A review on the advance in logging evaluation of fine-grained sedimentary rocks

As the source rock and reservoir of tight/shale oil and gas, fine-grained sedimentary rocks have become the focus and frontier of research. Logging evaluation of fine-grained sedimentary rocks plays an important role in selecting sweet spots in the exploration and development of unconventional oil and gas. However, the conventional logging evaluation of fine-grained sedimentary rocks is restricted by their complex composition, small particle size, complex pore structure, poor connectivity between pores and throats, strong heterogeneity, different fluid occurrence states in various reservoir spaces, and diverse assemblage of sources and reservoir. By analyzing the research progress of fine-grained sedimentary rocks in geological research and logging evaluation, the key points of logging evaluation of fine-grained sedimentary rocks are summarized, including: sedimentary cycle, source rock, reservoir property, oil-bearing, mobility and fracability. The logging evaluation methods of key geological and engineering parameters such as total organic carbon content, effective porosity, laminae density index, oil saturation, mobile fluid saturation, brittleness, in-situ stress and fracture toughness are discussed in detail. The important role and application of new technology logging in the classification and evaluation of fine-grained sedimentary rock sweet spots are clarified. The application and innovation of well logging, especially new log techniques in fine sediment in recent years, are described. This approach further underpins decision making towards technical studies on sweet spots, which also provides guidance into the exploration and development of new energy and helps to achieve carbon-neutral earlier.