There are several challenges associated to the pre-salt development at the Santos basin, such as long distances from the coast, low temperature reservoirs, high pressures, high water depth, among others. Additional aspects contributing to the complex production scenario are related to fluid characteristics and flow assurance. In particular, the high CO 2 content in the dissolved gas is an important characteristic that should be also analyzed, because CO 2 is not only a heavy component, when compared to lighter components present in the gas phase, but has also a high Joule-Thomson coefficient. This affects pressure drop and specially the mixture cooling behavior during decompression. The cooling effect is expected to be strong at high production rates. Thus, the objective of the present work is to evaluate these effects under present and future production scenarios, taking into account increasing CO 2 contents due to re-injection strategies.Two different field configurations were investigated and a variety of operating conditions was used, along with real and model fluids ranging from 5% to 50% CO 2 content (molar basis). PVT data for the model fluids with high CO 2 content were generated by a simulated swelling test with CO 2 of an existing mixture with lower CO 2 content. A parametric study was carried out aiming at investigating primarily the total pressure and temperature drop in the pipeline when the total CO 2 content of the mixture is increased. Furthermore, variation of the fluid properties along the well, flowline and riser was evaluated. Results are also discussed in view of the impact of increasing CO 2 contents and the challenges experienced during simulation of such flows.
Clean-up operations of oil and gas wells are carried out when newly drilled wells are started up and tested for the first time. An optimal clean-up can be important for the production properties of complex wells. As the clean-up process is highly dynamic in its nature, a conventional steady state approach for simulation is of limited value. In the current work a clean-up case study of a dual branch long horizontal well at the Åsgard field was undertaken using a commercial transient multiphase flow simulator. Eleven production zones located along the main and lateral horizontal wellbores were modelled in detail with separate zone productivities (obtained from petrophysical data analysis) and different numbers of sand screens with inflow control device (ICD) in each zone. Simulations of different clean-up scenarios were performed prior to the real operation and the results were used to plan the clean-up. The simulations supported the decision to clean-up both the lateral and the mainbore simultaneously in one operation. The operational data from the clean-up operation were compared to the model results and valuable data for tuning of the model were obtained. After tuning a good match between the simulation results and the operational data was obtained, also quantitatively. The study confirmed that dynamic simulations can be a useful tool to predict and understand the behaviour of a clean-up operation. 1. Introduction The Åsgard field development is located in the Haltenbanken area off mid-Norway and comprises three fields - Smørbukk, Smørbukk Sør (South), and Midgard. The field was developed in the late 1990'ies with a subsea production system and two production facilities, Åsgard A (FPSO) and Åsgard B (gas processing platform). In addition a storage and offloading vessel (Åsgard C) receives the liquid production from Åsgard B as shown in Figure 1.
Frigg Cessation was the first major North Sea field decommissioning project. The project was a pioneering effort with a steep learning curve. The Frigg field platforms included both steel jackets and concrete gravity based structures with a total steel weight to be removed of about 87 000 tons. The paper deals with three aspects of the job seen from the contractor's point of view:The execution plan and methods developed prior to contract award.Unforeseen issues and consequent changes that had to be dealt with in order to execute the work.Lessons learned and key recommendations to operators and contractors alike. The Frigg Cessation project was completed in 2010, two years before contractual completion date. Scope of Work and Platform Overview The scope of work consisted of management, engineering and procurement of all necessary labour and plant resources to prepare for.the safe removal and disposal of onshore, including the safe handling and disposal onshore of hazardous waste, six topsides and three jackets, in total about 87 000 tons of steel. The concrete structures were not part of the removal scheme and were left in place.
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