Chemically-induced pulsed fracturing method

<u>FIELD</u>

0001This disclosure relates to a method to increase the stimulated reservoir volume in a reservoir formation. More specifically, this disclosure relates to a method to increase the stimulated reservoir volume by increasing the fracture network using an exothermic reaction component.

<u>BACKGROUND</u>

0002Hydraulic fracturing fluids containing proppants are used extensively to enhance productivity from hydrocarbon reservoir formations, including carbonate and sandstone formations. During hydraulic fracturing operations, a fracturing treatment fluid is pumped under a pressure and rate sufficient for cracking the formation of the reservoir and creating a fracture. Fracturing operations usually consist of three main stages including a pad fluid stage, a proppant fluid stage, and an overflush fluid stage. The pad fluid stage typically consists of pumping a pad fluid into the formation. The pad fluid is a viscous, gelled fluid which initiates and propagates the fractures. The proppant fluid stage involves pumping a proppant fluid into the fractures of the formation. The proppant fluid contains proppants mixed with a viscous, gelled fluid or a visco-elastic surfactant fluid. The proppants in the proppant fluid are lodged in the fractures and create conductive fractures through which hydrocarbons flow. The final stage, the overflush stage, includes pumping a viscous gelled fluid into the fractures to ensure the proppant fluid is pushed inside the fractures. While the three stages have different aims, all three make use of highly viscous and/or gelled fluids to achieve those aims.

0003A downside of the traditional method is that a high volume of gelled or polymeric materials can be left behind in the fractures. The gelled materials can be concentrated around the proppant in the fractures or can be freely in the fractures. The gelled material acts to block the fractures reducing the fracture conductivity. The hydrocarbons which flow from the reservoir formation are unable to move the gelled materials. Traditional methods for cleaning the fractures involve viscosity breakers or other elements to breakdown the fluid. These traditional methods suffer from an inability to completely cleanup the fractures, leaving residual viscous material and reduced conductivity.

0004In addition, unconventional gas wells require an extensive fracturing network to increase the stimulated reservoir volume and to create commercially producing wells. One commonly employed technique is multi-stage hydraulic fracturing in horizontal wells, which is very costly and may not provide the required stimulated reservoir volume. Moreover, traditional hydraulic fracturing methods use huge amounts of damaging gels pumped downhole as noted above. Even with traditional breakers, significant amount of polymeric material cannot be recovered and, therefore, fracture conductivity is reduced. <patcit id="pcit0001" dnum="US2013126175A"><text>US2013/126175</text></patcit>, <patcit id="pcit0002" dnum="US5411093A"><text>US5411093</text></patcit>, <patcit id="pcit0003" dnum="US2013126169A"><text>US2013/126169</text></patcit>, and <patcit id="pcit0004" dnum="US2013180720A"><text>US2013/180720</text></patcit> relate to methods of stimulating hydrocarbon-bearing formations using in-situ gas generation.

0005Therefore, a method that increases the stimulated reservoir volume of unconventional gas wells is desired. A method that minimizes the volume of fracturing fluid required, while increasing the volume of fluid recovered regardless of the type of reservoir or well is also desired.

<u>SUMMARY OF THE INVENTION</u>

0006This disclosure relates to a composition and method to increase the stimulated reservoir volume in a reservoir formation. More specifically, this disclosure relates to a composition and method to increase the stimulated reservoir volume by increasing the fracture network using an exothermic reaction component.

0007In a first aspect, a method of increasing a stimulated reservoir volume in a wellbore in a gas-containing formation is provided. The method includes the steps of reducing the temperature of the wellbore to a temperature below 48.8°C (120°F) during a pre-pad injection or a pre-flush with brine; mixing an exothermic reaction component in an aqueous solution to achieve a pre-selected solution pH, wherein the exothermic reaction component is capable of reacting at a pre-selected wellbore temperature to generate a pressure pulse and wherein the pre-selected wellbore temperature is increased by increasing the pre-selected solution pH, wherein the exothermic reaction component comprises an ammonium containing compound and a nitrite containing compound, wherein the pre-selected solution pH is between 5.7 and 9, mixing the aqueous exothermic reaction component with a viscous fluid component to form a fracturing fluid, the viscous fluid component incrasing the viscosity of the fracturing fluid and being capable of fracturing the gas-containing formation to create fractures, and a proppant component, the proppant component carried to the fractures by the viscous fluid, the proppant component includes a proppant, the proppant operable to hold open the fractures, to form a fracturing fluid, injecting the fracturing fluid into the wellbore in the gas-containing formation to create fractures which are held open by the proppant, and generating the pressure pulse when the exothermic reaction component reaches the wellbore temperature, the pressure pulse generated at a pressure between about 500 psi and about 340,000 psi is generated and is capable of creating auxiliary fractures extending from the fracture caused by the fracturing fluid, wherein the auxiliary fractures create a fracture network, wherein the fracture network increases the stimulated reservoir volume. Fracturing fluid is used in a primary operation to create fractures. The auxiliary fractures extend from the fractures caused by the fracturing fluid to create a fracture network. The auxiliary fractures can be caused by the reaction of the exothermic reaction component.

0008The exothermic reaction component includes an ammonium containing compound and a nitrite containing compound. In certain aspects of the present disclosure, the ammonium containing compound is NH₄Cl and the nitrite containing compound is NaNO₂. In certain aspects, the pre-selected solution pH is between 6.5 and 9. In certain aspects of the present disclosure, the wellbore temperature is in a range between 48.8°C (120°F) and 121.1°C (250°F). The pressure pulse is between 3,400 kPa (500 psi) and 340,000 kPa (50,000 psi).

0009In a second aspect, a method of increasing a stimulated reservoir volume in a wellbore in a gas-containing formation is provided. The method includes the steps of reducing the temperature of the wellbore to a temperature below 48.8 °C (120°F) during a pre-pad injection or a pre-flush with brine; mixing an exothermic reaction component in an aqueous solution to achieve a pre-selected solution pH, wherein the exothermic reaction component is capable of reacting at a pre-selected wellbore temperature to generate a pressure pulse and and wherein the pre-selected wellbore temperature is increased by increasing the pre-selected solution pH, wherein the exothermic reaction component comprises an ammonium containing compound and a nitrite containing compound, wherein the pre-selected solution pH is between 5.7 and 9, injecting the exothermic reaction component into the gas-containing formation in the absence of both a viscous fluid component and a proppant component, and generating the pressure pulse when the exothermic reaction component reaches the pre-selected wellbore temperature, the pressure pulse is capable of creating auxiliary fractures, wherein the auxiliary fractures connect to the fractures to create a fracture network, wherein the fracture network increases the stimulated reservoir volume.

