Drilling and Completing High-Angle Wells in High-Density, Cesium Formate Brine—The Kvitebjørn Experience, 2004-2006

Abstract

Summary Drilling and completion fluids based on cesium formate brines were selected by Statoil for use in the development of the high-pressure/high-temperature (HP/HT) Kvitebjørn field. CsFo brine was selected primarily to minimize well-control problems and maximize well productivity. These important benefits had been recognized by Statoil in previous HP/HT drilling and completion operations over the past 5 years. The use of the same fluid system for both drilling and completion gives the additional benefits of simplified operations, reduced waste, and elimination of fluid-incompatibility problems. The challenge on the Kvitebjørn field was to drill long, deviated well paths through significant sequences of shales into reservoirs with pressures as great as 81 MPa (11,700 psi) and temperatures up to 155°C (311°F). So far, the CsFo brine has enabled the successful drilling and completion of seven high-angle, HP/HT production wells on Kvitebjørn, two completed with a cemented/perforated liner and five with sand screens. Additionally, an extended-reach exploration well was drilled from the Kvitebjørn platform to the Valemon structure. The 705-m (2,313-ft) -long reservoir section of this 7380-m (24,213-ft) -long well with an inclination of 69° was drilled successfully with the same CsFo fluid system. In all these wells, the CsFo-brine system once again demonstrated clear performance benefits such as very low equivalent circulating densities (ECDs), moderate-to-high rates of penetration (ROPs), good hole cleaning, and excellent wellbore stability while logging. Quick, trouble-free, safe, and robust completion operations were also accomplished, and the wells that have been put on production show high production rates with low skin. Full openhole formation evaluation of the Kvitebjørn reservoir has been carried out successfully with logging-while-drilling (LWD) tools. The evaluation has been aided by the development of a novel logging-interpretation solution for a LWD density tool, in which the extremely high photoelectric effect of cesium-rich filtrate plays a vital role. CsFo brine has helped Statoil to achieve a record of zero well-control incidents in all 15 HP/HT-drilling operations and 20 HP/ HT-completion operations in the Kvitebjørn, Kristin, and Huldra fields over a period of 5 years.