| Micro-scale experimental study has demonstrated promising advantages in addressing problems associated with the rock and flow properties in the petroleum engineering area. In this study, we report results from a micro scale experimental study of stress dependencies of the rock and flow properties under triaxial hydrostatic stress. we employed computed- microtomography to perform two single-phase flow experiments, one with brine and one with nitrogen, and four two-phase flow experiments, with oil and brine, on miniature Berea core samples to measure stress sensitivity of absolute permeability, pressure drop across the core, average porosity, pore size distribution, and fluid occupancy of each phase. Experiments were conducted by first gradually increasing the hydrostatic confining pressure from 600 to 2000 psig and then subsequently reducing it back to 600 psig while the pore pressure maintained at 500 psig. The results indicate that absolute permeability varied in each compaction confining pressure in the single-phase flow experiment due to the pore space deformation. Meanwhile, both single-phase experiments with brine and nitrogen showed a similar sensitivity of porosity to triaxial compaction pressure, whereby porosity was reduced by about 4-6% when the hydrostatic confining pressure increased from 600 to 2000 psig. Part of the observed permeability and porosity reduction during the loading process was irreversible while the hydrostatic pressure unloaded. In the two-phase flow experiments, the effect of loading and unloading hydrostatic stress on fluid occupancy of each phase showed the saturation of each phase was sensitive to the confining compaction pressure and also the pore space deformation alters the connectivity of each phase in the core sample. The results also demonstrate that due to the pore space deformation, the volume of each phase along the sample varies. In addition, the volume of oil blobs was changed by applying different hydrostatic stress. The experimental results indicate that the rock and flow properties and fluid occupancies in the natural porous medium are stress sensitive at the micro-scale. |
