Floating Drilling: The First 30 Years-Part 1
- W.H. Silcox (Standard Oil Co.)
- Document ID
- Society of Petroleum Engineers
- Journal of Petroleum Technology
- Publication Date
- January 1983
- Document Type
- Journal Paper
- 17 - 22
- 1983. Society of Petroleum Engineers
- 1.14 Casing and Cementing, 4.2.4 Risers, 1.6.1 Drilling Operation Management, 1.7 Pressure Management, 1.5 Drill Bits, 4.1.6 Compressors, Engines and Turbines, 4.5.4 Mooring Systems, 4.1.5 Processing Equipment, 4.5 Offshore Facilities and Subsea Systems, 1.11 Drilling Fluids and Materials, 1.6 Drilling Operations, 1.10.1 Drill string components and drilling tools (tubulars, jars, subs, stabilisers, reamers, etc), 1.10 Drilling 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.
Two basic parameters make drilling from a floating vessel different fromdrilling on land. These parameters are motion and distance. The motion comesparameters are motion and distance. The motion comes from continuous movementof the ocean's surface. which affects the drilling vessel floating on it. Thedistance is the depth of the water between the drilling vessel and the oceanfloor.
Vessel motion can be resolved into six components. As shown on Fig. 1, theseare the linear displacements of heave, up and down motion alone, the verticalaxis of the vessel: surge, back and forth motion along the longitudinal axis;and sway, sideways motion along the transverse axis; and the angulardisplacements of roll about the longitudinal axis, pitch about the transverseaxis, and about the vertical axis. These six motion components can, andgenerally do, occur simultaneously. This creates a whole series of problems notencountered in land drilling. Accommodations problems not encountered in landdrilling. Accommodations had to be nude for these motion before floatingdrilling could become the reality it is today.
The distance between the drilling vessel and the ocean floor (or, moresimply, the water depth) created another set of operational and equipmentproblems that have been solved to the degree that floating drilling has beenaccomplished successfully in water depths just short of 5,000 ft. Plans are nowin the hardware stage for drilling in waters as deep as 7,000 ft, and theproblems associated with drilling in waters in excess problems associated withdrilling in waters in excess of 10,000 ft are being addressed. There is littledoubt that when the need to drill in these greater water depths arises, thecapability will be there.
This paper describes some of the floating drilling problems associated withmotion and distance and how problems associated with motion and distance andhow they were solved. Part 1 discusses basic steps in floating drilling and thedrilling systems and vessels that have been developed to accommodate motion.Part 2 (to appear next month) discusses drilling and Part 2 (to appear nextmonth) discusses drilling and station-keeping systems developed to accommodateincreasing water depths.
Drilling From a Floating Vessel
Before going into the problems resulting from motion and water depth, itmight be best to first describe how a well is drilled from a floating vessel.The sequence of events in this description is not necessarily that followed forevery well drilled from a floating vessel, but it is a method that has workedin the past and will continue to be used in the future.
Before the start of drilling, the usual activities have to take place.Seismic lines are run and interpreted, a wellsite is picked, the drillingvessel is selected, a contract is written and executed, and the vessel ismobilized to the wellsite and surveyed in on location. Drilling is now ready tobegin. Refer to Fig. 2 for the following sequence of events.
Step 1 in drilling from a floating vessel is to lower the temporaryguidebase to the ocean floor. The temporary guidebase is generally 12 x 12 ftand is outfitted with a bullseye, observed by TV for levelness determination.This base is run on drillpipe detachably connected to it with a J-tool orhydraulic connector. Four wire-rope guidelines are attached to the sub-basebefore it is lowered. The base may be loaded with weighted rotary mud so thatnecessary tension can be pulled in the guidelines when drilling equipment ispulled in the guidelines when drilling equipment is lowered to the ocean floor.With the base on bottom, the drillpipe running string is marked at the kellybushing, averaging out the vessel heave, so that the water depth may bedetermined by measuring the pipe when it is pulled. This measurement, correctedfor tide, is the water depth from the kelly bushing to the ocean floor used inall subsequent drilling, logging, casing, and testing operations.
Step 2 consists of running the drilling assembly, made up of the bit, drillcollars, bumper subs, and drillpipe, down the guidelines, through the temporaryguidebase, into the ocean floor to drill the hole for the structural casing.This hole must be drilled carefully to ensure that it is kept within 1 ofvertical. because it later will control how vertical the blowout preventer(BOP) stack will be when it is landed on the wellhead.
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