SLICKWATER HYDRAULIC FRACTURING WITH EXOTHERMIC REACTANTS

Abstract

Compositions and methods for increasing a stimulated reservoir volume in a hydrocarbon-bearing formation in fluid communication with a wellbore, one method including drilling a plurality of lateral extensions at varying depths in the formation extending from a vertical wellbore using slickwater hydraulic fracturing fluid, the slickwater hydraulic fracturing fluid comprising at least one friction reducer; and injecting an exothermic reaction component into the plurality of lateral extensions to create a plurality of fractures extending outwardly from and between the plurality of lateral extensions to create a multilateral fracture network.

Claims

1. A method of increasing a stimulated reservoir volume in a hydrocarbon-bearing formation in fluid communication with a wellbore, the method comprising the steps of: drilling a plurality of lateral extensions at varying depths in the formation extending from a vertical wellbore using slickwater hydraulic fracturing fluid, the slickwater hydraulic fracturing fluid comprising at least one friction reducer; and injecting an exothermic reaction component into the plurality of lateral extensions to create a plurality of fractures extending outwardly from and between the plurality of lateral extensions to create a multilateral fracture network, wherein injection of the exothermic reaction component reduces required application of proppant by between about 100 lbs. and about 10,000 lbs. of proppant.

2. The method of claim 1, where the steps of drilling and injecting are carried out simultaneously.

3. The method of claim 1, where the step of injecting is carried out after the step of drilling.

4. The method of claim 1, the method further including the use of concentric coiled tubing operable to inject components of the exothermic reaction component separately where the exothermic reaction component reacts to produce pressure and heat once disposed in a lateral extension of the plurality of lateral extensions.

5. The method of claim 1, further comprising the steps of: mixing the exothermic reaction component in an aqueous solution to achieve a pre-selected solution pH, wherein the exothermic reaction component is operable to react at a pre-selected reservoir temperature to generate a pressure pulse; injecting the fracturing fluid into the wellbore in the hydrocarbon-bearing formation; and generating a pressure pulse when the exothermic reaction component reaches the pre-selected reservoir temperature, where the pressure pulse is operable to create at least a portion of the plurality of fractures.

6. The method of claim 1, wherein the exothermic reaction component comprises an ammonium containing compound and a nitrite containing compound.

7. The method of claim 6, wherein the ammonium containing compound comprises NH.sub.4Cl and the nitrite containing compound comprises NaNO.sub.2.

8. The method of claim 5, wherein the pre-selected solution pH is between 5.7 and 9.

9. The method of claim 5, wherein the reservoir temperature is in a range between 48.8° C. (120° F.) and 121.1° C. (250° F.).

10. The method of claim 5, wherein the pressure pulse is between 500 psi and 50,000 psi.

11. The method of claim 5, wherein the pressure pulse creates fractures in less than 10 seconds.

12. The method of claim 5, wherein the pressure pulse creates fractures in less than 5 seconds.

13. The method of claim 1, wherein the slickwater hydraulic fracturing fluid further comprises at least one component selected from the group consisting of: a biocide, a surfactant, and a scale inhibitor.

14. The method of claim 1, wherein mixing the exothermic reaction component with the slickwater hydraulic fracturing fluid causes a less than 20% change to an original viscosity of the slickwater hydraulic fracturing fluid.

15. The method of claim 1, wherein mixing the exothermic reaction component with the slickwater hydraulic fracturing fluid causes a less than 10% change to an original viscosity of the slickwater hydraulic fracturing fluid.

16. The method of claim 1, wherein the exothermic reaction component is injected at between about 1 volume % and about 50 volume % of total fluids injected during the steps of drilling and injecting.

17. The method of claim 1, wherein the exothermic reaction component is injected at between about 10 volume % and about 30 volume % of total fluids injected during the steps of drilling and injecting.

18. The method of claim 1, wherein the steps of drilling and injecting are each repeated at least twice and are carried out alternatingly.

19. The method of claim 1, wherein the exothermic reaction component causes a non-combustive redox reaction to release heat and gas to create at least a portion of the plurality of fractures.

20. (canceled)

21. A hydraulic fracturing fluid composition comprising: slickwater hydraulic fracturing fluid, wherein the slickwater hydraulic fracturing fluid comprises at least one friction reducer, and an aqueous exothermic reaction component composition, wherein the aqueous exothermic reaction component composition comprises between about 1 volume % and about 50 volume % of the hydraulic fracturing fluid composition and changes an initial viscosity of the slickwater hydraulic fracturing fluid by less than about 20%, and wherein the aqueous exothermic reaction component composition has a pre-determined initial pH to react in situ in a hydrocarbon bearing formation proximate a formation temperature to release heat and gas through a non-combustive redox reaction for creating a plurality of fractures in the hydrocarbon bearing formation, wherein the aqueous exothermic reaction component reduces required application of proppant by between about 100 lbs. and about 10,000 lbs. of proppant in the hydraulic fracturing fluid.

22. The composition of claim 21, wherein the aqueous exothermic reaction component composition changes an initial viscosity of the slickwater hydraulic fracturing fluid by less than about 10%.

