Method for improving isolation of flow to completed perforated intervals

1. A method of building a plug in a horizontal wellbore which penetrates a subterranean formation, the method comprising:

(a) pumping a fluid pill into the wellbore wherein the fluid pill comprises a suspended well treatment composite, the well treatment composite comprising a core having a dissolvable diverter and a deformable particulate, a viscosifying agent and a crosslinking agent, wherein the viscosifying agent and crosslinking agent are coated onto the core;

(b) disassociating at least a portion of the dissolvable diverter from the core of the well treatment composite and rendering a modified fluid pill comprising the deformable particulate and viscosifying polymer and crosslinking agent coated onto the deformable particulate;

(c) blocking at least a portion of a high permeability zone of a subterranean formation with the disassociated dissolvable diverter;

(d) diverting the flow of the modified fluid pill from a high permeability zone to a lower permeability zone of a subterranean formation;

(e) allowing at least one fracture in the lower permeability zone of the subterranean formation to partially close;

(f) at least partially preventing the deformable particulate from entering the at least one fracture by forming a thickened gel containing the deformable particulate, wherein the thickened gel is formed by the in-situ reaction of:

(i) the crosslinking agent disassociated from the core; and

(ii) viscosifying polymer disassociated from the core; and

(g) forming a fluid-impermeable plug with the thickened gel containing the deformable particulate.

2. The method of claim 1 , further wherein at least one of the following conditions prevail:

(i) prior to step (b), pumping a displacement fluid down the wellbore to displace the fluid pill into the formation; or

(ii) prior to step (f), pumping a displacement fluid down the horizontal wellbore to slowly displace the fluid pill after the at least one fracture in the zone has partially closed.

3. The method of claim 1 , wherein the deformable particulate is an ultra lightweight (ULW) particulate.

4. The method of claim 1 , wherein the core of the deformable particulate is porous.

5. The method of claim 1 , wherein the suspended well treatment composite is neutrally buoyant in the fluid pill.

6. The method of claim 1 , wherein the fluid pill further contains sand or a ceramic.

7. The method of claim 1 , wherein the dissolvable diverter comprises at least one compound of the formula:

or an anhydride thereof

wherein:

R 1 is —COO—(R 5 O) y —R 4 or —H;

R 2 and R 3 are selected from the group consisting of —H and —COO—(R 5 O) y —R 4 ;

provided both R 2 or R 3 are —COO—(R 5 O) y —R 4 when R 1 is —H and further provided only one of R 2 or R 3 is —COO—(R 5 O) y —R 4 when R 1 is —COO—(R 5 O) y —R 4

R 4 is —H or a C 1 -C 6 alkyl group;

R 5 is a C 1 -C 6 alkylene group; and

each y is 0 to 5.

8. The method of claim 7 , wherein the diverter further comprises an aliphatic polyester having the general formula of repeating units:

where n is an integer between 75 and 10,000 and R is selected from the group consisting of hydrogen, alkyl, aryl, alkylaryl, acetyl, heteroatoms, and mixtures thereof and aliphatic polyester is poly(lactide).

9. The method of claim 1 , wherein the dissolvable diverter is selected from the group consisting of phthalic anhydride, terephthalic anhydride, phthalic acid, terephthalic acid, gilsonite, rock salt, benzoic acid flakes, polylactic acid and mixtures thereof.

10. The method of claim 1 , further comprising, prior to step (g), applying a short pumping burst to displace the modified fluid pill after the fracture has partially closed.

11. A method of building a plug in a horizontal wellbore, the method comprising:

(a) pumping a fracturing fluid into the horizontal wellbore at a pressure sufficient to create or enlarge a fracture in the subterranean formation penetrated by the wellbore;

(b) pumping into the wellbore a fluid pill having a well treatment composite suspended therein, the well treatment composite comprising a solid core comprising a dissolvable diverter and a deformable particulate and a viscosifying polymer and crosslinking agent coated onto the core;

(c) pumping a displacement fluid down the wellbore and displacing the fluid pill further into the wellbore in proximity to a perforation tunnel in a desired location;

(d) flowing the fluid pill into a high permeability zone, blocking at least a portion of the higher permeability zone with the dissolvable diverter, forming a modified fluid pill and flowing the modified fluid pill into a lower permeability zone of the formation, wherein the modified well treatment composite has a core comprising the deformable particulate and viscosifying polymer and crosslinking agent coated onto the deformable particulate;

