Fluid interaction mechanism and diagenetic reformation of basement reservoirs in Beier Sag, Hailar Basin, China

Abstract

Based on analysis of core observation, thin sections, cathodoluminescence, scanning electron microscope (SEM), etc., and geochemical testing of stable carbon and oxygen isotopes composition, element content, fluid inclusions, and formation water, the fluid interaction mechanism and diagenetic reformation of fracture-pore basement reservoirs of epimetamorphic pyroclastic rock in the Beier Sag, Hailar Basin were studied. The results show that: (1) Two suites of reservoirs were developed in the basement, the weathering section and interior section, the interior section has a good reservoir zone reaching the standard of type I reservoir. (2) The secondary pores are formed by dissolution of carbonate minerals, feldspar, and tuff etc. (3) The diagenetic fluids include atmospheric freshwater, deep magmatic hydrothermal fluid, organic acids and hydrocarbon-bearing fluids. (4) The reservoir diagenetic reformation can be divided into four stages: initial consolidation, early supergene weathering-leaching, middle structural fracture-cementation-dissolution, and late organic acid-magmatic hydrothermal superimposed dissolution. Among them, the second and fourth stages are the stages for the formation of weathering crust and interior dissolution pore-cave reservoirs, respectively. Key words: Hailar Basin, Beier Sag, epimetamorphic pyroclastic rock, basement reservoir, fluid interaction mechanism, diagenetic reformation