Abstract
Restoration of the cap rock to ensure lateral isolation as barrier is crucial to avoid any contamination of shallow aquifer(s). As per federal Law shallow aquifer shall be protected from hydrocarbon and water bearing formations during entire well life cycle. Attention should be paid to the sub-surface barriers starting from design of a new well till the phase of permanently plugged and abandoned (P&A) where the intention of never being re-use or re-enter the well.
Keeping in mind the risk of contamination of aquifers a detailed requirement has been established to ensure the isolation between water or hydrocarbon formation(s) and shallow aquifer(s) during design and construction phases by achieving integral annulus cement.
During the operation phase the barriers are monitored and validated, in case of abnormality diagnostics are performed to mitigate the risk.
At the end of well life cycle, it must be permanently P&Aed. A documented process has been implemented with enough, type and position of well barriers to prevent undesired hydrocarbon flow from reservoir to the aquifer or to surface.
A robust well integrity management system has enabled the delivery of high quality of wells. This includes proper monitoring and verification of barriers during the well construction process.
This has ensured protecting shallow aquifer from any source of inflow thereby complying to the local regulations that requested to first detect source of inflow, hydrocarbon formation that shall be protected. at the time of P&A the sealing formation in between them shall have a good cement in addition to that wellbore shall be plugged with a material that provide sealing, bonding and durability as the well will not be reentered. The process ensures capturing information for the well, right from the construction stage, any changes happened during the well intervention and till the P&A stage.
During the operations stage the barriers are monitored and tested to ensure that they are performing as required.
Implementing the robust process has ensured that the contamination of the shallow aquifers is minimized and ensured no loss of valuable hydrocarbon to these aquifers.
The process flow has been based to ensure compliance with the local Federal law and build on the international practices with inputs from local condition and lesson learnt. The process also has inputs from the concession holders to make the process cost effective and robust.
