Modelling of a Gas Cap Gas Lift System

Imperial Users onl

Optimal control of the heave motion of marine cable subsea-unit systems

One of the key problems associated with subsea operations involving tethered subsea units is the motions of support vessels on the ocean surface which can be transmitted to the subsea unit through the cable and increase the tension. In this paper, a theoretical approach for heave compensation is developed. After proper modelling of each element of the system, which includes the cable/subsea-unit, the onboard winch, control theory is applied to design an optimal control law. Numerical simulations are carried out, and it is found that the proposed active control scheme appears to be a promising solution to the problem of heave compensation

Determination of stress state in deep subsea formation by combination of hydraulic fracturing in situ test and core analysis: A case study in the IODP Expedition 319

[1] In situ test of hydraulic fracturing (HF) provides the only way to observe in situ stress magnitudes directly. The maximum and minimum horizontal stresses, SHmax and Shmin, are determined from critical borehole pressures, i.e., the reopening pressure Pr and the shut-in pressure Ps, etc, observed during the test. However, there is inevitably a discrepancy between actual and measured values of the critical pressures, and this discrepancy is very significant for Pr. For effective measurement of Pr, it is necessary for the fracturing system to have a sufficiently small compliance. A diagnostic procedure to evaluate whether the compliance of the employed fracturing system is appropriate for SHmax determination from Pr was developed. Furthermore, a new method for stress measurement not restricted by the system compliance and Pr is herein proposed. In this method, the magnitudes and orientations of SHmax and Shmin are determined from (i) the cross-sectional shape of a core sample and (ii) Ps obtained by the HF test performed near the core depth. These ideas were applied for stress measurement in a central region of the Kumano fore-arc basin at a water depth of 2054?m using a 1.6?km riser hole drilled in the Integrated Ocean Drilling Program (IODP) Expedition 319. As a result, the stress decoupling through a boundary at 1285?m below seafloor was detected. The boundary separates new upper layers and old lower ones with an age gap of ~1.8?Ma, which is possibly the accretionary prism. The stress state in the lower layers is consistent with that observed in the outer edge of accretionary prism

Subsea fluid sampling to maximise production asset in offshore field development

The acquisition of representative subsea fluid sampling from offshore field development asset is crucial for the correct evaluation of oil reserves and for the design of subsea production facilities. Due to rising operational expenditures, operators and manufacturers have been working hard to provide systems to enable cost effective subsea fluid sampling solutions. To achieve this, any system has to collect sufficient sample volumes to ensure statistically valid characterisation of the sampled fluids. In executing the research project, various subsea sampling methods used in the offshore industry were examined and ranked using multi criteria decision making; a solution using a remote operated vehicle was selected as the preferred method, to compliment the subsea multiphase flowmeter capability, used to provide well diagnostics to measure individual phases – oil, gas, and water. A mechanistic (compositional fluid tracking) model is employed, using the fluid properties that are equivalent to the production flow stream being measured, to predict reliable reservoir fluid characteristics on the subsea production system. This is applicable even under conditions where significant variations in the reservoir fluid composition occur in transient production operations. The model also adds value in the decision to employ subsea processing in managing water breakthrough as the field matures. This can be achieved through efficient processing of the fluid with separation and boosting delivered to the topside facilities or for water re-injection to the reservoir. The combination of multiphase flowmeter, remote operated vehicle deployed fluid sampling and the mechanistic model provides a balanced approach to reservoir performance monitoring. Therefore, regular and systematic field tailored application of subsea fluid sampling should provide detailed understanding on formation fluid, a basis for accurate prediction of reservoir fluid characteristic, to maximize well production in offshore field development

Application of SIMULINK to Emulate Subsea Production System (SPS) Control Functions

Subsea control systems in subsea production system (SPS) play a vital role in the safe and productive operation of any oil or gas field. These systems operate in extreme environments, thus making the installation and commissioning the system risky and costly. For a new developer, a better understanding on how the system works is needed to ensure that the system will meet all design specifications and reduce the risk and costs associated with installation and commissioning. Hence, leading oil and gas companies are turning to simulation software where the whole subsea control systems from the Hydraulic Power Unit to the Subsea Control Module can be modeled. This project aims to develop a SIMULINK model for a specific SPS and to assist in ensuring that the system will function accordingly. The scope of the project is to concentrate on the movement of the gate valve in subsea control system where the flow of an oil and gas is controlled. The methodology of the project involves collection of technical details and data regarding subsea control modules, identify elements of the control system, arrangement block diagram notation of the SIMULINK software, the acquisition of the SPS design parameters, and the development of SPS control system equation. Simulation result shows that the gate valve is fully open at 10cm within 0.075s. This will be useful to conduct a sensitivity analysis in the matter of SPS changing key design parameters. Moreover, this project will give lots of advantages to a new developer to understand the system well before developing the actual SPS control system

Design optimization of oilfield subsea infrastructures with manifold placement and pipeline layout

