(31d) On the Mechanisms of Sequenced Fracturing

Fracturing over long horizontal intervals while using only limited-entry techniques for diversion leaves areas along the wellbore understimulated. Improving wellbore coverage is addressed by using diverters, often in the form of particulates designed to temporarily plug the formation and direct fluids away from the stimulated areas. The success of the wellbore coverage and the overall stimulation are dependent on the ability to formulate a diverter that is effective at plugging, and that can be transported from surface to downhole with little dispersion. The considerations for successful diversion and overall fracturing treatment are integrated in a technique called sequenced fracturing.

Sequenced fracturing was studied with the objective of understanding how diverters are transported and how they plug fractures and generate effective diversion. Based on a review and experiments, methods to prevent dispersion of the particles could be compared and mechanisms of diverter failures investigated. Simulations were used to investigate the effects of diversion on the pressure response and overall quality of the stimulation.

Results from laboratory experiments, computer simulations, and well performance evaluations were analyzed collectively to reach three main conclusions. First, particulate diverters are effective at plugging fractures provided they can be transported from surface to downhole with minimal dispersion. The use of fiber is instrumental in minimizing the adverse effects of wellbore dispersion on diversion effectiveness. Second, effective diversion should rely on plugging the near-wellbore area. Computer simulations show that diverter misplaced in the fracture, at an excessive distance from the wellbore, is more likely to fail under differential pressure. Third, computer simulations showed that pressure response and impact on stimulation are functions of the rock and the well completion. Examples are provided to illustrate how in-situ stress configuration affects pressure response and stimulation effectiveness of a sequenced fracturing treatment.