A Methodology for Finding the Optimal Location of the Processing Facility in Offshore Oil and Gas Developments
Master thesis
Permanent lenke
http://hdl.handle.net/11250/2615711Utgivelsesdato
2017Metadata
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Sammendrag
To ensure a sustained and economically feasible production of hydrocarbons in offshore oil and gas developments, it is essential that the oil recovery technique, location of the processing facility and the pipeline design is optimized according to flow assurance considerations. With cost and flow assurance as the main considerations, the aim of this thesis has been to develop a methodology for finding the optimal location of offshore processing facilities.
The methodology has been developed as an optimization algorithm that comprises the use of asimple pipeline design model along with cost models and surrogate models. The steps of themethodology have been formulated in a general fashion to be applicable for different types ofoffshore developments. The optimization algorithm seeks to minimize a cost function dependenton pipeline and umbilical costs provided that constraints in the fluid pressure, temperatureand velocity are satisfied for all production pipelines to avert flow assurance issues such as hydrate/wax formation and slugging. The constraint parameters are described by surrogatemodels based on data generated in pipeline simulations (Beggs & Brills (1979), Aspen HYSYS).
Optimization formulations, models and parameters have been implemented in Matlab for theevaluation of two cases based on the offshore development of the oil fields Alta, Gohta and Filicudi in the Barents sea. All the steps in the optimization procedure have been thoroughly explained, and includes running the required pipeline simulations, building the surrogate models, evaluating the accuracy of the models, formulating the optimization problems and finally evaluating the optimization results. Both cases consider the development of Alta, Gohta and Filicudi as a joint development with all fields being tied to an FPSO. The case study evaluates the effects of using two different oil recovery techniques, with Case 1 benefiting from the use of gas lift at all three oil fields, and Case 2 benefiting from the use of subsea boosting at all fields.
The results of both case studies predict the optimal FPSO location to be as close to the Alta oil field as possible. For Case 1, the FPSO location is predicted to be approximately 7 km off from Alta, while the FPSO location for Case 2 is predicted to be right next to Alta. The fluid temperature and pressure for both Alta and Gohta were predicted to be well above the minimum limit of 20oC and 30 bar, respectively. Consequently, sensitivity analyzes were conducted on the maximum allowable velocity in the production pipelines. The analyzes show that the costs of the production pipelines could be reduced for both fields by allowing a higher maximal velocity at the expense of adding erosion allowance to the pipeline thickness to make up for higher erosion rates. The resultsfrom both cases imply that Filicudi is the most challenging field to produce from considering flow assurance aspects. The temperature and pressure of Filicudi are the lowest of the three oil fields, and the low velocity prediction from the optimization results suggest that production from this field is a major challenge for both the oil recovery techniques that were evaluated.