23. The composition of claim 21, wherein the exothermic reaction component comprises an ammonium containing compound and a nitrite containing compound in a molar ratio between about 9:1 to 1:9.

24. The composition of claim 21, wherein the ammonium containing compound comprises NH.sub.4Cl and the nitrite containing compound comprises NaNO.sub.2.

25. The composition of claim 21, wherein the pre-determined initial pH is between 5.7 and 9.

26. The composition of claim 21, wherein the slickwater hydraulic fracturing fluid further comprises at least one component selected from the group consisting of: a biocide, a surfactant, and a scale inhibitor.

27. The composition of claim 21, further comprising a hydroxide compound to modify pH of the hydraulic fracturing fluid composition.

28. (canceled)

29. The composition of claim 21, wherein the at least one friction reducer comprises polyacrylamide.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] These and other features, aspects, and advantages of the present disclosure will become better understood with regard to the following descriptions, claims, and accompanying drawings. It is to be noted, however, that the drawings illustrate only several embodiments of the disclosure and are therefore not to be considered limiting of the disclosure’s scope as it can admit to other equally effective embodiments.

[0023] FIG. 1 is a schematic diagram of a prior art slickwater hydraulic fracturing system in a wellbore with lateral fractures proceeding into a reservoir.

[0024] FIG. 2 is a schematic diagram of a fracture network created in embodiments of the present disclosure using slickwater hydraulic fracturing with an exothermic reaction component.

[0025] FIG. 3 is a graph showing varying-pressure pressure pulses created at varying pH for an exothermic reaction component.

[0026] FIG. 4 is a graph showing varying reaction triggering or activation temperatures at varying pH for an exothermic reaction component.

[0027] FIG. 5 is a pictorial representation of a low-viscosity slickwater fracturing fluid mixed with an exothermic reaction component, which maintains low viscosity for use as slickwater.

[0028] FIG. 6 is a graph showing the viscosity effects of adding an exothermic reaction component at varying concentrations to slickwater hydraulic fracturing fluid.

[0029] FIG. 7A is a pictorial representation of an Eagle Ford shale column hydraulically fractured with conventional fracturing fluid.

[0030] FIG. 7B is a pictorial representation of an Eagle Ford shale column fractured using an exothermic reaction of an exothermic reaction component.

[0031] FIG. 7C is a cross-sectional pictorial representation of the Eagle Ford shale column fractured using the exothermic reaction of an exothermic reaction component from FIG. 7B.

[0032] FIG. 8A is a pictorial representation of a Scioto sandstone column hydraulically fractured with conventional fracturing fluid.

[0033] FIG. 8B is a pictorial representation of a Scioto sandstone column fractured using an exothermic reaction of an exothermic reaction component.

[0034] FIG. 8C is a cross-sectional pictorial representation of the Scioto sandstone column fractured using the exothermic reaction of an exothermic reaction component from FIG. 8B.

[0035] FIG. 9 is a graph representing a pumping sequence for slickwater hydraulic fracturing fluid and an exothermic reaction component.

DETAILED DESCRIPTION

[0036] So that the manner in which the features and advantages of the embodiments of systems of and methods of making multilateral fracture networks with slickwater hydraulic fracturing and one or more exothermic reaction component, as well as others, which will become apparent, may be understood in more detail, a more particular description of the embodiments of the present disclosure briefly summarized previously may be had by reference to the embodiments thereof, which are illustrated in the appended drawings, which form a part of this specification. It is to be noted, however, that the drawings illustrate only various embodiments of the disclosure and are therefore not to be considered limiting of the present disclosure’s scope, as it may include other effective embodiments as well.

[0037] Referring first to FIG. 1, a schematic diagram is shown of a prior art slickwater hydraulic fracturing system in a wellbore with lateral fractures proceeding into a reservoir. In wellbore system 100, wellbore 102, either cased or open-hole, proceeds in situ into a hydrocarbon-bearing reservoir 103, and production tubing 104 is disposed within the annulus of wellbore 102. Lateral fractures 108 proceed laterally outwardly from wellbore 102 into hydrocarbon-bearing reservoir 103, in the embodiment shown substantially perpendicular to wellbore 102. Oil, gas, and other fluids are transmitted from hydrocarbon-bearing reservoir 103 through lateral fractures 108 to production tubing 104 at production points 106, which in some embodiments can include perforations. Thereby, oil, gas, and other fluids are transmitted from hydrocarbon-bearing reservoir 103 through production tubing 104 to the surface. In the embodiment shown, lateral fractures 108 are created by lateral hydraulic fracturing with slickwater hydraulic fracturing fluid at a pressure greater than the breakdown pressure of the rock in hydrocarbon-bearing reservoir 103.

[0038] Slick water or slickwater fracturing generally refers to a method or system of fracking involving adding chemicals to water to increase the fluid flow via reduced viscosity. In some instances, fluid is pumped down the wellbore as fast as 100 bbl/min. to fracture shale, for example. Without using slick water, pumping rates are about 60 bbl/min.

