A review on breakdown pressure in hydraulic fracturing of subsurface geologic formations: Influencing factors, reduction strategies and research gaps

Hydraulic fracturing is a commonly used stimulation technique for production optimization in various geological formations such as tight sandstone, shale, coal bed methane, and heat extraction in geothermal reservoirs. Breakdown pressure is a vital component in hydraulic fracture job design, which is affected by various parameters including rock strength and depth. Various methods including modelling and experimental approaches exist to quantify the breakdown pressure. There have been many strategies to reduce this pressure for efficient and economical hydraulic fracture jobs, especially when this pressure exceeds pump capacity. This study provides a detailed review of breakdown pressure in terms of fundamentals, influencing factors, and estimation approaches. In addition, different strategies are also presented to reduce the breakdown pressure along with cost analysis. Lastly, research gaps pertinent to this area are highlighted for emphasis in future research. Specifically, it has been found that high breakdown pressure is associated with challenges, but there are no comprehensive techniques and strategies to lower this pressure in formations with very high in situ stress profiles or complicated tectonic settings. Developing such methods is important to minimize operational failures, lower costs and reduce the environmental risks during reservoir exploitation. This study reviews the fundamentals, influencing factors, and estimation methods of breakdown pressure and provides a deep understanding of the strategies for its reduction. The study also presents the cost analyses, and highlights research gaps for future investigation.