Smart Fluid Processing at Reduced Footprint – Separation Redefined
Authors: Manion Catherine , McCrackin Sheldon , Joshi Mahendra , Wang Paul , Pal Subrata 
Published: October 2018

Efficient processing of fluids from flowing wells is an important function on a topside facility to maintain optimum hydrocarbon production. Many oil and gas facilities face the additional challenge of limited available footprints to process additional capacity. Normally, onshore facilities move process fluids from the wellhead to a de-sander unit, and then to a 2-phase or 3-phase separator unit. In offshore and onshore production facilities, fluids from multiple wells are sometimes co-mingled in a manifold and processed through two or three separation stages with progressively lower pressures to separate gas, crude oil, and produced water. Sequential pressure letdown and numerous fluid pump-around loops to separator vessels and interconnected piping with pumps, valves, and instrumentation occupy a large space on a wellsite. To add processing flexibility in an ever-changing fluid composition (water cut, gas vapor fraction (GVF), and solids loading) from co-mingled production wells and to remove the bottleneck at the topside processing capacity, a chemically enhanced, smart compact separation system has been developed.

The new separation system is based on the centrifugal (CF) separation principle. After comprehensive laboratory testing and Computational Fluid Dynamics (CFD) model validation for separated fluid streams, the system was tested in field conditions at an unconventional wellsite to benchmark mechanical reliability, separation effectiveness, and robustness. The modular design concept of this new system enables operation at 200 to 10,000 bbl/d fluid capacity at nominal increments by adding units in parallel. The system is designed to handle 30 to 99% water cut and normally encountered solids or fines concentrations. This technology is also able to handle ever-changing fluid conditions at the well such as production decline or water cut changes by using a digital interface that controls the separator operation based on inlet fluid conditions. This smart, compact separation system enables efficient separation and reduces the need for over-sized separation vessels.

A 2,000 bbl/d, two-phase (oil/water) system has consistently achieved residual oil-in-water (OIW) levels below 400 ppm in the water outlet without chemical addition enhancement. The residence time for separation is less than a minute for the 2,000 bbl/d prototype unit, enabling it to be used as an alternative to a freewater knockout (FWKO) vessel. The prototype unit has a 4-in. diameter housing that is mounted on an 8-feet cast-iron frame with a 15-hp electrical motor coupled as the prime mover. The lab and long-term field test results have also indicated that the CFD simulations can effectively reveal the mechanism of oil-water separation as well as validation of separator sizing parameters for various flow capacities. The refined control algorithms are still in development phase, but when completed they will control the separator dynamically as flow conditions change in the well. A field trial to test chemical demulsifying agents will determine the final separation efficiency of this system.