Chiles Offshore opted for versatility and flexible management in powering its new Explorer Class jackups.

In early 1997, Chiles Offshore Inc. saw a need for high-performance, long-legged drilling rigs to drill gas wells in the deeper waters of the continental shelf in the Gulf of Mexico. The conventional rigs built in the 1980s were of limited use on the region's high-temperature, high-pressure deviated and subsalt wells.
The solution required more rig power, mainly to support significantly higher mud-pump capacities and auxiliary equipment. To serve this emerging market segment, Chiles began developing its Explorer Class ultrapremium silicon control rectifier (SCR) jackup rigs in April 1997. The first two of these rigs, the Magellan and the Columbus, have drilled several challenging wells in the Gulf and met or exceeded customers' expectations for completion time.
Each rig is equipped with three National Oilwell 14P220 Triplex mud pumps, rated at 2,200 hp, and with fluid ends rated at 7,500 psi. The primary generators are four electronically controlled Caterpillar 3516B diesel engines rated at 1,855 hp. Each engine drives an SR4 600 V, 60-cycle AC generator delivering 2,150 kVA continuous power. Each rig also has an auxiliary generator identical to the primary units and configured to be brought online for emergency rig power when necessary.
Two additional rigs are under construction: the Discovery, being built in Singapore and scheduled for launch in February 2002; and the Galileo, being built in Brownsville, Texas, and scheduled for launch in summer 2002.
The Explorer Class rigs deliver the high-pressure, high-volume drilling fluids required for challenging conditions in the Gulf. Leg lengths of 544 ft (166 m), 511 ft (156 m) and 477 ft (145 m) also come into play as the rigs operate in the deeper waters of the continental shelf.
The Chiles Explorer Class rigs are LeTourneau Super 116 Class independent-leg cantilever jackups. They employ a LeTourneau electric rack-and-pinion elevating system. Chiles developed the Columbus and Magellan rig SCR systems to provide substantial power capacity and high flexibility. Critical considerations included fuel economy, emissions control and power-to-weight ratio (power density).
The company opted for five Cat 3516B diesels, rather than two or three larger engines, to provide operating flexibility and enhance backup power capacity. The four-engine primary power configuration lets rig personnel bring horsepower online in smaller blocks as load increases and to keep one or more engines in reserve for emergencies or for use during maintenance and service periods.
The 16-cylinder 3516B has a 6.7-in. bore, 8.5-in. stroke and 4,764 cu in. displacement. A direct-injection fuel system and low-friction three-ring piston design help maximize fuel economy. Electronic unit fuel injectors automatically adjust fuel delivery for changes in load and speed. Sensors relay the engine's operating status to the onboard computer, which determines exactly when to inject fuel, and for how long.
Brake-specific fuel consumption is 0.346 lb/bhp-hr. Emissions are compliant with US Environmental Protection Agency and International Maritime Organization regulations. The engines produce less than 1 g/hp-hr hydrocarbons, less than 8.5 g/hp-hr carbon monoxide, less than 6.9 g/hp-hr nitrous oxides and less than 0.4 g/hp-hr particulate matter.
An onboard electronic control system uses the Caterpillar Advanced Diesel Engine Management II (ADEM II) modules to record operating data and protect the equipment against adverse operating conditions.
Critical to the design was the ability to deliver the power necessary to complete deviated wells, subsalt wells and wells with temperatures up to 450°F (232°C) at bottomhole. The three 2,200-hp mud pumps far exceed the capacity of conventional rigs, which typically carry two or three 1,600-hp pumps.
The difficult drilling conditions for which the rigs were designed dictated ample reserve power - a power-system failure could result in a stuck drill pipe and loss of the well.
During drilling operations, all operating engine-generators share load equally. Under typical conditions, two of the four primary-power engine-generators can carry the entire SCR electrical load. During times of peak demand on mud pumps, mud coolers and hoisting machinery, a third unit comes online, still leaving the fourth primary engine-generator in reserve. This arrangement enables rig personnel to perform scheduled maintenance on the engine-generators on a staggered basis without requiring rig downtime.
The use of a fifth 3516B package as the auxiliary generator provides additional reserve power. Typically, auxiliary generator engines are sized at 300 hp to 400 hp, mainly for essential lighting and hotel load. The Columbus and Magellan use an 1,855-hp 3516B configured for 600 v power, rather than the traditional 480 v.
If an engine-room fire or other event should disable the primary power system, the emergency generator can backfeed 600 v power to the SCRs. This enables rig personnel to pull up into the casing or circulate drilling fluids until primary power is restored.
Under some extremely difficult conditions, the Columbus and Magellan rigs have required all four engine-generators for drilling. For this reason, Chiles is building both its new rigs with five 3516B engine-generators as primary power and an additional 3516B as the auxiliary power unit.
The 3516B packages arrive for installation on a factory-built base with three-point mounting to maintain precise alignment between engine and generator, even during substructure flexing. This minimizes vibration and helps extend bearing and coupling life.
The ADEM II control and monitoring system provides engine deration, alarm or shutdown strategies for conditions including low oil pressure, low and high water temperature, low water level, overspeed, crankcase pressure, aftercooler temperature, air inlet restriction, exhaust stack temperature and oil and fuel filter differential pressure.
The control system includes onboard diagnostics to help speed troubleshooting and service. In addition, the system continuously records engine operating data that is useful in troubleshooting and trend analysis. For example, power factor data collected by the electronic monitoring system and displayed in the driller's cabin contributed to Chiles' decision to add a fifth primary-power generator on its two new rigs.
The electronic engine controls are in keeping with the rigs' highly automated drilling system, designed to maximize efficiency and safety. Rig operators work in two Hitec Cyberbase driller control stations supplied by National Oilwell.
The automated controls enhance safety and efficiency on the rig floor. The system also reduces stress on the crew. Joystick and keypad controls regulate mud pumps, drawworks, top drive, rotary, slips and SCR system. The cabin is designed to provide an unobstructed view and the best possible line of sight to machinery and personnel on the rig floor.
While the system requires employees more thoroughly trained than those on conventional rigs, it also improves safety and the control over the process, increases sensitivity and enables drillers to manage multiple tasks more effectively.
As development of oil and gas resources moves steadily into deeper water and increasingly difficult conditions, the marketplace will demand rigs with enhanced power and capability. The Chiles Explorer Class rigs are designed to respond to that market need for years to come, serving the offshore industry in the Gulf of Mexico and worldwide.
Since the Columbus and Magellan rigs emerged from shakedown in the shipyard, the engine-generators on both have recorded greater than 98% uptime.