Active heating technologies can be applied to subsea pipelines to tackle challenging reservoir flow assurance constraints that could take place during production shut down and normal subsea field operation (i.e. hydrate, gelling, wax and/or high oil viscosity). Implementation of active heating to subsea pipelines enables i) field architecture simplification and ii) long subsea tie-backs. The Electrically Trace Heated Pipe-in-Pipe (ETH-PIP) is a standard reelable PIP system enhanced with up to 4-off trace heating cables and 2-off fiber optic (FO) cables, for temperature monitoring purposes, spiraled against the inner pipe and covered by high thermal performance insulation allowing a high thermal system efficiency. The high thermal efficiency combined with a primarily resistive electrical system makes the ETH-PIP the most energy efficient active heating technology. Long power heating/transmission line can be described by the fundamental parameters resistance/inductance of conductor and capacitance/conductance of insulation. The analysis of the overall heating system can be assessed using three alternative models: i) the most simple and compact RL model where only total resistance and total inductance of line is included, ii) more advanced RLC model where the total capacitance of insulation is additionally included and iii) the most advanced distributed RLGC (resistance, inductance, conductance, capacitance) model where total length of line is modelled as a chain of shorter RLGC segment lengths. The accuracy of each model depends on multiple aspects such as: heating/transmission line parameters, required heating power, total length of line, mode of operation, environmental conditions, etc. The proper and careful selection of the appropriate model to ensure effective computation and results accuracy is paramount. The paper includes the detailed description of each heating/transmission line model. Additionally, each model is illustrated on a set of theoretical examples.
The study focuses on the in-place hydrodynamic behavior and Flow Induced Response of a novel design of Free Standing Riser (FSR) system tensioned by a ‘Flat-Buoy’. The paper presents results review of both Experimental and Numerical approaches initiated in the framework of a comprehensive Research & Development program. Experimental and numerical study conclusions converge on the excellent hydrodynamic Stability of such FSR system. First, wind tunnel campaign, based on Reynolds similitude, has focused on the flow features over the fixed Flat Buoy. No Vortex Shedding has been clearly highlighted. Moreover, results have pointed out a more pronounced dependence of the hydrodynamic coefficients to the flow incidence than to the Reynolds number. Secondly, basin model tests, based on Reduced Velocity similitude, have highlighted the stability of such scaled FSR system concluding to maximum Cross-Flow and In-Line amplitude such as A/D<0.35 (A represents the amplitude and D the Buoy diameter). In parallel, hydrodynamic stability has been investigated Benchmarking Computational Fluid Dynamic (CFD) methods. Preliminary validation steps have pointed out ability of such CFD approaches to globally predict both Wind Tunnel and Basin Test results. Finally, extending CFD and Fluid Structure Interaction (FSI) modeling to full-scale configuration, stability of the FSR tensioned by a Flat-Buoy has been proved.
Subsea oil and gas production can utilize a number of technical solutions to ensure efficient and cost- effective operation. There are two main technologies applied to address flow assurance challenges in case of particularly long tieback reservoirs: subsea active heating and subsea boosting. The production from distant reservoirs with challenging flow assurance conditions may require application of both mentioned systems. In such case, one challenge relies on the selection of a power supply infrastructure for both systems, considering all possible optimization aspects. In the conventional approach, the implementation of both systems is realized independently. Subsea active heating system and subsea boosting system are supplied and monitored from topside by the separate power strings. However, the development of subsea technologies allows to review the approach and consider integration of both systems, enabling reduction of topside infrastructure for general cost savings. The purpose of this article is to present the integrated system composed of Electrically Trace Heated Pipe in Pipe (ETH-PIP) and subsea boosting pumps where Variable Speed Drive (VSD) is required. The role of both system is shortly presented. Next, a proposal of an integrated power system for subsea heating and boosting is illustrated and discussed on a case study example. The analysed field layout is characterized by a long tie-back to a production facility where both subsea boosting and active heating systems are necessary operating in the relevant power modes. The results of analysis allow to conclude that the presented solution can be valuable alternative to traditional approach of complex subsea system topologies.
