Roxar has determined that the accuracy required for water detection in gas wells can only be met with a new technical development, extending the water detection capability in gas wells beyond traditional multiphase technology. Hence, the company's WetGas meter was developed with a sensitivity to water detection 200 times better than the state-of-the-art performance from multiphase meters.

Water is a challenge!

Gas as an energy source is a rapidly growing business and several major developments are being implemented or planned worldwide. New developments and older gas fields face several challenges, and one of the most important is the determination of the water production profile. Typical areas of concern related to influx of water into the gas production are:

Scaling in the production system. Water, especially saline water, can have a dramatic effect on the scaling in pipes and pipelines.

Catastrophic water breakthrough. Water coning and blockage of the well can cause significant reduction on the well's production.

Hydrate formation and corrosion. Increased water production requires increased injection of chemicals for prevention.

These problem areas can develop very rapidly. A key for managing them is to know exactly when and how much water is being produced. This requires very sensitive, accurate and reliable measurements of the water in the gas stream.

Longer and longer tiebacks

Traditionally, the water has been managed by a "worst-case" scenario planning of expected water production, with sampling at the surface location to monitor the production. Currently we see longer and longer subsea tiebacks being utilized, and while development with 100-mile (160-km) tiebacks is in place, planning of fields with more than 313-mile (500-km) tiebacks is ongoing. With these distances, the time lapsed between water occurrence in a well and detection at a shore based facility will be days or even weeks. The effect of the water may already have advanced into non-manageable consequences, and hence metering at the wellhead is a definite requirement.

Industry requirements

Industry requirements regarding water detection are becoming more and more demanding as technology is becoming available. The RFM multiphase meter is widely recognized in the industry as being one of the best meters available. It utilizes the optimal technology for water measurement, i.e. dielectric measurement. For wet gas applications (98% to 100% gross volume factor or GVF) this meter has a sensitivity in water detection of 1%. It was quickly determined by operators that there was a need for higher water detection accuracy in such wells, and Roxar, therefore, developed the WetGas meter with water sensitivity in the range of 0.01%. Two years later, operators of subsea gas fields are defining requirements down to 0.005%. This means that the industry requires a detection sensitivity of 120 liters of water per hour in a 10 million standard cu m/day gas well. Traditionally, multiphase flow meters are sometimes mistakenly believed to deliver adequate accuracy and sensitivity for gas wells. However, the sensitivity to water in gas conditions for the meter will be in the range of 1%, i.e. 25,000 liters/hour for the same well conditions. Other multiphase meters available in the market, utilizing other types of technology, will be five to 10 times less sensitive. Based on this, dedicated wet gas meters with advanced water detection capabilities were required to meet industry requirements.

The tool

The tool allows accurate measurement of hydrocarbon flow rates and water, with a very compact mechanical solution allowing easy and cost-efficient installation. The meter provides accurate and sensitive water measurement using advanced microwave-based dielectric measurements as well as accurate gas and condensate flow rates based on standard delta pressure devices. It has been developed together with major subsea operators to ensure that the industry requirements are met, and is used for flow assurance and well allocation in a host of applications worldwide.

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