Commensurate with knowing what problems sand causes – erosion, filling, interference, or increased OIW content – is then knowing where to remove the sand. A primary directive is to solve the right problem.

The first two of the four-nodes of separation use the multiphase desander – the wellhead desander is upstream of the choke while downstream of the choke is the wellstream desander. If replacement of chokes is a hindrance to sustained production, then remove the sand at the wellhead. However, if the goal is to prevent solids from settling in the separator then sand should be removed from the manifold.

Node 1: Wellhead – Upstream of the Choke

Process

• Removes solids closest to source
• Isolate specific sand problem wells
• Protects choke, piping, separator, valves, and PW system
• Utilizes available (lost) pressure from choke
• Free gas improves separation efficiency
• Sand removed at wellhead cleaner and easier to handle and transport

Mechanical

• Low actual gas volume yields compact size
• System integrated into existing well slot/bay structure (non-skid design)
• API design has lower size/weight compared to ASME
• Designed for full shut-in pressure (no PSV required)

Node 2: Wellstream – Between Choke and Separator (Production or Test)

Process

• Protects separator and water treating
• Does not protect choke or flow lines
• Isolate specific sand producing headers
• Utilizes available post-choke pressure (separator inlet)
• High gas void fraction improves separation efficiency
• Sand still relatively clean and easy to handle and transport

Mechanical

• Higher actual volume of fluids (gas) due to lower operating pressure results in larger diameter desander
• Lower pressure rating: ASME design
• PSV required for vessels

The next article covers the development history of the multiphase desander.

References

1. Rawlins, C.H. 2017. “Separating Solids First – Design and Operation of the Multiphase Desander”, paper 185658-MS presented at the SPE Western Regional Meeting, Bakersfield, CA, 23-27 April.