Water!
Modern deep drilling rigs with extensive hydraulic equipment can sink wells quickly, quietly and safely.
In nine years the oil reserves in the U.S.A. will be exhausted. That was the forecast made by the United States Geological Survey in the year 1919. Neither does anyone today know how much fossil energy actually still lies under our feet. One thing is sure, however. Anyone wanting to tap new gas and oil reserves or geothermal sources will have to drill deep.
One drilling head nibbled its way more than 4,000 meters down in the ground at the Bavarian community of Dürrnhaar before the triumphant cry was heard: “Water!” The liquid from these extremely hot springs, running at up to 140 degrees Celsius, is used to produce about five megawatts of current at a geothermal generating plant — enough to supply zero-emission electricity to about ten thousand households.This hydrothermal energy source was developed with a special unit built by the Herrenknecht Vertical GmbH.
“Terra Invader” is the name given this deep drilling rig that, when compared with conventional units, exhibits some special features. In spite of its tremendous power — dynamic torque of 48,000 Newton meter — the system works so quietly that at a distance of no more than 150 meters the noise is no greater than a radio being played at normal indoor listening levels. That’s an important factor for geothermal projects within sight of residential buildings. In addition to this sophisticated noise abatement system, the system is engineered for great drilling speed and the maximum possible jobsite safety.
The cylinder-driven lifting unit can both raise the string and apply 100 tons of pressure.
Cylinder-powered lift unit applies pressure
In most large-scale drilling units a rope winch is used to raise the links of pipe. Drilling is accomplished only with the rotary movement and the pipe string’s own weight. In the Terra Invader the lifting unit, powered with cylinders, can not only raise pipe. It can also apply up to 100 tons of pressure. That can make for rapid advance particularly when starting to drill or where underground strata present difficulties. Piston excursion in the tandem cylinders is 22 meters. Cascaded hydraulic choke controls make for closely metered operation of the drilling head.
When designing these cylinders especially for this application, Rexroth pulled together its international experience in offshore and onshore drilling technologies. Additional hydraulic cylinders hold the rotary clamps on the drilling pipe. This clamping requires careful application of power to hold the drilling string, weighing as much as several hundred tons, without damaging it. To accomplish this, Herrenknecht uses hydraulic cylinders with path measurement and atorque indicator. A two thousand kilowatt hydraulic power unit with twelve axial piston pumps delivers the required flow. The operator can split output between the lifting unit and the rotation turntable itself, boosting the energy efficiency of the system and noticeably lowering operating costs.
The pipe handler feeds lengths to the rig and disassembles the string, both automatically.
A focus on job safety
The engineers paid particular attention to jobsite safety. On most drilling rigs up to three workers have to move the individual lengths of drill pipe manually, using a hoisting winch, turn them upright, and screw them down or unscrew them. In the Herrenknecht Vertical rig this hazardous work is done by a hydraulically driven, semi-automatic, cylinder-powered pipe handler. It picks up the individual joints of pipe, up to 19.5 meters long, from the rack and moves the pipe, drilling stem and casings into the vertical, aligned on the hole. Disassembling the string is also automatic. Here the rig pulls up the entire string, unscrews the individual lengths and lays them aside in an orderly fashion. Speed of 500 meters per hour minimizes nonproductive refitting times.
In Germany the Terra Invader will be found at work above all in geothermal projects in the North German Basin, the Upper Rhine Trench and the Molasse Basin in southern Germany. On the international market, exploration and development operations use the deep-drilling rigs to open up new oil and gas deposits at great depths.
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