The Influence Of CBM Drilling Engineering Effect Of The Gas In Dafosi Mine Field

Under the condition of abundant CMB resources in China,low rank CBM resources have great potential and some breakthroughs have been made,however the overall utilization degree is still low.The low rank CBM resources are abundant in Dafosi mine field,since the CBM wells are deployed,some completed CBM Wells have obtained certain industrial airflow,but the overall gas production effect is not good.Previous research on the effect of coalbed methane exploration and development in mining field are mainly concentrated on the coal reservoir physical characteristics and gas-bearing,production system and well type optimization,etc.,the evaluation of different well types and engineering parameters is rarely involved,the analysis of the relationship between gas production and well type can provide a basis for surface development of coalbed methane.In this paper,the data of drilling parameters,fracturing drainage and production of vertical and horizontal CBM Wells were collected from the geological exploration of coal fields in Dafosi mine field,the characteristics of coal reservoir are studied,and the principle of well layout and type selection is optimized,presented the key parameters of CBM well drilling and completion,simulated gas production effects of different well types,analyzed the influencing factors of gas production in CBM,The following main insights are drawn:(1)According to the analysis results of geological data,the no.4 coal seam in Dafosi mine field has a large thickness,moderate burial,good stability,relatively simple structure,low coal reservoir pressure,high permeability coefficient of coal seam and permeability,which provide favorable conditions for the production and migration of coalbed gas.(2)the drilling practice results show that the vertical well body of surface CBM well in dafosi well field usually adopts two-opening structure,while the multi-branch horizontal well adopts three-opening structure.The drilling fluid performance requirements of vertical well and horizontal well are consistent in the first and second vertical section.After drilling,both vertical and horizontal Wells adopt conventional cement sealing and cementing.In vertical Wells,casing perforation method is selected for completion while in horizontal Wells,open hole completion method is adopted to minimize reservoir damage.(3)The production process of coalbed methane is relatively complex,which can be divided into saturated water single-phase flow,unsaturated water single-phase flow and gas-water two-phase flow.Most coalbed methane Wells newly put into production on the surface of Dafosi mine field have produced gas.(4)Productivity simulation results of different well types show that the average peak gas production of horizontal Wells is 10000m3/d,the average peak gas production of vertical Wells is about 1600m3/d,and the output of one horizontal well is roughly equivalent to that of six vertical Wells.The software simulation results show that the optimal length of the reasonable horizontal section of the surface horizontal well is 3000-3300m.(5)The research results show that the production of CBM Wells is mainly affected by the structural characteristics,the buried depth of coal seam,the total amount of sand added by fracturing,the sand ratio,and methane emerging time,especially the structural characteristics and gas breakthrough time have a significant impact on the gas production effect of CBM Wells.