Preparation And Evaluation Of Coal Seam Temperature Environment Friendly Drilling Fluid System

Coalbed methane is a kind of unconventional natural gas resource,which is clean,high quality and widely distributed.The amount of coalbed methane resources in China is third in the world,of which the depth of coalbed methane accounts for about two-thirds of the total CBM resources.However,compared with other countries in the world,such as the United States,Canada,Australia and other countries,China’s CBM,especially the deep coalbed methane exploration and development is fallen behind.Along with the enhancement of people’s environmental protection consciousness and the development of drilling fluid technology,the environmental friendly drilling fluid technology which is suitable for the exploration of coalbed methane will become the hot spot of CBM exploration and development technology.Firstly,in this paper,the present situation of environmental friendly drilling fluid CBM drilling fluid technology is analyzed and prospected.The characteristics of coalbed methane reservoir,especially the characteristics of deep coalbed methane reservoir are analyzed.Compared with other countries,the geological conditions of coalbed methane reservoir in our country are complicated after the coal forming period,and the structure of coal bed gas reservoir is seriously damaged.But the lithology and physical properties of the deep coal bed gas reservoir are affected by high temperature and high pressure,and the geological condition is more complex.In this paper,the environmental acceptability of drilling fluid and the effect of high temperature on drilling fluid system are analyzed.The influence mechanism of high temperature on clay,treatment agent and drilling fluid is different.On the basis of ensuring the environmental friendly performance of the treatment agent,the modified natural polymer processing agent which can improve filtration and rheology property of the well wall after high temperature is selected.It can increase the molecular weight and counteract the destructive effect of the degradation,so as to maintain and even increase the efficacy of the treatment agent,which is equivalent to the further improvement of the treatment agent.In the drilling fluid based on the theory of environmental friendly,for shallow coalbed gas reservoir characteristics,preferably coated inhibitors of 80A51,CX-127 and filtrate reducer DFD-2 combined with hollow density regulation and temporary plugging effect of bead and acid solution of ultrafine calcium carbonate,bentonite 400mLwater+0.4%Na₂CO₃+2%bentonit+20%microsphere+0.6%80A51+0.3%CX-127+1.5%Ultrafine calcium carbonate+1.5%DFD-2+20%hollow to form a complete set of application in the shallow coal seam gas;for deep coal seam gas characteristics,combined with high temperature drilling fluid with high temperature in theory,environmental friendly drilling fluid system based on the theory,optimized environmental performance good high temperature filtration agent LSP-7,thickening agent,HEC ultra low permeability plugging agent OCL-BST-2,inhibitor PA-2,non fluorescence lubricant SDR-1 optimization based on high;The formula of the environmental friendly drilling fluid system is as follows in laboratory:400mL water+0.4%Na₂CO₃+2%bentonit+0.3%HEC+2%PA-2+2%SDR-1+2%OCL-BST-2+4%LSP-7,CBM reservoir temperature stability system two sets of drilling fluid in their respective suitable for good rheology and filtration performance is good;strong inhibition,good anti salt,anti calcium and anti pollution ability of cuttings;the effect of reservoir protection,drilling fluid pollution after the core permeability recovery at a rate above 85%;good environmental performance,processing agent and non-toxic,easily degradable drilling fluid.