Tests eyed for Cagayan Basin natural gas find

State-run Philippine National Oil Co.-Exploration Corp. (PNOC-EC) managed to flow gas from the Mangosteen-1 well in Service Contract (SC) 37 in the Cagayan Basin but further tests are needed to check if the reserves are of commercial quantity.

A project report released by the Department of Energy (DOE) showed that gas flows detected by PNOC-EC only confirmed the presence of the resource, not its viability.

“Simulation tests must be done for better estimates on the volume, optimal flow rate and other relevant reservoir properties and the commercial viability of the prospect,” DOE said.

The state-owned oil and gas exploration firm began drilling on March 21 this year and focused gas flow tests on two zones. Formation fluids were allowed to flow from the well to the surface to determine the type of fluids and how fast they could be produced.

PNOC-EC was unable to flow gas in commercial volumes from the Mangosteen-1 well due to restricted gas flow.

“However, they were still able to flow and flare gas twice for a short period from the accumulated gas in the separator,” DOE said.

A separator in oil field terminology is a pressure vessel used to separate well fluids produced from oil and gas wells in onshore and offshore drilling operations. PNOC-EC is the upstream oil and gas subsidiary of the Philippine National Oil Co.

Cagayan Basin is one of the 16 sedimentary basins in the Philippines. Based on the “Philippine Petroleum Resource Assessment, Vol. 8-Cagayan Basin” of the DOE, it has a potential unmapped resource of 1,938 billion cubic feet (bcf) of gas and 26 million barrels of oil. The potential mapped resource is 123 bcf of gas and 3 million barrels of oil.

There are two service contracts in Cagayan Basin: SC 37 operated by PNOC-EC and SC 52 operated by Frontier Oil Corp., a private company that recently deferred plans to list on the Philippine Stock Exchange.

SC 37 used to host the commercial operation of the San Antonio Gas Field. It opened on July 4, 1994, as the Philippines’ first commercial gas field and provided electricity through the San Antonio gas power plant to more than 10,000 households in Isabela province.

However, the gas reserves were exhausted after 14 years and the gas power plant was shut down on July 31, 2008. By that time it had generated a total of 187,482.12 megawatt-hours of power with total gas output from the San Antonio-1A well of 3.54 bcf.

On March 21, 2015, PNOC-EC spudded another drilling, now called Mangosteen-1 well, in Barangay (village) Balintocatoc, Santiago City, Isabela. The Mangosteen prospect has an estimated recoverable resource potential of about 71 bcf based on the original target, which is significantly higher than that of the San Antonio gas field with only 4 bcf.