# EXAMPLE WELL KILL CALCULATION ANSWERS

## Well control from a floating vessel example answers

**The Severnoye Siyaniye semi-submersible drilling rig in Yuzhno-Kirinskoye field**

**At first glance, the SCIP is higher than the MAASP and there is a risk of the shoe breaking down. However, it should be remembered that the choke line is seawater (0.445 psi/ft) since the gradient of the mud is:**

**13.0 x 0.052** = 0.676 psi/ft

**True SICP ** = 1375 – 1800 x (0.676 – 0.445)

= 1375 – 415

= **960 psi**

**Therefore, the MAASP is not exceeded**

**The approximate gradient of the influx can now be calculated from the formula shown above:**

**G influx** = **G mud** minus **SICP **minus** SIDPP** divided by the **Height of the influx**

**Height of the influx **= **Pit gain** divided by **Annular Capacity**

= 30 ÷ 0.0836

= **359 ft**

**The influx can therefore be assumed to be gas and problems relating to gas migration and expansion should be anticipated.**

**If it is decided to kill the well at 3.5 bbl/min and to include the choke line pressure drop in the initial circulating pressure, what would be the final circulating pressure be? No other safety factors are to be used. **

**Using the calculation above, mud weight required to kill the well (W2) is given by:**

= **W1** plus **SIDPP** divided by **Depth** times by **0.052**

= **13.0** plus **750** divided by **8800** times by **0.052**

= **13.0** plus **1.6**

= **14.6 ppg**

**Looking at the kill mud calculation using the formula above for the well:**

**The formation pressure** is (**8800** x **13** x **0.052**) + **750** = **6698.8 psi **(calculated)

A tendency to round off calculations is considered the norm; we must look at the Kill Mud with a little more safety in mind.

**Kill mud = SIDPP **divided by **TVD** (true vertical depth) x **0.052** plus **13** ppg

**W2** = **750** divided by **8800** times by **0.052** plus **13** ppg

= **1****4.64 ppg** (rounded up to two places after the point)

**Hydrostatic Pressure with rounding off to: 14.6 = **6680.96 (**underbalanced**)

**14.63 ** = 6694.68 (**underbalanced**)

** 14.638** = 6698.34 (**underbalanced**)

** 14.64** = 6699.26 (**on balance**)

**A more realistic weight would be 14.7 ppg this would give a very slight overbalance; **= **6726.72 psi** = (**+27.92 psi** **overbalance**)

## Using Riser PSCR vs Choke Line PSCR for Well Kill Calculations

**Many people who work through Subsea Well Control calculation for the first time, often ask why the slow circulating pressure (SCR) through the riser is used, when the well is circulated through the choke line, and choke line slow circulating pressures is not included?**

**The following calculations are with the choke line friction losses included; this will show that the wellbore is going to be over pressurised by this choke line friction value.**

**So, adjustments must be made; To enable the friction to be released through the choke.**

**Compare these pressures when calculating ICP and FCP**

**USING RISER SCR (psi)**

**ICP** = **SIDPP** add **SCR**

= ** 750 **add **800**

= **1550 psi**

**FCP** = **800** times **14.7** divided by **13.0**

**FCP** = **901 psi**

**USING CHOKE LINE FRICTION (psi)**

**ICP** = **SIDPP** add **SCR **add** CLFL**

= ** 750 **add **800 add 450**

= **2000 psi**

**FCP** = **1250** times **14.7** divided by **13.0**

**FCP** = **1414 psi**

**It can be noted from the two examples, if the choke line friction loss pressure is used for the kill calculations, the ICP and FCP will over pressure the well by 450 psi at start-up, and 513 psi at FCP.**

**This extra pressure could cause formation damage.**

**It is also unnecessary to hold this extra CLFL pressure in the well, as, in using the riser SCR pressure for our calculations, we can then back off the value of CLFL from the well by auto- choke manipulation (casing gauge) during the start-up procedures.**