--> --> Identification of Effective Tight Reservoir Based on the Mechanism of Interface Energy of Nanpu Sag, Bohai Bay Basin, Eastern China

2018 AAPG International Conference and Exhibition

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Identification of Effective Tight Reservoir Based on the Mechanism of Interface Energy of Nanpu Sag, Bohai Bay Basin, Eastern China

Abstract

The lower limit of physical properties of an effective reservoir is not a certain value as the depth of oil and gas exploration increasing. In addition, the degree of hydrocarbon enrichment in the same reservoir also differs greatly. Based on the mechanism of interfacial energy, the study can explain the reason and mechanism of the changing of effective reservoir discrimination criteria with buried depth and establish an discrimination criterion that meets the geological characteristics of subsurface. In addition the research can explain the difference in the hydrocarbon content within the same reservoir. Numerical calculations and geostatistical analysis were applied in this study. First, the pore throat radius distributions of different lithologies (mainly sandstone and mudrocks) at different buried depth were calculated. 367 sets of porosity and permeability data of mercury injection experiment were used to establish the equation of pore throat radius and physical properties (Eq.1). Furthermore, the change rule of capillary force ratio between the surrounding mudrocks (fm) and the sandstone reservoir (fs) with burial depth was obtained by combining 13140 well logging data with rules above (Eq.2-3). Second, the relationship between fm to fs and petroliferous property of the reservoir was established. The reservoirs were divided into the oil and gas layer, the oil and gas-bearing water layer, the water layer, and the dry layer. According to the distribution trend of fm/fs of the effective reservoir with buried depth, the critical conditions for the effective reservoir distribution are determined. rs=-2.92-7.98lg(Φ)+1.16[lg(K)-lg(Φ+K)]-8.81[lg(2Φ)-lg(2K)] (1); rm=6259.1H^(-1.6542) (2); Em/Es=fm/fs=(2σcosθ/rm)/(2σcosθ/rs)=rs/rm (3) (Where rs and rm are the pore throat radius of sandstone and mudstone, μm; Φ is the porosity of sandstone, %; K is the permeability of sandstone, mD; H is the buried depth of the strata, m; fm and fs are the interface energy of mudstone and sandstone, J; fm and fs are the capillary force of mudstone and sandstone, N. ) On the basis of geostatistical analysis, physical simulation experiments mainly simulated the hydrocarbon migration in sandstones of different particle sizes and thicknesses to investigate the changes of the critical conditions controlled by the interface energy with the burial depth increasing. Based above, an effective reservoir discrimination criterion is established in study area:rs≥0.038μm, H≤6120m, Φ≥2.3%