0010The exothermic reaction component includes an ammonium containing compound and a nitrite containing compound. In certain aspects of the present disclosure, the ammonium containing compound is NH₄Cl and the nitrite containing compound is NaNO₂. In certain aspects, the pre-selected solution pH is between 6.5 and 9. In certain aspects, the wellbore temperature is in a range between 48.8°C (120°F) and 121.1°C (250°F). In certain aspects of the present disclosure, the pressure pulse is between 3,400 kPa (500 psi) and 340,000 kPa (50,000 psi).

0011The method of increasing a stimulated reservoir volume in a wellbore in a gas-containing formation according to the first aspect is disclosed. The method comprises the steps of mixing an 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 wellbore temperature to generate a pressure pulse, and mixing the aqueous solution with a viscous fluid component to form a fracturing fluid, the viscous fluid component operable to fracture the gas-containing formation to create fractures, and the fracturing fluid further comprising a proppant component, the proppant component carried to the fractures by the viscous fluid component, the proppant component comprises a proppant, the proppant operable to hold open the fractures. The method further comprises the steps of injecting the fracturing fluid into the wellbore in the gas-containing formation to create fractures, and generating the pressure pulse when the exothermic reaction component reaches the pre-selected wellbore temperature, such that the pressure pulse is operable to create auxiliary fractures, wherein the auxiliary fractures create a fracture network, wherein the fracture network increases the stimulated reservoir volume.

0012The exothermic reaction component comprises an ammonium containing compound and a nitrite containing compound. In other embodiments, the ammonium containing compound comprises NH₄Cl and the nitrite containing compound comprises NaNO₂. The pre-selected solution pH is between 5.7 and 9. Still in other embodiments, the wellbore temperature is in a range between 48.8°C (120°F) and 121.1°C (250°F). The pressure pulse is between 3,400 kPa (500 psi) and 340,000 kPa (50,000 psi). In some embodiments, the pressure pulse creates the auxiliary fractures in less than 10 seconds. Still in other embodiments, the pressure pulse creates the auxiliary fractures in less than 5 seconds.

0013The method of increasing a stimulated reservoir volume in a wellbore in a gas-containing formation according to the second aspect comprises the step of mixing an 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 wellbore temperature to generate a pressure pulse and injecting the exothermic reaction component in the gas-containing formation to create fractures. The method further comprises the step of generating the pressure pulse when the exothermic reaction component reaches the pre-selected wellbore temperature, such that the pressure pulse is operable to create auxiliary fractures, wherein the auxiliary fractures connect to the fractures to create a fracture network, wherein the fracture network increases the stimulated reservoir volume.

0014The exothermic reaction component comprises an ammonium containing compound and a nitrite containing compound. In other embodiments, the ammonium containing compound comprises NH₄Cl and the nitrite containing compound comprises NaNO₂. The pre-selected solution pH is between 5.7 and 9. In yet other embodiments, the wellbore temperature is in a range between 48.8°C (120°F) and 121.1°C (250°F). In other embodiments, the pressure pulse is between 3,400 kPa (500 psi) and 340,000 kPa (50,000 psi). In certain aspects, the pressure pulse creates the auxiliary fractures in less than 10 seconds. In other aspects, the pressure pulse creates the auxiliary fractures in less than 5 seconds.

0015Disclosed herein is a method for hydraulic fracturing of a hydrocarbon-bearing formation, the method comprising the steps of determining a wellbore temperature at a depth within the hydrocarbon-bearing formation, and determining a length of time for which a hydraulic fracturing fluid needs to reach the depth within the hydrocarbon-bearing formation and reach the wellbore temperature at the depth. The method further comprises the steps of mixing an exothermic reaction component in an aqueous solution to achieve a pre-selected solution pH, wherein the exothermic reaction component is operable to react at the wellbore temperature at the depth within the hydrocarbon-bearing formation to generate a pressure pulse, and mixing the aqueous solution with a viscous fluid component to form the hydraulic fracturing fluid, the viscous fluid component operable to fracture the gas-containing formation to create fractures, and the fracturing fluid further comprising a proppant component, the proppant component carried to the fractures by the viscous fluid component, the proppant component comprises a proppant, the proppant operable to hold open the fractures.

0016The method further comprises the steps of injecting the fracturing fluid into the wellbore in the gas-containing formation to create fractures, and generating the pressure pulse when the exothermic reaction component reaches the wellbore temperature, such that the pressure pulse is operable to create auxiliary fractures, wherein the auxiliary fractures create a fracture network, wherein the fracture network increases the stimulated reservoir volume. In some embodiments, the exothermic reaction component comprises an ammonium containing compound and a nitrite containing compound. In some embodiments, the ammonium containing compound comprises NH₄Cl and the nitrite containing compound comprises NaNO₂. Still in other embodiments, the pre-selected solution pH is between 5.7 and 9. In still other embodiments, the wellbore temperature is in a range between 48.8°C (120°F) and 121.1°C (250°F).

0017In certain aspects, the pressure pulse is between 3,400 kPa (500 psi) and 340,000 kPa (50,000 psi). In some embodiments, the pressure pulse creates the auxiliary fractures in less than 10 seconds. Still in other embodiments, the pressure pulse creates the auxiliary fractures in less than 5 seconds.

