Alternative Method to Achieving Rock-To-Rock Barrier for Plug and Abandonment Using Hydro-Mechanical Perforating Tool

This paper outlines our experience with a hydro-mechanical perforating tool in the abandonment process of a Chevron exploration well in the Mediterranean Sea. The objective of the abandonment was to safely secure the well in accordance with industry standards and local regulatory requirements. The abandonment plan and verification methods were designed to ensure full zonal isolation of formation fluids within the well and from the seabed. Hydro-mechanical perforating techniques were employed to successfully execute the objective. To isolate potential flowable units properly, the abandonment plan was broken down into three zones. The first, or lower zone covered the open hole with cement plugs across Oligocene age sands to prevent crossflow and secure reservoir integrity. The next, or middle zone, covered the Miocene age gas sand behind 14" casing. It included two verified barriers (primary and secondary) that were placed to ensure the isolation of the uncemented Miocene gas sands behind the 14" string. The primary barrier was established by placing 150-m (MD) of cement above the Miocene sand within a hydro-mechanically perforated interval of 14" casing and was verified to provide a rock-to-rock barrier via a bradenhead block squeeze. The secondary barrier was established via a Cut & Pull 14" operation and placement of a rock-to-rock cement barrier with a mechanical base. The last, or upper abandonment zone, covered shallower sands and included two independently verified 100-m barriers placed via the block squeeze method with cement plugs leveraging 200-m of explosive free, mechanical perforations. In this paper we will share best practices and lessons learned when using a hydro mechanical perforation tool in a complex deepwater P&A operation.