Bio-corrosion and acid stimulation in geothermal operations: abstract + presentation

Geothermal Energy (GE) is the natural heat energy stored in the rocks and water in the Earth’s interior. GE is a green renewable energy source as compared to conventional sources such as fossil fuels. It provides long-term energy with lower carbon footprint than other renewable energy. However, corrosion and poor or low permeability in geothermal systems are the pervasive issues. Corrosion affects the major components up- and downstream. Corrosion caused by biotic factors is difficult to forecast compared to abiotic corrosion. For that reason, the influence of microbial metabolites on the electrochemical kinetics of carbon steel –biotic corrosion requires thorough investigation. Also, poor or low permeability in geothermal reservoirs is a perennial concern even in highly convective geothermal systems. Techniques typically used in oil and gas reservoirs to enhance reservoir quality can be used in geothermal reservoirs. For example, increasing permeability helps to create heat convection and allows better heat flow from the subsurface to the surface. Acid stimulation can be used to increase permeability however, acid stimulation sometimes fails due to either poor stability of the acid or undesirable interaction between clay minerals in the cap rock and the acid. In this study, bio-corrosion and acid stimulation are studied under simulated non–volcano geothermal conditions. The influence of Extracellular Polymeric Substrates (EPS)-biofilm, acetic and L-ascorbic acids on bio-corrosion are investigated. The electrochemical techniques (PotentioDynamic Polarization (PDP) and Electrochemical Impedance Spectroscopy (EIS)), Inductively Coupled Plasma - Optical Emission Spectrometry (ICP-OES), X-Ray Diffraction (XRD) and pH measurements are implemented in characterization. Subsequently, the interaction of green chelating agents (BCA-1 and BCA-2) and clay minerals (kaolinite and smectite) under CO2 flooding are studied. The research shows that the simulated EPS–biofilm under anaerobic conditions has no influence on accelerating corrosion which is in contrary to results reported in some literature. In addition, the presence of acetic and L-ascorbic acid accelerates corrosion on test coupons. The increase in corrosion rate with acetic acid is in agreement with the available literature while that with L-ascorbic acid contradicts. On the other hand, results on compatibility of clays with green chelating agents show that both have low precipitate of minerals. This makes both green chelating agents suitable for improving the reservoir quality as they have limited reactions with clays. This is the first time to report these findings on BCA-1 and BCA-2. Understanding the influence of metabolites on corrosion enables the development of better strategies to avoid or decelerate corrosion. Moreover, understanding compatibility of clays and green chelating agents would help to increase porosity and consequently permeabilit