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旋转钻井法技术现已发展到可以钻凿直径为20英尺(6.1米)、深度超过3000英尺(914.4米)的井筒。把适当高度的预制混凝土井壁下沉到井底,并在井底进行组装的永久支护方法也已经得到发展。用这种方法支护的井筒,既可承受井底静水压力又不漏水。 还研究过其他两种支护方法。一种是钢井圈,焊接后悬浮下沉,另一种是混凝土井壁,在地面连接后悬浮下沉。用钢井圈支护一般用于较小直径的井筒,但是,当井筒净直径为14英尺(4.27米)时,用钢井壁比用混凝土井壁几乎贵两倍。在悬浮下沉混凝土井壁时遇到两个问题:一是在地面连接井壁所需时间,另一个是在悬浮过程中,万一有一
Rotary drilling techniques have now been developed to make it possible to drill a borehole 20 feet (6.1 meters) in diameter and more than 3000 feet (914.4 meters) deep. Permanent methods of supporting prefabricated concrete shaft walls of suitable height to the bottom of the well and assembling them at the bottom of the well have also been developed. The wellbore supported in this way can withstand hydrostatic pressure at the bottom of the well without leaking water. Also studied two other support methods. One is the steel well ring, suspended after welding subsidence, the other is the concrete shaft wall, suspended in the ground after the connection sink. Wellbore supports are generally used for smaller diameter shafts, but when the net diameter of the shaft is 14 ft (4.27 m), the steel shaft wall is almost twice as expensive as the concrete shaft wall. Two problems are encountered when suspending the concrete shaft wall in suspension: one is the time required to connect the shaft lining on the ground, and the other is during the suspension, if there is one