Abstract

The objective of this study is to quantitatively assess the flow, thermal and geomechanical response of sloping oceanic accumulations of hydrates to stimuli that can induce dissociation, such as depressurization-induced gas production activities, with emphasis on the evaluation of the geomechanical stability of the well assembly and of the reservoir. Using numerical simulation, we analyze the coupled flow, thermal, thermodynamic, chemical and geomechanical processes involved in the response of sloping hydrate accumulations exposed to dissociation-inducing stimuli associated with depressurization-based activities for the production of gas from the hydrate-bearing sediments. The study includes a sensitivity analysis of the system behavior to the angle of the slope in order to determine its effect on the system behavior, and cover the system long-term behavior following the cessation of the stimuli.

We determine that gas production from hydrate-bearing media may cause subsidence that increases stresses along the well and reduces gas production, but does not appear to enhance the risk of hillslope stability while production continues. The risk of oceanic landslides increases slightly after the end of gas production as a result of the increase in the pressure in the reservoir where the hydrate (which imparts the bulk of mechanical strength to the unconsolidated oceanic sediments) is depleted or exhausted, but at no time is the system stability compromised for any slope angle.

The paper provides an integrated quantitative analysis of the coupled processes that are involved in dissociating hydrates using themost advanced simulators, and makes significant contributions to the evaluation and risk assessment of potential problems associated with future production from oceanic hydrate deposits, in addition to providing insights that may lead to mitigation of the problems.

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