Study on Hydraulic Fracture and Proppant Distribution Characteristics in Chang 7 Member Core Samples from the Ordos Basin

The main development target in the Qingcheng Shale Oil of China's Ordos Basin is the Chang 7 member of the Yanchang Formation. It comprises fine-grained sediments from semi-deep to deep lacustrine facies, with a formation thickness of approximately 110m, vertically divided into three sub-layers: Chang 7_1, Chang 7_2, and Chang 7_3. Among these, Chang 7_1 and Chang 7_2 feature lithological assemblages of mud shale interbedded with multiple thin layers of siltstone to fine sandstone, termed "interbedded shale oil," which is the primary target for current large-scale development. Compared to North American and other Chinese shale oils [Zou, 2013; Wu, 2024, Yuan, 2023], the interbedded shale oil in the Ordos Basin exhibits characteristics such as high organic carbon abundance (3-28%), thin single sand bodies (3-5m), rapid vertical and lateral sand-mudstone variations, low formation pressure coefficient (0.7-0.8), and complex topography, presenting significant overall development challenges [He, 2024; Fu, 2020, Li, 2022]. In recent years, effective development has been achieved through horizontal well staged fracturing with volumetric fracturing technology [Gao, 2020;, Ma, 2023,; Xu, 2025]. However, as the development scale expands and the characteristics of the developed shale oil reservoirs become more complex [Ma, 2023; Lei, 2025], the urgent need arises to enhance the iterative upgrading of fracturing technology. Key challenges in hydraulic fracturing research include insufficient understanding of fracture spatial geometry and proppant placement. Current evaluation methods primarily rely on indirect techniques such as microseismic monitoring and numerical simulation, lacking direct evidence of fracture characteristics and failing to accurately reflect the actual underground fracture morphology and propping conditions. In 2014, North America initiated research on Hydraulic Fracturing Test Sites (HFTS). These projects integrate various fracturing monitoring techniques with post-fracturing coring, using multiple methods to constrain understanding of hydraulic fracture propagation geometry and propping, providing a basis for evaluating volumetric fracturing technology and optimizing designs [Elliott, 2018; Courtier, 2017; Trowbridge, 2018; Gale, 2021]. These projects offer valuable lessons for oilfield operators building HFTS, such as using dyed proppant to locate coring fractures within specific treatment stages [Elliott, 2018]; employing high-density microseismic clouds to guide coring well placement, successfully identifying 1cm-thick quartz sand layers on artificial fracture faces [Courtier J, 2017; Trowbridge, 2017]; and identifying reopened natural fractures through CT scanning and core observation [Gale J, 2021]. Significant differences exist between North American marine shale oil and Chinese shale oil reservoir characteristics, as well as fracturing technical models, making direct application of conclusions inappropriate. Therefore, establishing a HFTS for comprehensive fracture research is highly meaningful. To enhance understanding of induced fracture morphology and proppant placement, Changqing Oilfield, drawing on North American HFTS practices, established the Qingcheng Shale Oil HFTS in the Longdong area in 2022. The project primarily encompasses three components: "Integrated geological-engineering design pre-fracturing, Fracturing response inversion and fitting during fracturing, Post-fracturing coring analysis and evaluation." This paper focuses on the coring analysis and evaluation part. It details the coring workflow, establishes criteria for identifying fracture types and proppant, studies the spatial distribution of fractures and proppant placement characteristics in Qingcheng shale oil, and proposes optimization directions for future fracturing designs.