'Tight gas' is referred to as gas trapped in extremely low-permeable (tight) formations. To facilitate gas production from these tight gas reservoirs - as found in the North German basin - the joint venture partners applied state-of-the-art drilling and production methods. As to the Leer Z4 well, experts from both energy companies decided to combine the horizontal drilling method with so-called frac procedures.
In the first stage, the well has been drilled vertically. At a depth of about 3,000 meters, the well was kicked-off, drilled deviated and finally horizontally to hit the previously defined target in the Rotliegend formation. Following five months' drilling operations covering a total footage of 5,683 meters, Leer Z4 reached target in a vertical depth of 4,424 meters. In a further stage, several successful hydraulic fracs were performed into the reservoir rock, increasing gas flow behavior and thus facilitating flow into the borehole. To achieve this result, a specially designed sand-charged fluid was injected into the borehole under high pressure which produced fractures in the rock formation, starting of from the borehole. Acting as filling material, this special sand is designed to keep the fractures open while being permeable enough to open up the gas a passage to the borehole.
The positive results of a production test revealed that commercial production from this gas reservoir is possible through the implementation of highly sophisticated techniques. Right now, the joint venture partners Gaz de France and Wintershall are in the process of installing the required surface facilities (gas dehydration unit and infrastructure). Production is expected to come on stream as early as spring 2006.
Tight Gas - Natural Gas Reserves of the Future?
Indeed, both partners think there will be potential for further drilling projects of such kind in Lower Saxony. Experts of both Wintershall and Gaz de France Produktion Exploration Deutschland GmbH believe that current 3D-seismic data interpretations might reveal the existence of further potential of tight gas reservoirs in the Ostfriesland region. Even considering the fact that - from the technical point of view and thus in terms of money - exploration of these reservoirs will be a real challenge, both companies still believe that prospects are promising to strengthen gas production from domestic fields on the international energy market.
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