Abstract
Shale reservoirs are characterized by low porosity and low permeability, and volume fracturing of horizontal wells is a key technology for the benefits development of shale oil resources. The results from laboratory and field tests show that the backflow rate of fracturing fluid is less than 50%, and the storage amount of fracturing fluid after large-scale hydraulic fracturing is positively correlated with the output of single well. The recovery of crude oil is greatly improved by means of shut-in and imbibition, therefore attracting increasing attention from researchers. In this review, we summarize the recent advances in the migration mechanisms and stimulation mechanisms of horizontal well high pressure forced soaking technology in the reservoirs. However, due to the diversity of shale mineral composition and the complexity of crude oil composition, the stimulation mechanism and effect of this technology are not clear in shale reservoir. Therefore, the mechanism of enhanced oil recovery by imbibition and the movable lower limit of imbibition cannot be characterized quantitatively. It is necessary to solve fragmentation research in the full-period fluid transport mechanisms in the follow-up research.
Highlights
Continental sediments are dominant in China’s shale oil, showing remarkable heterogeneity, great lateral variation, relatively low porosity, low-pressure coefficient, and heavy oil quality to a certain extent [1]
The results showed that the influence of the dynamic contact angle depends on the pore size and can be explained as the influence of the nonlocal flow field
The results show that the changes of pore size distribution and pore geometry will affect the water imbibition, and the fluid density ratio has a significant effect on water displacement behavior
Summary
Continental sediments are dominant in China’s shale oil, showing remarkable heterogeneity, great lateral variation, relatively low porosity, low-pressure coefficient, and heavy oil quality to a certain extent [1]. Many scholars put forward the fracturing technology of injecting energy increasing fluid (water, CO2) to supplement the formation energy and adding oil displacement agent into the fracturing fluid to achieve enhanced oil recovery [6, 7]. This technology has made some achievements in the development of tight oil, but the mechanisms of EOR by imbibition and displacement with multiscale porous are unclear and even controversial. In the multiscale space after fracturing, the strong interaction of complex fluid and rock interface has a great influence on the flow of shale oil
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