Saudi calcium bentonite: a novel modifier for enhanced foamed underbalanced drilling performance.

Underbalanced foam drilling (UBFD) requires stable foam systems that maintain low density and high carrying capacity under elevated pressure and temperature (EPT) conditions. However, achieving foam stability and performance in challenging drilling environments remains critical. This study explores the novel application of Saudi calcium bentonite as an additive to enhance the performance of ammonium alcohol ether sulfate (AAES)-based foams, addressing stability, rheology, and resistance to hydrocarbon contamination. AAES-based foams were prepared using synthetic seawater in a mildly alkaline environment, with and without Saudi calcium bentonite at various concentrations. Foam stability and viscosity were evaluated under ambient and EPT conditions (1000 psi, 90 °C) using dynamic and high-pressure foam analyzers, while hydrocarbon contamination tests assessed robustness. Rheological properties, including yield strength and viscosity, were measured to evaluate cuttings transport efficiency. The addition of 4 g/L Saudi bentonite significantly improved foam stability, evidenced by an extended half-life (+ 80 min) and enhanced liquid retention. Rheological analysis revealed a fourfold increase in viscosity at low shear rates and a ninefold enhancement in yield strength, enabling superior cuttings transport. The AAES-bentonite foam outperformed a commercial drilling foam in stability and viscosity while maintaining resistance to hydrocarbon contamination. The results suggest Saudi calcium bentonite as a promising additive for UBD foam systems, delivering enhanced stability, rheology, and contaminant resistance under challenging drilling conditions. This advancement supports more efficient and sustainable UBD operations in saline and high-temperature environments.