流体流动和岩石变形耦合对井壁稳定性的影响

无论是过平衡钻井,还是欠平衡钻井过程,都可能导致井周围地层孔压力改变,这样就使我们通过假定地层孔隙压力恒定而得到的井周应力分布和地层的安全钻井液密度范围与实际偏离。滤饼质量直接影响到井周围流体流动的情况和井壁附近地层的孔隙压力。定量地计算分析了滤饼质量和流体流动对井周地层径向应力、周向应力、轴向应力和剪应力的影响,结果表明,一方面,随着滤饼质量的提高,井筒内流体在正压差下向地层中流动的能力和程度逐渐减小,井壁地层孔隙压力逐渐趋于原始地层孔隙压力,井壁岩石所受到的径向应力逐渐增大,井壁的稳定性逐渐变好;另一方面,地层颗粒间的接触应力逐渐增大,岩石抵抗张性破裂的能力增强,地层的破裂压力提高,井壁稳定性变好。滤饼质量好坏对低渗透地层的影响尤其显著。

EFFECTS OF FLUID-FLOW AND ROCK-DEFORMATION COUPLING ON WELLFACE STABILITY

It is possible that pore pressure of formation around bore-hole is changed whenever during the overbalanced drilling or the under-balanced drilling. The change of pore pressure affects stress distributions around borehole and wellface stability. Filter cake quality will affect formation pore pressure around borehole. The effects of filter cake quality on radius stress, hoop stress,axial stress and tangential stress have been studied quantitativelyin this paper. The result show that, with filter cake quality in-creasing, the support of drilling fluid acting on borehole wall in-creases, the ability that formation around borehole resists tan-gential failure increases and wellface stability improves. On the other hand, the stresses between rock grains increase the ability that formation around borehole resists tensile failure increases and wellface stability improves. The effect of filter cake qualityon wellface stability of low permeability formation is much sharply.