Gas migration in clay barriers

Citation
St. Horseman et al., Gas migration in clay barriers, ENG GEOL, 54(1-2), 1999, pp. 139-149
Citations number
11
Categorie Soggetti
Geological Petroleum & Minig Engineering
Journal title
ENGINEERING GEOLOGY
ISSN journal
00137952 → ACNP
Volume
54
Issue
1-2
Year of publication
1999
Pages
139 - 149
Database
ISI
SICI code
0013-7952(199909)54:1-2<139:GMICB>2.0.ZU;2-M
Abstract
Controlled flow-rate gas injection experiments have been performed on pre-c ompacted samples of KBS-3 specification Mx80(1)buffer bentonite using heliu m as a safe replacement for hydrogen. By simultaneously applying a confinin g pressure and backpressure, specimens were isotropically-consolidated and fully water-saturated under predetermined effective stress conditions, befo re injecting gas using a syringe pump. Ingoing and outgoing gas fluxes were monitored. All tests exhibited a conspicuous threshold pressure for breakt hrough, fractionally larger than the sum of the swelling pressure and the b ackpressure. All tests showed a post-peak negative transient leading to ste ady-state gas flow. Using a stepped history of flow rate, the flow law was shown to be nonlinear. With the injection pump stationary (i.e. zero applie d flow rate), gas pressure declined with time to a finite value. When gas h ow was re-established, the threshold value for gas breakthrough was found t o be significantly lower than in virgin clay. There is strong evidence to s uggest that the capillary threshold for gas entry is of such a magnitude th at normal two-phase flow is impossible. Gas entry and breakthrough are ther efore accompanied by the development of pathways which propagate through th e clay from gas source to sink. In the absence of these pressure-induced pa thways, initially water-saturated bentonite is impermeable to gas. (C) 1999 Published by Elsevier Science B.V. All rights reserved.