Method of gravel packing a well

A method of gravel packing a wellbore penetrating a subterranean formation comprising:

• preparing a gravel packing slurry by admixing (i) an aqueous liquid containing at least a trace amount of at least one divalent cation with (ii) a polymer derivative that is chemically modified by reacting at least one member selected from hydroxyethyl cellulose and hydroxypropyl cellulose with a vinyl phosphonic acid in the presence of a redox system, (iii) a crosslinking activator comprising a Lewis base or a Bronsted-Lowry base and (iv) a particulate agent,
• introducing said slurry into a zone to be gravel packed within said wellbore penetrating said subterranean formation;
• introducing an acidic fluid into said zone to be gravel packed within said wellbore;
• contacting said slurry with said acidic fluid whereby the pH of said slurry is reduced whereby the viscosity of said slurry decreases;
• and,
• depositing said particulate agent within said zone within said formation to form a permeable pack.

A method of gravel packing a highly deviated wellbore penetrating a subterranean formation comprising:

• preparing a base gel by admixing an aqueous liquid containing at least a trace amount of at least one divalent cation with a cellulose ether derivative that is chemically modified by reacting a hydroxyalkyl cellulose with a vinyl phosphonic acid in the presence of a redox system;
• filtering said base gel to remove unhydrated cellulose derivative and any other insolubles present therefrom;
• admixing a sufficient quantity of a crosslinking activator comprising a Lewis base or Bronsted-Lowry base, which is substantially free of polyvalent metal ions, with said base gel to effect crosslinking of said gel;
• admixing a particulate agent with said gel to form a slurry;
• introducing said slurry into a zone in the wellbore penetrating the subterranean formation which is to be gravel packed;
• introducing an acidic fluid into said zone in the wellbore penetrating the subterranean formation which is to be gravel packed;
• contracting said slurry with said acidic fluid in said zone whereby the pH of said slurry is caused to decrease whereby the viscosity of said slurry is caused to decrease;
• and
• depositing said particulate agent within said zone within said formation to form a permeable pack.