Numerical Simulation Of Fluid-solid Coupling In Decomposition Of Diagenetic Gas Hydrate

With the rapid development of economy,people's dependence on energy is increasing.Conventional energy such as oil and natural gas has been unable to meet the needs of rapid economic development.Gas hydrate,as an efficient and clean new energy,can be a powerful supplement to traditional energy,has attracted widespread attention at home and abroad because of its shallow buried,abundant reserves,high efficiency combustion and low pollution characteristics.However,gas hydrate is a kind of metastable material.The uncontrollable decomposition of gas hydrate can easily lead to drilling accidents,such as wellbore instability,geological hazards and environmental impacts.Therefore,strengthening the research of gas hydrate reservoir stability is of great theoretical and practical significance.In this paper,taken the permafrost diagenetic gas hydrate as the research background,the occurrence characteristics and logging response of gas hydrate are discussed,including reservoir mode,occurrence mode,logging response,reservoir parameters and so on,and based on the conventional logging method,a program for calculating mechanical parameters of diagenetic gas hydrate reservoir considering different occurrence modes is worked out with VB language.Secondly,through the analysis of the gas hydrate decomposition process,combined with porous medium coupling theory,considering the effect of pore pressure variation and temperature change on reservoir deformation,a dynamic parameter model about porosity and permeability and the fluid-solid coupling mathematical model of the diagenetic gas hydrate was built.Thirdly,the COMSOL Multiphysics numerical simulation software is used to simulate the established mathematical model about the fluid-solid coupling of diagenetic gas hydrate,and the changes in the stress state of the reservoir,the change of the reservoir physical parameters and the deformation of the reservoir after the well opening are analyzed.Finally,based on well logging data and geological background of DK-1 well in the permafrost region of Qilian Mountains,the mechanical parameters of reservoir in this area are calculated,and the stress state and wellbore deformation of two drilling methods,included micro under balanced drilling and micro over balanced drilling are analyzed.Through the above study,a set of calculation method for calculating the mechanical parameters of diagenetic gas hydrate reservoir is established based on conventional logging principle,and a safe drilling method suitable for diagenetic gas hydrate drilling is obtained.It lays a foundation for the research on the reservoir stability related to diagenetic gas hydrate drilling.