STACKED RIG REFURBISHED FOR ULTRADEEP GAS DRILLING

Jan. 9, 1995
Thor Novig , Waldhorst Gutsche ITAG Tiefbohr GmbH & Co. KG Celle, Germany A heavy drilling rig, cold stacked for several years, recently underwent numerous structural, equipment, and computer upgrades for drilling ultradeep (8,000 m) gas wells in Germany. The technical improvements on the rig included supplementary installations and modifications to safety, quality, engineering, noise abatement, and environmental protection systems.

Thor Novig, Waldhorst Gutsche
ITAG Tiefbohr GmbH & Co. KG
Celle, Germany

A heavy drilling rig, cold stacked for several years, recently underwent numerous structural, equipment, and computer upgrades for drilling ultradeep (8,000 m) gas wells in Germany. The technical improvements on the rig included supplementary installations and modifications to safety, quality, engineering, noise abatement, and environmental protection systems.

In late 1993, ITAG Tiefbohr GmbH & Co. KG signed a contract with BEB Erdgas und Erdol GmbH (Shell/Esso) to drill deep gas wells in Lower Saxony, Germany. These drilling operations require a rig capable of drilling horizontal wells and ultradeep wells.

The basic drilling rig - an Ideco E-3000 rig with diesel-electric drive system - had been acquired by ITAG from OMV AG in Austria. In the Vienna basin, this rig had completed only one well with a depth of about 8,000 m. Because of low oil and gas prices and the high cost of drilling ultradeep wells in a geologically difficult area, the rig was shut down and stacked for several years.

In early 1994, ITAG began reconstructing the rig to conform with current technical standards. The engineering, planning, and manufacturing proceeded simultaneously, and the rig was recommissioned (Rig 27) after only 6 months of construction work (Fig. 1). During the project, engineers from BEB and ITAG conferred regularly to coordinate the detailed specifications of the rig.

With a maximal hook load of 700 tons, the drilling rig is one of the heaviest of its kind in Europe. The rig has a drilling depth range of 7,000-8,000 m, and the top drive system enables horizontal drilling. The rig is specially designed with an electrical drive system, modern drilling fluid treatment system, and noise abatement measures for the sensitive environment in Western Europe.

RIG SITE

The rig and ancillary equipment were built compact and designed for minimal-sized surface locations. With changes to the layout and power station modifications, the surface area for the drilling site was decreased by 50% compared to the original layout.

A clear-cut division of the drilling site into exterior and interior zones ensured satisfying the environmental and water protection requirements for compliance with legal regulations. The power stations, hydraulic units, diesel fuel tank, and all rig components that contact drilling fluid are located within the site's interior zone. The exterior zone is used only for vehicle traffic, materials stock, workshop containers, safety and sanitary installations, and office containers for the operator, contractor, and service companies.

The drilling site is surrounded by a channel for controlled discharge of surface water from the exterior zone through an oil trap to a collecting basin.

MAST

In the original version of the rig, the mast was not suited for installation of a top drive system, so several mast modifications and supplementary equipment were necessary. The mast height had to be extended by 3 m to provide sufficient path length for the traveling block with top drive. Also, the rear side of the mast had to be recessed at several points for top drive clearance. Additional girders were installed to support the top drive rail system. Maintenance and service platforms were also constructed and installed in the mast. Solid wall cladding was added to both the finger board and the mast area around the finger board.

Emphasis was placed on the possibility of installing the top drive rails, service platforms, and cladding on the mast horizontally without exceeding the load limits while the mast is erected.

The rail distribution and rear mast structure were designed such that the rails, with the exception of the lower rail pair, could remain in the mast sections during rig moves between locations.

TOP DRIVE

A top drive system was required for the deep horizontal drilling projects planned (Fig. 2). The electrically powered top drive has a power rating of 745 kw and a load-bearing capacity of 4,500 kN. Installation of the top drive required comprehensive modifications in the mast and in the electrical control system.

