In Situ Water Blocking Measurements and Interpretation Related to Fracturing Operations in Tight Gas Reservoirs

Abstract

Abstract Invasion of aqueous drilling, completion or fracturing fluids can reduce the relative permeability to gas and thereby causes a waterblock. In the case of low permeability formations, the capillary pressure tends to be high because of the small pore size. Clean up of water blocks requires high draw down unless water vaporization by the flowing gas is improved by using specific additives like alcohols. The purpose of this work is to investigate fracture face damage by measuring relevant petrophysical parameters: absolute permeability damage and gas return permeabilities. Measurements are performed in representative conditions of a fracturing operation in a tight gas formation: cores with an absolute permeability of 10 microDarcy set at Swi, experimental pressure of 200 bars for the fracturing fluid invasion. Water and gas saturations during the invasion of the fracturing fluid as well as during the gas back flow are monitored thanks to a XRay equipment. Adding alcohol in the fracturing fluid has a striking effect on resolving the water block. Cake formation on the simulated fracture face is also discussed. Numerical simulations are performed to assess relative permeabilities from the experimental results. It is shown that the hysteresis of gas and water relative permeabilities has a strong impact on the rate of water removal. Sufficiently high pressure draw down is crucial to overcome capillary forces and initiate alcohol assisted vaporization process. Water removal by water vaporization is assessed and compared to the experimental results.