两向水平应力不等条件下泥浆密度的确定

降低泥浆液柱压力对油气层的压差和保持井壁稳定是钻井工程亟待解决的问题,对于地应力异常地区显得更为迫切。为了解决油气层污染和井壁稳定的难题,在弹塑性力学理论和岩石力学理论的基础上,应用摩尔—库伦屈服准则,阐述了井眼周围岩石弹塑性状态的形成机理及应力、位移的分布情况,推导出了井眼塑性屈服范围和泥浆液柱压力、水平地应力以及岩石强度的关系式。与其它理论相比,该理论所确定的保持井眼稳定的泥浆密度范围更广,有利于降低对油气层的压差和近平衡钻井。同时,也提出了一些具体技术来保证这一理论的应用。

Defining Mud Density Under Conditions of Unequal Horizontal Stresses

Lowering pressure difference on production zone and keeping well wall stability are problems much needed to be solved in petroleum engineering, espe-cially in areas with abnormal rock stress. Based on the theory of elasto-plasticity and rock mechanics, applying Mohr-Coulomb yield criteria, this paperpresents a mechanism of elasto-plastic state occur-ring in rocks around the wellbore, describes the cor-responding distribution of stress and displacement, and formulates the equation relating mud hydraulicpressure, horizontal rock stress to rock strength.Compared with other approaches, range of mud den-sity values required for a stable well wall is wider in this approach, which is beneficial to lowering pres-sure difference on production zone and to performing near balance drilling.