[0039] Slick water systems and processes generally include friction reducers, for example polyacrylamides. Biocides, surfactants, and scale inhibitors can also be used. Friction reducers help speed application of the mixture. Biocides such as bromine prevent organisms from clogging fractures and creating scale downhole. Surfactants help keep sand and/or other proppants suspended. Methanol and naphthalene can be used for biocides. Hydrochloric acid and ethylene glycol may be utilized as scale inhibitors. Butanol and ethylene glycol monobutyl ether (2-BE) are used in surfactants. Slickwater typically uses more water than earlier fracturing methods.

[0040] FIG. 2 is a schematic diagram of a fracture network created in embodiments of the present disclosure using slickwater hydraulic fracturing with an exothermic reaction component. In wellbore system 200, wellbore 202, either cased or open-hole, proceeds in situ into a hydrocarbon-bearing reservoir 203, and production tubing 204 is disposed within the annulus of wellbore 202. Lateral fractures 208 proceed laterally outwardly from wellbore 102 into hydrocarbon-bearing reservoir 203, in the embodiment shown substantially perpendicular to wellbore 202. Oil, gas, and other fluids are transmitted from hydrocarbon-bearing reservoir 203 through lateral fractures 208 to production tubing 204 at production points 206, which in some embodiments can include perforations. Thereby, oil, gas, and other fluids are transmitted from hydrocarbon-bearing reservoir 203 through production tubing 204 to the surface. In the embodiment shown, lateral fractures 208 are created by lateral hydraulic fracturing with slickwater hydraulic fracturing fluid.

[0041] In FIG. 2, lateral extension fractures 210 proceed outwardly from lateral fractures 208 and are disposed between and throughout lateral fractures 208. In some embodiments, lateral extension fractures 210 fluidly connect separate lateral fractures 208. In the embodiment shown, lateral extension fractures 210 are created by one or more pressure pulse during the application of one or more exothermic reaction component during one or more fluid injection stages, with or without slickwater. One or more exothermic reaction component can be injected into lateral fractures 208 during creation of lateral fractures 208 with slickwater hydraulic fracturing fluid to create lateral extension fractures 210, and/or one or more exothermic reaction component can be injected into lateral fractures 208 after creation of lateral fractures 208 with slickwater hydraulic fracturing fluid to create lateral extension fractures 210.

[0042] Also in FIG. 2, transverse fractures 212 are shown disposed between lateral fractures 208 and lateral extension fractures 210. Transverse fractures 212 can fluidly connect one or more lateral fracture 208 and/or one or more lateral extension fracture 210. In the embodiment shown, transverse fractures 212 are created by one or more pressure pulse during the application of one or more exothermic reaction component during one or more fluid injection stages. One or more exothermic reaction component can be injected into lateral fractures 208 and/or lateral extension fractures 210 during creation of lateral fractures 208 and/or lateral extension fractures 210 with slickwater hydraulic fracturing fluid to create transverse fractures 212, and/or one or more exothermic reaction component can be injected into lateral fractures 208 and/or lateral extension fractures 210 after creation of lateral fractures 208 and/or lateral extension fractures 210 with slickwater hydraulic fracturing fluid to create transverse fractures 212.

[0043] Using an exothermic reaction component with slickwater hydraulic fracturing fluids allows for the creation of a fracture network comprising lateral fractures 208, lateral extension fractures 210, and transverse fractures 212. The fracture network of FIG. 2 comprising lateral fractures 208, lateral extension fractures 210, and transverse fractures 212 allows for increased fluid recovery to the surface of oil, gas, and other fluids versus the prior art system of FIG. 1. In some embodiments, lateral extension fractures 210 and/or transverse fractures 212 comprise micro-fractures, or fractures smaller than lateral fractures, 208. In some embodiments, lateral extension fractures 210 and/or transverse fractures 212 comprise enhanced natural fractures, such as pre-existing fractures in hydrocarbon-bearing reservoir 203. In the embodiment of FIG. 2, by use of the exothermic reaction component, proppant injection, such as sand or ceramic material, can be reduced or eliminated which prevents blocking of fractures and production points 206.

[0044] FIG. 3 is a graph showing varying-pressure pressure pulses created at varying pH for an exothermic reaction component. As shown at greater pH values, the exothermic reaction activation time increases (shown by the sharp spikes in pressure, or a pressure pulse). Additionally, greater pressure pulses are obtained proceeding from pH 6 to pH 7 to pH 8 to pH 9. In some embodiments, different pH values of an exothermic reaction component mixed with slickwater fracturing fluid can be used in different stages of a fracturing operation, and the exothermic reaction causing a pressure pulse would be triggered at different times and/or temperatures (see also FIG. 4). By controlling exothermic reaction component activation time through pH and/or activation temperature and/or application of microwaves, the reaction can be controlled according to depth in a wellbore and/or lateral distance from a wellbore into a hydrocarbon-bearing reservoir. For example, where a greater-pressure pressure pulse is desired at a further lateral distance from a wellbore, a greater pH such as pH 9 can be applied in a slickwater formulation comprising the exothermic reaction component to delay activation of the reaction and have the reaction occur at a greater lateral distance from the wellbore.

