Cyclic Injection Scheme to Reduce Breakdown Pressure in Hydraulic Fracturing Wells: Case Study

Abstract Globally, the development of unconventional resources has drastically played a pivotal role in the energy supply. The economic production from the unconventional reservoirs is a great challenge where these tight producing zones often exhibit extremely high in-situ stress with low permeability conditions, necessitating the hydraulic fracturing stimulation of each horizon to define fluid and assess productivity. This extreme in-situ stress condition poses a considerable high breakdown pressure, making the hydraulic fracturing techniques challenging when implemented to these types of reservoirs and often treatment parameters approach the equipment capabilities and operational limits without breaking down the formation or creating any fractures. Consequently, conventional techniques have yielded unsatisfactory outcomes, rendering the wells economically unviable. In this paper, a new approach has been developed to help reduce the formation breakdown pressure during the hydraulic fracturing treatment. The new approach encounters injection of hydraulic fracturing fluid in a series of hydraulic pulses schemes to induce fatigue failure damage and weaken rock tensile strength. This paper discusses the fatigue damage mechanism and constitutive relationship for rock subjected to cyclic stress. The mechanical response of rock under both monotonic and cyclic stress loading will be examined. The rate of fatigue damage evolution is influenced by the number of load cycles, stress amplitude and accumulated plastic deformation. This case study presents hydraulic fracturing technique, to reduce rock tensile strength, and induce fatigue damage to one of extremely in-situ stressed reservoirs which could not be broken-down by conventional hydraulic fracturing technique. The results of cyclic fracturing technique are summarized. The cyclic injection scheme fatigue response of rock reduces formation breakdown pressure by 16% compared to the results obtained in conventional hydraulic fracturing.