Window sidetracking technology in ultra-deep Well Yuanba 12-1H

The gas reservoir in Changxing Group of Yuanba Gasfield is very huge. Owing to the fact that the gas reservoir is buried about 7 000 m underground, many technical difficulties such as multi-pressure system, high bottom hole temperature, high bottom hole pressure and high bottom hole hydrogen sulfide content are encountered. In the course of drilling of Well Yuanba 12-1H as the first development well to which the window sidetracking technology is applied, the technical difficulties such as ultra-deep window opening point, low drillabillity of formation, and difficult transmission of measurement signal in ultra-deep well and high temperature of formation have been encountered. On the basis of the target and actual wellbore trajectory, the wellbore trajectory design program has been optimized, the position of window opening point has been properly selected, the collar of casing and complicated formation have been avoided, the slip packer whipstock and special milling cone for hard formation have been used to carry out the window opening operation, the temperature-resistant wireless MWD tools and screw drill tools which are suitable for small wellbore have been selected, the combination of drilling tools have been optimized and adjusted, and the window sidetracking drilling technology suitable for ultra-deep well Yuanba has been formed. As for the well, the window is opened from the location of which the depth is 6 330 m, the window open time is 26 h, the sidetracking is completed at the depth of 6 955 m, the maximum hole deviationinclination is 62.4 °, the whole-angle change rate is controlled as lower than 16 (°)/100 m, the total sidetracking footage is 625 m, and the depth of various gas pools encountered is 88.6 m, all of which guarantee the achievement of geological objective, and provide the relatively strong technical support for operation in similar wells.