The effect of microstructure and rock mineralogy on water imbibition characteristics in tight reservoirs

Abstract

Published studies have suggested that the spontaneous imbibition induced by the high capillary force of tight rocks is a significant mechanism responsible for low flowback efficiency (<30%). However, due to the complex pore structure and mineral composition, the imbibition characteristic is complicated and requires further investigation. In this paper, comparative imbibition experiments were conducted on 12 core samples from different tight formations. The authors investigate the water imbibition characteristics of tight rocks with different mineralogy, pore connectivity and pore-size distribution. The results show that three key parameters of practical application value (i.e., the initial imbibition rate, late imbibition rate and imbibition capacity) can be used to present the imbibition characteristics. The water imbibition capacity is partially dependent on the clay mineral content and type, as shown by the positive correlation between imbibition capacity and total clay content, especially the amount of smectite and illite/smectite mixed-layer clay. In addition, the behaviors of imbibition curves vary greatly in the different tight rocks, which could be, at least in part, controlled by the pore size distribution and pore connectivity. To a large extent, well-developed macropores tend to have good pore connectivity and large time exponents at the initial imbibition region, and well-developed mesopores and micropores tend to have poor pore connectivity and large time exponents at the late imbibition region.