Negative Other LL with DNO

Oselvar (A-1 H, A-2 H, A-3 HT2) – P&A

What actions are required:

d

PSA Finding

• Deviation from internal guidelines and NORSOK stating that 4 double barriers were needed to plug sufficiently but used only 2 barriers.
• Uncertainties regarding the determination of flow potential zones in addition to fluid type, density, and testing, was not detailed clearly.
• The process surrounding the “flow potential determination” testing was unclear as to what determines and approves if there is a risk of flow or not.
• Insufficient qualification of Hordaland fm. as barrier, through formation leakage testing.
• CBL logs proved only 10m qualified 13 3/8″ casing cement, not 30m as NORSOK states.
• Old filing system resulting in information and lessons from Kvitebjørn PP&A being hard to locate for future plugging.
• Only one pressure test was performed to verify the use of Hordaland as a barrier element outside 13 3/8″ casing and in addition it was not over a longer interval (30m) so there were uncertainties attached to the length of the barrier.

PSA Comments

Risk/oppertunity: • Lean P&A – reduced no. of barriers.
Comments: • Statoil could prove through simulations and studies that the flow potential in the overburden would not demand additional barriers and that 2 were sufficient for the whole well. However, there were a lot of uncertainties related to determining fluid type, density, and formation permeability in these flow simulations.