M. Ben Clennell¹
(1) Universidade Federal da Bahia, CPGG-IEGO, Salvador, Brazil

Abstract: Capillary controls on gas movement and clathrate phase stability in marine gas hydrate systems

As exploration moves into deeper waters, the likelihood of encountering gas hydrates in offshore operations increases. Natural gas hydrates accumulations tend to be dispersed when sourced from shallow biogenic gas, but can be concentrated in areas where gases seep upwards–e.g., above and around hydrocarbon fields. To date the dispersed nature of hydrate occurrences, the deep waters in which they occur, difficulties of detection and the necessity to supply large amounts of energy to release the gas have ruled out commercial exploitation. Nevertheless, natural clathrates are currently being investigated as future strategic energy resources. There is also the possibility of a hydrate layer acting as an unconventional trap to liquid oil or free phase gas reservoirs below. Our findings are also relevant to incidental encounters with gas hydrates that may occur during exploitation of conventional hydrocarbons in deeper waters. In this contribution we review capillary properties of deep marine sediments (muds and turbidite sands), and examine physical and thermodynamic controls on hydrocarbon migration pathways and hydrate growth mechanisms in them. We present results showing the influence of sediment properties on phase equilibrium. Gas migration to and through the hydrate zone, permitted by capillary breaching and fracturing, is investigated. Prospectivity of hydrocarbon traps at the base of the hydrate stability zone and geotechnical / environmental hazard issues are discussed.

AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana