羌塘盆地天然气水合物钻探试验井工程井壁稳定性分析

Analysis on Wall Stability of Gas Hydrate Drilling Test Well in Qiangtang Basin of Tibet

摘要:

基于三维快速拉格朗日有限差分法多孔介质流固耦合理论及弹塑性极限平衡理论，根据羌塘盆地天然气水合物钻探试验井工程QK-2井实钻资料，分析在渗流条件下井壁失稳机理，并对失稳段井壁稳定性进行了数值模拟分析，研究在不同钻井液密度下井径周围围岩应力分布和井眼坍塌或拉裂变形规律，为羌塘盆地天然气水合物钻探试验井工程确定地层不坍塌（不缩径）、不压漏的钻井液安全密度窗口，以便为钻井井身结构设计及合理钻井液密度的确定提供依据。

关键词:天然气水合物;钻探;井壁稳定性;钻井液安全密度窗口;羌塘盆地

Abstract:

Based on three-dimensional fast Lagrangian finite difference method of fluid-solid coupling theory of porous medium and elasto-plastic limit equilibrium theory, according to the QK-2 well drilling data of gas hydrate drilling test well in Qiangtang basin, the analysis is made on the mechanism of borehole instability under the condition of seepage and the numerical simulation analysis is also made on the wall stability of instable section to learn stress distribution of surrounding rock around the well and deformation laws of borehole collapse or crack in different drilling fluid density. The safe density window of drilling fluid is determined for no formation collapse (diameter reducing) and no leakage for the gas hydrates drilling test well in Qiangtang basin, so as to provide the evidences for the determination of casing program design and reasonable drilling fluid density.

Key words:〗gas hydrate; drilling; well wall stability; drilling fluid density window; Qiangtang basin