Abstract
Among all risks that may posed to offshore platforms, one of severest is ship collision that associated with huge physical and financial damages. An oil tanker collided with a jacket on the South Pars gas field in 2015. The operator faced the challenges of killing a perforated HPHT gas well, wreck removal of platform, plug back and securing the remained wells that all were drastically damaged. The operation had to deal with harsh offshore weather conditions, lack of offshore facilities, put a balance cement plug using coiled tubing in the HT brine medium, lack of a straight path for coiled tubing run in hole, and had to provide an operational safe method while keeping the highest quality.
A dynamic positioning multi-purpose barge used in this operation in conjunction with a new designed deck for well intervention. A flexible hose connected from the designed deck bottom to inside the 10 3/4″ casing cut entrance, to prepare a straight path for coiled tubing string.
A gas tight and right angle set cement slurry designed in order to prevent unpredicted gas migration. The coiled tubing cementing operation and fluids hydraulic designed to have uncontaminated and stable slurry column at the end of the displacement in the brine medium. This goal achieved by using compatible high viscous pill and mud push fluids in bottom and top of cement slurry column to prevent instability, fingering, falling downwards, and consequently contamination of cement slurry with brine. The displacement and pull-out-of-the-hole method also designed in such a way to minimize the risk of flash setting of cement slurry in high temperature brine medium. This method prevents sticking of coiled tubing string while its maintain the stability of fluids interfaces.
This paper is a detailed description of all the operational and engineering challenges after the collision and the methods to overcome them except wreck removal and tie back phases. The advantages of using these novel concepts resulted in an operational safe method for salvage operation and securing the wells. This paper can be used as a guideline when encountered with such rare situation.
