Better information from downhole meters improves optimization and response times.

The rise in multilateral and multizone completions has increased the need for a better monitoring of the contribution from each producing zone. With this clear need, topside and subsea multiphase metering technology has continued to mature and is rapidly increasing market penetration.
The next natural step for the operators is to move this technology further down into the reservoir. By doing so, more precise information concerning production optimization and reservoir response is achieved, ultimately leading to increased recovery from the reservoir. This represents a significant shift in mindset from a few years ago, when such thorough information from the reservoir was not possible.
The requirement for permanent downhole monitoring of production parameters, other than just temperature and pressure, brings with it new and demanding challenges. With deeper and hotter fields to be developed, there are also increased performance expectations, such as the ability to sustain higher pressures and temperatures. Combined with long lifetime expectancies of the wells, this adds up to the requirement of improved system reliability.
In response to industry demand, Roxar has developed a new IWIS (intelligent well interface standardization)-compliant intelligent downhole network (IDN). The system has been made modular and is designed to meet the increased performance expectations, as well as the industry need for standardized solutions. This network will enable sensors to be connected to form a complete sensor system for downhole production surveillance and control.
The IDN will allow up to 32 sensors to be attached - all of which will provide input to manage a whole range of production wells or separate zones simultaneously. The IDN will communicate to all sensors, so if a failure of one sensor occurs, all other sensors will still be able to communicate to the surface.
Flow measurement technology
Multiphase flow metering has become common for most field developments when installing both dry and subsea wellheads. This provides huge cost savings to the operators by avoiding costly test separators and test lines. In addition, the continuous monitoring of all phases during production makes the optimization of daily production more precise.
The increased use of extended-reach wells with multiple production targets, or multilaterals with several branches has presented the need to pinpoint not only production data from each wellhead but from each producing zone along the wellpath. The only way to continuously monitor the production performance parameters of each individually perforated zone of a multilayer well is by downhole sensors between each production zone. Well control by permanently installed sensors will provide a cost-efficient alternative to logging operations.
Optimum well control will increase both the daily production and the total recovery from the well. For this, complete multiphase measurement is required, including the following measurements:
• temperature and pressure;
• water cut;
• gas fraction;
• sand rate; and
• flow velocity.
The first measurements - temperature, pressure and water cut - are already proven technologies in permanent downhole applications, while gas fraction, sand rate and flow velocity are currently under development. Such measurements are required for optimum control of the inflow to the well, in particular to avoid water or gas breakthrough, which can have a devastating effect on production flow, particularly in gas injection wells. Such measurements are also needed in the case of multiple drain holes.
The above parameters are being developed as individual modules or building blocks, each of them providing vital information for optimal control. Combined with the flow velocity measurement, the individual flow rates of oil, gas and water can be measured, providing a complete downhole multiphase metering system.
For multiple zone wells, the downhole composition and flow measurements will allow for optimum control of each individual zone. The system will give early warnings of transient behavior such as slugs, enabling topside processing to be adjusted in advance of the otherwise unexpected event. Together with topside or subsea multiphase measurements, this will ensure optimal reservoir control, increased production rates and total recovery.
Network in detail
At the topside (or subsea) node of the IDN, a downhole network card (DHNC) is used. This interface card acts as a master node and receives data from the downhole nodes as well as supplying the downhole instrumentation with power. Using one or alternatively two electrical lines, up to 32 nodes can be supplied with power and communicate with one DHNC. The DHNC acts as a communication gate between topside and the well, being placed typically at the wellhead. The data is then passed on to a surface acquisition system. Figure 1 is an illustration of the downhole architecture.
Each node consists of a modem, translating information to and from the common communication and power line. The node also hosts power supply and can communicate with several different sensor elements.
Interface module
The signal processing unit, the downhole interface module (DIM) acts as a general purpose sensor interface card. DIM is a custom-designed multichip module for downhole applications.
DIM has mainly been developed as a general-purpose network node but is also specially designed to handle signal processing for quartz-based pressure measurements. Nearly all the application-specific integrated circuits in the DIM are built with Honeywell's Silicon on Insulator (SOI) technology, which is prequalified to 436°F (225°C). This provides the user with not only high-temperature specification but also extended lifetime expectancy compared with conventional hybrid technology. The DIM acts as a building block for the new portfolio of downhole sensor devices.
The high-temperature/long-life components include analog functions for node communications, power supply regulation and distribution, sensor signal conditioning, and analog-to-digital conversion. Digital functions include programmable control and signal-processing blocks that may be tailored to the specific function(s) of the node, and also program and data storage. These components provide flexibility to process signals from a wide range of proprietary and third-party sensors.
Network integrity protection
The integrity of the IDN is well protected against possible short circuits on any of the connected instruments and will not influence the performance of any of the other nodes attached to the network. Open circuits could be critical, as the network is based on a closed-loop current system. However, the IDN components are prepared for such failures by open circuit fuses, which will automatically bypass units that go into an open circuit state. If the network cable is cut for any reason, the instruments above the cut will still be able to operate by cable fuse protection.
Downhole network card
The DHNC acts as the network communication master and network power supply unit. It acts as the interface between topside communication and the downhole network. At the surface, it can be interfaced with data acquisition and control software or any other distributed control system. The DHNC is fully IWIS compatible and is run on a Linux operating system.
The DHNC will perform management of diagnostics data, both from the downhole nodes and from itself. This includes polling algorithms, failure evaluation and alarm settings, of critical importance to ensuring the integrity of the data being transmitted. It is also important for technical enhancements of the system, as downhole instrumentation is rarely retrieved for further examination.
The DHNC also allows for the reprogramming of downhole modules in case software upgrades or a change in downhole configuration is required. It is also possible to alter filter settings and polling sequences, change polling rate, or the communication baud rate.
Conclusion
Moving multiphase metering technology downhole enables operators to more closely monitor and control flow behavior in wells with multiple producing zones. This results in higher daily outputs for the operator without risks to production, such as excessive sand or water. Using mature multiphase technology reduces technology risks and results in proven interpretation techniques as well as the monitoring leading to a more precise modeling of the reservoir.
The combined effect is a better reservoir understanding and ultimately an increased recovery of assets.

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