Clay swelling inhibition mechanism based on inhibitor-water interaction: A COSMO-RS molecular simulation approach

The inclusion of clay stabilizers in water-based fluids (WBFs) during drilling, imparts WBFs with clay swelling-inhibitive properties. This protects the formation from damage due to the enhanced reduction of the swelling components (clay portions) of the formation by these chemicals during drilling. With the increasing demand for ‘green’ clay stabilizers for WBFs, knowledge of their inhibitive mechanisms is necessary for their effective selection and usage. Earlier, we proposed Amino acids (AAs) as effective “green and cheap’ clay stabilizers, However, the mechanisms through which AAs and other clay stabilizers perform shale stabilization have not been adequately described in open literature. This study is a follow-up work employed to evaluate and succinctly describe all the inhibition mechanisms utilized by AAs to prevent the swelling of the reservoir formations. Furthermore, we discovered a novel mechanism for describing the inhibitive potentials between clay stabilizers in WBFs. Herein, we employed five experimental techniques alongside a modelling tool - COSMO-RS, to evaluate and describe the inhibitive mechanisms of six AA clay stabilizers. This study confirmed that the interaction of AA and the water component of the WBF is a significant factor for AAs effective stabilizing potentials. This is an addition to literature which only highlights the interactions of clay stabilizers and clay minerals for the stability of the formation. This work evaluated all the possible interactions during a clay stabilization process and utilized statistical analyses to compare the percentage contributions of all the interactions among the clay stabilizers (AAs), clay minerals and WBFs. It was revealed that 38% of the swelling inhibition potentials of AAs depend on their interactions with the water component of the WBFs. Concurrently, 28% of the AAs inhibition potentials are based on their ability to modify the surface of reactive clays, while 15% is based on AAs ability to replace the exchangeable cations of swelling clays resulting in the strengthening of the clay's cleavage spacing. Lastly, 18% of AAs stabilizing potentials are based on their ability to neutralize the reactive moieties of swelling clays. The percentage distribution reveals that the effective interactions of AAs with the WBFs significantly contribute to their effectiveness in stabilizing shale formations. This study is essential as it provides researchers with a holistic methodology to characterize and evaluate clay stabilizers.