Single- and Multifractal Dimension Variation of the Pore-Fracture System in Tight Sandstone by Using High-Pressure Mercury Intrusive Tests and Its Influence on Porosity–Permeability Variation

Abstract

Micro-structures of the pore-fracture size distribution of target sandstone samples are studied through high-pressure mercury intrusion (HPMI) experiments, and the compressibility coefficient is quantitatively described by using overlying pressure porosity−permeability tests. Then, four single and multifractal models were used to quantitatively describe the fractal characteristics of mercury intrusion curves, and the relationship between different fractal models and pore structure parameters is analyzed. Furthermore, the applicability of fractal models in characterizing pore-fracture structures was explored. The results are as follows: (1) fractal model results show that fractal dimensions of type A by using Sierpinski (D S ) and thermodynamics models (D M ) are larger than those of type B, and fractal dimensions of type A by using Menger (D M ) and multifractal models (D −10 −D 10 ) are smaller than those of type B. (2) The Menger model is used to describe heterogeneity of smaller pore size distribution, which is proportional to volume percentage of pores with the diameter smaller than 100 nm; the thermodynamic model is used to describe heterogeneity of medium pore size distribution, which is proportional to the volume percentage of pores with a diameter of 100∼1000 nm; The Sierpinski model is used to describe heterogeneity of larger pore size distribution, which is proportional to volume percentage of pores with the diameter larger than 1000 nm; (3) permeability decreases in the form of power function with the increase of confining pressure, and the compressibility coefficient and permeability variation coefficient decrease with the increase of the compressibility coefficient. There is no significant correlation between the compressibility coefficient, permeability variation coefficient, and pore structure parameters.

The Reservoir Sensitivity of Triassic Baikouquan Formation in Mahu Depression

“…It can be seen that the main glutenite is mainly composed of tuff and metamorphic mudstone, and the maturity of reservoir composition and structure is low. Through core measurement and mercury injection test, it is concluded that the average porosity of this reservoir is 10.5%, the average permeability is 9 × 10 −4 µ m 2 , the average displacement pressure is 0.58 MPa, the average capillary radius is 0.58'm, and the average mercury removal efficiency is 38.3% [13]. Therefore, it can be considered that this reservoir has low porosity and low permeability and poor pore structure.…”

“…The reservoir studied belongs to continental sedimentary rocks, which is mainly composed of sandstone, mudstone and shale [12]. The fine grain size of sandstone leads to extremely low reservoir porosity, and, at the same time, many pore structures such as dissolution pores, cementation pores and intergranular gaps are formed [13]. Through the observation of core microscope and the analysis of whole rock composition, it is considered that the lithology of the studied reservoir is mainly glutenite, followed by medium-fine sandstone [13].…”

“…The fine grain size of sandstone leads to extremely low reservoir porosity, and, at the same time, many pore structures such as dissolution pores, cementation pores and intergranular gaps are formed [13]. Through the observation of core microscope and the analysis of whole rock composition, it is considered that the lithology of the studied reservoir is mainly glutenite, followed by medium-fine sandstone [13]. The maximum particle size of gravel is more than 8 cm, mostly 1~2 cm, and the particles keep line contact and point-line contact, which is characterized by pressureembedding pore cementation.…”

Quantitative characterization of the carbonate rock microstructure considering topological features: a case study from the Gaoshiti–Moxi block of the Sichuan Basin

“…For pores with fractal characteristics, the fragmentation and regularity of the pore system can be described by the fractal dimension (Han et al, 2023;Jiang et al, 2023). The relationship between pore radius and fractal dimension is expressed in Eq.…”

A New Method for Calculating the Influx Index in Gas-Drive Reservoirs: A Case Study of the Kela-2 Gas Field

“…Furthermore, according to the definition of the displacement index, a combined static/dynamic iterative method was used to establish the displacement index chart for the Kela-2 gas field. In this chart, the gas displacement index represents the percentage of natural gas driving energy in the total driving energy [35].…”