[0045] As noted, pH also affects the reaction triggering temperature, so once again greater pH values can be used to have deeper stimulation of a hydrocarbon-bearing reservoir. The pH of slickwater hydraulic fracturing fluid formulations with one or more exothermic reaction component can be fixed to one value, or changed during various pumping stages to have deeper and deeper stimulation. For example, pumping in one stage can start with pH 7, and then be increased to pH 8, pH 9, and pH 10 while pumping in various stages. Basic reagents, such as sodium hydroxide, can be added to slick water to increase pH without otherwise impacting the slickwater, described further infra.

[0046] FIG. 4 is a graph showing varying reaction triggering or activation temperatures at varying pH for an exothermic reaction component. As shown, the reaction triggering temperature of one or more exothermic reaction component, optionally mixed with slickwater hydraulic fracturing fluid, can increase with increasing pH, and as described with regard to FIG. 3 allows for increased fracturing via increased pressure pulses at increased depths and/or increased lateral distances from a wellbore. In some embodiments, an exothermic reaction component includes an ammonium ion and a nitrite ion, for example ammonium chloride and sodium nitrite, with each between about 1 molar and 9 molar in solution, optionally at a 1:1 molar ratio.

[0047] FIG. 5 is a pictorial representation of a low-viscosity slickwater fracturing fluid mixed with an exothermic reaction component, which maintains low viscosity for use as slickwater. Laboratory testing showed no compatibility issues or precipitation when adding an exothermic thermochemical reagent to slick water. Different water sources, with different friction reducers, were tested and all showed no compatibility issues with aqueous exothermic thermochemical additives. The effects of exothermic thermochemicals on slickwater viscosity were studied. There was no significant effect on viscosity, as described in FIG. 6.

[0048] FIG. 6 is a graph showing the viscosity effects of adding an exothermic reaction component at varying concentrations to slickwater hydraulic fracturing fluid. As shown for slickwater compositions between 1 gallon slickwater additive per 1,000 gallons water (gpt) to 4 gpt, the addition of thermochemicals (TC) does not substantially alter the viscosity, for example the viscosity change is less than about 20% or less than about 10%.

[0049] Plug samples of 2 inch by 3 inch Eagle Ford and Scioto sandstone were fractured, using slickwater and thermochemicals as fracturing fluids (FIGS. 7 and 8). With thermochemical application, the plugs were completely split apart, while with slickwater alone the fractures were smaller and the rocks did not split apart. Therefore, thermochemicals can create extra fracturing beyond conventional hydraulic fracturing with slickwater, and surprisingly and unexpectedly a larger stimulated reservoir volume (SRV) is created.

[0050] FIG. 7A is a pictorial representation of an Eagle Ford shale column hydraulically fractured with conventional slickwater fracturing fluid. FIG. 7B is a pictorial representation of an Eagle Ford shale column fractured using an exothermic reaction of an exothermic reaction component. FIG. 7C is a cross-sectional pictorial representation of the Eagle Ford shale column fractured using the exothermic reaction of an exothermic reaction component from FIG. 7B.

[0051] FIG. 8A is a pictorial representation of a Scioto sandstone column hydraulically fractured with conventional slickwater fracturing fluid. FIG. 8B is a pictorial representation of a Scioto sandstone column fractured using an exothermic reaction of an exothermic reaction component. FIG. 8C is a cross-sectional pictorial representation of the Scioto sandstone column fractured using the exothermic reaction of an exothermic reaction component from FIG. 8B.

[0052] FIG. 9 is a graph representing a pumping sequence for slickwater hydraulic fracturing fluid and an exothermic reaction component. The cooling effect of a fracturing fluid on downhole temperature was simulated as show in FIG. 9. FIG. 9 shows that having the exothermic reaction triggering temperature around 140° F. is sufficient to have the reaction pulse inside the reservoir, so multiple side fractures will be created around the main induced hydraulic fractures.

[0053] One sequence of pumping thermochemicals with slickwater during hydraulic fracturing of an unconventional well is described in Table 1. For fracturing one stage of an unconventional well, five fracture clusters will be created, in the example shown. For each cluster, 400 barrels of thermochemicals will be injected to create multiple fractures around the cluster. Volumes of thermochemical fluid and the number of stages can vary depending on the well and reservoir conditions.

TABLE-US-00001 Example Pumping Sequence for Exothermic Thermochemicals with Slickwater Hydraulic Fracturing Fluid During Fracturing of an Unconventional Reservoir. Well Stage Fluid Type Pump Rate in Barrels per Minute (bpm) Est. Rate Slickwater (SW) 10 Acid Injection 15 wt.% HCl 10 Spacer SW 15 PAD 1 Exothermic Thermochemicals 92 Slug 1 SW 92 PAD 2 Exothermic Thermochemicals 92 0.25 pound proppant added per thousand gallons fluid (PPA) SW 92 0.5 PPA SW 92 0.75 PPA SW 92 Sweep 1 Exothermic Thermochemicals 92 0.5 PPA SW 92 0.75 PPA SW 92 1.0 PPA SW 92 1.25 PPA SW 92 Sweep 2 Exothermic Thermochemicals 92 0.5 PPA SW 92 0.75 PPA SW 92 1.0 PPA SW 92 1.25 PPA SW 92 Sweep 3 Exothermic Thermochemicals 92 0.5 PPA SW 92 0.75 PPA SW 92 1.0 PPA SW 92 1.25 PPA SW 92 Flush SW 92 Total

