TX 75083-3836 U.S.A., fax 1.972.952.9435. AbstractDrilling and completion fluids based on cesium formate brines were selected by Statoil for use in the development of the high pressure high temperature Kvitebjørn field. Cesium formate brine was selected primarily to minimize well control problems and maximize well productivity. These important benefits had been recognized by Statoil in previous HPHT 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 of up to 81 MPa (11,700 psi) and temperatures up to 155°C (311°F). So far the cesium formate brine has enabled the successful drilling, completion, and logging of 7 high angle HPHT 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 7,380 m (24,213 ft) long well with an inclination of 69°, was successfully drilled with the same cesium formate fluid system.In all these wells the cesium formate brine system once again demonstrated clear performance benefits such as very low ECDs, moderate to high 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 open-hole formation evaluation of the Kvitebjørn reservoir has been carried out with 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. Using photoelectric factor and bulk density data, combined with resistivity measurements from both the LWD drill pass and the ream pass, produces a very reliable and consistent net reservoir definition. The final interpretation result matches the core porosity from different lithologies in 3 different wells.Cesium formate brine has helped Statoil to achieve a remarkable record of zero well control incidents in all 15 HPHT drilling operations and 20 HPHT completion operations in the Kvitebjørn, Kristin, and Huldra fields over a period of 5 years.

Formate brines have been in use since 1995 as non-damaging drill-in and completion fluids for deep HPHT gas condensate field developments. The number of HPHT fields developed using formate brines now totals more than 40, and includes some of the deepest, hottest and highly-pressured reservoirs in the North Sea. The well completions have been both open-hole and cased-hole.An expectation from using formate brines as reservoir drill-in and completion fluids is that they will cause minimal damage to the reservoir and help wells to deliver their full productive potential over the life-time of the field. The validity of this expectation has been tested by examining the long-term hydrocarbon production profiles of eight HPHT gas condensate fields in the North Sea where only formate brines have been used as the well completion fluids. In five of these fields the wells were drilled with oil-based muds and completed by perforating in cased hole with high-density formate brines. In another two of the fields the wells were drilled with formate brines and completed with screens entirely in open hole using the same brines.The last of the eight fields was drilled with formate brine and the wells were then completed with same fluid in either open hole or cased hole.The results of the production analysis provide a unique insight into the impact of a single type of specialist drill-in and completion fluid on the rate of recovery of hydrocarbon reserves from deeply-buried reservoirs in the North Sea.

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.

TX 75083-3836 U.S.A., fax 1.972.952.9435. AbstractDrilling and completion fluids based on cesium formate brines were selected by Statoil for use in the development of the high pressure high temperature Kvitebjørn field. Cesium formate brine was selected primarily to minimize well control problems and maximize well productivity. These important benefits had been recognized by Statoil in previous HPHT 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 of up to 81 MPa (11,700 psi) and temperatures up to 155°C (311°F). So far the cesium formate brine has enabled the successful drilling, completion, and logging of 7 high angle HPHT 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 7,380 m (24,213 ft) long well with an inclination of 69°, was successfully drilled with the same cesium formate fluid system.In all these wells the cesium formate brine system once again demonstrated clear performance benefits such as very low ECDs, moderate to high 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 open-hole formation evaluation of the Kvitebjørn reservoir has been carried out with 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. Using photoelectric factor and bulk density data, combined with resistivity measurements from both the LWD drill pass and the ream pass, produces a very reliable and consistent net reservoir definition. The final interpretation result matches the core porosity from different lithologies in 3 different wells.Cesium formate brine has helped Statoil to achieve a remarkable record of zero well control incidents in all 15 HPHT drilling operations and 20 HPHT completion operations in the Kvitebjørn, Kristin, and Huldra fields over a period of 5 years.