Research On Damage Mechanism And Drilling Fluid System Of Coalbed Methane Reservoir In J Block Of Eastern Ordos Basin

On the basis of clarifying the research purpose and significance of this paper and fully collecting the previous research data,the research status of reservoir damage mechanism and drilling fluid system at home and abroad is investigated in detail,and the coal gas reservoir characteristics of block J are studied in detail from the aspects of reservoir development characteristics,pore structure characteristics,cleat development characteristics,etc.Based on the analysis of reservoir damage mechanism,it is considered that stress action,solid particles of drilling fluid,coal swelling,water lock damage,polymer type,incompatibility and sensitivity are the main damage mechanisms of coalbed methane reservoir.On this premise,the drilling fluid system suitable for block J is deeply studied,and two kinds of drilling fluids suitable for block J are selected through experimental research on the basis of determining the base slurry Polymer NDHE-21 and HD-DJC,with the concentration of 0.2%;JLS-FDJ,with the concentration of 0.4%;FJE-1 and JDE-1,with the concentration of 0.7%;PAM-CM,with the concentration of 0.2%and lubricant RHJ-21,with the concentration of 0.1%The optimized environment-friendly drilling fluid system for block J is:River water+2%KCl+0.2%NDHE-21+0.4%JLV-FDJ+0.7%FJE-1+0.2%PAM-CM+0.1%RHJ-21。Through comprehensive performance evaluation of the optimized drilling fluid system,it is found that the drilling fluid has good rheological property,filtration property,p H value,temperature resistance,etc.;it has strong permeability recovery ability,with an average recovery rate of more than 95%;it has strong resistance to Na Cl and Ca₂SO₄ It has good anti pollution ability,no biological toxicity,no chemical toxicity and easy degradation.The damage to coalbed methane reservoir in block J is very low,which can meet the basic performance and drilling requirements of drilling fluid.