Offshore Mobile Drilling Units
Offshore mobile drilling units as we know them today are sophisticated pieces of machinery. However, this was not always the case. The original units were simply land rigs taken into shallow waters and placed on a structure for drilling. The same drilling techniques that had been developed on land were used on the first offshore rigs. These techniques worked for some time, but the need to drill in deeper waters created a new type of engineer the offshore structural design engineer. And along...
Stability and Moving
Stability is simply the ability of a rig to remain afloat. The subject of stability is further divided under the two headings of a Intact Stability and b Damaged Stability. For every rig, the designer or builder should furnish the rig owner with a Stability Booklet which, at a very minimum, should contain a Hydrostatic Properties , b Cross Curves of Stability, c Statical Stability Curves, and d Dynamic Stability Curves, Items c and d should be sufficient to cover the normal operating range of...
Chronology Of Submersible Rigs
CHRONOLOGY OF JACKUP RIGS, 1953-1969 In 1955, the first 3-legged jack-up appeared on the scene Figure 1-6 . The rig was the R. G. LeTourneau jack-up, the Scorpion, for Zapata Offshore Company. The Scorpion, an independent leg jack-up, used a rack and pinion elevating system on a truss framed leg. The rig worked very successfully for several years but was lost during a move in the Gulf of Mexico. The Scorpion was closely followed by The Offshore Company Rig No. 54. For Rig No. 54, however, a...
Multiple Well Man foldProduction Station
The station consists of three basic hardware components the base, the wellhead connector assembly, and the subsea work enclosure. It also includes a number of associated supporting subsystems. A full-scale prototype has been constructed and tested. The prototype base Figure 4-6 is composed of structural piping and is about 50 feet square, 26 feet high. It weighs approximately 140 tons in air, with positive buoyancy in water with pipes unflooded. A circular base was designed to serve as a...
A WAVE LENGTH L CHARACTERISTIC LENGTH Vck
Fig. 1-48 Yaw transfer functions, Aker H-3, HeadingJi 45 a Stationary Conditions Short term Statistics Stationary conditions do not imply that the ocean surface is constant or repeats itself, but rather that the statistical parameters are constant. An irregular sea such as that shown in Figure 1-49 may be described by linearly superimposing a gTeat number of regular waves with different frequencies, H WAVE HEIGHT T ZERO UPCROSSING PERIOD H. SIGNIFICANT WAVE HEIGHT- T AVERAGE APPARENT ZERO...
Submersible Work Vehicles
There are a number of small submarines on the market today. Depending upon the job, they can be very useful and effective. Most are expensive, but under certain circumstances they can provide the most economical means of accomplishing a task. Beyond diver depths, subs can be extremely valuable. Subs are used for salvage work, inspections, surveys and scientific assignments. 1. Dobbins, P., Undersea Operations ant Equipment, School of Offshore Operations Presentation, Houston, Texas 1972. 2....
The Manifold Center
The manifold center is designed to commingle production from several subsea wells, each in an LPS wellhead cellar, and deliver the mixed flow stream through a single pipeline to a nearby production platform or shore base. It serves the same purposes as a land-type production manifold as it permits study of an individual well's producing characteristics. It also provides the means to use TFL tools on any of the completions connected to the manifold. The prototype manifold center Figure 4-14 is...
Info Lub
Fig. 1-57 Weibull distributions of visual wave heights. In determining the total wave forces on fixed offshore structures, the force on long, slender, cylindrical elements of arbitrary cross-section form is of great interest to the designer. The wave and current forces on these elements for in- PROBABILITY OF EXCEEDANCE Q l-P H PROBABILITY OF EXCEEDANCE Q l-P H Fig. 1-58 Predicted long term distributions of wave heights. stance, piles may be reasonably well predicted by applying the Morison...
Well Completion
The wells are designed to permit drilling, landing the tree, and completion using a conventional floating drilling rig. Tub-ingless completions are a part of the prototype SPS, as this design fits the requirements of the system. The wells will have the capability of vertical reentry workover if necessary. Control of valves and other parts of the SPS is through a closed hydraulic system as a basic power source. The pressure in the system is subsea-generated with all equipment mounted on a...
Underwater Welding and Habitats
Hot taps, pipeline repairs and structural repairs can be performed with a high degree of effectiveness. A habitat which is large enough to accommodate two diver-welders and the structural member to be repaired is lowered to the work site, sealed around the pipeline, and then dewatered with compressed air or some other inert atmosphere. The two most common welding techniques are known as TIG and MIG and require both training and skill to achieve code grade results. In addition, special equipment...
