Method for improving hardness of subterranean formation

Abstract

The method comprises: introducing an aqueous carrier liquid comprising ammonium phosphate into a subterranean formation comprising carbonate minerals; and interacting the carbonate mineral with the ammonium phosphate salt to convert at least a portion of the carbonate mineral to a hydroxyapatite mineral; wherein the hardness of the subterranean formation is increased after formation of the hydroxyapatite mineral.

Description

Technical Field

[0001] The present disclosure relates generally to subterranean stimulation operations and, more particularly, to the chemical consolidation of carbonate minerals within subterranean formations. Background Art

[0002] Stimulation procedures are commonly used during oil and gas production to increase the productivity of underground formations by increasing the permeability of the formation matrix. Common stimulation procedures include hydraulic fracturing and matrix acidizing, or acid fracturing.

[0003] Hydraulic fracturing introduces fluid at high pressure into a subsurface formation to create conductive pathways (commonly referred to as fractures) within the formation matrix. These fractures can increase the permeability of the subsurface formation and improve hydrocarbon production. Hydraulic fracturing operations typically utilize microparticles (called proppants) to keep the fractures open after the hydraulic pressure is released. Matrix acidizing creates pores within the subsurface formation by dissolving portions of the formation matrix, thereby creating flow channels (commonly referred to as wormholes). Acid fracturing operations can combine aspects of hydraulic fracturing and matrix acidizing to increase the permeability of subsurface formations.

[0004] While hydraulic fracturing and matrix acidizing can be desirable for increasing the permeability of subsurface formations, these operations are not without challenges. In soft or ductile subsurface formations, proppant may become embedded in fractures, thereby reducing the effective fracture width. The term "embedding" and its alternative grammatical forms refer to the process by which proppant particles, when subjected to compressive stress within a fracture, are at least partially pushed into the formation matrix, thereby reducing the effective fracture width compared to the width of a fully open fracture. Matrix acidizing may weaken the mechanical integrity of the formation matrix and lead to wormhole collapse. Even if the subsurface formation is not particularly soft or ductile overall, acid may weaken fracture asperities during an acid fracturing operation and result in at least partial fracture closure. Regardless of the cause, these types of subsurface formation damage may reduce hydrocarbon production from stimulation operations by failing to achieve optimal permeability improvement. These types of formation damage may be particularly prevalent when stimulating subsurface formations containing carbonate minerals. Summary of the Invention

[0005] The following summarizes various details of the present disclosure to provide a basic understanding. This summary is not a comprehensive overview of the present disclosure, nor is it intended to point out certain elements of the present disclosure or describe its scope. Instead, the primary purpose of this summary is to present some concepts of the present disclosure in a simplified form before presenting a more detailed description below.

[0006] According to an embodiment consistent with the present disclosure, a method for hardening carbonate minerals within a subterranean formation includes: introducing an aqueous carrier fluid comprising an ammonium phosphate salt into the subterranean formation comprising carbonate minerals; and interacting the carbonate minerals with the ammonium phosphate salt to convert at least a portion of the carbonate minerals into hydroxyapatite minerals. The hardness of the subterranean formation increases upon formation of the hydroxyapatite minerals.

[0007] In other embodiments consistent with the present disclosure, a method for stimulating a subterranean formation in conjunction with carbonate mineral hardening includes: stimulating the subterranean formation comprising carbonate minerals by matrix acidizing, hydraulic fracturing, or any combination thereof; after stimulating the subterranean formation, introducing an aqueous carrier fluid comprising an ammonium phosphate salt into the subterranean formation; and converting at least a portion of the carbonate minerals into hydroxyapatite minerals by interacting the carbonate minerals with the ammonium phosphate salt. The hardness of the subterranean formation is increased upon formation of the hydroxyapatite minerals.

[0008] Any combination of the various embodiments and implementations disclosed in this specification can be used in another embodiment consistent with the present disclosure. The above and other aspects and features can be understood through the following description, drawings and claims of certain embodiments according to the present disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 is a box plot comparing the Brinell hardness of limestone and chalk samples before and after treatment with diammonium phosphate.

[0010] Figure 2 is an SEM image of a limestone sample treated with diammonium phosphate.

[0011] Figure 3 is an SEM image of a chalk sample treated with diammonium phosphate. DETAILED DESCRIPTION

[0012]

[0014] Embodiments according to the present disclosure relate generally to subterranean stimulation operations and, more particularly, to chemical consolidation of carbonate minerals within subterranean formations.

