Changes

==Through tubing rotary drilling==

==Through tubing rotary drilling==

Through tubing rotary drilling is a relatively inexpensive method of creating a short-length to moderate-length sidetrack of an existing well (with a step-out of up to 1000 m [3381 ft], sometimes longer). Slim-bore drill pipe is used to drill the well, and the benefit of this is that the drill pipe is narrow enough to be run through the existing production tubing (Reynolds and Watson, 2003). This eliminates the time and cost involved with pulling the completion in an existing well to start drilling and then rerunning it after the well has reached total depth. Through tubing rotary drilling has been used in the Gullfaks field in the Norwegian North Sea. 4-D seismic data is used to identify remaining oil targets. Many of these targets are small but can be drilled cheaply by the use of through tubing rotary drilling. This has contributed to a reversal of the oil production decline at the late mature stage of field life (Todnem et al., 2005).

Through tubing rotary drilling is a relatively inexpensive method of creating a short-length to moderate-length sidetrack of an existing well (with a step-out of up to 1000 m [3381 ft], sometimes longer). Slim-bore drill pipe is used to drill the well, and the benefit of this is that the drill pipe is narrow enough to be run through the existing production tubing (Reynolds and Watson, 2003). This eliminates the time and cost involved with pulling the completion in an existing well to start drilling and then rerunning it after the well has reached total depth. Through tubing rotary drilling has been used in the Gullfaks field in the Norwegian North Sea. 4-D seismic data is used to identify remaining oil targets. Many of these targets are small but can be drilled cheaply by the use of through tubing rotary drilling. This has contributed to a reversal of the oil production decline at the late mature stage of field life.<ref>Todnem, A. C., L. Arnesen, and R. Gaaso, 2005, 4D seismic and through tubing drilling and completion wells extend life on the Gullfaks field: Presented at the Society of Petroleum Engineers/IADC (International Association of Drilling Contractors) Drilling Conference, February 23–25, Amsterdam, Netherlands, SPE Paper 92551, 10 p.</ref>

==Wells, the production geologist's tool kit==

==Wells, the production geologist's tool kit==