Study On Clean F Racturing Fluid Of Coalbed Gas

Based on coal reservoir geology and reservoir properties of Qinshui Basin,and did some study on the clean fracturing fluid system of coalbed gas.On the basis of measurement and analysis of coal reservoir physical properties,the most suitable clean fracturing fluid formulation for the area was selected and do evaluations of its performance,and compareing with the performance of conventional fracturing fluid.Physical properties of reservoir rock experimental results show that,the mercury intrusion curve of coal samples belong to fractured pressure mercury curve.Coal reservoir rocks have relatively high elastic modulus and Poisson's ratio,which is in low hardness and easily broken,and it has a strong sensitivity to stress.In the stress sensitivity experiments we found that when confining pressure reaches 0.14MPa,rock reservoir permeability starts to behave abnormally,as the permeability starts to decrease.This is due to the excessive pressure makes the coal matrix shredded,and blocking the pores of coal and rock,resulting in decreased permeability.Permeability damage caused by the stress is up to 87.6%.When the concentration of viscoelastic surfactant reaches a certain value,the molecular form into a rod-like micelles,and later,turns into well compliance wormlike micelles with the effect of counter ions.Such entangled wormlike micelles will form a crosslinked network structure,so that there is a substantial increase in viscosity.Performance evaluation results show that clean fracturing fluid has a good performance on carrying sand,and has a good shear capacity.Core damage experiments showed that the smaller the coal and rock porosity is,the slower the permeability recovery is.