Borehole-to-surface TFEM Technique Applications in Geologically Complex Areas

Borehole-to-surface time-frequency domain electromagnetic (TFEM) method has been applied in delineating oil/gas and water boundary. The technique has achieved significant improvements over the past 10 years and has become an important technique for oilfield development. Recently this method has been applied in a newly found oil and gas target in a mountainous area in the western plateau of China. Due to the complexity of the oilfield development area, some new technical measures have been taken when using the TFEM technique, such as multi-well joint operation program, multi-source excitement for multi-target layers, terrain correction, and then extracting effective induced polarization anomalies and high resistivity anomalies through dual frequency amplitude and tri-band phase anomaly. Drilling results have confirmed the effectiveness of the borehole-to-surface TFEM method in this oilfield. Based on the integrated interpretation result, confirmed oil-bearing areas within the oilfield are enlarged and provided very important basis for the selection of hydrocarbon reservoir delineation wells.

The borehole-to-surface TFEM survey results show that joint operation program of multiple source wells can evaluate relatively large area of hydrocarbon traps. Multiple downhole source positions and graded source excitation can be used for detecting multi-target layers. A simple data processing method can depress terrain’s effect, and then the high polarization anomalies and high resistivity anomalies reflecting hydrocarbon reservoirs are effectively extracted using the dual frequency amplitude anomaly and tri-band phase anomaly. Finally, potential hydrocarbon accumulation areas can be effectively evaluated and mapped. Drilling results have confirmed the validity of the method and this method provides an effective means for the delineation of hydrocarbon boundary and the selection of evaluation wells in newly developing oilfields.