Forced imbibition in tight sandstone cores

Abstract

Spontaneous imbibition (SI) generally occurs under forced pressure (pressure difference between hydraulic fluid pressure and original pore pressure) during a shut-in period. However, the experimental study of SI is commonly performed at atmospheric pressure and the effect of forced pressure is often neglected. In this study, the mechanism of SI in tight sandstone samples under forced pressure (forced imbibition, FI) was studied. A new experimental method for forced imbibition was firstly constructed based on low-field nuclear magnetic resonance(LF-NMR) measurements. After that, a correlation between SI and FI was discussed. Finally, a new dimensionless time model considering the effect of forced pressure for FI was constructed. The results showed that 96.76%-97.25% wt% of the oil was distributed in nano-pores (0.1 ms ≤ T2 ≤ 100 ms) of core samples, occupying the major pore space. The ultimate oil recovery for FI was significantly improved relative to that of SI, which was associated with the synergetic effect of enhanced SI and compaction. The new dimensionless time model for FI was proved to be effective and it provides a new method to calculate shut-in time at field scale.

Keywords

• tight sandstone
• forced imbibition
• lf-nmr
• dimensionless time model
• shut-in time