Analysis Of The Hydromechanics Factors Impact On Hydraulic Fracturing In-situ Stress Measurement

The viscous drilling fluid in the geological drilling borehole has a great influence on in-situ stress measurement.For exploring a result between different attributes of hydraulic influence factors and rock breakdown pressure value,this paper designs and carries out hollow cylinder test according to the different hydromechanics factors.Meanwhile combining with the relevant experimental data could apply to the in-situ measurement,and improve the accuracy.In the process of this study,the work is from the following aspects respectively:Collecting the influence factors of the in-situ stress measurements and discussing the effects of hydromechanics factors on rock breakdown pressure emphatically;Collecting relevant test data about liquid injection rate and establishing the fitting equation;Designing and carrying out hollow cylinder test according to the different viscosity and density respectively,meanwhile analyzing data and fitting curve;The results of test are applied to the in-situ stress measured data and the correction formulas are used to analyze the stress data correction.Based on the above research,the main results are as follows:?1?Hydromechanics factors includs hydraulic friction,fluid injection rate,viscosity,density and compressibility.Pressure in the drilling borehole would be influenced by the hydromechanics factors based on KGD model and PKN model,the classic fracture mechanics model of hydraulic fracturing:Pressure in the borehole increases as the fracturing fluid viscosity or fluid injection rate increases.?2?Hydraulic friction includs processing head loss and local head loss.It is found that processing head loss in the water hose is very large through an example analysis.So people should control processing head loss in the water hose while in-situ stress measurement.Processing head loss in the drill pipe is little and it increases with increasing depth.So it is suggested that pressure acquisition device should be installed in the underground fractured interval.Liquid injection rate includes pressure loading rate q and flow rate Q.Based on data statistics about rate and breakdown pressure from relevant literature,fitting relationship of tensile strength and two types of rate could be obtained:P_b=3.2894ln?q?+22.374?P_b=3.2894ln[QK/?V+Q·?t?]+22.374.?3?Rock breakdown pressure reveals obviously relationship with high viscosity of the aqueous solution.The breakdown pressure ratio decreases at first and then increases with viscosity ratio increases.It is obtained the fitting relationship between tensile strength and viscosity:P_bi/P_b1=7E-06??_i/?₁?²-0.0018??_i/?₁?+0.9988.It is obtained the fitting relationship between breakdown pressure ratio and density ratio according to fracturing test used by different density mud:P_bi/P_b1=0.6095??_i/?₁?²-1.5331??_i/?₁?+2.2503.This formula could be used to correct the in-situ stress data.As the com-pressibility of hydraulic oil is large different with water,the paper introduces compliance coefficient C to provide a reference to compressibility and breakdown pressure.The average rock breakdown pressure from hydraulic is 1.26¹.82 times of water.And system compliance calculated by hydraulic oil is 1.24 times of water in this instance which falls within the above range.It reveals that conclusion is reliable relatively.?4?The fitting curve obtained by density and viscosity test could correct the in-situ stress data.Breakdown pressure P_b and the maximum horizontal principal stress S_H deviation reduced to 71.2%and 43.5%revised by density factor.And P_b and S_H deviation reduced to 49.2%and 25.5%revised by viscosity factor.While P_b and S_H deviation reduced to 16.8%and 1.13%revised by comprehensive density and viscosity factors.It shows that good correction results are obtained revised by comprehensive density and viscosity which could provide a reference method to correct in-situ stress data and show positive meaning.