欠平衡井底附近岩石应力状态分析

由于欠平衡钻井具有大幅度提高钻速、有效保护油气层和降低钻井成本等优点，被广泛应用于国内外各大油田，但对欠平衡钻井井底岩石应力状态特点的相关研究较少。本文以欠平衡钻井井底附近井眼为研究对象，通过分析地应力、孔隙压力、液柱压力等对井底岩石机械力学特征变化的影响，来研究欠平衡条件下非渗透性井壁和渗透性井壁岩石的破碎效率、井斜、井壁稳定等问题。研究结果表明：井底附近岩石力学性质受地应力、孔隙压力、井眼及液柱压力等的综合作用。非渗透岩石时，欠平衡钻井破岩效率高，机械钻速大，井壁集中力大，易井斜；渗透井壁时，随渗透率的增大，欠平衡钻井破岩效率降低，机械钻速减小，井壁集中力减小，井斜倾向变小。

STUDY OF ROCK STRESS STATE NEAR THE BOTTOM TO UNDERBALANCE DRILLING

Underbalance drilling was applied to each oil field at home and abroad, due to the advantage of increase the penetration rate substantially, protect the reservoir effectively and reduce the drilling costs. But in respect of rock stress state characteristics near the bottom, relatively speaking, the study was rarely.Take the borehole near the bottom in underbalance drilling as the research object, through analyze the relationship between terrestrial stress, pore pressure, fluid column pressure and characteristics of rock mechanics in the bottom, to study the rock crushing efficiency, well deviation and hole stability of non-permeable wellbore and permeable wellbore in under balance pressure drilling. The result shows that the mechanical properties of rocks near the bottom are subject to the combined effect of terrestrial stress, pore pressure and fluid column pressure. In non-permeable rock, the rock crushing efficiency, the penetration rate and the well concentrated force trend to increase, the well trend to inclination. In non-permeable rock, with the permeability increase, the rock crushing efficiency, the penetration rate and the well concentrated force trend to decrease, the tendency toward inclination become lower.