A new gas content evaluation method for organic-rich shale in deep reservoir base on the digital core

Quantitative computing of shale gas content in deep reservoir is of great significance for shale gas resource evaluation and providing effective well production strategies. Although many scholars have proposed some improvement and optimization methods for gas content measurements, it is still difficult to get the accurate gas content because of the gas lost and pore structure change during the drilling core process in deep reservoir. In this paper, we proposed a new method for evaluating the gas content of shale in deep reservoir based on the digital core. First, the core-scale digital-experimental model for shales ware generated by the core-scale reconstruction method based on SEM, EDS images and experimental data. Then a digital core compressibility method, by considering the coupled effects of the confining pressure in deeply buried formation and the interstitial fluid pressure in the rock, was proposed to obtain the pore and fracture structure of the shale rock in deep reservoir with high temperature and pressure. It was found that the radius of pores, the aperture of fractures, and the connectivity of the shale rock decreases sharply in the deep reservoir. Second, the absolute adsorption amount for organic pores and inorganic pores in different mineral under deep reservoir condition were calculated separately based on the molecular dynamics (MD) model, and the regular of adsorption amount depending on the pore structure are summarized. Finally, the total gas content of the shale rock can be quickly calculated based on the digital-experimental core and the regular of adsorption amount obtained in the above step. The results obtained in our paper can help us to preliminarily understand the quality of shale reservoirs.