Experimental Study of Formation Damage Caused by Complete Water Vaporization and Salt Precipitation in Sandstone Reservoirs

摘要

Vaporization of water during both gas reservoir development and CO_2 geological sequestration in saline formations can cause salt precipitation with rapid loss of formation porosity and permeability. In this work, laboratory experiments were conducted to evaluate the effects of complete formation water evaporation and salt precipitation on the physical properties of sandstone samples by analyzing the decreases in both core porosity and permeability and the changes of pore distribution after salt precipitation using capillary flow porometry. Experimental results indicated that porosity can be decreased by 14.6 % and permeability can be decreased by 83.3 % due to salt precipitation under the experimental condition (100 ℃ and 0.101 MPa). The higher the salinity and lower the initial formation permeability, the greater is the decrease in permeability. The permeability reduction can be approximated with a power-law relationship to the porosity reduction. Sodium chloride (NaCl) was the major precipitated salt crystal. The precipitated salt will cause small pores to be blocked, which leads to reduced total pore volume and total effective pore volume. The experimental results also suggested that the impact of salt precipitation on pores with smaller diameter was found to be greater than on those with larger diameter.