Production rates in unconventional plays can decline dramatically, up to 70% in the first year. Refracturing—by today's understanding—is a remedial production operation often done because original fracturing failed to contribute any significant amount of flow, performance of the initial completion has degraded over time to below operationally or economically acceptable limits, or significant unfractured pay exists in the well.
Developments in nondamaging, degradable diverters with outstanding plugging efficiency have opened new opportunities for protecting existing fractures by plugging them and then fracturing zones that were previously bypassed because of inefficient zone coverage or refracturing zones that were inefficiently fractured initially. In fact, these new diverters enable zonal isolation for horizontal wells with multiple perforation clusters and for temporarily plugging perforations for re-stimulation treatments instead of squeezing the perforations and sealing them off. With multistage operations becoming the industry norm, operators need easily deployable diversion technologies that will protect previously stimulated perforations and enable adding new ones to untreated perforations or bypassed zones.
This paper reviews in-stage Diversion, including a brief discussion of diverter candidate selection in terms of production and risk assessment to ensure return on investment. Also included is an explanation of underlying mechanisms controlling the diversion process and the use of advanced modeling techniques to enhance efficiency of diversion operations. Then a case study is discussed to highlight how temporary and degradable chemistry can be used to enhance zone coverage, to provide temporary isolation between zones in shale fracturing operations, and to achieve multiple effective fracture treatments within the same stage. These degradable chemical diverting agents form a solid impermeable barrier or seal that in time will break or degrade to liquid form, leaving the existing zone that was diverted open to permit flow.