Effect of drilling fluid penetration on plastic radius of horizontal directional drilling borehole

Based on the field data of horizontal directional drilling(HDD) project,theory analysis and sample testing were used to deduce calculation formula of plastic radius in HDD borehole.The testing results were analyzed.The results show that,when the pressure difference is zero or ground pressure is larger than slurry pressure,plastic radius tends to be a constant with little change.When pressure difference is less than 1.0 MPa,plastic radius increases exponentially with the increment of drilling fluid penetration.When pressure difference is more than 1.0 MPa,plastic radius shows an exaggerated range beyond the penetration radius.