Analysis and enlightenment of porosity differences between shale plug samples and crushed samples

Shale porosity is one of the important parameters for shale reservoir quality evaluation and shale gas reserve calculation, so it is very important to accurately measure shale porosity. There are many methods to measure shale porosity. Liquid saturation and helium saturation methods are applied to core plugs and crushed samples. At present, there are few comparative studies on the measurement results of the porosity of plug samples and crushed samples, and the differences between them are even less reported. Firstly, the porosity of plug samples is measured using different measurement methods. Then, the plug samples are crushed and the porosity of the crushed samples is measured, and the factors affecting porosity are analyzed. Finally, the differences between the porosity of the plug samples and the crushed samples are compared. The experiment results show that the porosity of shale plug samples (helium saturation method) is the connected porosity of shale, and the porosity of crushed samples is the total porosity of shale, and the latter is 0.65%-2.40% higher than the former, which accounts for 11.21%-44.36% of the total porosity. There are several reasons. (1) The injection pressure of helium saturation method is too low. (2) The samples are not evacuated. (3) A large number of unconnected pores in the shale plug samples are not effectively saturated with helium. The correlation between different mineral components and the porosity of plug and crushed samples shows that the unconnected pores mainly exist in organic matter and a small amount in clay minerals. Appropriate chemical reagents can be added in the process of reservoir transformation to effectively modify the structure of organic matter and clay minerals, and release shale gas in these disconnected pores as far as possible, so as to improve shale gas recovery.