TABLE-US-00002 Example Pumping Sequence for Exothermic Thermochemicals with Slickwater Hydraulic Fracturing Fluid During Fracturing of an Unconventional Reservoir. Well Stage Slickwater Fracturing Design 350 Klbs. Design (90 -10%) Stage Volume (Gallons) Total Volume (Barrels) Proppant Conc. (PPA) Cumulative Volume (Barrels) Proppant Type Proppant Volume (Pounds) Est. Rate 210 5 0.0 5.0 None n/a Acid Injection 3000 71 0.0 76.4 None n/a Spacer 2100 50 0.0 126.4 None n/a PAD 1 16820 400 0.00 526.9 None n/a Slug 1 4000 95 0.25 622.1 100 mesh 1,000 PAD 2 16820 400 0.00 1022.6 None n/a 0.25 pounds proppant added per thousand gallons fluid (PPA) 16000 381 0.25 457.4 100 mesh 4,000 0.5 PPA 18000 429 0.50 886.0 100 mesh 9,000 0.75 PPA 22000 524 0.75 1409.8 100 mesh 16,500 Sweep 1 16820 400 0.00 1810.2 None n/a 0.5 PPA 20000 476 0.50 2286.4 100 mesh 10,000 0.75 PPA 30000 714 0.75 3000.7 100 mesh 22,500 1.0 PPA 40000 952 1.00 3953.1 100 mesh 40,000 1.25 PPA 48000 1143 1.25 5096.0 100 mesh 60,000 Sweep 2 16820 400 0.00 5496.4 None n/a 0.5 PPA 18000 429 0.50 5925.0 100 mesh 9,000 0.75 PPA 30000 714 0.75 6639.3 100 mesh 22,500 1.0 PPA 45500 1083 1.00 7722.6 100 mesh 45,500 1.25 PPA 60000 1429 1.25 9151.2 100 mesh 75,000 Sweep 3 16820 400 0.00 9551.7 None n/a 0.5 PPA 10000 238 0.50 9789.8 40/70 light weight proppant (LWP) 5,000 0.75 PPA 12000 286 0.75 10075.5 40/70 LWP 9,000 1.0 PPA 17000 405 1.00 10480.2 40/70 LWP 17,000 1.25 PPA 4000 95 1.25 10575.5 40/70 LWP 4,000 Flush 11500 274 10849.3 n/a Total 495,410 11,795 350,000

[0054] In some embodiments of the disclosure, a multilateral hydrocarbon recovery network in a hydrocarbon-bearing formation with a multilateral fracture network is drilled with underbalanced coiled tubing and fractured, in part, using an exothermic reaction component before, during or after slickwater treatment. Systems and methods can be applied in an open-hole recovery well or a cased-hole recovery well. If a vertical well is cased, perforations can be used to aid in the drilling of primary horizontal laterals. From primary laterals extend branched horizontal laterals at similar or variable vertical depths and horizontal lengths, depending on the target reservoir formation. From branched horizontal laterals extend one or more plurality of fractures forming an overall fracture network which increases recovery of hydrocarbons from the formation to the branched horizontal laterals and ultimately up through a vertical recovery well.

[0055] Horizontal laterals are generally about 100 feet (ft.) to about 300 ft., for example about 200 ft., vertically spaced apart and can be located at similar or variable vertical depths depending on the landing of the lateral in the target reservoir formation. Created fractures, such as for example lateral extension fractures 210 and transverse fractures 212 in FIG. 2, may extend from about 10 ft. to about 100 ft., for example about 50 ft., outwardly from a lateral depending on the mechanical properties of the formation. Mini-fractures may extend only about a few feet to about 10 ft., but a plurality of mini-fractures can greatly increase lateral connection to producing zones.

[0056] Multilateral wells of the present disclosure, including multilateral fracture networks, cause, in some embodiments, extreme reservoir contact (ERC). In some embodiments, a multilateral fracture network recovery system, such as that shown in wellbore system 200 in FIG. 2, can be drilled from a vertical well using a rotary drilling rig, and then several multilaterals can be drilled using underbalanced coiled tubing drilling, which is cost effective, efficient, and does not adversely affect a hydrocarbon-bearing formation by damaging rock permeability with drilling fluids, which can occur in conventional overbalanced drilling schemes and hydraulic fracturing.

[0057] Before, during, or after the drilling of multilaterals with slickwater, such as for example lateral fractures 208 in FIG. 2, one or more exothermic reaction component can be injected to further enhance the stimulated reservoir volume by creating mini-fractures, such as for example lateral extension fractures 210 and transverse fractures 212 in FIG. 2, and thus maximize reservoir contact with a recovery well.

