TECHNICAL FIELD

[0001] A method of pumping a fluid and a reactive solid into a mineral formation, wherein the fluid reacts with the mineral formation to produce a nucleation product, and a cement formed by the method.

BACKGROUND

[0002 j Shale oil and gas resources are being widely developed in the United States and elsewhere even though the environmental consequences are still poorly understood (Kargbo et al., Environmental Science & Technology 2010, 44, (15), 5679-5684). On a regional scale, seepage and leakage of fracturing fluids, contaminated native brines and natural gas into ground water resources is of great concern (Osborn et al., Proceedings of the National Academy of Sciences 2011, 108, (20), 8172- 8176). These leaks could impact air and water quality both during the production stages of the well life cycle, and once the original operation is shut down during which time leaks may persist for decades (Burnham et al., Environmental Science & Technology 2011, 46, (2), 619-627). On a global scale, shale gas development is a concern because greenhouse gas emission resulting from its extraction and consumption will negatively impact the climate (Khosrokhavar et al. Environ, Process. 2014, 1-17). One estimate is that up to 100 Gigatonnes of carbon are stored in the recoverable hydrocarbons of shale formations, which is greater than seven times current annual global emissions (Pachauri et al., Contribution of Working Groups I, II and III to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. In 1PCC, Ed. Geneva, Switzerland, 2007). Given both the near field and global risks, methods to manage the present and future implications of shale production must be developed (King et al., Thirty Years of Gas Shale Fracturing: What Have We Learned? In Society of Petroleum Engineers: 2010).

[0003] The boom in shale gas extraction has been enabled largely by two technologies, horizontal drilling and hydraulic fracturing (Kerr et al., Science 2010, 328, (5986), 1624- 1626). Horizontal drilling provides access to a large area! extent of a shale formation's typically deep and thin hydrocarbon bearing zones from a single well pad. Pressurized aqueous fluids are then forced through perforations within these horizontal well segments to create dense fracture networks that cut across gas-conducting bedding planes. Proppants, most often sand, are used to keep the fractures open during fracture fluid fiowback and hydrocarbon production stages (Weaver et a!., Sustaining Fracture Conductivity. In Society of Petroleum Engineers: 2005). Following production, these flow paths cou!d enable fluid migration and contaminant transport into overlying sedimentary formations where faults and abandoned wells could then conduct these fluids into near-surface formations, posing a long-term risk to groundwater resources (Darrah et al., Proceedings of the National Academy of Sciences 2014, 201322107.).

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[0006] The following United States patents are incorporated by reference in their entirety into this application. US 7,128,153 B2. US 7,032,660 B2. US 7,077,198 B2. US 7,063,145 B2.

[0007] Fig. 1 shows an exemplary application of a method of the invention, wherein this method is used in a shale gas extraction operation.

[0008] Fig. 2 is a micrograph showing shale particles before and after carbonization according to a method of the invention.

DETAILED DESCRIPTION

N0009] A method of pumping a fluid and a reactive solid into a mineral formation, wherein the fluid reacts with the mineral formation to produce a solid reaction product is disclosed. In one embodiment the fluid comprises C0 ₂ . In another embodiment the fluid comprises water and C<¾. In one embodiment the solid reaction product is the result of a carbonation reaction. In another embodiment the solid reaction product is a calcite, amorphous silica, or other nucleation or precipitation product. In one embodiment the C0 ₂ is supercritical C0 ₂ . In another embodiment the C0 ₂ is from a waste stream. In one embodiment the water is a solution of carbonates. In another embodiment the carbonates have a concentration of greater than or equal to 0.1 M, or greater than or equal to 1.0 M, or greater than or equal to 10.0 M. In one embodiment the carbonates are carbonic acid, in another embodiment the carbonates are bicarbonates. In some embodiments the water is an alkaline solution. In some embodiments the alkaline solution has a pH of 7 or greater, or 8 or greater, or 9 or greater, or 10 or greater, or 1 1 or greater, or 12 or greater.

[00010] In one embodiment, the reactive solid comprises a mineral. In another embodiment the mineral is comprised of one or more of quartz, calcite, amorphous silica, dolomite, kaolinite, illite, mica, and others. In another embodiment the mica comprises one or more of phlogopite, muscovite, biotite, and others. In another embodiment the reactive solid comprises a divalent silicate. In another embodiment the reactive solid comprises one or more of magnesium and calcium silicate. In another embodiment the reactive solid comprises a material selected from one or more ofbrucite (Mg(OH) ₂ ), chrysotile (Mg3Si ₂ 05(OH) ₄ ), forsertite (Mg ₂ Si0 ₄ ), harzburgite (CaMgSi ₂ 0 ₆ +(Fe,Al)),olivme ((Mg, Fe)2Si0 ₄ ), orthopyroxene CaMgSi ₂ 0 ₆ +(Fe,Al)), serpentine (Mg ₃ Si ₂ Os(OH) ₄ ), wollastonite (CaSiC^), and others. In another embodiment the material consists of wollastonite (CaSi0 ₃ ).

