Section milling technology of liners and hangers of sidetracking wells under double-sets pressure system

Well Shen 301S is a sidetracking well under double-sets pressure system in burial hill block of Liaohe Oilfield. In the original well completion process, the intermediate casing with Ø177.8 mm was used for isolating the upper high pressure formation and the liner with Ø127 mm was hanged for the completion in the lower low-pressured reservoir. During sidetracking, if the window was opened above the hanger, two sets of pressure system would be faced and the target horizon could not be drilled to because of the serious phenomena of upper collapse and lower loss in the drilling process; if the window was opened inside the liner with Ø127 mm, the problems such as window sidetracking in the slim hole of the deep well, high pump pressure in the construction, great difficulty in well completion would occur. However, if sidetracking was carried out after the liner hanger with Ø127 mm in the intermediate casing with Ø177.8 mm and the liner were section milled below the burial hill surface by adopting high-efficient section milling technology, the above problems would be solved at the same time. Therefore, adaptive drilling fluid system was optimized and special section milling tools were developed. Then sidetracking for the old well Shen 301S was successfully achieved by optimization of section milling parameters and construction technology. The section milling task of the liner with Ø127 mm for 183.14 m was finished only in 12.4 days (pure section milling time was 6.63 days) for this well and reduced footage of the single tool could reach over 200 m. High-efficient section milling technology provides a kind of effective technical method for sidetracking in multi-sets of pressure system in the slim hole hanged with liners, layer adjusting in the horizontal well hanged with liners, sticking pipe string treatment during drilling and producing remaining oil.