Fluid Injection Test - introduction
On November 2006, our laboratory started series of water injection experiments at the drill site in Dakeng near Taichung (NE) in central part of Taiwan. In this area there are two boreholes- A and B (2003m and 1359m deep), which are drilled through the Chelungpu Fault Zone with the slip zone at the depth 1111.2m and 1137.2m (respectively). That fault zone raptured during Chi-Chi Earthquake on September 21th, 1999.
It is known, that permeability after earthquakes at fault zones temporarily
increases. Subsequently occurs a fault healing process. Our target is to estimate this fault healing process and present a fault healing curve (pic.1) after earthquake events.
To do so, we have to carry out series of test, few months apart, which data will be ploted on the graph.
We use our boreholes- B as an injection hole, A- as a response one. Pic.2 shows simplified situation of our system. Injected high pressure water goes through the fault zone (red line) to borehole A, where sensors detect this arrival. A and B are 39 meters apart. We suspect that response should arrive /more or less/ on sixth day from the beginning of the test.
There are four parts of our experiment:
1)Water injection 3 MPa to borehole B for 6 days long.
2)Interinjection time, monitoring pressure relaxation in borehole B and pressure increase in borehole A.
3)Water injection 5 MPa to borehole B for 6 days long.
4)Monitoring pressure relaxation in boreholes B and and pressure increase in hole A.