Application of SP Monitoring in the Pohang Geothermal Field

포항 지열 개발지역에서의 SP 장기 관측

  • 임성근 (한국지질자원연구원 지하수지열연구부) ;
  • 이태종 (한국지질자원연구원 지하수지열연구부) ;
  • 송윤호 (한국지질자원연구원 지하수지열연구부) ;
  • 송성호 (농어촌연구원 지하수연구실) ;
  • ;
  • 조병욱 (한국지질자원연구원 지하수지열연구부) ;
  • 송영수 (전북대학교 자원 에너지공학과)
  • Published : 2004.08.01

Abstract

To delineate geothermal water movement at the Pohang geothermal development site, Self-Potential (SP) survey and monitoring were carried out during pumping tests. Before drilling, background SP data have been gathered to figure out overall potential distribution of the site. The pumping test was performed in two separate periods: 24 hours in December 2003 and 72 hours in March 2004. SP monitoring started several days before the pumping tests with a 128-channel automatic recording system. The background SP survey showed a clear positive anomaly at the northern part of the boreholes, which may be interpreted as an up-flow Bone of the deep geothermal water due to electrokinetic potential generated by hydrothermal circulation. The first and second SP monitoring during the pumping tests performed to figure out the fluid flow in the geothermal reservoir but it was not easy to see clear variations of SP due to pumping and pumping stop. Since the area is covered by some 360 m-thick tertiary sediments with very low electrical resistivity (less than 10 ohm-m), the electrokinetic potential due to deep groundwater flow resulted in being seriously attenuated on the surface. However, when we compared the variation of SP with that of groundwater level and temperature of pumping water, we could identify some areas responsible to the pumping. Dominant SP changes are observed in the south-west part of the boreholes during both the preliminary and long-term pumping periods, where 3-D magnetotelluric survey showed low-resistivity anomaly at the depth of $600m\~1,000m$. Overall analysis suggests that there exist hydraulic connection through the southwestern part to the pumping well.

References

  1. 송성호, 2001, 자연전위법을 이용한 수리시설물 누수 탐지, 교육학 박사학위논문, 서울대학교
  2. 송윤호, 이태종, 이성곤, Uchida, T, Mitsuhata, Y., and Graham, G. B., 2004, 포항 지역 지열개발을 위한 3차원 MT 탐사, 대한 지구물리탐사학회/한국물리탐사학회 공동학술대회, 한국해양연구원, 260-265
  3. Corwin, R. E, and Hoover, D. B., 1979, The self-potential method in geothermal exploration, Geophysics, 44, 226-245
  4. Corwin, R. E, and Morrison, H. E, 1977, Self-potential variations preceding earthquakes in central California, Geophys. Res. Lett., 4, 171-174
  5. de Groot, S. R., and Mazur, P, 1962, Non-Equilibrium Thermodynamics, North-Holland, New York, 405-452
  6. Ishido, T, 1981, Streaming potential associated with hydrothermal convection in the crust: a possible mechanism of selfpotential anomalies in geothermal areas (in Jap., with Engl. Abstr.),1. Geotherm. Res. Soc. Jpn., 3,87-100
  7. Ishido, T, 1989, Self-potential generation by subsurface water flow through electrokinetic coupling, in Detection of Subsurface Flow Phenomena, Lecture Notes in Earth Sciences, 27, edited by G.-P. Merkler et al., 121-131, Springer-Verlag, New York
  8. Ishido, T., Kikuchi, T., and Sugihara, M., 1989, Mapping thermally driven upflows by the self-potential method. in: Hydrogeological regimes and their subsurface thermal effects, Geophy. Monogr., 47, IUGG Vol. 2, AE. Beck et al. (Eds), AGU, 151-158
  9. Ishido, T, and Pritchett, J. w., 1996, Numerical simulation of electrokinetic potentials associated with subsurface fluid flow. In: Proc. Workshop on Geothermal Reservoir Engineering, Stanford University, 143-149
  10. Lee, D. S., 1977, Chemical composition of petrographic assemblages of igneous and relate rocks in south Korea, J. Korea. Inst. Mining Geo!., 10; 75·92
  11. Matsushima, N., Kikuchi, T, Tosha, T, Nakao, S., Yano, Y, and Ishido, T, 2000, Repeat SP measurements at the Sumikawa geothermal field, Japan, In: Proc. World Geothermal Congress, Kyushu-Tohoku, Japan, 2725-2730
  12. Onsager, L., 1931. Reciprocal relations in irreversible processes. 1, Physical Review, 37, 405-426
  13. Sill, W. R., 1982, Self-potential effects due to hydrothermal convection-velocity crosscoupling, DOE/ID/l2079-68
  14. Sill, W. R., 1983, Self-potential modeling from primary flows, Geophysics, 48, 76-86
  15. Yasukawa, K., Bodvarsson, G. S., and Wilt, M., 1993, A coupled self-potential and mass-heat flow code for geothermal applications, Trans. Geotherm. Resour. Counc., 17,203-207
  16. Yasukawa, K. and Mogi, T, 1998, Topographic effects on SP anomaly caused by subsurface fluid flow - numerical approach-. Butsuri-Tansa, 51, 17-26. (in Japanese with English abstract)
  17. Yasukawa, K., Andan, A, Kusuma, D. S., Uchida, T, and Kikuchi, T, 2002, Self-potential mapping of the Mataloko and Nage geothermal fields, central Flores, Indonesia for applications on reservoir modeling, Bull., Geological Survey of Japan, 53, 285-294
  18. Yasukawa, K., Kusdinar, E., and Muraoka., H., 2002, Reservoir response to a well test identified through a self-potential monitoring at the Mataloko geothermal field, central Flores, Indonesia, Bull., Geological Survey of Japan, 53, 355-363
  19. Yasukawa, K., Mogi, T, Widarto., D., and Ehara, S., 2003, Numerical modeling of a hydrothermal system around Waita volcano, Kyushu, Japan, based on resistivity and self-potential survey results, Geothermics, 32, 21-46