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Abstract The commercial application of Intelligent Well Technology is fast approaching the ten year milestone. Expanding the range of advanced completion and monitoring products with particular focus on reliability engineering has been the main theme for this sector. As this technology has matured, research focus has shifted to Intelligent Field or Smart Field concept studying the potential of wide-scale automation and optimization.

This paper describes the development of Intelligent Well surface control systems, aimed particularly at providing automation and optimization of well based processes as a means to achieve advanced well management. A simple layer model is proposed describing an increasing level of control and automation.

Data standards and connectivity are discussed as the vehicle to achieve wide-scale integration of advanced well management, as this capability is portrayed as one of the stepping stones of Intelligent Fields. Well Based Processes – The starting point

An Intelligent Well (IW) provides the means to control the process of producing hydrocarbons from or injecting fluids into the reservoir. There are three elements to performing control: process outputs, controlled variable and manipulated variable. The process outputs are those parameters selected to describe the state of a system and are monitored continuously by sensors (process observability). The controlled variable is the parameter through which the process outputs are controlled (e.g. zonal pressure, flow, water cut, etc) and the manipulated variable is the parameter of the system used to control the process (e.g. valve position). The relationship between the controlled and manipulated variables is defined by the control algorithm (supported by static inputs to define and calibrate the control model in the decision space) and the control strategy implemented. The implication is that the downhole valve flow trim and the accuracy and resolution to position the

valves are the fundamental parameters to deliver effective control of the well process.

The flow control valves can be divided into two main categories with respect to their control capability. There are binary and multi-position valves. A binary valve provides two setting options for the manipulated variable: open or close position. A multi-position valve provides a much wider range of options for the manipulated variable and can be further divided into discrete or continuous type depending on the trim design. The discrete valve allows for stepped changes of available valve positions. The number of finite positions depends on application specifics and sleeve operating philosophy and mechanics. Continuous valves allow for infinite position placement within the prescribed flow area boundary when mechanically coupled with an adequate control system; this design provides a finer resolution to the control process. Continuous valves can also be deployed with a control system that delivers less accuracy and resolution in position placement. This solution can be defined as continuous multi-position.

A binary valve is appropriate in situations where the objective (or driver) is the exclusion of a zone when the production of unwanted fluids (water or gas) cannot be managed once the breakthrough occurs. The downhole flow control valve would be closed position thus resulting in loss of production form the associated zone.

The discrete multi-position valve is most suitable in applications that are required to meet changing control objectives such as gas lift, where the amount of gas injected can be adjusted as function of produced fluid composition, available injection and reservoir pressures, or in injection wells where the reservoir sweeping efficiency can be improved by optimized allocation of injection fluids.

The continuous infinite valve is usually beneficial in applications that require a tighter control. A WAG well, requiring the control of both water and gas injection) is a typical example alongside management of gas problems in oil producers and controlled pressure drawdown at the wellbore and sand face completion.

Field Management Requirements When the optimal solution for controllability (possibility to force the process into a particular stage) and observability (ability to “observe” the process through output measurement) of the IW system is established, the design of the IW surface control and downhole infrastructure should address the operational philosophy at field level. While project specific

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Intelligent Well Automation—Design and Practice D. Mathieson, SPE, C. Giuliani, SPE, A. Ajayi, SPE, and M. Smithson, WellDynamics Inc.

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constraints are numerous, those that should be at the forefront of any applications are: • Requirement for on-line data and control • Constraints from existing field infrastructures • Automation, control and optimization capability

On-Line Data and Control The streaming of data from field sensors to a variety of monitoring systems, ranging from alarms servers and graphing products to the more sophisticated expert systems, define the concept of online data. This capability is critical where early detection or prediction of process disturbances is required. Similarly, on line control, defined as the ability to control the IW process on-demand through existing field infrastructure, is best deployed in those applications where the time between the decision to intervene on the well and the intervention must be kept to a minimum. This feature is desirable when control loop ref 1, automation or remote operation is a requirement. Requirement for on-line data and control may be driven also by accessibility of the well site or safety concerns.

The solutions for data and control may not always be integrated; an on line data system could be combined with a campaign of well interventions carried out using a portable control system unit. However, more often a random sampling (i.e. field operator traveling to the well site according to a predefined schedule) of the well metrology is implemented alongside the portable unit. Both solutions are characterized by considerable lag time between the occurrence of the well process disturbance and the needed modification to the well process with the intervention (i.e. manipulation of downhole flow control valves). Such design of IW control system is suitable for those applications where no sudden or frequent variations to the well process are requested or expected. Other reasons relate to limited field infrastructure or excessive cost to put infrastructure in place.

