Horizontal well construction
Under Horizontal well drilling is defined as the establishment of a horizontal filter well . Various drilling methods were and are used.
The Ranney method
Starting from a concrete shaft that is sunk vertically up to a few meters into the aquifer (groundwater aquifer) , with the Ranney method a slotted, thick-walled, welded steel pipe is driven horizontally into the aquifer. This means that the filter tube is also a protective tube and there is no need for a bed of gravel around the filter. As a result of the thick walls of the pipe, only large slot widths are possible, which quickly lead to sand guides in the well or which only allow the method to be used in uneven, coarse sand or gravel. Another disadvantage is that, as a result of the uncontrolled propulsion, the tip of the propulsion tends to move upwards, depending on the type of soil.
The Fehlmann process
The Fehlmann process developed by the Swiss entrepreneur Fehlmann represents an improvement in this technology. Here, a drill pipe / protective pipe is first driven from the shaft. Then the flushing and delivery rods are removed and the filter and full pipes are installed centrally in the borehole (protected by the drill pipe). After removal with the full pipe / filter pipe string, the drill head is pushed / pulled off the casing pipes and remains in the ground. The drill pipes are now gradually pulled.
The Preussag process
An improvement in the Fehlmann process was achieved in the 1950s with the development of the Preussag gravel jacket well. With essentially the same type of tunneling as with the Fehlmann method, this allows the installation of an artificial gravel bed adapted to the existing soil and the filter used. The advantage of this technology is that larger drilling diameters can be used and a suitable gravel bed can be installed in the annular space between the drill pipe and the filter pipe. In this way, the capacity of the well is increased and greater security against sand flow and clogging tendencies in later operation is achieved.
The Hori-Well procedure
Disadvantages of the above-mentioned horizontal well construction methods are that on the one hand they are driven very imprecisely and uncontrolled and they can hardly be used, especially in larger gravel layers and coarse soil material, as well as in marl and clay lenses. For these reasons, the company Herrenknecht and Matthias Bertram developed the "Hori-Well process" for the production of horizontal filter wells. A drilling method is used here which is known in the field of microtunnelling .
Special types of boring heads cover the ground almost completely (including stones and rubble) and use cone crushers to crush the material so that it can be hydraulically conveyed away . Even the smallest deviations from the target line are detected with the help of a laser system and corrected with the help of the control cylinder. Marl and clay lentils can be loosened with the help of a high pressure water jet. The drill head does not remain in the ground, as with traditional methods, but is pulled again.
The drill head of the Hori-Well procedure
Material flow in the Hori-Well process
literature
- Erich Bieske, Wilhelm Rubbert, Christoph Treskatis: Bohrbrunnen . 8th edition. Verlag Oldenbourg, Munich 1998, ISBN 3-486-26388-9 .