Abstract

Hydraulic fracturing and drilling are commonly and widely used in many formations, particularly in unconventional reservoirs, such as tight sandstone reservoirs and so on. Whereas, during the fracturing or drilling process, large quantities of fluids are lost in the formation. Specially, many gas wells suffer a loss in productivity as a result of liquid invasion into the rock matrix. Liquid invasion is referred to as "water blocking", which is the primary damage that occurs in tight reservoirs and in low-permeability and ultra-low-permeability reservoirs. Some methods and materials, like methanol, are used to eliminate "water blocking", but only providing a temporary solution to the problem.

This paper introduces a hydrophobic wettability function and mechanisem that effectively eliminates "water blocking" on the tight sandstone. The results from wettability experiments using tight sandstone show that hydrophobic wettability function on the sandstone surface, making a contact angle greater than 90°. The inner wall of capillary tube changes wettability and the capillary pressure becomes a positive driving force rather than a negative resistance. The experimental studies demonstrate that altering the wettability of tight sandstone to produce a hydrophobic surface is a viable method for recovering permeability and eliminating "water blocking".

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