弱面地层的直井井壁稳定力学模型

MECHANICS MODEL OF SIDEWALL STABILITY OF STRAIGHT WELLS DRILLED THROUGH WEAKLY CONSOLIDATED FORMATIONS

弱面地层在较小的钻井液柱压力下先于岩石本体破坏，引起井壁垮塌，甚至在高密度钻井液情况下也难以维持井壁稳定。我国西部钻井中常遇此类问题。本文从弱面模型出发建立大倾角地层的井壁稳定力学模型，详细分析倾角地层的倾角和走向对井壁稳定性的影响，认为弱面地层的坍塌方位主要集中在走向与水平最小地应力夹角在90±20度范围内，在钻遇此地层时，若维持井壁稳定所需的钻井液密度过高，可采用合理的井眼轨迹进行大斜度井钻井。

Weakly consolidated formations are damaged earlier than rock under lower drilling fluid column pressure, causing wellbore sloughing, even can't keep sidewall stable when using high density drilling fluid. Taking weak formation mechanics model as the point of departure, mechanics model of sidewall stability for high dip formations is established. Effect of formation dip and strike on sidewall stability is analysed in detail. Analysis result shows that the azimuths of collapse of weak formations are concentrated within the range of 90 ± 20 degree (the angle between the formation strike and the direction of minimum horizontal earth stress). When drilling through these formations, if drilling fluid density is too high for maintaining sidewall stability, high - angle drilling can be conducted using rational trajectories.