Growing global demand for natural gas has pushed oil and gas companies to increase the development of sour gas fields, which contain about a third of the world’s gas reserves.
The defining chemicals in sour gas are often hydrogen sulfide (H2S) and carbon dioxide (CO2), though in some cases, other sulfurous compounds such as carbonyl sulfide and mercaptans are also found. The higher concentrations in sour gas demand more intensive and more expensive development processes.
In the Middle East, developing sour gas fields have become a priority of local governments because of soaring regional gas consumption. In addition to tapping the development of new sour gas fields, companies in the region are also facing the issue of increasing level of sourness in operating fields in which the levels of H2S and other contaminants that were negligible on startup have become a problem later in production.
UAE: Moving Ahead
Fareed Abdullah, senior vice president (Bab and Gas) at Abu Dhabi Company for Onshore Oil Operations (ADCO), said the development of sour gas fields in the United Arab Emirates is a priority given the growing gas requirements for power generation, gas injection to boost oil production, and the rising petrochemical sector.
“It is expected that the Shah field will produce first gas in the fourth quarter of 2014, and the importance of future sour fields such as Bab, Hail, and Shuwaihat plus others under evaluation is underlined by the current activity levels and consideration within the Abu Dhabi National Oil Company (ADNOC) Group,” he said recently at the Sour Oil and Gas Advanced Technology conference in Abu Dhabi.
“When the Shah field is operational in 2014, it is expected to increase gas capacity by 10.34 Bcm/yr, and all aspects of this project will serve as benchmarks for future sour gas development,” he said.
ADNOC selected Shell to participate in a 30-year joint venture to develop the Bab sour gas reservoirs in Abu Dhabi. Shell will hold a 40% equity stake with ADNOC holding 60%. The two companies are beginning commercial and technical work leading up to the development of Bab, which is 150 km southwest of Abu Dhabi. Gas from the field will supply local markets.
During the bidding process for the USD 10 billion deal, Shell recommended exporting the sulphur while another major bid recommended reinjecting it back into the reservoir. Once developed, the Bab field will produce 500 MMcf/D to 800 MMcf/D, but expertise is required to handle the large amounts of sulfur generated from the estimated 15% H2S content of the gas.
ADNOC has also sent letters to companies inviting them to submit bids for the offshore Hail sour gas field. With a CO2 content of 11%, Hail is less toxic than Shah or Bab. Because it is located in ecologically fragile shallow waters, ADNOC will proceed cautiously. Estimates suggest that Hail could produce up to 1 Bcf/D.
The country has also opened up development plans for the Shuwaihat field, inviting Wintershall and OMV to conduct technical evaluations for potential development and production.
Oman: Handling Acid
In Oman, the Petroleum Development Oman (PDO) is continuing efforts on the Harwell project and other projects involving sour gas reinjection. PDO said it faces major technical challenges in developing sour gas fields, including acid gas increasing over the life of a field and its effects on the design of surface processing facilities.
Faced with the issue of disposing acid gas, PDO had three options: to inject it in gas and condensate fields; to inject it in oil fields; or to split it.
“The best option to take that would mitigate all the design issues is to equally share it, because if you put it in one of the fields, there is too much souring in it, and we do not want the design to be suboptimal,” said Ahmed Al-Azizi, a process engineer at PDO. “You are trying to minimize the extent of the material that you are injecting.”
In addition to the technical challenges, local regulatory specifications must be met. “The main challenge was to reduce the sulfur content in the gas to less than 5 ppm and also to meet Oman’s SO2 emission regulations of 35 mg/Nm3,” said Al-Azizi.
The combination of the regulatory requirements made the design of the gas processing and sulfur recovery facilities challenging. “This required the utilization of the best-in-class solutions in order to comply with the standards,” he said.
Saudi Arabia: Karan Up, Kidan Unsure
In Saudi Arabia, Saudi Aramco has begun production from the offshore nonassociated sour gas field Karan, which is designed to produce 1.8 Bscf/D of dry gas by this year. The gas is processed through a number of trains that include facilities for gas sweetening, acid gas enrichment, gas dehydration, and supplementary propane refrigeration. The onshore facilities also include a cogeneration plant, a sulfur recovery unit with storage tank, substations, and a transmission pipeline linked to Saudi Arabia’s Master Gas System.
Another sour gas field in Saudi Arabia is Kidan, located in the Empty Quarter. The field is operated by a joint venture between Saudi Aramco and Shell called the South Rub al-Khali Company. News reports have surfaced that Shell may pull out of the project.
Kuwait: Challenging Conditions
In Kuwait, Shell is assisting Kuwait Oil Company (KOC) with high-pressure/high-temperature (HP/HT) sour gas fields, in which deep exploration wells present challenging drilling conditions. Among the major challenges are the hostile environment and poor rock properties with low porosity and low permeability as well as H2S content between 3.5% and 12% and CO2 content between 0% and 2.5%. In addition, KOC has encountered challenges related to heavy mud.
“The project is of critical strategic importance for the state of Kuwait for power generation and to reduce reliance on imports,” said Mohammad Ahmad Husain, chief executive officer of Equate and former deputy chairman and deputy managing director of planning and gas at KOC.
“Jurassic development is particularly challenging and hard to handle because of the difficult reservoirs, deep wells, HP/HT, H2S, new facilities, tough operations, sulfur production, high HSE standards, and close monitoring,” he said. “We have limited experience and resources in this area.”
To develop this project, Husain said that finding a foreign partner, such as Shell, will help KOC achieve its target.
“The partner should have expertise in similar Jurassic-type projects,” he said. “We also expect the partner to transfer technology and to train KOC staff,” he added, stressing the importance of knowledge transfer in this sector of the industry.
The project is currently facing delays, as the Parliament is examining the technical services agreement.