Acid gas removal membranes revolutionize CO2 management for EOR operations, Permian Basin

Cynara™ H₂S and CO₂ separation membranes have provided Kinder Morgan with an energy-efficient modular solution for bulk CO₂ removal from natural gas. The operator is now recovering high-purity CO₂ for enhanced oil recovery (EOR) while simultaneously reducing opex and generating a revenue stream from significant natural gas liquids (NGL) recovery.

Kinder Morgan’s SACROC facility in Texas was designed to treat natural gas containing limited quantities of CO₂, using the Benfield and amine processes. As time went by and gas production increased, the facility could not cope with the growing and variable quantities of CO₂.

Traditional amine treatment systems for CO₂ removal were not viable because of the prohibitively large size required for such high CO₂ concentrations. On the other hand, reinjecting the entire gas stream without processing it would lead to suboptimal EOR performance (because of reduced miscibility) and the loss of valuable NGL. After a thorough assessment of various options, Kinder Morgan chose membrane technology for its multiple benefits:

• High-purity CO₂ is recovered at elevated pressures, reducing reinjection costs.
• Natural cooling of gas in the membrane process results in NGL production, providing a significant revenue stream.
• The modular and compact technology eliminates exposure to solvents, reducing HSE risk.
• Capex and opex are lower compared with other technologies.

Highly selective Cynara membranes provided the ideal solution for bulk CO₂ removal. Thousands of hollow fibers made of a cellulose triacetate (CTA) base material are packaged within each cylindrical membrane element. As pressurized feed gas flows along the fiber bundle, CO₂ preferentially permeates to the bore side of each fiber. This permeate flows out at the end of the fiber and is collected for EOR, while the hydrocarbon-rich nonpermeate gas continues through the plant for further processing.

By enabling recovery of high-purity CO₂ at elevated pressures, Cynara membranes have reduced compression requirements for reinjection. The methane-rich nonpermeate stream is processed using a smaller amine system to produce fuel gas for facility operations. The vertical membrane housing design enables natural drainage of condensed hydrocarbons, facilitating recovery of valuable NGL.

Starting with 50 MMcf/d of gas containing 40–60% CO₂, the membrane plant gradually expanded to handle 750 MMcf/d and 91% CO₂. In addition, approximately 250 MMcf/d were being processed by spiral wound cellulose acetate (CA) membrane technology from a third party. After a study found that horizontal Cynara membranes demonstrated about 20% incremental NGL recovery and 40% more capacity, Kinder Morgan switched to using Cynara membranes exclusively.

Supporting one of the largest EOR operations in the world—producing ~20,000 BOPD—the SACROC plant currently processes 1,000 MMcf/d of natural gas. The membrane system removes 17.7 million metric tons of CO₂/year, resulting in the additional recovery of 18,000 bbl/d of condensate, which provides a substantial incremental revenue stream. Moreover, the high-purity CO₂ recovered from the membrane system has reduced the need to purchase pure CO₂, significantly lowering opex. The success of the SACROC facility over the past 40 years has made it a showcase for the EOR industry, inspiring the adoption of Cynara membrane technology in multiple EOR projects across Texas and Louisiana as well as offshore Brazil.