Cesium/potassium formate reservoir drill-in fluid (RDF) and solids-free brine redefine performance standards for drilling and completion of a high-pressure gas reservoir section through highly permeable sandstone with interbedded shale/coal. The fluids delivered outstanding operational performance and an above-target productivity index (PI).
Deploying 2.19 g/cm3/18.28 lb/gal cesium formate brine in HPHT perforating operations brings significant health, safety and environmental benefits and delivers productive wells with low mechanical skins. The BP-operated Rhum field in the North Sea consists of three subsea development wells tied back to the Bruce platform. The field offered a number of development challenges.
Cesium formate brine has provided the hydrostatic well-control required for safely carrying out essential remedial work on the casing hangers of seven offshore HPHT wells, and in a number of further interventions and suspensions in Elgin, Franklin and Glenelg wells over nine years. In deploying cesium formate brines in these fields, TOTAL created new health, safety and environmental standards for completion and workover brines in the North Sea.
Low-solids formate brines used in combination with managed pressure drilling (MPD) delivered highly productive wells in a fractured carbonate reservoir without incurring excessive fluid losses while drilling. No acid stimulation was required.
Six reservoir sections were drilled and completed with cesium / potassium formate brine in the HPHT Huldra field in the North Sea. Statoil has reported that the six Huldra wells drilled and completed with formate brines are each producing with excellent average productivity indices of around 1.9 million scf/day/psi. The Huldra project manager says: “For the specific conditions of the Huldra field there is no realistic fluid alternative for successfully drilling and completing the wells.”
Nine reservoir sections were drilled and seven completed with cesium/potassium formate brine in the North Sea's Kvitebjørn field from 2004 to 2007. Per Cato Berg, Lead Drilling Engineer for Kvitebjørn, says: “Supported by our tests and data, we feel that cesium formate gives the best productivity for the wells. We have tested formation damage with water- and oil-based alternatives, and cesium formate comes out best.”
Five reservoir sections have been drilled and completed using cesium/potassium formate brine in the Kvitebjørn field since 2007. The reservoir sections were drilled using MPD technology with a specially designed drilling fluid based on low ECD cesium/potassium formate brine, which proved the best solution for improving the fracture gradient.
Drilling and completing with cesium/potassium formate brines delivers four problem-free wells and 100% of recoverable reserves over ten years in this gas-condensate field located in the North Sea. Wells were successfully drilled horizontally and completed in open hole.
TXM successfully used high-density cesium formate brine as well control fluid during the appraisal of a extreme HPHT basin-centred gas accumulation in Hungary. The well was later suspended three times with cesium formate. The longest suspension period lasted about six months.