DRILLING BARGES : A drilling barge consists of a barge with a complete drilling rig and ancillary equipment constructed on it. Drilling barges are suitable for calm shallow waters (mostly inland applications) and are not able to withstand the water movement experienced in deeper, open water situations. When a drilling barge is moved from one location to another, the barge floats on the water and is pulled by tugs. When a drilling barge is stationed on the drill site, the barge can be anchored in the floating mode or in some way supported on the bottom. The bottom-support barges may be submerged to rest on the bottom or they may be raised on posts or jacked-up on legs above the water. The most common drilling barges are inland water barge drilling rigs that are used to drill wells in lakes, rivers, canals, swamps, marshes, shallow inland bays, and areas where the water covering the drill site in not too deep.
CAT 3512B : Average rating: 1000 kw
SUBMERSIBLES RIGS: Submersible drilling rigs are similar to barge rigs but suitable for open ocean waters of relative shallow depth. The drilling structure is supported by large submerged pontoons that are flooded and rest on the seafloor when drilling. After the well is completed, the water is
pumped out of the tanks to restore buoyancy and the vessel is towed to the next location.
JACK - UP RIGS:
Jack-up drilling rigs are similar to a drilling barge because the complete drilling rig is built on a floating hull that must be moved between locations with tug boats. Jack-ups are the most common offshore bottom-supported type of drilling rig. Once on location, a jack-up rig is raised above the water on legs that extend to the seafloor for support. Jack-ups can operate in open water or can be designed to move over and drill through conductor pipes in a production platform. Jack-up rigs come with various leg lengths and depth capabilities (based on load capacity and power ratings). They can be operated in shallow waters and moderate water depths up to about 450 ft.
SEMI - SUBMERSIBLE RIG: Semi-submersible drilling rigs are the most common type of offshore floating drilling rigs and can operate in deep water and usually move from location to location under their own power. They partially flood their pontoons for achieving the desired height above the water and to establish stability. “Semis” as they are called may be held in place over the location by mooring lines attached to seafloor anchors or may be held in place by adjustable thrusters (propellers) which are rotated to hold the vessel over the desired location (called dynamically positioned).
DRILLSHIP: Drillships are large ships designed for offshore drilling operations and can operate in deepwater. They are built on traditional ship hulls such as used for supertankers and cargo ships and move from location to location under their own power. Drillships can be quite large with many being 800 ft in length and over 100 ft in width. Drillships are not as stable in rough seas as semi-submersibles but have the advantage of having significantly more storage capacity. Modern deepwater drillships use the dynamic positioning system (as mentioned above for semisubmersibles) for maintaining their position over the drilling location. Because of their large sizes, drillships can work for extended periods without the need for constant resupply. Drillships operate at higher cruising speeds (between drillsite locations) than semi-submersibles.
WELL SERVICES ENGINES
Drilling rigs use direct current generators and motors that have an approximate efficiency of 68%. Actual efficiency in conjunction with drilling machinery is 87.5% due to additional losses in the power requirements of field induction generators, cooling blower, commutator temperature, brushes, and feeder cable length. In this system, the available energy is limited for the reason that only one DC generator. can be electrically linked to a DC motor. resulting in 1600 H.P. available to drive the winch.
DC (SCR) Drilling Rig
On a DC drilling rig, alternate current (AC) produced by one or more AC generator sets is converted into direct current (DC) by means of a silicon-controlled-rectifier (SCR) system. They obtain an efficiency of 68%; whose available energy is concentrated in a common bar (PCR) and can be partially or totally channeled to the drilling machinery (rotary, winch and pumps) that is required.
AC (VFD) Drilling Rig On an AC powered rig, AC generator sets (diesel engine plus AC generator) produce alternating current that is operated at variable speed via a variable-frequency drive (VFD)
AC versus DC Drilling Rig
Apart from being more energy efficient, AC powered rigs allow the drilling operator to more accurately control the rig equipment, thus enhancing rig safety and reducing drilling time.
AC Drilling Rig Advantages
- Efficient energy consumption due to a high power factor (minimum 95%).
- Precise speed regulation over a wider speed range.
- Constant high power even at low speed.
- Full torque at zero speed.
- Regenerative braking for safe and efficient control of the drawworks.
- Convenient and safe autodriller system for managing and controlling parameters such as weight on bit (WOB), rate of penetration (ROP), and rotary torque control.
CAT 3512B : Average rating: 1000 kw
