Smart Choke - A Simple and Effective Slug Control Technology to Extend Field Life
Authors: Yaw Sheng Ying , Lee Chia Yee , Haandrikman Gert , Groote Gijsbert , Asokan Shankar , Malonzo Michelle Enciso 
Published: March 2015

Slugging in pipeline-riser systems is becoming more common as the petroleum industry matures. Current trends of developing deepwater fields and producing from marginal fields via subsea tie-backs to existing facilities often lead to slugging. Slugging also occurs in fields approaching end of life, due to decreased gas coupled with increased water productions. Slugging is a major problem for offshore operations because it causes large fluctuations in gas and liquid production which may cause platform trips and riser vibrations. These will lead to production deferment, riser integrity/safety issue, and potential abandonment for fields operating near end of life.

The most recent slug control technology in Shell is the Smart Choke. This technology utilizes a single control valve which is installed between the riser top and first stage separator. It is an active slug control device which regulates liquid and gas flow by manipulating the control valve opening. Compared to conventional slug management techniques which require large footprints and high capital/operating costs, Smart Choke is compact and cost-efficient.

Smart Chokes have been installed in the Gulf of Mexico, Nigeria and Malaysia. The pipelines had large fluctuations in pressure and gas/liquid flowrates due to hydraulically unstable flowline/riser system. The installed Smart Chokes were tested to be effective in suppressing riser-induced slugs and controlling slugs initiated within horizontal pipelines. Deployments to-date has shown for example field life extensions of over one year or production gains of about 5 to 10%.

This paper presents the implementation of Smart Choke from feasibility study to site implementation in a Malaysian field. It is the first project that integrates Smart Choke control into a platform control system for easier operation. Field data are presented to demonstrate how Smart Choke has extended the field life through the control of slugs. As a result, the shut-in field which was planned for abandonment could continue production.

Introduction

Pipelines are used in offshore production to transport hydrocarbon fluids in multiphase flow i.e. gas, condensate/oil and water from satellite wells to topside facilities for processing. When producing hydrocarbons in multiphase flow, the outlet of the pipeline may encounter irregular production of the different fluid phases. This irregularity may occur due to changes in operating conditions as the fluid flows through the pipeline, geometrical layout and/or fluid compositions. Major process upsets may occur if the fluctuations in gas and/or liquid production at the end of the pipeline cannot be accommodated by the receiving processing facilities. Large fluctuations in gas/liquid production i.e. slugging, will lead to difficulty in controlling the liquid level at the first stage separator and increase the risk of liquid carryover into the downstream gas processing train. Production may have to be constrained to prevent the gas/liquid fluctuations from exceeding topsides facilities limit. Severe cases of slugging may also cause platform trips and shutdowns due to high liquid level or high gas pressure, riser vibrations or impact the mechanical integrity of vessel internals. These will lead to production deferment, riser and mechanical integrity/safety concern and potential abandonment for oil/gas fields operating near end of life.