Reservoirs in the Xing’anling Group in the
Suderte Oil Field, Hailar Basin exhibit ultra-low to low
permeability and high tuffaceous material content. This
study comprehensively analyzed diagenesis and quality
evolution of these low-permeability reservoirs using thin
sections, SEM samples, rock physical properties, pore
water data, as well as geochemical numerical simulations.
Calcite and analcite are the two main types of cements
precipitated in the eodiagenetic stage at shallow burial
depths in the reservoirs. These two cements occupied significant
primary intergranular pores and effectively retarded
deep burial compaction. Petrography textures suggest
selective dissolution of massive analcite and little dissolution
of calcite in the mesodiagenetic stage. Chemical
calculations utilizing the Geochemist’s Workbench 9.0
indicated that the equilibrium constant of the calcite
leaching reaction is significantly smaller than that of the
analcite leaching reaction, resulting in extensive dissolution
of analcite rather than calcite in the geochemical
system with both minerals present. Numerical simulations
with constraints of kinetics and pore water chemistry
demonstrated that the pore water in the Xing’anling group
is saturated with respect to calcite, but undersaturated with
analcite, leading to dissolution of large amounts of analcite
and no dissolution of calcite. Significant secondary intergranular
pores have formed in analcite-cemented reservoirs
from selective dissolution of analcite in the mesodiagenetic
stage; the analcite dissolution formed preferential flow
paths in the reservoirs, which promoted feldspar dissolution;
and dissolution of such minerals led to the present
reservoirs with medium porosity and low permeability.
Calcite-cemented tight reservoirs have not experienced
extensive dissolution of cements, so they exhibit ultra-low
porosity and permeability.