Use of Induction-Log Measurements in Monitoring Flood-Front Movement

摘要

This paper provides a quantitative method of analyzing flood-front movement using resistivity measurements from induction logs. Induction logs have often been used to monitor flood-front movement in enhance oil recovery (EOR) operations and to estimate changing hydrocarbon saturation in flooded reservoir formations. Previously, these measurements have been analyzed as follows: First, the pre-flood brine saturation is determined from a resistivity log run prior to flooding operations. After flooding commences, induction resistivity logs are run and are compared with the pre-flood logs: changes in log resistivities indicate movement of the flood front. Finally, the post-flood brine saturation is calculated from an induction resistivity log run after the flood front has passed. In the previous analysis of induction log data, temporal movement of the flood front was not modeled adequately, and profiling the oil bank was not possible. To profile the flood front and the trailing oil bank, and to better understand the movement of the flood front, it is necessary to monitor changes in the log resistivity in more detail and to analyze the log responses using a model that incorporates flood-front movement. We provide a model that includes a flood front and an oil bank near a monitoring well, and calculate induction log responses to the front and the bank. The changes in the iog resistivity are shown as a function of the distance to the front. This method provides information helpful in understanding flood dynamics in EOR processes. In particular, we find that conventional induction logs can identify any gradual resistivity change that occurs within 2-m lateral width as a sharp resistivity change. A resistivity block in a formation must be at least about 4-m wide in the lateral direction before an induction tool to distinguish it from other blocks. Difference between the deep and medium induction may be useful in identifying resistivity surge (i.e., an oil bank) whose width is between about 0.5 and 4 m. In addition, the method in our analysis is applicable in designing a new induction-type resistivity tool for monitoring and profiling flood-front movements in a pre-designated depth of investigation and for an anticipated flood profile.