[00011] In one embodiment the reactive solid comprises an alkaline waste product material. In another embodiment the alkaline waste product comprises a material selected from one or more of blast furnace slag from steel manufacturing, bottom ash, fly ash, kiln dust, mine tailings, municipal solid waste ash, paper mill waste, steelmaking slag, and others.

[00012] In one embodiment of the method the reaction occurs at conditions typical of a deep geological formation, for example a formation located 1000 meters below ground or deeper, or 1500 meters below ground or deeper, or 2000 meters below ground or deeper, or 2500 meters below ground or deeper, or 3000 meters below ground or deeper. For example, the reaction may occur at different pressures. In another embodiment the reaction occurs at 15-25 MPa. In another embodiment the reaction occurs at 18-22 MPa. The reaction may also occur within a range of different temperatures. In another embodiment the reaction occurs at 40-175 °C. In another embodiment the reaction occurs at 70-100 °C. In some embodiments the reaction may be pressurized by a pump.

[00013] In one embodiment of the method the reaction occurs via a dissolution reaction in which a solid donates a divalent cation, followed by a precipitation reaction in which a solid phase material nucleates within the mineral formation.

[00014] In one embodiment of the method the mineral formation is a fractured shale formation. In another embodiment the mineral formation is wellbore material. In another embodiment the mineral formation is a porous mineral formation, in another embodiment the mineral formation is a fractured mineral formation. In another embodiment an analysis is performed to determine optimum chemistry for a particular application.

[00015] In one embodiment of the method the carbonate material partially or completely seals a fissure in the mineral formation. In another embodiment the carbonate material partially or completely closes a fractured shale formation. In another embodiment the carbonate material cements the shale formation.

[00016] In one embodiment the fluid further comprises a proppant. In another embodiment the reactive solid comprises a proppant. In one embodiment the fluid further comprises a lubricant. In another embodiment the fluid further comprises a surfactant. In another embodiment the fluid is further comprised of polyolefin. [00017] In one embodiment the method is used to sequester carbon. In another embodiment the method is used to stabilize fractured shale to reduce seismicity. In another embodiment the method is used to decrease fluid connectivity to minimize leakage. In another embodiment the decrease in fluid connectivity reduces the porosity and permeability of the mineral formation. In another embodiment the reactive solid is used as a proppant, allowing the formation to settle back to its pre-fracture geometry.

[00018] In one embodiment of the method the reactive solid is first added, and the fluid is added later. In another embodiment the reactive solid is added along with a cement mixture.

[00019] In one embodiment the reactive solid comprises nanoparticles. In another embodiment the nanoparticles are designed to target leaking fractures in a mineral formation.

[00020] In one embodiment the method is used for enhanced oil recovery. In another embodiment the method is used to recover methane from methane hydrate formations.

[00021] Another aspect of this disclosure relates to a cement formed by reacting carbon dioxide with a reactive solid under deep geological formation conditions. In one embodiment the cement is a carbonate, a silicate, or a mixture of carbonates and silicates. In one embodiment the deep geological formation conditions comprise a pressure of 15-25 MPa. In another embodiment the deep geological formation conditions comprise a pressure of 18-22 MPa. In another embodiment the deep geological formation conditions comprise a temperature of 40-175 °C. In another embodiment the deep geological formation conditions comprise a pressure of 70-100 °C.

[00022] In one embodiment the cement reduces the porosity and permeability of a mineral formation.

DETAILS DESCRIPTION OF THEF FIGURES

[00023] Fig. 1 shows one potential embodiment of the method. In this embodiment, the method is used to seal a shale formation. In Fig. la, a conventional shale fracturing well operation is shown. A borehole 101 in the shale, containing a casing 102 is used to extract natural gas 105. Off of the borehole 101 may exist fractures 104 and organic materials such as kerogen 103 contained therein. Proppants 100 are used to maintain well integrity and aid in extraction of natural gas.

