Mitigation of bitumen and asphaltene accretion to the drillstring and other drilling components has become an important task due to the increasing production of oil sands and heavy oil deposits. When drilling through oil sands or encountering a bituminous zone, numerous problems can occur due to the extreme adhesive nature of the bitumen. Drillstrings and other tubulars can become coated, causing stuck pipe and undesired nonproductive time (NPT). Surface equipment such as shaker screens, can become fouled, resulting in poor drilling fluid properties. Common methods to counter the adhesive nature of bitumen have involved solvation of the bitumen into the drilling fluid. However, these methods not only contaminate the drilling fluid (resulting in disposal concerns), but can also negatively affect the fluid's properties, such as rheology.
This field trial utilizes a water-based mud and examines the effectiveness of a new polymer additive to mitigate the adhesive nature of bitumen, thereby preventing the occurrence of wellbore accretion. The bituminous cuttings are rendered non-adhesive, transported by the drilling fluid to the surface, and separated by conventional solids control equipment. In this fashion, the drilling fluid properties are not altered, and the water-based mud can be disposed of without the environmental issues of a contaminated fluid. Field trials and lab results have shown that small additions of this bitumen stabilization polymer to water-based drilling fluid renders the bitumen non-adhesive. Field trials have been completed in northern Canada and show extremely positive results with this polymer additive. It was shown that when the tar sands interact with the polymer additive, the tar becomes non-adhesive, and remains non-adhesive following contact with aqueous solutions. By preventing the bitumen from solvating or dispersing into the drilling fluid, the bituminous cuttings can easily be surface-separated. Torque and drag issues commonly seen while drilling through oil sands were also alleviated with use of this polymer additive.