The Marnock field is a retrograde gas/condensate accumulation in the U.K. central North Sea with a 9,123-psi bottomhole pressure and 310 degreesF bottomhole temperature. The development plan called for six horizontal wells with average reservoir sections 2,460 ft long. Drilling was conducted in two phases and has delivered four wells capable of the original plateau rate expected from six wells. Main,well-completion challenges were installing downhole sand control in a horizontal well, flowback of 1.9 specific gravity (SG) drilling mud through sand screens, and use of an isolation valve to allow the upper completion to be installed underbalanced. The four weds completed are capable of delivering sand-free production with individual well rates as much as 120 MMscf/D.