Application of Reliability Analysis Techniques to Intelligent Wells
- Brian K. Drakeley (ABB Offshore Systems) | Neil I. Douglas (ABB Offshore Systems) | Knut E. Haugen (ABB Corporate Research) | Endre Willmann (ABB Corporate Research)
- Document ID
- Society of Petroleum Engineers
- SPE Drilling & Completion
- Publication Date
- June 2003
- Document Type
- Journal Paper
- 159 - 168
- 2003. Society of Petroleum Engineers
- 3.2.2 Downhole intervention and remediation (including wireline and coiled tubing), 5.1.2 Faults and Fracture Characterisation, 1.6 Drilling Operations, 4.6 Natural Gas, 1.7.5 Well Control, 4.5.7 Controls and Umbilicals, 5.6.11 Reservoir monitoring with permanent sensors, 4.3.4 Scale, 2.3.3 Flow Control Equipment, 2 Well Completion, 3.3 Well & Reservoir Surveillance and Monitoring, 4.1.5 Processing Equipment, 4.1.2 Separation and Treating, 4.5 Offshore Facilities and Subsea Systems, 2.3 Completion Monitoring Systems/Intelligent Wells, 2.4.3 Sand/Solids Control
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This paper describes the overall methodology and quantitative techniques applied during the development of an intelligent well control and communication system to ensure high system reliability and availability. In particular, the anticipated reliability impact of introducing high-temperature (HT) electronics technology together with redundancy for critical components is quantified.
One of the main challenges when analyzing the reliability performance of novel technology is to establish appropriate input data. Hence, a methodology applied to establish and validate reliability data is presented.
Harsh installation and operating conditions make a zero failure expectation for a 10-year life span appear unrealistic. The solution to this paradox is to assume that there will be some failures and to combat this by developing a highly fault-tolerant system.
The methodology described in this paper also has broader potential applications to other oil and gas system development projects. It brings to our industry practices that are frequently employed in the aerospace and nuclear industries.
A widely accepted definition is that an intelligent well is one that has all three of the following capabilities.
Flow segregation. Individual zones/laterals in a well are isolated from each other, and flow (production or injection) out of or into them can be remotely controlled by means of downhole flow control device (FCD).
Well parameter monitoring. Wellbore and/or reservoir characteristics (e.g., P, T, and Q) can be remotely monitored in real time.
Well performance optimization. The wellbore characteristics are evaluated, and the knowledge gained is actually used to determine if any of the FCDs should be adjusted to maximize the overall well performance. The evaluation is performed manually at present, but in the future it could be by means of a closed-loop operation.
It is also widely accepted that an intelligent well can provide added value in a number of areas. Briefly, the benefits may include one or more of the following.
Reduced well life-cycle costs.
Accelerated production profiles.
Reduced well-intervention frequency and costs (also resulting in improved operational safety).
However, the economic gains offered by any intelligent well system are illusory unless the equipment proves reliable in service. For example, in subsea well applications, repair is an extremely expensive option, yet it is the subsea well applications in which the operators currently have the most to gain.
The overall objective of the intelligent well reliability project has and continues to be to ensure the provision of satisfactory system reliability and operational performance on a long-term basis for all well applications, including high pressure/high temperature (HP/HT). To achieve this objective, systematic component criticality assessments and reliability performance simulations are applied as decision-making tools during the design process. This ensures that the end design is "reliability driven" and that any "reliability killers" have been eliminated.
An increasing number of oil and gas operating companies have already taken the bold step of deploying intelligent well systems. By the end of 2000, such systems had been deployed in more than 30 wells worldwide. Perhaps not surprisingly, with the new technology introductions in our industry there have been somewhat mixed results.
For many applications, simple, direct, hydraulic-controlled sliding sleeves with on/off control only can be used as the FCD. Even though there may be no provision for transmission of reservoir data back to the surface, they do provide a certain degree of intelligent control. Other reservoirs require the use of the so-called high-end systems that provide infinitely variable choking capabilities within the FCD, reservoir parameter monitoring, and system performance diagnostics.
Encouragingly, oil and gas operators increasingly accept the technology with time and improved reliability. A sign of this acceptance level is the fact that requirements for subsea control systems and tree systems to be compatible with intelligent well technology is becoming the norm rather than the exception. This trend also indicates an increased awareness that the interface issues between the subsea and downhole hardware need to be addressed up front; otherwise, downhole systems' alternatives can be severely restricted.
In determining the desired reliability of an intelligent well system, a multitude of variables must be considered, such as equipment capital costs and available technology, against the consequences of system failures. These variables will obviously change from one reservoir and field application to another.
Many clients seek failure-free operating periods of 10 years or more, yet it is quite possible that the wells will need to be worked over for other reasons in advance of that time frame.
It is worth noting that most FCD suppliers have included the capability to mechanically override the remote actuation system. For remedial action through well intervention, the tool is equipped with a disconnect device that essentially converts it into a standard sliding sleeve that can be actuated by wireline or by coiled-tubing-conveyed shifting tools.
Since 1997, Asea Brown Boveri (ABB) has been developing a downhole intelligent well system. The techniques described in this paper have been used to guide the development process (i.e., it is not just a methodology to be used at the completion of the development to come up with a reliability prediction that satisfies client processes).
The selected intelligent well control and communication system is based on an architecture that uses dissimilar redundancy and fault-tolerant design features to enhance system reliability. The system is applicable to both production and injection wells.
The FCD can be operated by means of electrical, hydraulic, or electrohydraulic actuation. One of these operational means is selected as primary and the other as the secondary, or backup, operational mode. In the unlikely event that the primary means undergoes a system failure, the backup mode can be enacted.
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