Study On Geological Conditions Affected To Production Of Coalbed Methane Well Of Broken Soft Coal Reservoir

The broken soft coal seams in China have the advantages of abundant occurrence layers,wide distribution area,high content of coal bed methane and abundant resources.However,it is undeniable that the low reservoir pressure,poor permeability of the reservoir,which has increased risk of outburst,low strength of coal mechanics and many difficulties in drilling and bore quality.Therefore,broken soft coal seam belongs to a typical coal seam,which has the feature of strong adsorption,difficult extraction and outburst easily.Thus people can actively research the restraint mechanism,and influence law of the geological conditions related to the development of broken soft coal reservoirs on the productivity of gas wells,which will optimize the development of coal bed methane(CBM),along with the optimization of well type and well pattern,together with formulate reservoir modification projects,and the relevant stimulation measures of gas wells.Furthermore,it is of great theoretical significance to effectively avoid all kinds of risks in the exploration,as well as the development of CBM in such coal reservoir areas,to effectively promote the safe production along with the development of CBM industry and coal industry,which is in the crushed and soft coal reservoir areas.Therefore,this paper took Zhaozhuang well in Jincheng mining area of Qinshui coalfield,as well as the Luling well in Sudong mining area of Huaibei coalfield as further research objects,combed and analyzed the relevant geological background of CBM,the physical characteristics of coal reservoir and the current development status.Through dissecting coal measures and coal body structure,collecting related samples and a series of testing experiments,the paper mainly analyzed the relationship between reservoir geological characteristics and gas content of coal bed 3#coal seam in Zhaozhuang well and 8#+9#+10#coal seam in Luling well,along with some geological factors that could influence CBM enrichment and gas well production in development.Through simulation,the data of different development geological conditions and development engineering adaptability of CBM mineral dressing were predicted.Thus,the well pattern of CBM development was optimized.In the research of the main research results are as follows:(1)The models of tectonic thermal metamorphism and hydraulic closure superimposed enrichment in Zhaozhuang slope belt are constructed.Zhaozhuang well is divided into shallow monoclinal enrichment area,deep monoclinal enrichment area and shallow transitional zone.The shallow monocline enrichment area is relatively rich in CBM,and its gas-bearing property is second only to the deep gentle monocline enrichment area.The deep monoclinal enrichment area is beneficial to CBM enrichment,but it is not conducive to CBM mining because of the increase of buried depth and the decrease of permeability.Medium structural deformation in shallow transitional zone is conducive to improving the percolation conditions of coal reservoir,which is not conducive to CBM enrichment,but conducive to CBM development.The enrichment of CBM in the Luling well is controlled by sedimentary environment,structural characteristics,hydrogeological conditions and reservoir physical properties in the Luling thrust nappe belt leading edge bend-slip fold-rich gas model.It can be divided into three types of CBM distribution patterns:slow monoclinal faults develop hydrologic sealing differential escape areas,flat monoclinic faults do not develop hydrologic sealing and enrichment areas,steep monoclinal faults develop hydrologic sealing areas.(2)The physical properties of Luling and Zhaozhuang reservoir are compared with the development geological conditions.Compared with the Luling area,Zhaozhuang has poor pore connectivity,vertical principal stress and fracture,small reservoir pressure,small effective desorption and high content of Broken soft coal,which may be the reason why Zhaozhuang has high gas content but difficult to extract gas.There are four types of CBM development areas in the study area:rich gas monoclinic type,rich trainsion type,gas-bearing monoclinnic type and gas-bearing complex type.(3)This paper pointed out that the process of injecting liquid carbon dioxide or liquid nitrogen with reactive water fracturing fluid is superior to the conventional process of reactive water fracturing,closed coring is an effective measure for efficient extraction of straight well CBM Wells.And the restriction factors of key technology of CBM development under the condition of Broken soft coal reservoir are expounded.In a well with a low content of Broken soft coal,even if the permeability is low,the ideal gas production effect can still be achieved by selecting a suitable development plan.The main factor affecting horizontal well mining is the adaptability of engineering deployment and geological conditions.(4)The CBM-SIM software is used to simulate two wells with high gas production in Luling.The daily gas production in 2015 of the two wells was between268.82~1592.65m~3/d,168.01~1427.22m~3/d,and the cumulative gas production in2015 were 351.04 104 m~3,271.36 104 m~3,and 250m×300m,respectively.The wells in the production period of 2015 had earlier peak production time and higher average production.