More on Offshore Drilling

A jack-up rig consists of a movable platform which can be jacked up and down the (usually) three supporting legs. The video clip below shows one of the typical designs. These provide a common means of drilling in water, where the water depth is relatively shallow - say, 50 to 400 feet.

Jack-ups will be floated out to location and the legs then lowered independently until they are bedded securely and the platform is level and above wave height. It is clear that their use would be restricted when

there are strong currents or an unstable seabed.

A semi-submersible is a floater drilling rig. In this case, a deck is supported by a tubular structure, and by two hulls to provide buoyancy. Again, the deck carries equipment, accommodation modules, a helicopter pad and typical layout is shown in the below video clip.

Semi-submersibles can move easily from one location to another either by being towed or under their own thrusters power. They are mainly used, therefore, for exploration and appraisal drilling where this ease of movement is essential.

When on location, the semi-sub (as it is often helipad called) takes on water ballast (into the two hulls, etc). This will lower the structure in the water and lower the centre of gravity. In this position it is shielded from the effects of rough water at the surface and achieves a high degree of stability.

A semi-sub can operate in deeper water than a jack-up. Its maximum operating water depth depends on the type of mooring system employed. Some semi-subs use anchors with wire and chain to hold them on station. Others use dynamic positioning which is a system of computer controlled thrusters, to maintain their position. Modern semi-subs using anchors may, in exceptional circumstances, drill in water up to 3,000 feet deep.

Semi-subs using dynamic positioning systems are capable of drilling in even deeper waters, up to 6,000 to 10,000feet deep.

The drilling equipment in the semi-submersible is more sophisticated compare to a jack-up and more costly as the semi-sub has various sea motions while afloat and the drilling system on board has to be able to function at the same time deal with the heave motions while the rig is afloat. Some drilling systems may be able to discoupled from the vessel in case of severe and uncontrollable situation such as unexpected storm or harsh environment and for the safety of the crew, the drilling riser may be released after the sub-sea LMRP/BOP is being shut from the well.

In comparison to semi-submersibles, a jack-up has some advantages:

a) Lower construction costs. Semi-sub usually cost almost double of that of jack-up or more
b) Less personnel required to run the rig. Jack-up has about 120men compared to Semi-sub with 200men onboard
c) Because of (a) and (b) lower day rates.
d) The possibility to work over a fixed platform.
e) It is cheaper for the operator to use a jack-up:
 -Less powerful tug boats to move the rig while it is afloat
 -No mooring system required, no lost time to run anchors. But some rigs now come standard with anchors
 -Less maintenance costs.
 -Surface BOP without sub sea system.
 -Simple well head assembly.
f) Less down time:
 -No wait on weather due to motions.
 -Drilling equipment can be handled faster and easier.

However, the jack-up have some disadvantages:

a) Limited water depth. The maximum water depth for the largest JU is 450ft. Semi-sub could work up to 10,000feet on the latest design.
b) Depends on bottom condition. The bottom soil conditions may cause a punch through or deep leg penetration. Semi-sub does not have such issue as it is afloat while drilling operation is carrying out.
c) In case of a blow-out the rig can not move off location whereas a semi could.
d) More fragile. Many incidents and damages during moving and because of a punch through. Statistics have shown that over 75% of the incidents occur under tow or during jack-up/jack-down operations.
e) Safe operations require strict procedures.

The table below show some of the different jackup designs ( excluding KeppelFELS design of A-class, Super A, B-class, Super-B,etc ) and its capability in terms of size, VDL capacity,etc :

Types of Drilling Rig Capability

Some key personnel on board the drilling rig and their roles and responsibility :-

Tool pusher - In overall charge of rig operations, implementing the drilling plan and compliance with all safety requirements. Reports to the company representative.

Driller - In charge of the drilling process and operations. Responsible for compliance with the drilling plan and for the drilling crew. Reports to the tool/tourpusher.

Assistant driller - Assists the driller. Usually responsible to the driller for the operation of bulk storage equipment (for handling mud chemicals, etc.) and for the mud flowline system. Reports to the driller.

