Acoustic logging response law in shales based on petrophysical model

Abstract

Shale acoustic logging response law is complex due to the multiple minerals and pores, which limits the application of acoustic logging in shale reservoir parameter evaluation, therefore clarifying the shale acoustic logging response law is of great importance. Different petrophysical models are adopted for the equivalence of organic matter, clay, matrix minerals, and fractures, in Wufeng-Longmaxi shale formation in the Jiaoshiba area. Finally, the self-consistent approximation model is used to combine different components, and a shale petrophysical model with a complex pore structure is constructed. The model verification results show it has good predictability for shale. Based on the model, the effect of different mineral compositions and different types of pores are studied. The results show that: 1) The effect of clay and organic matter is very complex, and the variation laws of layered clay (organic matter) and dispersed clay (organic matter) on the acoustic wave are consistent. 2) Layered clay or organic matter leads to the formation anisotropy increase, which makes the acoustic time difference greater than that of containing dispersed clay (organic matter). 3) The fracture is the main control factor of anisotropy, and the anisotropy of gas-bearing fracture is higher than that of water/oil fracture.