CompactSep™ - Compact Subsea Gas-Liquid Separator for High-Pressure Wellstream Boosting

Abstract

Subsea separation has successfully been implemented on the Troll and Tordis fields operated by Statoil, Pazflor (Total), Marlim (Petrobras), and Perdido and Parque das Conchas/BC-10 (Shell). One objective of subsea separation is to separate gas and liquid to optimize working conditions for subsea pumps enabling high recovery factors. The objective of this work was to qualify a two-stage, compact, inline gas-liquid separation system with full turndown and slug handling capabilities, consisting of already proven components: one Gas-Liquid Cylindrical Cyclone (GLCC) and one InLine DeLiquidiser.CompactSep and its separator components and control system were qualified through a comprehensive, large-scale, real fluid and high pressure test programme at K-lab, a Statoil large scale test facility in Norway. This was done in a Joint Industry Project with Statoil as operator and Chevron, Petrobras, Total, and FMC Technologies as participants. The tests were performed with realistic fluids -59°API condensate and 25°API crude, recombined with natural gas -and at realistic pressure conditions, from 25 to 90 bar, with and without inlet slug flow. The separation requirements for the CompactSep system were a liquid output with gas volume fraction GVF Ͻ 0.1 and gas output with gas volume fraction GVF Ͼ 0.995 downstream the separator system. The pressure drop limits were 2 bar (soft target) and 5 bar (hard limit). Separate and stricter requirements were set for the system's individual separator components.The main results were: a wide operating range where the performance requirements were fulfilled, 99% to 99.9% separation efficiency, gas qualities (GVF) between 0.995 and 0.999, and liquid qualities (GVF) between 0.02 and 0.1. The operational boundaries were challenged to determine the onset of liquid carry over and gas carry under. The actual operating range exceeded the design and performance predictions. The system handled slugging and start-up scenarios. The control system stabilized the process with relatively slow control valves.The work developed and qualified an inline separator system with full turndown and slug handling capability. Qualification was performed at a wide range of realistic conditions and with high quality reference and performance measurements. Comparison of CompactSep and conventional subsea separation stations shows significant cost and weight reductions for the compact solution. What can be done subsea can be done topside. The CompactSep separator is a viable alternative to conventional vessels for topside applications where size and weight must be limited.

Nonlinear State and Parameter Estimation for a Gas-Liquid Cylindrical Cyclone

“…The bias of these estimates are larger than for the UKF, but with equally small variance. A general observation of the controlled variables show acceptable control performance for the changes in inlet conditions with respect to the experimental start-up response in [3]. RMS values of the control error e ctrl =x −x ref and closed-loop system error e sys =x −x ref are given in Table IV to enable objective evaluation of their performance.…”

“…This separator is preferred for subsea applications over large gravity-based separator due to its simple and compact construction that allow for installation at deep waters and remote operation requiring little maintenance [2]. The performance of the separator depends on several variables and therefore, multiple sensors are required to achieve efficient operation [3].…”

An Analysis of Inlet Inclination on the Performance of a Gas-Liquid Cylindrical Cyclonic Separator

“…Kouba et al, [2] measured the pressure drop across GLCC separator to estimate liquid holdup under zero-net liquid flow condition. Kristiansen et al, [20] measured the pressure drop across GLCC separator only for the purpose of obtaining pressure drop as the operating parameter rather than a performance parameter. There is a need to evaluate the effect of inlet geometry on the pressure drop across the gas leg of the separator to decide the best inlet design.…”

Adaptive feedback linearizing control of a gas liquid cylindrical cyclone

“…The gas liquid cylindrical cyclone or GLCC is a widely used separation device and is currently installed in over 6000 onshore gas production and processing plants around the world [1]. While popular in onshore production, the GLCC has yet to reach the same popularity in subsea and offshore production and processing facilities.…”

“…In ultra deep waters (≥ 3000 m), the required size of the gravity separators makes the installation and maintenance economically challenging [2]. When the size of gravity separators increases, so does their weight and there is a limited amount of ships available for installation of such large vessels [1]. This is why the offshore and subsea industry is leaning towards more compact separation technology such as the GLCC.…”