Distributed Acoustic Sensing Interrogator Oil Gas CCS | SLB

Optiq distributed acoustic sensing interrogator

Compact, low-power unit handles long fiber lengths with high detection sensitivity and low false-alarm rate

Image of distributed acoustic sensing interrogator.

How it improves performance

A component of SLB Optiq™ fiber-optic solutions, the distributed acoustic sensing (DAS) interrogator features high sensitivity and dynamic range. These characteristics are key enablers of several fiber-optic monitoring applications.

How it handles extended lengths of fiber

The unit contains two optical modules, which can simultaneously interrogate sensing fibers, each up to 65 km long. As a result, it has a 130-km range, ideal for pipeline integrity monitoring, where it provides >90% accuracy even before system tuning with machine learning algorithms and <1% nuisance alarm rate. For subsea applications, where the sensing fiber can be longer, a subsea optical amplifier can extend the interrogator's range.

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Multiphase production flow profiling in wells with low gas fraction and in high-rate wells

Oil or water inflows usually produce less vibration than gas. Consequently, instruments with high DAS sensitivity are essential for quantifying these inflows and differentiating phase fractions from noise.

Conversely, in high-rate wells, especially gas producers with ICDs or wells undergoing hydraulic fracturing, the high noise signal can saturate the DAS response and challenge inflow or outflow profiling. The wide dynamic range of the fiber-optic DAS interrogator ensures acquisition of high-quality data for more accurate interpretation of zonal flows.

Transient analysis requires changing the drawdown, and the interrogator’s high sensitivity enables reducing the amplitude of the change to minimize unwelcome production losses while preserving data quality. The small spatial sampling interval enables higher-resolution data interpretation along the wellbore and is critically important for distinguishing flow-related features from other acoustic data.

Injectivity profiling

Injection produces small vibrations (acoustic signals), which are mostly associated with water flowing out to the formation behind the casing. Even more challenging conditions are encountered postinjection—during warmback—with low wellbore afterflow or crossflow rates, which generate low-amplitude vibrations. High DAS sensitivity and dynamic range address these challenges.

Well and caprock integrity determination

Leak detection to remedy well integrity issues often requires the ability to detect weak vibrations and accurately locate them along the wellbore.

For monitoring caprock integrity and OOZI, the analysis is based on quantitative interpretation of DAS signal variations in the vicinity of the unintended fracture initiation point. High DAS sensitivity is extremely important for improving the accuracy of locating the initiation point and estimating fracture parameters. The interrogator’s dynamic range ensures reliable detection of fractures and OOZI, enabling greater injection volumes without risking caprock damage.

Monitoring production pipelines with multiphase flow for leaks, theft, and pigs

Typical oil and gas upstream production flowlines contain highly corrosive multiphase fluids and are exposed to multiple external events that can lead to the fluids leaking into the environment. Moreover, pipelines are often key infrastructure assets both domestically and internationally, sometimes bridging continents. The ability to deliver fluids such as crude, refined petrochemical products, chemicals (e.g., ammonia), dry or wet natural gas, CO2, and hydrogen is of core importance to operators and governments.

Continuously monitoring the health and integrity of the pipeline protects your license to operate, improves economics, and saves the environment from leaks caused by corrosion, theft, and geohazards. By using DAS technology, operators can quickly locate pinhole leaks as small as 1 mm.

Where gathering networks are located on harsh terrain, the DAS solution provides advance warning of subsidence due to landslides or cavern collapse due to poor weather conditions or mining activities.

Pigging is a regular but precarious task for maintaining the internal health of a pipeline. The high level of sensitivity and fidelity provided by the DAS interrogator helps you track the pig and its speed without use of field crews, estimate its time of arrival at a given point, locate areas of potential blockage, count welds along the pipeline, and map the operational window of the pig.

Existing telecom fiber-optic cables laid along or strapped to flowlines can be used for DAS. Alternatively, SLB can support retrofitting fiber-optic cables on surface pipelines or trenching alongside buried ones to provide the infrastructure for 24/7 remote monitoring.

Seismic data acquisition

Optiq Seismic™ fiber-optic borehole seismic solution enables acquisition of zero-offset, walkaway, and many more types of vertical seismic profiles (VSPs); 3D seismic surveys; and 4D seismic surveys for reservoir monitoring in minutes rather than the hours or days required using conventional methods.

Over a one-month period, DAS systems located across the world were used to monitor earthquakes to provide insights into how a potential global monitoring system based on DAS might look. Systems for the centralization of data will, over the long term, pave the way for improved detection methods and early warnings for seismic events to reduce the impact on the lives and livelihoods of those affected.