Drilling through oil sands poses a special challenge as a result of the sticky nature of bitumen and the unconsolidated nature of oil sands. Although bitumen adheres to drilling tools, causing high torque and drag and a reduced rate of penetration (ROP), the unconsolidated oil sands impose an additional difficulty associated with maintaining a gauge wellbore. Common methods to counter the adhesive nature of bitumen have involved the dissolution of the bitumen into the drilling fluid, which contaminates and impairs the drilling fluid and jeopardizes the wellbore stability. This paper presents a novel solution to overcome these issues. Through thoughtful design and formulation, a new oil sands drilling fluid (OSDF) system has been developed that contains a key multifunctional polymer additive as a bitumen modifier, filtration control agent, and lubricant. A comprehensive evaluation of this fluid system was made through a series of tests, including bitumen accretion, shear stability, fluid loss, foaming tendency, and lubricity. From all test results, the new OSDF demonstrated excellent performance in the prevention of bitumen accretion and the reduction of mud contamination. It also provides a low foaming tendency, good fluid loss control, enhanced lubricity, and operational flexibility at the full pH range. In addition, to be able to monitor the content of the key polymer additive at the rig site, two new field methods were developed to accurately quantify its concentration in the drilling mud. All of these advantages should provide superior rig performance in terms of avoidance of tool accretion and bit balling, enhanced wellbore stability, reduced torque and drag, and facilitation of running liner after the completion of drilling. This new development is an engineered solution that takes all aspects of oil sands drilling into consideration

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