[0013] The present disclosure solves the difficulties associated with increasing the production of soft and tough formations (e.g., underground formations containing carbonate minerals). In particular, the present disclosure solves the above problems by increasing the hardness of carbonate minerals in underground formations, thereby enhancing the mechanical strength of the formation matrix to reduce the possibility of proppant embedment and micro-asperity weakening. The hardness improvement of carbonate minerals can be achieved by chemical consolidation, as discussed in more detail below. Although chemical consolidation has been used to harden sandstone formations and other siliceous formations, this technology is rarely used in carbonate formations and is not the method described in the present disclosure.

[0014] The concept of chemical consolidation in sandstone formations and other siliceous formations is based on the deposition of mineral phases in the existing formation matrix, thereby binding individual rock particles together to strengthen the formation matrix or harden the formation matrix. In the present disclosure, chemical consolidation of carbonate formations can be achieved by changing the carbonate mineralogy, that is, converting carbonate minerals into harder minerals through dissolution-precipitation reactions. In particular, carbonate minerals can be treated with ammonium phosphate salts of the present disclosure to convert at least a portion of the carbonate minerals into hydroxyapatite minerals, thereby achieving the above-mentioned purpose. Advantageously, the conversion of carbonate minerals to hydroxyapatite minerals can be completed in a short time under mild reaction conditions, as described below.

[0015] As used herein, the term "proppant" refers to particles that are mixed with hydraulic fracturing fluids to hold fractures open after the water pressure generated during hydraulic fracturing is released.

[0016] As used herein, the term "matrix acidizing" refers to treating a subterranean formation with a fluid containing an acid that reacts with the formation matrix. A "fluid" may include liquids, gases, or both liquids and gases.

[0017] This disclosure describes methods for increasing the hardness and / or strength of a subsurface formation containing carbonate minerals. The increased hardness and / or strength of the subsurface formation can be achieved by chemical consolidation using an aqueous carrier fluid containing an ammonium phosphate salt. In some embodiments, the increased hardness and / or strength of the subsurface formation can be performed in conjunction with a stimulation procedure, either before, during, or after the stimulation procedure is performed.

[0018] In some embodiments, the methods of the present disclosure may include: introducing an aqueous carrier fluid comprising an ammonium phosphate salt into a subsurface formation comprising carbonate minerals; and interacting the carbonate minerals with the ammonium phosphate salt to convert at least a portion of the carbonate minerals into hydroxyapatite minerals. The hardness of the subsurface formation may be increased after the hydroxyapatite minerals are formed. As a non-limiting example, the increased hardness may be characterized as a Brinell hardness. In some embodiments, the subsurface formation may be stimulated prior to forming the hydroxyapatite minerals via chemical consolidation.

[0019] Thus, in some embodiments of the present disclosure, the method may include first stimulating a subsurface formation comprising carbonate minerals by subjecting the subsurface formation to matrix acidification, hydraulic fracturing, or any combination thereof. After the subsurface formation has been stimulated, a treatment may be introduced into the subsurface formation to promote conversion of at least a portion of the carbonate minerals into a second mineral, preferably a hydroxyapatite mineral. The treatment may include introducing an aqueous carrier fluid comprising an ammonium phosphate salt into the subsurface formation. After converting the carbonate minerals into the second mineral, preferably a hydroxyapatite mineral, the subsurface formation may exhibit increased hardness.

[0020] In the present disclosure, the underground formation may contain carbonate minerals, preferably calcium-containing carbonate minerals (e.g., calcium carbonate) with a Mohs hardness of 3. Examples of calcium-containing carbonate minerals that can be enhanced by the present disclosure may include, but are not limited to, calcite, aragonite, vaterite, dolomite, and the like, and any combination thereof. The calcium carbonate may be limestone, chalk, marble, or any combination thereof.

[0021] In the present disclosure, carbonate minerals can be converted into hydroxyapatite minerals by interacting the carbonate minerals with ammonium phosphate salts. Suitable ammonium phosphate salts can include, for example, diammonium hydrogen phosphate, ammonium dihydrogen phosphate, or a combination thereof. Preferably, the ammonium phosphate salt comprises, consists of, or consists essentially of diammonium hydrogen phosphate. Ammonium phosphate salts (e.g., diammonium hydrogen phosphate) can convert carbonate minerals (e.g., calcium carbonate) into hydroxyapatite minerals via a dissolution-precipitation reaction. Hydroxyapatite is a phosphate mineral with a Mohs hardness of 5. Therefore, converting carbonate minerals into hydroxyapatite minerals can increase the hardness of underground formations to promote their strengthening. The dissolution-precipitation reaction of calcium carbonate and diammonium hydrogen phosphate occurs according to Reaction 1.

