A comprehensive system for the separation and handling of sand from produced fluids was designed and installed in a Chevron facility in the Gulf of Mexico. This system involves two multicone desander systems, one on the water outlet and one on the oil outlet of an LP separator, to provide separation of sand from produced fluids. The separated solids are collected, dewatered, and transported to a unique, simple solids handling system designed for complete fluid containment and safe handling. The focus of this paper is to present the design of the separation and handling system, and discuss the various challenges encountered during and after commissioning. The topics covered include desander operation (pressure drop and separation), slurry discharge from the desander, dewatering of slurry, recycling of fluids, and transport of the collected solids from platform to shore.
All oil and gas wells produce solids, in varying concentration, with the produced fluids. These solids may originate from the reservoir, such as sand, clay or silt, or they may be corrosion by-products from downhole tubing or other process equipment. These solids are normally smaller than 250 micron in diameter and vary in concentration for different fields, with a typical range of 5–250 PPM. This type of solids is designated as "natural" solids, although corrosion products may not be natural, as opposed to "artificial" solids, such as fracture sand, which may be larger. The system described is designed to handle "natural" solids.
Even at relatively low flow rates and velocities, solids can cause considerable problems in a production system. Severe erosion of pipe work and valves can be experienced in high pressure production. As solids accumulate in tanks and gravity separators, the conditions for bacterial growth and associated production of hydrogen sulfide become ideal. This in turn can be a source of further corrosion. Accumulation of solids in process vessels can also affect retention time and thereby reduce separation performance. Typical solids handling scenarios require solids removal periodically by sand jetting or shutting the system down and digging them out by hand. Either method is only a partial solution at best, and both can significantly impact the quality and quantity of oil production.
Solid liquid hydrocyclones, termed "desanders" for this paper, are a superior alternative to conventional equipment, such as plate interceptors or filters. Desander are a solution that can remove solids on-line, in a controlled fashion, without system disruption or shutdown. Their weight and size is usually 10% of standard equipment, and the capital cost is proportionally lower. Desanders require little, if any, operator interaction, and due to the fact they have no moving parts, maintenance is minimal. Benefits and operation of solid liquid hydrocyclones are detailed in the Appendix. Due to a combination of new drilling technologies, tighter environmental regulations, and more compact production facilities with higher uptime requirement, the need for a sound solids control strategy is greater than ever. Desanders are a proven technology providing a robust solution to these challenges.
Sand Production Difficulties
The South Pass 78 Field is located in the Gulf of Mexico, and comprises approximately 41 production wells routed from 3 satellite platforms.