Industrial oil and gas have been found in the volcaniclastic rocks of the Huoshiling Formation erupted underwater in the continental lacustrine basin of the Changling fault depression in the Songliao Basin

which has broad exploration prospects. The study focuses on the reservoir space characteristics

physical properties and pore structure differences of the underwater eruption pyroclastic rock reservoirs in the Huoshiling Formation

and analyzes the reasons

for the differences in physical properties of different types of reservoirs and their formation and evolution processes. There are mainly the following four aspects: ① Tuff

with its high volcanic glass content

predominantly features devitrification and dissolution pores as its main reservoir spaces. Coarser particle sizes in tuff correlate with improved physical properties

including larger and more abundant pores. Sedimentary tuff

rich in clay minerals

exhibits mainly interstitial spaces between these minerals and poorer physical properties. Tuffaceous sandstone

with high levels of soluble components like feldspar

debris

and laumontite

is characterized by dissolution pores. ② The average porosity is 2.43%

and the average permeability is 0.076×10

-3

μm

2

. Coarse-grained tuff exhibits the highest porosity

followed by tuffaceous sandstone and fine-grained tuff

with sedimentary tuff displaying the poorest physical properties. ③ Devitrification significantly contributes to the high porosity yet ultra-low permeability observed in tuff reservoirs. Organic acid dissolution during the middle diagenesis stage

resulting from two separate oil and gas fillings

further enhances porosity. Additionally

fractures serve as conduits for organic acids and deep hydrothermal fluids

promoting further dissolution that connects dispersed dissolution pores and enhances reservoir space effectiveness. ④The coarse-grained tuff reservoir in the near-source facies gas-carrying subaqueous pyroclastic flow subfacies is a favorable target for oil and gas exploration.