Existing Field Infrastructure

Historically, when referring to the field infrastructure, power and RTU communication standards were the only criteria required to design a surface system. While they are critically important for a specific application, additional factors such as field control system implementation philosophy, field historian accessibility and connectivity between the process and the business networks are now as important in the definition of the design criteria for IW control systems (fig. 1). As IW are deployed to mitigate uncertainty and risks or manage complex downhole architectures, field communication infrastructure should always be designed as open architecture ref 2 in order to both facilitate late integration of critical subsystem and better allocation of the system functionality among the different field processes. Field communication infrastructure that does not allow for open architecture may force the IW control system to be embedded into the field control system.

Integrating the IW control system into the field process network as a sub-system, allows the IW capability to evolve as new technology reaches the market; this is because the connectivity with the field control system occurs at the

application layer instead of the data layer. Embedding, on the other hand, often freezes the development as the field control system providers may have little interest in the implementation of other service company products. Automation, Control and Optimization

It is important to identify the requirement for automation, control and optimization in the different processes. Automation, for instance, can have several applications in an IW control system. For asset managers such as Production Engineers, automation can be applied to execute pre-defined sequences of operations triggered by user defined events ref 1 (e.g. start a pressure build up when a downhole valve is closed).

To the IW completion design, automation delivers control of downhole flow control valves and data acquisition from deployed sensors. As flow control valves act as the manipulated variable to control the well process, it is obvious that the repeatability and consistency of operation delivered by automation is at the foundation of any advanced well management control and optimization capability.

Advanced Well Management algorithms, reservoir performance, downhole valve profile and automated operation of downhole flow valves are all part of the design inputs for the IW control system and its surface components. How they interact to deliver control is simple: advanced well management (e.g. well output) establishes the set point for the controlled variables (e.g. zone pressure, zonal or total well flow, water cut, etc) and IW process controller converts this input into the required downhole valve position and the automated operation of the manipulated variable takes place. As the relationship between the controlled variable and the manipulated variable is specific to the design of the downhole valve flow trim ref3, it is reasonable to implement any well process automation closely coupled to the IW control system or, for simpler tasks, embedded into the IW control system.

Optimization algorithms to enhance the performance of the system would follow a similar pattern. The optimization module generates the set point for several processes within the field concurrently, with one or more related to the process controlled variable. Most of the optimization functions connect the business requirements of the Operator to the production process and have space application and modeling demands that go beyond the capability of an IW Control System and are implemented in the business network (Fig.1)

Surface Control System Design Philosophy

The Surface Control System is an extension of the downhole IW control system architecture. The great majority of IWs deployed to date rely on locomotive power to be delivered from surface to a downhole flow control valve by means of hydraulic or electrical conduits. The addition of downhole mechanical or electronic devices may be necessary to deliver an increased control over the flow control valve movement. These elements constitute the downhole control system architecture. Similar downhole control methodology on the market follow a simple classification:

Direct Hydraulic, a system based on direct connectivity between the source of pressurized hydraulic fluid at surface and the downhole actuator. This system requires a minimum

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number of control lines emerging from the well equal to the number of downhole devices to be operated hydraulically. Positioning of the valve may depend on downhole mechanical devices or surface equipment.

Multi-drop Hydraulic, a system based on sharing a reduced number of control lines among several downhole actuators and selectively establishing the connection between an actuator and the source of pressurized hydraulic fluid. This system requires the number of control lines emerging from the well to be less than the number of downhole devices and it is most suited for those applications where well completion architectures do not allow for numerous control lines. Positioning of the valve actuator may depend on downhole mechanical or surface equipment.

Integrated Flow Control and Monitoring, a system based on integrating flow control and sensing into the same power and communication infrastructure, capable of selectively operating one or multiple actuators through the available locomotive power. Positioning of the valve actuator is typically very accurate with a high degree of resolution and obtained with a close-loop control implemented within the downhole electronics.

Downhole Monitoring, is often used in combination with surface metrology to acquire feedback on the well production or injection processes after any of the manipulated variables is adjusted. Established permanent downhole gauges (PDGs) are primarily based on electronic or fiber optic systems. They allow monitoring of similar well process parameters such as pressure, temperature, flow and some aspects of flow composition. Electronic based system may be preferred for applications where valve position and high accuracy and resolution for pressure and temperature measurement are critical. Fiber optic, on the other hand, is more effective in distributed measurement (pressure and temperature). Dedicated downhole monitoring is typically used in combination with hydraulically operated systems to provide comparable capability to the integrated flow control and monitoring systems. It has an advantage of greater system flexibility as well as improved mission reliability.

