Characterization of Physical Field and Flow Assurance Risk Analysis of Subsea Cage-Sleeve Throttling Valve

The subsea production system is presently widely adopted in deepwater oil and gas development. The throttling valve is the key piece of equipment of the subsea production system, controlling the safety of oil and gas production. There are many valves with serious throttling effect in the subsea X-tree, so the hydrate formation risk is relatively high. In this work, a 3D cage-sleeve throttling valve model was established by the numerical simulation method. The temperature and pressure field of the subsea throttling valve was accurately characterized under different prefilling pressure, throttling valve opening degree, and fluid production. During the well startup period, the temperature of the subsea pipeline is low. If the pressure difference between the two ends of the pipeline is large, the throttling effect is obvious, and low temperature will lead to hydrate formation and affect the choice of throttling valve material. Based on the analysis of simulation results, this study recommends that the prefilling pressure of the subsea pipe is 7–8 MPa, which can effectively reduce the influence of the throttling effect so that the downstream temperature can be kept above 0°C. At the same time, in regular production, a suitable choke size is opened to match the production, preventing the serious throttling effect from a small choke size. According to the API temperature rating table, the negative impact of local low temperature caused by the throttling effect on the temperature resistance of the pipe was considered, and the appropriate subsea X-tree manifold material was selected to ensure production safety. The hydrate phase equilibrium curve is used to estimate the hydrate formation risk under thermodynamic conditions. Hydrate inhibitors are injected to ensure downstream flow safety.

Optimization approach for Arctic field development design using subsea production systems

Russian experience in the design of trunk pipelines and Arctic studies have been used to develop an efficient model and method for Arctic field development design using the subsea production system (SPS). Compared to 2D models used in the past, the new design technique offers an opportunity to make 3D models and can be used for optimization of offshore field development projects. The proposed optimization model is based on the Bellman - Ford algorithm developed for 3D networks. This approach has been used for the first time to capture key features and specific subsea production system design processes. The algorithm and block diagrams developed for the proposed SPS design method is universal. This method can be used to address tasks of a more general nature. Optimization of the particular case between a single start point (well location) and single end point (SPS facility) is implemented as a separate software package, but the scope of applications is not limited by such cases and may be extended even further. It can also be very efficient for Arctic subsea field development.

On the Subsea Production System Availability with Resident Drones. A Reliability, Availability, Maintenability RAM Analysis

The challenge in the Oil&Gas industry to remain competitive in a low oil price whilst dealing with minimization of operational risk and uptime asset maximization is leading offshore Companies to evolve thought proactive and predictive maintenance approaches. In the event of unplanned intervention due to anomalies or warning messages at the dispatching center, the decision on the size of the support vessel and its utilization for straordinary maintenance could be time consuming with potential high cost impact, also due to loss of production. Even the new generation of remote condition and monitoring systems, which allow to improve the capability of operators for early warnings and surveillance, provide a reliable solution for emergencies. In this context, resident subsea drones enable on-demand inspection whilst eliminating the need for support vessel and allow operator to manage the risk in continued operations also for dangerous areas restricted to human access. A case study relevant to a new subsea field development have been conducted. Distinctive Reliability, Availability and Maintainability (RAM) analyses have been performed with the aim to get insight on the subsea production system availability considering a resident drone and to demonstrate how the so called "stategic maintainability" can be applied successfully in the decision-making process while reducing the OPEX. The former related to conventional IMR (Inspection, Maintenance & Repair) based on Condition Based and RBI, Risk Based Inspection approach, the latter related to strategic maintenability with resident drones. The application of such analysis required a multi-disciplinary approach together with the possibility of processing historical data in operating conditions. Historical data sources (e.g. OREDA dataset) were collected to obtain failure rates and active repair times typical of subsea equipment. Direct experience gained in over forty years of inspection and maintenance activities together with recent developments on subsea resident robotics allow the understanding of real internvention timing. Results show that resident subsea drones applied for early inspection and light intervention are confirmed timely and costless solution respect to conventional IMR services. They represent the first aid for environmental surveillance and subsea inspection in case of emergency and provide a relevant saving of subsea production un-availability. The economic value emerged from the presented case study represents a step change for OPEX optimization and motivates Best-in-Class Operators to get an insight case-by-case for both green and aging fields.

Troll Phase 3: The Next Step for a Groundbreaking Giant

An important driver for maximizing value creation for the Troll Phase 3 gas project offshore Norway was to identify means to reduce the pressure drop in the value chain from the reservoir to the onshore terminal. Using a design-to-cost approach in the concept selection phase, this has affected design of the wells, subsea production system, pipeline and the new inlet separator on the Troll A platform; all of which have been designed to preserve the energy from the reservoir as much as possible. The final design has enabled a significant increase of the project value by accelerated gas deliveries, reduction of the energy consumption and thus lowering the CO2 emissions. Calculations show that 1 bar pressure drop in the Troll Phase 3 value chain increases the project NPV (8%, pretax) with approx. 45 Million USD and reduces the power consumption by 11 GWh/year. The well tubing size was increased to 9 5/8", reducing the required number of wells by ~40%. Factoring both wells and subsea facilities, this optimized well concept alone represents a total cost saving of nearly 300 million USD. The project has piloted a modification to the Vertical X-Mas Tree (VXT) design featuring an increase from 5 1/8" to a 7" production wing outlet to minimize the pressure drop across the subsea production system. This VXT design has become the new company standard for gas field developments. The big bore wells and subsea production system design also ensures acceptable gas velocities in the late production phase with low reservoir pressure. The total reduced pressure drop obtained through these and other measures is estimated to 19 bar, realizing a project NPV improvement of approx. 850 million USD (8%, pretax).

