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DFOS as an alternative to conventional offshore gas kick-detection methods

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The ability to read wellbore flow dynamics and predict and control influx is central to effective well control. Detecting early signs of kicks can ensure smooth operations by allowing operators the time they need to shut in the well and prevent a blowout. However, detecting gas influx in an offshore environment is particularly challenging due to factors such as currents, wave motions, the effect of high hydrostatic pressure on the influx, and more. 

 

Limitations of conventional kick-detection methods 

Deepwater well control is further challenged by narrower safe mud windows due to the increased water depth, making a gas kick more likely. Although API standards provide guidelines on blowout prevention, the recommendations are based on conventional kick-detection technology and often fail to meet the requirements of deeper risers and mobile offshore drilling units. 

Conventional well control procedures have historically proven to be reliable but are not void of limitations. Mud Pit Volumetrics, for example, rely on large surface volume change to detect downhole influx. Differential Flow, on the other hand, needs precise inlet and outlet flow measurements which are not easy to determine with traditional flow meters. In addition, both examples are kick-detection methods that rely on surface measurements which not only makes them unsuitable for mobile offshore drilling units but also further narrows the operators’ response time window. 

 

Distributed fiber optic sensing as an alternative for Early Kick Detection 

Recent advancements in distributed fiber optic sensing (DFOS) have proven that optical fiber is a viable alternative for downhole monitoring that offers real-time measurements with high spatial resolution. Specially designed optical fiber cables can be deployed on marine risers with minimal interference. Fiber in metal tubes or FIMT is our core product, and it does remarkably well at protecting the fragile fibers from a harsh environment such as that of an offshore wellbore. There are three ways FIMT can be deployed in an upstream setting – permanent installation, semi-permanent installation, and temporary installation. Permanent installation is when the FIMT is cemented behind the casing during well completion. A temporary installation is when the optical fiber cable is used in a retrievable wireline/slickline configuration. A semi-permanent installation is when the FIMT is clamped to the tubing.  

Deploying FIMT in a semi-permanent manner allows operators to have access to real-time downhole measurement data for a relatively low capital and operational cost. Moreover, this application allows the tracking of gas movements both inside the tubing and in the annulus using distributed fiber optic sensing, which allows for a more accurate early gas-kick detection. 

 

Additional data from DFOS 

In addition to early kick-detection, an optical fiber cable within the wellbore provides a range of other data crucial to ensuring smooth operation and reduced downtime. Applications such as leak detection, flow rate monitoring, sand detection, and fluid injection profiling can all be achieved via distributed acoustic sensing. Different applications require different cable designs. E.g., at shallow depths and in a non-acidic environment, a solution such as our Stranded Single Layer FIMT could suffice. However, in harsh environments such as ultradeep water, higher temperature wells, and the presence of corrosion inhibitors, a more robust solution might be needed, such as our Harsh Environment Cable or our Self-supporting Downhole Cable. 

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