Three-dimensional inversion of the mise-a-la-masse data using a directional borehole

摘要

The mise-a-la-masse method was developed to explore the mineral deposits using the conductive outcrop as an electrode. However the new method using a well casing as a line source has been carried out to find the geothermal reservoirs in recent years. This method is also utilized as the electrode configuration of 4-D survey (Fluid Flow Tomography; FFT) in order to visualize the transient phenomena of subsurface fluid flow such as geothermal fluid, petroleum and ground water. We have developed the data analysis program of the mise-a-la-masse survey to delineate the anomalous resistivity zone associated with a geothermal reservoir by assuming the homogeneous earth model. Also we have developed a 3-D inversion program to treat the complex resistivity distribution using a vertical line source. However actual geothermal wells are almost inclined, we have to taking the inclined wells into account in order to obtain the more accurate results. We have derived theoretical formula for an arbitrarily shaped inclined line source and developed 3-D inversion programs in order to analyze the mise-a-la-masse data. As a result of 3-D inversion using the numerical data that were calculated by 3-D forward program, it is found that more accurate results can be obtained by using inclined line source compared to the conventional vertical line source. Considering that most petroleum and geothermal wells are inclined wells, we are able to get the more accurate results and higher resolutions in data analysis by using the method accounting for the inclined line source. The inversion program considering an inclined line source proposed in this paper would become a powerful tool to analyze the mise-a-la-masse data.