<u>BRIEF DESCRIPTION OF THE DRAWINGS</u>

0018These 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 scope as it can admit to other equally effective embodiments. <ul id="ul0001" list-style="none"><li><figref idref="f0001">FIG. 1</figref> is a graphic representation of the effect of the cleanup fluid on the viscosity of the residual viscous material.</li><li><figref idref="f0002">FIG. 2</figref> is a graphic representation of the heat and pressure generated by the exothermic reaction component.</li><li><figref idref="f0003">FIGS. 3a and 3b</figref> are pictorial representation of the residual viscous material before and after the reaction of an exothermic reaction component of the cleanup fluid.</li><li><figref idref="f0004">FIG. 4</figref> is a graphic representation of the block design of the rock samples for the unconfined tests described herein.</li><li><figref idref="f0004">FIG. 5</figref> is a graphic representation of the block design of the rock samples for the confined tests described herein.</li><li><figref idref="f0005">FIG. 6</figref> is a pictorial representation of pre and post treatment of the white cement rock sample using the method of the present disclosure.</li><li><figref idref="f0005">FIG. 7</figref> is a pictorial representation of pre and post treatment of the portrait cement rock sample using the method of the present disclosure.</li><li><figref idref="f0006">FIG. 8</figref> is a pictorial representation of pre and post treatment of the Indiana limestone rock sample using the method of the present disclosure.</li><li><figref idref="f0006">FIG. 9</figref> is a pictorial representation of pre and post treatment of the Shale rock sample using the method of the present disclosure.</li><li><figref idref="f0007">FIG. 10</figref> is a pictorial representation of a cement rock sample for use in a confined test.</li><li><figref idref="f0008">FIG. 11</figref> is a graphic representation of the effect of the method of the present disclosure under 13,800 kPa (2,000 psi) biaxial stress for confined test #5.</li><li><figref idref="f0008">FIG. 12</figref> is a pictorial representation of the cement rock sample after confined test #5.</li><li><figref idref="f0009">FIG. 13</figref> is a graphic representation of the effect of the method of the present disclosure under 27,600 kPa (4,000 psi) biaxial stress for confined test #6.</li><li><figref idref="f0009">FIG. 14</figref> is a pictorial representation of the cement rock sample after confined test #6.</li><li><figref idref="f0010">FIG. 15</figref> is a graphic representation of the resultant temperature and pressure pulse due to the reaction of the exothermic reaction component at an initial pressure of zero kPa (zero psi) and 200% solution volume.</li><li><figref idref="f0010">FIG. 16</figref> is a comparison of the initial pressure to the resultant maximum temperature and maximum pressure of the pressure pulse due to the reaction of the exothermic reaction component.</li><li><figref idref="f0011">FIG. 17</figref> is a graphic representation of the results from a test using a fracturing fluid prepared by mixing an exothermic reaction component and a viscous fluid component, where the reaction was triggered by adding a viscosity breaker to the fracturing fluid.</li><li><figref idref="f0011">FIG. 18</figref> is a graphic representation of the effect of the chemical concentration and solution volume on resultant pressure pulse.</li><li><figref idref="f0012">FIG. 19</figref> is a graphic representation of the effect of initial pressure and pH on wellbore temperature at which a reaction of exothermic reaction component is triggered.</li><li><figref idref="f0013">FIG. 20</figref> is a pictorial representation of a mixture of the fracturing fluid including the viscous fluid component, the exothermic reaction component, and the proppant component.</li><li><figref idref="f0013">FIG. 21</figref> is a pictorial representation of a mixture of the fracturing fluid including the viscous fluid component and the exothermic reaction component.</li><li><figref idref="f0013">FIG. 22</figref> is a pictorial representation of the fracturing fluid post-reaction of the exothermic reaction component.</li><li><figref idref="f0014">FIG. 23</figref> is a graphic representation of the effect of reaction of the exothermic reaction component on the viscosity of the fracturing fluid.</li><li><figref idref="f0014">FIG. 24</figref> is a graphic representation of the effect of reducing the wellbore temperature to delay reaction of exothermic reaction component.</li><li><figref idref="f0015">FIG. 25</figref> is a graphic representation of the porosity distribution in a tight core sample before the application of an exothermic reaction component to the core sample.</li><li><figref idref="f0016">FIG. 26</figref> is a pictorial representation of a tight core sample before the application of an exothermic reaction component to the core sample.</li><li><figref idref="f0016 f0017">FIGS. 27-28</figref> are Environmental Scanning Electron Microscope (ESEM) images of a tight core sample before the application of an exothermic reaction component to the core sample.</li><li><figref idref="f0017">FIG. 29</figref> is a MR-CT-scan analysis (nuclear magnetic resonance combined with X-ray computed tomography for core analysis) of a tight core sample before the application of an exothermic reaction component to the core sample.</li><li><figref idref="f0018">FIG. 30</figref> is a graphic representation of the porosity distribution in a tight core sample before and after the application of an exothermic reaction component to the core sample.</li><li><figref idref="f0019">FIG. 31</figref> is a pictorial representation of a tight core sample after the application of an exothermic reaction component to the core sample.</li><li><figref idref="f0019 f0020">FIGS. 32-33</figref> are ESEM images of a tight core sample after the application of an exothermic reaction component to the core sample.</li><li><figref idref="f0020">FIG. 34</figref> is a MR-CT-scan analysis of a tight core sample after the application of an exothermic reaction component to the core sample.</li></ul>

<u>DETAILED DESCRIPTION</u>

0019A method for improved hydrocarbon recovery from a formation due to cleanup of a residual viscous material is described. The hydraulic fracturing operation fractures the formation using fracturing fluid to create fractures. Formations include sandstone and carbonate, for example.

0020The fracturing fluid includes the viscous fluid component and the proppant component. The viscous fluid component has a viscosity. The viscous fluid component is operable to increase the viscosity of the fracturing fluid. Viscous fluid components include viscosified water-based fluids, non-viscosified water-based fluids, gel-based fluids, gel oil-based fluids, acid-based fluids, and foam fluids. Gel-based fluids include cellulose derivatives and guar-based fluids. Cellulose derivatives include carboxymethyl cellulose, hydroxyethyl cellulose, carboxymethyl hydroxyethyl cellulose, hydroxypropyl cellulose, and methyl hydroxyl ethyl cellulose. Guar-based fluids include hydroxypropyl guar, carboxymethyl guar, guar cross-linked boron ions from an aqueous borax/boric acid solution and guar cross-linked with organometallic compounds. Organometallic compounds include zirconium, chromium, antimony, and titanium salts. Gel oil-based fluids include aluminum phosphate-ester oil gels. In at least one embodiment, the viscous fluid component is an aqueous guar solution, having a concentration of guar gum between about 0.1% and about 15%, between about 0.1% and about 10%, between about 1% and about 10%, between about 2% and about 8%, and between about 4% and about 6%.

