Cross‐borehole electromagnetic induction for reservoir characterization

Abstract

Audio-frequency cross-borehole electromagnetics (EM) is aninteresting alternative to existing techniques for reservoir characterization. With this method signals may be propagated several hundreds of meters &rough typical sand/shale reservoirs and data may be collected at high accuracy with a high sensitivity to thk subsurface resistivity A vertical component, cross-borehole EM field system has been designed and built by Lawrence Livermore and Lawrence Berkeley laboratories for reservoir evaluation and monitoring. This system was deployed at the British Petroleum test facility in Devine, Texas for testing. The site is in a region of simple, flatlying geology so that collected data could be unambiguously interpreted with layered models. The results of the test showed that crosshole EM profiles in wells spaced 100 meters apart data could be repeated in 24 hours to better than one percent and that the profile data could be fit to layered models within this same tolerance.The derived models showed a close correspondence with the borehole induction log.

Iterative electromagnetic Born inversion applied to earth conductivity imaging

“…However, the work of Zhou (1989) showed that a low frequency analog to diffraction tomography is useful in determining the orientation of fractures in a fracture zone. Wilt, et al (1991) have demonstrated that single frequency measurements can be made in oil wells separated by loom, while Wilt and Schenkel(1992) and Hanson, et al ( 1991) have shown that these type of cross well measurements are useful in monitoring environmental injection processes. In this thesis methods will be developed to both model the audio frequency EM response to conductivity changes caused by these processes, and to interpret data collected in cross-well EM surveys.…”

“…EOR injection processes will be simulated with forward models and the resulting conductivity images analized for accuracy. The theory for a more complicated, one dimensional layered background model will be incorporated into the imaging scheme and then applied to field data collected by Wilt, et al (1991). Finally as in the preceeding chapters we will use the 2D cylindrically symmetric imaging scheme on synthetic data generated with 3D models to determine the limitations of the simplified cylindrical geometry.…”

“…Thus his work focused on using the vertical magnetic fields to image the conductivity structure. In practice however, data are collected at discreet points over a smaller vertical distance than we would hope for (e.g.. Wilt, et al 1991). Because of this, the horizontal magnetic field sensitivity plots have been examined to determine the benefits, if any, of measuring this component of the field.…”

Crosshole EM for oil field characterization and EOR monitoring: Field examples

“…With these simple analog systems, we have collected high-quality data at a variety of fields at borehole separations from 10 to 300 m using frequencies from 100 Hz to 100 kHz [3]. Data is typically repeatable and reciprocal to 1 percent.…”