Derrickman - Responsible for the storage and movement of tubulars in the derrick and monitoring the mud systems. Reports to the driller.

Roughneck - Works on the rig floor. Responsible for general rig floor activities under the direction of the driller/assistant driller. Reports to the driller.

Rustabout - A member of the general workforce, assisting with the movement of materials,cleaning, painting, etc.

Drilling Operation and components

Drilling Completion

Formulas for Drilling and Prod



Rig Functions

Drilling Mud Technology

Drilling Mud Technology

More on Offshore Drilling

A jack-up rig consists of a movable platform which can be jacked up and down the (usually) three supporting legs. The video clip below shows one of the typical designs. These provide a common means of drilling in water, where the water depth is relatively shallow - say, 50 to 400 feet.

Jack-ups will be floated out to location and the legs then lowered independently until they are bedded securely and the platform is level and above wave height. It is clear that their use would be restricted when

there are strong currents or an unstable seabed.

A semi-submersible is a floater drilling rig. In this case, a deck is supported by a tubular structure, and by two hulls to provide buoyancy. Again, the deck carries equipment, accommodation modules, a helicopter pad and typical layout is shown in the below video clip.

Semi-submersibles can move easily from one location to another either by being towed or under their own thrusters power. They are mainly used, therefore, for exploration and appraisal drilling where this ease of movement is essential.

When on location, the semi-sub (as it is often helipad called) takes on water ballast (into the two hulls, etc). This will lower the structure in the water and lower the centre of gravity. In this position it is shielded from the effects of rough water at the surface and achieves a high degree of stability.

A semi-sub can operate in deeper water than a jack-up. Its maximum operating water depth depends on the type of mooring system employed. Some semi-subs use anchors with wire and chain to hold them on station. Others use dynamic positioning which is a system of computer controlled thrusters, to maintain their position. Modern semi-subs using anchors may, in exceptional circumstances, drill in water up to 3,000 feet deep.

Semi-subs using dynamic positioning systems are capable of drilling in even deeper waters, up to 6,000 to 10,000feet deep.

The drilling equipment in the semi-submersible is more sophisticated compare to a jack-up and more costly as the semi-sub has various sea motions while afloat and the drilling system on board has to be able to function at the same time deal with the heave motions while the rig is afloat. Some drilling systems may be able to discoupled from the vessel in case of severe and uncontrollable situation such as unexpected storm or harsh environment and for the safety of the crew, the drilling riser may be released after the sub-sea LMRP/BOP is being shut from the well.

In comparison to semi-submersibles, a jack-up has some advantages:

a) Lower construction costs. Semi-sub usually cost almost double of that of jack-up or more
b) Less personnel required to run the rig. Jack-up has about 120men compared to Semi-sub with 200men onboard
c) Because of (a) and (b) lower day rates.
d) The possibility to work over a fixed platform.
e) It is cheaper for the operator to use a jack-up:
 -Less powerful tug boats to move the rig while it is afloat
 -No mooring system required, no lost time to run anchors. But some rigs now come standard with anchors
 -Less maintenance costs.
 -Surface BOP without sub sea system.
 -Simple well head assembly.
f) Less down time:
 -No wait on weather due to motions.
 -Drilling equipment can be handled faster and easier.

However, the jack-up have some disadvantages:

a) Limited water depth. The maximum water depth for the largest JU is 450ft. Semi-sub could work up to 10,000feet on the latest design.
b) Depends on bottom condition. The bottom soil conditions may cause a punch through or deep leg penetration. Semi-sub does not have such issue as it is afloat while drilling operation is carrying out.
c) In case of a blow-out the rig can not move off location whereas a semi could.
d) More fragile. Many incidents and damages during moving and because of a punch through. Statistics have shown that over 75% of the incidents occur under tow or during jack-up/jack-down operations.
e) Safe operations require strict procedures.

The table below show some of the different jackup designs ( excluding KeppelFELS design of A-class, Super A, B-class, Super-B,etc ) and its capability in terms of size, VDL capacity,etc :

Types of Drilling Rig Capability

Some key personnel on board the drilling rig and their roles and responsibility :-

Tool pusher - In overall charge of rig operations, implementing the drilling plan and compliance with all safety requirements. Reports to the company representative.

