Liner Cementing through Precise Pressure Control in the Ultra-Deep Well Tian-X Located at the Southern Margin of the Junggar Basin

The well Tian-X is an exploratory well located at the Anjihai anticline (an anticline in the Huomatu anticline zone) in the south edge thrust belt in the Junggar Basin. The 6^th interval (Ф139.7 mm) penetrates a long open hole section of the well with coexistence of high and low pressure zones and narrow annular clearance, and the sandstone reservoir is developed with abundant pores and has active oil and gas. The safe drilling window in this interval is only 0.02 g/cm³, and mud losses have frequently happened during drilling. Narrow safe drilling window also causes difficulties in dynamically balancing the formation pressures and problems such as well kick and mud losses during casing running are quite prone to happen, resulting in poor cementing quality. To solve these problems, precise pressure management during casing running has been performed. Using the precise pressure management equipment, pressures at the wellhead during casing running and well cementing can be precisely controlled an the pressures at the points of mud losses an points of well kicks along the borehole were controlled in the scope of the safe window, thereby realizing pressure balance inside the wellbore. In cementing the liner string, the wellhead pressure was precisely controlled and the cement slurry returned to the designed depth in one circulation, and the cementing techniques were designed specifically to suit for the wellbore conditions. The well cementing job was performed successfully. IBC well logging interpretation shows that the job quality of the cementing section is 100% qualified, no gas channeling occurred at the bell nipple when mud density was reduced. This technology has provided a precious experience and reference significance for cementing wells with narrow drilling windows at the south edge of the Junggar Basin.