Developing Dynamic Killing Technique for Off-bottom Killing Condition

DOI: 10.14800/IOGR.1291

Abstract

Dynamic killing is a non-conventional well control technique that employs annular pressure loss in conjunction with hydrostatic pressure to halt well influx. This method is particularly applicable in off-bottom conditions, where the drill bit is away from the well's bottom. Off-bottom conditions are common during tripping operations, where surface pressure may not accurately reflect bottom-hole conditions. Ignoring the region beneath the drill bit necessitates higher kill rates, which may exceed equipment limits, such as maximum rated surface pressure.

In this study, the effect of kill fluid falling below the drill bit was examined in terms of critical influx velocity. A Python program was developed to model single-phase and two-phase flow conditions within the drill string, annulus, and below the bit. The focus was on accurately modeling the area below the bit, using three different approaches: static, dynamic zero net liquid holdup (ZNLH) flow, and countercurrent two-phase flow.

Two gas influx scenarios were employed to test, verify, and assess these modeling approaches. Results indicated that the static ZNLH approach required the highest kill rate, while the countercurrent two-phase flow approach required the lowest. In terms of bottom-hole pressure, the static ZNLH approach resulted in the lowest pressures, whereas the countercurrent two-phase flow approach yielded the highest pressures.

Temperature significantly impacts the properties of the kill fluid, such as density and viscosity, even when water is used. Additionally, reducing the kill string depth logarithmically increases the required kill rate. The critical gas velocity, which influences the kill fluid's fall-off at a certain depth, decreases with increasing gas influx rate.This work provides a roadmap for applying dynamic kill techniques in off-bottom conditions, accommodating both low and high gas influx rates.