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

Authors:
Publisher website
Google Scholar
Abstract
Summary: Carbonate acidizing remains a fundamental stimulation strategy; however, a long-standing limitation persists. While acid treatments effectively increase permeability through carbonate dissolution, they also weaken the rock matrix, which can accelerate fracture conductivity collapse under high closure stress and limit applicability in weaker carbonate formations. This degradation of rock strength reduces the longevity and effectiveness of both matrix acidizing and acid fracturing, presenting a structural challenge for many carbonate reservoirs, particularly soft carbonates, and reservoirs subjected to high stresses. An acidic phosphate-based material (PBM) eliminates this tradeoff by simultaneously strengthening carbonate rock [tensile strength 2–5x, Brinell hardness (BH) + 30–50%, yield strength + 2.4x, Young’s modulus + 2.3x] while maintaining or enhancing permeability across multiple lithologies at temperatures up to 130°C, demonstrated across more than 90 new laboratory experiments. API fracture conductivity testing in Indiana limestone confirmed that post-acid PBM treatments maintain up to three orders of magnitude higher conductivity at closure stresses up to 10,000 psi compared with HCl-only baselines. Salinity plays a critical role: NaCl carrier fluids (1–3.2 M) significantly improved injectivity, dissolution patterns, strength enhancement, and permeability retention relative to distilled water. The acidic nature of the system enables direct compatibility with conventional acid systems such as 15% HCl and hydrochloric replacement (HCR) modified acid, allowing use either as a post-flush or coinjected additive. This study expands the operational envelope of the technology to higher temperatures, multiple carbonate lithologies, and acid integration pathways, and provides robust mechanistic insight into the dual function of the treatment. The combined results outline a practical, deployable approach to achieving long-lived fracture conductivity and extended production performance in weak carbonates and high-stress conditions, offering a pathway to extend production life and reduce costly restimulation interventions.

This publication has 28 references indexed in Scilit: