Smarter oil and gas production

Tackling excess carbon dioxide

By Janet Pinheiro
December 16, 2021

Elements Magazine
Technology

Carbon dioxide (CO₂) moves silently between our air, land, plants, animals, and people. Without CO₂, natural life on Earth would not survive.

Bonded by one carbon and two oxygen atoms, CO₂ uses its delicate lightness to perform life sustaining functions for our planet. For instance, devoid of CO₂, plants could not make food.

Global industrialization has increased greenhouse gases (GHG) — such as CO₂, methane (CH4), nitrous oxide (N2O), and water vapor (H2O) — emitted into our atmosphere. CO₂, our life sustaining friend, has also become our climate change adversary.

Catching carbon

Today we have too much CO₂ in the atmosphere. Carbon capture, utilization and storage (CCUS) is widely regarded as one of the primary ways toward managing the world’s excessive CO₂ emissions.

The emissions reduction technology prevents CO₂ from being released into the atmosphere, and instead, it can be applied across the energy system. Capturing carbon is used to help improve the quality of natural gas, and with advanced technology, CO₂ can now be removed and sequestered.

First, CCUS captures CO₂ at the source or directly from the air, and then, the technology compresses the CO₂ down to one-500th of its large atmospheric size. After the CO₂ is compressed, it can be transported for underground storage, or it can be recycled for a useful purpose.

Aramco’s Hawiyah NGL recovery plant separates and compresses CO₂ from natural gas, before sending it 85 kilometers through a pipeline to a custom-built reinjection facility in ‘Uthmaniyah, where it is returned to the Ghawar oil and gas field.

Returning carbon to its source

A solitary steel web of pipes and tanks rises above central Saudi Arabia’s desert sands. Operating quietly within the metal configuration is a CO₂ capture and enhanced oil recovery project.

At the Hawiyah natural gas liquids (NGL) recovery plant, CO₂ is captured and reinjected back into the world’s largest discovered conventional onshore oil field, Ghawar.

At standard temperature and pressure, CO₂ is a colorless gas of minimal weight. Compressing CO₂ transforms it into a supercritical state.

Every four hours during his work shift, Hawiyah NGL plant operator Omar N. Almodrhim checks the pressure and tests the functionality of the CO₂ unit, which has prepared CO₂ to be returned underground since 2015.

Seven compression stages

Hawiyah NGL receives gas from the nearby Haradh gas plant. After separating the CO₂ from the gas, an internally-geared compressor uses seven stages to compress the CO₂.

At the fifth stage, the CO₂ is routed to a gas dehydration unit, before being returned to the compressor for stages six and seven. The final stage compresses the gas to 1,500-1,600 psi, then pipes it 85 kilometers in an 8-inch alloy steel pipeline to the pilot site at ‘Uthmaniyah.

Here, the CO₂ is released into four injector wells. Produced fluids from four adjacent oil producing wells travel through a trunk line to the separation plant for further processing in a fit-for-purpose high-pressure production trap.

Since 2015, up to 800,000 tons of CO₂ have been reinjected at the ‘Uthmaniyah pilot site. The project is achieving both sizable CO₂ sequestration, along with enhanced oil recovery

At ‘Uthmaniyah the high-pressure CO₂ arrives at a tightly controlled row of four injector wells, four producer wells, and two observation wells — the latter four connected in real-time with flow measurement devices and remote-controlled choke valves, and outside operator Mohammed M. Alrashdi examines the product level of one of the project’s vessels.

Carbon reinjection into Ghawar oil field
The Middle East'smost advanced large-scale CO₂ capture and reinjection project handles up to 800,000 tons of CO₂ that is reinjected each year since July 2015

Oil field sequestration

There are compelling reasons to inject CO₂ into an oil and gas reservoir. Oil reservoir fluids — made up of oil, dissolved gas, salty water and some hydrogen sulfide (H2S) — are typically under pressure.

Extracting fluids means natural underground pressure can decrease over time. Flowing compressed CO₂ into a maturing oil field facilitates easier oil recovery by swelling stubborn droplets.

Importantly, injecting CO₂ for sequestration prevents it from being emitted into the atmosphere. It is a “carbon management solution” to sequester CO₂ into oil reservoirs, explains the project’s team lead, Sunil L. Kokal, principal scientist with Aramco’s EXPEC Advanced Research Center.

“Capturing and injecting compressed carbon dioxide into an oil and gas reservoir is a technological solution to help the world reduce its emissions,” said Kokal. “Careful monitoring of our Hawiyah project shows a substantial portion of the CO₂ remains stored in the Ghawar field.”

“Most of the captured CO₂ is staying sequestered underground in the reservoir. Sequestration means the CO₂ can no longer behave like a greenhouse gas.”

At the Shaybah oil field, in Saudi Arabia’s remote Rub’ al-Khali (Empty Quarter) desert, lean natural gas is returned back to the reservoir. The site’s natural gas liquid recovery plant removes high-value natural gas liquids (NGL) — a key raw material for chemicals and vehicle fuel blends — from Shaybah’s gas.

After the NGL is removed, the leftover H2S, CO₂ and residual gas go back into the field. This use of waste gases reduces GHG emissions and also assists with oil recovery.

Mitigating emissions

Energy efficient industrial operations, when compared to their less efficient counterparts, can simultaneously reduce GHG emissions and operating costs. Actions to reduce energy usage in hydrocarbon production include cogeneration systems, renewables such as solar and wind, and flare gas recovery systems.

Helping to safeguard against leaks of invisible gas is cutting-edge technology, wisely-maintained infrastructure, and smart innovation. Also crucial are trained people diligently following production procedures, and safety measures.