Reactive flow in a fracture: scale effects in the interpretation of seismic measurements.

Abstract

In this study, a fracture in a carbonate rock is chemically eroded to determine if changes in hydraulic properties can be determined from seismic measurements. Hydraulic and seismic measurements were made prior to and after the invasion of a hydrochloric acid in an initially water‐saturated fracture in limestone. Seismic measurements were collected before, during and after the reactive fluid flow. Two methods for monitoring the seismic response of the sample were used:1) a detailed compressional‐wave transmission map of the sample;and 2) seismic measurements as a function of scale. In the second method, the region probed by the seismic beam varied from 15 mm to 30 mm to 60 mm to determine the effect of scale in interpreting the changes in fracture properties. To vary the size of the region probed, a set of acoustic lens was developed to collimate the seismic wavefront over different widths. The measured signals for both experiments were analyzed for wave attenuation and frequency content as a function of scale. The results show that the scale of measurement affects the interpretation of the effect of acid etching on the seismic properties of fractures. Using seismic techniques to monitor geochemical changes in fractures requires the appropriate choice of the seismic probe in terms of size and area of coverage.