Method of maintaining the permeability of hydrocarbon reservoir rock

Claim 1

A method of maintaining and stabilizing the permeability of subsurface hydrocarbon reservoir rock containing clay particles and, where clay damage has occurred, of improving the permeability of the rock, said method comprising: (a) injecting down a well bore traversing said rock an aqueous solution of alkaline earth metal hydroxide and a salt of an alkaline earth metal the concentration of alkaline earth metal cation in the solution being greater than 10,000 ppm and the pH value of the solution being greater than 10; (b) forcing said solution under pressure out into the reservoir rock formation and away from said well bore; (c) maintaining the pressure to prevent the solution from flowing back into the well bore and to cause the solution to remain within the rock formation for a time period and with a volume which is: (1) insufficient to consolidate sand, but (2) sufficient (i) in respect of expansible clay particles, to alter their electrical behavior, thereby causing them, in hydrated form, to occupy a smaller effective volume than prior to the altering, and (ii) in respect of non-expansible clay particles and originally expansible clay particles whose electrical behavior has thus been altered pursuant to (i), chemically to transform them into clay particles which are capable of permanently adhering to rock substrates, thereby to decrease the existing sensitivity of both expansible and non-expansible clay particles to fluids and permanently to change the clay particle structure so as to prevent future sensitivity of fluids (d) thereafter releasing the well head pressure, thereby enabling solution to flow back into the well bore.

Claim 2

A method of maintaining and stabilizing the permeability of subsurface hydrocarbon reservoir rock containing clay particles and, where clay damage has occurred, of improving the permeability of the rock, said method comprising: (a) injecting down a well bore traversing said rock an aqueous solution of alkaline earth metal hydroxide and a salt of an alkaline earth metal the concentration of alkaline earth metal cation in the solution being greater than 10,000 ppm and the pH value of the solution being greater than 10; (b) forcing said solution under pressure out into the reservoir rock formation and away from said well bore; (c) maintaining the pressure to prevent the solution from flowing back into the well bore and to cause the solution to remain within the rock formation for a time period and with a volume which is: (1) insufficient to consolidate sand, but (2) sufficient (i) in respect of expansible clay particles, to alter their electrical behavior, thereby causing them, in hydrated form, to occupy a smaller effective volume than prior to the altering, and (ii) in respect of non-expansible clay particles and originally expansible clay particles whose electrical behavior has thus been altered pursuant to (i), chemically to transform them into clay particles which are capable of permanently adhering to rock substrates, thereby to decrease the existing sensitivity of both expansible and non-expansible clay particles to fluids and permanently to change the clay particle structure so as to prevent future sensitivity of fluids (d) thereafter releasing the well head pressure, thereby enabling solution to flow back into the well bore.