Expro's horizontal well test separator is designed to separate 3-phases of well effluent; measuring accurately the gas, oil, and water produced from the well. A 4th phase of separation can be integrated to the design for potential sand/solid removal. The 4th phase process will help optimise the 3-phase capability by removing accumulated sands that will reduce the oil water retention time and reduce possible damage to the liquid flow meters and downstream equipment. The sand/solids removal is done by a sparging line for lifting, agitating sand/solid and then flushing out via a drain line. The well test separator can be used in conventional well testing and integrated into a flowback/clean-up package for new completions or stimulated wells.