We conducted fracturing experiments on cylindrical Berea sandstone samples using Synthetic-Based Mud (SBM). Several injection cycles were carried out on each rock sample to measure the Fracture Initiation Pressure (FIP) and the stable Fracture Propagation Pressure (FPP) at various confining pressures. The measured FIPs were compared – and found to be in good agreement – with Rummel's model for FIP. The stable FPPs were measured using base SBM and SBM with Lost Circulation Material (LCM), and compared with the large-scale fracturing experiments conducted at the Drilling Engineering Association (DEA) 13 investigation. Our study shows that the stable FPP changes linearly with the minimum horizontal stress (Sh), and does not depend on the maximum horizontal stress (SH). In addition, for borehole diameter equal to or greater than 0.5 inch, the stable FPP is not affected by the borehole size. We propose an experimental approach to predict the stable FPP for arbitrary in-situ stresses, borehole size, and fluid formulation.
Drilling Induced Fractures (DIF) grow as the borehole pressure exceeds the fracture pressure. In an intact rock, the DIF growth occurs in two phases: fracture initiation and fracture propagation (Morita et al., 1996). Fracture initiation occurs when the borehole pressure exceeds the FIP and results in formation of small DIFs near the borehole. Fracture propagation occurs when the borehole pressure is maintained above the FPP. During the fracture propagation phase, the formed DIF grows significantly in size (van Oort and Vargo, 2008). Enlargement of the DIFs result in formation of large fracture networks, which can create lost circulation problems. Lost circulation – the uncontrolled flow of drilling fluid into the geological formation – results in significant loss of drilling fluid. Severe lost circulation problems can complicate well delivery and increase the non-productive time. In extreme cases, they may lead to losing the well or necessitate drilling costly sidetracks (see e.g., Gradishar et al., 2013).