The top drive system comprises the following compact-design components: Swivel, electric motor, two-speed transmission, and a connection make-up unit. All top drive functions are remotely controlled from the control station. The two-speed gear allows transmission of torque up to 75,000 Nm and rotational speeds up to 237 rpm to the drillstring. The motive power for the top drive system is supplied through the service loop, which is a bundle of electric cables and hydraulic and pneumatic hoses. The air for cooling the dc-electric motor and ensuring explosion protection is supplied by a fan and piping from the explosion-free zone.

This top drive can drill with entire pipe stands (28 m long) without interruption. Using stands for reverse reaming in the borehole is also possible, offering advantages for drilling horizontal wells. During round trips, functions such as opening and closing the kelly cock, making and breaking of the drillstring connections at the top drive, inserting and extracting the threaded pins, swiveling and rotating the elevator, and opening and closing the elevator can be performed by remote control from the driller's console.

SUBSTRUCTURE

Because of the new layout of the rig components, the stairway system to the substructure also had to be rearranged. With the new design, the derrick floor is accessible from three sides. The stairway along the combination ramp is thereby intended as an emergency exit only. Another stairway leads to the mud tanks and the mud pump area, and the third leads from the doghouse down to a resting platform and from there to the ground.

The entire rig floor has been modernized. For noise abatement, the floor has been completely surrounded with 4-m high soundproof walls. The driller's console has been enlarged to accommodate additional instruments and monitors. The console is protected against wind and weather with a removable, acoustically insulated cabin. The pneumatic winches on the rig floor have been replaced with hydraulic winches. Further noise abatement measures included soundproofing of the combination ramp.

In the substructure several channels were installed for routing cables and hoses for electric, hydraulic, and pneumatic power. Because the channels are covered, the walking surface of the rig floor is level and freely accessible. Beneath the rotary table a basin (drip pan) has been installed to collect drilling fluid. This basin is on a rail system and can be moved away from the borehole during blowout preventer nippling up/down.

DRAW WORKS

The Ideco E-3000 draw works have a power rating of 2,240 kw. For noise abatement, the draw works were completely encapsulated with a large segmented hood. The hood consists of several wall and roof elements for easy assembly. The spacious interior of the, machine housing provides sufficient access for service and maintenance work on the draw works. Service doors were added to the walls where space limitations hindered service accessibility. The drilling line passes through a soundproof opening in the roof. Below the draw works, the substructure has likewise been provided with a soundproof closure.

Because the rig was stacked for a prolonged time, the water cooling system had to be replaced. The water cooling system was converted to a proven design using a water tank and heat exchanger.

Furthermore, because of more stringent safety requirements in recent years, the control system of the eddy current brake had to be designed into an automatic braking system conforming with the state-of-the-art in rotational speed monitoring.

POWER STATION

The power station consists of five Caterpillar D-399 diesel engines with a total power rating of 3,525 kw and five Kato three-phase generators with a total rating of 5,835 kva. The generator sets are mounted on base frames. The frames and roof structures are closely spaced, so the external soundproof wall cladding forms a connected enclosure for the power station.

To improve noise abatement and decrease the floor space, the previously separate radiators and fans were integrated in the power station. The power station includes a small workshop with a materials stock. The diesel engines and generators were completely overhauled and rebuilt.

MUD SYSTEM

The two 1,600 hp Ideco mud pumps have a power rating of 1,340 kw each. To save surface space and decrease the number of loads, the electrically driven charging pump was installed on the main frame of the pump.

Because of the industry trend toward higher circulation pressure, and for better maintenance, the high-pressure fluid ends had to be redesigned for installation of wear plates on the pump cylinders.

The tank facility for the drilling fluid was thoroughly redesigned and reconstructed. The mud tank setup included a space-saving design of the entire piping system, a new trip tank, four additional elevated tanks, three compressed-air bulk silos for barite and salt, and the mixing equipment. To avoid the use of sack goods with waste and dust, the feed hopper for mixing the mud additives is charged from small containers (Fig. 3).

