Multi-Scale and Multi-Dimensional Imaging of Mineral Matrix Pore-Fracture Networks in Lower-Thermal-Maturity Lacustrine Shale: Examples from the Paleogene Shahejie Formation, Bohai Bay Basin

Abstract

The pore-fracture network within shale significantly controls the microscopic storage of hydrocarbons. The Paleogene lacustrine Shahejie Formation of Bohai Bay Basin represents an outstanding lower-thermal-maturity example of a mineral matrix pore-fracture system. Recent studies have shown that most pores in Shahejie shale detectable by high-resolution electron microscopy are associated with an inorganic mineral matrix instead of organics. However, because of the lack of both qualitative and quantitative data on nanometer to micrometer scales, such microstructures have limited the ability to predict hydrocarbon storage feature. Representative Shahejie shale samples come from the Well F39X1 to investigate the pore-fracture network using a synergistic multiscale multi-dimensional workflow by field emission scanning electron microscopy, multi-scale CT, and FIBSEM. Investigations in both 2D and 3D and across cm−mm−μm−nm length scales indicate heterogeneity at every scale and dimensions. From 2D SEM images, clay flake-hosted interparticle pores, rigid grain-hosted interparticle pores, intraparticle dissolution pores, grain-rim microfractures, intragranular microfractures, and matrix microfractures are identified with varying numbers, sizes, and geometries. Large field-of-view 2D scanning electron microscopy images were also used to quantitatively and statistically study the abundance and size of pores and fractures. Using multi-scale CT techniques, pores and fractures from centimeter to nanometer scales were observed with preferential propagation along the mineral aggregate-rich laminations, resulting in an interconnected pore-fracture network. Using FIBSEM, the mineral/organic particles and their related pore phases were visualized, quantitatively computing the pore size and abundance. The visual results suggest that the mineral matrix pore-fracture network in lacustrine Shahejie Formation plays a key role as the liquid hydrocarbon storage space. The application of these techniques to the lower-thermal-maturity shale reservoirs provides important insights into estimating and visualizing rock microstructural heterogeneity and preliminarily establishing a liquid hydrocarbon microscopic storage model.

Quantitative Characterization of Elastic Parameters and Its Implications for Reservoir Evaluation: A Case Study on High Clay-rich Continental Shale

“…With the continuous advancement of petroleum exploration and development, coupled with technological progress, unconventional oil and gas has emerged as a burgeoning field in recent years. − China possesses abundant shale oil resources, particularly in terms of high-maturity shale oil reserves. In recent years, significant advancements have been achieved in the exploration and development of continental shale oil resources in China, primarily located within basins such as Junggar, Ordos, Santanghu, Sichuan, and Bohai Bay. − Shale oil reservoirs exhibit nanopore structures and possess extremely low permeability characteristics, necessitating the implementation of hydraulic fracturing to enhance the seepage pathway for achieving a stable oil flow. − In order to successfully execute hydraulic fracturing operations on site, it is imperative to predefine the geometric configuration of fractures and perform geomechanical modeling. The parameters such as geostress, Young’s modulus, and Poisson’s ratio constitute the fundamental data of geomechanics and exert a decisive influence on the shape, height, and length of fractures. , Utilizing logging curves continuously to derive parameters such as Young’s modulus and geostress in the reservoir can effectively guide the optimization of fracturing segment design and perforation distribution …”