Natural fractures and their effects on reservoir reconstruction in Lower Cambrian shale, southeast Chongqing, China

摘要

Natural fractures in shale are important for the preservation and exploitation of shale gas. The classification of fracture types and characterization of system parameters would help to better evaluate reservoir properties. An evaluation of the relationship between natural fractures and hydraulic fractures may help to predict the effects of fracturing on reservoir properties and assist fracturing design. This study focuses on fractures in Lower Cambrian marine shale in southeast Chongqing, China. The fracture system is characterized in detail through observations and descriptions of several outcrops, cores, and thin sections. Hydraulic fracturing experiments were conducted using a large-size triaxial simulator, enabling us to discuss the effects of natural fractures on the creation of hydraulic fractures in a reservoir. The shale contains three primary fracture types: structural fractures, digenetic fractures, and abnormal pressure fractures. High-angle shear fractures (75 degrees-90 degrees from bedding) are the dominant type of seepage fractures observed in the study area. Three sets of tectonic fractures were formed during three tectonic movements. East-west fractures formed mainly in the Yanshanian. Hydraulic fracturing experiments indicated that the Lower Cambrian shale had a good level of reconstruction. The interference between natural fractures and hydraulic fractures has resulted in the segmentation. This study maybe have some reference for fracturing parameter design.