Anticipating and controlling transient response is a critical design activity for ensuring both safety and integrity of the operational subsea system. Predicting transient effect, commonly known as surge pressure, is of high importance for offshore industry. It involves detailed computer modelling that attempt to simulate the complex interactions between flowline and fluid, aiming at efficient flow assurance and consequently flowline and riser systems integrity. Bijupirá and Salema water injection systems, located in the Campos Basin, offshore Brazil, have been operating since 2003. The operational teams have raised concerns, whether the system is adequately designed to protect the subsea system against possible surge pressures during the event of sudden closure of a valve. Researches, referred to transient effects, clarify that is necessary to evaluate the system performance under current and desired operating conditions. The main goal of this paper is to predict the surge pressure in flowline and riser of the water injection system due to valve closure. A supplemental simulation has been performed in order to evaluate conditions that would keep the water injection surge pressure below Maximum Allowable Operating Pressure (MAOP) of the subsea equipments. According to the simulations results, the maximum surge pressure occurs throughout the manifold and jumper region, and the worst case occurs when all valves are simultaneously closed in Bijupirá and Salema production fields. The maximum surge pressures verified in simulations may reach values greater than the operating desired pressure, which may cause damage to the water injection system integrity. In order to avoid surge pressures greater than MAOP, which corresponds to 255 bar, the simulations indicated that when a pressure of 230 bar occurred on the turret, injection flow rate should not exceed 12000 bbl/day. Therefore, conventional techniques to solve complex problems in this area need to be improved, and computational simulations may contribute to establish the operating control system and guarantee its integrity during operating life.
Predicting transient effects, known as surge pressures, is of high importance for offshore industry. It involves detailed computer modeling that attempts to simulate the complex interaction between flowline and fluid in order to ensure efficient system integrity. Platform process operators normally raise concerns as to whether the water injection system is adequately designed in order to be protected against possible surge pressures during sudden valve closure. This report aims to evaluate the surge pressures in Bijupirá and Salema water injection systems due to valve closure, through a computer model simulation. Comparisons among the results from empirical formulations are discussed and supplementary analysis for the Salema system was performed in order to define the maximum volumetric flow rate that the design pressure was able to withstand. Maximum surge pressure values of 287.76 bar and 318.58 bar, obtained using empirical formulations in Salema and Bijupirá respectively, have surpassed the operating pressure design, while the computer model results have shown the highest surge pressure value to be 282 bar in the Salema system.
Nowadays, anticipating and controlling transient response is a critical design activity for ensuring both safety and integrity of the operational subsea system. Predicting transient effect, commonly known as surge pressure, is of high importance for offshore industry. In order to determine the installation of protection equipments to avoid surge pressure effects, the operational teams have raised concerns, whether the system is adequately designed to protect the subsea system against possible surge pressures during the event of sudden closure of a valve. Researches, referred to transient effects, explain that is necessary to evaluate the system performance under current and desired operating conditions. The main goal of this paper is to predict the surge pressure during unforeseen closure valves at Refrigerated LPG and Gasoline (C5+) pipeline systems. In these systems the valves are located downstream the flowlines. Detailed computer modeling attempts to simulate the complex interactions between flowline and fluid, aiming at providing efficient flowline system integrity. These models are based on Transient Methodology which is defined for a set of nonlinear partial differential equations that relate fundamental variables with pressure head and flow velocity. The solution of differential equations has been carried out by Finite Difference Method that transforms these equations into characteristic equations. These can be accurately solved through high-speed digital computers. Flowmaster, Chicago, USA, was the software used to develop the analysis models. The software offers an advanced graphical interface to build networks and resultant graphics. The results from Flowmaster have been validated through a defined methodology that applies the Characteristics Method based on Wylie and Streeter assumptions. Simulations considering the fluid as gasoline have shown a sudden damping of pressure wave when the valve closure time was 10 seconds, leading to the restoration of the initial flow conditions. The analysis using the Method of Characteristics, however, does not exhibit this sudden damping, although a gradually reduction of fluctuations around the initial pressure are observed. The transient analysis through Flowmaster for Refrigerated LPG leads to a pressure envelope that shows a change of the flow direction triggering a cyclical process until the restoration of the initial operational conditions.
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