Rheological behavior of oil-based drilling foams

• Oil-based foams tested in this investigation show non-Newtonian behavior.
• Like aqueous foams, rheology of oil-based foams greatly depends on quality and base-liquid viscosity.
• Wall-slippage is evident in the small pipe size used.
• Pressure loss reduction of up to 30% was observed due to wall slip.
• As expected, the averaged bubble size of oil-based foams increased with foam quality.

The application of foam in the petroleum field has been around since the late sixties. Foam has been successfully used in stimulation as well as drilling. It has desirable properties which make it very suitable for underbalanced drilling (UBD) and other oilfield applications such as cementing, well stimulation and fracturing. Aqueous foams have been in the industry for a long time. As a result, in the past, foam research was more focused on characterization of aqueous foams to optimize their hydraulic and hole cleaning performance (solids carrying capacity). Currently, modern foams such as polymer-based and oil-based foams are becoming more popular due to their superior performance. However, flow behavior of modern foams is complex and not well-understood.The principal objective of this study is to investigate flow behavior of oil-based foams. In order to achieve the study objective, experiments were performed using a recirculating flow loop that has three pipe viscometers. Tests were conducted at room temperature (25 ± 2 °C) and elevated pressure (0.67 MPa). Base liquid was prepared by mixing diesel (68%), mineral oil (30%) and surfactant (2%). Nitrogen was used as the gas phase. Foam quality (i.e. gas volume fraction) was varied from 34 to 68%. The effect of foam quality on bubble size was also investigated to provide further insight into the behavior of oil-based foams.Results showed non-Newtonian behavior of oil-based foams which becomes more prominent as foam quality increases. Moreover, like aqueous and polymeric foams, rheology of oil-based foams greatly depends on quality and base-liquid viscosity. Wall-slip effect was observed in the small diameter pipe (13.4 mm). The averaged bubble size of oil-based foams increased with foam quality.