米国カリフォルニア州ロストヒルズ油田で実施した,坑井問電磁および

弾性波トモグラフィーによる貯留層モニタリングの試み

抄録

Reservoir monitoring is the key issue to design the optimum plan for recovery enhancements of hydrocarbon production. The Technology Research Center of Japan National Oil Corporation has conducted extensive field measurements to validate the current cross-hole technologies at the Lost Hills Oil Field, California in the first quarter of 2000. The experiments were composed of cross-hole electromagnetic surveys between fiberglass cased boreholes in both frequency domain and time domain methods together with seismic tomography. The time domain electromagnetic survey was designed to test the newly developed time domain down-hole transducer. However, the tool was broken down during the measurement. For the frequency domain electromagnetic method, we conducted three kinds of experiments, which are time lapse analysis with previously measured data, multi-frequency survey for higher resolution analysis, and measurement with setting up transducer in a steel cased hole. Multi-stage multi-disk borehole seismic source, which has been developed in collaboration between JNOC and OYO corporation was employed for seismic tomography.
The subsurface velocity profile from seismic tomog raphy was utilized to calculate the formation porosity. Since the standard calculation procedure of sonic porosity is not adequate to apply for the diatomite reservoir because of its nature of high porosity despite very low permeability, a correction function was developed and employed. Then the resistivity profile was incorporated into estimation of fluid saturation in the reservoir by Archie's equation. The resultant values of porosity and water saturation are quite reasonable in comparison with reported ranges for this field.
Assuming that the regional compaction being related to reduction of reservoir porosity has not been significant from 1997 to 2000 based on the ground subsidence in the area, we calculated a fluid saturation profile since the beginning of water flooding. We revealed the manners of fluid saturation change in the reservoir during water flooding through the time lapse analysis.