Legacy Well Protection Refrac Mitigates Offset Well Completion Communications in Joint Industry Project
Authors: Courtier James , Gray Danny , Smith Michael , Stegent Neil , Carmichael James , Hassan Magdy , Ciezobka Jordan 
Published: August 2016

Abstract
Fracture stimulation of infield or offset wells in unconventional developments can involve communication between the legacy (parent) wells and newly drilled offset (child) wells. Production from the legacy well results in a decrease in reservoir pressure and stress, which can cause pressure sinks that ultimately lead to fracturing fluid communicating between the child and parent wells. Depending on the reservoir conditions, completing infield wells can result in production losses for the parent well, and in some cases, the parent well might never fully recover its full production potential. One of the current strategies used to minimize offset well completion communication with a parent well is to perform a preemptive protection refracture of the parent well. However, for the majority of these restimulations, the operator does not receive confirmation of refracturing effectiveness—even after production data from the refractured well become available.
Under the auspices of the Gas Technology Institute, the Department of Energy helped fund a research project hosted by Laredo Petroleum (the operating company) in the Wolfcamp to better understand, among other things, the relationship between lateral well placement, production interference between laterals, effectiveness of completion sequences, and hydraulic fracture geometry in unconventional reservoirs. Two vertically stacked parent wells that had been producing for approximately 15 months were chosen as the subjects for this study. The two vertically stacked parent wells were landed in the Upper and Middle Wolfcamp formations in the Midland basin of West Texas. The objective of the study was to understand the impact of refracturing these two wells immediately before the stimulation of 11 offset child wells (part of a development program within a production corridor setting) with regard to the reservoir pressures and stresses surrounding both the parent and child wells. Conclusions were drawn based on well treatment and downhole microseismic data, which were acquired during the restimulation of the two parent wells and the completions of the 11 child wells, and data from radioactive (RA) tracers that were pumped during the refractures. Overall, microseismic analysis revealed positive pressure protection effects were achieved during the refracture.
Downhole microseismic data for the refractured wells focused on events that occurred both near the wellbores and in the far-field and the time at which they occurred relative to the execution of the restimulation. Results from the first restimulated parent well indicated that less than half of the well was successfully restimulated and, therefore, only a portion of the reservoir between the laterals was repressurized. This resulted in the development of asymmetric fractures in the offset child well in the lower pressure portion of the reservoir, while the section that was repressurized resulted in symmetric fracture development. Using real-time microseismic monitoring during the completion of the parent wells allowed for an immediate review of the acquired microseismic data and on-site adjustments to the pump schedule. As a result, the restimulation of the second parent well appeared to have more effectively repressurized the reservoir and promote the creation of symmetric fractures during the completion of the offset child well that was landed in the same formation (as the second refracture parent well). RA tracer results were in alignment with the microseismic data.