Foam Stability Analysis at High pH and Saline Environments for Underbalanced Drilling Operations

Aqueous foams have been used in many underbalanced drilling applications, and their success significantly relies on foam stability. Many studies in the literature have investigated different drilling-foam systems with different surfactants and additives. However, very limited studies reported the foam performance in a high pH environment that is highly recommended for drilling operations to avoid corrosion. Moreover, the stability of the drilling-foam systems should be tested against formation influxes, e.g., brine. However, it is fairly covered in the reported studies. Therefore, this study presents an experimental investigation to evaluate the stability of a set of surfactants (anionic and zwitterionic) at high pH conditions that mimic a typical drilling environment. These surfactants are ammonium alcohol ether sulfate (CPID), coco amido propyl dimethyl betaine, alpha-olefin sulfonates, and coco amido propyl hydroxysultaine. Moreover, the effect of water salinity on the foam stability was investigated. A commercial drilling-foam blend was used as a reference. The tests were conducted using water samples with different salinities, i.e., deionized water, synthetic sea water, and formation water. The analysis of the foam properties such as foam bubble count, structure, foam half-life, and liquid drainage was conducted using a sophisticated foam analyzer. The surfactants used for foaming exhibited have varying impact on foaming properties, i.e., foam stability, structure, and foamability, with increasing water salinity. Therefore, it is recommended to investigate them independently to evaluate their compatibility with different water salinities. The results showed that the surfactant: Ammonium alcohol ether sulfate (CPID) is suggested to be a good potential candidate for UB drilling applications. This is because it showed good compatibility with different water salinities with no considerable impact on its formability. Moreover, it showed promising stability which increases with increasing water salinity, unlike the other tested surfactants. The analysis also showed that CPID surfactant had very comparable foam characteristics to the commercial blend and hence promotes its potentiality to be a good drilling foam. This study would help provide a better understanding of the drilling foam in a mildly alkaline environment. Besides, it is substantial to improve operational safety and cost control, as well as mitigate the risks associated with the application of foam drilling.