An Experimental and Theoretical Analysis of Diverter System Performance.

Abstract

Diverter systems, used as an alternate means of well control while drilling surface hole, have a demonstrated history of failure. Of particular interest in this dissertation are failures related to excessive backpressure, such as mechanical failure of surface equipment or the loss of the rig due to foundation collapse. Critical flow effects, neglected by current design practices, are shown both experimentally and theoretically to have a significant effect on backpressure. Critical flow is modeled by quantifying exit pressures and by including fluid acceleration pressure losses in backpressure calculations. "Systems analysis" of diverter operations is developed and applied to a field example, proving its effectiveness as a design method. In addition to incorporating critical flow effects, this analysis also considers wellbore and reservoir performance. Computer programs and calculation methods developed to perform the systems analysis are discussed. Design procedures culminate in a method by which diverter vent line diameter, conductor depth, and drilling depth are related to identify a safe interval over which to operate the diverter system.