摘要
反循环钻进与正循环钻进的冲洗液流向不同,同时反循环钻进孔径一般比正循环钻进的孔径大,反循环钻进仍沿用正循环钻进用的开放式翼状钻头,由于孔内冲洗液中心流速高,边沿流速低,孔底边沿排岩屑不畅,特别是在粘土地层钻进常引起糊钻,致使钻进效率受到极大的影响。把钻头的翼板顶部改成封闭(即挡水罩)式,使冲洗液先流到钻头边沿再到中心钻杆,这样孔底排屑较彻底;另外把钻头底唇改成收敛式的(即倒漏斗状),使岩屑翻起的方向与水流方向一致,加强钻头的排岩能力,阻止粘土滞留及粘结钻头的可能性,保持孔底清洁,从而提高了反循环的钻进效率。
The reverse circulation drilling is different from the direct circulation drilling in the direction of circulation fluid. Furthermore the fomer has a bigger bore diameter than the latter. The reverse circulation drilling retains the open wing bit in veiw of the higher fluid velocity at the centre,lower fluid velocity at the margin, and difficulty in clearance of cuttings at the margin of the bit bottom(which frequently gives rise to bit freezing and hampers drilling, especially in clay layers). The author believes that if the upper part of the wing panel of the bit is made enclosed, the circulation fluid will reach the margin of the bit first, and then go on to the pipe at the centre, with cuttings being removed quite well. In addition, if the bit face narrows upward (like an upside-down funnel), the cuttings will be transported in the same direction as the circulation fluid, so that the clearance of cuttings will be improved and the possibility of stagnant clay and bit freezing will be eliminated to certain degree so as to raise the efficiency of the reverse circulation drilling.
