Systematically analyze the geological conditions of coalbed methane.The influence of various geological parameters on the productivity was studied.Secondly,the evaluation index of the favorable area was selected,and the favorable area was figured out.On this basis,the coalbed methane development strategy in the study area was propsed.The exploration area and resource potential are clarified,and a scientific basis is provided for the exploration and development of coalbed methane resources in the area.The following main research results and understandings have been obtained.(1)Through systematic geological research in the study area,the characteristics of coalbed methane geological conditions in this area were revealed,and the impact of various geological parameters on productivity was analyzed.The coal-bearing strata in the study area are the Taiyuan formation and Shanxi formation with a thickness of 210?270 m.The main target strata are the coal group No.3 and 6 with a thickness of 4?8 m?2?7.5 m,respectively.The overall thickness of coal seam shows the trend that the two ends of the north and south are thicker and the middle part becomes thinner.The spacing of each coal seam varies from 2?30 m,and the buried depth is generally less than 2500 m.There has low permeability and low gas content as a whole.In general,it presents a monoclinic structure which is inclined to the east and west.The hydrogeological conditions in the area are relatively simple.It belongs to the residual coalbed methane enrichment mode of slope zone,and its biodegradation zone and saturated adsorption zone are beneficial to the development of coalbed methane.(2)Studied and analyzed the influencing factors of favorable zones,established optimization criteria,and carried out prediction of favorable zones.Based on the structure,reservoir and coalbed methane recoverability of the study area,8 elements,such as structural conditions,thickness,top and bottom plate lithology,hydrodynamic conditions,gas content,reservoir permeability,buried depth,and coal body structure,were determined.The optimal selection criteria of favorable zone in middle-rank coal were constructed.The study area is divided into three classes of favorable areas,the structure of the class I area is relatively simple,the buried depth is shallow 1600 m,the coal seam thickness is large,the gas content is high,the area is 400 km~2.The buried depth of class II area is 1600?2500 m,and the gas content has increased.The thickness of class II is uneven,covering an area og1415 km~2.Class III far scenic area,is buried depth at 2500 m.The total gas-bearing area of I and II is 1815km~2,and the resource amount is 5398×10~8m~3.(3)The development strategies of multi-layer combined production in vertical wells and segmental fracturing in single-branch horizontal wells were studied and determined.The works were on the basis of favorable zones optimization and through the appraisal well test effect evaluation.The development geological conditions are that the permeability of main coal seams in the study area is low,however,multi-coal seams develops.The three coal group,coal group No.3 and 4 and No.6 in deep have stable development and high gas content.The development technologies of multi-layer co-recovering in vertical well and multi-section fracturing in single branch horizontal well were proposed.As the full-scale development does still not reach in the whole region,full-scale development and new evaluation wells need to be deployed in the enabling areas.A recent development programme had been designed and deployed.To expand the exploration results in the north favourable area,three single-branch horizontal wells were deployed.While to implement the information in the south favourable area,two vertical wells were deployed.