Forschungs- & Entwicklungsinformationsdienst der Gemeinschaft - CORDIS

Hard rock directional drilling at high temperature

I:Drilling: The drilling rig was operated by ENEL, a partner of the EEIG's, under the supervision of Southern International Inc. which was also acting as �maître d�oeuvre� for the work and shared "de facto" this task with the EEIG "EMC". The latter provided the necessary logistic support. SHELL, also a partner in the EEIG, for its part played a consultancy role in the operations.

The depth and the trajectory of the wells are in line or very close with the project's objectives. I.1.GPK3:The drilling operations on well GPK3 were carried from 25 June 2002 to 13 November 2002. The total time taken was a little less than 5 months.

Overall, the work took place without any major incidents except for a slight anomaly which occurred when installing the internal casing. The casing shoe is not resting on a restriction in the well diameter as planned, but got stuck about 25 m above the objective. As a result, the casing is anchored to the granite by the packers and the column of cement above them.

The total cost of the drilling work came to just over 5 750 000 Euros. I.2.GPK4: The drilling operations on well GPK4 were carried from 29 August 2003 to 15 April 2004. The total time taken was a little more than 7.5 months. This was about 60% more than the time required to drill GPK3. This was mainly due to the fact, that GPK4 had to be drilled with a horizontal deviation of 1200 m from the wellhead in order to achieve the 600m separation at 5000m depth.

Two technical incidents occurred during the drilling operations and gave rise to insurance pay-outs. Due to the instability of the open hole section, the 9-5/8" internal casing had to be put into place before the final depth of the well was reached, thus protecting the already drilled hole. The total cost of the well came to 8 250 000 Euros, including a little bit more than 1 000 000 Euros which were covered by the project's insurers. II: Wells trajectories II.1.Definition of the well trajectory: It was decided that the separation between the injection and a production wells will be in the range of 600m. In both cases, GPK3 and GPK4, an elliptical area of 150 to 200m to the SSE of the bottom of the previous well has been defined as the target area. The situation in Soultz, in the Rhine Valley, is in so far specific as the direction of the maximum horizontal compressional stress and the strike direction of joints are close. This obviously apparently facilitates the positioning of wells as the fluid flow will be dominated by these two factors.

However, microseismicity showed that at the location in Soultz two different stress controlled fracture opening mechanisms can be observed: shearing and tensile opening. Thus a limited risk to create sub-parallel flow paths always remains.

Consequently, not knowing which opening mechanism will be dominating in the next stimulation experiment, in the case of Soultz, the well targets were positioned in a compromise location in between shear stress and maximum compression, thus theoretically allowing to link fractures through both opening mechanisms. II.2:Directional drilling: Several problems were observed during the directional drilling of the deviated, deep wells in granite.

Mainly the failures of the MWD system (measurement while drilling) caused severe difficulties. One drilling incident occurred as the drill pipe got stuck due to wellbore breakouts while a wireline survey was performed.This incident clearly shown the risk associated with these wireline surveys at great depths. MWD failures cannot be related to the failure of a single component. In fact a whole series of tool components was involved. They appear to be caused by a combination of mechanical and temperature related problems.The rough drilling conditions in granite cause problems with downhole vibrations. The high circulation temperatures tend to weaken the electronic components, even the electronic boards themselves. The combination of these two impacts results in �random� tool failures. Directional wells in granite cause excessive drill string and reamer wear. III Special equipment III.1Annular sealing package: A special equipment is required at the well head to allow the production casing to grow and shrinking according to the well temperature. The casing is sliding inside a lubricated packing which at the same time isolates and seals the outer casing annulus annulus.

The new equipment operational up to temperatures of the order of 200ºC and pressures of 35 MPa has been designed and installed on the three well heads. Its behaviour will be assessed during the next phase of the project. III.2 Drilling techniques: A new generation of drilling bits showed, during the drilling of the wells GPK3 and GPK4, performances notably higher than those observed during the previous drilling of well GPK2. The lifespan of the bits was often between 70 and 80 hours, which indicates a level of performance comparable to what can be achieved when drilling sedimentary terrain.

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67250 Kutzenhausen
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