Interpretation Of Multifrequency Crosswell Electromagnetic Data With Frequency Dependent Core Data

Download or read book Interpretation Of Multifrequency Crosswell Electromagnetic Data With Frequency Dependent Core Data written by J. Roberts and published by . This book was released on 2005 with total page 6 pages. Available in PDF, EPUB and Kindle. Book excerpt: Interpretation of cross-borehole electromagnetic (EM) images acquired at enhanced oil recovery (EOR) sites has proven to be difficult due to the typically complex subsurface geology. Significant problems in image interpretation include correlation of specific electrical conductivity values with oil saturations, the time-dependent electrical variation of the subsurface during EOR, and the non-unique electrical conductivity relationship with subsurface conditions. In this study we perform laboratory electrical properties measurements of core samples from the EOR site to develop an interpretation approach that combines field images and petrophysical results. Cross-borehole EM images from the field indicate resistivity increases in EOR areas--behavior contrary to the intended waterflooding design. Laboratory measurements clearly show a decrease in resistivity with increasing effective pressure and are attributed to increased grain-to-grain contact enhancing a strong surface conductance. We also observe a resistivity increase for some samples during brine injection. These observations possibly explain the contrary behavior observed in the field images. Possible mechanisms for increasing the resistivity in the region include (1) increased oil content as injectate sweeps oil toward the plane of the observation wells; (2) lower conductance pore fluid displacing the high-conductivity brine; (3) degradation of grain-to-grain contacts of the initially conductive matrix; and (4) artifacts of the complicated resistivity/time history similar to that observed in the laboratory experiments.