U.S. Geological Survey Toxic Substances Hydrology Program--Proceedings of the Technical Meeting, Colorado Springs, Colorado, September 20-24, 1993, Water-Resources Investigations Report 94-4015

Use of Well Logs to Prepare the Way for Packer Strings and Tracer Tests: Lessons from the Mirror Lake Study

Abstract

Although well logs can never replace conventional aquifer-testing techniques, a carefully designed suite of borehole measurements can identify the distribution of fractures along well bores. This information can be used to improve the effectiveness of hydraulic testing and water sampling. After nearly a decade of logging research at the Mirror Lake site, we have developed a combination of conventional and new techniques that have proven especially effective in preparing the way for subsequent installation of packer strings and tracer-test analysis. The approach consists of four steps: (1) characterizing the general structure and lithology of the rock mass by interpreting conventional well logs, (2) identifying and characterizing individual fractures by obtaining acoustic televiewer and other borehole image logs, (3) identifying the few fractures intersecting the well bore that produce water during pumping by running high-resolution flow logs in pumped and observation boreholes, and (4) inferring the pattern of fracture connectivity in the rock mass adjacent to boreholes by analyzing transient flow in boreholes at carefully selected locations between producing fractures. The application of this analysis allows geochemists and hydrologists to identify those locations where packers can be set to prevent communication between conductive fractures and to design efficient procedures for otherwise time-consuming aquifer and tracer tests.