Cementing Under Pressure in Well-Kill Operations: A Case History From the Eastern Mediterranean Sea
- Kristian Johnstone (Rashid Petroleum Co. RASHPETCO/British Gas) | Alex Gill (Rashid Petroleum Co. RASHPETCO/British Gas) | Tom Conlon (Rashid Petroleum Co. RASHPETCO/British Gas) | Mahdy Bahr (Rashid Petroleum Co. RASHPETCO/British Gas) | Syed Arshad Waheed (Halliburton Ltd.)
- Document ID
- Society of Petroleum Engineers
- SPE Drilling & Completion
- Publication Date
- June 2008
- Document Type
- Journal Paper
- 176 - 183
- 2008. Society of Petroleum Engineers
- 1.14 Casing and Cementing, 7.2.3 Decision-making Processes, 2 Well Completion, 4.3.1 Hydrates, 1.6.9 Coring, Fishing, 3 Production and Well Operations, 1.7 Pressure Management, 2.2.3 Fluid Loss Control, 4.6 Natural Gas, 2.2.2 Perforating, 1.3.2 Subsea Wellheads, 4.5.10 Remotely Operated Vehicles, 1.6.1 Drilling Operation Management, 3.2.2 Downhole intervention and remediation (including wireline and coiled tubing), 1.10.1 Drill string components and drilling tools (tubulars, jars, subs, stabilisers, reamers, etc), 1.14.3 Cement Formulation (Chemistry, Properties), 1.6.1 Drilling Operation Management, 1.7.5 Well Control, 1.6.11 Plugging and Abandonment, 1.10 Drilling Equipment, 1.6 Drilling Operations
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Well control can be an unpleasant experience. In its initial stages the problem often appears unconquerable and weeks can pass without progress.
This paper is about the successful abandonment of such an episode of well control, in deepwater (i.e. greater than 300 m water depth), that was initially suspended with a closed-in subsea BOP. The BOP held in place a sheared 5-in. drillpipe that had been intermittently blowing dry gas and formation cuttings to the rig floor for 20 days.
The objective of the well-recovery operations was to re-enter the well and properly abandon it without creating another uncontrolled situation. All operations were to be conducted in compliance with HSE protocols.
It was paramount to have total control of the well at all times necessitating two BOP stacks. This contingency resulted in the suspension of a heavy load on the seabed, subject to excessive bending moments during bad weather. The well head arrangement was essential but the time loss caused by weather conditions was becoming intolerable. New and innovative plans made during the well-control operations cut 3 to 4 weeks of uninterrupted operation down to 5 days of operation. Cementing under pressure was the key abandoning solution. Several scenarios were drawn up for this eventuality and this paper elaborates on the decisions, choices, and solutions made during the final abandonment operation.
Pre-Intervention Status of Well. A blowout occurred on the exploration Well A while drilling the 12 ¼-in. section, after having set the 13 3/8-in. intermediate casing. The rig crew was safely evacuated. After the initial blowout incident, the well flowed up the annulus for 4 days before the remotely operated vehicle (ROV) activated closure of the lower pipe variable bore rams (VBR) on the seabed (Fig. 1). Flow of dry gas and formation continued intermittently up the drillstring for a period of 20 days until the ROV activated the blind-shear ram (BSR). The well was left alone thereafter for several months while a recovery plan was put in place. During this time the seabed was monitored regularly and revealed gas leaking from the closed BSR.
It was estimated that over 10,000 bbl of equivalent mass (solids) exited from the drilled hole section during the blowout. Therefore, whether to expect a large gas-filled void downhole or a collapsed wellbore owing to the unconsolidation of the formation caused by the large amount of rock removal was uncertain.
Because the status of the openhole section was unknown and gas was possibly breaching out of the 13 3/8-in. casing shoe, simply bullheading kill-weight fluid down the wellbore to control the well might not have been effective. Not only would vast quantities of mud be required to fill the void, but removal of such a large volume of gas would be an arduous and time-consuming operation with no guarantee of success. The well-intervention philosophy was therefore focused on achieving isolation within the 13 3/8-in. casing shoe. Kill-weight mud would first be pumped into the formation to assess whether it could at least control the wellhead pressures.
Well Intervention Objectives
The primary objective of the recovery phase was to isolate both drillpipe and annulus from the blowout zone within the 13 3/8-in. casing, facilitating long-term wellbore abandonment in a manner that posed no risk to personnel or allowed further uncontrolled release of gas. The closed-in BOPs were also to be recovered from the seabed. In the event that the intervention campaign was not successful, the base case was to abandon the intervention operation and proceed with drilling a relief well and intersecting the subject well for a well-kill operation.
It was understood at the outset that an entry to a pressurized wellbore would be attempted and as a result the first course of business was to implement a dual-barrier policy wherever possible. Once well control at the seabed was guaranteed, the well would be re-entered and the existing "cut" pipe would be dressed off with a milling assembly, allowing a tie-back string run to have full connection to surface. This wellbore configuration would then allow pumping of fluids or carrying out activities such as perforating the drillpipe at an optimum depth, isolating the drillpipe with a bridge plug, and retrieving the pipe for cement abandonment. Fig. 2 illustrates the final configuration of the abandoned well. Coiled tubing (1 ¾-in.) would also be used for cleaning out the drillpipe if it was found to be plugged with debris at a depth shallower than the 13 3/8-in. casing shoe. It was estimated that the well-abandonment operation would take approximately 5 weeks (ideal time) to complete.
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