Munich, June 27, 2008
High-pressure air assists prospecting for crude oil and natural gas deposits
|View of a drilling platform
Due to the worldwide increase of consumption of natural gas and crude oil, the international crude oil companies involved are constantly trying to develop and exploit further energy resources on our planet. In the process, high-pressure air supplements seismic techniques used to explore the earth’s crust by means of sound waves and to represent it graphically.
As competent specialists in the high-pressure sector, BAUER KOMPRESSOREN GmbH in Munich and its English subsidiary BAUER KOMPRESSOREN UK LIMITED, hereinafter called BAUER UK, provide tailor-made installations for seismic applications to such international crude oil companies.
What is seismics?
This method is a part of applied geophysics and is based on the propagation of seismic waves in the earth’s crust.
The waves emanating from a seismic source (for example airguns, vibrators etc.) propagate through the ground. At layer boundaries, that is, a place where different materials with different elastic parameters come into contact with one another, components of the waves are reflected and return to the surface. Geophones or hydrophones (marine seismics) located at the surface receive the reflected waves; a recorder (seismograph) logs the signals of the geophones and saves them. The interpretation of these seismic data enables a depth model to be created. Seismograms (graphic representations of the measuring results) or model calculations derived from them allow the formulation of statements about the underground structures.
|Workstation recording point
Generally, there is a distinction between:
As stimulation blank cartridges, falling weights or compressed air are some of the methods used.
Geophones record the signals.
For application from marine craft, so-called airguns (working with 140 bar high-pressure air) are used for generating sound waves.
They are arranged in line, 3 to 5 m under water, astern the research vessel.
The measurement is carried out by hundreds of hydrophones installed in an oil-filled hose (streamer) having a length of up to 2000 m. The streamer is fixed at the stern of the research vessel.
Arrangement of the airguns and streamer (hose) with integrated hydrophones
Why is seismics applied?
The prospecting for natural gas and crude oil deposits involves extremely high costs and economic risks. Therefore it is important to identify the regions where there are good chances of successfully locating such deposits. For this reason, geophysical explorations are made before any drilling. By means of the 3D seismics, for example, which has been developed during the last 15 to 20 years, it is possible to carry out a three-dimensional exploration of the structure of the bedrock up to depths of 5000 m with a precision never reached before. It is not always possible to say with certainty whether a deposit located by means of measurement technology can actually be exploited economically. Absolute certainty can only be achieved by drilling.
The high-pressure station for seismic applications
With the aid of compressor blocks from BAUER Munich, the subsidiary company BAUER UK configures and builds the tailor-made, diesel driven high-pressure installations required to meet the very special desires of the world’s leading service companies.
Purchasers of such installations include such prestige-companies as e.g. Schlumberger, Baker Hughes and the French company Sercel. These firms, whose application profiles are very diversified, employ on average worldwide between 30,000 and 70,000 staff.
|Container version with HP compressor block K 28.0, turbodiesel engine; volume flow rate 3.5 m³/min, 250 bar
|Container version with screw-type/booster combination, turbodiesel engine; volume flow rate 7 m³/min, 250 bar
The scope of supply in this sector comprises installations providing throughputs from 1.47 m3/min to 3.5 m3 /min of free air. The working overpressures are set to 350 bar max..
For even higher consumption requirements, BAUER UK offers a newly configured installation concept providing a throughput of 7 m³/min max. of free air.
This new and robust version has been developed for testing oil pipelines and is currently being used successfully.
The higher capacity is based on a screw-type/piston compressor version.
A single-stage screw-type compressor from BAUER ROTORCOMP serves as the preliminary stage up to 12 bar. The final pressure of 250 bar is generated by a newly developed and proven 3-stage, air-cooled booster, model BK 24. The interstage and afterstage coolers are water-cooled and equipped with a closed cycle cooling system. The ventilator for the water cooler and the circulating pump is driven hydraulically via a hydraulic motor. The system is mechanically driven by an efficient turbodiesel engine from Deutz.
The installations convey the highly compressed air to storage batteries (350 bar) whose total capacity can vary between 150 and 600 l, depending on the compressor performance. From the storage batteries, the high-pressure air is fed into a pressure-reducing station with a dual-type dome loaded pressure regulator. The high air flow rate of the pressure reducer (adjusted to about 137 bar) is distributed to 4 similar air outlets. They are connected to the airguns via flexible pipes at the stern of the research vessel.
In order to prevent freezing of the airguns, it is possible to deliver versions with regeneration dryers on demand which dry the conveyed compressed air to a pressure dew point of -20 °C.
The low-volume flow rate compressors are powered by tried and tested diesel engines from Caterpillar-Perkins. All systems are fully automatically started, stopped and monitored by a modern, freely programmable control and monitoring unit; all faults on the compressor or diesel engine are displayed on a screen. If no compressed air is taken from the system, a pneumatic pressure relief device installed after the 4th compressor stage ensures that the compressed air is exhausted via a silencer and that the compressor continues running at a constant rotational speed. When a demand for pressure then has to be met, the relief valves will close and the installation will return to its initial capacity.
The installations can be delivered as assembly unit in a robust and stowable steel frame structure or as a container version for offshore use, equipped with all necessary auxiliary attachments.
All installations are manufactured according to the highest standards and are certified for marine seismics by Det Norske Veritas.
Based on the well developed and refined compressor construction technology and many years of experience in special plant construction, the BAUER group, as a competent supplier for leading crude oil service companies, has been not only able to maintain its market domination in this sector but even to extend it.
L. Kühlwein, graduate engineer, project engineer in the industrial sector