Abstract
Low-permeability reservoirs have tiny pores with winding and complicated pore throats. The oil recovery efficiency of low-permeability reservoirs can be enhanced through the displacement of reservoir oil through imbibition. In the present study, experiments were conducted to investigate variations in the imbibition height of hydrophilic and weakly-hydrophilic rock samples under different interfacial tensions. An imbibition model considering imbibition resistance and bending of pore throats was established based on fractal theory. According to the experimental results, variations in the imbibition height of low-permeability rock samples with time can be divided into three stages. In the first stage, the capillary force plays a dominant role, while the viscous force and gravity have very slight effects. The imbibition height first increases rapidly and then levels off to a constant rate. With the increase in interfacial tension, the imbibition rate in the first stage increases, the ultimate imbibition height increases initially and then decreases, and the contribution of the imbibition height in the first stage to the ultimate imbibition height becomes greater. There is an optimal interfacial tension that causes the ultimate imbibition height to reach its maximum. The calculated results obtained from the proposed imbibition model are consistent with the experimental results, indicating that the model can accurately reflect the change in the imbibition height in low-permeability reservoirs in the first stage.
Highlights
Abundant oil and gas resources are present in lowpermeability reservoir formations, which are widely distributed all over the world
Imbibition refers to diffusion under the action of capillary force, as the wettingphase fluid enters the pore throat of rock spontaneously and displaces the nonwetting-phase fluid in the pore [5]
The reason is that the increase in interfacial tension increases the capillary force which serves as the driving force, facilitating imbibition
Summary
Abundant oil and gas resources are present in lowpermeability reservoir formations, which are widely distributed all over the world. Low-permeability reservoirs have small pore radii, few effective pores, and complicated pore throats with abundant microcracks [1]. It is difficult for traditional water-flooding to displace crude oil from capillary tubes in such a system [2]. Methods for the efficient development of low-permeability reservoirs have been widely studied in the petroleum industry [3]. Research and practice indicate that the displacement of oil through imbibition can significantly enhance the recovery of fractured reservoirs [4]. Imbibition refers to diffusion under the action of capillary force, as the wettingphase fluid enters the pore throat of rock spontaneously and displaces the nonwetting-phase fluid in the pore [5]
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