Background And History
Dynamic positioning is a technique of automatically maintaining the position of a floating, unanchored vessel within a specified tolerance by using generated thrust vectors to counter the forces of wind, wave, and current forces tending to move the vessel away from the desired location. Design evolution and improvements in reliability allow station keeping by dynamic positioning for extended periods. Increases in available power and advances in sophistication of control equipment allow station...
Production Risers
On fixed production platforms the tubes running from the platform deck to each subsea wellhead are called connectors. After the oil runs up the connectors and thcough the processing equipment, it is then pumped from the deck down to the marine pipeline through the production riser. The three basic types of production risers are the J tube, the reverse J, and the bending shoe methods. The production riser actually contains a bundle of pipes. These individual pipes include the production,...
Lockheed Petroleum Services System
The subsea oil and gas production system developed by Lockheed Petroleum Services Ltd. LPS consists of three basic parts the wellhead cellar, the manifold center, and the service capsule. The system is completely diverless and all components are maintained at one atmosphere of pressure. It is fully automated for remote operation, is capable of through-flow-line TFL tool operation, and can be designed for any water depth. The first system was installed in the Gulf of Mexico in Main Pass Block...
Strength on Location
A typical stress range curve for one location at a joint on a jack-up leg is shown in Figure 6-8. Two requirements must be Fig. 6-8 Typical effects of static and fatigue loading on structure of mobile offshore drilling units. Fig. 6-8 Typical effects of static and fatigue loading on structure of mobile offshore drilling units. satisfied for North Sea operation static and fatigue criteria. Static criteria are well understood and have been used in the design of units for many parts of the world....
SpaceOut and Landing Procedure with PosiTest Packer
During the test, the length of hoth the major and minor pipe strings are subject to change. These lengths can either increase or decrease, depending on the changes in temperature and pressure. A minimum of two 2 slip joints are run between the two strings to allow for this expansion or contraction. One slip joint, provided with a safety valve, is installed on the lower end of the major pipe string. The other slip joint is installed on the upper end of the minor string. One 1 drill collar is run...
Unitized Blowout Preventer Stacks
Depending on the casing program and expected drilling conditions, marine drilling operations can be carried out by using two separate riser sizes and corresponding blowout preventer stacks, or by using one single riser size and blowout preventer stack. When using two risers and two blowout preventer stacks, the system consists normally of a 24 inch riser and 20 inch blowout preventer stack. This blowout preventer stack is installed on the 20 inch surface casing. After a 17V2 inch hole has been...
PCT Testing String
For a better understanding of the new testing system. Figure 5-3 illustrates the relative location of each component in the string. Starting at the lower end, the string is composed of 2. Perforated or slotted tail pipe. 9. At least 90 feet of drill collars for sand which may settle from produced fluid. 10. Cushion displacement valve for spotting cushion. 11. Rotary type reverse circulation valve, 12. Pressure internal actuated reverse circulation valve. 13. Minor string collar weight required...
The Seal Systems
Subsea Equipment Associates, Limited SEAL is an international consortium owned by British Petroleum, Compagnie Fran aise des Petroles, Groupe Deep, Westinghouse Electric, and Mobil Oil Company. The consortium has developed two subsea production systems the SEAL Single-Well Completion and the Multiple-Well Manifold Production Station. The single-well system is designed for individual wells drilled vertically with production rates ranging to 10,000 barrels day. It is suitable for step-out wells...
Basic Test System
The principal objective of the formation test is the same, whether it is conducted from a floating vessel or a stationary rig. The test, however, is performed with different techniques and tool systems for the two types of rigs. When conducting testing operations on a stationary rig such as a jack-up, platform, or land type rig Figure 5-1 there is no relative motion between the rig and the well in a vertical direction. On this type of rig, conventional testing systems which are STATIONARY RIG...
Annular Blowout Preventers
Purpose Of Annular Blowout Preventers The annular blowout preventer BOP is the most widely used blowout preventer in the oilwell drilling industry. The purpose of BOP's in general is to close the well bore in the event that the well starts a kick. Ram preventers historically are limited to either blind rams which are closed to control the well provided no tools are in the well bore and to a specific pipe size, if pipe is in the hole. This normally precludes closing on tool joints, kellys, etc....
