Initial rise of bubbles in cohesive sediments by a process of viscoelastic fracture

• Main Authors: Algar, Christopher K, Boudreau, Bernard P, Barry, Mark A
• Format: Journal Article
• Language: English
• Published: American Geophysical Union 14.04.2011
• Subjects: Bubbles; Fracture; Methane; Viscoelasticity

An understanding of the mechanics of bubble rise in sediments is essential because of the role of bubbles in releasing methane to the atmosphere and the formation and melting of gas hydrates. Past models to describe and predict the rise of other buoyant geological bodies through a surrounding solid (e.g., magmas and hydrofractures) appear not to be applicable to bubbles in soft sediments, and this paper presents a new model for gas bubble rise in soft, fine-grained, cohesive sediments. Bubbles in such sediments are essentially “dry” (little if any free water) and grow through a process of elastic expansion and fracture that can be described using the principles of linear elastic fracture mechanics, which assume the existence of a spectrum of flaws within the sediment fabric. By extending this theory, we predict that bubbles initially rise by preferential propagation of a fracture in a (sub) vertical direction. We present a criterion for initial bubble rise. Once rise is initiated, the speed of rise is controlled by the viscoelastic response of the sediments to stress. Using this new bubble rise model, we estimate rise velocities to be of the order of centimeters per second. We again show that capillary pressure plays no substantive role in controlling bubble growth or rise. This research was funded by the U.S. Officeof Naval research through grants N00014‐08‐0818 and N00014‐05‐1‐0175(project managers J. Eckman and T. Drake). Support was also provided bythe Natural Sciences and Engineering Council of Canada and by the KillamTrust. Author Posting. © American Geophysical Union, 2011. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 116 (2011): B04207, doi:10.1029/2010JB008133.