Gas Saturation: A Key Factor in Assessing Oil and Gas Field Viability
Determines Yield and Productivity of Oil Fields
High Initial Costs for East Sea Oil Field's First Steps
Continuous Drilling Needed to Find High-Saturation Traps
"The gas saturation of Daewanggorae is not high, making it difficult to consider it an economically viable gas field."
On the 6th, the Ministry of Trade, Industry and Energy disclosed the preliminary analysis results of Daewanggorae, the first drilling target in the East Sea deep-sea gas field, mentioning 'gas saturation.' Gas saturation is a key indicator that determines the commercial viability of oil and gas fields. Generally, when assessing the economic feasibility of a gas field, factors such as the quality of the reservoir and cap rock, and whether the gas saturation is sufficient, are considered. Among the seven promising structures in the East Sea deep-sea gas field project, the largest, Daewanggorae, did not reveal gas saturation levels sufficient to convert it into a production block during drilling. Even if an underwater area containing oil or gas is discovered, actual oil and gas field development can be thwarted depending on the saturation levels.
Discovering Oil and Gas Fields Is Not the End... 'Saturation' Must Be Considered
West Capella, which conducted exploratory drilling of the Daewang whale promising structure. Photo by Yonhap News
During underwater oil exploration, the drilling ship inserts a long drill hole into the seabed rock, drills a hole, and collects some rock samples from the strata for analysis. Gas saturation is also investigated at this time. Gas saturation is the percentage of the volume occupied by gas in the pores (empty spaces) of the rock.
Rocks containing oil or gas deposits are called 'reservoir rocks.' Reservoir rocks have tiny, densely packed pores through which fluids flow. In other words, high gas saturation means that natural gas or oil is abundant inside the reservoir rock. Conversely, low gas saturation means that the pores in the reservoir rock are more likely to contain useless substances such as brine instead of oil or natural gas.
Typical form of reservoir rock. Fluids stored in tiny pores within the rock flow through. Thailand Chulalongkorn University Petroleum Geology Archive
For this reason, resource exploration companies first calculate gas saturation to determine the productivity of an oil field. Professor Lee Cheol-woo of Chungbuk National University, a domestic authority on oil resource exploration, explained, "Generally, a saturation of 70% is accepted as the standard for economically viable oil fields," but added, "This is not an absolute figure, and the economic saturation threshold always varies depending on the structure of the promising oil field area and transportation costs."
The Gulf of Mexico, a major underwater oil field in the United States, is a representative example. Although many oil fields in the Gulf of Mexico have relatively low saturation, they are still considered economically viable because of the abundant existing oil development infrastructure and the ease of transporting extracted resources to ports.
The government judged that the gas saturation of Daewanggorae is insufficient but did not disclose specific saturation figures. However, experts speculate that the expected saturation level required to secure economic viability was initially high due to the characteristics of the East Sea oil field located in deep water.
Professor Lee said, "To extract gas from a deep-sea oil field and bring it inland, pipelines must be connected or offshore transportation infrastructure must be constructed. Materials used in the oil and gas industry are very expensive," adding, "In the case of the Gulf of Mexico oil fields in the U.S., although saturation is not high, many gas pipelines are already laid, so the additional development cost burden is low, making it sustainable. On the other hand, the East Sea is just beginning development, so the initial capital burden is high, requiring higher saturation."
To Find Oil Fields with High Saturation... "The Only Way Is to Keep Drilling"
Even though the gas saturation of Daewanggorae is not high, it does not mean that the entire East Sea deep-sea oil field project has failed. On the 13th, Minister of Trade, Industry and Energy Ahn Deok-geun stated during a National Assembly government questioning session, in response to People Power Party lawmaker Kang Seung-gyu's question about whether drilling would be abandoned, "We plan to consistently continue exploratory drilling operations in the future."
The Ministry of Trade, Industry and Energy did not secure economic viability from the first drilling results at Daewanggorae but confirmed that the overall petroleum system structure is sound, and plans to use the data obtained from this drilling to adjust the prospect evaluation materials for exploratory drilling of the remaining six promising structures. This is because if gas has passed through Daewanggorae, there is a possibility that gas exists near the six adjacent promising structures.
Professor Lee explained, "Gas is light, so it tends to move upward through the reservoir layer. It accumulates where a solid rock layer forms a barrier; this is called a 'trap,' and resources are extracted by drilling holes precisely at these locations."
He added, "There are multiple traps within the entire promising structure, and it is a mystery which trap the gas has moved to. Ultimately, the only way is to drill each trap one by one and visually confirm. Resource-rich countries like the U.S. and Saudi Arabia have also found oil fields through numerous attempts and failures," emphasizing this point.
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