[0022] 10CaCO3+5(NH4)2HPO4→Ca 10 (PO4,CO3)6(OH,CO3)2+5(NH4)2CO3+3CO2+2H2O

[0023] Reaction 1

[0024] Where CaCO3 is calcium carbonate, (NH4)2HPO4 is ammonium hydrogen phosphate. The original hydroxyapatite is Ca 10 (PO₄)₆(OH)₂. Write the products of Reaction 1 to demonstrate that carbonate defects can exist within the hydroxyapatite structure under certain circumstances. Ammonium carbonate ((NH₄)₂CO₃) is soluble and does not precipitate with hydroxyapatite. Other phosphate minerals that can be formed by the dissolution-precipitation of calcium carbonate and diammonium hydrogen phosphate include dicalcium phosphate and / or octacalcium phosphate dihydrate. Under certain circumstances, these species may form intermediates during hydroxyapatite precipitation.

[0025] Ammonium phosphate salts (e.g., diammonium hydrogen phosphate) can be introduced into the subsurface formation in an aqueous carrier fluid. Suitable aqueous carrier fluids can include, for example, fresh water (e.g., stream water, lake water, or municipal treated water), salt water (saline solutions), seawater, brine, non-potable water (e.g., gray water or industrial process water), formation water, produced water, well water, filtered water, distilled water, or any combination thereof. Produced water can include formation water obtained from a subsurface formation or flowback water generated after stimulation of the subsurface formation with an appropriate treatment fluid. As used herein, the term "brine" refers to a saturated aqueous salt solution. The "saline solution" has a lower salt concentration (salinity) than brine.

[0026] The concentration of the ammonium phosphate salt (e.g., diammonium hydrogen phosphate) in the aqueous carrier liquid can be from about 0.1 M to about 5 M, or from about 0.1 M to about 1 M, or from about 0.5 M to about 1.5 M, or from about 1 M to about 2 M, or from about 1.5 M to about 2.5 M, or from about 2 M to about 3 M, or from about 2.5 M to about 3.5 M, or from about 3 M to about 4 M, or from about 3.5 M to about 4.5 M, or from about 4 M to about 5 M, or from about 0.1 M to about 2 M, or from about 1 M to about 3 M.

[0027] In addition to methods for producing hydroxyapatite to promote hardness enhancement, other treatments may be suitable for converting carbonate minerals into secondary minerals (other than hydroxyapatite) having enhanced hardness. Suitable treatments may include, but are not limited to, tetraethyl orthosilicate, calcium hydroxide, calcium alkoxides, zinc sulfate, zinc nitrate, zinc chloride, barium chloride, sodium fluoride, ammonium fluoride, hydrofluoric acid, cadmium nitrate tetrahydrate, cadmium chloride, lead (II) nitrate, bacteria (e.g., Myxococcus xanthus and / or Bacillus sphaericus), the like, and any combination thereof.

[0028] Techniques including, but not limited to, X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and the like, and any combination thereof, can be used to confirm the presence of a second mineral (e.g., hydroxyapatite) formed by converting a carbonate mineral with a suitable treatment (e.g., diammonium phosphate). For example, XRD and / or SEM can be used to visualize the surface of a subsurface formation (or a core sample obtained therefrom) before and after the introduction of the treatment. The surface of the subsurface formation may undergo physical changes after the carbonate mineral is converted to the second mineral (e.g., hydroxyapatite). After the introduction of the treatment, techniques such as EDS can be used to confirm the presence of new ions (e.g., phosphorus) in the subsurface formation.

[0029] The conversion of carbonate minerals to hydroxyapatite minerals (or other minerals having increased hardness relative to carbonate minerals) can be performed in conjunction with stimulation operations. Suitable stimulation operations can include hydraulic fracturing and / or matrix acidizing. Generally, stimulation operations can be performed before converting carbonate minerals to hydroxyapatite minerals.

