CNOOC Flows 800,000 cu m/d of Gas from Bohai Ultra-Deep Volcanic Well

By Priya Raman

CNOOC has tested natural gas at roughly 800,000 cubic meters (28 million cubic feet) per day from an ultra-deep volcanic reservoir in the Bohai Sea. The company calls it a discovery. The flow rate is real. What's missing is just as telling.

What did the well actually deliver?

The well sits in central Bohai, near the Bozhong Sag — the largest hydrocarbon-rich sag (a subsided basement depression that fills with sediment and source rock) in the basin. Drilling penetrated more than 120 metres of cumulative gas pay in volcanic formations. Total depth reached 5,770 metres, CNOOC reported.

Volcanic reservoirs are unforgiving targets. Pore systems are heterogeneous, and reservoir prediction has historically been difficult in Bohai's complex subsurface. That is CNOOC's own framing, not an outside assessment. The takeaway: a 120-metre gas column in volcanic rock at nearly 5,800 metres is a technical result worth noting.

Which technology made it possible?

CNOOC credited its independently developed multi-source broadband three-dimensional (3D) seismic technology — seismic imaging that captures a wider frequency range for sharper subsurface pictures — plus new reservoir prediction methods. These tools, the company said, identified favourable gas-bearing zones in the ultra-deep volcanics.

The claim of independent development is routine for CNOOC. The verification is not public. Still, a test this size in a previously unpredictable play suggests the workflow performed.

What did CNOOC's chief geologist say?

Xu Changgui, Chief Scientist and Chief Geologist of CNOOC, framed the well in strategic terms. "Exploration in China's offshore areas has achieved a major leap from shallow to deep and ultra-deep formations," he said.

"The success of this well has opened up a new play for offshore ultra-deep natural gas exploration and expanded the scope of deep oil and gas exploration in Bohai," Xu said. He added that the find is "of positive significance for accelerating the ultra-deep exploration process in Bohai and for building a major gas province of one trillion cubic meters in Bohai."

A trillion-cubic-metre gas province is a goal, not a reserve figure. No well test proves it.

What is not in the announcement?

Two omissions stand out. CNOOC did not disclose estimates of recoverable resources. It also gave no plans for commercial development — no appraisal schedule, no tie-back concept, no startup window.

A single high-yield test well does not establish a field. It establishes potential. Appraisal drilling will decide whether this is a play opener or an isolated sweet spot in a difficult volcanic section. Until those wells are drilled, the 800,000 cu m/d figure describes one completion, not a supply base.

What happens next?

The Bozhong Sag carries the bulk of Bohai's exploration promise, in CNOOC's telling, and the company expects the discovery to widen the opportunity set across the region. Watch for the appraisal programme, a recoverable-resource estimate, and any sanctioned development plan in central Bohai. Those three items — none yet announced — will convert this week's flow test into a project.