Restimulation of Unconventional Reservoirs: When Are Refracs Beneficial?

Abstract

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 In addition to a summary of published results, this paper will introduce a significant amount of previously unpublished data regarding refrac treatments of horizontal laterals completed in the Middle Bakken.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.

Analytical Solution and Simulation of Oil Deliverability Analysis for Reorientation Hydraulic Fracture in Low-Permeability Reservoirs

“…The benefit of existing refracture wells has been proved by a lot of studies [4,5]. Compared to drill new wells, refracture operations have been an economical way for improving oil deliverability [6][7][8][9].…”

Verification of Fracture Reorientation and Analysis of Influence Factors in Multiple Fracturing Treatment

“…Unconventional reservoir formations are considered to be with low permeability and porosity, and underground liquid seepage is hard to achieve during the producing process. Profitable productivity can be obtained only by implementing stimulation treatment [1,2]. However, after long-term production, the productivity of wells with initial fracturing treatment will decrease due to improper or small-scale fracturing treatment, closure of initial fracture, fines plugging, deformation and cracking of proppants, and borehole contamination [3,4].…”

Research on stress alternation effects and fracture reorientation for refracturing treatment

“…The mechanism of refracturing treatment includes reopening the initial fracture, creating a new fracture, and reorienting the new fracture. 5 It has been proven that fracture reorientation will greatly enhanced oil recovery, since the new fractures intersect a region with more residual oil and higher pressure. 6 The new fractures will initiate from the well bore and propagate to the direction perpendicular to the initial fracture.…”