The Electrically Trace Heated Blanket (ETH-Blanket) is a new offshore intervention/remediation system currently in development by TechnipFMC for the efficient remediation of plugs due to hydrates or wax in subsea production and injection flowlines. The ETH-Blanket consists of a network of heating cables placed underneath an insulation layer which is laid onto the seabed above the plugged flowline. By applying electrical power to the cables, heat is generated by Joule effect which warms up the flowline content until hydrate dissociation or wax plug remediation through softening or complete melting. As part of a Joint Industry Project (JIP) between TechnipFMC, Shell and Total, full-scale thermal testing of an ETH-Blanket prototype was carried out in Artelia facilities (in Grenoble, France). This testing was performed to verify the capability of the ETH-Blanket system to increase the temperature of the fluid inside a pipe sample above a target temperature (hydrate dissociation temperature or wax disappearance temperature) for various conditions. The impact of lateral misalignment of the ETH-blanket on the pipe and of the pipe burial depth were studied. Moreover, the tests were carried out on two pipe samples, with different designs and insulation properties. In parallel, CFD models of the test set-up were built to replicate the thermal behaviour of the ETH-Blanket. The combination of these models with the measured heating efficiency of the prototype allowed characterising the performances of the system in real subsea conditions. This paper presents the description of the full scale thermal testing conditions. Results of the different tests are detailed and the impact of the different parameters on the ETH-Blanket thermal performances are assessed, focusing on natural convection effects, thermal losses and the overall data gathering process.
This paper provides an overview of the work completed to design, qualify, manufacture and integrate electrical and optical double barrier penetrators with the Electrically Trace Heated Pipe-in-Pipe (ETH-PiP) as part of the Neptune Energy Fenja Development Project. Typical subsea penetrator systems in the oil and gas industry, such as pumps, compressors and X-trees are designed to be retrievable, to enable periodic refurbishment as well as providing the option for replacement, if required. However, the ETH-PiP architecture makes retrieval of system components complicated and uneconomical. Both the electrical and optical dual barrier penetrator system designs have to comply with a set of ETH-PiP specific criteria, such as to be maintenance free over a 25 years service life, prevent water ingress to the pipeline, provide pressure containment for operational media (in an unlikely scenario where the inner pipe bursts) and guarantee minimum footprint to allow an optimum integration onto the Pipeline End Termination (PLET) structure. In addition, the electrical system has to comply with a medium voltage rating (i.e. 5.0/8.7kV) to ensure a wide range of possible ETH-PiP architectures. The optical system has to maintain insertion loss below 0.5dB and a back reflection below -45dB to comply with the stringent requirements of distributed temperature monitoring sensor system over long distances. The qualification program of the electrical dual barrier penetrator system was performed in accordance with IEC 60502-4 and SEPS-SP-1001. A tailor made sequence had to be developed for the optical system, based on guidance from SEAFOM-TSD-01, considering that the system partly falls outside the associated standard application. The electrical dual barrier penetrator system qualification sequence was developed in two phases; firstly, the electrical transition contacts in the feedthrough chamber were qualified in accordance with IEC 60502-4 and secondly, four electrical double barrier penetrator prototypes were manufactured to allow the completion of the qualification sequence defined as per SEPS-SP-1001. The optical dual barrier penetrator system qualification employed the manufacturing of three prototypes to execute the pre-defined qualification sequence. Following the individual qualification of the electrical and optical dual barrier penetrator systems, subsequent welding and full-scale assembly trials were performed to ensure that the maximum allowable temperatures within the penetrators would not be exceeded during welding to the PLET, and to proof test the assembly procedure. Electrical verification testing was also undertaken during these trials to verify that the integrity of the penetrators had been maintained during the assembly and that the PLET arrangement did not give rise to any electrical stresses that could result in excessive deterioration of the penetrators. Integration of the four electrical and two optical dual barrier penetrator systems to the project PLET was completed in Q1 2020, with the actual subsea installation of the first ETH-PiP section including the PLET in Q3 2020.
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