0021The proppant component includes a proppant. The proppants in the proppant fluid are lodged in the fractures and create conductive fractures through which hydrocarbons flow. Any proppants capable of holding open conductive fractures are suitable for use in the present embodiments. In some embodiments, the proppant component includes a viscous carrier fluid having a viscosity. Viscous carrier fluids include viscosified water-based fluids, non-viscosified water-based fluids, gel-based fluids, gel oil-based fluids, acid-based fluids, and foam fluids. Gel-based fluids include cellulose derivatives and guar-based fluids. Cellulose derivatives include carboxymethyl cellulose, hydroxyethyl cellulose, carboxymethyl hydroxyethyl cellulose, hydroxypropyl cellulose, and methyl hydroxyl ethyl cellulose. Guar-based fluids include hydroxypropyl guar, carboxymethyl guar, guar cross-linked boron ions from an aqueous borax/boric acid solution, and guar cross-linked with organometallic compounds. Organometallic compounds include zirconium, chromium, antimony, and titanium salts. Gel oil-based fluids include aluminum phosphate-ester oil gels.

0022The hydraulic fracturing operation may use a one stage fracturing fluid, in which the fracturing fluid includes both the viscous fluid component and the proppant component, in which the viscous fluid component carries the proppant component to the fractures. The hydraulic fracturing operation may use a multi-stage fracturing fluid in which the viscous fluid component is injected into the formation, followed by the proppant component in the viscous carrier fluid. The injection of the proppant component may be followed by injection of additional viscous fluids to ensure the proppants are placed in the fractures. The additional viscous fluids have a viscosity. The viscosity of the viscous fluid component, the viscous carrier fluid, and additional viscous fluids may be the same. The viscosity of the viscous fluid component, the viscous carrier fluid, and additional viscous fluids may be different. The injection of the fracturing fluid ceases after the proppants are placed in the fractures and the fracturing fluid is allowed to seep from the fractures.

0023The hydraulic fracturing operation leaves residual viscous material in the fractures. Residual viscous materials include carboxymethyl cellulose, hydroxyethyl cellulose, carboxymethyl hydroxyethyl cellulose, hydroxypropyl cellulose, and methyl hydroxyl ethyl cellulose, guar gum, hydroxypropyl guar, carboxymethyl guar, guar cross-linked with boron, aluminum phosphate-ester oil gel, and guar cross-linked with organometallic compounds. Organometallic compounds include zirconium, chromium, antimony, and titanium salts. The residual viscous material may be a gelled material. The residual viscous material may be a polymeric material. The residual viscous material may be guar gum. The residual viscous material has a viscosity greater than the fracturing fluid. The residual viscous material may surrounding and/or adjacent to the proppants placed in the fractures.

0024The cleanup fluid acts, after the proppants have been placed in the fractures, to remove the residual viscous material. The cleanup fluid may be mixed with the fracturing fluid. Where a multi-stage fracturing fluid is used, the cleanup fluid may be a component of the fluids used at each stage of the hydraulic fracturing operation. The cleanup fluid may be added only to the fluid of the final stage of the hydraulic fracturing operation. The cleanup fluid may be pumped to the fractured formation as a separate step following the hydraulic fracturing operation.

0025The cleanup fluid includes an acid precursor and an exothermic reaction component. The reaction of the exothermic reaction component results in a release of kinetic energy and thermal energy. The reaction of the exothermic reaction component generates heat and increases the pressure. The generated heat increases the temperature of the surrounding fluids, including fracturing fluid remaining in the fractures and residual viscous material. The increase in temperature reduces the viscosity of the fracturing fluid. The increase in temperature reduces the viscosity of the residual viscous material left in the fractures to create a reduced viscosity material. The reduced viscosity material flows from the fractures of the formation to the wellbore. The increase in pressure provides lift energy to push the reduced viscosity materials through the wellbore toward the surface. The removal of the residual viscous material increases the conductivity of the fractures. Increased conductivity of the fractures increases seepage of the fracturing fluid, improves fracturing efficiency, minimizes need for additional fracturing jobs, minimizes time between fracturing and well production, and increases hydrocarbon flow, which translates to increased hydrocarbon recovery.

0026The acid precursor is 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. The acid precursor may be triacetin. The acid precursor may be acetic acid.

0027The exothermic reaction component includes one or more redox reactants that exothermically react to produce heat and increase pressure. Exothermic reaction components may include urea, sodium hypochlorite, ammonium containing compounds, and nitrite containing compounds. 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. The exothermic reaction component includes nitrite containing compounds. Nitrite containing compounds include sodium nitrite and potassium nitrite. The exothermic reaction component includes both ammonium containing compounds and nitrite containing compounds. The ammonium containing compound may be ammonium chloride, NH₄Cl. The nitrite containing compound may be sodium nitrite, NaNO₂.

0028The exothermic reaction component may include two redox reactants: NH₄Cl and NaNO₂, which react according to the following: <chemistry id="chem0001" num="0001"><img file="EP3132001B1_D0001.tif" /></chemistry>

0029In a reaction of the exothermic reaction components according to the above equation, generated gas contributes to the reduction of the viscosity of the residual viscous material.

0030The exothermic reaction component is triggered to react. The exothermic reaction component is triggered within the fractures.

0031The exothermic reaction component is triggered by heat. The wellbore temperature is reduced during a pre-pad injection or a pre-flush with brine and reaches a temperature below (120°F) 48.8°C. The fracturing fluid of the present disclosure is then injected into the well and the wellbore temperature increases. When the wellbore temperatures reaches a temperature greater than or equal to 48.8°C (120°F), the reaction of the redox reactants is triggered. The reaction of the redox reactants may be triggered by temperature in the absence of the acid precursor. The exothermic reaction component is triggered by heat when the exothermic reaction component is within the fractures. The cleanup fluid may be introduced to the fractures following the hydraulic fracturing operation. Dual-string coiled tubing is used to introduce the exothermic reaction component and the acid precursor to the wellbore. The exothermic reaction component may include NH₄Cl and NaNO₂. The acid precursor is acetic acid. The acetic acid is mixed with NH₄Cl and is injected in parallel with the NaNO₂, using different sides of the dual-string coiled tubing. The exothermic reaction component and the acid precursor mix within the fractures.

0032In an 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. Formations include Indiana limestone, Beria sandstone, and shale. 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 68,900 kPa (10,000 psig).

