Study of the effect of fracture fluids viscosity and borehole diameter on hydraulic fracturing breakdown pressure using a newly developed true triaxial apparatus

A new apparatus which allows laboratory Hydraulic fracturing experiments under true triaxial compression was developed at Shahrood University and laboratory hydraulic fracturing experiments were conducted to investigate the dependence of breakdown pressure upon two factors which could influence the use of the hydrofrac technique for in-situ stress determinations namely: the viscosity of fluid and borehole diameter. Therefore, in this study, by using the new apparatus we examined if the fracture pressure will change with viscosity of fluids and borehole diameter. In this regard, Some ۳۰۰ mm cube specimens of concrete were made and used in this study. It should be noted that, three steel rods of ۳۰, ۵۰ and ۸۰ mm outer diameter were buried for a simulated borehole in the specimens. Meanwhile, ۳ types of Hydraulic oil (۴۶H, ۶۸H and ۱۰۰H) were injected to boreholes of different diameters. In this study, to examine the effect of viscosity of fracturing fluid and borehole diameter on hydraulic fracturing breakdown pressure, some tests were conducted. Results show that breakdown pressure decreases with increasing borehole diameter and also there is an inverse relationship between breakdown pressure and viscosity of fracturing fluid. In other words, it decreases with increasing viscosity of fracturing fluid.

Keywords:

Hydraulic fracturing , Injection fluid , Borehole diameter , Breakdown pressure