Control and Automation – Layer Model The manner in which downhole sensing and flow control systems are combined and deployed to control the well process is at the base on the layer model. The degree of control with which the production engineer intends to manage the well process should dictate which level of functionality of the downhole control architecture and associated surface equipment. This may also require connecting an IW system to other well based systems such as ESP, surface choke and gas lift systems ref 1. The following classification of process control level is proposed for the purpose of this article: • On / Off • Discrete Multi-Position • Continuous, low resolution and accuracy • Continuous, high resolution and accuracy Manual Systems, typically designed for hydraulically operated downhole control systems, rely on the field operator’s knowledge of the downhole control system to

manipulate the flow control valves to the required position and its operational feedback to confirm the new position. These systems supply the locomotive power necessary to operate downhole actuators and provide a method to manually distribute it to the downhole actuators. Regardless of the system being portable or permanently installed in the proximity of well, the operator is required to travel to the well site.

Manual systems do not typically include a data acquisition system for downhole sensors. If downhole metrology is present, it would be available to the operator as external feedback onto which an assessment of the operation success should be made. Manual systems provide the lowest level of control capability and are typically associated with On / Off and Step control.

Automated Systems, are designed for repeatability and consistency of downhole flow control valve as their primary objective. The operator is no longer required to be intimately familiar with the details of the downhole control system operation and feedback, but can shift his attention to the well performance. Automated systems are designed to operate individual well with specific downhole architecture and would comprise similar basic equipment to the manual counterpart. This is the entry level for advanced well management.

Automated systems often include or are connected to data acquisition systems from which they can obtain feedback on the process being controlled. This feature enables automated systems to contain simple well process automation and control loops which do not require complex modeling.

Automated systems can either be deployed as permanent or portable units. Permanent solutions are typically connected to the field communication infrastructure and are available on line for remote operation. Portable units, designed to be easily transported to the field, are normally operated on site (offline) or remotely if an ad hoc communication network with the control centre is available or established at the well site. When automated systems are deployed offline data can still be streamed into expert systems or, in most cases, analyzed after intervention.

IW Supervisory Systems, deployed in conjunction with automated systems, are designed to bring together supervision and control for all IW completions deployed as well as external connectivity.

For field development where the IW completions are critical elements of the field exploitation strategy, an IW supervisory system has the significant advantages: • Provides integration at application level for easy data

and control transfer to and from other field control and asset management systems

• Provides a deployment base for computational intensive well management capability and advanced automation sequence spanning multiple processes

• Facilitates the introduction of modification to hardware and control philosophy to any IW system deployed in the field

• Relieves field control system providers from developing an in depth understanding of IW control system and control strategy

• Allows any combinations of downhole architectures and functionality

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• Provides Well centered data processing and data storage ref 4

IW Supervisory Systems offer the most in terms of IW functionality packaged into a single product.

From Intelligent Well to Intelligent Field The Intelligent Field concept integrates all the systems that affect the recovery of hydrocarbons from source to delivery to the customer. From reservoir, through the wells, artificial lift systems, the gathering systems, manifolds, separation and upgrading systems, to the products custody transfer and disposal of effluents, the Intelligent Field interconnects and brings together a number of processes. The objective of the Intelligent Field technology is to improve the efficiency, individually and collectively, of all the above processes. This is not likely to be achieved by the construction of massive monolithic process model, control system and data storage which embeds all of the necessary functionality, but by the integration and interaction of each of the main systems which constitute it. Earlier in this article, the case was made for IW control system with increased levels of control and automation ranging from manual systems to advanced well management. The philosophy of integrating IW into Intelligent Field should reflect the criticality of managing the well process in the context of the field exploitation plans.

For field applications where the IW is utilized to optimize production, measure effluents or automate well surveillance processes or any other task which is computational intensive or requires specialized knowledge of advanced well management, the IW control system is one of the systems constituting the backbone of the Intelligent Field solution. The process control infrastructure is such that the Intelligent Field would see the IW Control System as a peer to the Field Control System (Fig. 1).The process network provides concurrent access to in-field well controller controlling the different well systems such as IW, ESP, Gas Injection and Surface Choke to name a few. The field control system supervisory application has access to IW, downhole monitoring and any other functionality available through the IW well controller through the IW Supervisory Systems. Conversely, the IW supervisory application is able to define or “recommend” to the field control system operator new settings or notify unplanned operating conditions. A similar solution can be proposed for monitoring only application that require specialized and computer intensive calculations.

