HR: 1330h
AN: H42F-1141    [PDF]
TI: Effects of Sand-Filled Hydraulic Fractures during Air Sparging
AU: * Hall, R J
EM: cherd_8@yahoo.com
AF: Clemson University, 340 Brackett Hall, Clemson, SC 29634 United States
AU: Murdoch, L C
EM: lmurdoch@clemson.edu
AF: Clemson University, 340 Brackett Hall, Clemson, SC 29634 United States
AU: Falta, R W
EM: faltar@clemson.edu
AF: Clemson University, 340 Brackett Hall, Clemson, SC 29634 United States
AB: The effectiveness of air sparging is limited in fine-grained formations, such as clay-rich saprolite, where low permeability restricts flow rates. The purpose of this work is to investigate the effectiveness of using hydraulic fractures to increase the performance of air sparging in relatively low permeability materials. The approach has been to conduct step-rate, air-injection tests into conventional wells and wells intersecting fractures, and then to evaluate the results of these tests using analytical and numerical models. Fieldwork is being conducted in an area underlain by saprolite weathered from granitoid gneiss. Permeability of the saprolite ranges from 1x10-12 to 5x10 -12 m2 according to slug test data. Five wells have been used for testing: three non-fractured and two fractured wells. Well tests involved injecting air at constant pressure and monitoring transient flow rates until the flow approximately equilibrated over 10 to 60 minutes, then incrementally increasing pressure and repeating the flow monitoring. Field results were expressed in terms of the initial specific sparge capacity (Q/(P-H-E)) where Q is mass flow rate, P is injection pressure, H is hydrostatic pressure, and E is air entry pressure. The specific sparge capacity of conventional wells ranges from 0.3 to 0.6 m3/(Mpa min), whereas it is several times greater for fractured wells (0.8 to 3.5 m3/(Mpa min)) at the field site. Field data have been analyzed using analytical and numerical models. We use the step-rate data and invert an analytical solution adapted from Philip (J. Contam. Hydro., 1998) to estimate the in situ relative permeability function during sparging. This approach indicates that permeability ranges from 0.4x10-12 to 2x10-12 m2, which is remarkably similar to the slug test data. It also indicates that the in situ air entry pressure is approximately 31 kPa, and the exponent constant in the Gardner relative permeability function ranges from 0.12 to 0.25 m-1. Numerical analyses have been conducted using TOUGH2 to estimate gas distribution from the transient data, and to evaluate the effects of fracture length and thickness on sparging performance.
DE: 1719 Hydrology
DE: 1831 Groundwater quality
DE: 5104 Fracture and flow
SC: Hydrology [H]
MN: 2003 Fall Meeting