BAO Jinrui, HUANG Yulong, LIU Shuo, REN Xianjun, HAN Jiaoyan, ZHANG Hongxia, NIU Penghui
World Geology. 2025, 44(4): 623-634.
The Huoshiling Formation in the Longfengshan Gas Field, southern Songliao Basin, has achieved
cumulative proved gas reserves exceeding 10 billion cubic meters, demonstrating favorable reservoir properties and
exploration potential in deep volcaniclastic rock sequences. Clarifying the characteristics and controlling factors of
high-quality volcaniclastic reservoirs aids in expanding favorable zones for deep-buried gas reservoir exploration and
facilitating the deployment of development wells. Based on the drill core description, blue-dyed epoxy-resin impreg
nated thin section observation, scanning electron microscopy analysis, the porosity-permeability measurements and
high-pressure mercury injection tests, a systematic study was conducted to characterize the lithology, lithofacies,
and reservoir development patterns of volcaniclastic rocks, in order to clarify the controlling factors and spatial
distribution of high-quality reservoirs. The results reveal that the Huoshiling Formation in the Longfengshan Gas
Field is composed of thirteen lithological types in four categories of volcaniclastic rocks, formed in both subaerial
and subaqueous environments, and dominated by volcaniclastic deposits of explosive facies. Four distinct pore types
were identified, the intergranular pores, intragranular pores, intracrystalline pores, and microfractures. The
intergranular and intragranular porosity constitute the predominant reservoir space, especially for the volcanic breccia
which exhibits the highest porosity, 37% and 53% of intergranular and intragranular pores, respectively. The
porosity of volcaniclastic reservoirs ranges from 1. 6% to 13. 8%, and the permeability ranges from 0. 002 ×10-3 μm2
to 0. 751 ×10-3 μm2. They are classified as medium-porosity/ low-permeability reservoirs, developing micron-scale
and nano-scale pore throats, the maximum throat ranges from 0. 020 μm to 2. 830 μm. Eogenetic chlorite cementa
tion and albitization coating of the particles effectively inhibited compactional porosity loss, thereby preserving inter
granular pores. Devitrification of volcanic glass/ ash matrix in shallow burial stage, and the organic acid dissolution
in deep burial diagenesis significantly enhances secondary porosity development, composing a key factor that controls
the development of high-quality volcaniclastic reservoirs. Three subfacies exhibit the highest proportions of high-quality
reservoirs (porosity > 6%), including diatreme subfacies of volcanic conduit facies, subaqueous volcaniclastic flow
deposits and fallout subfacies of explosive facies, which can be regarded as priority targets for deep gas exploration.