[0030] Hydraulic fracturing can be performed to increase the permeability of underground formations and increase the amount of hydrocarbons produced therefrom. During the fracturing operation, a hydraulic fracturing fluid (typically containing a plurality of proppant particles and various optional components to adjust the density and viscosity of the fracturing fluid) is pumped into the underground formation at a pressure higher than the fracture gradient pressure of the underground formation. The hydraulic pressure causes cracks in the underground formation to open, thereby increasing its permeability. Once the hydraulic pressure is released, the proppant particles are disposed in the cracks and keep them open. The material comprising the proppant particles can be selected based on the specific application and properties required, such as the depth of the underground formation where the proppant particles are to be placed and the compressive strength of the proppant particles at a specified underground depth under reservoir conditions. In some cases, the chemical properties of the underground formation may also be considered when selecting suitable proppant particles. Optionally, a protective and / or hardening coating, such as a resin or epoxy coating, can be applied to the proppant particles to modify or customize the density or mechanical strength of the selected base proppant material.

[0031] Hydraulic fracturing can include three main stages: a pad phase, a proppant-containing fluid phase, and a displacement fluid phase. The pad phase can include pumping a pad fluid into a subsurface formation, which can initiate and propagate fractures in the subsurface formation. The proppant fluid phase can include pumping a proppant-containing fluid into fractures in the formation, which can promote proppant retention in the fractures and create conductive fractures through which hydrocarbons can flow. The displacement fluid phase can include pumping a displacement fluid into the fractures to push the proppant deeper into the fractures.

[0032] Matrix acidizing can similarly be performed to increase the permeability of a subsurface formation and increase the amount of hydrocarbons recovered therefrom. During matrix acidizing, an acidizing fluid can be used to stimulate the production of a subsurface formation by dissolving at least a portion of carbonate minerals in the formation matrix, thereby promoting the formation of wormholes therein. In carbonate formations, the acid in the acidizing fluid can dissolve a portion of the formation matrix, thereby increasing the porosity of the formation matrix. The acidizing operation can form a plurality of asperities within the subsurface formation (i.e., asperities associated with the wormholes formed therein).

[0033] Suitable acidifying fluids may comprise aqueous acid solutions, which may comprise any one or combination of one or more strong acids and / or one or more weak acids. The term "strong acid" refers to the logarithmic acid dissociation constant (pK a ) value is less than or equal to 1.0. The term "weak acid" refers to any acid with a pK aAny acid with a value greater than 1.0. Strong acids that may be present in an acidizing fluid for a carbonate formation may include, but are not limited to, hydrochloric acid, hydrobromic acid, nitric acid, sulfuric acid, and the like, and any combination thereof. Weak acids that may be present in an acidizing fluid for a carbonate formation may include, but are not limited to, acetic acid, formic acid, methanesulfonic acid, trifluoromethanesulfonic acid, trifluoroacetic acid, and the like, and any combination thereof. In a non-limiting example, the aqueous acid solution may contain one or more strong and / or weak acids in a concentration range of about 10 wt% to about 70 wt%, or about 25 wt% to about 60 wt%, or about 30 wt% to about 50 wt%, or about 45 wt% to about 60 wt%, or about 35 wt% to about 50 wt%, based on the total mass of the acidizing fluid.

[0034] Suitable acidizing operations may include pumping a displacement fluid (also referred to as a flushing fluid) into the underground formation after the acidizing fluid. The displacement fluid may force the acidizing fluid deeper into the underground formation and promote wormhole formation therein to increase the porosity of the formation matrix. The displacement fluid may be pumped until all or nearly all of the acidizing fluid is forced into the underground formation. In some cases, the acidizing fluid may be incompatible with fluids already present in the underground formation (e.g., drilling fluid). If fluid incompatibility is an issue, a barrier fluid may be pumped into the underground formation before the acidizing fluid is introduced. The barrier fluid may provide isolation between the fluids already present in the underground formation and the acidizing fluid introduced therein.

[0035] The stimulation process of a subsurface formation, particularly a soft or ductile subsurface formation containing carbonate minerals, may further weaken the mechanical integrity of the formation matrix, or the subsurface formation may already have inherent structural weaknesses even without stimulation. In the case of inherent or stimulation-induced structural weaknesses, proppant embedment, increased structural weaknesses, and / or weakened fracture asperities may result. According to the disclosure herein, treating the subsurface formation after stimulation to form hydroxyapatite minerals via chemical consolidation can increase the hardness of the subsurface formation, thereby reducing proppant embedment and / or increasing the strength of fracture asperities.

[0036] To determine whether the hardness of the subsurface formation has been increased, the hardness of the subsurface formation can be assessed before and after the introduction of ammonium phosphate and the conversion of carbonate minerals to hydroxyapatite minerals. Suitable testing procedures for assessing strength enhancement may include Brazilian disc testing, unconfined compression testing, ultrasonic pulse velocity testing, micro-drilling, scratch testing, indentation (e.g., using a Brinell hardness tester), pulse hammering, and the like, and any combination thereof. Testing procedures for determining Brinell hardness are described in detail in the examples below.

