Evaluation of a
Large Volcanic Gas Play in the Northern Songliao Basin, Northeast
China
Luthi, Stefan M.1, Li Guo Xin2,
Wang Yu Hua3, Yang Feng Ping3, Zhao Jie3, Jeff
Meisenhelder4, Sherif Farag4, Yang Xing Wang5,
Zhu You Qing5, Hou Hui Jun5, Zhang Shu Pin5,
Wu Chuan5, Wu Jie5, Thomas J. Neville5,
Michael Conefrey6, Huang Wei3 (1) Delft University of
Technology, 2628 RX Delft, Netherlands (2) PetroChina, Beijing, China (3)
PetroChina, DaQing, China (4) Schlumberger Oilfield Services, Beijing, China
(5) Schlumberger Data and Consulting Services, Beijing, China (6) Consultant,
Winchester, VA
Discovery of a gas accumulation in Lower
Cretaceous volcanic rocks in the Songliao Basin, Northeast China, has led to a thorough
evaluation of the prospect with the goal of assessing its economic viability.
The gas is contained in rhyolitic pyroclastics and lava flows, and
subordinately in the overlying conglomerates. The volcanic sequence structure
forms a saddle along a fault where the volcanic vents were located. Trapping
conditions are best described as combined stratigraphic-structural, since no
full closure exists. Coal-bearing strata in the underlying sediments are
considered the source rock. The volcanics consist in about equal parts of lavas
and pyroclastics, and their vertical and lateral distribution patterns allowed
reconstructing the sequence of volcanic events. Porosity is vesicular and
fractured in the lava flows, and microporous, vuggy and leached in the
pyroclastics. Petrophysical analysis indicated that the volcanics are
throughout their entire thickness within a capillary transition zone, and that
saturations have to be obtained from a saturation-height function above free
water level as well as the capillary pressure curves from the various
lithologies. A logging suite that includes geochemical logging, NMR
measurements and borehole imaging has been found to be best suited for
evaluating these unusual reservoir rocks. A semi-deterministic reservoir model
was used to calculate reserves in-place and showed the accumulation to be
economic. Field development has started in 2006 and shows promising results.