Basic Research On Drainage Design Of Deep CBM Wells

The reserves of deep coalbed methane(CBM)resources in my country far exceed those of shallow coalbed methane.The exploration and development of deep coalbed methane resources is of practical significance in alleviating my country’s energy tensions,ensuring safe coal production,reducing pollution and protecting the environment.However,because the development of deep coalbed methane resources in my country is in the initial stage,there is a big difference in geological conditions between deep coal seams and shallow coal seams.The application of shallow CBM development theory to deep coalbed methane development is not ideal.In order to achieve high-efficiency development of deep CBM,this paper combines the geological characteristics of deep CBM wells on the basis of shallow CBM wells and conventional oil and gas well development theories to study the problem of coal pulverized coal during the drainage process of deep coalbed methane wells and improve the development of deep coalbed methane wells.Drainage efficiency,to provide certain theoretical support for the formulation of a design scheme for deep coalbed methane wells.The main research progress is as follows:(1)Analysis of the adhesion characteristics of pulverized coal in the wellbore of deep coalbed methane wellsThrough the establishment of a mechanical model for the adhesion of pulverized coal to the wall of deep coalbed methane wells,it is analyzed and determined that the main removal method of pulverized coal particles adhering to the wall of deep CBM wells is rolling removal.On this basis,it is deduced that it is suitable for the wall adhesion of deep coalbed methane wells.The calculation formula of the maximum particle size of pulverized coal particles is attached,and the formation mechanism of pulverized coal agglomeration is determined,revealing the reasons for the serious adhesion of pulverized coal in deep coalbed methane wells.Combined with the coal adhesion experiment on the pipe wall,the priority of the various factors affecting the coal adhesion was determined,and it was proposed to increase the flow rate of the well fluid and reduce the pipe wall roughness to reduce the coal adhesion.(2)Analysis of the characteristics of deep coalbed methane well liquid carrying pulverized coal and optimization of drainage planAiming at the geological characteristics of deep CBM wells,considering the influence of pulverized coal particle composition on the basis of oil well sand carrying theory,the particle sedimentation experiment is used to determine the particle sedimentation terminal velocity shape influence coefficient α,and the vertical wellbore sedimentation terminal velocity formula of different components of pulverized coal particles is derived.Based on the geological characteristics of deep coalbed methane wells,a simulation experiment platform was designed and built,and liquid pulverized coal-carrying experiments were carried out to reveal the influence of factors such as well fluid flow rate,well fluid temperature,particle mesh number,and particle composition on the characteristics of liquid pulverized coal-carrying properties.There are three stable periods in the stage characteristics.According to the characteristics of the pulverized coal particles produced in each stage and the effective particle carrying rate,combined with the adhesion characteristics of the pulverized coal on the wall of the deep coalbed methane well,the optimal well fluid flow rate for the liquid-carrying pulverized coal production is calculated.Based on ensuring the economy of drainage and extraction,a small amount of sandy particles are naturally deposited and the main idea of minimizing the adhesion of pulverized coal on the pipe wall is the optimization plan for deep coalbed methane well vertical wellbore liquid-carrying pulverized coal production.(3)Research on gas-carrying characteristics of deep coalbed methane wellsCombined with the geological characteristics of deep CBM wells,the annular gas carrying liquid were divided into two different types: drag liquid carrying and mist flow carrying liquid.Based on the conventional gas well gas liquid carrying theory,combined with their respective characteristics,the deep coalbed methane wells are deduced separately.Based on the formula for calculating the volume and the critical liquid-carrying volume of mist flow,annulus drag and mist flow-carrying experiments of deep coalbed methane wells are carried out to verify and supplement the theoretical analysis.At the same time,the problem of gas-carrying pulverized coal may be caused by gas-carrying liquid production is studied.In stages according to the state of pulverized coal particles,and the critical flow rate of gas-carrying pulverized coal is determined,which provides a certain theoretical basis for the prevention and control of gas-carrying pulverized coal problems in deep coalbed methane wels.