Study of Fractal and Multifractal Features of Pore Structure in Tight Sandstone Reservoirs of the Permian Lucaogou Formation, Jimsar Sag, Junggar Basin, Northwest China

Changcheng Han; Guan Li; Shunhua Dan; Yi Yang; Xudong He; Ming Qi; Geng Liu

doi:10.1021/acsomega.2c03717

Study of Fractal and Multifractal Features of Pore Structure in Tight Sandstone Reservoirs of the Permian Lucaogou Formation, Jimsar Sag, Junggar Basin, Northwest China

ACS Omega. 2022 Aug 23;7(35):31352-31366. doi: 10.1021/acsomega.2c03717. eCollection 2022 Sep 6.

Authors

Changcheng Han^{1

2}, Guan Li², Shunhua Dan³, Yi Yang², Xudong He², Ming Qi², Geng Liu²

Affiliations

¹ Xinjiang Key Laboratory for Geodynamic Processes and Metallogenic Prognosis of the Central Asian Orogenic Belt, Urumqi 830047, China.
² College of Geology and Mining Engineering, Xinjiang University, Urumqi 830047, China.
³ Zhundong Oil Production Plant, Xinjiang Oilfield Company, PetroChina, Karamay 834099, China.

Abstract

The primary factor impacting the tight sandstone reservoirs and fluid flow capacity represents the pore-throat structure. On the basis of petrophysical characteristics test, scanning electron microscopy (SEM), and casting thin-section examination of tight sandstone reservoir specimens from the Permian Lucaogou Formation in Jimsar Sag, Junggar Basin., the full-size pore-throat parameters and distribution characteristics were determined by constant-rate mercury injection (CRMI) analysis. Using fractal theory and multifractal theory, the pore architectures of sandstone pores are analyzed. Mercury intrusion capillary pressure (MICP) is used to compute the dimensions of fractals using various fractal models and multifractal characteristics. Analysis is done on the relationships between tight sandstone pore architectures and fractal and multifractal characteristics. According to the research, a network of tightly packed sandstone pores may be assessed using the dimensions of fractals computed from a 3D capillary model. When displacement pressure is increased, the dimensions of fractals rise; when permeability, pore-throat diameter, and variable coefficient are increased, it falls. Tight sandstone pores exhibit multifractal features, according to the multifractal analysis, and multifractal parameters may depict the size, concentration, and asymmetry of the pore size distribution (PSD). Sandstone's PSD is comparable when its multifractal parameters (Δα, Δf, α₀, α₁, α₂) are identical. Pore diameters of tight sandstone are positively connected with information dimensions D ₁ and correlation dimensions D ₂, and information dimensions D ₁ have a greater impact on PSD than correlation dimensions D ₂. Additionally, the 3D capillary model's dimensions of fractals and D ₁ exhibit a substantial negative association. These findings play a significant guiding role in the quantitative characterization of unconventional reservoir pore structures. The multifractal technique is effective to define the heterogeneity of the sandstone pore system and to differentiate between distinct PSD in heterogeneity.