Intelligent well systems (IWS) are slowly building traction as early adopters gain confidence in their reliability and long-term profitability potential.

A 5-year joint development between Baker Oil Tools (BOT) and Petrobras has culminated in the successful implementation of an all-electric deepwater intelligent wells system completion, and brings optimism to an industry known for its conservative approach to new ideas.

It is to Petrobras' credit that it held fast to its conviction that being able to monitor its deepwater wells' production at the completion, analyze the production data and use the resulting information in its well and field management programs would help achieve production optimization. The road to ultimate success was tough and full of pitfalls that might have deterred others. But Petrobras had one advantage. Given that most of its offshore production is in ultradeep waters where drilling and production costs are extremely high, it saw IWS as a necessity, rather than an option.

With its ability to forestall interventions, or eliminate them altogether, IWS can provide major cost savings. At the same time, IWS' ability to control production can maximize profits in dozens of ways. As the old saying goes, "Necessity is the mother of invention," and Petrobras set up a strategic initiative titled PROCAP 3000 to manage the inventions necessary to deliver the needed technology to produce economically its deepwater reservoirs.

The challenge

Petrobras set some tough requirements. First, it wanted to develop completion systems that would help meet standardization guidelines. These were designed to minimize capital expenditures and inventories of systems and spare parts, as well as accelerate training of field personnel. But standardization flies in the face of the customized solutions needed to solve a particular well problem. BOT would have to deliver a standardized package that could produce well-specific results. Much of the required standardization had to do with the subsea infrastructure (types and sizes of trees and tubulars in use), communications and control systems that link downhole monitors and valves with surface and remote production managers, upper completion requirements and workover contingencies.

Fortunately, one of the key benefits of IWS is its ability to reduce or eliminate workovers, so those costs should be greatly reduced, but no one was willing to give up on the possibility that a workover might be necessary, so the system had to be designed to allow an intervention with minimal risk. Usually, tubing disconnection devices are used to reduce trip time in working over deep completions, but in the case of the first well, Petrobras determined the benefits of running a tubing disconnect didn't outweigh the risks associated with running it.

The solution

BOT proposed to run an all-electric IWS system in Petrobras' 8-MLS-67HA-RJS well. The well is in the Marlim Sul field in 3,540 ft (1,079 m) of water, and is tied back to the P-40 dynamically-positioned production semisubmersible by a 3.7-mile (6-km) umbilical. The well was completed in two zones and serves as a water injector well. It was necessary to provide individual control over each injection zone through a single 51/2-in. casing string. Pressure and temperature data were to be continuously monitored from both zones using a flow measurement unit, and production was to be controlled with an intelligent production regulator (IPR), both of which had to communicate to surface through the existing subsea architecture. After analyzing all the requirements and constraints, it was decided to separate the IWS system from the lower horizontal gravel pack completion and the upper sandface completion. This was accomplished by designing a 51/2-in. annular injection connection from the upper IPR to the upper zone and a concentric bypass from the 31/2-in. lower IPR to inject into the lower zone. An expansion joint was provided to accommodate the completion tubing and pass the twisted pair power and control cables, which were protected inside 1/4-in. stainless tubing.

Proprietary software to be designed compatible with the existing surface control system allowed data acquisition and communication from the completion to the production vessel well as transmission of control commands to the IPR valves. Petrobras' system allows full remote monitoring and operation of the well from anyplace in their network.

Reliability assurance

Petrobras engineers were confident that the proposed IWS system would perform as designed because during the early stages of PROCAP 3000 they had installed the completion in one of their land wells in Rio Grande do Norte. Except for the subsea penetrations, the completion was a dual water injector representative of the Marlim Sul project. Following extensive testing in BOT's facility, the completion was run in May 2001. Through April 2002, the completion was monitored and the control valves were exercised several times to ensure reliable operation. In the meantime, the subsea interface hardware was assembled. Satisfied with the performance of the downhole components, the completion was pulled from the land site and shipped to Petrobras' facility in Macae, where it was married to the subsea hardware and rigorously tested as a complete system.

Installation and commissioning

As occasionally occurs in the oil business, the installation experienced some significant delays not related to the IWS system. As a result, the lower gravel pack completion was installed separately and the well was temporarily abandoned. While it was waiting for wellsite operations to resume, Petrobras laid the subsea flowlines and control umbilicals that tied the subsea tree back to the P-40. After a 7-month delay, completion operations were resumed at the MLS-67 well. Another false start was recorded while the well was cleaned out, but by July of 2003 the final installation was accomplished and the completion was commissioned.

Currently, the well is performing as designed. Fifteen hundred b/d of water are being injected; 5,700 b/d into the upper zone and 9,300 b/d into the lower zone. Using the PC-based control system, water injection to either zone can be continuously monitored and controlled with the result that field production can be optimized with minimal risk of water breakthrough or gas coning into producing wells.

Intelligent wells. Are they worth it?

The answer to this question is a qualified "yes." The production monitoring technology is fairly mature, as is the communications and data processing technology. Subsea tree design has progressed to include environmental feed-throughs to route necessary control and power lines through the tree, and subsea connectors are available for all sorts of applications including fiber optics. They can be reliably connected and disconnected at the seabed using remotely operated vehicles.

With the control valves, reliability is as good as can be determined by today's experience. Both hydraulic and electrically-powered valves are in use throughout the world, and each day of trouble-free operation sets a record. How much experience is required before operators will have the confidence they need to routinely specify these valves remains to be seen. But Petrobras' systematic approach under the auspices of PROCAP 3000 has paid off. The company has satisfied itself that reliable systems can be designed, and verified through realistic testing before an expensive rig is mobilized to install them.

Several valuable lessons were learned on the MLS-67 project. The first was already a well known adage: "Haste makes waste." Companies that set out to install a completion to optimize production and eliminate intervention over the life of the well need to maintain that perspective as they design and test proposed solutions. They learned that an investment of time and money to assure long-term reliability is worth much more than any short-term savings that may result from skipping a step. In addition, they learned that a synergistic multi-disciplinary operating environment must be established to get maximum benefit from an IWS system. Standardization and good documentation are required to build a legacy of efficiency and confidence among those who come to operate the facility in the future. And both the operator and its service partners must lay the groundwork for development of best practices for IWS installations that will smooth the way for subsequent completion projects.

It may be difficult to justify economically the MLS-67 IWS completion on its own merits. However, the lessons learned and the technology assembled and implemented have proven to be invaluable in laying the groundwork for future completions. Importantly, it greatly reduces the risk factors, by substituting actual experience for what had previously been theory and conjecture. With 75% of its wells in deepwater, Petrobras' necessity has driven it to success in yet another frontier.

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