fax 01-972-952-9435. AbstractThe Marnock field is located in the Eastern Trough, UK Central North Sea, some 130 miles east of Aberdeen in water depths of 300 feet. The reservoir is Triassic fluviatile sandstone. Reservoir fluid is gas condensate at a temperature of 310°F and pressure of 9100 psi at 11500 feet (3500 metres) TVD.The main risks of drilling the reservoir sections and in running the sand face completions for Marnock come from the combination of high permeability and horizontal well geometry with HTHP conditions. Hydrostatic profiles change constantly with operation due to temperature changes and this increases the risk of well control incidents and lost circulation. Stuck pipe and stuck screen incidents are also statistically significant in these wells.In addition to drilling risks, post-well intervention is costly, high risk, and technology-limited due to the horizontal HTHP conditions. Therefore, the prevention of formation damage and completion impairment has to be addressed in the drilling phase. Decision making, in determining the balance of risks to productivity requires a full understanding of all the factors affecting drilling, completion and production.With these operational difficulties, novel measurement technologies and focused mud management were used to mitigate the risks associated with barite sag, differential sticking, insufficient hydrostatic, formation damage and ECD induced losses. This paper highlights the techniques used on Marnock to successfully manage mud to drill and complete the wells.