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Abstract 132
Mechanical and Petrophysical Characterisation and Wellbore Stability Management in Gas Hydrate-Bearing Sediments
Tan, C.P., M.B. Clennell, R. Freij-Ayoub, B. Tohidi and J. Yang
Alaska Rocks 2005: The 40th U.S. Symposium on Rock Mechanics (USRMS), Anchorage, Alaska, June 25-29 (2005).
As the number of oil and gas fields being developed in deepwater and onshore arctic environments increases, greater emphasis should be placed on quantifying the hazards to drilling operations posed by gas hydrates. In spite of gas hydratebearing sediments having been drilled successfully in the past, it is important, as future drilling operations progress into deeper and ultradeep waters, to develop a sound understanding of gas hydrate-related hazards and thereby identify ahead of time when problems are likely to occur. In this paper, the requirements to develop a comprehensive risk management capability for drilling in gas hydrate-bearing sediments are described, with an emphasis on laboratory measurements of mechanical and petrophysical properties of such sediments and their variation with the degree of hydrate saturation and during progressive dissociation. Correlations and relationships were developed between pre- and post-hydrate dissociation sediment properties from a combination of the test data. The requirements for modelling time-dependent wellbore stability in gas hydrate bearing sediments as a result of complex interactions between numerous geomechanical-chemical-thermodynamic processes, and examples of modelling results are presented and discussed. In addition, the concept of a drilling fluid design optimisation methodology, in terms of mud weight
and type, chemical additives and temperature, for safe drilling in such sediments is described.

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