Thermodynamic modeling hexamethylenetetramine adsorption on sandstone

Excessive water production in oil wells presents a significant operational challenge, often requiring the use of in-situ gel treatments to block water-producing zones. However, a major challenge in the effectiveness of these treatments lies in the adsorption of gelant components onto reservoir rocks during injection, which can hinder gel formation. This research presents a novel thermodynamic investigation into the adsorption behavior of HMTA, a commonly used crosslinker, on sandstone reservoir rocks. The novelty of this study is that it provides a comprehensive thermodynamic analysis of adsorption in porous media, which has been scarcely explored in the literature. Additionally, we compare the adsorption behavior across various porous media, an approach that is rare in current research. Understanding the adsorption of HMTA in sandstone reservoirs is crucial for developing more effective gelant formulations and optimizing treatment strategies to address water production issues in oil wells. The study utilized batch experiments over a temperature range of 25-80 °C to evaluate HMTA adsorption on quartz grains. The findings revealed that the adsorption process follows the Langmuir isotherm model, indicating monolayer adsorption driven primarily by hydrogen bonding. Adsorption capacity increased with temperature, ranging from 64 to 93 mg/g-rock, confirming the endothermic nature of the process. The thermodynamic analysis further revealed that the adsorption of HMTA is spontaneous, characterized by positive enthalpy (∆H° = 16.57 kJ/mol) and entropy (∆S° = 94.5 J/mol⋅K), along with negative Gibbs free energy at all tested temperatures. Core flooding experiments on sandstone cores with a 100,000 mg/L HMTA solution corroborated the batch experiment results, although lower adsorption capacities (30-54 mg/g-rock) were observed due to the complexity of the porous medium.