Abstract:

Archean basement rock in Jiyang Depression has gradually become one of the focuses of hydrocarbon exploration. At present, the research on the characteristics of basement rock reservoir and the conditions of hydrocarbon accumulation in this area is not mature. On the basis of core observation, thin section identification, macroelement analysis, XRD, scanning electron microscopy, nuclear magnetic resonance and well seismic data analysis, the development characteristics of Archean basement rock reservoir and favorable geological conditions for hydrocarbon accumulation in Jiyang Depression are studied. The results show that the rock types of Archean basement rock reservoir in Jiyang Depression are mainly granites, gabbro, felsic gneiss, plagioclase amphibolite and cataclastic rock. Developed weathered crust type and inside type reservoir; The physical properties of the weathered crust are best in the semi-weathered zone, and the reservoir space is the solution pore, solution fracture, structural fracture and solution expansion fracture. The porosity of the reservoir is concentrated in 2.2%~3.8%, the average permeability is 2.79×10^-3 μm², and the average density of imaging logging fractures is 1.4 bars/m. The weathering crust is dominated by Class Ⅱ reservoirs, followed by class Ⅰ reservoirs. The inside type reservoir space is dominated by structural fractures, followed by a small number of dissolution fractures, with porosity ranging from 1.1% to 1.9%, average permeability of 1.69×10^-3 μm², and average density of imaging logging fractures of 0.6/m, which is dominated by Class Ⅲ reservoirs, followed by class Ⅱ reservoirs. The basement rock reservoir in Chengbei area is adjacent to the hydrocarbon-generating depression of the Yellow River Estuary, and hydrocarbon migrated along the top unconformity and tectonic fault of the Archean basement rock buried hill, overlying the lower Paleozoic Cambrian-Ordovician carbonate rocks, and the mudstones of the Paleogene Sha3 and Sha4 provide effective sealing. Finally, hydrocarbon accumulated in weathering crust and inside fractures at the top of basement rock during the Ming Huazhen period (3.0~1.5 Ma) of Neogene Pliocene. The research results are of great significance to the hydrocarbon exploration of basement rock in Jiyang Depression.

Key words: Jiyang depression, Archean, basement reservoir, hydrocarbon accumulation model