f THE VIRTUAL PACKER METHOD – INTERVAL-SPECIFIC DATA FROM WIRELINE LOGS IN OPEN BOREHOLES

Many site characterization studies involve heterogeneous aquifers with multiple water producing intervals providing multiple pathways for the propagation of contaminants. Specific producing zones are often sampled by isolating individual intervals with straddle packers. Such sampling is both time consuming, requiring use of expensive equipment and drill-rig mobilization, and fraught with potential difficulties such as the inability to seat packers in rough or unstable boreholes. Efficient use of straddle packers also requires knowledge of the specific intervals to be tested, and usually occurs at times different from the initial application of borehole geophysics. High-resolution borehole flow logging conducted in tandem with remote water sampling can provide interval-specific results without the cumbersome use of packers, and without previous knowledge of the producing zones. The flow log data can be analyzed to identify the location of producing zones, giving estimates of transmissivity and hydraulic head for each. When the relative inflow from each zone under sampling conditions is known, mass balance methods can be used to estimate contaminant concentration in water sampled by wireline from depth intervals between zones. Hydraulic tomography has likewise been conducted with packers in borehole pairs, and cross-hole flowmeter experiments provide similar information about flow paths between boreholes. The primary limitation in using wireline logs for these applications is one of dynamic range, where the contribution from zones with two or more orders of transmissivity below that of the primary zone are not identified in the data. In many applications this drawback is offset by the flexibility and efficiency inherent in the use of wireline logs in open boreholes.