Ship collision with offshore platform is one of the rare events in oil and gas industry and generally associates with huge physical and financial damage. An oil tanker collided with a jacket in the South Pars gas field and caused tough conditions for the operator to restore the jacket and wells to their original state. The crucial stages after the accident were killing a perforated well, wreck removal and cutting the wells below the section they had been bent or distorted and finally the wells abandonment by cementing coiled tubing operation on a dynamic positioning barge. This paper focus on engineering design of a platform for coiled tubing injector head and pressure control equipment on the barge as well as finding a way that coiled tubing string pass through the gap between the platform and the underwater cut point of wells. For this purpose, a deck was proposed to build on the barge having a heavy duty flexible steel pipe extended from the deck to inside the wells cut point. Various measures should be implemented to design this structure in order to have an operational safe method. The structure had to have sufficient strength to resist the forces applied on it especially during the operation in the predominant weather condition of Persian Gulf in the monsoon season. Therefore, a comprehensive study was conducted to determine stresses applied on the structure subjected to different types of wave velocities using finite element method. The engineering design and simulation led to construct the proposed deck extending over the port side of the barge and elevating between the main deck and mezzanine deck with a long 4" flexible steel pipe at its bottom. In order to verify the engineering design and simulation before the operation, the structure load tested up to 40 metric tons. This paper will peer over the challengeable engineering design of the deck for coiled tubing well abandonment under the condition of insufficient offshore facility.
Cement behind casing, as the critical component of well integrity is a real challenge all over the world. Despite the efforts drilling operators and service providers dedicate to this phase of well construction in the South Pars gas field, final set cement quality does not establish zonal isolation in 9 5/8" casing and 12 1/4" openhole section. In order to study this issue, twenty-four wells have been analyzed based on theoretical analysis, close hands-on operations and track record of cementing in the field. Data were acquired from the daily drilling reports, data acquisition system of cement units, mud logging records, daily mud reports, cement slurry laboratory test sheets and wireline log records. The main effective factors on cement quality have been studied in four groups namely: well preparation, slurry design, mud removal and post-cementing practices. Good and poor quality cement in all wells have been compared with actual field parameters using a cementing displacement simulator software. Structural stress model has also performed for one of the wells whose cement was prone to be impacted by post cementing practices. Results have been obtained over one year of parallel laboratory testing, field experience, simulation and evaluation. The simulations results illustrate turbulent flow is not practical for cementing of this section and effective laminar flow technique shows an efficient alternative, however all criteria of this technique could not have been fully met due to some well restriction. The results reveal mud removal parameters in terms of casing centralization have significant effects on the final cement quality in this field. Cement quality devastation persisted even in cases where the cement slurry properties were modified and used in four wells in order to evaluate slurry design impact degree on final set cement quality. The stress model results illustrate that imposed stress on the well exceeds the compressive and tensile strength of the cement sheath. These results reinforce the idea that mud removal and post cementing practices govern the cement quality in the field. This paper is a comprehensive study of all effective parameters on cement quality in 9 5/8" casing cementing and highlight the main sources of cement quality devastation in the field and it can be used as a guideline for cementing similar cases around the world.
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.
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