Understanding and Mitigating Depletion Effects in Infill Wells for Optimized Production
Authors: Ajisafe Foluke , Reid Mark , Porter Hank , Fox Derek , Wigger Eric , Drouillard Matthew , Defeu Cyrille , Marquez Aleida , Vidma Konstantin , Abivin Patrice , Ajose-Ogunlana Damilola , Srinivasan Karthik 
Published: August 2019

Production interference between parent and infill wells has become of utmost importance in unconventional reservoirs across the U.S. due to sub-par production performance of child wells as well as possible loss of production to the parent well. To mitigate production interference between parent and child wells, operators have applied various measures such as refracturing, repressurization of the parent well, and reducing child well stimulation jobs; these measures can be costly and yield mixed results. This study demonstrates the benefits of reservoir modeling to understand the effects of parent well production depletion on child wells at different well spacing as well as the use of successful mitigation strategies such as near-wellbore diverters and fracture geometry control to mitigate frac hits between wells drilled as close as 800 ft apart. A multidisciplinary integrated workflow was applied in a multiwell pad in the Bakken consisting of one parent and two child wells. The parent well was completed and produced for about 7 years, after which the two child wells were drilled 1,300 and 800 ft, respectively, on each side of the parent well. High-tier vertical logs were used to build a geomechanical and petrophysical model for the pad. The model was used for hydraulic fracture modeling and production history match of the parent well, after which the reservoir pressure depletion profile was used in a geomechanics simulator for an updated in situ stress state at 7 years. The updated stress state was then used for fracture modeling of the two child wells. The child well 800 ft from the parent well showed more hydraulic fractures directly hitting the parent well. The child well at 1,300 ft showed fewer hydraulic fractures directly hitting the parent well. The pressure depletion profile around the parent well had more negative impact on the child well at 800 ft away compared to the child well at 1,300 ft away because of its proximity. To eliminate this negative effect, fracture geometry control technology was used in the hydraulic fracture model for the child well 800 ft away from the parent well. It showed to be successful in reducing the occurence of frac hits to the parent well, diverting hydraulic fracture growth away from depleted regions around the parent well. During the actual operation, the results were confirmed with high-frequency pressure monitoring. Details of the field deployment of the fracture geometry control technology are discussed in detail in Vidma et al. (2019). No pressure communication was observed in stages pumped with the fracture geometry control technology.

The child wells were completed and put on production without any sanding damage to the parent well, saving the operator approximately USD 400,000 and more than 2 weeks of deferred production if cleanout had been required. Actual production results showed superior performance in the child well at 1,300 ft away compared to the child well at 800 ft away. This confirms that the pressure depletion profile had more impact on the child well 800 ft away compared to the child well at 1,300 ft. Reservoir modeling is critical to understanding the level of pressure depletion in a producing well and its effect on child wells at different well spacing. It has also proven helpful in designing an optimum fracture geometry control pill to minimize the occurrence of frac hits that could damage parent well productivity.