Enabling Technologies for Low Cost Subsea Field Development

The oil and gas industry faces many challenges as it is committed to provide energy to a world in transition. Declining prices impose constraints to new developments, either greenfield or brownfield. Additionally, the industry’s commitment to long-term value creation with reduced carbon footprint is confronted with the traditional solutions for well construction, production and processing, which consume significant amount of energy with corresponding high CO2 emissions. In this scenario, subsea production and processing technology has been a key enabler for the exploitation of oil and gas resources. This paper presents a holistic review of trends in subsea technology development over recent years which have direct impact on the heart of the subsea production system, namely the subsea tree. The technological developments considered are in different subsea applications such as robotic automation, communication systems, and all-electric systems. The objective of the ongoing research is to perform structural and fundamental analysis of subsea production and injection systems and address the question on how technological developments can be utilized to design an overall better subsea production system so the industry may fully benefit from the economic and ecological impact brought by the joint use of these technologies. Opportunities for reevaluating barrier philosophy to identify technical and economic opportunities for design simplifications of subsea trees that still leave enough pressure barriers in all operational modes are also considered. The analyses presented indicate the current stage of the examined technologies and their potential at reducing both capital and operational cost of subsea systems. These results will be the basis for the future evaluation of improved and new design solutions within the scope of the ongoing project performed by the Norwegian University of Science and Technology and its industrial partners.

Design and Development of All-Electric Surface-Controlled Subsurface Safety Valve System

Summary The subsurface safety valve (SSV) is an essential device of a subsea production system. The hydraulic SSV is widely used, but it has some drawbacks when used in deep water: It needs a long pipeline from platform to wellhead, and brings additional pressure loss. The system needs higher pressure and manufacturing costs, but the response is slower. To solve the problem, a new all-electricsurface-controlled SSV (E-SCSSV) system consisting of an E-SCSSV body and a control system is developed. The innovative structural designs include electric-drive mechanisms and a magnetic coupler that can transfer linear motion. The mechanical property of E-SCSSV body is analyzed to determine the ability to resist well pressure. The coupling rule of the magnetic coupler is studied through experiment and finite-element analysis. The dynamics of the failure-safety mechanism is investigated to obtain the optimal performance and combination of structural parameters. Using sensors on the E-SCSSV body, the operation status of the E-SCSSV can be monitored. An E-SCSSV system prototype has been developed to validate the function of the E-SCSSV. Reliability requirements are discussed. Compared with existing SSVs, the biggest advantage of the E-SCSSV is its quick response.

Proxy Model for Real-Time Estimation of Cool Down Time of Subsea Production System to Prevent Hydrates Formation

Objectives/Scope The benefits of real-time estimation of the cool down time of Subsea Production System (SPS) to prevent formation of hydrates are shown on a real oil and gas facility. The innovative tool developed is based on an integrated approach, which embeds a proxy model of SPS and hydrate curves, exploiting real-time field data from the Eni Digital Oil Field (eDOF, an OSIsoft PI based application developed and managed by Eni) to continuously estimate the cool down time before hydrates are formed during the shutdown. Methods, Procedures, Process The Asset value optimization and the Asset integrity of hydrocarbon production systems are complex and multi-disciplinary tasks in the oil and gas industry, due to the high number of variables and their synergy. An accurate physical model of SPS is built and, then, used to develop a proxy model, which integrates hydrate curves at different MeOH concentration, being able to estimate in real time the cool down time of SPS during the shutdown exploiting data from subsea transmitters made available by eDOF in order to prevent formation of hydrates. The tool is also integrated with a user-friendly interface, making all relevant information readily available to the operators on field. Results, Observations, Conclusions The integrated approach provides a continues estimation of cool down time based on real time field data (eDOF) in order to prevent formation of hydrates and activate preservation actions. An accurate physical model of SPS is built on a real business case using Olga software and cool down curves simulated considering different operating shutdown scenarios. Hydrate curves of the considered production fluid are also simulated at different MeOH concentration using PVTsim NOVA software. Off-line simulated curves are then implemented as numerical tables combined with eDOF data by an Eni developed fast executing proxy model to produce estimated cool down time before hydrates are formed. A graphic representation of SPS behavior and its cool down time estimation during shutdown are displayed and ready to use by the operators on field in support of the operations, saving cost and time. Novel/Additive Information The benefits of real time estimation of the cool down time of SPS to prevent hydrates formation are shown in terms of saving of time and cost during the shutdown operations on a real case application. This integrated approach allows to rely on a continue, automatic and acceptably accurate estimate of the available time before hydrates are formed in SPS, including the possibility to be further developed for cases where subsea transmitters are not available or extended to other flow assurance issues.

Selection of the optimal subsea production system using original software

Due to the high relevance of the offshore oil and gas fields’ de-velopment, the authorsexaminethe technology of subsea mining, which is gaining popularity in the Russian Federation. The main types of subsea production system constructions were analyzed and a number of factors, which affect the development of offshore oil and gas fields, were proposed. An algorithm for the software product was created which allows after geo-logical exploration and the discovery of industrial oil and gas recourses to optimize the planning process and to save time and material costs for the company at the preliminary stages of planning. The software product algo-rithm based on such factors asdepth and size of the field, duration of ice season of the region, remoteness of the field from the coast, the level of development of transport infrastructure and the complexity of geological structure.