SHALLOW DEPTH EXPERIMENTATION ON A METHOD FOR EXTRACTING HEAT FROM DEEP DRY HOT ROCKS
An artificial heat exchanger has been developed between two 200 m deep boreholes, drilled 30 m apart in a low permeability granite formation, by hydraulically stimulating preexisting weakness planes identified by various logging techniques. The geophysical method which revealed the most efficient for identifying weakness planes has been a specially designed electrical log which provides both dip and strike of the planes, as well as sonic logs (Darcilog) which indicated the depth of intersection between the planes and the boreholes. Borehole water chemistry analysis has been successfully used for determining those of the planes in which natural flow occured whilst thermal logs revealed very efficient to locate production zones during injection tests as well as planes along which flow had occured during previous circulation tests. Some of these weakness planes were successfully stimulated by injection of fluid under pressure but seismo-acoustic activity investigation along with thermal logs, as well as reconnaissance through a new inclined well, revealed that flow away from the boreholes occured mostly along a preexisting horizontal altered zone. The geometry of this hydraulic connection allowed for a 48 days circulation test at flow rates varying from 3 m**3/h to 5 m**3/h with a hydraulic impedance equal to about 14 MPa/m**3/h and fluid losses smaller than 5 % ; the larger the flow rate, the lower the hydraulic impedance. The efficient area of this heat exchanger was estimated to be of the order of 2000 m**2 by chemical tracing and 1000 m**2 by thermal tracing.
Bibliographic Reference: EUR 9702 EN (1985) MF, VOL. I, 98 P., BFR 150 + VOL. II, 103 P., BFR 300, EUROFFICE, LUXEMBOURG, POB 1003 - NO BLOW-UP AVAILABLE!
Availability: Can be ordered online
Record Number: 1989123041500 / Last updated on: 1987-01-01
Available languages: en