[0058] Fracturing systems and methods of the present disclosure can be applied in, for example, tight formations, sandstone formations, carbonate formations, and in gas wells, including those wells in unconventional reservoirs with low permeability rocks. Fracturing fluids used in overbalanced drilling can be damaging to a formation’s permeability, and the disclosed systems and methods here result in enhanced productivity of gas wells, for example. An exothermic reaction component, for example optionally containing one or more exothermic reacting chemicals, for example a nitrite ion and an ammonium ion, applied either separately or together before, during, or after slickwater fracturing to lateral fractures 208 in FIG. 2 can create outwardly extending fractures, including mini-fractures, when triggered, such as for example lateral extension fractures 210 and transverse fractures 212 in FIG. 2. Exothermic reaction components containing an ammonium ion and nitrite ion for example have been shown to be suitable for creating fractures in tight formations.

[0059] Disclosed systems and methods enhance productivity of tight gas wells, for example, by increasing stimulated reservoir volume beyond currently existing fracturing and completion methods.

[0060] With concentric coiled tubing, two fluids can be injected separately into a target lateral and then combined, for example an ammonium ion containing fluid and a nitrite ion containing fluid, to provide control over the placement of and reaction of exothermic chemicals in a particular lateral. In some embodiments, a single exothermic reaction component can be introduced with encapsulated chemicals, such that the chemicals do not react to produce heat and pressure until they are proximate the sand face in a given lateral.

[0061] Maximizing reservoir contact with multilaterals and stimulating them with at least one exothermic reaction component in addition to slickwater provides a greater stimulating effect over existing multistage fracturing methods performed in horizontal wells. Underbalanced coiled tubing drilling (UBCTD) in multilateral openhole completion wells aids in reducing and eliminating damage caused to formations by overbalanced drilling.

[0062] In some embodiments, exothermic chemicals are pumped downhole after all the multilaterals have been drilled and completed using UBCTD. In other embodiments, certain amounts of exothermic chemicals are pumped downhole during UBCTD of multilaterals. In some embodiments, exothermic chemicals are pumped into the toe of each drilled lateral using a concentric coiled tubing that will pump each of the chemicals alone or separately, such that they meet and react once they reach the formation. Concentric coiled tubing is a type of coiled tubing with a pipe inside the coil tubing pipe to enable the application of exothermic chemical injection into the zone of interest in a particular lateral drilled in a multilateral well drilled using UBCTD.

[0063] Injection of exothermic chemicals into the toe of a lateral and moving the concentric coil tubing out of the lateral towards the heel of the lateral while the exothermic chemicals are being pumped provides a unique method of stimulating a given lateral. The process can be repeated into another lateral until all laterals in a multilateral well have been treated and a multilateral fracture network is created, with a certain of permeability and connectivity between different multilaterals.

[0064] If a multilateral well drilled using UBCTD is drilled in an ultra-tight formation, the drilled and completed laterals can be hydraulically fractured using slickwater fluids, and the exothermic chemical may be included in the fracturing fluids to further create more micro fractures that will enhance the stimulation treatment.

[0065] Ultra-tight formations include those reservoir rocks where permeability can be as low as the nano-Darcy range making production of the hydrocarbons nearly impossible without a large stimulation treatment.

[0066] The exothermic reaction component can include one or more redox reactants that exothermically react to produce heat and increase pressure. The exothermic reaction components do not combust, but release heat, gas, and pressure during a triggered or activated redox reaction. Exothermic reaction components include urea, sodium hypochlorite, ammonium containing compounds, and nitrite containing compounds. In at least one embodiment, the exothermic reaction component includes ammonium containing compounds. Ammonium containing compounds include ammonium chloride, ammonium bromide, ammonium nitrate, ammonium sulfate, ammonium carbonate, and ammonium hydroxide. In at least one embodiment, the exothermic reaction component includes nitrite containing compounds. Nitrite containing compounds include sodium nitrite and potassium nitrite. In at least one embodiment, the exothermic reaction component includes both ammonium containing compounds and nitrite containing compounds. In at least one embodiment, the ammonium containing compound is ammonium chloride, NH.sub.4Cl. In at least one embodiment, the nitrite containing compound is sodium nitrite, NaNO.sub.2.

[0067] In at least one embodiment, the exothermic reaction component includes two redox reactants: NH.sub.4Cl and NaNO.sub.2, which react according to Equation 1:

[00001]$\begin{array}{l}{\text{Equation 1: NH}}_4{\text{Cl + NaNO}}_2\stackrel{\left(H^{+}and/or\Delta Hand/ormicrowaves\right)}{.fwdarw.}\\ {\text{N}}_2+\text{NaCl}+{\text{2H}}_2\text{O}+\text{Heat}\end{array}$

[0068] In a reaction of the exothermic reaction components according to the above equation, generated gas can contribute to a reduction of viscosity of residual viscous materials in the fractures of a formation possibly left behind from well fracturing operations (for example guar), and the heat and gas generated can also reduce the viscosity of viscous hydrocarbons, such as for example asphaltenes, further increasing hydrocarbon recovery. Concentrations of exothermic reaction components in a solution can be between about 1 M and about 9 M, in some embodiments. For example, an exothermic reaction component can include a 3 M NH.sub.4Cl and 3 M NaNO.sub.2 aqueous solution. The molar ratio of components can vary between about 1:1 and about 1:9. The volume amount of exothermic reaction component solution added to slickwater can vary between about 1 V% and about 50 V%, or between about 5 V% and about 40 V%, or between about 10 V% and about 30 V%, or between about 15 V% and about 25 V%.

