Permeability reduction in wide fractures: the use of fiber-gels

• Mineral fiber gels outperformed plain and synthetic fiber gels in reducing brine permeability in 4-mm-wide fractures. • The addition of fibers and reduced polymer content lowered gel placement pressure while increasing brine flow resistance. • Sequential fiber-gel treatments raised the post-flush pressure gradient from 0.65 to 1 MPa/m — the main achievement of this study. While reducing permeability in fractures is challenging, it offers potential for minimizing water cut. In this work, 4-mm-wide fractures were treated with polymer or polymer-fiber gels. The gel formulation containing 0.75 wt% polymer and 1.5 wt% mineral fibers achieved a maximum brine post-flush pressure gradient of 0.65 MPa/m. In contrast, the use of plain 1.5 wt% polymer gel resulted in only 0.45 MPa/m. Remarkably the extrusion of the polymer-fiber gel required a lower pressure gradient than the subsequent brine post-flush (0.35 vs. 0.65 MPa/m). These results indicate that incorporating mineral fibers into the gel, while reducing the polymer concentration, can lower the gel placement pressure and at the same time increase resistance to brine flow. This effect is attributed to the accumulation and interlocking of fibers, which form a barrier. In other experiments, gels with 3–13 mm synthetic fibers did not raise the post-flush brine pressure gradient above ∼0.15 MPa/m. Overall, mineral fiber gels were more effective than synthetic ones. The concept of plugging wormholes within the gel filter cake was also evaluated. Injection of a gel with 6-mm-long synthetic fibers into a fracture containing a gel filter cake increased the extrusion pressure gradient from ∼0.75 to 1.5 MPa/m but had no effect on brine flow. However, in another test, sequential injection of gels containing 13 mm synthetic fibers and gels containing mineral fibers into the same fracture increased the post-flush pressure gradient from 0.65 to 1 MPa/m. This result is considered the main achievement of the study.