Abstract
Spontaneous imbibition phenomenon caused by capillarity plays an important role in the production of tight sandstone gas. Understanding the effects of bedding direction on liquid imbibition is important as it can give insights into water block phenomena that can negatively impact gas production. In this paper, four tight sandstone specimens were cored from Sichuan Basin, China with different bedding directions (i.e., the angles between the bedding plane and the horizontal plane of four specimens are 0 degrees, 45 degrees, 60 degrees and 90 degrees, respectively). Nuclear magnetic resonance (NMR) technique was used to monitor the fluid distribution changes during the spontaneous imbibition processes of these specimens. The results show that such tight sandstone exhibited strong hydrophilicity with the small pores dominating throughout the imbibition process. The T2 spectra for all four rocks specimens not only increased upward but also shifted to larger relaxation times due to brine intake along the minerals surface (further indicating the hydrophilic characteristics of this rock). For such tight sandstone, capillary force and friction resistance between the fluid (brine) and mineral surfaces controlled the imbibition processes. For the 0 degrees, 45 degrees and 60 degrees specimens, "stop illusion" phenomena which the imbibed brine volume had a tiny increase during a long period occurred. However, this was not observed in the 90 degrees specimen (where the bedding direction and fluid flow direction are parallel). This is largely attributed to the significant tortuosity in the flow for the 0 degrees, 45 degrees and 60 degrees specimens compared to the 90 degrees specimen, leading the smallest friction resistance existed in the 90 degrees specimen. Among these four specimens, the 0 degrees specimen had the slowest imbibition rate and lowest imbibition efficiency, while the 90 degrees specimen exhibited the fastest rate and highest efficiency. With the aim of maximizing gas production, this work provides some guidance for the selection of directional fracturing and injection-production methods in the exploitation and production of tight sandstone gas field.
NSTL
Elsevier