Buffer-regulated treating fluid positioning process

Claim 2

A well treating process comprising dissolving in an aqeous liquid at least one each of a cellulose ether, a fluoride salt, a weak acid, and a weak acid salt; arranging the composition and relative amounts of the solution components to provide a temporarily viscous solution that is weakly acidic but is capable of dissolving clay and has a selected relatively high viscosity that is significantly reduced in response to a time-temperature exposure of selected severity; and flowing the temporarily viscous fluid into a subterranean location at a rate such that it at least substantially reaches the location to be treated before its viscosity has been significantly reduced.

Claim 3

The process of claim 1 in which at least a portion of the temporarily viscous solution is combined with relatively inert material, to form a treating solution having substantially the same acidity and viscosity properties, prior to flowing it into the subterranean location.

Claim 4

The process of claim 2 in which the relatively inert material includes solid particles adapted to form a sand or gravel pack or a fracture-propping mass of particles.

Claim 5

The process of claim 1 in which a relatively small proportion of strong acid is mixed with the temporarily viscous solution to increase its initial rate of reaction and reduce the duration of its relatively high viscosity.

Claim 6

The process of claim 1 in which the temporarily viscous solution is arranged to have a pH of from about 2 to 4.

Claim 7

The process of claim 1 in which the temporarily viscous solution is flowed into a fracture within a subterranean earth formation and, before flowing it into the fracture, the composition and proportions of its components are arranged to provide a relatively high pH.

Claim 8

The process of claim 6 in which slugs of the temporarily viscous solution are alternated with slugs of a relatively fast-acting acidic material.

Claim 9

A well treating process comprising dissolving in an aqueous liquid at least one each of a cellulose ether, a fluoride salt, a weak acid, and a weak acid salt; arranging the compositions and proportions of said soluteS to provide a temporarily viscous solution that is weakly acidic but is capable of dissolving clay and has a viscosity that is significantly reduced in response to a time-temperature exposure of selected severity; combining the temporarily viscous solution with relatively inert material to the extent desired to provide an earth formating treating fluid having properties of acidity and viscosity substantially equaling those of the solution; and flowing the earth formation treating fluid into a subterranean location to be treated before the solution viscosity is significantly reduced.

Claim 10

A well treating process comprising dissolving in an aqueous liquid at least one each of a cellulose ether, a fluoride salt, a weak acid, and a weak acid salt; arranging the compositions and proportions of said soluteS to provide a temporarily viscous solution that is weakly acidic but is capable of dissolving clay and has a viscosity that is significantly reduced in response to a time-temperature exposure of selected severity; combining the temporarily viscous solution with relatively inert material to the extent desired to provide an earth formating treating fluid having properties of acidity and viscosity substantially equaling those of the solution; and flowing the earth formation treating fluid into a subterranean location to be treated before the solution viscosity is significantly reduced.

Claim 11

The process of claim 8 in which the earth formation treating fluid contains suspended solid particles adapted to form a permeable mass of particles in the subterranean location to be treated.

Claim 12

The process of claim 8 in which a relatively small proportion of a strong acid is mixed with the temporarily viscous solution to increase its initial rate of acidization reaction and reduce the duration of its relatively high viscosity.

Claim 13

The process of claim 8 in which the compositions and proportion of the components of the the temporarily viscous solution are arranged to provide a relatively high pH and the earth formation treating fluid containing that solution is flowed into a fracture within a subterranean earth formation.

Claim 14

In a well treating process in which a self-breaking viscous fluid having a selected initial viscosity is injected into a selected subterranean location in response to a selected injection pressure, an improved process for ensuring that the viscosity-breaking occurs at a selected time after the solution has reached the selected location, which process comprises: determining the magnitude of the time-temperature exposure of fluid that flows from a surface location to the selected subterranean location at the rate established by the selected injection pressure; determining the pH at which an aqueous solution that contains enough cellulose ether to provide the selected viscosity mixed with an acid capable of inducing the breaking of the viscosity becomes a solution in which the viscosity-breaking occurs at the selected time after the solution has been subjected to a time-temperature exposure of the determined magnitude and is maintained at the temperature of the selected subterranean location; and injecting as said self-breaking viscous fluid a cellulose ether-thickened aqueous solution having a pH substantially equaling the determined pH.

Claim 15

In a well treating process in which a self-breaking viscous fluid having a selected initial viscosity is injected into a selected subterranean location in response to a selected injection pressure, an improved process for ensuring that the viscosity-breaking occurs at a selected time after the solution has reached the selected location, which process comprises: determining the magnitude of the time-temperature exposure of fluid that flows from a surface location to the selected subterranean location at the rate established by the selected injection pressure; determining the pH at which an aqueous solution that contains enough cellulose ether to provide the selected viscosity mixed with an acid capable of inducing the breaking of the viscosity becomes a solution in which the viscosity-breaking occurs at the selected time after the solution has been subjected to a time-temperature exposure of the determined magnitude and is maintained at the temperature of the selected subterranean location; and injecting as said self-breaking viscous fluid a cellulose ether-thickened aqueous solution having a pH substantially equaling the determined pH.

Claim 16

The process of claim 12 in which the pH of said injected fluid is established by a dissolved mixture of at least one weak acid and one weak acid salt in a ratio that buffers the pH at substantially the determined pH.

Claim 17

The process of claim 12 in which said injected fluid contains at least one dissolved salt of hydrofluoric acid.

Claim 18

The process of claim 14 in which said injected fluid has a pH of from about 2 to 4.

Claim 19

The process of claim 16 in which the selected location is a subterranean region in contact with earth formation in or around the borehole of a well.

Claim 20

The process of claim 16 in which the weak acid salt comprises a mixture of at least one salt of hydrofluoric acid and at least one salt of an organic acid.

Claim 21

THe process of claim 18 in which the weakly acidic solution contains an amount of strong acid that is significant but less than equimolar relative to the amount of weak acid.

Claim 22

The process of claim 18 in which the strong acid is hydrochloric acid.

Claim 23

The process of claim 20 in which the pH of the buffer regulated solution is, initially, from about 2 to 4.