Experimental Evaluation of Spontaneous Imbibitions and Water Injection in Tight Sandstone Oil Reservoirs

Spontaneous imbibition and displacement are important mechanisms in water flooding. This paper is aimed to evaluate the performance of water imbibition and injection in tight sandstone oil reservoir. Imbibition tests were first done to assess potential contributions to displacement and oil recovery. Then, a subsequent water injection at constant pressure was conducted in cores with permeability less than 0.1 mD and larger than 0.1 mD to explore the extent to which oil can be displaced and to evaluate fluid flow behavior. Finally, water injection at constant velocity was implemented to simulate displacement under reservoir condition and to analyze flow characters during injection. Results showed that water imbibition enhanced recovery more significant in cores with permeability less than 0.1 mD than that in cores with permeability larger than 0.1 mD. The recovery obtained was 19.2–26.7% and 6.7–7.6%, respectively. The subsequent water injection at constant pressure enhanced recovery further from 6.7–7.6% to 35.2–37.7% in cores with permeability larger than 0.1 mD. However, it did not make sense in cores with permeability less than 0.1 mD. There were a narrow area for oil/water co-flow and a sharp decrease in oil permeability at the initial stage. Meanwhile, the recovery during water injection at constant velocity was 57.7% and 42.9%, respectively. It presented high injection pressure in the upstream, and the quasi-threshold pressure gradient reached 80–200 MPa/m, which was hard to implement in reservoir. The injection pressure increased with the decrease in permeability. It also reveals that dominant channels exist and may lead to early water breakthrough which is negative for recovery enhancement.