Wind Wave and Current Forces on Offshore Structures
The forces produced by wind, wave, and current are the primary design loads on mobile drilling units and other offshore structures. These forces are dynamic and ever-changing rarely can they be expressed as a mathematical function of time. They are statistical in nature and should, if possible, be handled by means of statistical tools. The most commonly used method so far for evaluating wave loads on an offshore structure has been to base the calculations on one or more design waves of...
Note Annual Preventers
ARE 5000 PSI WORKING PRESSURE RATING FOR IS 3 4 Zl- 1 4 SUES Fig. 3-11 Subsea blowout preventer stack. 16 - 3 4 - 5000 18-3 4 amp 21-1 4 10000 16 - 3 4 - 5000 18-3 4 amp 21-1 4 10000 Fig. 3-11A Subsea blowout preventer stack. Fig. 3-11A Subsea blowout preventer stack. only one annular preventer. The redundancy of this system is obviously inferior to the arrangement in Figure 3-11. Figure 3-12 has an identical annular preventer arrangement to Figure 3-11. Here, however, the annular preventers...
The Wellhead Cellar
The original LPS wellhead cellar is basically a vertical cylinder Figure 4-11 . It has a lower semiellipsoidal head and an upper hemispherical head penetrated by an upwardly inclined opening called a bullnose port. Flow lines leaving the wellhead or Xmas tree pass through this port. Above the hemispherical Fig. 4-11 Lockheed vertical production system. Fig. 4-11 Lockheed vertical production system. head is a short section of vertical cylinder, called a teacup, which provides a mating surface...
Basic Components Of An Exploratory Riser System
Figure 2-10 illustrates the arrangement of the riser system. It is important to note that the riser is not a simple piece of equipment but rather a complex system of component parts. A list of the sources foT components of basic riser equipment and the manufacturers of each component has been prepared Table 2-1 . Many manufacturers produce individual parts of the sub-sea riser system but only a very few supply the entire equipment package. Table 2-1 was compiled from the 1974 Composite Cataiog...
Causes Of Blowouts
Good planning, execution, and analysis will reduce frequency and severity of kicks, while a true commitment to understanding kicks will eliminate loss of wells resulting from blowouts and stuck pipe. Nevertheless, kicks can occur in any drilling operation conducted with a view towards attaining maximum effectiveness, These relatively infrequent kicks need not be unduly dangerous nor time-consuming when proper and prompt action is taken. Pressure unbalance leading to a kick may result from one...
Strength during Tow
Figure 6-7 illustrates the effect of roll on the stresses which occur in the legs of a jack-up during ocean tow. Similarly, the flexure of the structure of a semisubmersible cannot exceed the allowable stress values. Several accidents have occurred with jack-up units during tow in rough seas, in which the legs have been damaged or even lost. The units must therefore be designed to withstand these stresses. Based partly on theory and partly on practical experience, the criterion of a 20 off...
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sheaves to form a loop around the cylinder. Expansion force of the compression loaded cylinder or retraction force of the tension loaded cylinder attempts to expand the wireline loop. Thus, the force develops a pull or tension in the wire rope. One end of the wireline is connected to the tensioner or rig and the other end is reeved across an idler diverter sheave and to the top of the marine riser Figure 2-7 . Force in the cylinder is thus translated to wireline tension and then to tension in...
Reverse Circulation
After the test and prior to pulling the tools from the hole, all recovered formation fluids must be removed from the string and replaced with mud for safety and prevention of pollution. This can be done either during or after the final shut-in period. It is preferable to reverse circulate during the final shut-in period since valuable rig time is saved and sand produced into the pipe string will be kept in motion and not allowed to settle out during this period. The reverse circulating valve...
Governmental Regulatory Agencies
Most nations have an arm of the government such as the U.S. Coast Guard, the U.K. Department of Energy, and the Norwegian Maritime Directorate which is responsible for the safety of ships and offshore drilling units operating in their waters. While the classification societies are concerned mainly with the structural integrity and seaworthiness of the vessel, the governmental bodies are concerned primarily with the safety of the people on board and, increasingly, with environmental concerns....
Application to Platform Risers
The LPS dry flow-line pull-in technique has been adapted to large-diameter pipelines used to move oil from a production platform. In this application, the platform riser pipe is equipped with a connector chamber, or pressure hull, having a top flange which will mate with the LPS service capsule Figure 4-19A . The riser pipe penetrates the wall of the pressure hull and is welded to a larger-diameter pipe section. This in turn is flanged to the bullnose penetrator. At the time of installation, a...