[0037] The hardness of the subsurface formation resulting from the conversion of carbonate minerals to hydroxyapatite minerals may depend on the form of the carbonate minerals within the subsurface formation. For example, a subsurface formation containing carbonate minerals may include carbonate minerals in the form of calcium carbonate, where the calcium carbonate may be in the form of limestone or chalk. Subsurface formations containing chalk may experience a greater increase in hardness than subsurface formations containing limestone. Without being bound by theory or mechanism, the greater increase in hardness of subsurface formations containing chalk may be due to the lower initial hardness of chalk than limestone. In other words, chalk has greater potential for improvement in hardness than limestone.

[0038] As non-limiting examples, a subterranean formation containing carbonate minerals in the form of limestone may exhibit an increase in Brinell hardness of about 5% to about 10%, or about 5% to about 6%, or about 5.5% to about 6.5%, or about 6% to about 7%, or about 6.5% to about 7.5%, or about 7% to about 8%, or about 6.5% to about 7.5%, or about 8% to about 9%, or about 7.5% to about 8.5%, or about 9% to about 10%, or about 5% to about 8%, or about 6% to about 9%, or about 7% to about 10% when diammonium phosphate is used to convert at least a portion of the calcium carbonate to hydroxyapatite in accordance with the present disclosure.

[0039] As another non-limiting example, in accordance with the present disclosure, a subterranean formation containing carbonate minerals in the form of chalk may exhibit an increase in Brinell hardness of about 25% to about 35%, or about 25% to about 30%, or about 26% to about 31%, or about 27% to about 32%, or about 28% to about 33%, or about 29% to about 34%, or about 30% to about 35% after converting at least a portion of the calcium carbonate to hydroxyapatite using diammonium phosphate.

[0040] By increasing the hardness of a subsurface formation after the carbonate minerals are converted to hydroxyapatite minerals, the subsurface formation can exhibit reduced proppant embedment and / or increased asperity strength. For example, as measured relative to the embedment of the proppant particles in the plurality of fractures prior to the formation of the hydroxyapatite minerals, the embedment of the proppant particles in the plurality of fractures can be reduced by about 25% to about 35%. During a Brinell hardness test, proppant embedment can be assessed by measuring the indentation distance. Similarly, as measured relative to the asperity strength prior to the formation of the hydroxyapatite minerals in the subsurface formation, the asperity strength within the subsurface formation can be increased by about 20% to about 50%. Asperity strength can be measured by a pulse hammer technique to measure mineral hardness.

[0041] The embodiments disclosed in this specification include:

[0042] A. A method for hardening a carbonate mineral. The method comprises: introducing an aqueous carrier fluid comprising an ammonium phosphate salt into a subterranean formation comprising carbonate minerals; and interacting the carbonate minerals with the ammonium phosphate salt to convert at least a portion of the carbonate minerals into hydroxyapatite minerals; wherein the hardness of the subterranean formation is increased after the hydroxyapatite minerals are formed.

[0043] B. A method for stimulating a subterranean formation and hardening carbonate minerals therein. The method comprises: stimulating a subterranean formation containing carbonate minerals by matrix acidizing, hydraulic fracturing, or any combination thereof; introducing an aqueous carrier fluid containing an ammonium phosphate salt into the subterranean formation after stimulating the subterranean formation; and converting at least a portion of the carbonate minerals into hydroxyapatite minerals by interacting the carbonate minerals with the ammonium phosphate salt; wherein the hardness of the subterranean formation increases after the hydroxyapatite minerals are formed.

[0044] Each of embodiments A and B may have one or more of the following additional elements in any combination:

[0045] Element 1: The carbonate minerals include calcium carbonate.

[0046] Element 2: wherein the calcium carbonate is in the form of limestone.

[0047] Element 2A: wherein the Brinell hardness of the subsurface formation increases by about 5% to about 10% after formation of the hydroxyapatite mineral.

[0048] Element 3: wherein the calcium carbonate is in the form of chalk.

[0049] Element 3A: wherein the Brinell hardness of the subsurface formation increases by about 25% to about 35% after the formation of hydroxyapatite mineral.

[0050] Element 4: wherein the ammonium phosphate salt comprises diammonium hydrogen phosphate.

