Restimulation of Unconventional Reservoirs: When Are Refracs Beneficial?

Restimulation treatments have been attempted in a wide variety of reservoirs, and more than 140 papers have been published documenting the success and failure of these efforts. A database of these published examples has been compiled and analyzed to identify the mechanisms responsible for production improvement following restimulation with propped fractures (refracs). A portion of this database was recently published (Vincent 2010), and specific field examples were highlighted to demonstrate that refrac treatments can improve production by numerous mechanisms, including: Enlarged fracture geometry Improved pay coverage through increased fracture height in vertical wells Greater lateral coverage in horizontal wells or initiation of more transverse fractures Increased fracture conductivity compared with initial frac Restoration of fracture conductivity loss caused by embedment, cyclic stress, proppant degradation, gel damage, scale, asphaltene precipitation, fines plugging, and other factors Increased conductivity in previously unpropped or inadequately propped portions of fracture Use of more suitable fracturing fluids Reorientation caused by stress-field alterations, leading to contact of new rock This paper will briefly review restimulation attempts in six Canadian reservoirs of interest to the local audience, and will then present a more detailed review of restimulation of horizontal wells in the unconventional Bakken oil formation. In addition to a summary of published results, this paper will introduce a significant amount of previously unpublished data regarding refrac treatments of horizontal laterals completed in the Middle Bakken. This study will identify several additional concerns and opportunities with restimulating horizontal wellbores that were not previously identified in literature reviews. This organized summary of field results and references will provide significant value to readers evaluating or designing restimulation treatments.