Logging Rock Physical Responses and Determining a Characterization Method for Fractures with Different Geological Geneses in Tight Sandstone

Natural fractures are important reservoirs and migration channels for tight oil and gas systems, and the various geological geneses of fractures are key factors that determine whether tight oil and gas can be produced. Therefore, research on identifying and characterizing the origins of fractures has become critical, especially the challenge of using conventional logging data to identify and characterize fractures with various geological geneses, and an efficient characterization method is urgently needed. First, core observation, thin section analysis, core sample test analysis, numerical simulation, core calibration of borehole-imaging logs, and borehole-imaging log calibration of conventional logs are performed to identify the sensitive logging curves and log response characteristics of fractures with different geological geneses. Second, the response characteristics of and differences in the log and rock physical properties of tight sandstone with fractures, without fractures and with fractures having different origins are analyzed, and the logging eigenvalue and rock physical eigenvalue models, which are comprehensive identification methods, are established, as are criteria for determining the different causes of fractures in tight sandstones. Finally, the two models are applied to identify and characterize the geological geneses of fractures in tight sandstone reservoirs in Sichuan. The effect of using the logging eigenvalue and the rock physical eigenvalue models to identify fractures is consistent with that using an imaging log.