Characteristics of fracture propagation in radial wellbores of shale oil reservoirs with multiple lithologic layers
Midium-high mature continental shale oil is a major substituted field in oil and gas exploration and development,but facing some challenges such as multi-lithology interaction and low degree of longitudinal reformation.How to fully activate longitudinal production zone is the key to achieve volume fracturing and obtain high and stable production of shale oil.For this reason,a novel idea of cross-layer fracturing in radial wells was proposed,which aims to guide longitudinal multi-layer fracture initiation by penetrat-ing the interlayer and lithologic interface through radial borehole,thus solving the problem of limited fracture height.In order to de-termine the feasibility of above idea,a true tri-axial cross-layer fracturing experiment was conducted.By means of CT scanning and 3D fracture reconstruction technology,the paper clarifies the characteristics of fracture initiation and penetration induced by radial well,and analyzes the influence law of vertical stress difference,displacement and radial well length on the fracture initiation and penetration.The results indicate that the radial well has the ability of guiding fracture propagation and promoting longitudinal frac-ture penetration,which can effectively reduce the difficulty of fracture penetration through layers and increase the longitudinal frac-ture propagation height.With the increase of vertical stress difference,the effect of fracture propagation induced by radial well is en-hanced,and the fracture initiation changes from cross-layer cracking mode to simultaneous multi-layer cracking mode,crossing the lithology interface.The fracture is dominated by low-strength layers under low displacement,and increasing displacement is condu-cive to longitudinal fracture propagation across layers.With the increase of radial length,the wellbore has the enhanced ability.of in-ducing fractures to cross the layer interface.The key findings are expected to provide solutions to the limitation of longitudinal frac-ture propagation height in continental shale oil reservoirs.
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