Natural bridging as a tertiary well control method in deep-water wells: A case study from Caspian Sea

Blowout is the uncontrolled flow of reservoir fluids into the well, which can cause different types of problems during the drilling operations. In high-pressure formations with low rock strengths, it is more likely to occur self-killing through bridging mechanisms. The underbalanced conditions that are induced during developing a kick, leading into sufficient instability in exposed formations such that the borehole bridges over and kick kills itself. In this research, the potential of natural bridging is studied in one of the deep-water wells in the Caspian Sea to figure out whether this natural phenomenon is able to terminate the uncontrolled influxes of formation fluids into the borehole. For the reason, a series of semi-integrated numerical simulators are employed to evaluate wellbore pressure profile and wellbore instability as a function of time under blowout conditions. Applied analyses to a particular blowout scenario indicated that rock fragments falling off the wellbore wall are suspended in the two-phase flow (a mixture of gas and drilling mud) during developing the kick. As a result, cavings settlement is less not probable to plug the wellbore. On the other hand, suspension of rock fragments gradually increases the solid concentration of fluid phase until it hits a critical value at a certain time after the beginning of the kick, thereby bridging occurs before developing the kick into a blowout.