Large quantities of ceramic proppants find use in hydraulic fracturing every year. These proppants, however, are not interchangeable or commodity products but consist of unique materials and structural features that determine their practical mechanical properties. Exposing ceramic proppants to any amount of acid in fluids can alter their internal microstructure leading to a change in mechanical and production performance. While hydrochloric and hydrofluoric acids typically attack glassy phases due to the presence of silicon dioxide, other silicate dominant phases in the ceramic microstructure are also vulnerable to attack, such as mullite with its documented reactivity to hydrofluoric acids. The extent of acid attack on the ceramic microstructure depends on not only the acid concentration but also the temperature and time conditions which the well conditions dictate. Surface roughness, presence of surface porosity or cracks on the ceramic proppant, acts as an additional factor that decreases acid resistance. Acid attack of ceramic structures will result in the formation of high stress concentration regions in the proppant pack leading to an increase in fines generation at lower closure stresses. Selecting proppants based upon their phase chemistry and the expected well conditions can mitigate much of the damage the acid can cause to the ceramic microstructure.
This paper documents the change in mechanical behavior of ceramic proppants due to exposure to an acid environment. The results show that the acid significantly alters the ceramic microstructure and eventually changes the proppant pack characteristics which will affect production performance. The results of the paper will permit operators to select a ceramic proppant made from the appropriate material and microstructure to meet the requirements of their specific application. The operator will gain further insight into proppant performance issues that may improve long-term production.
Authors: Tihana Fuss (Saint-Gobain Proppants), E. Michael Snyder (Saint-Gobain Proppants), Daniel C. Herndon (Saint-Gobain Proppants), Walter T. Stephens (Saint-Gobain Proppants)