This work presents a practical and effective optimization method to design subsea production networks, which accounts for the number of manifolds and platforms, their location, well assignment to these gathering systems, and pipeline diameter. It brings a fast solution that can be easily implemented as a tool for layout design optimization and simulation-based analysis. The proposed model comprises reservoir dynamics and multiphase flow, relying on multidimensional piecewise linearization to formulate the layout design problem as a MILP. Besides design validation, reservoir simulation serves the purpose of defining boundaries for optimization variables and parameters that characterize pressure decrease, reservoir dynamics and well production over time. Pressure drop in pipelines are modeled by piecewise-linear functions that approximate multiphase flow simulators. The resulting optimization model and approximation methodology were applied to a real oilfield with the aim of assessing their effectiveness.Este trabalho apresenta um método de otimização prático e eficaz para o projeto de redes de produção submarinas em campos de petróleo offshore, o que compreende o número de coletores, sejam manifolds ou plataformas, sua localização, atribuição de poços a esses coletores e diâmetro de dutos que interligam todos os elementos da rede. Ele traz uma solução rápida que pode ser facilmente implementada como uma ferramenta para otimização de layout e de estudos baseados em simulação. O modelo proposto compreende a dinâmica do reservatório e fluxo multifásico em dutos, baseando-se na linearização multidimensional por partes para formular o problema de otimização de layout como programação inteira linear mista. Além da validação da solução ótima obtida pelo método, a simulação de reservatórios define limites para as variáveis e parâmetros do modelo que caracterizam a perda de carga, a dinâmica do reservatório e a produção de óleo dos poços ao longo do tempo. A perda de carga nas tubulações é modelada por funções lineares por partes que aproximam resultados obtidos pelos simuladores de fluxo multifásicos. O modelo de otimização foi aplicado a um verdadeiro campo de petróleo offshore com o objetivo de avaliar sua efetividade

Subsea inspection and monitoring challenges

Master's thesis in Offshore technology : industrial asset managementThis paper uncovers and suggests solutions for the challenges to control change over time more reliable and cost effective. Front-end concept engineering, design, inspection and monitoring strategies, technologies, systems and methods for Life-of-Field are recommended. Autonomous underwater vehicles (AUV) are identified as a possible cost- efficient opportunity to reduce cost of inspections and monitoring operations while safeguarding asset integrity. A recognized design spiral methodology is used to perform a front-end concept evaluation of an AUV system. Investigation of key technological limitations and new developments within underwater communication, energy storage and wireless power transmission is performed. It further enables opportunities such as AUV recharging station on the seafloor for better utilization. One major learning point is through the use of numerical models and the outcome being a better and more hydro effective hull design. One expectation from this paper may be the aid to collaborating partners in their design work

Subsea Production Control System Modelling

Subsea control systems in subsea production system (SPS) play a vital role in the safe and productive operation of any oil or gas field. These systems operate in extreme environments, thus making the installation and commissioning the system risky and costly. For a new developer, a better understanding on how the system works is needed to ensure that the system will meet all design specifications and reduce the risk and costs associated with installation and commissioning. Leading oil and gas companies turned to identify the critical responses and behaviors expected from the designed system through simulation software, where the whole subsea control systems from the Hydraulic Power Unit to the Subsea Control Module can be modeled. In this report, a case study from Cadlao field off the shores of Philippines is used to perform a simulation study on. The field uses a direct hydraulic control system, which from the literature review done, is considered to be the building stone of all other control systems available. The simulation was made by a new simulation tool called Agito ITI SimulationX. The simulation results are then compared with those from the actual field outputs recorded from the Cadlao field. The results of the simulation and the discussion showcases the response of the gate valve actuator and its relation with umbilical hose and Directional Control Valve. Comparison between the experimented results and the simulated results were made to stand upon relativeness of the simulated results

Subsea Production System (SPS) Control Modelling

The motivations of this project work are to develop a simulation model for a direct hydraulic control system, find the effect of changing key parameters to the system’s response time, and also to demonstrate Emergency Shut Down (ESD) feature which is a requirement for the subsea production control systems (SPCS). The methodology of this project involves selecting a control system to be studied which is a direct hydraulic control system, gathering technical details and data regarding the control system and components that constitute the control system, and translating the technical details and concepts into acceptable simulation forms in the simulation’s software. This project used SimulationX to simulate the developed model. The developed model consist of a hydraulic power unit, a topside control panel, hydraulic lines, a subsea control module and two actuator valves. The Cadlao oil field has been selected as the case study and simulation models were built according to the Cadlao field’s SPCS. The simulated model is validated by comparing the Cadlao’s performance curves and the acquired results. The simulation is done by varying 3 parameters which are umbilical length, umbilical diameter, and actuator size. Each parameter is tested to study its influences on the signal time and shift time. To find the effect of umbilical length on the signal time, umbilical lengths of 6000 ft, 12000 ft, and 18000 ft have been used. Time taken are 47 s, 110 s, and 195 s respectively. For the simulation using different umbilical diameters, 0.15 inch, 0.35 inch and 0.50 inch have been used. Time taken to fully pressurize the umbilical are 111 s, 39 s and 48 s respectively. For the second part, to find the effect of varying parameters on shift time, three parameters are changed (umbilical length, umbilical diameter and actuator diameter). 6000 ft, 12000 ft and 18000 ft umbilical lengths have been used and the recorded shift times are 13 s, 21 s and 31 s respectively. For the simulation using different umbilical diameters, 0.15 in, 0.35 in and 0.50 in have been used and the recorded shift times are 113 s, 19 s and 13 s respectively. Lastly, sensitivity analysis is done using three different piston diameters. Diameters of 6 in, 9 in and 12 in have been used and the recorded shift times are 28 s, 36 s and 56 s respectively. Lastly, emergency shut-down simulated showed that the actuator is able to return to fail safe condition in 33 s