CHEMICAL STIMULATION OPERATIONS FOR RESERVOIR DEVELOPMENT OF THE DEEP CRYSTALLINE HDR / EGS SYSTEM AT SOULTZ-SOUS-FORÊTS ( FRANCE )

The main objective of the European HDR/EGSproject at Soultz is the installation of a geothermal pilot plant for power production by the end of 2008. After drilling of the three 5000 m deep wells to form a triplet with two producers (GPK2 and GPK3) and a central injector (GPK3), the wells were hydraulically stimulated through massive water injection. In addition to hydraulic stimulation, a series of chemical stimulation operations were undertaken to achieve increasing the performance of the wells and the nearwellbore permeability of the geothermal reservoir. Several acid systems such as hydrochloric acid (HCl), Regular Mud Acid (HCl-HF) and Organic Clay Acid (C6H8O7-HF-HBF4-NH4Cl) were injected to dissolve minerals deposits in the wellbore as well as filling materials of fractures in the vicinity of the wells. Also a high-pH chelating agent (NTA) was tested as alternative to the more usual acid treatments. Whereas acid treatments have resulted in a productivity improvement of the production wells (GPK2 and GPK4) up to 50%, almost no amelioration was obtained in the injection well GPK3. The use of chelating agents resulted in some productivity deterioration of GPK4. The results of stimulation experiments were evaluated using short-term hydraulic tests, conventional pressure transient analysis, interference pressure data, microseismic monitoring, temperature and flow logs. This combination of evaluation techniques helped in getting insight into the origin of the productivity enhancement.

[1]  J. Pinault,et al.  Tracer testing of the geothermal heat exchanger at Soultz-sous-Forêts (France) between 2000 and 2005 , 2006 .

[2]  Chrystel Dezayes,et al.  Deep-seated geology of the granite intrusions at the Soultz EGS site based on data from 5 km-deep boreholes , 2006 .

[3]  Albert Genter,et al.  Permeability and alteration within the Soultz granite inferred from geophysical and flow log analysis. , 2006 .

[4]  Philippe Lutz,et al.  The deep EGS (Enhanced Geothermal System) project at Soultz-sous-Forêts (Alsace, France) , 2006 .

[5]  Hiroshi Asanuma,et al.  Creation of an HDR reservoir at 5000 m depth at the European HDR project , 2006 .

[6]  Benoît Valley,et al.  STRESS STATE AT SOULTZ-SOUS-FORÊTS TO 5 KM DEPTH FROM WELLBORE FAILURE AND HYDRAULIC OBSERVATIONS. , 2007 .

[7]  Laurent André,et al.  Review on chemical stimulation techniques in oil industry and applications to geothermal systems by , 2007 .

[8]  K. Pruess,et al.  CHEMICAL STIMULATION IN NEAR-WELLBORE GEOTHERMAL FORMATIONS: SILICA DISSOLUTION IN THE PRESENCE OF CALCITE AT HIGH TEMPERATURE AND HIGH pH , 2007 .

[9]  T. Bérard,et al.  How close to failure is a granite rock mass at a 5 km depth , 2007 .

[10]  S. Thórhallsson,et al.  Stimulation of geothermal wells in basaltic rock in Iceland , 2006 .

[11]  Tianfu Xu,et al.  Calcite dissolution in geothermal reservoirs using chelants , 2006 .

[12]  R. Baria,et al.  MICROSEISMIC MONITORING OF THE WORLD ’ S LARGEST POTENTIAL HDR RESERVOIR , 2004 .

[13]  D. M. Yglopaz,et al.  ACID STIMULATION OF INJECTION WELLS IN THE LEYTE GEOTHERMAL POWER PROJECT, PHILIPPINES , 2003 .

[14]  R. Malate,et al.  MATRIX STIMULATION TREATMENT OF GEOTHERMAL WELLS USING SANDSTONE ACID , 2003 .

[15]  Z. Sarmiento,et al.  CASING PERFORATION AND ACID TREATMENT OF WELL SK-2 D MINDANAO 1 GEOTHERMAL PROJECT , PHILIPPINES , 2003 .

[16]  Albert Genter,et al.  Fracture analysis and reservoir characterization of the granitic basement in the HRD Soultz project (France) , 1995 .

[17]  J. Strawn.  Results of acid treatments in hydrothermal direct heat experiment wells , 1980 .