Pore Structure Characterization and Reservoir Quality Evaluation of Analcite-Rich Shale Oil Reservoir from the Bohai Bay Basin

Abstract

Pore characteristics and shale oil reservoir quality strongly influences the petroleum occurrence, enrichment, and economic production. In this work, to characterize the pore system and evaluate the reservoir quality of analcite-rich shale oil reservoir, a total of 33 shale samples from the second member of the Paleogcene Kongdian Formation (Ek2) of Bohai Bay Basin were examined using a suite of techniques, including total organic carbon (TOC) content, X-ray diffraction (XRD), field emission SEM, gas (CO2 and N2) physisorption, and mercury injection porosimetry (MIP). Six typical shale lithofacies are identified, and their pore characteristics are compared to reveal the factors affecting shale reservoir quality. The mineral matrix-related pore (e.g., intergranular and intragranular pores) is the dominant pore type in different shale lithofacies, with few organic matter (OM)-hosted pores being observed. Analcite-rich siliceous shale exhibits the largest specific surface area (SSA) and micropore volume, while the smallest is observed in analcite-rich mixed shale lithofacies. In contrast, the volume and SSA values of mesopores for siliceous shale are the largest, while mixed shale has the smallest values. Multipermeabilities of five connected pore networks were determined using the Katz-Thompson equation, and the permeability of microfractures or interlayer bedding cracks is at the micro-Darcy scale, as reflected by the first two inflection points. Permeability values for the other three inflection points reflect the matrix pore system within a nano-Darcy range. Siliceous shale has the high matrix permeability and good pore connectivity, which is favorable for fluid flow. Authigenic analcite mineral has different effects on pore development and reservoir quality depending on the shale mineral composition and diagenesis processes. Some primary pores were lost during the filling of analcite mineral in the early diagenesis period, but some intergranular pores were also protected by the rigid framework formed by analcite minerals. In addition, some secondary dissolution pores are generated during the reaction between analcite and organic acids discharged from the source rocks within the oil generation window, and the reservoir porosity and permeability can be greatly improved. Except for analcite, the TOC content is also an important factor controlling reservoir quality.

Geological Controlling Factors of Oil Content in the Paleogene Kongdian Formation, Bohai Bay Basin

“…X-ray diffraction (XRD) is an effective technique for quantifying the mineral composition of rock samples. The XRD experiments on powder E k 2 shale samples (<74 μm) were carried out using the SmartLab SE instrument produced by Rigaku, as described by Munson et al X-ray fluorescence (XRF) is a fast and nondestructive method for analyzing the spatial element distribution and stratification of samples. , The abundances of major elements, e.g., Al, Ca, Si, Fe, Mn, K, of bulk E k 2 samples (with an observed flat surface area of 2 cm × 2 cm) were measured by the micro-XRF M4 Tornado Plus manufactured by Bruker. Thin sections were prepared and observed in rectangular areas (2 cm × 2 cm) using a Leica DM750P optical microscope to further visualize the lamination characteristics of the shale samples.…”

Influence of Shale Mineral Composition and Proppant Filling Patterns on Stress Sensitivity in Shale Reservoirs

“…The mineral composition of shale is complex, primarily composed of clay minerals (layered silicates), other common soil minerals (such as framework silicates like quartz and feldspar, as well as carbonates), and highly cemented aggregates of organic matter. The lithofacies of shale can be classified based on its mineral composition [14,15]. Studies have shown that shale of different lithofacies exhibits variations in mechanical properties [16,17].…”

Control of Physical Properties by the Matching between Rock Components and Pore Structure in Shale Reservoirs of the Permian Lucaogou Formation, Jimusar Sag

“…Shale oil reservoirs are recognized for their tightness and pronounced heterogeneity, posing significant challenges for exploration and development efforts within the shale oil industry. − The assessment of physical properties, critical for pinpointing productive layers and achieving efficient extraction, is closely linked to the reservoir’s rock components (RC) and pore structure (PS). − Consequently, delving into the intricacies of RC and PS is essential for unlocking the potential of shale oil, a topic of growing scholarly interest. Technological advancements in high-resolution analytical methods, such as scanning electron microscopy (SEM), energy-dispersive spectrometry (EDS), and fluid injection techniques, have facilitated deeper insights into the micro- to nanoscale attributes of RC and PS in shale oil reservoirs. ,− These studies have revealed a diverse range of RC and a complex array of PS, underscored by their significant heterogeneity and the fundamental interplay among varying RC and PS. ,− Nonetheless, the exploration of these inter-relationships has largely been confined to qualitative analyses.…”