[0051] Element 5: The method further includes: performing a stimulation operation on the underground formation before forming the hydroxyapatite mineral.

[0052] Element 6: Wherein the stimulation operation includes hydraulic fracturing, matrix acidizing, or any combination thereof.

[0053] Element 7: wherein the stimulation treatment comprises hydraulic fracturing, and the hydraulic fracturing introduces a plurality of fractures into the subterranean formation; wherein a plurality of proppant particles are placed in the plurality of fractures during the hydraulic fracturing.

[0054] Element 7A: wherein embedment of the proppant particulates in the plurality of fractures is reduced by about 25% to about 35% relative to embedment of the proppant particulates in the plurality of fractures prior to forming the hydroxyapatite mineral.

[0055] Element 8: wherein the stimulation treatment includes matrix acidizing, and the matrix acidizing forms a plurality of asperities in the subsurface formation.

[0056] As non-limiting examples, exemplary combinations suitable for A and B include, but are not limited to: 1, 1 and 2 and / or 2 and 2A, or 1 and 3 and / or 3 and 3A, and 4; 1, 1 and 2 and / or 2 and 2A, or 1 and 3 and / or 3 and 3A, and 5; 1, 1 and 2 and / or 2 and 2A, or 1 and 3 and / or 3 and 3A, and 5 and 6; and 1, 1 and 2 and / or 2 and / or 2 and 2A, or 1 and 3 and / or 3 and 3A, and 4-6. With respect to B, any of the foregoing may be further combined with 7, 7 and 7A, or 8. Other exemplary combinations suitable for B include, but are not limited to, 7 and 7A; 7 and 8; and 7, 7A, and 8.

[0057] This disclosure also relates to the following non-limiting items:

[0058] Item 1. A method comprising:

[0059] introducing an aqueous carrier fluid comprising an ammonium phosphate salt into a subterranean formation comprising carbonate minerals; and

[0060] interacting a carbonate mineral with an ammonium phosphate salt to convert at least a portion of the carbonate mineral into a hydroxyapatite mineral;

[0061] The hardness of the underground formation increases after the formation of hydroxyapatite minerals.

[0062] Item 2. The method according to Item 1, wherein the carbonate mineral comprises calcium carbonate.

[0063] Item 3. The method according to Item 2, wherein the calcium carbonate is in the form of limestone.

[0064] Item 4. The method of Item 3, wherein the Brinell hardness of the underground formation increases by about 5% to about 10% after the hydroxyapatite mineral is formed.

[0065] Item 5. The method according to Item 2, wherein the calcium carbonate is in the form of chalk.

[0066] Item 6. The method of Item 5, wherein the Brinell hardness of the underground formation increases by about 25% to about 35% after the hydroxyapatite mineral is formed.

[0067] Item 7. The method according to any one of Items 1 to 6, wherein the ammonium phosphate salt comprises diammonium hydrogen phosphate.

[0068] Item 8. The method according to any one of items 1 to 7, further comprising:

[0069] The subsurface formation is stimulated prior to the formation of hydroxyapatite minerals.

[0070] Item 9. The method of Item 8, wherein the stimulation operation comprises hydraulic fracturing, matrix acidizing, or any combination thereof.

[0071] Item 10. A method comprising:

[0072] stimulating a subterranean formation containing carbonate minerals by matrix acidizing, hydraulic fracturing, or any combination thereof;

[0073] After stimulating the subterranean formation, introducing an aqueous carrier fluid comprising an ammonium phosphate salt into the subterranean formation; and

[0074] converting at least a portion of the carbonate mineral into a hydroxyapatite mineral by interacting the carbonate mineral with an ammonium phosphate salt;

[0075] Among them, the hardness of the underground formation increases after the formation of hydroxyapatite minerals.

[0076] Item 11. The method of Item 10, wherein the stimulation treatment comprises hydraulic fracturing, and the hydraulic fracturing introduces a plurality of fractures into the subsurface formation;

[0077] Therein, a plurality of proppant particles are placed in a plurality of fractures during hydraulic fracturing.

[0078] Item 12. The method of Item 11, wherein embedment of the proppant particles in the plurality of fractures is reduced by about 25% to about 35% relative to embedment of the proppant particles in the plurality of fractures prior to forming the hydroxyapatite mineral.

[0079] Item 13. The method of Item 10, wherein the stimulation treatment comprises matrix acidizing, and the matrix acidizing forms a plurality of asperities in the subsurface formation.