For less calculation-intensive process automation, effective downhole system control strategy or well integrity related solutions, automation must be deployed at the well site. A local communication network allows for the different well controllers to exchange data upon which automated process can be implemented. This solution would not negate the requirement for supervisory system but would remove any uncertainty related to well site to control room communication infrastructures.

In cases where Intelligent Wells are installed with the sole purpose to reduce intervention time and cost, the IW control system is easily embedded into the field control system and used only as a mean to manipulate the valves.

Integration to Intelligent Field Automation and control loops have been implemented to well-centered processes for quite some time in control systems for surface chokes, surface gas injection valves and ESP systems. Operator familiarity with the IW completion technology has increased to the point that automation and control loops may be introduced in IW control systems ref 5 with a plan to address stability and safety.

Key to achieving a wide scale application of these advanced well management capabilities is the ease of integration into field control systems and Intelligent Field. This can be achieved with open architecture and adoption of industry standards.

TCP / IP, is one of the emerging standards for process control networks. This system supports several data protocols on the same physical layer, although it does not provide inherent interoperability between application layer protocols. However, TCP / IP allows for in-field controllers from different sub-system on the same network making expanding the communication infrastructure relatively easy (if bandwidth for data throughput exist). This capability is also available in wireless technology, though with limitations.

OPC, in recent years, has gained considerable market share as application layer protocol to exchange data. Built on DCOM technology, OPC does show some limitation on complex network or crossing gateway between business and process networks. This technology is evolving towards a new standard, OPC UA (Unified Architecture), which will address the above issues.

PRODML, The upstream oil and gas industry is actively working to establish standards for application connectivity. PRODML (PRODuction xML) is an industry initiative whose objectives are to achieve data and control interchange using XML as underlying technology (www.ProdML.org).

Conclusions Control system is one of the IW elements key to a successful deployment of IW technology and the future of Intelligent Field. It links and integrates the process control capability of the IW downhole hardware to the data analysis and decision making processes as well as the intervention phase.

The starting point of designing an IW control system should be a clear understanding of the degree of control required by the well process and whether enough parameters are monitored to provide observability to the system. Control specifications should then be set to make certain that the process controller model selected provides the necessary stability and robustness with the selected control strategy. A map of systems functionality and interfaces should also be drawn up to best determine in which componet (e.g. in-field controller, supervisory software, business network) automation and optimization algorithms should be implemented.

For some applications, most of these steps are not necessary because limited control is required. More generally, most of these steps are not implemented as the IW control system is not an integral part of the IW system design. The authors concur with the vision that there are no technical barriers ref1,5 to the implementation of automated processes including control loops. However, it is important that

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communications infrastructures and the field control system philosophy allow for data exchange through the relevant systems at either in-field controller level or application level. The challenge is to bring the decision on IW further forward in the field development plan to make sure that infrastructure are designed with this requirement in mind.

An IW system, modular in hardware and software design and based on open architectures and industry standards, will enable deployment of automation and control capabilities in most field control system architectures, thus delivering advanced well management modules fully integrated with the Intelligent Field technology.

Nomenclature

IP Internet Protocol OPC OLE for Process Control OLE Object Linking and Embedding RTU Remote Terminal Unit TCP Transmission Control Protocol WAG Water-Alternate-Gas

References [1] Going, W.S., Anderson, A.B., Vachon, G.P.: “Intelligent Well

Technology – The Evolution to Closed-Loop Control,” paper OTC 17796, presented at OTC Conference 2006, Houston, Texas, 1 – 4 May

[2] Hiron, S.: “Networking Subsea Completion Using Industrial Standards,” paper SPE 71532, presented at 2001 SPE ATCE 2001, New Orleans, Louisiana, 30 September – 3 October.

[3] Konopczynski, M. and Ajayi, A.: “ Design of Intelligent Well Downhole Valves for Adjustable Flow Control,” paper SPE 90664, presented at SPE ATCE 2004, Houston, Texas, 26 – 29 September 2004

[4] Leonard, S.:”MatrikonOPC Hub and Spoke Architecture”, white paper

[5] Going, W.S. et all: “Intellegent Well Technology: Are We Ready for Closed-Loop Control?, paper SPE 99834, presented at SPE Intelligent Energy Conference 2006, Amsterdam, The Netherlands, 11 – 13 April

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TCP / IP

Fiscal Metering

Intelligent Well

Control

Field Control System

SafetySystem

SecurityGateway

Historians AssetManagment

User Interface

Business SoftwareSolution

Field Devices

FieldControllers

Intelligent WellsSurface ChokeESPGas InjectionsChemical Injectionetc

Business Network

Process Network

User Interface

Figure 1 – Business and Process networks connectivity overview