Testing accident analysis and preventive measures for ultra-deep sulfur-bearing gas wells in Yuanba Gas Field

With a burial depth of approximate 7 000 m, and as high as 157 ℃of downhole temperature, the gas reservoir in Changxing Formation in Yuanba gas field is of complex working condition and downhole geological condition, so the testing is hard to carry out, where high risks such as string being buried, stuck or falling off and malfunction of tools may occur. Based on theory analysis and field test, corresponding preventive measures for various accidents have been made by means of analyzing a large number of onsite accident cases. Well kill was enabled after seal liquid circulation in stead of traditional direct well kill; furthermore, the drilling fluid was optimized. In this way, drilling fluid parvafacies and precipitation and other problems were solved, and the string was less likely to be buried and stuck; construction hydraulic parameters were optimized to eliminate the risk that tools might be punctured or corroded; RTTS packer central tube and hydraulic anchor jaws were improved to avoid the fracture of packer central tube while improving the stability of packer setting; the reasonable control of the frequency of oil tube running reduced the risk of oil tube falling off. The above measures have been successfully applied in over 10 wells including well YB205, which effectively reduced accident rate in Yuanba gas field testing. They can be used as reference in well operation of the same kind.