The successful drilling of an oil and gas well relies upon the application and maintenance of innovative technology. In order to improve drilling efficiency, all pertinent data needs to be reviewed appropriately and lessons learned need to be drafted and realized. This is particularly important with challenging extended-reach wells. Due to the very low permeability in the target formation, long horizontal laterals are desirable to improve oil recovery and maximize productivity. Long lateral lengths are limited by frictional losses from torque and drag. In this environment, a drilling fluid that is able to maintain low lubricity coefficients is required. In addition, the fluid must be environmentally sound and cost-effective. An underbalanced high-performance brine drilling fluid (HPBDF) was introduced as an alternative to the weighted oil-based fluid required in use.
As expected, different fluids require different strategies. When using a HPBDF, monitoring lubricant concentration and use is best practice. Using field measurements to adjust concentrations, the desired lubricity was achieved and maintained while minimizing lubricant use. Low lubricity coefficients correspond with reduced pipe wear and decreased torque and drag. By planning, monitoring and maintaining the HPBDF, the operator successfully achieved higher rates of penetration (ROP) resulting in shorter drilling times. In this application, low viscosity brines improved wellbore cleaning due to turbulent flow cuttings transport. This reduced time spent on clean up cycles and tripping times as compared to offset wells drilled with oil-based fluids.
The brine density eliminated the need for barite and minimized the solids in the drilling fluid. Suspended drilled solids in the HPBDF can increase abrasion and lead to increased torque and drag and directional tool wear and failures. When solids accumulated in the HPBDF, a dewatering system was used to flocculate the solids and remove them through a centrifuge to produce clean brine. Techniques were improved to provide clear brine while minimizing lubricant loss. For example, application of a high-performance fluid conditioner prevented lubricant loss in the dewatering process.
This paper discusses the use of HPBDF in drilling over 50 wells and the challenges overcome. It also details the equipment used and highlights the comprehensive technique for evaluating lubricity and its correlation to torque and drag. The resulting performance improvements reduced drilling costs by over 20%.