Pore Structure and Fractal Characteristics of Distinct Thermally Mature Shales

Abstract

To investigate the shale pore structure and fractal characteristics during thermal evolution, 30 shale samples from two wells with contrasting maturities (the Ro values of Yanchang samples are 0.71–1.06% and the Ro values of Longmaxi samples are 2.79–3.41%) were subjected to field emission-scanning electron microscopy observation, low-pressure N2 adsorption experiment, and other analytical measurements. The Frenkel–Halsey–Hill model was used to obtain the double-fractal dimensions (D1 and D2) of shale pores for different suits of samples. Analysis shows that the shale pores undergo a complicated evolution process with the increase of thermal maturity. Hence, the evolution trends of pore structure parameters with distinct thermal maturity are not in the same trend. The pore volume and porosity have a trend of increasing first and then decreasing with increase of Ro, which is mainly related to hydrocarbon generation of organic matter (OM). With the increase of Ro, the average pore size and specific surface ...