Driller - In charge of the drilling process and operations. Responsible for compliance with the drilling plan and for the drilling crew. Reports to the tool/tourpusher.

Assistant driller - Assists the driller. Usually responsible to the driller for the operation of bulk storage equipment (for handling mud chemicals, etc.) and for the mud flowline system. Reports to the driller.

Derrickman - Responsible for the storage and movement of tubulars in the derrick and monitoring the mud systems. Reports to the driller.

Roughneck - Works on the rig floor. Responsible for general rig floor activities under the direction of the driller/assistant driller. Reports to the driller.

Rustabout - A member of the general workforce, assisting with the movement of materials,cleaning, painting, etc.

Drilling Operation and components

Drilling Completion

Formulas for Drilling and Prod



Rig Functions

Drilling Mud Technology

Drilling Mud Technology

More on Offshore Drilling

A jack-up rig consists of a movable platform which can be jacked up and down the (usually) three supporting legs. The video clip below shows one of the typical designs. These provide a common means of drilling in water, where the water depth is relatively shallow - say, 50 to 400 feet.

Jack-ups will be floated out to location and the legs then lowered independently until they are bedded securely and the platform is level and above wave height. It is clear that their use would be restricted when

there are strong currents or an unstable seabed.

A semi-submersible is a floater drilling rig. In this case, a deck is supported by a tubular structure, and by two hulls to provide buoyancy. Again, the deck carries equipment, accommodation modules, a helicopter pad and typical layout is shown in the below video clip.

Semi-submersibles can move easily from one location to another either by being towed or under their own thrusters power. They are mainly used, therefore, for exploration and appraisal drilling where this ease of movement is essential.

When on location, the semi-sub (as it is often helipad called) takes on water ballast (into the two hulls, etc). This will lower the structure in the water and lower the centre of gravity. In this position it is shielded from the effects of rough water at the surface and achieves a high degree of stability.

A semi-sub can operate in deeper water than a jack-up. Its maximum operating water depth depends on the type of mooring system employed. Some semi-subs use anchors with wire and chain to hold them on station. Others use dynamic positioning which is a system of computer controlled thrusters, to maintain their position. Modern semi-subs using anchors may, in exceptional circumstances, drill in water up to 3,000 feet deep.

Semi-subs using dynamic positioning systems are capable of drilling in even deeper waters, up to 6,000 to 10,000feet deep.

The drilling equipment in the semi-submersible is more sophisticated compare to a jack-up and more costly as the semi-sub has various sea motions while afloat and the drilling system on board has to be able to function at the same time deal with the heave motions while the rig is afloat. Some drilling systems may be able to discoupled from the vessel in case of severe and uncontrollable situation such as unexpected storm or harsh environment and for the safety of the crew, the drilling riser may be released after the sub-sea LMRP/BOP is being shut from the well.

In comparison to semi-submersibles, a jack-up has some advantages:

a) Lower construction costs. Semi-sub usually cost almost double of that of jack-up or more
b) Less personnel required to run the rig. Jack-up has about 120men compared to Semi-sub with 200men onboard
c) Because of (a) and (b) lower day rates.
d) The possibility to work over a fixed platform.
e) It is cheaper for the operator to use a jack-up:
 -Less powerful tug boats to move the rig while it is afloat
 -No mooring system required, no lost time to run anchors. But some rigs now come standard with anchors
 -Less maintenance costs.
 -Surface BOP without sub sea system.
 -Simple well head assembly.
f) Less down time:
 -No wait on weather due to motions.
 -Drilling equipment can be handled faster and easier.

However, the jack-up have some disadvantages:

a) Limited water depth. The maximum water depth for the largest JU is 450ft. Semi-sub could work up to 10,000feet on the latest design.
b) Depends on bottom condition. The bottom soil conditions may cause a punch through or deep leg penetration. Semi-sub does not have such issue as it is afloat while drilling operation is carrying out.
c) In case of a blow-out the rig can not move off location whereas a semi could.
d) More fragile. Many incidents and damages during moving and because of a punch through. Statistics have shown that over 75% of the incidents occur under tow or during jack-up/jack-down operations.
e) Safe operations require strict procedures.

