Abstract:

In order to find relatively high-quality reservoirs under the background of deep burial and strong heterogeneity, this paper takes Pinghu Formation in Xihu sag of East China Sea basin as an example. Based on the combination of intuitive micro-area observation, indirect mercury intrusion characterization and porosity/permeability test, the types of diagenetic facies are first divided based on reservoir sedimentology analysis, and then the differential reservoir capacity characteristics of different diagenetic facies are clarified, and the reservoir capacity of diagenetic facies is evaluated. The study shows that the Pinghu Formation is deposited in a deltaic-tidal transitional system with bi-directional hydrodynamic conditions of rivers and tides. The sand bodies are primarily developed in submerged divergent channels, estuarine dams, tidal channels, sand flats, and mixed flats, which are mainly fine-grained and very fine-grained. Lithologic characteristics are mainly feldspathic sandstones and lithic feldspathic sandstones. Three types of diagenetic phases are classified based on the difference in intensity of diagenetic types, including feldspathic dissolution facies, ductile-rich compaction facies, and calcareous cementation facies. The porosity-permeability and pore structure of the same diagenetic facies type are uniform, while the physical properties vary significantly among diagenetic facies. The three types of diagenetic facies are evaluated in terms of porosity, permeability and maximum connected pore throat radius. Among them, the porosity of feldspar dissolution facies is more than 15%, the permeability is more than 10.0×10-3μm2, the maximum connected pore throat radius is more than 5.0 μm, and the physical properties are better than ductile-rich compaction facies and calcareous cementation facies. Therefore, feldspathic dissolution facies is the most favorable reservoir sand body type.

Key words: Xihu sag, Pinghu Formation, deep-buried, heterogeneity, diagenetic facies, mercury pressure injection, East China Sea basin