Experimental study on the hydraulic fracture propagation of laminar argillaceous limestone continental shale

Abstract

Laminar argillaceous limestone continental shale is an important oil reservoir in Jiyang Depression, Bohai Bay Basin of China. Affected by the laminar structure, the spatial propagation morphology of hydraulic fracturing is not clear. To reveal the propagation law of hydraulic fracturing pathway in laminar marl continental shale, the mineral content and basic rock mechanics test are firstly carried out on the cores from the wells in Jiyang Depression. Secondly the similar material cores with standard-size and large-size are manufactured and processed. Finally, combined with physical model experiments, acoustic emission and moment tensor inversion techniques, the hydraulic fracturing experiments on the large-size cores under different stress differences are conducted. The experimental results show that the in situ stress (confining stresses), laminar structure, and lithological distribution jointly affect the propagation mode of fractures. As the horizontal stress difference increases, the stimulated reservoir volume gradually decreases, and the number of shear fractures decreases accordingly. Macroscopically, the pump pressure curve shows obvious fluctuation in the case with lower horizontal stress difference, which is the external performance of hydraulic fracture initiation–obstruction–turning–penetrating–obstruction–turning. The content of brittle and plastic minerals has a significant impact on the fracture complexity, particularly the layers with high argillaceous content have a significant inhibitory effect on fracture propagation. The weakly cemented lamination or bedding plane is easy to capture the fracture and make it propagate along the bedding plane, thereby increasing the complexity of fracture network. The research results are expected to provide a theoretical reference for design and optimization of hydraulic fracturing parameter in continental shale oil exploration and development.

Study on the Difference of Fracture Extension in Hydraulic Fracturing of Marine and Continental Shales Based on Optical Scanning Technology

“…Based on hydraulic fracturing technology, the exploitation of marine shale gas has achieved significant success, and three major shale gas fields, including Fuling, Changning, and Weiyuan-in the Wufeng and Longmaxi Formations 2 of 16 of the Sichuan Basin of China, which are particularly large marine shale gas-producing areas-have realized the industrialized exploitation of shale gas by using hydraulic fracturing technology [13][14][15]. Compared with marine shale oil and gas reservoirs, continental shale oil and gas reservoirs are characterized by longitudinal lithological interlayers, high viscosity content, and relatively well-developed stratigraphic fractures, which indicates that the relevant technologies applied to marine shale gas development are not fully applicable to continental shale gas development [16][17][18][19][20]. Therefore, it is particularly important to study the differences in fracture extension in hydraulic fracturing of marine and continental shales.…”