Separating Solids First - Design and Operation of the Multiphase Desander

Abstract

Sand production is a common challenge for processing facilities and well test equipment, as solids degrade the mechanical integrity and separation efficiency of surface equipment through erosion, settling, and plugging. Where exclusionary sand control methods fail or do not exist, inclusionary surface handling methods can be used to maintain or increase the total hydrocarbon production. The best approach is to remove sand at the wellhead, which protects all downstream flow lines and equipment. The multiphase (wellhead) desander was developed in the late 1990s as a unit operation to separate solids at wellhead conditions. This technology has been deployed in onshore and offshore production, well cleanup, and well testing operations. In addition to protecting downstream equipment, wellhead desanding enables the easier design and operation of solids-handling systems. Multiphase desanders were developed from solid-liquid cyclones used in the mining industry. Laboratory and pilot-plant tests conducted in 1994-1995 defined an initial hydraulic model, which was applicable in mixed-phase flow. The liquid-based model was paired with a dense-gas pneumatic cyclone model. The pressure drop and solids removal efficiency of the resulting multiphase model were evaluated at the Wytch Farm producing facility in Dorset, UK in 1995. This approach continues to be refined using field data, and the current mechanistic-empirical model has a high accuracy across the 0-100% gas void fraction range. The hydraulic and pneumatic models are discussed with respect to the pressure drop, solids removal, turndown, and slugging. Mechanical design improvements, including material selection, construction to API-6A code, and apex-flux balancing, have doubled the multiphase desander operating life while reducing the size and weight by 40%. Design improvements are discussed with respect to the system layout and proper operation. A comparison is made between single and multiple cone vessel designs with respect to the particle size, solids concentration, and fluid partitioning. Facilities Sand Management All oil and gas wells produce sand; therefore, all production facilities must be capable of managing sand in the flow streams. The most common methods of sand management attempt to exclude solid particles from the well flow using a production limit or completion string. When these approaches are not

The Subsea Sand Management Challenge – What to Do with the Sand?

“…Surface sand handling is termed Facilities Sand Management (FSM). Sand coproduction, which requires FSM technology, is shown to increase hydrocarbon recovery (Rawlins 2017). This approach completes the well without a completion string -either barefoot or open-hole with large slots.…”

“…This is the first, and the highestpressure location where sand can be removed. The separation of sand with a wellhead desander (WHD) protects the choke, flow lines, separator, and produced water treating equipment (Rawlins 2017). This application has been in use for more than 20 years.…”

“…A completion includes a hardware barrier at the wellbore-reservoir interface that permits oil and gas production while preventing solids from flowing with the fluids. Over-completion prevents full hydrocarbon flow, and under-completion permits sand production (Rawlins 2017). Completion hardware has a finite operating life, with replacement required upon failure.…”

“…This technology has the highest throughput-to-size ratio of any separation device and allows the separated sand to collect into a separate, isolatable accumulator. The multiphase desander can remove solids down to 20 microns using the process pressure and has an adjustable performance (Loong et al, 2014, Rawlins, 2017. S-2: Filter/Screen.…”