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本文综合国外关于水力压裂裂缝的起裂和扩展的研究,提出了垂直裂缝和水平裂缝的起裂判据并分析了影响裂缝延伸方向的各种因素。文章认为裂缝的形成主要决定于井壁上的应力状态,而确定及影响此应力状态的因素有:地壳应力、地层的孔隙压力、井内液体压力、压裂液向地层中的渗滤流动以及被压裂地层的机械物理性质,并对此进行了较详尽的分析。作者注意到目前国外正引用线弹性断裂力学来分析裂缝延伸的方向及延伸的阻挡问题,提出裂缝的延伸方向主要取决于地应力,认为不论井壁上初始形成的裂缝方位如何,在远离井眼后,裂缝便趋于垂直最小主地应力的方向。扩缝压力除了取决于最小主地应力外,还与裂缝的类型、尺寸及岩石材料的性质有关。文章中还分析了地层岩性的变化、交耳面的性质、裂隙面的存在、压裂液的比重及其滤失,地应力分布的变化等对裂缝端部应力强度因子的影响,认为这是判断裂缝继续延伸或产生阻挡作用的重要依据。
Based on the researches on the initiation and propagation of hydraulic fracturing in foreign countries, this paper presents the criteria for initiation and propagation of vertical fractures and horizontal fractures and analyzes various factors that affect the direction of fracture propagation. It is believed that the formation of fractures is mainly determined by the stress state on the shaft lining. Factors that determine and influence this stress state include crustal stress, formation pore pressure, fluid pressure in the well, diafiltration flow of fracturing fluid into the formation, Fracture stratum mechanical and physical properties, and carried out a more detailed analysis. The author noticed that the current overseas reference line elastic fracture mechanics to analyze the direction of the crack extension and extension of the blocking problem, proposed that the fracture extension direction mainly depends on the geostress, that regardless of the initial formation of wellbore fracture orientation, After that, the cracks tend to be perpendicular to the direction of the smallest principal earth stress. In addition to the expansion pressure depends on the minimum principal stress, but also with the type of fracture, size and the nature of the rock material. The paper also analyzes the influence of stratigraphic lithology, the nature of the ear surface, the existence of the fracture surface, the proportion of fracturing fluid, the loss of filtration and the variation of the distribution of ground stress on the stress intensity factor at the crack tip. It is an important basis for judging whether cracks continue to extend or have a blocking effect.