Study On Low Damage Completion Fluid In Coal Seam Wells In Deep Coal Seam

China is rich in CBM resources. Basically, with the completion of the shallow exploration, it has been an inevitable trend to explore and develop CBM1000m down, which constitutes a direction of the development of non-conventional energy. However, compared with shallow coal seam, deep coal seam has more difficulties characterized large temperature gradient, high stress, high degree of metamorphism and poor pore structure preparation, which put forward higher requirements on the construction of well drilling in deep coal seam. In the actual drilling process of this kind of reservoir, the reservoir protection are rarely considered. There are two particular representatives, the poor yield of single well exploitation in current deep seam gas and the resulting composite cost difficult to reduce, which have become a serious obstacle to China’s CBM development. Therefore, it is imperative to develop completion fluid that is available for CBM well in deep coal seam and of minor damage.Based on coal NO.3and NO.15in Shizhuang North block of Qinshui Basin, this thesis makes a physical characteristic comparison of them, and analyze the rule of coal rock physical property changing with coal seam depth. On the basis of reservoir characteristics, this thesis study the damage mechanism of the reservoir through the sensitivity experiment, and targeted determines the basic formula of low-damage deep completion fluid system for coalbed methane wells of deep coal seam.A large number of indoor experiments are made to optimize tack producer, density regulator, fluid loss additive, clay stabilizer, temperature stabilizer, strong inhibitor and other agents in the system. In addition, it has formed a set of completion fluid formula with low density and little damage and it has also evaluated formula’s temperature resistance, suspension stability, rejection capability, corrosion inhibition and reservoir protection performance.This low-damage completion fluid system has XC and CMC-HV as tack producer, hollow glass beads as density regulator, which CMC-HV, hollow glass beads and CaCO3can co-work to reduce System filtration quantity.It forms a set of well completion fluid system formula of good performance and well solves the common difficulties in low-density completion fluid system of poor stability and poor rheological property, with strong inhibitor,temperature stabilizer,clay stabilizer and corrosion inhibitor. Experiments show that the completion. fluid system has good thermal stability,which is quite aimed at the characteristics of deep coal seam with high temperature;It’s also well aimed at the characteristics of coal seam with general low pressure based on adjustable density in range of0.74-1.03g/cm3, the good performance and strong stability of the system; with effective protection to the reservoir, the damage rate of fluid to reservoir permeability is only about10%. Therefore, the study on the completion fluid technology has both strong theoretical significance and important practical value.