Electric & Mechanical Drilling Rig—All Drive Modes Explained

Electric generators powered by large diesel engines (the prime movers) generate electricity that move the heavy rig equipment such as the rotary table (or top drive), mud pumps and drawworks.

Electric drill rigs are more expensive than mechanical rigs, but offer some nice advantages in return.

• Safer: Stepless speed regulation allows for accurate control of the circulating, hoisting, and rotating equipment. Computerized driller’s cabin with touch screens for the display and control of drilling parameters.
• More reliable: As generator sets are installed in parallel, shutting down a single unit for repair or maintenance normally can be done without interrupting normal drilling operations.
• More flexible: Generator sets can be added or removed as required.

Sovonex electric drilling rigs are available in two types that either use direct current (DC) or alternating current (AC) to power the rig components:

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.

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).

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.

• 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.

On mechanical drilling rigs, also called power rigs, the rotary energy of the diesel engines is transferred directly to the drawworks, mud pumps, and rotary table (or top drive) via a system of chains (chain drive) or belts (belt drive), torque converters and clutches.

In addition, a separate generator set produces electricity to power the lighting system of the rig as well as small AC motors used by equipment of the mud control system.

Most truck-mounted drilling rigs are mechanical drilling rigs where the diesel engine or engines that are mounted on the carrier drive both the drawworks and the rotary table. In addition, each mud pump has its own diesel engine driving the pump via belts or chains.

Although mechanical drilling rigs are less expensive than electric drilling rigs, they are less reliable due to the fact, that the failure of a single main engine can can bring drilling to a halt. The main drives of a mechanical drilling rig are also less precise to control.

On an electro-mechanical drilling rig, at least the drawworks is driven via the direct transfer of rotary power from the main diesel engines.

The rotary table (or top drive), on the other hand, runs on electricity produced by one or more separate generator sets. The electric power for the lightning system and smaller equipment like the shale shaker and degasser, is also produced this way.

As for the solid control system, either electric or mechanical mud pumps can be installed, depending on customer preferences.

With the diesel engines and drawworks mounted on the truck, the drawworks of a truck or trailer-mounted drilling rig is always driven mechanically.

Due to size constraints on a mobile rig’s standard substructure, installing an electric rotary table would be difficult, the rotary table also is driven mechanically by the prime movers on the truck.

The mud pumps, however, can be driven electrically by a separate generator set, as can the top drive, if required.

• Less expensive than a full electric drilling rig
• The most important drive on a rig, the rotary table or top drive, is powered electronically and can thus be precisely controlled thanks to stepless speed regulation.