Study On Geological Characteristics Of The Deep CBM And Adaptability Of Horizontal Well Development Techniques With Them In The Southern Yanchuan Block

Southern Yanchuan is the production block with the largest overall development depth of coalbed methane and the largest number of fractured horizontal wells in operation.Due to the "three high" geological conditions of "high geostress,high geothermal temperature and high reservoir pressure",the geological adaptability of fracturing production technology of coalbed methane vertical wells is poor,which hinders the deep coalbed methane to a certain extent.Commercial development.It is of great theoretical and practical significance to deepen the understanding of the geological characteristics of deep CBM and reveal the geological adaptability of horizontal well fracturing technology to transform coal reservoirs.Based on the exploration and development data of coalbed methane and the exploration of Engineering practice,this paper divides the development geological model of coalbed methane on the basis of deep research on the enrichment law and development geological characteristics of deep coalbed methane,systematically explores and evaluates the mechanism of geological adaptability of horizontal well development technology,and then develops the geological adaptability.The field application effect of horizontal well development technology is summarized and evaluated,and the geological suitability of horizontal well fracturing technology is demonstrated.The main achievements of the paper are as follows:(1)High in-situ stress and overall low permeability are the special development geological conditions of deep coalbed methane;geological structure and groundwater dynamic conditions are the main controlling factors for deep coalbed methane enrichment;favorable areas for deep coalbed methane enrichment and gas-rich and high permeability development units are developed in secondary structural high points,groundwater sealing or retention environment;There are three CBM enrichment zones and one high permeability zone in the study area,and the CBM enrichment zone is located in well S3,well S16 and well S23.The controlling factors are detained water environment,secondary anticline high point and structure-buried depth,high permeability area is located in S23-S6-S16-S18 area,which is affected by faults and secondary structures as low in-situ stress area,and there are five types of coalbed methane development areas in the study area: rich gas and high permeability type,rich gas and low permeability type,poor gas and high permeability type,gas permeability type and gas-bearing low permeability type.The gas-rich and high permeability type is located in the superposition of the enrichment zone and the high permeability zone,which is suitable for vertical well fracturing;the gas-rich and low permeability type is located in the superposition of the high geostress and the enrichment zone,which is a special development geological model of deep coalbed methane,and the effect of vertical well fracturing is poor;the other three types of development geological models are not available for the time being.The economic feasibility of the development.(2)Low permeability of deep coal reservoir controlled by high geostress,large drainage area of horizontal well and high efficient volume fracturing are the key mechanism of geological adaptation between horizontal well development technology and deep coal reservoir,and the horizontal well fracturing technology has the strongest geological adaptation than other horizontal well development technologies.Horizontal wells can expand the area of drainage and pressure reduction and generate new fractures to improve the permeability of coal seams by communicating the cleavage-fracture system,which is the key mechanism for adapting the geological characteristics of deep high-stress and low-permeability coalbed methane.The pilot test shows that the contaminated zone near the wellbore of the horizontal well with non-fracturing screen tube has poor permeability and difficult pressure conduction,which is not conducive to the reduction of coal seam pressure and is only suitable for the development of high permeability coalbed methane.Fracture,numerical simulation shows that the stimulation effect is remarkable,and it is most suitable for the deep coalbed methane geologic characteristics;the area suitable for the development of fractured horizontal wells is located near well S3-S21 in the southwest and well S5 in the east,and the development geological model is mainly rich in gas and low permeability.(3)Optimizing the development technology of deep coalbed methane horizontal wells according to geological suitability,and forming a set of development technology system of subsection fracturing horizontal wells suitable for deep coalbed methane.Segmental fracturing U-type horizontal well has the strongest geological adaptability.The optimum wellbore structural parameters of this well type are 800-1000 m in length,parallel to the coal seam elevation isoline,fracturing in 4-6 sections,and the fracture spacing is 150-250 m.The drilling technology system with underbalanced drilling technology,tertiary borehole structure,dual-inclined borehole trajectory,landing control,horizontal directional drilling control and cashmere drilling fluid as the core has been formed by optimization.Fracturing fluid,properly enlarging the scale of fracturing fluid and precursor fluid,controlling sand addition,sand ratio and construction displacement are the core of drillable bridge plug fracturing technology.After optimization,the fracturing parameters are 800-1000 m3 fracturing fluid,300-400 m3 precursor fluid,40-50 m3 sand addition per segment,8 m3/min construction displacement and 8-9% sand ratio.On the premise of continuity,stability and slowness,four stages of coalbed methane drainage are divided.According to the production characteristics of each stage,the drainage management system with the control of liquid level drop as the core is worked out.0 to 20 m.(4)The production practice shows that the horizontal well development technology system has improved the drilling quality and the effect of fracturing reconstruction.The stimulation effect is remarkable and the geological adaptability is strong.It is worthy of further popularization and application.The optimized drilling technology system can rapidly drill and shorten the drilling cycle on the premise of improving the coal seam drilling rate and protecting the coal reservoir;the optimized subsection fracturing technology improves the efficiency of fracturing transformation,and the fracturing fracture formed is longer and less harmful to the coal reservoir;the horizontal section length of the horizontal well S3-U1-P is 650.4 m,and the fracturing fracturing of the four sections is divided.Gas production is 5.2-18.5 times that of vertical wells and investment cost is 3.5 times that of vertical wells.The horizontal section of S3-V1-P1 is 778 m long and fractured in 6 stages;the horizontal section of S3-V1-P2 is 440 m long,and the daily gas production of S3-V is 5.6-11.5 times that of vertical wells,and the investment cost is 7 times that of vertical wells.The comparison of development effect shows that U-type horizontal well with fracturing section has the best stimulation effect and the strongest geologic adaptability,followed by V-type horizontal well with fracturing section,and the screened completion and non-fracturing horizontal well has the worst stimulation effect.