Abstract
Air/gas drilling is an acknowledged practical technology for its significant advantages in rate of penetration enhancement, lost circulation prevention and hydrocarbon reservoir protection. Air/gas drilling technology, however, can only be applied to dry formations in nowadays. When formation drilled water produces, air/gas drilling needs to be converted to mist drilling, foam drilling or liquid mud drilling, which can result in dramatic reduction of drilling speed. This problem becomes the bottleneck to further extend gas drilling applications in a larger scale in China. Aiming at solving water influx problems in the field application of gas drilling, a new technical method was proposed through in-house research. The water production zone and water cut of drilled formation are predicted using the seismic, logging data and the seepage mechanics theory. When the drilled formation begins to produce large volume of water, a material (water absorbent) is injected to promptly absorb the downhole produced water and remove it out of the wellbore, so as to maintain the normal gas drilling. Furthmore, as drilling goes into well sections with incompetent or large water-cut formations, the expanded tube is employed to mechanically plugging the complex borehole section, which enables the air/gas drilling to be continuecd. Based on this solution, a water absorbent with high efficiency was screened out. Related operational procedures of absorbent injection and expanded tube plugging were studied. Field pilot test shows that with the technique, the borehole section in air/gas drilling can be extended, making the best use of air/gas drilling to increas penetration rate, which hence plays an important role for promoting the use and the advancement of air/gas drilling technology.
