From reservoir modeling and engineering through multiphase metering and corrosion and formation water management, production optimization strategies are a major part of operators’ focus. Yet, just as operators know more about their reservoirs than ever before—through a combination of pressure, temperature, fluid and flow datasets—when it comes to accessing information downhole and, in particular, behind the well casing, operators too often fall short.

Accessing information downhole

Accurate and real-time pressure information downhole is crucial to production optimization. The lack of such information can result in the need for well intervention techniques, such as logging, perforating and plug setting. The access to such information is particularly useful when making reservoir management decisions related to metering, production allocation or choke settings. There are a number of downhole monitoring innovations and existing technologies available to meet these challenges.

Emerson, for example, has developed a variety of gauges based on quartz crystal measurements designed for the most extreme of well conditions. The gauges continuously transmit digitized pressure and temperature data to the surface, from where data are acquired, processed and distributed.

Such gauges are being deployed in production, injection, observation and highly complex multizone intelligent wells around the world where they generate reliable and real-time downhole information crucial to reservoir operations. Equinor’s (formerly Statoil) Gullfaks C production platform in the North Sea, for example, has been using Emerson’s Roxar downhole gauges, uninterrupted and without maintenance or replacement, for more than 22 years.

The need for flexibility

Another key driver in downhole operations is the need for network flexibility and for operators to be able to read not only gauge information but also downhole information from other types of instruments, such as position sensors, downhole multiphase sensors and other monitoring systems.

To this end, Emerson’s Roxar Intelligent Downhole Network can carry signals from the wellbore to the customer monitoring system while allowing operators to install multiple sensors on a single cable to form a complete asset management system downhole. In this way, the system also can form an interface with sandface monitoring and other well control tools.

Going behind casing strings

Yet, it is behind the well casing and in the annulus that there is perhaps the biggest information gap in production optimization. A completed well normally consists of at least two annuli, with the annulus B often located between different casing strings.

The annulus B is important because it is the area most likely to see the first indication of high pressures farther down the well. Such high pressures can lead to the deterioration of cement seals or loss of casing integrity, and injection or reservoir gas migrating vertically along the outside of the casing. This can lead to uncontrolled gas escaping at the surface during workover operations and, in worst-case scenarios, a shallow gas blowout with significant offshore safety concerns.

Despite the annulus B’s importance, once the sealing and cementing takes place, operators are often unable to access this vital pressure and temperature information and confirm or monitor well barrier integrity in accordance with industry standards.

The result is that in many cases the completion engineer is faced with either increasing the pressure ratings of the casing to compensate for worst-case scenarios (with the accompanying costs) or relying on shallow well zones to absorb pressure rises, which is an inexact science.

In some instances, wells have even been unnecessarily shut down in an effort to protect well integrity. The lack of such information also makes it difficult for operators to meet integrity monitoring standards, such as American Petroleum Institute (API) RP 90 and NORSOK D-010.

A downhole sensor system

To address this information gap and meet the need for compliance, Emerson has developed the Roxar Downhole Wireless PT Sensor System.

The system, part of the integrated downhole network, provides operators with access to online displays and trending of previously unreachable temperature and pressure subsurface data behind the well casing. It has been tested at 225 C (437 F) and can withstand pressures of up to 20,000 psi. The result for operators is achieving online integrity verification without any impact on production.

The Roxar Downhole Wireless PT Sensor System provides operators with access to online displays and trending of previously unreachable temperature and pressure subsurface data behind the well casing. (Source: Emerson Automation Solutions)

The system, which has a technology readiness level of 7 based on API recommended practices, and consists of a wireless reader, a wireless pressure and temperature transponder and antennae, can generate early warnings of abnormal conditions so that remedial action can be taken.

The sensor is installed externally to the steel casing and may be cemented into place in the well. Continuous power and data to and from the sensor are then transmitted wirelessly through the steel casing to ensure maximum well integrity for the life of the well and enable any anomalies to be detected early and in real time (something that would not be the case with periodic testing). The sensor system may be placed at any depth in the well completion.

In addition, the system is powered using an inductive coupling system developed in-house with no need for batteries, making it ideal for harsh environments and the HP/HT surroundings often found offshore. As part of an integrated downhole network, the system also adds minimal rig time or risk to regular well monitoring installation activities.

North Sea downhole application

The Roxar Downhole Wireless PT Sensor System has already generated significant direct savings for operators due to reduced testing requirements and more time to focus on production optimization. More than 30 downhole wireless systems have been installed to date.

The successful first deployment of the new system took place in 2014 on Equinor’s Skuld Field in the Norwegian North Sea, helping Equinor achieve well integrity monitoring and offshore safety, adhere to Norwegian legal requirements and improve control over its production operations.

One recent deployment of multiple systems was in the Maria Field offshore Norway in 2017, providing the operator Wintershall with improved well integrity monitoring and offshore safety. In this case, the pressure and temperature monitoring system allows Wintershall to verify that the predicted pressure buildup falls within the design criteria, and an alarm trigger point has been implemented in case pressures potentially outside the system design are reached.

It is through integrated technologies such as these that operators will have the information they need to make informed decisions on well integrity, adhere to regulatory requirements, ensure offshore safety and enable their wells to produce at optimal levels.

At a time of middling oil prices where production optimization is more important than ever, it is encouraging to see that technologies are rising to the occasion and bringing added certainty to well integrity, offshore safety and production operations.