Multi-level Monitoring Well Completion Technologies and Their Applicability in Karst Dolomite

摘要

This paper presents a comprehensive review of commercially available multi-level well completion technologies to simplify the selection of a reliable and cost effective, multi-level completion method for specific karst sites. Karst formations present substantial monitoring well completion challenges especially when a single core hole spans several distinct zones of secondary porosity including micro-scale fracture networks and macro-scale voids, cavities, and caves. Designing a cost effective well completion strategy that isolates and reliably samples these features is often an important element of environmental investigations of contaminated karst. A number of technologies are commercially available that permit the installation of multiple sampling intervals within a single borehole. These technologies were initially designed for application in solid rock or stable boreholes; however, they are also applicable for karst formations. During an environmental investigation of groundwater impacted with chlorinated solvents in the Knox Group dolomite of the Valley and Ridge Province of Eastern Tennessee, several core holes were advanced to depths ranging from 66 to 176 feet (20.1 to 53.6 meters) below ground surface. The identification of numerous distinct voids and fractured zones, which intersected groundwater impacted with chlorinated solvents, required a vertically discrete monitoring network; however, the cost and complexity of core hole advancement prohibited drilling of separate core holes for each monitoring point. Hence, this review. Technologies considered included the Westbay, Solinst Waterloo multi-level, BarCad III, Solinst Continuous Multi-channel Tubing (CMT), and Water FLUTe systems as well as the more traditional nested small diameter wells. Each technology was evaluated against a number of criteria including the ability to isolate multiple sampling zones, ease of installation, requirements for sampling, sample quality, durability/longevity, material and installation costs, and sampling cost and complexity. The water FLUTe system provided the best combination of features to address the specific conditions encountered in the karst dolomite at the site.