Workers on the West Capella drillship engage in drilling below the seabed in the Daewang Gorae block with potential gas and oil reserves in the waters off Pohang, North Gyeongsang Province, in this January photo. Courtesy of Korea National Oil Corp.

The initial exploratory drilling for the government's oil and gas exploration and development project in the East Sea showed some indications of gas, but the volume appears far from sufficient to develop it into an economically viable gas field, a senior official of the energy ministry said Thursday.

However, the official said that the first drill site, known as Daewang Gorae, has a geological structure that appears promising for oil reserves, adding that the ministry plans to begin attracting foreign investors for further drilling in one of the six remaining "promising" blocks designated by the government.

After drilling over 3 kilometers below the seabed in Daewang Gorae and taking core samples, the Korea National Oil Corp. determined the block contained a gas reserve with such a low saturation level that it was deemed unpromising and further exploration was unnecessary.

"We found traces of hydrocarbons — an organic compound indicating signs of gas — in the block. But they were either remnants in a dismissible volume or from an unknown source rock somewhere," the official told reporters in Sejong.

"Although the block's natural conditions in terms of source rock, cap rock and reservoir for an oil reserve looked more promising than we thought, the outlook for a gas reserve was not promising based on data like amplitude versus offset."

The official said it is now time to study the core sample excavated from the first drill site, after exploratory drilling wrapped up on Tuesday. It came 47 days after West Capella began drilling in the waters off Pohang, North Gyeongsang Province. The government plans to select a private firm through an auction this month for the examination of the specimen, which will take about six months.

On a separate track, the government will begin seeking foreign investors for the second drilling next month.

Prior to the initial exploratory drilling, the government had come up with a report on seven offshore drill sites that seemed promising for oil and gas reserves. Now that the first block is complete, the official said the government has now secured critical information to update the report.

The government announced its plan last year for the deep sea energy exploration project. However, it was met with concerns and backlash from politicians who criticized the uncertainty and financial risks, as the project's success was not guaranteed.

"Deep sea energy exploration projects rarely succeed on their first try," the official said, adding that further drilling is required to search for reserves. "For now, we will draft conditions for foreign investors so that we can secure enough funds for more drilling."