Slimhole development in the Gulf of Thailand

The ability to drill many wells at absolute minimum cost is one of the most significant factors for an operator to have long-term financial success in the Gulf of Thailand (GOT). In partnership with PTTEP and MOECO, UNOCAL has been exploring for gas in the GOT since 1962, with first production occurring in 1981. During this period, the partnership has set 73 platforms, drilled more than 900 wells, and produced over 2.6 Tcf of gas and 96 MM bbls of condensate. Development drilling and completion design has changed incrementally many times, with an average well going from 60 days and $5 MM in 1980 to 9 days and $1.3 MM in 1994 (Figs 1 and 2). The well design was completely overhauled and a slimhole design with monobore completion was implemented in 1994. By the end of 1996, completed wells were averaging 6 days and $750 M with time and cost still coming down. Many technical challenges have been overcome to achieve the slimhole drilling time and cost savings, including optimizing hole size, casing depth, drill string design, PDC bit design, drilling tools, BHA performance, and wellhead equipment. Additional challenges to produce and manage the wells have also been overcome, including perforating, wireline, and coil tubing tools. Increased reserves recovery is expected as a result of improved zone accessibility and better liquid lifting capability. Redesign of the wellhead platforms is also in progress as a result of the smaller wells. Slimhole development has completely transformed the future of GOT operations and has paved the way for operators to continue providing a long-term economic supply of gas to the Kingdom of Thailand.