Influence of fluid pH on the permeability of tight sandstone reservoir

The rang of stratum fluid pH is from 4 to 9 in general. Once the pH of the fluid invading reservoir is too high or too low, it is inevitably happened that invasion fluid not matches with reservoir fluid and mineral so as to cause reservoir damage. Taking the tight sandstone reservoir of Xianxiqun Formation as an example, the comprehensive evaluation experiment of changing the reservoir permeability by gradually increasing or decreasing fluid pH is carried out and the result shows the clay mineral microstructure damage caused by high pH makes the clay minerals such as illite and chlorite etc. dissolve, disperse, migrate and decrease, the permeability; low pH fluid can destroy the crystal microstructure of chlorite, which makes the Fe2+, Fe3+, Mg2+ within the structure separate to cause Fe(OH)3 and Mg (OH)2 deposit and plug up pore throat.