Interpretations of field hydraulic tests in explosion-fractured coal: Hoe Creek, site characterization to Experiment No. 1
In connection with in situ coal gasification, we have performed hydraulic testing at Hoe Creek. This report contains a synopsis of the hydraulic program and summaries of all hydraulic tests. The particular aspects of hydraulic testing in modestly permeable coal seams that produce analytical difficulties are the effects of (1) installing several casings close together, which causes changes in the storage coefficient and perturbations of the flow regime; (2) using large well-casings relative to the low formation transmissivity, which causes prolonged well-bore storage effects; and (3) anisotropy due to fractures and explosive fracturing. The most successful methods of testing in situ coal permeability have been long-time, drawdown tests and dual-well tests. Single-well slug tests provide a rapid measure of the vertical variation in hydraulic conductivity for a local region. The least successful method of testing has been short-term drawdown tests. Hydraulic tests show three major permeability regions surrounding the two explosion centers of Experiment No. 1: an inner core out to 10 feet with an average equivalent isotropic permeability of 10 darcys (D), an enhanced region of 10 to 50 ft with an average equivalent isotropic permeability of 1.5 D, a transition zone of 50 to 100 ft with an average equivalent isotropic permeability of 0.3 D. There is an areal anisotropy with maximum permeability in the E-W direction and minimum permeability in the N-S direction. An unpredicted low permeability ridge separated the two explosion centers. Results also suggest that the radial distribution of permeability enhancement vs distance from the shot area follows an inverse distance (l/r) power law, from the enhanced region through the transition zone in the eastern-quadrant shot interaction area, containing four of the five environmental monitoring wells. The reduction of permeability along the axis of minimum permeability appears to follow a (l/r)/sup 4/ decrease.
- Research Organization:
- California Univ., Livermore (USA). Lawrence Livermore Lab.
- DOE Contract Number:
- W-7405-ENG-48
- OSTI ID:
- 6747574
- Report Number(s):
- UCRL-52438
- Country of Publication:
- United States
- Language:
- English
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