Research on Gas Hydrate Wellbore Stability Based on D-P Criterion
During drilling operations,drilling fluid generates heat exchange with hydrate formation,and the invasion of drilling fluid affects the stability of the hydrate.Both situations cause changes in the stress field around the well,leading to complexities such as wellbore collapse,which restrict the efficient development of gas hydrate resources.In the paper,a thermo-fluid-solid coupling circumferential stress model of deviated hydrate well was built according to the theory of linear thermoelastic porous media.Then,by introducing the Euler's transformation and considering the random magnitudes and directions of 3D in-situ stress,the D-P criterion was used to strengthen the influence of intermediate principal stress on hydrate wellbore stability,and understand the influences of the fac-tors such as borehole inclination/azimuth,hydrate saturation,sidewall permeability and drilling fluid temperature on hydrate wellbore stability.The results show that the inclination has a greater influence on the wellbore stability.For every 30° increase in inclination,the collapse pressure changes by 0.155 MPa;for every 30° increase in azi-muth,the collapse pressure changes by 0.112 MPa.In the decomposition process of hydrate from high to low satu-ration,the formation strength slowly decreases in the early stage and rapidly decreases in the later stage.The in-crease in effective porosity of hydrate formation leads to an increase in drilling fluid invasion,resulting in a de-crease in effective stress of the formation,which further leas to the deformation and fracturing of the formation and an increase in the risk of wellbore instability.Hydrate formation is more sensitive to drilling fluids above the phase equilibrium temperature(285 K).For every 1 K increase,the equivalent density of collapse pressure is increased by about 0.006 9 g/cm3;conversely,hydrate formation is rather dull to drilling fluids.At the time of drilling,the selection of appropriate high inhibitory and low-temperature drilling fluids can help control the decomposition of hydrates and reduce drilling fluid invasion,thereby reducing the risk of hydrate wellbore instability.The research results provide reference for investigating gas hydrate wellbore stability.
natural gas hydratewellbore stabilityD-P criterioncollapse pressurethermo-fluid-solid coupling
万方数据
维普
