UNDER BALANCED DRILLING PRACTICES IN SULIGE GAS FIELD OF CHANGQING

Sulige gas field features low formation pressure coefficient, low average permeability, low abundance and low production rate. Based on such reservoir characteristics, under balanced drilling technology began to be applied in this area from 1999, and natural gas was used as the drill in circulation medium when drilling the pay zone. Research work was conducted on such aspects as prediction of formation water production, formation stability, and optimum gas injection parameters, and a model of borehole collapsing gradient pressure, as well as a bit selection method was established based on which. This natural gas UBD technology was field tested in Shan242, Su35-18, Su39-14-1 and Su39-14-4, and the tests results showed that the penetration rate was dramatically improved, in which the ROP of Su35-18 reached 18 m/h, which is over 9 times than that of the offset well; the natural gas drilling interval of Su39-14-4 reached 1092 m, and it’s the longest hole interval drilling with natural gas. In general, such technologies as formation water production prediction, formation stability evaluation, hole cleaning and HSE procedures for natural gas drilling were preliminary formed.