Injection Parameters That Promote Branching of Hydraulic Cracks

Fluid injection into rock formations can either produce complex branched hydraulic fractures, create simple planar fractures, or be dominated by porous diffusion. Currently, the optimum injection parameters to create branched fractures are unknown. We conducted repeatable hydraulic fracturing experiments using analog-rock samples with controlled heterogeneity to quantify the fluid parameters that promote fracture branching. A large range of injection rates and fluid viscosities were used to investigate their effects on induced fracture patterns. Paired with a simple analytical model, our results identify the threshold at which fracture transitions from an isolated planar crack to branched cracks when closed natural fractures exist. These results demonstrate that this transition can be controlled by injection rate and fluid viscosity. In relation to the field practices, the present model predicts slickwater and lower viscosity fluid injections promote fracture branching, with the Marcellus shale used as an example. Plain Language Summary Hydraulic fracturing involves injecting fluid under high pressure into wells to create fractures. This is a key technique that enables economic hydrocarbon production from tight petroleum-bearing formations whose ability to produce is otherwise too low. The same technique has also been researched for geothermal energy exploitation. Previous studies demonstrate that hydraulic fractures can either grow as planar or bifurcate into multiple branches. Branched fractures provide a larger surface area which is beneficial for increasing gas production from wells. Except for a 2019 incomplete theoretical study by the authors, the conditions that cause branching were until now experimentally unverified, and so one had to rely on intuitive guessing how to achieve it and optimize it. To address this problem, we conducted laboratory hydraulic fracturing experiments to quantify the injection rates and fluid viscosities that will cause branching. Our results indicate that fractures can transition from a single planar crack to branched cracks when the fluid viscosity is in an optimum range for a given injection rate. We also propose a theory to predict our experimental results and apply our results to field applications. This provides a useful new capability to improve the control of hydraulic fracturing.

Automated summary

This study experimentally determined the effects of injection rate and fluid viscosity on fracture branching, showing that these parameters can control the transition of fractures from planar to branched, thereby improving gas production efficiency.