One piece of equipment has remained virtually unchanged since the beginning of the century - the drilling derrick itself. Some developments have taken place - steel has replaced wood, for example - but the basic concept has remained the same. Until now.

To maintain profitable operations through periods of low oil and gas prices, the industry is focusing on lowering the total cost of producing oil and gas by making the exploration and production process more cost-effective.
By developing new technology for every phase of the process, from 3D seismic to cost-effective subsea or floating production installations, the industry has reduced lifting costs significantly during the past 10 years.
EDM AS in Norway has used its extensive experience within the drilling and manufacturing industry to patent a rig concept using proven technology that has been repackaged and improved. The result is a drilling tower that does not have the traditional crown and traveling blocks, drawworks or wire. The concept is purely mechanical - with no hydraulic cylinders.
The EDM rack-and-pinion hoisting system (Figure 1) has been developed to:
simplify the hoisting process;
reduce weight and lower the center of gravity;
improve safety and the working environment;
ease maintenance;
streamline rig up/rig down;
ensure accurate control;
increase cost-effectiveness;
use standard components; and
expand push and pull capacity.
The concept uses a chain of jointed I-beams with racks on both sides; each link is about 3ft. The chain rack is pushed up or pulled down by stationary AC or hydraulic motors connected to the rack by pinions.
The motors and the control systems are in the machine room in the lower section of the tower. All the weight taken by the topdrive is transmitted down the chain of I-beams and absorbed by the pinions.
This lowers the center of gravity and reduces the function of the tower from a load-bearing structure to a guide that supports the rack and prevents it from buckling.
The drilling rig concept is applicable to both onshore and offshore drilling applications. Using the push and pull concept, it is possible to use the same unit for drilling, workovers and snubbing operations. A patented anti-buckling device makes it possible to snub into the wells with single, double or triple stands of drill pipe (Figure 2).
Most of the required maintenance is completed within the machine room in the lower part of the tower. Due to the controlled environment, it is possible to use standard equipment (motors and gearboxes) that have standard, non-oilfield specifications if replacement is required.
The offshore and onshore units have a modular design to save time and simplify rig up and rig down. A prototype has been built and tested at EDM's fabrication yard in Stavanger.

Mechanical innovations
EDM engineers in Norway have designed the following mechanical equipment systems for the new class of rigs.
Rack-and-pinion drilling rig concept
(patent pending).
The rack-and-pinion system offers considerable weight savings, faster rig up/rig down time, a significantly lower center of gravity and simpler technical solutions.
The concept has been used for years but with the rack being fixed and the pinions running up and down the rack. For jackup applications, the rack is attached to the legs and the drilling module climbs up the rack using pinions. In the EDM rig, the pinions are attached to the lower portion of the tower (mast), placing the center of gravity below the drilling floor. By attaching the pinions permanently and moving the rack up and down, the loads are kept on the lower portion, not at the crown as on conventional rigs. The concept has a significant advantage over conventional rig designs for offshore and land applications.
EDM US is developing other uses for the concept, such as pumping jacks, offshore pipe laying, elevators for high-rise buildings and highway boring machines.

Unique heave compensation system (patent pending).
The heave compensation system uses accumulated energy from the down movement of the drillstring and vessel to reduce the energy required from the AC motors and achieve accurate heave compensation.

Anti-buckling system (patent pending).
The anti-buckling system will enable the rack-and-pinion drilling rigs to be used for snubbing operations by applying additional weight on the bit when required. The system can be made for single, double and triple drill pipe lengths.

Riser tensioning concept
(patent pending).
The rack-and-pinion riser tensioning system is based on the same concept as the rack-and-pinion rig. The tensioning system can significantly reduce the required space and weight requirements compared to existing systems. The platform that holds the riser can be used as a working platform or elevator in the moonpool when not used for riser tensioning purposes.

Telescoping mousehole
(patent pending).
The telescoping mousehole allows for parallel operation where stands can be made up or broken down concurrent to the ongoing drilling operation.

Circular finger board (patent pending).
The circular finger board allows for a more efficient use of the allocated space and simplifies the movement made by automatic pipe handlers, thus reducing the pipe-handling operation.

Pipe handling equipment
(patent pending)
The HTV (horizontal to vertical)/VTH (vertical to horizontal) pipe handler can accept pipe from 27/8 in. tubing to 9in. drill collars without changing any components.

The land rig design philosophy
The modular land rig concept is designed and constructed with:
l a steel-plated mast for single, double, triple or quadruple operation;
l hoist machinery based on the pinion-rack principle with AC electrical motor drive frequency controlled. It can pull (hoist) as well as push downward (snubbing mode);
l the lower part of the mast that serves as the substructure as well as the engine room and MCC room;
l a modular design, facilitating easy movement by trailer. Rig up/rig down takes less than a day;
l a mast complete with top drive and dolly, pipe-handling system, utility winches, service loops and standpipes;
The rig is transported in two parts, which can be erected and in operation within 12 hours. With improvements in safety and a small footprint this rig is suitable for all onshore locations (Figure 3).
Advantages include the elimination of the drawworks with no traveling block or crown block and no drill line. Automatic pipe handling can be integrated. The weight of the unit is 120 tonnes with a lifting capacity of 100 to 350 tons. It has a racking capacity of up to 8,000m.

Benefits
Health, environmental and safety requirements are included in every area of the design to minimize manual work, keep noise limits below the required regulations, reduce risk for personnel injury and equipment damage, and reduce stress and risk of environmental spills.
The rack-and-pinion rig concept can be used onshore and offshore with little change to the basic design (Figure 4). Due to the low center of gravity and low weight, the rig is ideal for a floating or fixed offshore installation, claims its maker. The rig-up time, for example, on an existing platform can be achieved within 2 days due to the modular design and low weight (maximum lift of 20 metric tons).The rig should prove to be one of the most cost-effective drilling, snubbing and workover units on the market due to its flexibility and easy mobilization and demobilization features.