0033In the method of the present disclosure, the exothermic reaction component is mixed to achieve a pre-selected solution pH. The exothermic reaction component is mixed with the viscous fluid component and the proppant component to form the fracturing fluid. The fracturing fluid is injected into the wellbore in the gas-containing formation to create fractures and the proppant(s) holds open the fractures. The exothermic reaction component reacts and upon reaction generates a pressure pulse that creates auxiliary fractures. Fracturing fluid is used in a primary operation to create fractures. The auxiliary fractures extend from the fractures caused by the fracturing fluid to create a fracture network. The fracture network increases the stimulated reservoir volume. In some embodiments, the injection of the hydraulic fracturing fluid including the viscous fluid component and/or the proppant component and/or the overflush component and/or the exothermic reaction component does not generate foam or introduce foam into the hydraulic formation including the hydraulic fractures.

0034The exothermic reaction component reacts when the exothermic reaction component reaches the wellbore temperature. The wellbore temperature is between about 37.8°C (100°F) and about 121.1°C (250°F), alternately between about 48.8°C (120°F) and about 121.1°C (250°F), alternately between about 48.8°C (120°F) and about 110°C (230°F), alternately between about 60°C (140°F) and about 98.9°C (210°F), alternately about 71.1°C (160°F) and about 87.8°C (190°F). In at least one embodiment, the wellbore temperature is 93.3°C (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.

0035When the exothermic reaction component reacts, the reaction generates a pressure pulse and heat. The pressure pulse is generated within milliseconds from the start of the reaction. The pressure pulse is at a pressure between about 3,400 kPa (500 psi) and about 340,000 kPa (50,000 psi), alternately between about 3,400 kPa (500 psi) and about 138,000 kPa (20,000 psi), alternately between about 3,400 kPa (500 psi) and about 103,000 kPa (15,000 psi), alternately between about 6,900 kPa (1,000 psi) and about 68,900 kPa (10,000 psi), alternately between about 6,900 kPa (1,000 psi) and about 34,000 kPa (5,000 psi), and alternately between about 34,000 kPa (5,000 psi) and about 68,900 kPa (10,000 psi).

0036The pressure pulse creates auxiliary fractures. The auxiliary fractures extend from the point of reaction in all directions without causing damage to the wellbore or the fractures created due to the step of injecting the fracturing fluid. 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.

0037The exothermic reaction component may be injected into the wellbore in the absence of the viscous fluid component and the proppant component and allowed to react to generate the pressure pulse.

0038The method to increase a stimulated reservoir volume may also perform the method to cleanup a residual viscous material as described herein. The method of the present disclosure can be adjusted to meet the needs of the fracturing operation. The fracturing fluid includes an exothermic reaction component that may react to both create auxiliary fractures and to cleanup residual viscous material from the fracturing fluid. The fracturing fluid may include an exothermic reaction component that reacts to only create auxiliary fractures. The fracturing fluid may include an exothermic reaction component that reacts to only cleanup residual viscous material.

0039A method to increase the stimulated reservoir volume of a 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. The method to increase a stimulated reservoir volume may be performed to create fractures and auxiliary fractures in cement.

EXAMPLES

0040<ul id="ul0002" list-style="none"><li><b>Example 1.</b> An exothermic reaction component of a cleanup fluid consisting of 3M NH₄Cl and 3M NaNO₂ was added to a solution of 1% by volume guar at room temperature, see <figref idref="f0003">FIG. 3</figref>. The exothermic reaction component was triggered by heat. The viscosity of the solution was measured before, during, and after the reaction using a Chandler viscometer. Prior to reaction of the exothermic reaction component, the viscosity of the residual viscous material was 85 cP. <figref idref="f0001">FIG. 1</figref> is a graph of the viscosity following the reaction of the exothermic reaction component. The graph shows that the viscosity of the residual viscous material was reduced to less than 8.5 cP. <figref idref="f0003">FIG. 3b</figref> shows the solution, including the residual viscous material after the reaction of the exothermic reaction component.</li><li><b>Example 2.</b> An aqueous solution of an exothermic reaction component was prepared from 3M NH₄Cl and 3M NaNO₂. The aqueous solution was placed in an autoclave reactor at room temperature and an initial pressure of 6,900 kPa (1,000 psi). The reaction temperature was increased. The reaction was triggered at about 48.8°C (120°F), see <figref idref="f0002">FIG. 2</figref>. Due to the reaction, the temperature in the reactor reached a temperature of 285°C (545°F) and a pressure of 23,290 kPa (3,378 psi), see <figref idref="f0002">FIG. 2</figref>.</li><li><b>Example 3.</b> In Example 3, two autoclave reactors, were used to study the reaction kinetics of the exothermic reaction component. One autoclave reactor was rated up to 68,900 kPa (10,000 psi) and 500°C with a total volume of 3 L. The other autoclave reactor was rated up to 138,000 kPa (20,000 psi) and 500°C with a total volume of 80 ml. The experimental parameters were monitored and controlled remotely by computer. Real time pressure and temperature data were recorded every 2 seconds in an effort to capture the resultant pressure-temperature behavior during the reaction of the exothermic reaction component. The set-up simulated the pressure and temperature that would occur in a wellbore as a result of injecting the exothermic reaction component in the wellbore and triggering the reaction. The study assumed that the wellbore was drilled in a zero permeability formation to match that of the autoclave reactor. Such an assumption can be considered an approximation of a shale formation, even though a shale formation will have some permeability. The study allowed three independent variables to be tested: molarity of the exothermic reaction component, initial pressure inside the autoclave reactor, and ratio of the volume of the exothermic reaction component to the volume of the autoclave reactor</li><li><b>Example 4.</b> In Example 4, rock sample tests were conducted to test the fracturing potential of the method of the present disclosure. The rock samples created for use in Example 4 were rectangular blocks with dimensions of 20.3 cm x 20.3 cm x 20.3 cm (8" x 8" x 8") and 25.4 cm x 25.4 cm x 25.4 cm (10" x 10" x 10"). The rock samples were created from Indiana limestone, Beria sandstone, shale, and cement. The limestone, sandstone, and shale blocks were taken from outcrop samples. The cement rock sample was cast from mixing water and cement at a weight ratio of water to cement of 31:100. Table 1 shows the physical and mechanical properties for the rock samples.</li></ul><tables id="tabl0001" num="0001"><table frame="all"><title><b>Table 1. Properties of Rock Samples for Tests 1 through 4</b></title><tgroup cols="5"><colspec colnum="1" colname="col1" colwidth="52mm" /><colspec colnum="2" colname="col2" colwidth="26mm" /><colspec colnum="3" colname="col3" colwidth="28mm" /><colspec colnum="4" colname="col4" colwidth="32mm" /><colspec colnum="5" colname="col5" colwidth="24mm" /><thead><row><entry valign="top"><b>Property</b></entry><entry valign="top">Test #1</entry><entry valign="top">Test #2</entry><entry valign="top">Test #3</entry><entry valign="top">Test #4</entry></row></thead><tbody><row><entry>Sample Material</entry><entry>White Cement</entry><entry>Portrait Cement</entry><entry>Indiana Limestone</entry><entry>Shale</entry></row><row><entry>Dimension</entry><entry>8x8x8"</entry><entry>8x8x8"</entry><entry>10x10x10"</entry><entry>10x10x10"</entry></row><row><entry>Porosity</entry><entry>29%</entry><entry>24.2 %</entry><entry>28%</entry><entry>3.8 %</entry></row><row><entry>Bulk Density, gm/cc</entry><entry>1.82</entry><entry>2.01</entry><entry>1.82</entry><entry>2.50</entry></row><row><entry>Young's Modulus, psi</entry><entry>1.92 x10⁶</entry><entry>2.1 x10⁶</entry><entry>1.92 x10⁶</entry><entry>2.66 x10⁶</entry></row><row><entry>Poisson's ratio</entry><entry>0.26</entry><entry>0.19</entry><entry>0.26</entry><entry>0.20</entry></row><row><entry>Uniaxial compressi ve strength, psi</entry><entry>3,299</entry><entry>3,147</entry><entry>3,229</entry><entry>4,965</entry></row><row><entry>Cohesive strength, psi</entry><entry>988</entry><entry>1,317</entry><entry>1,067</entry><entry>1,268</entry></row><row><entry>Tensile strength, psi</entry><entry>Not Available</entry><entry>Not Available</entry><entry>271</entry><entry>Not Available</entry></row><row><entry>Internal friction angle</entry><entry>28°</entry><entry>10.1°</entry><entry>23°</entry><entry>36°</entry></row></tbody></tgroup></table></tables>

