Abstract

Why the world drilling limit envelope shows an irregular triangle as a whole and how to break its limitations? Many scholars have carried on the related researches, the authors also give theoretical reason, including the influence of borehole space, bearing capacity of drilled formation, mechanical factors and hydraulic factors. In this paper, the authors provide the effects of drill pipe tripping in/out and casing running on the world drilling limit envelope. Meanwhile, the drilling extended-reach limit optimization model is also established, its parameters include objective and subjective factors. The objective factors mainly refer to the formation factor; and subjective factors mainly include three types of parameters: drilling constraint parameters, wellbore design parameters and specific operating conditions. The subjective factors in the drilling extended-reach limit optimization model is mainly divided into the following three situations: the variation of drilling constraint parameters, the variation of wellbore design parameters, the drilling constraint parameters and the wellbore design parameters change simultaneously. In addition, the horizontal extended-reach well (ERW) is the well type which most frequently breaking world drilling record in recent years, and also the well type most likely to break the drilling world record in the future. Moreover, the concept of effective extended-reach limit is proposed. The borehole trajectory design is optimized using genetic algorithm, reducing the well's extension in non-reservoir formation and improving the effective extended-reach limit, so as to break the world drilling limit envelope. This work provides a practical tool for explaining why the world drilling limit envelope shows an irregular triangle and how to break the envelope's limitations, which is of great significance for the development of drilling engineering and improvement of economic benefits.

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