[0069] The exothermic reaction component is triggered to react. In at least one embodiment, the exothermic reaction component is triggered within the laterals in addition to or alternative to triggered in pre-existing fractures. In at least one embodiment of the present disclosure, an acid precursor triggers the exothermic reaction component to react by releasing hydrogen ions, and in some embodiments the acid precursor is completely consumed by the exothermic reaction such that no residual acid remains to damage the formation or the well.

[0070] In at least one embodiment, the exothermic reaction component is triggered by heat. The wellbore temperature and temperature of laterals can be reduced during a pre-pad injection or a pre-flush with brine and reach a temperature below 120° F. (48.9° C.). A slickwater fracturing fluid of the present disclosure can then be injected into the well and the wellbore temperature increases from the heat of the formation. When the wellbore and lateral temperatures reach a temperature greater than or equal to about 120° F., for example, depending on the composition of the exothermic reaction component, the reaction of redox reactants is triggered. In at least one embodiment of the present disclosure, the reaction of the redox reactants is triggered by temperature in the absence of the acid precursor. In at least one embodiment of the present disclosure, the exothermic reaction component is triggered by heat when the exothermic reaction component is within multi-branched laterals, optionally proximate pre-existing fractures.

[0071] In at least one embodiment, the exothermic reaction component is triggered by pH. A base can be added to an exothermic reaction component of the present disclosure to adjust the pH to between about 9 to about 12. In at least one embodiment the base is potassium hydroxide. The exothermic reaction component, optionally along with other components such as slickwater fracturing fluid, with the base is injected into the formation. Following the injection of the fracturing fluid, an acid is injected to adjust the pH to below about 6. When the pH is below about 6, the reaction of the redox reactants is triggered. In at least one embodiment of the present disclosure, the exothermic reaction component is triggered by pH when the exothermic reaction component is within the fractures.

[0072] Dual-string coiled tubing can be used to introduce the exothermic reaction component and the acid precursor to the wellbore and the laterals. In at least one embodiment, the exothermic reaction component includes NH.sub.4Cl and NaNO.sub.2. The acid precursor can include acetic acid in addition to or alternative to HCl. In some embodiments, the acetic acid is mixed with NH.sub.4Cl and is injected in parallel with the NaNO.sub.2, using different sides of the dual-string coiled tubing. The exothermic reaction component and the acid precursor mix within the multilaterals.

[0073] In an alternate embodiment of the present disclosure, a method to increase a stimulated reservoir volume in a gas-containing formation is provided. The gas-containing formation can include a tight gas formation, an unconventional gas formation, and a shale gas formation. The stimulated reservoir volume is the volume surrounding a wellbore in a reservoir that has been fractured to increase well production. Stimulated reservoir volume is a concept useful to describe the volume of a fracture network. The method to increase a stimulated reservoir volume can be performed regardless of the reservoir pressure in the gas-containing formation. The method to increase a stimulated reservoir volume can be performed in a gas-containing formation having a reservoir pressure in a range of atmospheric pressure to 10,000 psig.

[0074] In methods of the present disclosure, the exothermic reaction component is mixed to achieve a pre-selected solution pH. The pre-selected solution pH is in a range of about 6 to about 9.5, alternately about 6.5 to about 9. In at least one embodiment, the pre-selected solution pH is 6.5. The exothermic reaction component can be mixed with a slickwater fracturing fluid, a viscous fluid component, and/or a proppant component to form a fracturing fluid. The fracturing fluid is injected into the wellbore in the gas-containing formation to create fractures and a proppant(s) holds open the fractures.

[0075] The exothermic reaction component reacts, and upon reaction generates an optional pressure pulse that creates auxiliary fractures. Fracturing fluid can be used in a primary operation to create fractures extending from multilaterals. Auxiliary fractures or mini-fractures can extend from larger fractures caused by the fracturing fluid, and all of these types of fractures extending from multilaterals at varying depths create a multilateral fracture network. The multilateral fracture network increases stimulated reservoir volume. In some embodiments, injection of a hydraulic fracturing fluid including a viscous fluid component in addition to or alternative to a proppant component in addition to or alternative to an overflush component in addition to or alternative to an exothermic reaction component does not generate foam or introduce foam into the hydraulic formation including the hydraulic fractures and multilaterals.