The mixing hopper and the three pressured silos have scales to control amounts of drilling fluid additives. For monitoring the tank contents, all tank compartments are equipped with an ultrasonic fluid-level measuring system.

Additionally, a large gas separator with a gas line and a flare 15-m high with electrical ignition were installed for safe handling of kicks.

The drilling fluid treatment and solids control facilities were also completely redesigned as a closed-loop system. Linear shale shakers with adjustable slope for ultrafine screening, four 10-in. demanders with individual shut offs, and thirty-two 4-in. desilters (sets of four for each of eight cyclones) with individual shut off were installed. The demanders and desilters are fed by separate centrifugal pumps with rotational speed control. Individual and group shut offs ensure optimal operation even with small borehole diameters.

The solids control system also has a provision for temporary connection of a third linear shale shaker for drilling upper hole sections.

The underflow from the desander and desilter is routed to a common collecting tank and then centrifuged.

INSTRUMENTATION

The silicon controlled rectifier (SCR) switching station was completely overhauled by the manufacturer in England. Supplementary installations and modifications were necessary, especially for the top drive control system. The entire electric power distribution system for 380/220 y, including the rotational speed control for the demanders and desilters, was accommodated in a new motor control center.

Because of current requirements on the instrumentation for measuring drilling parameters and the current methods of data processing, the existing instrumentation and recording system was replaced with a new digital system. The majority of the sensors provide electrical output signals, and most of the instruments in the driller's console were made digital. For safety reasons (redundancy), the weight indication, weight on bit, and pump pressure are also measured hydraulically and shown on conventional analog instruments.

All drilling parameters are stored in a central memory unit so the incoming data can be processed with a microprocessor system. Graphs of important drilling parameters can be displayed simultaneously on a monitor for each working mode (drilling or round trip) for the drilling personnel in the control station. The system not only indicates instantaneous values, but also allows a simultaneous presentation of the past historical data for an 8-hr period. Thus, important trends in the drilling process can be better interpreted and incipient problems in the borehole can be recognized earlier.

The conventional drill floor recorder was replaced with a computerized multichannel recorder. A lighting system with explosion-proof floodlamps and a new internal communication system with five stations were installed.

All these electrical and electronic modifications required 14,000 m of new cables.

OTHER EQUIPMENT

Because of the prolonged storage, the seven dc motors for the draw works, rotary table, and mud pumps had to be completely disassembled, cleaned, and equipped with new bearings. The windings were dried, and all electrical terminals were replaced.

Several other components were required to complete the drilling rig. These facilities included a 50 cu m double-walled diesel fuel tank, a central hydraulic power system for auxiliary winches and drillstring handling equipment, remote control of mud pumps and choke manifold, and conversion of the grasshopper to a central supply route for electric, hydraulic, and pneumatic power between the ground and the floor. About 6,000 kg of paint were applied for corrosion protection and appearance.

THE AUTHORS

Thor Novig is the managing director of ITAG Tiefbohr GmbH & Co. KG in Celle, Germany. He has worked for ITAG since 1978, and has held positions as engineering manager and drilling manager. Novig earned a BS in mechanical engineering in Norway and an MS in petroleum engineering from the Technical University in Clausthal, Germany. He is a member of DGMK (a German association of geologists and oil field engineers).

Waldhorst Gutsche is engineering manager of the drilling department of ITAG Tiefbhor GmbH & Co. KG in Celle, Germany. He has worked for ITAG since 1979, and he is involved in the design, specification, and manufacture of drilling rig components. Gutsche has a degree in mechanical engineering from the University of Hannover and a PhD in petroleum engineering from the Technical University in Clausthal.

Copyright 1995 Oil & Gas Journal. All Rights Reserved.