(e) allowing at least one fracture within the horizontal wellbore to at least partially close, the modified well treatment composite remaining suspended within the modified fluid pill;

(f) pumping the displacement fluid down the horizontal wellbore to slowly displace the modified fluid pill;

(g) increasing the viscosity of the modified fluid pill to form a gelled fluid by the in-situ reaction of:

(i) the crosslinking agent as it is disassociated from the deformable core; and

(ii) viscosifying polymer disassociated from the deformable core; and

(h) at least partially preventing the gelled fluid containing the deformable particulate from entering the at least one fracture in the zone, wherein the gelled fluid forms a fluid-impermeable plug within the wellbore.

12. The method of claim 11 , wherein the diameter of the deformable particulate in the fluid pill is greater than the diameter of a proppant used during fracturing of the wellbore.

13. The method of claim 11 , wherein the at least one fracture in step (e) is at least partially closed by varying the pumping rate of the displacement fluid.

14. The method of claim 11 , further comprising, prior to step (f), stopping the pumping of the displacement fluid, wherein the modified fluid pill is stationary within the wellbore.

15. The method of claim 14 , further comprising the step of varying the density of the deformable particulate such that the deformable particulate does not settle out while the fluid pill is stationary.

16. The method of claim 11 , further comprising continuing pumping a fluid down the wellbore until a pressure rises within the wellbore.

17. The method of claim 11 , wherein the dissolvable diverter comprises at least one compound of the formula:

or an anhydride thereof

wherein:

R 1 is —COO—(R 5 O) y —R 4 or —H;

R 2 and R 3 are selected from the group consisting of —H and —COO—(R 5 O) y —R 4 ;

provided both R 2 or R 3 are —COO—(R 5 O) y —R 4 when R 1 is —H and further provided only one of R 2 or R 3 is —COO—(R 5 O) y —R 4 when R 1 is —COO—(R 5 O) y —R 4

R 4 is —H or a C 1 -C 6 alkyl group;

R 5 is a C 1 -C 6 alkylene group; and

each y is 0 to 5.

18. The method of claim 17 , wherein the diverter further comprises an aliphatic polyester having the general formula of repeating units:

where n is an integer between 75 and 10,000 and R is selected from the group consisting of hydrogen, alkyl, aryl, alkylaryl, acetyl, heteroatoms, and mixtures thereof and aliphatic polyester is poly(lactide).

19. The method of claim 11 , wherein the dissolvable diverter is selected from the group consisting of phthalic anhydride, terephthalic anhydride, phthalic acid, terephthalic acid, gilsonite, rock salt, benzoic acid flakes, polylactic acid and mixtures thereof.

20. The method of claim 11 , wherein the deformable particulate is an ultra lightweight (ULW) particulate.

21. The method of claim 20 , wherein the ULW deformable particulate is porous.

22. The method of claim 11 , wherein the at least one fracture is at least partially closed in step (e) by reducing the pumping rate of the displacement fluid.

23. The method of claim 11 , wherein the diameter of the deformable particulate is greater than the diameter of a proppant used during fracturing of the wellbore.

24. The method of claim 11 , wherein the fluid pill in step (b) is pumped through a coiled tubing.

25. A method for building a plug in a horizontal wellbore comprising:

(a) suspending a well treatment composite within a fluid, the well treatment composite comprising a core of a dissolvable diverter and a deformable particulate and a viscosifying polymer and crosslinking agent coated onto the core;

(b) diverting the flow of the fluid pill to a low permeability zone of a subterranean formation penetrated by the wellbore;

(c) dissolving the dissolvable diverter to provide a modified fluid pill comprising a modified well treatment composite having a core comprising the deformable particulate and viscosifying polymer and crosslinking agent coated onto the deformable particulate;

(d) displacing the modified fluid pill;

(e) allowing at least one fracture in the low permeability zone of the horizontal wellbore to partially close;

(f) continuing to displace the modified fluid pill after the at least one fracture in the zone has partially closed, wherein a gelled fluid containing the deformable core bridges off forming a plug within the wellbore; and

further wherein during displacement of the modified fluid pill, the thickened gel is formed by the in-situ reaction of:

(i) the crosslinking agent after being disassociated from the deformable particulate; and

(ii) viscosifying polymer after being disassociated from the deformable particulate.