The anisotropic resistivity and the electric responses of the fractured formation
In oil exploration and formation evaluation, for example, in evaluation of regions with distinct dipping stratifications of sand and shale or with fractured formations of dominant direction, the existence of electrical anisotropy has substantial effects on the evaluation of the water saturation and other interpretation results. It usually results in large error in our conventional electric interpretation results when the standard model of a layered isotropic half-space is used, sometimes it leads to serious blunders.In this study, the current density and magnetic field are expressed in potentials of poloidal and toroidal scalars, and direct current (DC) apparent resistivity response due to point current sources in the layered half space with general anisotropy has been analyzed. The method of the state matrix analysis has been adopted, to first construct the general solutions of the electric and magnetic fields by using of the poloidal and toroidal scalars. The state matrix which propagates the electric and magnetic fields from the upper layer to the lower layers has been constructed by resorting to the continuity of the electric and magnetic fields and the coupling of the source on the earth, and the fields are calculated recursively from the bottom layer to the top layer. With regard to the unstable computation of the exponential term, a stable formulation has been derived from the state matrix through the transformation into the stable exponential relationship. For the TI medium, an integral of the Greens function is carried out because of the decoupling of the poloidal and toroidal functions. The validity of the numerical method has been validated against an analytic solution of a simple half space model with anisotropy. Results of a two-layer model has been shown to assess the feasibility of discerning the fractured formation and predicting the distribution of the fractures by using of the D.C. current survey.
layered medium arbitrary anisotropy poloidal and toroidal potential function fractured formation apparent resistivity
SHEN Jinsong GUO Naichuan
China University of Petroleum (Beijing), Beijing, China
国际会议
The 19th International Workshop on Electromagnetic Induction in the Earth(第十九届国际地球电磁感应学术研讨会)
北京
英文
818-823
2008-10-23（万方平台首次上网日期，不代表论文的发表时间）