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Soluble minerals are abundant in inter-salt shale oil reservoirs, and during the development process, phenomena such as dissolution and precipitation occur, affecting the structure of the reservoir. The study aims to investigate the effects of dissolution and precipitation of single minerals in high-salinity core samples on the pore structure and seepage patterns. First, by utilizing CT scanning, the study analyzes the dissolution of mineral in the core under different fluid mineralization levels, different fluid injection rates, and varying initial salt content in the core, as well as the changes in pore structure after mineral dissolution. Next, through gas injection experiments, the optimal gas injection pressure differential is selected, and the precipitation process during gas injection is precisely characterized using online CT scanning technology. Finally, online CT scanning technology is used to accurately characterize the oil-water two-phase flow process involving mineral dissolution.
The research results show that the higher the mineralization degree of the injected fluid, the lower the dissolution degree of the mineral salts in the saline core. At the same time, the injection of low/high concentration fluids during salt dissolution resulted in an inhibitory effect on salt dissolution. Real-time CT scanning showed that during the initial stage of gas injection, precipitation mainly consisted of small particles with diameters below 30 um, while in the later stages, the precipitated particles aggregated into larger ones. These precipitation were primarily distributed on the wall surfaces where the gas phase contacted the core skeleton. The two-phase displacement real-time CT scanning revealed that a large amount of mineral salts in the core were dissolved during the displacement process, with the remaining mineral salts mostly having particle sizes below 8 um, and the particles tended to take on a spherical shape. During the displacement process, the oil phase was continuously flushed out, with the remaining oil transforming from a continuous oil phase into isolated spherical droplets. After 5 PV of displacement, the remaining oil had a particle size distribution concentrated between 2-4 um, and the volume was mainly concentrated around 60 um3.
| Country | China |
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