Evaluation of the breakdown pressure to initiate hydraulic fractures of tight sandstone and shale formations

Hydraulic Fracturing has been used successfully in the oil and gas industry to enhance oil and gas production. Recent years have seen the great development of tight gas, coalbed methane, and shale gas. Different fluids were used as fracturing fluids in shale and sandstone formations, including the use of CO₂, N₂ and CO₂ foam, slick water, crosslinked solutions, and oil-based fracturing fluids. The objective of this study is to develop an experimental setup to measure the breakdown pressure to initiate the fractures in shale and tight sandstone cores. This study investigated the effect of injection flow rate, temperature, fluid viscosity, and fluid type on the breakdown pressure of different rock cores. 5 wt% KCl brine, slick water with a friction reducer, linear gel systems were used as a fracturing fluid. Kentucky, Scioto, Bandera, and Berea sandstone cores were used. Also, Mancos, Marcellus, and Barnett shale cores were used in this study. Finally, the behavior of the breakdown pressure was examined as a function of the back pressure (0, 100, 300 psi). The preliminary results show that the breakdown pressure increased as the injection flow rate increased. Where the breakdown pressure increased from 438 to 1,000 psi as the flow rate increased from 5 to 10 cm³/ min in case of 5 wt% KCl with Kentucky sandstone cores. The breakdown pressure increased in Marcellus shale to 1,800 psi in case of 5 wt% KCl at 5 cm³/min. As the fluid viscosity increased the breakdown pressure increased, it increased to 1,115 psi in case of 2 gptg friction reducer (5 cp) comparing to 5 wt% KCl (1.1 cp) case at 5 cm³/min. A straight line relationship was found between the breakdown pressure and the logarithmic scale of the fluid viscosity. This study will give recommendations for the fluid viscosity, type, and the injection flow rate that will improve the efficiency of the hydraulic fracturing operation.