0041Each rock sample had a simulated wellbore drilled in the center of the rock sample measuring 3.81 x 7.62 cm (1.5 x 3"), as shown in <figref idref="f0004">FIG. 4 and FIG. 5</figref>. For the unconfined tests, the vertical openhole wellbore was 7.62 cm (3") long and 3.81 cm (1.5") in diameter, as shown in <figref idref="f0004">FIG. 4</figref>. For the confined test, the vertical openhole wellbore was 3.81 cm (1.5") diameter cast all the way through the center of the block, as shown in <figref idref="f0004">FIG. 5</figref>. Samples of the exothermic reaction component were mixed with the viscous fluid component to create sample fracturing fluids with a loading of 4.79 mg/l (40 lbs/Mgal). The viscosity of the fracturing fluid was about 1,600 cP at a shear rate of 81 s^-1, at room temperature. The concentration of the exothermic chemical component was 3M and was used immediately after preparation. During the tests, the injection rate of the fracturing fluid into the vertical openhole wellbore was 30 cc/min.

0042The samples of the fracturing fluid were tested with and without confinement. For the confined stress testing, samples were loaded in a biaxial cell with equal horizontal stresses of 13,800 kPa (2000 psi) for one test, and 27,600 kPa (4000 psi) for another test. Approximating a depth of 2570 feet, these stresses represent gradients of 17.6 kPa/m (0.78 psi/ft), and 35.3 kPa/m (1.56 psi/ft), respectively. The fracturing fluid samples with the exothermic reaction component included were injected in the blocks and heat was applied using the biaxial plates.

Tests 1 through 4. Unconfined Testing Conditions

0043<i>Tests 1 and 2.</i> For tests 1 and 2, the rock samples were man-made cement blocks. The rock samples were preheated to 93.3°C (200°F). Then, the exothermic reaction component was injected in the rock samples at atmospheric pressure at a rate of 30 cc/min. As the injection neared completion and the reaction took place, multiple fractures were created, as shown in <figref idref="f0005">FIGS. 6 and 7</figref>. The fractures were longitudinal and perpendicular with respect to the vertical openhole wellbore. The fracture geometry indicated that fractures propagated from the wellbore to the sides of the sample, indicating that the pressure generated was greater than compressive strength of the samples. The breakdown pressure for the rock samples of test 1 and test 2 was 37,200 kPa (5,400 psi).

0044<i>Test 3.</i> For test 3, an Indiana limestone block sample was tested. The block was preheated to 93.3°C (200°F). Then, the exothermic reaction component was injected in the rock sample at atmospheric pressure at a rate of 15 cc/min. As injection neared completion and the reaction took place, fractures were created within two minutes as shown in <figref idref="f0006">FIG. 8</figref>. There were two longitudinal fractures and one perpendicular fracture with respect to the vertical openhole wellbore. The breakdown pressure for test 3 was 32,400 kPa (4,700 psi).

0045<i>Test 4.</i> In test 4, the test block was a Shale block sample with a drilled vertical openhole wellbore 5.08 cm (2") long and 3.81 cm (1.5") in diameter, to simulate a vertical well. In this test, the exothermic reaction component was injected first. Then the block was placed in a 93.3°C (200°F) oven. After 3 hours, the exothermic reaction component was triggered and the chemical reaction took place and fractures were created, as shown in <figref idref="f0006">FIG. 9</figref>. The time interval for the reaction to be activated simulated downhole-temperature recovery of the wellbore. The breakdown pressure for test 4 was 41,400 kPa (6,600 psi).

