IOGP SAFETY ALERT
BREAK OF FORMATION IN A NARROW MUD WEIGHT WINDOW DRILLING. WELL CONTROLLED USING THE MODIFIED WAIT AND WEIGHT METHOD
|Incident Date: — Time: —|
|Type of Activity: Drilling, workover, well services|
|Type of Injury: —|
|While drilling the 18 1/8” x 22” hole at 2721 mMD, (2717 mTVD) using pressure ramp drilling procedures with 11.5ppg mud weight (MW). The driller observed a 1% increase in flow, followed by pit volume totaliser (PVT) increase. After picking up off bottom with pumps running, a 7-8 barrel gain was observed. The well was then shut in with total pit gain of 14 bbls. Choke pressure increased to 109 psi over 5 min and subsequently broke down to 69 psi. The drill pipe pressure (DPP) remained steady at 60 psi (Non-ported float in string, did not bump float during shut in period to obtain actual shut in DPP due to casing pressure drop during initial shut in). The shut in casing pressure (SICP) then slowly built back up to 109 psi over approx 90 mins, and then suddenly dropped from 109 psi to 36 psi indicating formation break-down for second time. SICP stabilised at 36 psi for several hours while developing plan forward and consulting well control team in office.
Started kill operations using modified weight and wait method: zero choke safety margin, calculated kill mud to be 11.75 ppg. Initiate well kill while pumping 11.75 ppg surface mud weight (SMW) kill mud including first 200 bbls with 50 ppb loss circulation material (LCM) at 20 spm. Initially encounter 75% losses at 20 spm then observe partial returns, reduce rate to 10 spm and observe improving trend in return flow. As circulation continued with LCM entering open hole, able to resume full circulation at 10 spm and continue displacing annulus to kill weight mud.
There were no injuries during this incident and the well was successfully brought under control. Severe subsequent losses led to plug back and sidetrack.
What Went Wrong?:
Corrective Actions and Recommendations:
Findings were shared with the rig contractor and the offshore team.
safety alert number: 285
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