[0080] Item 14. The method of Item 13, wherein the plurality of microprotrusions are strengthened by about 20% to about 50% relative to a strength of the plurality of microprotrusions prior to forming the hydroxyapatite mineral.

[0081] Item 15. The method according to any one of Items 10 to 14, wherein the carbonate mineral comprises calcium carbonate.

[0082] Item 16. The method of Item 15, wherein the calcium carbonate is in the form of limestone.

[0083] Item 17. The method of Item 16, wherein the Brinell hardness of the underground formation increases by about 5% to about 10% after the hydroxyapatite mineral is formed.

[0084] Item 18. The method according to any one of Items 10 to 14, wherein the calcium carbonate is in the form of chalk.

[0085] Item 19. The method of Item 18, wherein the Brinell hardness of the underground formation increases by about 25% to about 35% after the hydroxyapatite mineral is formed.

[0086] Item 20. The method according to any one of Items 10 to 19, wherein the ammonium phosphate salt comprises diammonium hydrogen phosphate.

[0087] In order to facilitate a better understanding of the embodiments disclosed in this specification, the following examples of various representative embodiments are given. The following examples should not be understood as limiting or defining the scope of the present disclosure.

[0088] Example

[0089] Samples of Indiana limestone and Austin chalk were treated with diammonium phosphate to evaluate the hardness increase due to hydroxyapatite formation. Briefly, 3.8 cm x 7.6 cm (1.5 in x 3 in) samples were completely immersed in a 1 M diammonium phosphate aqueous solution under ambient conditions for 120 hours. After the samples dried, the Brinell hardness was measured on both sides of each sample, with measurements taken at five different points on each side.

[0090] Brinell hardness was measured using a Tinius Olsen FH-9 testing instrument. For chalk samples, an indentation was made using 62.5 kgf, and for limestone samples, an indentation was made using 125 kgf, each with a 5 mm indenter ball. After making the indentation, the indentation was examined under a microscope to determine the indentation diameter. The applied force and diameter were then used to calculate the Brinell hardness.

[0091] The measured hardness value at each location was compared with the hardness before treatment. Figure 1 Box plots comparing the Brinell hardness of limestone and chalk samples before and after treatment with diammonium phosphate (DAPO). The top and bottom whiskers represent the maximum and minimum Brinell hardness values measured for each sample, respectively, and the "x" data points represent the average Brinell hardness. The minimum, maximum, and average Brinell hardness values for each sample are also listed in Table 1. On average, treatment with DAP increased the Brinell hardness of the limestone samples by 7% and the chalk samples by 28%. In Table 1, HB represents the unitless Brinell hardness.

[0092] Table 1

[0093]

[0094] Scanning electron microscope (SEM) images of limestone and chalk samples were collected to observe changes in surface characteristics after treatment with diammonium phosphate to form hydroxyapatite. Figure 2 and Figure 3 SEM images of limestone and chalk samples after treatment with hydroxyapatite, respectively. Both SEM images show the presence of hydroxyapatite crystals on most of the surface of the samples. Figure 2 Position P1 in Figure 2 shows a point on the limestone surface where the conversion of calcium carbonate to hydroxyapatite is incomplete. In addition, EDS analysis of the limestone sample at position P1 confirmed the lack of phosphorus (and therefore the lack of hydroxyapatite). Other representative positions (e.g., P2) showed the presence of phosphorus by EDS, indicating the possible presence of hydroxyapatite. The EDS analysis is summarized in Table 2. Visually, the formation of hydroxyapatite in the chalk sample appears to be more complete ( Figure 3 ).

[0095] Table 2

[0096]

[0097] The terms used in this disclosure are for the purpose of describing specific embodiments only and are not intended to limit the present invention. For example, as used in this disclosure, unless the context clearly indicates otherwise, the singular forms "a", "an", and "the" are intended to include the plural forms as well. It should also be understood that when the terms "comprise", "contain", and / or "include" and their variations are used in this specification, they specify the presence of the features, wholes, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, wholes, steps, operations, elements, and / or components.

[0098] The directional terms used in this disclosure are for convention and reference purposes only and should not be construed as limiting. However, it should be recognized that these terms may be used with reference to an operator or user. Therefore, no limitation is implied or inferred. In addition, the use of ordinal numbers (e.g., first, second, third, etc.) is for the purpose of distinction and not for counting. For example, the use of "third" does not mean that there must be a corresponding "first" or "second". In addition, if used in this disclosure, the term "coupled" or "coupled to" or "connected" or "connected to" or "attached" or "attached to" may indicate the establishment of a direct or indirect connection and is not limited to either unless expressly mentioned as such.