Considerations for Marine Risers
Dr. D. Bynum, Jr. and Ramesh K. Maini A riser can be simply described as a conduit from the platform to the ocean floor which transmits the drilling mud and serves as a guide for the drill string. There are two broad classes of risers, those used for exploratory drilling operations and those used for production operations. In exploratory drilling, the riser tube running from the vessel down to the wellhead is normally called a riser while the fust casing joint running from the wellhead slightly...
Techniques To Control Catastrophic Blowouts
Control over a catastrophic blowout can be gained by any technique that blocks the escaping reservoir fluid either in the wellbore or in the formation. The method most frequently used is wellbore blockage, i.e., the recapping of a wild well. Relief well techniques, although more expensive to implement, have popular support because water pollution can be minimized by allowing the flowing wells to burn. Relief wells are sometimes drilled to establish direct connection with the wild-well bore...
Mark A Childers
Mark A. Childers is Supervising Engineer with Ocean Drilling and Exploration Company Odeco in New Orleans, Louisiana. He has worked in many phases of production and drilling and has specialized in the development of subsea drilling equipment and the design and analysis of floating drilling units. Mr. Childers is a member of the American Petroleum Institute's Task Group on Mooring Gear for Floating Structures, He holds several patents, is a registered Professional Engineer in Texas and...
Thrust Signals Turning Error Only
TL RN1NG ERROR PLUS TURNING ERROR PLUS LONGITUDINAL ERROR LONGITUDINAL ERROR PLUS LATERAL ERROR Fig. 1-112 Vector diagrams for position keeping, 2 Thruster-Four degrees of freedom. thruster freedom represent many possible arrangements. Some of the thruster logic arrangements were straightforward and simple such as the statement that those transverse thrusters operating out of 11 total are to equally share in the sway thrust assignment and when both main screws are operating they shall equally...
Submersible S Under Construction Today
10 12 14 10 18 20 2 2 24 26 28 PERIOD OF SEAS SECONDS time if mobility is required. Jn 1974 a large semisubmersible crossed the Atlantic in a record-breaking 21 days. The published data quote an average speed of 9.72 knots for the unit. This, of course, meant a considerable reduction in moving cost and a fair increase in productive time. On the other band, considering that once a unit has reached location it is generally in that area for a long time, propulsion units are not only unnecessary...
Analytical Review Of Exploratory Riser Systems
Analyses for exploratory riser design must include a large number of variables. The combined stress in the riser is due to both axial and hoop or circumferential stress. Hoop stress is caused by internal pressure of the mud column and pressure with kicks. External forces on the riser result from hydrostatic pressure which is calculated for the given water depth. The total axis stress is due to the tensioner load, riser buoyancy, riser weight, mud weight, current forces, and wave forces. With...
ChokeKill Valves
All underwater BOP stacks are equipped with valve manifolds to control access to the choke and kill lines attached to the marine riser. All BOP stacks, with the exception of some low pressure 20 inch single annular BOP stacks, are equipped for both choke and kill line operation. A basic bore size and pressure ratings of 31 inch, 5,000 psi working pressure and 3-1 16 inch, 10,000 psi working pressure have been standardized by the various manufacturers. There has been discussion, however, of...
Perforated Tail Pipe Pressure Recorder
Fig. 5-1 Testing system for stationary rig. operated by the up and down motion of the pipe string are used with a high degree of success. On the other hand, when a well is being tested from a floating vessel there is a perpetual cyclic motion between the vessel and the well in a vertical direction due to wave and tide action. This motion can vary in degree depending on weather conditions. For this reason, it is evident that the conventional system which utilizes up and down pipe string motion...
Classification Societies
The offshore drilling industry has adopted the practices ofthe shipping industry in accepting the established authority ofthe classification societies as certifying organizations. The worldwide classification societies are American Bureau of Shipping U.S.A. , Bureau Veritas France , Det Norske Veritas Norway , Germanischer Lloyd Germany , Japanese Marine Corporation Nippon Kaiji Kyokai Japan , Lloyd's Register of Shipping U.K. , and Registro Italiano Italy . The classification societies...
Working With The Classification And Certifying Authorities
It has been our experience in dealing with the classification societies that they are practical, experienced, and reasonable. They work closely with the rig owners and designers and are willing to consider the merit of any proposed exceptions or changes. However, they do require solid engineering back-up to justify any variances in policy they are asked to make. It is recommended that several steps be taken as early as possible in the planning of an offshore mobile drilling unit 1. Get to know...