The table below show some of the different jackup designs ( excluding KeppelFELS design of A-class, Super A, B-class, Super-B,etc ) and its capability in terms of size, VDL capacity,etc :

Types of Drilling Rig Capability

Some key personnel on board the drilling rig and their roles and responsibility :-

Tool pusher - In overall charge of rig operations, implementing the drilling plan and compliance with all safety requirements. Reports to the company representative.

Driller - In charge of the drilling process and operations. Responsible for compliance with the drilling plan and for the drilling crew. Reports to the tool/tourpusher.

Assistant driller - Assists the driller. Usually responsible to the driller for the operation of bulk storage equipment (for handling mud chemicals, etc.) and for the mud flowline system. Reports to the driller.

Derrickman - Responsible for the storage and movement of tubulars in the derrick and monitoring the mud systems. Reports to the driller.

Roughneck - Works on the rig floor. Responsible for general rig floor activities under the direction of the driller/assistant driller. Reports to the driller.

Rustabout - A member of the general workforce, assisting with the movement of materials,cleaning, painting, etc.

Drilling Operation and components

Drilling Completion

Formulas for Drilling and Prod



Rig Functions

Drilling Mud Technology

Drilling Mud Technology

Fundamental of floater naval architecture considerations

Ship or floater ( jackup or semi-submersible ) stability is a complicated aspect of naval architecture which has existed in some form or another for years. Historically, floaters stability calculations relied on rule-of-thumb calculations, often tied to a specific system of measurement. Some of these very old equations continue to be used in naval architecture books today, however the advent of the ship/floater model basin allows much more complex analysis.

When a ship, jackup or semi-submersible hull is designed, stability calculations are performed for the intact and damaged states of the vessel. Floaters are usually designed to slightly exceed the stability requirements (refer below), as they are usually tested for this by a classification society. Jack-ups are also considered in the stability calculation as the rig will at times move to other drillsite locations either by wet tow, in terms of staggered field tows or long ocean towage.

Intact stability calculations are relatively straightforward and involve taking all the centers of mass of objects on the vessel and the center of buoyancy of the hull. Cargo arrangements and loadings, crane operations, and the design sea states are usually taken into account.

Damaged stability calculations are much more complicated than intact stability. Finite element analysis is often employed because the areas and volumes can quickly become tedious and long to compute using other methods.

The loss of stability from flooding may be due in part to the free surface effect. Water accumulating in the hull usually drains to the bilges, lowering the centre of gravity and actually increasing the metacentric height (GMt). This assumes the floater remains completely stationary and upright or with slight heel or trim. However, once the ship or floater is inclined to any degree (a wave strikes it for example), the fluid in the bilge moves to the low side. This results in a list.

Stability is also lost due to flooding when, for example, an empty tank is holed and filled with seawater. The lost buoyancy of the tank results in that section of the ship lowers into the water slightly. This creates a list unless the tank is on the centerline of the vessel.

In stability calculations, when a tank is holed, its contents are assumed to be lost and replaced by seawater. If these contents are lighter than seawater, (light oil for example) then buoyancy is lost and the section lowers slightly in the water accordingly.

An Inclining test is performed on a ship or floater to determine its stability and the coordinates of its center of gravity. The test is applied to newly-constructed floaters greater than 24m in length. Inclining test procedures are specified by the International Maritime Organization and other international associations.

The weight of a floater can be readily determined by reading draughts and comparing with the known properties. The metacentric height (GM), which dominates stability, can be estimated from the design, but an accurate value must be determined by an inclining test. During the construction of the rig, weight control report updating the current design lightship weight of the vessel is done progressively from various inputs, eg, the steel weights, equipment weights,etc. from various design engineering disciplines.

