Numerical Investigation of the Osmatic Flow Impact on the Load Recovery and Early Well Performance

Abstract

The complexity of shale system coupled with the mystery of low fracturing fluid recovery has puzzled many researchers. Field reports from hydraulic fracturing operations performed on shale formation have highlighted the low recovery of the fracturing fluid. The fate of the hydraulic fracturing fluid is still controversial issue. However, literature has attributed the low load recovery to either trapping into the natural or created micro-fracture or imbibition to the matrix. Moreover, the impact of these fluids on the well performance is not well-understood. On one side, the well productivity will be improved due to the creation of complex fracture geometry developing larger stimulated reservoir volume and the creation of local stress areas due to clay swelling to squeeze the hydrocarbons out. On the other hand, the blockage of the natural fracture with the fracturing fluid and the permeability damage due to clay swelling might impair the productivity improvement. The shale membrane behavior was observed in the drilling operations and the application of the low salinity water flooding. Therefore, the incorporation of the chemical osmosis in the modeling of the hydraulic fracture cleanup will properly simulate the physical phenomena. Moreover, it might resolve the enigma of the impact of the elongated shut-in time on the well performance. In this study, a reservoir simulator capable of simulating the chemical osmosis and the concentration gradient driven flow is used to mimic the hydraulic fracture cleanup stage along with the well performance. The significance of the chemical osmosis on the load recovery and the salinity of the produced water is pointed out by simulating the same model with and without the osmatic flow.  Sensitivity analysis for the effect of the membrane efficiency, salinity contrast between the fracturing fluid and the formation brine, the reservoir temperature, natural fracture spacing, organic volume and shut-in time on the load and gas recovery is reported along with the relevancy factor of every parameter.

Keywords: osmosis, membrane efficiency, salinity contrast and shale