Sand dilation study and its effect on porosity and permeability during cyclic steam stimulation by in-situ imaging technique

Cyclic Steam Stimulation (CSS) is an effective and widely used technique to recover the heavy oil/bitumen. However, due to its complex nature, it has not been studied in detail experimentally. Most of the Canadian bitumen reservoirs have negligible steam injectivity, therefore to recover oil from such reservoirs, steam is injected at pressure higher than the overburden causing the pore pressure to increase and allow the disturbance in the sand, referred as sand dilation. This study aims to investigate changes in permeability and porosity of sand pack while varying net stresses occurring during CSS. New coreflooding equipment was designed, fabricated and commissioned aided with mechanical clamps to prevent leakages specially while reaching minimum net stress through providing strong grip between mandrels and rubber sleeve. To understand flow mechanism at the prevailing conditions, real time visualization study was carried out by using CT scanner. The images of in-situ fluid flow patterns with specific CT numbers were used to obtain a density map over the entire length of sand pack which was translated to porosity. Ottawa's sand with the highest concentration of 100-140 mesh was used for sand pack preparation by following the wet packing procedure. Methanol was used for this purpose. During the flooding test net stresses were increased and decreased in cycles by injecting steam and later hot water and at every phase scanning was done to apprehend the changes in the CT numbers and density. Permeability was also measured to understand the changes resulted due to varying net stresses. At minimum net stress the sand pack was fractured and the flow paths were confirmed from the CT images causing a radical change in permeability of 22.13% increase. This disturbance in sand during pore pressure variation was irreversible. However, not a considerable change in porosity was observed once the flow took place through the fractures. This research work has helped to understand the disturbance of sand by steam and hot water injection during CSS and identification of possible flow paths with help of CT images at real time. The changes reported in permeability are for the specific range of sand particle size, pressure and temperature conditions under which this study was conducted.