Well Kill Summary - Relief Well Kill

Kill fluid

Several different kill fluids can be used in the kill process. Water, brine or drilling mud can be used for dynamically killing a blowout from this well. For the simulations presented, mud at 1.8 sg (15ppg), 2.16 sg (18ppg), and seawater have been used as kill fluid.

Higher mud weights may be advantageous (as can be seen for case 1), but can lead to fracturing at the kill intersection point with subsequent high losses. High mud weights may be used in the initial phase of a kill operation if necessary, switching to a lighter mud when the inflow from the reservoir has stopped.

Water is often used initially to check the communication with the blowout well, although pump rates, pressures and power requirements for full dynamic water kills may be impractical for the actual kill operations.

Blowout and kill simulation results are summarised in table 5-4. An example of the full dynamic results are shown in Appendix B of this report.

Table -1: Kill summary Scenario 1 and 2

In addition to the above volume required to stop the inflow, the volume of the blowout well and the relief well must be calculated when planning the kill operation. Usually 2-3 hole volumes of the blowout wells is required to circulate out all of the gas from the blowout well and establish a safe hydrostatic wellbore condition.

Table -2: Volumes in well and relief wells, Scenario 1 and 2.

#) 2 hole volumes of blowout well assumed used.

After stopping the inflow from the reservoir, the sections below the kill point and the upper part of the well must be circulated and/or bull-headed free of gas. Once the outflow stops, cement can be pumped to block the well from restarting.

Both simulations and experience show that this normally takes 2-3 hole volumes after inflow stops in order to prevent the blowout from restarting during the cement operation

Losses to the formation during the kill operation are expected to be low, since direct intersection is assumed. The possibility of high losses increases when the kill mud weight utilized is well above the pore pressure gradient.

Number of relief wells

As indicated in the the tables, some of the scenarios are very difficult to kill due to the required kill rate. As a general rule of thumb, a kill rate which exceeds 100bpm will, in most cases, be impractical and two relief well s become mandatory.

Even though one relief well is sufficient in some cases, two relief wells may be started to increase the rate of success of such a complicated project.

If serious pollution or other environmental damage is being caused by the blowout, then two relief wells should be considered regardless of the intervention plans.

Further analysis of actual production rates, reservoir characteristics and risk assessment at the time of the blowout will provide more data to assist with the determination of drilling more than one relief well.