滨里海盆地巨厚盐膏层钻井液密度设计新方法

传统的盐膏层钻井液密度的设计方法是,根据井筒的液柱压力和盐岩的非线性粘弹性变形特点,分析不同液柱压力条件下井筒的缩径速率,然后根据现场安全钻井所允许的井眼缩径速率,确定合适的钻井液密度。在分析哈萨克斯坦滨里海盆地实钻井盐膏层钻井液密度的基础上,认为在钻进巨厚盐膏层时,只要控制井壁围岩的八面体剪应力,使盐岩不产生损伤扩容,即可保证盐层井段安全钻井。亦即给定盐岩井壁八面体剪应力处于扩容损伤边界值,就可以计算得到保持井壁稳定的钻井液密度安全窗口。3口井盐膏层钻井液密度的设计结果表明,利用该方法设计的钻井液密度完全可以满足现场安全钻井的要求。

New Drilling Fluid Density Design for Drilling Huge Gypsum Formation in Pre-Caspian Sea Basin

Conventional method to determine drilling fluid density for gypsum formations is,first calculating the shrink rate of well diameter under different mud hydrostatic pressure based on the hydrostatic pressure and the nonlinear viscoelasticity deformation feature of salt,then making the density to meet the requirement of the allowed shrink rate of well diameter for safe drilling practice.Based on analysis of drilling fluid density used while drilling gypsum formations in the Pre-Caspian Sea basin,it is concluded that gypsum formations can be penetrated safely only if proper control of shear stress from wellbore surrounding rock without salt damage dilation.That is,the safe drilling fluid density margin for stable wellbore wall can be calculated given boundary stress.The application in 3 wells indicates that it can meet the requirement for safe drilling.