Effect of Borehole Fluid and Casing on the Borehole Electromagnetic Responses

공내수 및 케이싱이 시추공 전자탐사 반응에 미치는 영향

  • 조성준 (한국자원연구소 자원연구부) ;
  • 김정호 (한국자원연구소 자원연구부) ;
  • 이명종 (한국자원연구소 자원연구부) ;
  • 정승환 (한국자원연구소 자원연구부) ;
  • 송윤호 (한국자원연구소 자원연구부)
  • Published : 1999.05.01

Abstract

As a practical developing step of electromagnetic (EM) tomography technique, we quantitatively analyzed the effects of borehole fluid and casing on the borehole EM responses. The EM response turns out to have nothing to do with the property of the borehole fluid except in the close vicinity of the transmitter, which shows the wide perspective of the application of borehole EM. Single-hole responses in the presence of the steel casing throughly reflect those of the casing itself since its extremely high induction number or shallow skin depth. EM responses through steel casing do show the information of the host medium. In the near field region which corresponds to low frequency or the vicinity of the borehole, however, we can not separate the signal containing the information of the host from that of casing. Otherwise, the severe attenuation of energy in the casing at high frequencies renders the signal undetectable. The optimum frequency is, therefore, to be chosen to extract the information of the host considering both the property of the casing and the skin depth of the medium and the practical technique to determine the casing property through single-hole measurements is required.