Determination of the pore-throat limits for water imbibition in tight sandstone reservoirs through NMR analysis

Imbibition is regarded as an important mechanism for the recovery of oil for tight sandstone reservoirs. In this work, imbibition characteristic of tight sandstone reservoirs is experimentally investigated by nuclear magnetic resonance (NMR) and mercury intrusion porosimetry (MIP) tests. Pore-throat limit for imbibition is determined and its relation to reservoir parameters is examined. The pore-throat boundaries for both imbibition and drainage process are differentiated. An imbibition mechanism of tight sandstone reservoir is proposed where the wetting phase enters smaller pores due to capillary effect and the non-wetting phase is drained through larger pores. Porosity is linearly proportional to the pore-throat limit for imbibition, whereas exponential relationships are discovered between permeability, clay content and the pore-throat limit for imbibition. This work provides an insight into the mechanism of oil displacement through the imbibition process by elucidating the impact of pore-throat size on such a process and, as a consequence, can be applied to screen the target formation and optimize the oil production process that will ultimately lead to an improvement of imbibition recovery rate.