摘要：钻井液排量的大小直接关系到大位移水平井延伸能力的高低,为获得最大的大位移水平井延伸极限,笔者从钻井液排量的角度出发,提出了排量的优化设计原则,并给出了最优钻井液排量的设计方法.综合利用大位移井的裸眼延伸极限原理和水力延伸极限原理,并考虑井眼清洁的需要从而确定钻井液的排量范围,最终以获得最大的水平段延伸极限为目标,确定最优钻井液排量值.应用该方法对1口大位移水平井进行分析可知,其排量允许范围为26.2~42.9 L/s,最优排量值为31.8 L/s,其对应的最大水平段延伸极限为6251 m.进一步研究表明:首先,在任意排量下,基于上述两原理获得的两水平段延伸极限值的最小值可以作为大位移水平井的水平段延伸极限;其次,两水平段延伸极限相等时的值即为最大水平段延伸极限,其所对应的排量值即为最优钻井液排量值;最后,该最优排量值既可以保证大位移水平井获得最大的井眼延伸极限,又可以满足井眼清洁的需要,井内压力也不会超过井壁稳定和钻井泵的最大承载能力.%Drilling fluid displacement has the direct effect on the extension capacity of extended-reach horizontal wells. To maxi-mize the extension limit of extended-reach horizontal wells, the displacement optimization design principle was put forward from the aspect of drilling fluid displacement, and the design method of optimal drilling fluid displacement was proposed. The displacement range of drilling fluid was determined by taking into consideration the demand of hole cleaning. According to open-hole extension limit principle and hydraulic extension limit principle of extended reach well comprehensively, the optimal displacement of drilling fluid was determined with the maximization of horizontal section extension limit as the ultimate target. This method was used to analyze one extended-reach horizontal well. It is shown that the allowed displacement is in the range of 26.2-42.9 L/s, and optimal displacement is 31.8 L/s, corresponding to the maximum horizontal section extension limit of 6251 m. Based on further studies, several understandings were obtained. First, for any displacement, the minimum extension limit of two horizontal sections which are obtained based on the above mentioned two principles can be taken as the horizontal section extension limit of extended-reach horizontal well. Second, the value in the occasion the extension limit of both horizontal sections is equal is the maximum extension limit of horizontal sections, and its corresponding displacement is the optimal displacement of drilling fluid. And third, at the optimal displacement, the extension limit of extended-reach horizontal well can be maximized, the demand of hole cleaning can be satisfied and the subsurface pressure is kept below the maximum bearing capacity of wellbore stability and drill pump.
