Understanding choke noise in sand detection

Noise from high differential pressure

Choke noise is typically categorized into two main types. One type occurs under high differential pressure across the choke, generating acoustic noise that interferes with the ultrasonic frequency range used for sand detection.

In such cases, noise levels are often highest at very small choke openings. For example, when the choke is opened by a few percent, the noise can be at its highest and mask the sand production signal. This is an important consideration during well start-up, particularly when bringing a new well online. ClampOn is often involved together with the operator during this phase, supporting data interpretation and monitoring the signal throughout the start-up process.

When high acoustic noise occurs at low choke openings, increasing the choke opening reduce the differential pressure, causing the noise to disappear.

An important additional factor is that sand production typically does not occur at very low choke openings, as the gas velocity is too low to transport particles. In gas wells, a velocity of approximately 5 m/s, and in some cases up to 10 m/s, is required to initiate sand transport.

This can be compared to sand movement in a desert: a certain wind speed is required before particles begin to move. At low wind speeds (below approximately 5–10 m/s), the sand remains stationary. As wind speed increases, smaller particles move first, followed by larger particles at higher velocities. The same principle applies in the flow line.

At very low choke openings, where noise levels are high, particle transport will normally not occur. In such cases, choke noise is typically not a concern. However, situations can arise where particle transport does occur while choke noise masks the sand signal. This must be carefully considered prior to start-up. ClampOn, together with the operator, should evaluate the conditions and associated risks to ensure a safe and controlled start-up.

Noise from choke operation

The second type of choke noise originates from the operation of the choke itself. This is particularly relevant for subsea chokes controlled by electric actuators, which can generate acoustic signals that influence the sand detector.

This type of noise is generally easier to identify and filter using ClampOn software. Since the acoustic response occurs only during choke movement, it can be clearly identified by comparing the choke operating trend with the raw signal trend.

Noise generated by choke operation typically appears with consistent amplitude levels. By correlating operational data with the raw signal, it becomes evident that these signatures are caused by choke movement rather than actual sand production. Software and AI-based filtering can effectively remove this type of noise.

Acoustic filtration in ClampOn Particle Monitors

Acoustic filtering in ClampOn Particle Monitors has improved significantly over the past 30 years. As a result, there are now installations where sensors are mounted directly on the choke while still achieving reliable sand detection and effective noise filtering.

In some cases, this location is selected because flow velocity is highest at the choke, which can enhance detection sensitivity. However, this is not the preferred installation point, and sensors are only mounted on the choke when necessary.

Support and optimization

If you experience challenges with choke noise in your sand monitoring system, ClampOn can assist in identifying and implementing solutions. This may involve adjustments to operational procedures, alarm limits, acoustic filtering in the sensor, or configuration of autozero and AI functions in the Sand Monitor software.