Sustaining Wormholes Mechanical Stability in Weak Acidized Carbonates Using Consolidants

Matrix acidizing is vital to enhance the production of tight carbonate formations. In weak carbonate rocks or acid over-dissolution, the rock is prone to failure upon developing wormholes. Strengthening agents can play a significant role in mitigating failure and supporting more extended productivity. In this study, we tested 0.1 M and 0.2 M zinc sulfate (ZnSO₄) and 0.5 M diammonium phosphate ((NH₄)₂HPO₄) as strengthening agents, which change the dominant host mineral into harder ones. Both agents were tested on two different types of acidized (i.e., wormholed) carbonate rocks, specifically Austin chalk and Indiana limestone. The impulse hammer and acoustics measurements evaluated the carbonate rocks’ mechanical properties before and after the treatment. In addition, scanning electron microscopy energy-dispersive X-ray spectroscopy (SEM–EDS) and scanning electron microscopy (SEM) were used to affirm the change of rock mineralogy into harder minerals after the treatment. The chemical treatment caused no noticeable change in the wormhole size and shape, as revealed by the scanned micro-computed tomography (micro-CT) images. The chemical treatment of the samples was conducted by core flooding the plugs at high pressure and temperature with 4–5 pore volumes of the chemicals and leaving them in the treatment solution for 72 h. As a result of the formation of harder minerals, the mechanical properties after the treatment showed improvement. Zinc sulfate raised the surface rock hardness of limestone by 16%, while diammonium phosphate showed a 30% increase when evaluated with the same technique. The most noticeable improvement happened to chalk after treatment with diammonium phosphate. Chalk impulse hammer hardness almost quadrupled with the diammonium phosphate. The acoustics measurements showed a similar result to the impulse hammer through an increase in the dynamic Young’s modulus and a decrease in Poisson’s ratio.