The influence of chelating agents on clays in geothermal reservoir formations: Implications to reservoir acid stimulation

Acid stimulation to enhance the permeability of geological reservoirs is the oldest technique still in use. Acid stimulation sometimes fails due to either poor stability of the acid or due to an undesirable influence on clay minerals in the reservoir formation. Among others, clay minerals in a reservoir formation govern the permeability of the reservoir. The interaction is investigated of biodegradable chelating agents (BCA1, BCA2 and BCA3) and clay minerals kaolinite-natural (KN) and montmorillonite-K10 (MM) in a hydrothermal reactor in which the conditions of a geothermal reservoir are simulated under a CO2 environment with temperature of 230 οC and pressure of 85 bars. The porisimetry, ATR-FTIR and infrared reflectance spectroscopy show changes on surface properties and structure of MM and KN which in turn suggest chemical interaction to take place. However, XRD results show insignificant changes on structure of MM and KN. The ICP-OES, pH, conductivity and salinity results show the chemical interactions (dissolution reactions) to take place on both KN and MM and therefore strongly support the results of the earlier techniques. The results show that BCA1 and BCA3 cause greater dissolution with lower precipitation as compared to BCA2 and no-BCA. Further, the R -values from multiple linear regression show that pH and BCAs’ function groups have strong influence on the normalized concentration of dissolved ions though the p-values are insignificant. The coefficient values show that the BCAs’ functional groups have more influence than pH. BCA1 and BCA 3 would therefore be useful acids for reservoir stimulation in improving permeability especially in geothermal reservoir formations which contain clay minerals.