[0099] Although the present disclosure has described several exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for its elements without departing from the spirit and scope of the present invention. In addition, it will be understood by those skilled in the art that many modifications may be made to adapt specific instruments, situations or materials to the embodiments of the present disclosure without departing from the essential scope of the invention. Therefore, the present invention is not limited to the specific embodiments disclosed or the best mode of carrying out the invention, but rather the invention will include all embodiments that fall within the scope of the appended claims. In addition, to the extent that a device or system or a component of a device or system is adapted, arranged, capable, configured, enabled, operable or operative to perform a specific function in the appended claims, the device, system or component is covered, regardless of whether the device, system or component or the specific function is activated, turned on or unlocked, as long as the device, system or component is so adapted, arranged, capable, configured, enabled, operable or operative.

[0100] While the present disclosure has been described with reference to a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments can be devised which do not depart from the scope of the present disclosure as described herein. Accordingly, the scope of the present disclosure should be limited only by the claims appended hereto.

[0101] All documents described in this disclosure are incorporated herein by reference for all jurisdictions in which such practice is permitted, including any priority documents and / or testing procedures, to the extent not inconsistent with this disclosure. As will be apparent from the foregoing general description and specific examples, although forms of the present disclosure have been shown and described, various modifications may be made without departing from the spirit and scope of the present disclosure. Therefore, it is not intended that the present disclosure be limited thereby. For example, the compositions described herein may not contain any component or composition not explicitly listed or disclosed herein. Any method may lack any step not listed or disclosed herein. Similarly, the term "comprising" is considered synonymous with the term "including." Whenever a method, composition, element, or group of elements is preceded by the transition phrase "comprising," it should be understood that we also contemplate the same composition or group of elements being preceded by the transition phrases "essentially consisting of," "consisting of," "selected from the group consisting of," or "is," and vice versa.

[0102] Unless otherwise indicated, all numbers used in this specification and the associated claims expressing quantities of ingredients, properties such as molecular weight, reaction conditions, and the like should be understood as being modified in all instances by the term "about". Accordingly, unless indicated to the contrary, the numerical parameters set forth in the following specification and the appended claims are approximate values that may vary depending upon the desired properties sought to be obtained by one or more embodiments described herein. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.

Claims

1. A method comprising: introducing an aqueous carrier fluid comprising an ammonium phosphate salt into a subterranean formation comprising carbonate minerals; and interacting the carbonate mineral with the ammonium phosphate salt to convert at least a portion of the carbonate mineral into a hydroxyapatite mineral; Wherein, the hardness of the underground formation increases after the formation of the hydroxyapatite mineral.

2. The method according to claim 1, wherein The carbonate mineral comprises calcium carbonate.

3. The method according to claim 2, wherein: The calcium carbonate is in the form of limestone.

4. The method according to claim 3, wherein: The Brinell hardness of the subterranean formation increases by about 5% to about 10% after forming the hydroxyapatite mineral.

5. The method according to claim 2, wherein: The calcium carbonate is in the form of chalk.

6. The method according to claim 5, wherein: The Brinell hardness of the subterranean formation increases by about 25% to about 35% after forming the hydroxyapatite mineral.

7. The method of claim 1, wherein the ammonium phosphate salt comprises diammonium hydrogen phosphate.

8. The method according to any one of the preceding claims, further comprising, before forming the hydroxyapatite mineral: Stimulating the underground formation.

9. The method according to claim 8, wherein The stimulation operation includes hydraulic fracturing, matrix acidizing, or any combination thereof.

10. The method according to claim 9, wherein: The stimulation treatment includes hydraulic fracturing, and the hydraulic fracturing introduces a plurality of fractures into the subterranean formation; wherein a plurality of proppant particles are placed in the plurality of fractures during the hydraulic fracturing.

11. The method according to claim 10, wherein: Embedment of the proppant particles in the plurality of fractures is reduced by about 25% to about 35% relative to embedment of the proppant particles in the plurality of fractures prior to forming the hydroxyapatite mineral.

12. The method according to claim 9, wherein The stimulation treatment includes matrix acidizing, and the matrix acidizing forms a plurality of asperities in the subterranean formation.

13. The method according to claim 12, wherein: The plurality of microasperities are strengthened by about 20% to about 50% relative to a strength of the plurality of microasperities prior to forming the hydroxyapatite mineral.

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