Interfaces between components are weakest links
Intelligent completion systems (ICS) integrate reservoir sensors and remotely controlled devices deployed permanently in the wellbore. The purpose is to minimize intervention and optimize reservoir production. Because these downhole devices are installed permanently, and thus are inaccessible, reliability is a top priority.
ICS systems are more than the sum of their parts because all aspects of the intelligent completion system must interact correctly for the system to operate. This includes everything from the customer's desktop to the tools downhole.
To design a better intelligent completion system, one first must examine the key links in the chain. Because each link must not only perform, but also interact properly with the whole system, this method allows one to identify and correct weaknesses in the system. This process is undertaken from the user's point of view and includes components from many providers: the completion, subsea pod, umbilical platform, and data management system.
A triage process is used to first identify critical points, then design experiments to expose these points to stress conditions that will accelerate the failure mechanism. Data from such experiments can be used in predicting the reliability of individual components and identifying the most likely failure modes. These results are then used in the design process to help strengthen the system against failure. Common failure modes are translated into redundancies in the design phase.
Field tests then show the reliability of the system once deployed. Because the reliability of the deployed system relies heavily on the quality of the installation process, the field test introduces the highest potential for failure by presenting the widest range of variables.
Using data gained from hundreds of permanent monitoring installations in the field, and close coordination between field and engineering teams, intelligent completion systems enjoy successful installation based on designs and techniques refined by these teams.
Deepwater ICSDeepwater wells have a complex geometry due to such advanced completion techniques as high-tier multilaterals. With the increased costs of deepwater development, intelligent completion systems will play an increasingly important role in the cost effective development of these wells. To make the best use of ICS technology, a systematic approach must be applied throughout the entire engineering, manufacturing, and deployment cycle.
ICS's eliminate the need for routinely required interventions through the use of remotely actuated downhole flow-control devices and real-time monitoring of downhole pressure, temperature, and flow. The following is a partial list of the benefits of using an ICS:
- Zonal flow regulation and shut-off for selective production or injection of well intervals
- Zonal pressure, temperature, and flow instrumentation for precise pressure determination of dynamic tubing at perforation depths and sandface
- Venturi-derived mass-flow determination and allocation combined remote flow control and instrumentation for selective inter-well interference testing to confirm isolation packer integrity, cement quality, and connectivity
- Transient pressure testing in individual zones with effectively no wellbore storage effects.
Functional requirementsDesign choices for an ICS system are governed by three principles: reliability, scalability, and enabling downhole pressure control. Of these, reliability is clearly the most important and should be reflected in every aspect of the development process.
Scalability means ICS systems that can conform to different well completion configurations, dimensions and production characteristics such as platform or subsea wellhead, horizontal wells, or multilateral wells; and the range of flow rates, and types of fluids.
Enabling downhole process controls covers the effective integration of the ICS into the overall production and reservoir optimization process. This requires a seamless interface of the ICS with existing rigsite master control systems, supervisory control and data acquisition, and reservoir modeling; as well as all the evolving industry standards. This integration allows direct connection of the production engineer, reservoir engineer, and asset manager with the information and controls required.
Mission profileThe starting point for the systematic approach is the mission profile. It provides metrics for testing and evaluation by using a disciplined, step-by-step methodology to determine all the system external or extrinsic para- meters and their boundaries. The profile describes all the possible conditions applicable to the system during its complete cycle from factory acceptance testing to transportation and installation and through all the possible conditions it can encounter during its operational life and final disposal.
This profile is a key starting point for the following step-by-step process.
In the design stage reliability risks are identified and classified. Past experience and core competence are used to cross check the design theory. Reliability growth is achieved concurrent with development by using reliability experiments to help with the evolution of the designs and refinement of the theoretical models used for reliability and lifetime estimates.
After system installation and operation, built-in reliability monitoring helps diagnose problems. The monitoring data also are used in forward failure modeling to replace postmortems. This is essential since recovery of the actual equipment for analysis is impossible.
A mathematical approach to reliability assessment of simple and parallel archetype designs for the ICS has been introduced but a definitive best design cannot be determined at present because critical in-service reliability data does not yet exist.
The theoretical and experimental results of this process are compared against the project's objectives and fed back into ongoing research and development to evolve and refine the reliability of the building blocks and to develop new technology for sensors, controls, materials, and processes.
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