欠平衡钻井是指在设计条件下 ,钻井液液柱静压头对井底所施加的压力低于要钻地层的压力时所进行的钻井作业。欠平衡钻井包括泡沫钻井、低密度钻井液钻井和注气欠平衡钻井等多种钻井方式。欠平衡钻井技术可减轻地层损害 ,提高机械钻速 ,克服漏失和卡钻 ,是开发枯竭油层的一种好 Underbalanced drilling refers to the drilling operation under the conditions of design where the pressure exerted by the hydraulic column hydrostatic head on the bottom of the well is lower than the pressure at which the formation is to be drilled. Underbalanced drilling includes many drilling methods such as foam drilling, low density drilling fluid drilling and underbalanced injection drilling. Underbalanced drilling techniques can reduce formation damage, increase ROP, overcome runoff and stuck pipe, and are a good way to develop depleted reservoirs