An experimental investigation of the effects of corrosion inhibitor on the mechanical properties of reservoir rock

Abstract

Geothermal energy is one of the more sustainable alternatives to fossil fuels that could facilitate the energy transition. The production of geothermal energy incorporates the use of corrosion inhibitors to protect the steel well-parts from the corrosive production fluid. The injection of inhibitors leads to a risk of exposing the reservoir rock to these solutions. Up until now no data has been published to describe the effects of the corrosion inhibitor on the mechanical reservoir rock properties. This thesis aims to remedy this situation by performing compressive triaxial experiments on rock samples which have been saturated with inhibitor solutions. Two rock types which are representative of geothermal reservoir rocks were tested using two different inhibitors. The results were compared to a set of control experiments performed on water-saturated samples. The sandstone experiments show no discernible difference between the different fluid-types. The limestone experiments do show a number of differences: The limestone samples that were saturated with the first inhibitor type saw an increase in rock cohesion and a decrease in internal angle of friction. In contrast limestone samples that were saturated with the second inhibitor saw a decrease in rock cohesion and an increase in internal angle of friction. The lack of difference between the sandstone samples could be attributed to the inert nature of the constituent minerals. Limestone minerals are chemically more reactive and even though the exact nature of the chemical processes which lead to the observed differences remains unclear, a number of potential explanations are provided. We suggest that the change in mechanical rock parameters in the limestone rock are a result of the adsorption of the inhibitor components onto the particle surface. This adsorption alters the particle surface charge which leads to a change of the electrostatic repulsive forces. Additionally the same adsorption may affect the interparticle friction of our rock samples.