In situ flow testing of a cement borehole seal in welded tuff

Abstract

Waste isolation at the Yucca Mountain repository site may require that penetration (boreholes, shafts, etc.) of the geological barrier be sealed to retard the migration of radionuclides to the accessible environment [1,2]. Cement is being considered as a part of multicomponent seals or plugs for the repository due to its relatively low permeability, high strength, longevity, and swelling capacity [3]. Cement or concrete has long been used as a hydrological barrier in underground mines [4] and in the oil and gas industry [5]. However, insufficient test data exists about the hydraulic performance of cement plugs under in-situ conditions. The primary objective of the present research is to determine experimentally the hydraulic conductivities of cement borehole plugs in welded tufts as affected by field installation and in-situ environment. The test results provide a data basis on the hydraulic behavior of cement seals in rock openings, which are applicable not only to the Yucca Mountain repository site, but also to other engineering practices, e.g. underground dams for seepage or flood control, sealing of abandoned oil or gas wells, and isolation of aquifers from contaminated groundwater. The present paper describes test methods, results and data analysis for the in-situ flow testing. The field results are compared with the results obtained from related experiments conducted in the laboratory.