Most drilling rigs operate in remote locations where a power supply is not available. Therefore, it must have a method of generating electrical power through generators. Diesel internal combustion engines power electrical power generators. Then, electricity is supplied to electric motors connected to the draw works, rotary table, and mud pumps. Depending on its size and capacity, the rig may have up to four prime movers, producing more than 3,000 horsepower. This is an old but widely used unit of power in the drilling industry.
Older rigs used steam power and mechanical transmission systems. Modern drilling rigs use electric transmission because it better enables the driller to apply power smoothly, avoiding vibration and chance of electric shock. Draw works and mud pumps use the most power from rigs, although both do not generally work at the same time.
Electric drill rigs cost more than mechanical rigs but offer more advantages in return:
- Safer – Stepless speed regulation allows for accurate control of the circulating, rotating, and hoisting equipment. A computerized driller’s cabin with touch screens that display and control drilling parameters.
- More reliable – As generator sets are installed in parallel, shutting down a single unit for repair or maintenance usually can be done without interrupting normal drilling operations.
- More flexible – Generator sets can be added or removed when needed.
Electric drilling rigs can be powered by two methods: direct current (DC) or alternating current (AC).
DC Drilling Rig
Alternate current (AC) made by one or more AC generator sets on a DC drilling rig is converted into direct current (DC) through a silicon-controlled-rectifier (SCR) system.
AC Drilling Rig
On an AC powered rig, the AC generator sets (diesel engine and AC generator) produce an alternating current that is operated at variable speeds by a variable-frequency drive (VFD).
AC vs. DC Drilling Rig
AC powered rigs are more energy efficient and allow the drilling operator to control the rig equipment more precisely, consequently enhancing rig safety and decreasing the amount of time spent drilling.
AC Drilling Rig Advantages
- Efficient consumptions of energy because of a high power factor (at least 95%).
- Accurate speed regulation over a broader speed range.
- Constant high power – even at low speed.
- Full torque at a speed of zero.
- Regenerative braking for efficient and safe control of the draw works.
- Convenient and safe auto driller system for controlling and managing parameters like rate of penetration (ROP), weight on bit (WOB), and rotary torque control.
- Electro-Mechanical Drilling Rigs
- On these rigs, the draw works are driven through the immediate transfer of rotary power from the primary diesel engines.
The rotary table or top drive, on the flip side, is powered by electricity generated by one or more different generator sets. Smaller equipment like the degasser and shale shaker are also built this way.
Either mechanical or electric mud pumps can be installed for the solid control system, depending on consumer preferences.
Electro-Mechanical Drilling Rig Advantages
- Less costly than a full electric drilling rig
- The rotary table or top drive is electronically powered so it can be accurately controlled because of the stepless speed regulation