Case Study: Lennox - The Race to Produce Oil Prior to Gas Cap Blowdown

Abstract

Abstract Ten years since production commenced from the Lennox Field and one year from the start of full gas cap blowdown, the challenge to produce oil from the Lennox oil rim has never been greater. The Lennox Field is one of six fields comprising the Liverpool Bay Development located in the UKCS, East Irish Sea. The Lennox oil rim is at a critical stage in the development of the asset as it transitions from an oil field to a gas field. The field was initially developed with horizontal and multi-lateral wells placed to maximise oil reserves and minimise movement of the gas-oil and oil-water contacts with re-injection of all produced gas to maintain reservoir pressure. Since other sources of gas in the area commenced their decline, Lennox must now sustain plateau nominated gas sales and as a result there is little time left to recover the remaining oil. In a first for the development, a dual lateral well (110/15a-L13/L13z) was drilled in mid 2005 as a sidetrack to a poorly performing single bore well and completed with an intelligent completion to supply gas lift gas from the gas cap. The intelligent completion will assist the well to flow, maximise oil recovery and eventually allow a simple conversion to a gas well. The well was a success with better than expected reservoir intersections and the initial oil rate exceeding predictions. The project, initially designed to address unswept oil in the Lennox Field, was expanded to apply the artificial lift technology used at L13 to mature Lennox wells to allow continuous lift at higher watercuts and lower reservoir pressure. The result has highlighted the need to continually re-evaluate opportunities and challenge existing development plans and assumptions. Introduction The Lennox Field is located in UK blocks 110/14a and 110/15a, in the East Irish Sea and is one of six oil and gas fields that comprise the Liverpool Bay Development (Figure 1). Lennox differs from the other fields in that it contains hydrocarbons in both an oil rim and gas cap. The Lennox gas is ultimately required to fulfill the gas sales contract, once the other gas fields in the development can no longer supply all the contracted gas demands, but in the meantime Lennox production has been focused on maximising production from a 45m thick oil rim, which provided plateau oil production rates of 40,000 stb/d.