Research and On-Site Application of “Stable Fluid Volume” Pressure Control Drilling Technology

In order to solve the problems of complex pressure control drilling technologies and excessive equipment matching and achieve balanced pressure drilling, the monitoring and identification methods of pressure balance in the well were first studied. The in-well pressure balance relationship and the state of pressure control drilling were analyzed. The pressure control principles, processes, and implementation method of “stable fluid volume” were studied, forming the "constant fluid level" automatic control technology to enable automatic control in “stable fluid volume” pressure control drilling. The fluid level control accuracy on the drilling site was maintained within 25 mm. The throttle valve could be adjusted to ensure “stable fluid volume” according to the changes in the circulating tank fluid level during drilling. This facilitated real-time balance between bottomhole pressure and formation pressure and ensured balanced pressure drilling. In on-site applications, a 35 MPa rotary blowout preventer was utilized, with a wellhead pressure not exceeding 7 MPa, and manual throttling control was adopted to successfully drill through the saltwater layer with a pressure coefficient of greater than 2.0 and zero pressure window, as well as the limestone fractured gas layer with a pressure coefficient of greater than 1.8 and zero pressure window, solving the drilling problem in Block B on the right bank of the Amu Darya River in Turkmenistan. Research has shown that compared with other pressure control methods, the supporting equipment of “stable fluid volume”pressure control drilling technology is simplified; the pressure control process is simple, and it has good on-site application value.