一种控制盐层段井眼闭合率的钻井液密度新公式

New formula of drilling mud density of the control wellbore closed rate in salt bed.

针对钻井过程中钻遇的盐层段井眼蠕变缩径问题,利用弹塑性力学理论,蠕变本构方程采用Heard蠕变方程,在平面应变和均匀地应力假设下,推导出控制井眼收缩的钻井液密度新公式,该公式与前人推导的公式不同。通过理论分析,指出产生差异的根本原因在于蠕变应力差(极坐标下表示的径向应力与切向应力之差)公式的推导上,用有限元法计算结果对理论公式进行检验,证明是可行的。对文中的力学模型采用有限元法建模、求解,利用求解结果对各应力差公式进行验证,得出:根据文中公式计算结果与有限元法计算结果完全一致,而据前人公式计算结果偏离有限元计算值较大,从而间接证明了该钻井液密度新公式的推导更严密,更准确。

Aimed at the problem of the salt bed wellbore creep and shrink under the drilling,based on the elasto-plastic mechanics theory and the head creep equation,the new formula of the control wellbore shrink rate was derived with in case of the plane strain and uniform in-situ stress,which was different from the old formula.By the theoretical analysis,the difference of the formula is the creep stress difference,the verification of the formula used the finite element method(FEM) was presented,it proved that the result of the theory formula is in agreement with the FEM,the result of the old formula was big error with that of the FEM.It proved that the new formula of the drilling mud density is correct.