Optimizing Hydraulic Fracturing in Carbonates: Integrating Matrix Strengthening with Permeability Enhancement

Abstract This paper presents laboratory results on a novel glass-based chemical treatment designed to consolidate and stimulate carbonate reservoirs. Core flood testing demonstrates that this treatment strengthens carbonate rock while enhancing matrix permeability, in both intact and pre-fractured chalk samples. The study explores the potential applications of these findings for improving matrix production and enhancing conductivity in hydraulic fracturing operations, particularly in weaker carbonate formations. Testing results from multiple projects and laboratories have been compiled and analyzed to evaluate strength enhancement and permeability improvement across various temperatures, injection conditions, and fluid formulations. Core flood experiments were conducted primarily on Mons chalk, Austin chalk, and Indiana limestone outcrop cores (5.5–20 cm in length), with some featuring pre-drilled holes to simulate existing fractures. Post-treatment return permeability and Brazilian tensile strength were measured to assess the effectiveness of the chemical treatment in both intact and fractured samples. Tri-axial testing was also performed on multiple untreated and treated Mons chalk samples to determine the geomechanical effects of the treatment. The treatment consistently enhances rock strength, with tensile strength increasing by up to 3.0 MPa (a 2 to 5-fold improvement over untreated samples). Additional Mons chalk strength improvements include a 1.9 to 2.4-fold increase in Yield strength, a 1.4 to 2.3-fold increase in Young's modulus, and a 1.1 to 1.2-fold increase in Bulk modulus. Simultaneously, post-treatment permeability regains range from 40% to over 1000%. Core flood tests exhibit two distinct outcomes: some demonstrate matrix treatment, while others show significant wormhole formation. Tests on pre-drilled cores and samples with wormholes indicate radial strength enhancement around voids, suggesting the potential to reinforce fracture faces in fractured carbonates. Strengthening and increasing permeability in the rock face surrounding fractures may enhance fracture conductivity and boost matrix production, ultimately improving oil recovery. Extensive testing across various parameters has deepened the understanding of optimal fluid formulations, the influence of injection parameters, and the effects of downhole conditions on treatment performance. These findings enable a more tailored approach to treatment design, maximizing its effectiveness in fractured carbonate reservoirs. This paper presents new laboratory testing of a novel chemical solution currently being trialed for consolidation in a chalk reservoir. It includes the first-ever tri-axial testing results with Mons chalk, core flood experiments and subsequent tensile strength testing with Austin chalk and Indiana limestone, and the reported fracture conductivity findings using Indiana limestone samples. The study explores the potential benefits of applying this treatment to hydraulically or naturally fractured carbonate reservoirs, highlighting its ability to enhance fracture conductivity while simultaneously improving matrix production in the surrounding rock.