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Compaction is an important part of diagenesis affecting porosity in conjunction with burial depth and time. However, the relation between initial porosity and sandstone compaction remains unclear. This paper aims to clarify the effect of initial porosity on the compaction of consolidated sandstone in the microdeformation stage via experiments, mathematical modeling, and statistical analyses. According to the physical experiments in the Ordos Basin, sandstone porosity decreases with increasing overburden load, and the porosity-decrease trends of two similar samples with different initial porosities converge gradually. Based on the Bingham visco-elasto-plastic stress–strain model, a theoretical model for the vertical uniaxial compaction of consolidated porous rocks was constructed. The equivalent viscosity coefficient (EVC) of consolidated sandstones was approximately estimated by a contrastive analysis and an iterative computation on the basis of the geologic statistical model proposed in this study. The results in Hangjin Qi show that the Young’s modulus and the EVC of low-porosity compaction trend (LPCT) are exponential and power-law functions of the corresponding porosity, respectively. The derivation of theoretical model indicates that the compressibility and the initial porosity of porous sandstone during microdeformation are positively correlated, in accordance with simulation experiments. The initial porosity affects the elastic modulus and the viscosity coefficient and consequently, the sandstone compaction during microdeformation stage. Such an effect can contribute to the improvements of both the compaction degree analyses of different burial processes in sandstone porosity evolution and reservoir quality evaluation. [ABSTRACT FROM AUTHOR]

Porosity evolution and reservoir quality are strongly affected by mechanical compaction. However, the compaction-induced porosity reduction process in sandstone reservoirs during the postaccumulation period and its effect on gas saturation remain poorly understood. By studying the sandstones in the Bayan'aobao area, we were able to quantify the porosity evolution and gas saturation variations caused by mechanical compaction during the postaccumulation period through fluid inclusion analysis and mathematical modeling. Moreover, we verified our findings by compaction experiments and geological statistics. Fluid inclusion microthermometry was employed to determine the hydrocarbon accumulation periods, and the highest homogenization temperature of the two-phase aqueous fluid inclusions coexisting with natural gas fluid inclusions, i.e., ~115 °C (with a corresponding geological age of ~140 Ma), was regarded as the beginning of the postaccumulation stages. With these data, we constructed an inversion evolution model (based on the geologic statistical model of sandstone mechanical compaction) for the postaccumulation period and determined the gas saturation changes (based on compaction porosity evolution). The modeling results indicate that the sandstone porosity decreased greatly during postaccumulation subsidence and increased slightly during late-stage uplift, while the gas saturation increased with both the porosity decrease during the postaccumulation subsidence and the porosity increases during the later uplift. The modeling results of subsidence are concordant with the compaction experiments, which also show that the larger the initial porosity, the greater the porosity reduction. The uplift modeling results demonstrate that an erosion-induced decrease in burial depth allowed the sandstone porosity to increase, which is supported by some scholars' findings (e.g., Neuzil and Pollock, 1983; Jiang et al., 2004; Zhang, 2013) and by the positive correlation between sandstone porosities and restored geologic unit thicknesses in the study area. However, the inversion modeling indicates that the reason for the porosity rebound in litharenites is that the increase in elastic porosity slightly exceeds the decrease in viscoplastic porosity, which would have been different if the uplift-induced erosion rate had been distinctly lower. Gas production test data and restored geologic unit thicknesses indicate that uplift and erosion may be able to enrich sandstone gas reservoirs to a certain extent, consistent with the calculated gas saturation variation results, but a full understanding of gas saturation evolution awaits further studies. The inversion model can provide a powerful tool for quantitative analysis of the sandstone compaction process during the postaccumulation period, which could be used for reference in other similar regions. • We studied postaccumulation sandstone porosity evolution by mechanical compaction in quantitative inversion modeling. • Compaction-induced porosity reduction differences are revealed in compaction experiments and inversion modeling. • Uplift-induced sandstone porosity rebound is indicated by inversion modeling and geological statistics. • Porosity increase in response to late-stage uplift would likely promote the enrichment of gas reservoirs. [ABSTRACT FROM AUTHOR]