The inclining test is usually done inshore in calm weather, in still water, and free of mooring restraints to achieve accuracy. The GM position is determined by moving weights transversely to produce a known overturning moment in the range of 1-4 degrees if possible. Knowing the restoring properties (buoyancy) of the rig or vessel from its dimensions and floating position and measuring the equilibrium angle of the weighted vessel, the GM can be calculated. Usually this kind of test takes less than two days, however for jackups, may take slightly longer as it involves spudding down the legs at the quayside after completing the test.

For U.S. flagged vessels, blueprints and stability calculations are checked against the U.S. Code of Federal Regulations (CFR) and SOLAS conventions. Ships are required to be stable in the conditions to which they are designed for, in both undamaged and damaged states. The extent of damage required to design for is included in the regulations. The assumed hole is calculated as fractions of the length and breadth of the vessel, and is to be placed in the area of the ship where it would cause the most damage to vessel stability.



NA Lecture Notes

MARIN, the Maritime Research Institute Netherlands, is one of the leading institutes in the world for hydrodynamic research and maritime technology. The services incorporate a unique combination of simulation, model testing, full-scale measurements and training programmes. MARIN provides services to the shipbuilding and offshore industry and governments. Today MARIN disposes of the following 7 test facilities: Shallow water basin, Deep water basin, High speed basin, Offshore basin, Seakeeping and Manoeuvring basin, Vacuum tank and Cavitation tunnel.

More about Drilling Rig components

The main functions of the offshore rotary drilling rig are as follows:

- Penetrating operations. The drill bit breaks down rock at the bottom-hole by the rotation under the weight. The rotating force of the rotary table is transmitted through the drill string to the bit. Some portion of the weight of drill collars is applied to the bit as the bit weight to push the bit against the rock.

- Hoisting operations. The drill string with the bit is lowered and lifted by the hoisting system, eg. Drawworks. The casing is also handled by the hoisting system.

- Conditioning and circulating the drilling fluids by the circulation system, eg. the mud pumps providing the high pressure mud to the well bore and return of the mud is being processed, filtered and clean through the shakers. The drill cuttings are contained into containers and shipped back to shore.

- Preventing the formation fluids from entering into the wellbore and controlling them to prevent collapse of the well.  More serious consequence, after the collapse of well, will be kicks and subsequently well blowout. The highly potential gas contained in the mud return will likely causes ignition of the gas on board and creating serious fire during the blowout.

The drilling fluids, conventionally known as muds, have lots of important functions in the offshore rig drilling. Main functions are as follows:

- Removal of cuttings from the bottom of the hole to the surface. Cuttings are separated from the mud at the shale shaker. The cuttings and samples of the mud may be further analyzed to study geological properties of the rocks penetrated, and to find out the indication of oil and gas in the formations.

- Controlling hydraulic pressure in the hole by adjusting the density of the mud to prevent collapse of the wall of the borehole, and to contain formation fluids in the formations.

- Cooling and lubricating the bit and the drill stem.

In the conventional system of the offshore drilling, the rotary table rotates the drill stem, but the down-hole mud motor and the top drive device are applied to rotate the bit in the directional and horizontal well drilling, or to improve operations in the vertical well drilling. The technical advancement of the measurement-while-drilling tools (MWD) and the logging-while-drilling tools (LWD) has contributed to the almost real-time acquisition of the down-hole information. Owing to these tools it has become easy to drill directional and horizontal wells.

Terminology :-

Casing: Steel pipe lowered into a hole drilled and bonded to formation by cement to keep the well safe.

Christmas tree: An assembly of valves installed at the top of a well to control the flow of oil and gas after the well has been completion.

Drill stem: A drilling assembly of tubulars, to rotate a bit at the bottom of the hole from the surface, which comprises of the kelly,the drill pipe, and drill collars.

Riser: Any pipe with the fluid flow upward in it. In offshore drilling a marine riser system is used to establish a connection between the rig and the seabed. In offshore petroleum production, production riser systems extend from the seabed to the deck of the production platform.

Well completion: A series of work to make a well ready for production after it has been drilled and tested. Although there are wide variations, it typically involves installing the production (deepest) casing, perforating the casing and installing tubing and the Christmas tree. A subsea completion or subsea-completed well is a well that sits entirely, that is, up to its Christmas tree, on the seabed.

RIG Components Guide