Floating Drilling: The First 30 Years-Part 2
- W.H. Silcox (Standard Oil Co.)
- Document ID
- Society of Petroleum Engineers
- Journal of Petroleum Technology
- Publication Date
- February 1983
- Document Type
- Journal Paper
- 271 - 275
- 1983. Society of Petroleum Engineers
- 1.7.5 Well Control, 1.11 Drilling Fluids and Materials, 1.10.1 Drill string components and drilling tools (tubulars, jars, subs, stabilisers, reamers, etc), 4.5.4 Mooring Systems, 1.6 Drilling Operations, 1.10 Drilling Equipment, 1.7 Pressure Management, 1.6.1 Drilling Operation Management, 4.2.4 Risers, 4.1.5 Processing Equipment
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Distinguished Author Series articles are general, descriptiverepresentations that summarize the state of the art in an area of technology bydescribing recent developments for readers who are not specialists in thetopics discussed. Written by individuals recognized as experts in the area,these articles provide key references to more definitive work and presentspecific details only to illustrate the technology. Purpose: to informthe general readership of recent advances in various areas of petroleumengineering.
Water Depth Accommodators-The Drilling System
For safety and well control, the BOP stack used in floating drilling ismounted on the wellhead at the ocean floor. The distance between the BOP stackand the fig floor presents operational situations not encountered in landdrilling. For example, one cannot simply jump down from the rig floor to turnthe hand-wheels to shut in a BOP when the stack is some 2,000 ft (600 m) underwater. A number of systems and components have been developed to solve problemsrelated to water depth.
Re-entry Systems. Re-entering a 3-ft (0.9-m)-diameter hole in the oceanfloor in shallow waters without too much current, say less than half a knot(0.9 km/h), isn't too difficult. Put that same hole under half a mile of waterin an area with 1- to 2-knot (1.8- to 3.7-km/h) currents and the problemobviously is more difficult.
Almost from the beginning of floating drilling, wire-rope guidelines havebeen used to guide drillstrings, casing, BOP stacks, and riser pipe into oronto subsea wells. In most instances the guidelines are anchored to the oceanfloor by the temporary guidebase. In some cases when the hole for thestructural pile is spudded without a temporary guidebase, the mud pumps wererun at full capacity as the bit entered the ocean bottom. This washed a largeconical hole in the ocean floor which, with luck, could be re-entered withoutguidelines. However, under these conditions, when the structural casing and thepermanent guidebase are run, the guidelines are attached to the permanentguidebase for subsequent re-entry operations.
With the advent of dynamically positioned drillships. guidelineless re-entrysystems were developed. These systems still used temporary and permanentguidebases; however, instead of using guidelines and guideposts, they werefitted with guidecones that provided a large target for the tools or casingbeing run. provided a large target for the tools or casing being run. TVcameras run through the drillpipe, casing or riser, and BOP stack (depending onwhat was being run) provided guidance into the hole or back onto the BOPprovided guidance into the hole or back onto the BOP stack. Combinations of TVand sonar also have been used for r-e-entry guidance. With the dynamicpositioning system the driller can take control of the drilling positioningsystem the driller can take control of the drilling vessel from his station andposition it as required for re-entry. Re-entry by means of these systems hasbeen made in waters as deep as 4,900 ft (1500 m).
Marine Risers. The first floating drilling systems did not use marine risersfor mud returns. Hoses connected below a rotating packer mounted on top of theBOP stack served to bring mud returns back up to the drilling vessel.
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