Tests 5 and 6. Confined Condition Testing

0046The confined condition tests simulated in the center of an 20.3 cm x 20.3 cm x 20.3 cm (8"x8"x8") cube, as shown in <figref idref="f0007">FIG. 10</figref>. The wellbore is 3.81 cm (1.5 inches) in diameter extending throughout the whole length of the sample, as shown in <figref idref="f0004">FIG. 5</figref>. The rock samples were then placed in a biaxial loading frame where two horizontal stresses of a given stress were applied while the vertical stress was controlled by mechanical tightening of the base and top plates. Then, the exothermic reaction component was injected in the rock sample at atmospheric pressure and room temperature at a rate of 15 cc/min. The rock sample was then heated for 2 to 3 hours until the reaction took place and fractures were created. Two tests were performed as follows:

0047In test 5, the applied horizontal stress was 13,800 kPa (2000 psi) in both directions, as shown in <figref idref="f0008">FIG. 11</figref>. The reaction was triggered at 75°C (167 °F). Upon triggering the reaction, three longitudinal fractures and one perpendicular fracture was created with respect to the vertical openhole wellbore, as shown in <figref idref="f0008">FIG. 12</figref>. The applied horizontal stress in test 6 was 27,600 kPa (4,000 psi) in both directions, as shown in <figref idref="f0009">FIG. 13</figref>. The test results of test 6 exhibited almost the same behavior as test 5. Four longitudinal fractures were created with respect to the vertical openhole wellbore, as shown in <figref idref="f0009">FIG. 14</figref>. The fracture geometry shows that the fractures were longitudinal with respect to the vertical openhole wellbore. The fracture geometry indicates that two sets of fractures propagated from the vertical openhole wellbore to the end of the rock sample, indicating that the pressure generated was greater than 55,200 kPa (8000 psi). Each created planar fracture propagated in the direction of one of the horizontal stresses, σ (h), and perpendicular to the direction of the other σ (h), as the applied stress is equal in both horizontal directions.

0048The confined tests confirm that the initial reservoir pressure does not diminish the pulse pressure and the ability of the pulse pressure to generate auxiliary fractures.

0049<b>Example 5.</b> An autoclave reactor, rated up to 68,900 kPa (10,000 psi) was used to test the chemical reaction of the exothermic reaction component. <figref idref="f0010">FIG. 15</figref> shows the reaction behavior with pressure pulse and temperature pulse. In the reactor test, the exothermic reaction component was placed in the autoclave at room temperature and pressure. Then, the temperature was increased until 48.8°C (120°F) was reached and the reaction was triggered. After the reaction was triggered, the pressure-rise time was less than 2 seconds, which was the low-limit of the autoclave reactor. The pressurizing rate affected the fractures generated in the rock sample. As shown in <figref idref="f0010">FIG. 16</figref>, the final pressure reached in the autoclave reactor is a function of the initial pressure in the autoclave reactor. In other words, Example 5 showed that the final pressure is the summation of the initial reactor pressure and the pressure generated by the reaction. However, the temperature was constant with the changes in initial pressure, at fixed chemical concentration and volume.

0050In another test, an exothermic reaction component was prepared with a viscous fluid component (4.79 g/l [401b/1000 gal]) to create a fracturing fluid, <figref idref="f0011">FIG. 17</figref>. The solution pH of the fracturing fluid was adjusted until a pre-selected solution pH of 9.7 was achieved. This buffered the solution, preventing a reaction at the set temperature of the experiment. Then, the fracturing fluid was injected into the autoclave reactor, which was preset to a temperature of 93.3°C (200° F). The exothermic reaction component was not triggered until the pre-selected solution pH was reduced to a reaction-triggering pH. The solution pH was reduced to 5.7 pH after one hour by injecting a viscosity breaker, at which point the exothermic reaction component reacted.

0051In <figref idref="f0011">FIG. 17</figref>, the reaction of the exothermic reaction component generated a pressure pulse. The ability to control the start of the reaction of the exothermic reaction rate by adjusting the pH provides for control of the reaction behavior before, during, and after injections into the formation for field applications. In the Experiment shown by <figref idref="f0011">FIG. 17</figref>, the reaction was triggered by controlling the pH. Other conditions that can be controlled to trigger the exothermic reaction include temperature and solution concentrations.

0052<b>Example 6.</b> The exothermic reaction component was tested using the autoclave reactor at different concentrations and solution volumes. The results showed that pressure is a function of concentration and solution volume. The greater the solution volume used, the greater the generated pressure, <figref idref="f0011">FIG. 18</figref>. Triggering of the exothermic reaction component causes a quick spike in pressure. Such a generation, spike, and subsidence of a pressure pulse can be seen in <figref idref="f0002">FIGS. 2</figref>, <figref idref="f0008">11</figref>, <figref idref="f0009">13</figref>, <figref idref="f0010">15</figref>, and <figref idref="f0011">17</figref>. At 50 % solution volume, as concentration increased 1M, 3M, and 4M, pressure generated increased from 6,810 kPa (988 psi), to 42,100 kPa (6,100 psi), to 114,000 kPa (16,600 psi) as measured using the autoclave reactor. Concentration was also shown to have an impact on generated pressure. At a 1M concentration solution, as the solution volume was increased from 50 to 100 vol %, the generated measured pressure increased from 6,810 kPa (988 psi) to 138,000 kPa (20,000 psi). The test results suggest that pressure can reach greater than 310,000 kPa (45,000 psi) at high concentrations and large volumes.

0053<b>Example 7.</b> The wellbore temperature was simulated to be 200°F at an initial reactor pressure of zero and a pre-selected solution pH of 6.5, as shown in <figref idref="f0012">FIG. 19</figref>. Once the wellbore temperature was reached, the reaction progressed very vigorously and the pressure pulse was generated in a millisecond. The minimum limit of the autoclave system was 2 seconds, so it was not possible to record the reaction pulse duration. When the initial autoclave reactor pressure was 2,400 kPa (350 psi) or higher, the wellbore temperature was stabilized around 50°C (122°F). When the solution pH was increased from 6 to 9, the wellbore temperature increased from 93.3 (200) to 110°C (230 °F), at zero initial pressure. At 3,400 kPa (500 psi) initial pressure, the wellbore temperature was increased from 50 (122) to 84.4°C (184 °F), as the solution pH increased from 6.5 to 9.

0054In some embodiments, once the aqueous solution comprising the exothermic reaction component reaches the wellbore temperature, the time for the pressure pulse to occur, including the time for the pressure pulse to be generated, spike, and then generally subside, is less than 10 minutes, or less than 1 minute, or less than 30 seconds, or less than 10 seconds, or less than 5 seconds, or less than 2 seconds, or less than 1 second, or in about 1 millisecond. Such a generation, spike, and subsidence of a pressure pulse can be seen in <figref idref="f0002">FIGS. 2</figref>, <figref idref="f0008">11</figref>, <figref idref="f0009">13</figref>, <figref idref="f0010">15</figref>, and <figref idref="f0011">17</figref>.

