Borehole-surface Resistivity Tomography And It’s Application In Faults Detection On Beishan

Borehole-surface resistivity tomography is a geophysical exploration method which producedfrom the close combination of single borehole and resistivity method. It has a high resolution and detection capabilities of structure of the borehole, surrounding medium and deep stratum. However, the deep geological environment such as faults development, hydraulic conductivity characteristics of the fracture and fault zone is a problem for high-level radioactive nuclear waste repository construction close concern of the safety.Therefore, under the situation of limited hydrogeological information obtained from the limited number, large spacing of boreholes, borehole-surface the resistivity tomography becomes important and imperative for the accurate assessment of preselected area for the preliminary investigation.It can expand the investigation to the surrounding of borehole and deep stratum, getting more information on the distribution and expansion of the fractures and faults. The paper focused on the study of borehole-surface resistivity tomography and faults detection, throughsensitivity analysis of array, forward modeling, water injection test in laboratory and field experiment, The most important results revealed from above experiments are as:The arrays of borehole-surface resistivity tomography commonly used, Dipole-Dipole array has a higher resolution on vertical direction even than that of Pole-Pole array in borehole-surface. However, Pole-Pole array in borehole-surface has a better resolution on horizontal direction.If the object is in contact with borehole then the Dipole-Dipole array has a better resolution to the abnormal boundary than that of Pole-Pole array for borehole-surface. When there is no contact of the array with the borehole the center of abnormal apparent resistivity that acquired from both arrays show a drift phenomenon.The laboratory experiment conducted in sandbox to simulation fault with water injection indicates that the inflow of water decreased the heterogeneity of sand. According to spatial and temporal distribution of apparent resistivity and inversion results, we can get the altitude, structure and permeability of the fault effectively.We carried out the field experiment to borehole BS12by using borehole-surface resistivity tomography successfully. Based on the measurements, preliminary structural information results were obtained about the formations surrounding of a borehole.