[0076] In at least one embodiment, the exothermic reaction component reacts when the exothermic reaction component reaches the wellbore temperature or the formation temperature. The wellbore temperature or formation temperature can be between about 100° F. and about 250° F., alternately between about 120° F. and about 250° F., alternately between about 120° F. and about 230° F., alternately between about 140° F. and about 210° F., alternately about 160° F. and about 190° F. In at least one embodiment, the wellbore temperature is about 200° F. In at least one embodiment, the wellbore temperature at which the exothermic reaction component reacts is affected by the pre-selected solution pH and an initial pressure. The initial pressure is the pressure of the exothermic reaction component just prior to the reaction of the exothermic reaction component. Increased initial pressure can increase the wellbore temperature that triggers the reaction of the exothermic reaction component. Increased pre-selected solution pH can also increase the wellbore temperature that triggers the reaction of the exothermic reaction component.

[0077] When the exothermic reaction component reacts, the reaction can generate a pressure pulse and heat, in a non-combustive reaction. The pressure pulse is generated within milliseconds from the start of the reaction. The pressure pulse is at a pressure between about 500 psi and about 50,000 psi, alternately between about 500 psi and about 20,000 psi, alternately between about 500 psi and about 15,000 psi, alternately between about 1,000 psi and about 10,000 psi, alternately between about 1,000 psi and about 5,000 psi, and alternately between about 5,000 psi and about 10,000 psi.

[0078] The pressure pulse creates fractures, including for example mini-fractures extending outwardly from and in between multilaterals. Fractures can extend from the point of reaction in all directions without causing damage to the wellbore or to multilaterals. The pressure pulse creates the auxiliary fractures regardless of the reservoir pressure. The pressure of the pressure pulse is affected by the initial reservoir pressure, the concentration of the exothermic reaction component, and the solution volume. In addition to the pressure pulse, the reaction of the exothermic reaction component releases heat. The heat released by the reaction causes a sharp increase in the temperature of the formation, which causes thermal fracturing. Thus, the heat released by the exothermic reaction component contributes to the creation of the auxiliary fractures. The exothermic reaction component allows for a high degree of customization to meet the demands of the formation and fracturing conditions.

[0079] In at least one embodiment, the acid precursor can be used to trigger the exothermic reaction component to react. In at least one embodiment, the exothermic reaction component is injected into the wellbore in the absence of a viscous fluid component and a proppant component and allowed to react to generate the pressure pulse.

[0080] In at least one embodiment, the method to increase a stimulated reservoir volume also performs the method to clean up a viscous material, for example asphaltenes, or a residual viscous material, for example guar. The method of the present disclosure can be adjusted to meet the needs of the fracturing operation. In one embodiment, a fracturing fluid includes an exothermic reaction component that reacts to both create auxiliary fractures and to cleanup residual viscous material from the fracturing fluid. In one embodiment of the present disclosure, a fracturing fluid includes an exothermic reaction component that reacts to only create auxiliary fractures. In one embodiment, a fracturing fluid includes an exothermic reaction component that reacts to only cleanup residual viscous material.

[0081] A method to increase the stimulated reservoir volume of a hydrocarbon-containing, for example gas-containing, formation is described herein. The method to increase a stimulated reservoir volume can be performed in oil-containing formations, water-containing formations, or any other formation. In at least one embodiment of the present disclosure, the method to increase a stimulated reservoir volume can be performed to create fractures and auxiliary fractures in cement. In some embodiments, microwaves can be applied in situ to aid in triggering an exothermic reaction component by lowering the activation energy of the exothermic reaction without substantially affecting the temperature of the exothermic reaction component.

[0082] An acid precursor can include any acid that releases hydrogen ions to trigger the reaction of the exothermic reaction component. Acid precursors include triacetin (1,2,3-triacetoxypropane), methyl acetate, HCl, and acetic acid. In at least one embodiment, the acid precursor is triacetin. In at least one embodiment of the present disclosure, the acid precursor is acetic acid.

[0083] Although the disclosure has been described with respect to certain features, it should be understood that the features and embodiments of the features can be combined with other features and embodiments of those features.

[0084] Although the disclosure has been described in detail, it should be understood that various changes, substitutions, and alterations can be made hereupon without departing from the principle and scope of the disclosure. Accordingly, the scope of the present disclosure should be determined by the following claims and their appropriate legal equivalents.

[0085] The singular forms “a,” “an,” and “the” include plural referents, unless the context clearly dictates otherwise. The term “about” in some embodiments includes values 5% above or below the value or range of values provided.

[0086] As used throughout the disclosure and in the appended claims, the words “comprise,” “has,” and “include” and all grammatical variations thereof are each intended to have an open, non-limiting meaning that does not exclude additional elements or steps.

[0087] As used throughout the disclosure, terms such as “first” and “second” are arbitrarily assigned and are merely intended to differentiate between two or more components of an apparatus. It is to be understood that the words “first” and “second” serve no other purpose and are not part of the name or description of the component, nor do they necessarily define a relative location or position of the component. Furthermore, it is to be understood that that the mere use of the term “first” and “second” does not require that there be any “third” component, although that possibility is contemplated under the scope of the present disclosure.

[0088] While the disclosure has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, it is intended to embrace all such alternatives, modifications, and variations as fall within the spirit and broad scope of the appended claims. The present disclosure may suitably comprise, consist or consist essentially of the elements disclosed and may be practiced in the absence of an element not disclosed.