0055In some embodiments, no viscous fluid component, such as, for example plant gum, is required to be used in combination with the exothermic reaction component(s). In some embodiments, the exothermic reaction creates a large amount of nitrogen gas quickly, which is produced to create pressure for the pressure pulse to create fractures in a hydrocarbon-bearing formation. In some embodiments, the pH of the exothermic reaction component aqueous solution is controlled to be above pH 4, or above pH 5, or above pH 6, or above pH 7, or above pH 8, or above pH 9, or at about pH 9.5.

0056<b>Example 8.</b> The exothermic reaction component showed compatibility with the viscous fluid component (here an x-linked gel) as shown in <figref idref="f0013">FIG. 21</figref>. The fracturing fluid with the viscous fluid component, the exothermic reaction component, and the proppant component was also prepared and showed compatibility as shown in <figref idref="f0013">FIG. 20</figref>. The fracturing fluid, without the proppant component, was activated in the autoclave reactor by heating to the wellbore temperature to trigger the reaction of the exothermic reaction component. The heat generated by the reaction reduced the viscosity of the viscous fluid component to produce a reduced viscosity material, without injecting the viscosity breaker, as shown in <figref idref="f0013">FIG. 22</figref>. Using a chandler viscometer, the viscosity of the fracturing fluid, containing the viscous fluid component and the exothermic reaction component, was measured pre-reaction and post-reaction. The viscosity of the fracturing fluid was reduced from 1600 cp to 10 cp, as shown in <figref idref="f0014">FIG. 23</figref>. The results show that the exothermic reaction component and this type of treatment can clean-up the fractures post a fracturing job.

0057<b>Example 9.</b> A pre-flush was injected into the wellbore to reduce the wellbore temperature from 121.1°C (250°F) to 37.8°C (100°F), as seen in <figref idref="f0014">FIG. 24</figref>. Then, the fracturing fluid was injected into the well. The wellbore temperature was allowed to rise and the point at which the reaction was triggered by the wellbore temperature was recorded. As can be seen in <figref idref="f0014">FIG. 24</figref>, it took around three hours for the wellbore temperature to reach 184°F, which was the wellbore temperature necessary to trigger the exothermic reaction component when the pre-selected solution pH was 9. The heat recovery of the well triggers the reaction of the exothermic reaction component at different time frames, in this test between 1 to 3 hours. The results suggest that the exothermic reaction component and to some extent the conditions in the wellbore can be tailored to meet the needs of the process, including providing additional time to place the fracturing fluids with the exothermic reaction component in the wellbore and the fractures.

0058Referring now to <figref idref="f0015 f0016 f0017 f0018 f0019 f0020">FIGS. 25-34</figref>, microscopic analysis of a sample treated by the reactive exothermic components of the present disclosure showed that no damaged zone is formed around the treated area; however, a synthetic sweetspot is created. A tight core sample with an air permeability of 0.005 nanoDarcy was chemically treated using a core flood system. The exothermic reaction component was injected through a drilled hole within the core sample at 2/3 of the total core sample length of 8.13 cm (3.2 inches). The core diameter was 3.81 cm (1.5 inches) with porosity of 1.35%.

0059Pre and post treatment MR-CT-scan analysis (nuclear magnetic resonance combined with X-ray computed tomography for core analysis), shown in <figref idref="f0017">FIGS. 29</figref> and <figref idref="f0020">34</figref>, respectively, shows significant density reduction. As shown, voids are scattered around the treated area throughout the core sample in <figref idref="f0020">FIG. 34</figref>. The change from <figref idref="f0017 f0018 f0019 f0020">FIG. 29 to FIG. 34</figref> reflects an increase in porosity in the sample around the treated area. Environmental Scanning Electron Microscope (ESEM) analysis was also performed before and after treatment by the exothermic reaction component. <figref idref="f0016">FIGS. 27</figref> and <figref idref="f0017">28</figref> show ESEM images of the sample taken before treatment with the exothermic reaction component, and <figref idref="f0019">FIGS. 32</figref> and <figref idref="f0020">33</figref> show ESEM images of the sample taken after treatment with the exothermic reaction component. Several backscattered electron topographical images were taken at different magnifications from different parts of the samples, but mainly from the center of the rock samples. The ESEM images show that microfractures were created along the core sample by the exothermic reaction component. The ESEM images also show submicron pores and micro-cracks.

0060The sizes of the pores were measured and found to be in a range of less than about 1 micron to about 50 microns. The concentration of the cracks and pores were mainly in the center of the rock, where the epicenter of the treatment took place. The exothermic reaction treatment has led to the initiation of micro-cracks and pores in the rock samples. The post exothermic reaction treatment MR-CT scan image of <figref idref="f0020">FIG. 34</figref> shows a significant increase in macro pores throughout the core and suggests a communication of an otherwise isolated system of micro, meso, and macro pores of the core with an overall permeability increase. <figref idref="f0015">FIG. 25</figref> shows the isolated porosity system of the core sample pretreatment, in which micro, meso, and macro pores are clearly not communicating to each other. However, post exothermic reaction component treatment results shown in <figref idref="f0018">FIG. 30</figref> show a strong communication between all pore sizes and an overall permeability increase.

0061The pre and post MR-CT scans shown in <figref idref="f0017">FIGS. 29</figref> and <figref idref="f0020">34</figref> respectively show significant porosity increase and created fractures due to the exothermic chemical reaction brought about by the exothermic reaction component. <figref idref="f0017">FIG. 29</figref> represents a high density, low porosity sample before treatment by the exothermic reaction component, while the dark regions 12 in <figref idref="f0020">FIG. 34</figref> represent low density and high porosity regions brought about by the exothermic reaction component. <figref idref="f0019">FIG. 31</figref> shows a tight core sample after treatment by the exothermic reaction component, and shows creation of fractures 10 perpendicular to the flow of injection, which are not present before treatment (<figref idref="f0016">FIG. 26</figref>). Clear reduction of density and porosity is noted. Fractures and voids are clearly shown in the samples.

0062Although the present 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.

0063The singular forms "a," "an," and "the" include plural referents, unless the context clearly dictates otherwise.

0064Optional or optionally means that the subsequently described event or circumstances can or may not occur. The description includes instances where the event or circumstance occurs and instances where it does not occur.

0065As used herein and in the appended claims, the words "comprise," "has," and "include" and all grammatical variations thereof are each intended to have an open, nonlimiting meaning that does not exclude additional elements or steps.

0066As used herein, 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.