Method of stimulation of brittle rock using a rapid pressure drop

Patent metadata

Field	Value
Publication number	US-10100626-B2
Application number	US-201415126404-A
Country	US
Kind code	B2
Filing date	May 19, 2014
Priority date	May 19, 2014
Publication date	Oct 16, 2018
Grant date	Oct 16, 2018

Abstract

A method and system for inducing secondary orthogonal fractures in an underground formation by introducing a proppant carrying fluid into a hydraulic fracture in an underground formation at high pressure is provided. The pressure of the proppant carrying fluid is lowered at a rate allowing the fluid to exit the formation while the proppant remains in place within the fractures. The pressure of the fluid is then rapidly reduced, creating fractures orthogonal to the surface of existing fractures by pushing remained proppant against hydraulic fractures walls. The orthogonal fractures can be opened with high pressure fluid and propped. In this way, the portion of the formation in fluid flow communication with the wellbore is increased.

First claim

The invention claimed is:

1. A method of hydraulic fracturing comprising:
(a) pumping a first fluid at a first pressure into a fractured formation having a plurality of fractures where each of said plurality of fractures has a first inner surface and a second inner surface, and where said fiat fluid contains a first proppant;
(b) reducing the pressure of said first fluid in said plurality of fractures at a trapping rate: such that said first fluid flows back out of said formation while said formation retains said first proppant in said fractures as a result of pressure transmitted from said first and second inner surfaces to said proppant, and wherein, said first fluid contains said first proppant at a concentration not to exceed the amount required to create a rarefied monolayer between said first inner surface and said second inner surface;
(c) further reducing the pressure of said first fluid in said formation at a secondary fracturing rate greater than said trapping rate such that said first proppant creates orthogonal fractures in said first and second inner surfaces as said first and second inner surfaces fracture around said proppant and
(d) pumping one or more secondary fluids and a second proppant into said fractured formation such that said orthogonal fractures open and said second proppant is introduced into said orthogonal fractures.

2. The method of claim 1 wherein step (d) comprises:
(i) pumping a second fluid into said fractured formation at a second pressure such that said plurality of first and second inner surfaces in said formation reopen;
(ii) increasing the pressure of said second fluid pumping into said formation from a second pressure to a third pressure such that said orthogonal fractures created by said first proppant open:
iii) pumping a third fluid containing the second proppant into said fractured formation at a fourth pressure such that said second proppant enters said orthogonal fractures.

3. The method of claim 2 , wherein prior to step (a) a formation is hydraulically fractured in order to create said fractured formation having said plurality of fractures with said first inner surface and said second surface.

4. The method of claim 3 wherein said fourth pressure is higher than the maximum horizontal in-situ stress of said formation and said first pressure is higher than the minimum horizontal in-situ stress of said formation.

5. The method of claim 1 wherein the pressure in step (b) is initially reduced at said trapping rate such that said first fluid flows on of said formation at a rate of from about 0.5 to about 1 barrel per minute.

6. The method of claim 5 wherein, once said trapping rate decreases below the minimum horizontal in-situ stress, step (c) is carried out at said secondary fracturing rate, where said secondary fracturing rate is performed at a rate sufficient to create said orthogonal fractures in said first and second inner surfaces of said plurality of fractures.

7. The method of claim 1 wherein said first proppant has a greater strength than said second proppant.

8. The method of claim 1 , wherein said first fluid has a lower viscosity than said second fluid such that the viscosity of said first fluid does not cause said first proppant to exit said formation in step (b) and said second fluid is able to cause said orthogonal fractures to open it step (d).

9. The method of claim 1 wherein said first fluid comprises one of nitrogen or carbon dioxide.

10. The method of claim 1 wherein the concentration of said first proppant in said first fluid is such to create proppant distribution in said fracture of from about 0.1 lb/ft 2 to about 0.4 lb/ft 2 and the concentration of said second proppant in said second fluid is in the range of from to 1to 15 ppg.

11. The method of claim 1 wherein the size of said first proppant is in the range of from 60 to 4 mesh and the size of said second proppant is in the range of from 200 to 10.

12. A system for hydraulic fracturing comprising:
(a)a fractured formation;
(b) a first proppant supply containing a first proppant;
(c) second proppant supply containing a second proppant;
(d) a first fluid supply containing a first laid;
(e) a second fluid supply containing a second fluid;
(f) a blending device adapted to connect to said first and second fluid supplies and said first arid second proppant supplies;
(g) a pumping device adapted to connect to said blending device and to a wellbore and further adapted to deliver said first proppant contained in said first proppant supply, said second proppant contained in said second proppant supply, said first fluid contained in said first fluid supply and said second fluid contained in said second fluid supply into said wellbore and into said fractured formation;
(h) a valve located bet between said pumping device and said wellbore adapted to control the delivery of said first and second fluids and said first and second proppants into and out of said wellbore;
wherein the system is configured to:
(i) pump said first fluid containing said first proppant at a first pressure into a fractured formation having a plurality of fractures where each of said plurality of fractures has first inner surface and a second inner surface;
(ii)reduce the pressure of said first fluid in said formation at a trapping rate such that said first fluid flows back out of said formation while said formation retains said first proppant in said fractures as a result of pressure transmitted from said first and second inner surfaces to said proppant, and wherein said system is configured such that said first fluid contains said first proppant at a concentration not to exceed the amount required to create a rarefied monolayer between said first inner surface and said second inner surface;
(iii) further reduce the pressure of said first fluid in said formation at a secondary fracturing rate greater than said trapping rate such that said first proppant creates orthogonal fractures in said first and second inner surfaces as said first and second inner surfaces fracture around said proppant; and
(iv) pump said second fluid containing said second proppant into said fractured formation such that said orthogonal fractures open aid proppant is introduced into said orthogonal fractures.

13. The system of claim 12 wherein said first fluid comprises at least one of nitrogen or carbon dioxide.

14. The system of claim 12 wherein the ratio of said first proppant to said first fluid delivered to said fractured formation by said pump is lower than the ratio of said second proppant to said second fluid delivered to said fractured formation by said pumping device.

15. The system of claim 12 wherein size of said first proppant is in the range of from 4 mesh to 60 mesh and size of said second proppant is in the range of from 200 to 10 mesh.

Assignees

• Halliburton Energy Services Inc

Inventors

• Martysevich Vladimir Nikolayevich
• Hampton Jesse Clay
• Chen Cheng

Classifications

• E21B43/267

  reinforcing fractures by propping · CPC title

• E21B43/164

  Injecting CO2 or carbonated water (in combination with organic material C09K8/594) · CPC title

• E21B43/26 Primary

  by forming crevices or fractures · CPC title