| Author's Name: WANG Bo1, SONG Guangyong1,2, ZHANG Ronghu2, ZENG Qinglu2, WANG Yanqing2,
SUN Xiujian3,WU Zhixiong1, LI Senming2, LI Yanan1, GONG Qingshun2 |
| Based on analysis of a large number of core samples, thin sections, scanning electron microscopy, X-ray
diffraction of whole-rock minerals, and well logging data, a systematic study is conducted on the favorable geological
factors and conditions for hydrocarbon accumulation in the bedrock (at depths exceeding 7 000 m) reservoirs in the
northern Qaidam Basin. The specific findings are as follows: (1) Intermediate-acidic granitic bedrocks serve as highquality reservoir lithologies. Under the coupled effects of multiple phases of metamorphism, tectonic fracturing,
weathering and erosion, and other favorable reservoir-forming factors, two genetically distinct effective reservoirs have
formed: weathering crust and interior reservoirs, with fractures and dissolution pores as the main storage spaces and
minimal impact from burial compaction. (2) Two effective sealing layers, namely Jurassic carbonaceous mudstones
(which are also source rocks) and Paleogene Lulehe Formation gypsiferous mudstones, provide condition for longdistance hydrocarbon migration and effective accumulation. (3) The synchronization of hydrocarbon generation periods
with conductive faults and trap formation periods offers excellent conditions for hydrocarbon enrichment and reservoir
formation. (4) The Jurassic high-maturity coal measure gas source rocks, primarily distributing in the depression area and
overlying the bedrocks, form a laterally adjacent source-reservoir association with the bedrock reservoirs, with faults and
the unconformity at the top of the bedrock serving as hydrocarbon migration pathways, resulting in two types of
hydrocarbon reservoirs: extra-source and intra-source. Controlled by differential or successive hydrocarbon migration
mechanisms, the reservoirs exhibit characteristics of oil accumulation at structurally high positions with low fullness and
abundance, and gas accumulation at structurally medium to low positions with high fullness and abundance. The research
indicates that the ultra-deep bedrocks still hold significant potential for hydrocarbon exploration. The analysis of the
favorable conditions for hydrocarbon accumulation and their spatiotemporal configuration in these ultra-deep bedrocks
can provide target areas for hydrocarbon exploration in this region and also contribute to a deeper understanding of the
reservoir-forming and hydrocarbon accumulation processes in deep to ultra-deep bedrocks. |
