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DEEP GENERALIZED GEOTHERMY PROGRAMME.

Objective

TO STUDY A METHOD FOR EXTRACTION OF HEAT FROM DEEP IMPERMEABLE ROCKS BY STIMULATION OF PREVIOUSLY EXISTING FRACTURES.
An in situ experiment on forced fluid percolation through a granitic rock mass has been carried out between 2 800 m deep boreholes, 100 m apart. The purpose of this experiment was to define a reliable method for extracting heat from hot, but relatively impervious, formations. First, the well III-8 was percussion drilled and then used to characterize the natural fracture network by various logging methods, determine the regional stress field and perform small scale injection test in order to determine the main flow direction at depth by location of induced microseismic activity. Then the second well, III-9, was drilled. Some more work on reconnaissance of the natural fracture network was conducted and a first circulation was developed between the 2 wells, with III-9 as the injection well. For this first circulation test the injection rate was 30 m{3}h{-1} with a 8.2 MPa wellhead pressure; the production rate was only 10.8 m{3}h{-1}. Next the downhold circulation system was improved progressively, mainly due to various sand injections in the production well. Finally hydrothermal characteristics of this system were evaluated through a 66 day circulation experiment at flow rates ranging from 20 m{3}h{-1} to 75 m{3}h{-1} and well head pressures ranging from 7.7 MPa to 12.6 MPa. The corresponding production rates ranged from 82.2% to 44.1% of injection rate whilst the corresponding hydraulic impedance of the system ranged from 1.9 to 1.3 GPa m{-3}s{-1}. For a 27 m{3}h{-1} injection rate, the efficient heat exchange area was evaluated to be of the order of 50000 m{2}. An important conclusion is that most of the flow occurs in a limited number of hydraulically conductive zones.
THIS IS A CONTINUATION OF WORK AT THE FRENCH HDR PROJECT SITE AT LE MAYET DE MONTAGNE, PREVIOUSLY SUPPORTED UNDER CONTRACT NO.EG-D1-002-F. THE WORK UNDER THE PRESENT CONTRACT ENTAILS THE DRILLING OF A SECOND 800M BOREHOLE INTO THE GRANITE, AND THEN STIMULATING NATURAL FRACTURES INTERSECTED BY THE BOREHOLE IN ORDER TO DEVELOP A CONNECTION WITH ANOTHER HOLE DRILLED EARLIER ABOUT 100 M AWAY. THE DEVELOPMENT OF THE FRACTURE SYSTEM IS BEING MONITORING BY AN EXTENSIVE MICROSEISMIC NETWORK. AFTER DEVELOPMENT OF A SUITABLE FRACTURE SYSTEM, A SERIES OF HYDRAULIC AND CIRCULATION EXPERIMENTS WILL BE UNDERTAKEN WITH THE AIM OF DEVELOPING AND CHARACTERISING THE RESERVOIR. THE TARGET IS TO DEVELOP A RESERVOIR WITH AN EFFECTIVE HEAT TRANSFER AREA OF AT LEAST 300 000 CUBIC METERS AND AN IMPEDANCE OF LESS THAN 1 MPA/1/S. TWO FURTHER BOREHOLES WILL BE DRILLED SUBSEQUENTLY TO INTERSECT THE RESERVOIR AND CHARACTERISE THE ZONES WITHIN WHICH FLUID FLOW HAS OCCURED.

Funding Scheme

CSC - Cost-sharing contracts

Coordinator

Centre National de la Recherche Scientifique (CNRS)
Address
4 Place Jussieu
75252 Paris
France