Abstract：
Spontaneous imbibition occurs widely in the hydraulic fracturing and the waterflooding process of low-permeability and tight oil reservoirs and is affected by various factors such as rock microstructure, fluid characteristics and boundary conditions. Accurately characterizing spontaneous imbibition is the key to effectively improve the recovery from tight oil reservoirs. In order to study the influence of micropore structures and wettability on spontaneous imbibition in tight oil reservoirs, in this paper,
we first establish the digital rock model based on CT scanning of tight sandstone samples from the Fan 154 block in the Shengli Oilfield. Then pore-scale spontaneous imbibition is simulated by using a lattice Boltzmann method based multiphase model. Finally, the evolution of the imbibition front and the characteristics of the recovery factor during spontaneous imbibition within three different pore structures and under different wettability conditions are analyzed. The results show that the imbibition rate is fast in a flaky pore structure with good connectivity, and the non-wetting fluid is mainly trapped by "snap-off", and the ultimate recovery degree is high. Pore structures with small pore size and good connectivity have stable spontaneous imbibition rates without big fluctuations, and the spontaneous imbibition phenomenon lasts for a long time. The non-wetting fluid is captured by "bypass" and "snap-off", and the ultimate recovery degree is generally good. The spontaneous imbibition rate of pore structures with flaky development but poor connectivity has obvious fluctuation. The non-wetting fluid is mainly trapped by "snap-off",
and the ultimate recovery degree is low; The change of wettability affects the evolution of the imbibition front. The smaller the wetting angle, the more wetting phase preferentially invades the pore corners, the two-phase interface is messy and dispersed, the main terminal interface exhibits obvious hysteresis, and the retention of the non-wetting phase after the leading edge of the imbibition front is obvious. However, the larger the wetting angle, the less the angular flow phenomenon, the more compact the morphology of the imbibition front, but the slower the imbibition rate and the lower the degree of imbibition. In the early stage of spontaneous imbibition, the counter-current imbibition process occurs strongly in many positions under strong wetting
conditions, in the later stage of spontaneous imbibition, the stronger the wettability, the more obvious the co-current imbibition
and the faster the rate of co-current imbibition, and the higher the ultimate recovery degree. The results are helpful to clarify the
characteristics of spontaneous imbibition and its influencing factors in fracturing development of tight oil reservoirs.
Key words：digital rock; tight sandstone; spontaneous imbibition; lattice Boltzmann method; wettability
Corresponding Authors： wangyong733.slyt@sinopec.com
Cite this article：WANG Yong, SUN Yeheng, LIANG Dong, CAI Jianchao. Spontaneous imbibition simulation of tight sandstone based on digital rock and lattice Boltzmann method. Petroleum Science Bulletin, 2020, 04: 458-466.
