Long-Term Cement Studies (LCS) - Overcoring borehole LCS06-001
In late 2010, the pre-grouted borehole LCS06-001 (link to grout pre-test) was overcored to obtain a detailed picture of fracture system and where the injected grout has penetrated to. Additionally, the opportunity was used to further develop the overcoring technique to be used for stabilising and sampling currently running experiments on fractures.
The following steps summarize the overcoring procedure (Fig. 1):
1. Drilling of the 300 mm overcoring hole around the central borehole to the starting position of overcoring
2. Drilling of the 200 mm borehole below the target overcoring (to break off core, if necessary) borehole to the starting position of overcoring
3. Drilling of small boreholes near the central borehole with a length of about 1.4 m from the start position with a 36 mm drilling rod
3/b. Installation of the long-sleeve single packer (3 m long) in the central borehole for sealing and to avoid resin flow towards the central borehole
3/c. Installation of resin packer system (incl. carbon fibre reinforcement) and performance of resin injection
4. Removal of the central borehole single packer and resin packer after resin solidification around the dummy
Steps 3 to 6 were repeated twice
4/b. Drilling of the 200 mm borehole below the target overcoring (to break off core, if necessary) borehole to the end position of the overcoring
5. Drilling of 300 mm overcore from start position to end position
5/b. Breaking out and removal of the 300 mm core. (A single packer of 1 m sleeve length was onsite available for retrieval of the core if it got stuck)
The result from the CT image analysis of a grouted fracture (after removing all sections with considerably different densities) shows distinct areas where grout has been observed as well from outside (see photograph on top right). Detecting grout fillings of finer fractures was not (yet) possible with this technique.
Long-Term Cement Studies (LCS) Experiment