China National Offshore Oil Corporation (CNOOC) has discovered an oil and gas well in ultra-deep volcanic formations in central Bohai, offshore China, more than 5,000m below the seabed.
According to the company, the well is situated next to the Bozhong Sag, said to be the largest hydrocarbon-rich sag in the Bohai region.
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The drilling reached a final depth of 5,770m and encountered over 120m of gas pay zone within volcanic rocks.
During testing, the well achieved daily output rates of around 800,000m³, equivalent to 28 million cubic feet (mcf), of natural gas.
CNOOC said that the result indicates new exploration potential in offshore ultra-deep volcanic rocks and contributes to ongoing natural gas exploration efforts in the Bozhong Sag.
The geological complexity of ultra-deep formations in the Bohai region has presented difficulties for reservoir prediction.
CNOOC chief scientist and chief geologist Xu Changgui said: “In recent years, CNOOC Limited has continued to strengthen theoretical innovation in deep and ultra-deep oil and gas enrichment in basins with high heat flow and strong activity, and to intensify research on key technologies.
“Exploration in China’s offshore areas has achieved a major leap from shallow to deep and ultra-deep formations. 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.
“It is of positive significance for accelerating the ultra-deep exploration process in Bohai and for building a major gas province of one trillion cubic metres in Bohai.”
CNOOC reports that it has improved its understanding of offshore ultra-deep oil and gas resources and has developed its own offshore deep multi-source broadband 3D seismic exploration technologies.
The company has also established new approaches for identifying quality reservoirs in ultra-deep buried hills, which enabled it to locate areas in the Bozhong Sag containing concentrations of volcanic natural gas and to drill a high-yield oil and gas well.
In December last year, CNOOC started production at the Xijiang Oilfields 24 Block development project.
