A New Method to Assess Stimulation of Sandstone Cores Damaged by Fines Migration

Abstract

Abstract Sandstone stimulation faces multiple challenges due to the heterogeneity of the formation and the sensitivity of its clay minerals. Fines migration results in lowering the formation productivity and complicates the stimulation process. Multiple field studies showed that treatment of fines migration is critical and can result in permanent damage of the wellbore. This study aims to locate, quantify, and describe the damage resulting of fines migration damage and its stimulation in sandstone formations and examine the impact of the clay content and its nature on the stimulation process. This work is structured to evaluate the stimulation of fines migration damage in Bandera, Berea, and Kentucky sandstones. Fines migration was induced by injecting deionized water to trigger the mobilization of the clay minerals in the core. Both HCl or formic acid, and mud acid stages were injected following the fines migration induction. The new formation damage evaluation methodology utilizes computed tomography (CT) and nuclear magnetic resonance (NMR) scanning before and after the fines migration induction and its stimulation. The data from CT and NMR were combined and processed to generate a 3D representation of the cores pore structure, which gives an insight on how the clay nature impacts the stimulation process and the pore system. The developed technique exhibited an excellent ability to visualize the core porosity distribution and the changes in the pore structure following the fines migration damage and the acid treatment. The 3D representation succeeded to assess the magnitude and the location of the formation damage due to fines migration and its stimulation. The injection of deionized water in the studied formations resulted in a different petrophysical responses, which came matching the prediction built on the mineralogy and porosity mapping using computed tomography data. These changes in pore structure prevailed as a controlling variable of the acidizing process. The stimulation of the damaged cores at 150 and 250°F resulted in the deposition of the alumino silicates toward the core outlet. These deposits are attributed to the acid leaching of the aluminum and iron ions from the alumino silicate structures. The high temperatures resulted in the deposition of alumino silicates closer to the injection point. The enhancement in permeability noticed in all of the studied formations showed to be due to the induction of narrow channels in between heavily deformed pore structures. This work added to the sandstone stimulation technology a new tool to assess the true impact of acid stimulation on fines migration damage. The high level of resolution of tracking the changes in the pore structure lay the road to optimize the treatments to enhance the productivity and lower the cost. This technique has a potential as a formation evaluation technique to evaluate other types of formation damage, such as fracturing fluids and water blockage.