Online available: 2025-04-29
Abstract: Carboniferous volcanic rocks in Dabasong area of Junggar Basin are widely distributed and change
rapidly in lateral direction. It is the key to study the reservoir to clarify the spatial distribution law of Carboniferous
volcanic rocks. However, in the process of exploration, it is found that the lithology of volcanic rocks is complex,
the volcanic edifices are incompletely preserved, and the eruption cycles are frequent. Based on core observation,
conventional logging curve data, isotope chronology data and three-dimensional seismic data of 6 wells, the authors
divide volcanic eruption cycles, depict volcanic edifices and lithofacies, analyze the matching relationship between
volcanic rocks distribution and fracture, and the oil and gas geological significance of volcanic eruption cycles. The
study shows that the Carboniferous volcanic rocks in the Dabasong area can be divided into four cycles: basic cycle 1
(323--319 Ma) develops basalt and basaltic tuff, with a thickness of about 425 m; the intermediate cycle 2 (311--
310 Ma) is andesite and andesitic tuff, with a thickness of 414 m; the intermediate-acid cycle 3 (310--306 Ma)
develops dacitic tuff and andesite, with a thickness of 281 m; the acidic cycle 4 (306--304 Ma) is rhyolitic tuff
with a thickness of about 174 m. The seismic explanation show that the volcanic edifices in the Dabasong area can
be divided into basic shield-shaped and intermediate-acid mound-shaped volcanic edifices. The basic volcanic rocks
in cycle 1 are widely distributed and the overall thickness is large. The volcanic edifices are mainly basic shield-
shaped volcanic edifices, and the distribution is mainly controlled by the NE--SW fault in the middle and late
Hercynian. The intermediate volcanic rocks in cycle 2 are the most widely distributed, and their distribution is
mainly controlled by the NE--SW fault in the middle and late Hercynian. The volcanic edifices are mainly interme-
diate-acid mound volcanic edifices, and the volcanic rocks are mostly central eruption. The intermediate-acid
volcanic rocks are distributed in cycle 3. The volcanic rocks are dominated by central eruptions with multiple thick-
ness centers, and the overall thickness is large. The volcanic edifices are dominated by intermediate-acid mound
volcanic edifices. The volcanic activity of cycle 4 is weakened, and the distribution area of volcanic rocks is signifi-
cantly reduced. The analysis of physical properties show that the high-quality reservoirs of volcanic rocks in cycles
2 and 3 are developed, and the physical properties of volcanic rocks are good, which can be used as a favorable
horizon for the exploration of volcanic oil and gas reservoirs in the Dabasong area.