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000 10,000 20,000 40,000 60,000 Fig, 1-76 Anchor holding power vs anchor dry weight forLWT and Stato type Offdrill II anchors, reasonably good indication of large anchor holding power. Where dynamic anchors do not perform acceptably, some contractors and operators have used piled type anchors with limited success. However, they are extremely expensive and time consuming to install. Explosive imbedding type anchors have never been used in floating drilling operations due to their limited...
Application To Fixed Offshore Structures
The wave loads on fixed offshore structures are normally evaluated by means of one of two basic methods a Design wave method Fig. 1-70 Jonswap and modified Pierson-Moskowitz wave spectra. Fig. 1-70 Jonswap and modified Pierson-Moskowitz wave spectra. The method to be used should be considered in each specific case with due regard to the design and purpose of calculation. Until now, most analysis regarding wave loads on fixed offshore structures has been based on a regular, sinusoidal design...
The Manifold
This unit Figure 4-20 is the heart of the entire system. It is Production line Gas-injection fine Waterflaod and production line Pump-down toot Une Production line Gas-injection fine Waterflaod and production line Pump-down toot Une Fig. 4-20 Production manifold for Exxon SPS. amp made up of all the necessary piping to carry out the assignments of the SPS. It is rectangular shaped with well-rounded corners to allow use of pump-down tools. In the prototype, its shape is almost square because the...
Tow Line Mooring Tension
Fig. 1-88 Required pretension vs water depth for ' a rated break strength of 3 in. chain to occur at 6 displacement see note . The next step is to select a water depth s to analyze. Figure 1-89 shows restoring force both with and without the two 2 leeward lines slackened, high line tension most loaded mooring line , and the high line tension anchor load vs. beam direction horizontal displacement in 600 foot water depths. Once again, Figure 1-89 is only valid for the stated conditions. Note that...
Dual Automatic Station Keeping System For Sedco 1
Fig. 1-119 Dual digital dynamic positioning simplified schematic. Fig. 1-119 Dual digital dynamic positioning simplified schematic. dard, high quality, interchangeable, industrial three mode controllers. Standardizing the controls allows plugging one common spare into either the surge, sway, or yaw control channel after setting the proportional band, rate, and reset to the channel's known settings. The advent of the mini-computer has really launched the digital computer into the control field....
Test Procedure
To complete the test phase now underway in the Gulf of Mexico, Exxon drilled three directional wells into a proven reservoir. The prototype unit was designed for only three wells, but the system can be expanded to as many as 40 wells according to Exxon engineers. The subsea test program culminates more than 300 man-years of research and development and represents an expenditure of more than 30 million. The overall program, visualized in Figure 4-24, involves tests of all the subsystems as well...
Direction Of Propagation 1
Fig. 1-62 Variation of particle velocity with depth below sea surface. Fig. 1-62 Variation of particle velocity with depth below sea surface. Slender elements like those just considered do not influence the velocity and acceleration field around the structure. A large body e.g., oil storage tank will, however, reflect the waves producing disturbances to the velocity and acceleration field. An increase in velocities and accelerations around the body may result. Consider for instance the...
Dynamic Positioning Controller
Purity of Position Determining Signals Dynamic positioning is a basic control problem in three degrees of freedom. A free body has six degrees of freedom in motion surge, sway, heave, pitch, roll, and yaw. The dynamic positioning system will be concerned only with surge bow-stern translational motion , sway port-starboard translational motion , and yaw rotational motion about the vertical axis . No attempt will be made to control pitch, roll, or beave by the dynamic positioning system. A first...
Requirements For C Las Si F Cat On And Certification
The first publication of rules pertaining to offshore mobile drilling units was the American Bureau of Shipping's Rules for Building and Classing Offshore Mobile Drilling Units in 1968. Since that time, the standards prescribed have been subjected to the test of actual application to a wide range of designs and a revised edition was published in 1973. Lloyd's Register published its Rules foT the Construction and Classification of Mobile Offshore Units in 1972. In 1973, Det Norske Veritas...
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Fig. 1-82 Required scope outboard of lower fairlead after pretensioning 3 in, chain-89.3 lb. ft. vs water depth as a function of maximum anticipated line tention. core, etc. Wire rope diameters up to 3Va inch have been used for mooring with the more common sizes being V-k to 3 inches. The wire rope should have an independent wire rope core IWRC center for crushing resistance and a zinc coating for corrosion protection since some of the wire rope will always be in the splash zone. Regular lay,...