ACID SOLUBILITY TESTING OF GREYWACKE CORE AND IMPLICATIONS FOR WELL PERMEABILITY ENHANCEMENT

Abstract

Acidizing of geothermal wells can be a cost-effective and attractive option to recover well permeability and productivity compared to drilling new wells. Understanding how the reservoir rock may react to acid injection is important to ensure that damage to the reservoir formation does not occur and also to help understand if permeability can be improved. In an effort to investigate the effect of acid stimulation on Greywacke core, a series of core plugs were extracted from core taken from an injection well hosted in Greywacke. These plugs were measured for porosity, density, seismic wave velocity, and permeability. The samples were then selected to have a first suite exposed to HCl acid, a second to both an initial HCl treatment followed by HCl/HF treatment and a third untreated to act as control. The samples were re-measured for changes in their physical properties following acid exposure. The initial HCl testing results show changes in physical properties across the samples. The HCl/HF testing also resulted in changes to physical properties. Permeability increased in all samples exposed to acid treatment. Further, after physical characterization, the samples were mechanically tested to determine Uniaxial Compressive Strength (UCS). Strength decreased in all samples treated with acid. The results of the testing are discussed here and the implications for changes to reservoir permeability and strength are explored with respect to acid treatments on both injection and production wells hosted in Greywacke.