Abstract
Gas hydrates have great potential as future energy resources. Several productivity and stability analyses have been conducted for the Ulleung Basin, and the depressurization method is being considered for production. Under depressurization, ground settlement occurs near the wellbore and axial stress develops. For a safe production test, it is essential to perform a stability analysis for the wellbore and hydrate-bearing sediments. In this study, the development of axial stress on the wellbore was investigated considering the coupling stiffness of the interface between the wellbore and sediment. A coupling stiffness model, which can consider both confining stress and slippage phenomena, was suggested and applied in a numerical simulation. Parametric analyses were conducted to investigate the effects of coupling stiffness and slippage on axial stress development. The results show that shear coupling stiffness has a significant effect on wellbore stability, while normal coupling stiffness has a minor effect. In addition, the maximum axial stress of the well bore has an upper limit depending on the magnitude of the confining stress, and the axial stress converges to this upper limit due to slipping at the interface. The results can be used as fundamental data for the design of wellbore under depressurization-based gas production.
Highlights
Gas hydrates are solid crystalline compounds which consist of water and guest molecules [1].Gas hydrates are formed under certain sets of high pressure and low temperature conditions, outside of which the gas and water species typically remain in separate phases [2]
The axial stress on the wellbore was largely affected by the coupling stiffness of the present study
The axial stress on the wellbore was largely affected by the coupling stiffness and, as shown in the distribution of confining stress, the confining stress varies with and, as shown in the distribution of confining stress, the confining stress varies with the depth of the wellbore
Summary
Gas hydrates are solid crystalline compounds which consist of water and guest molecules [1].Gas hydrates are formed under certain sets of high pressure and low temperature conditions, outside of which the gas and water species typically remain in separate phases [2]. Gas hydrates are solid crystalline compounds which consist of water and guest molecules [1]. The guest molecules are gas molecules such as methane, ethane, propane, or carbon dioxide. These guest molecules are combined by hydrogen-bonded water. This natural gas is a premium fuel because it burns cleanly and produces less carbon dioxide [3]. Most natural gas hydrate deposits appears to be in the form of ‘structure I’, with methane as the trapped guest molecule, and its fraction is more than 90% [5,6]
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