| Coal is an important energy source needed for China’s development and occupies an absolute proportion in the country’s energy consumption system,but gas has always been one of the major hazards that cannot be ignored in the process of coal resource development.For a long time,coal mine safety accidents caused by methane have brought huge economic losses and bad social impacts to the industry.Using coal seam drilling for gas extraction is the most common and useful method for coal seam gas prevention and control,but the common methods of dry auger drilling,air drilling and hydraulic slagging drilling are limited by geological conditions and technical conditions,and drilling in coal seam gas extraction holes,especially in soft coal seams,is very easy to have drilling accidents such as jamming,spraying,sucking and collapsing,which is difficult to achieve the purpose of efficient gas management and for Foam drilling not only can effectively overcome the defects of the above methods,but also has excellent hole protection and coal dust carrying performance.Therefore,in view of the excellent performance of foam drilling,this thesis develops an inorganic clay-based microfoam drilling fluid suitable for drilling the sealing section of gas extraction boreholes in loose coal seams through the preferential selection of foaming agent,foam stabilizer,modified bentonite material and filter loss reduction agent,and studies its hole protection and coal dust carrying performance.Firstly,ten kinds of foaming agents,four kinds of foam stabilizers,modified bentonite materials and three kinds of filter loss reducing agents were selected,the optimal use concentration and the optimal microfoam system formulation were determined by the preference experiment and response surface method.The experimental results showed that the optimal type of foaming agent was 20% AOS+80%SDS,and the optimal use concentration was 0.2%～0.6%;the optimal type of foam stabilizer was PAC-141,and the optimal use concentration was 0.4%～0.8%;the optimal use concentration of modified bentonite material was 2%～4%;the optimal type and use concentration of filter loss reducing agent were 2% carboxymethyl starch(CMS)+ 1%sulfonated phenolic(SMP);the best ratio of microfoam drilling liquid system is 4%bentonite + 0.6% compound foaming agent + 0.8% foam stabilizer + 1% sulfonated phenolic(SMP)+ 2% carboxymethyl starch(CMS).Secondly,the performance of microfoam drilling fluid system was tested by using six-speed rotational viscometer and medium pressure water loss meter,and the normal temperature values and variation law with mixing time of parameters such as apparent viscosity(AV),plastic viscosity(PV),dynamic shear force(YP),density(ρ),filtration loss(FL)and half-life(h1/2)of microfoam drilling fluid were clarified.Meanwhile,the anti-pollution performance,temperature stability performance,acidity resistance,reusability performance,environmental performance and toxicity of the microfoam drilling liquid system were evaluated.The experimental results show that the density of microfoam drilling fluid gradually becomes smaller and the half-life gradually lengthens with the extension of stirring time,while the system has strong anti-pollution performance,anti-salt performance,anti-temperature stability performance,anti-acid and alkali environmental performance,reusable performance,environmental performance and non-toxicity,and its maximum anti-salt concentration can reach 6%,the maximum anti-temperature strength exceeds 100℃,and it has a better range of PH9～11 performance,can be reused more than 6 times,the system is degradable and nontoxic to human body.Finally,the hole protection ability and coal dust carrying performance of the microfoam drilling fluid system were investigated by laboratory drilling experiments in soft coal seams and numerical simulation software.The experimental results show that the drilling performance of microfoam drilling fluid is stronger than that of water,and there are almost no obvious fissures around the drilled holes formed by microfoam drilling fluid.The volume fraction of coal dust deposited in the drill hole annulus decreases with the decrease of drill pipe eccentricity,increase of microfoam drilling fluid inlet flow rate,increase of drill pipe speed and decrease of coal dust capacity.The drilling efficiency and drilling rate can be improved by avoiding the eccentricity of drill pipe,increasing the flow rate of microfoam drilling fluid and increasing the drill pipe speed during the drilling operation in soft coal seams.The results of this thesis not only provide a new idea to improve the drilling quality of sealed section of coal seam gas extraction borehole,but also can effectively improve the production safety of coal mines.This thesis has 60 figures,22 tables and 116 references. |
PDF Full Text Request