Baoliang Yang

Characterization of pore structure and heterogeneity is crucial for exploring and evaluating shale oil and gas resources. Existing methodologies exhibit various limitations, and intuitive, quantitative description techniques are lacking. To address these issues, shales from the second member of the Funing Formation (E₁f₂) in the Subei Basin were studied in this study. A comprehensive research methodology was employed that combined petrological analysis, physical structure testing, and SEM images supplemented with multifractal analysis and partial least squares regression (PLSR) data processing to achieve nuanced qualitative and quantitative characterization of the heterogeneity in lacustrine shale pore structures. This study revealed that E₁f₂ shale pores predominantly consist of mesopores (2–50 nm) and macropores (>50 nm). A positive correlation was observed between the development of mesopores and calcite content, while a negative correlation exists with orthoclase content. Conversely, a positive correlation with plagioclase content was found in macropore development. The growth in total pore volume is inhibited by the total organic carbon (TOC) content. Employing multifractal methods to analyze pore morphology data extracted from scanning electron microscopy (SEM) images facilitated a quantitative characterization of the heterogeneity within the pore structures. The results showed that organic-medium mixed shale (OMMS) has the strongest heterogeneity. The weakest heterogeneity is exhibited by the organic-medium calcareous shale (OMCS). PLSR analysis indicates that the structural heterogeneity of the E₁f₂ shales is positively correlated with TOC content and negatively correlated with orthoclase content. Additionally, the type of pore influences the degree of heterogeneity. Increasing the total and macropore volume reduces the heterogeneity, while increasing the micropore (1f₂ shales.

Reservoir porosity evaluation is crucial for successful prediction of reservoir quality in deeply buried heterogeneous strata. Recent studies have demonstrated that high-quality reservoirs occur in deeply buried strata. However, little is known about the details of pores related to the good reservoirs. The northern Dongying steep slope sandy conglomerate was investigated to understand the porosity related to high-quality reservoir formation in sandy conglomerate using seismic data, well-logs, SEM-EDS, cathodoluminescence, and optical microscopy. The result reveals three genetic pores: primary, secondary, and mixed pores. The dissolution porosity consists of intergranular pores, intragranular pores, intercrystalline pores, and moldic pores. The intergranular dissolution and enlarged pores are the main contributors to good reservoir quality among the different pores. The index of compaction indicates that compaction is the crucial factor diminishing the reservoir quality in the progradation sequences, while cementation stands as the critical factor for porosity reduction in the retrogradation sequences. Comparing the reservoir properties reveals that the dissolution porosity is more significant in the Es4s than the Es4x, which renders the Es4s reservoir relatively good compared to the Es4x. This study demonstrated that for oil exploration in the fourth member of the Shahejie Formation, the Es4s should be prioritized.