[00024] Fig. lb shows one potential embodiment of the method of this disclosure. Fig. lb shows a fluid 111 being pumped into the borehole along with a reactive solid 110. The fluid and reactive solid flow into the fissures and begin to react with the surrounding shale to form carbonates. Fig. lc shows the end result of the method in this embodiment, wherein a solid carbonate has formed 122 along with other possible solid byproducts such as silica 121. These solid byproducts close the fissure 123, sealing the well and trapping the C<¾ 120.

[00025] Fig. 2 shows an electron micrograph of shale particles used in Example 1 below. Fig. 2 shows the shale particles before Fig. 2a and after Fig. 2b reaction with the fluid. Precipitated solid material is visible in Fig. 2b as a bulky surface coating on the shale particles.

EXAMPLE 1

[00026] Shale samples were obtained from Ward's Scientific (Oil Shale #47E7477).

CaSi0 ₃ (99%) and CaC(¾ (99%) were obtained from Sigma-Aldrich. Food-grade liquid CO2 was supplied by Robert's Oxygen. All reagents were used as received. Solid shale samples were ground using miller jars and sieved to obtain particles with diameters in the range of 39-177 urn. Reactants were packed in a stainless steel reactor (MS-13, HIP) at a 1:5 (CaSi0 ₃ tshale) mass ratio with DI water and pressurized with C0 ₂ to the desired reaction pressure using a syringe pump (500HP - Teledyne Isco). Temperature control was achieved using an oven (Despatch Inc.) with a shaker to ensure adequate mixing during the experiment. The changes in the composition of the samples were quantified using a PANalytical X'Pert Pro Multipurpose Diffractor (XRD) unit with monochromatic Cu-Ka radiation. T1O2 was chosen as the internal reference for its distinguishable peaks relative to shale and CaC0 ₃ . The morphological and elemental composition changes of mineral samples were characterized using a Quanta 650 Scanning Electron Microscope (SEM) coupled with energy dispersive X-ray (EDS) spectroscopy.

[00027] Quantitative XRD analyses were carried out to determine the extent of reaction and conversion of wollastonite to calcite at pressure and temperature combinations characteristic of shale formations. An internal Ti02 standard was used to calibrate the intensity of calcite peaks. The results summarized in Table 1 indicate that the reaction achieved greater than 50% conversion (measured in terms of CaC03 generation) after 24 hours. Table 1

[00028] Adhesion was studied under both equilibrium and dynamic conditions under reservoir pressure and temperature conditions (50 °C and 20 MPa) and a range of pH and ionic strength in fresh and carbonated synthetic brines on pendant droplets using methods previously reported (Wang et al., Environ. Sci. Technol. 2013, 47 (1), 234-241). Seven representative minerals including quartz, calcite, amorphous silica, dolomite, kaolinite, illite, and phlogopite mica were selected since these constitute most of the minerals on the pore surfaces in sandstones (Peters, Chem. Geol. 2009, 265 (1-2), 198-208). These minerals all have hydroxyl functional groups, for example, aluminol, silanol, silanediols and bridged hydroxyls, at the solid surface and are sensitive to the adjacent aqueous phase pH and ionic strength conditions. Phlogopite mica was selected as a model mica species recognizing that many of the surface characteristics of interest in adhesion (e.g., surface functional groups, surface roughness) are shared by other mica species (i.e., muscovite and biotite).

[00029] Mineral samples were prepared by sectioning high purity rocks (Ward's Natural Science), lapping the experimental surface according to the crystal structure with a diamond grinding wheel, and then polishing them with a series of silicon carbide sanding papers down to a roughness of 1-5 urn. Some of the surfaces did not need polishing. Phlogopite cleaved easily into basal plane sheets to create surfaces that are smooth on the scale of 10 s of nanometers. The high-purity amorphous silica was not polished and used as received since it was polished at the factory (Heraeus Quarzglas). Some of the phlogopite and silica surfaces were made rougher using the sand papers in order to study the effect of roughness on adhesion. Roughness was measured using a profilometer (Dektak 8, Veeco) for the rough surfaces and an AFM (Asylum Research cypher scanning probe microscope) for smooth surfaces. Before experiments, all equipment and samples were carefully cleaned following the protocol previously described (Wang et al., Water Resour. Res. 2012, 48, (8), W08518; Wang et al., Environ. Sci. Technol. 2013, 47 (1), 234-241). Extensive care was taken to exclude any source of contamination, especially organic matter which could strongly affect wettability. All samples were flushed with at least 200 mL (~10 times pressure vessel volume) brine solution over 1 h to equilibrate the surfaces of the minerals with the aqueous phase. All experiments were repeated at least three times.

[00030] To evaluate adhesion of C(½ droplets on the mineral surface, a modified form of the advancing/receding contact angle measurement was carried out. To more closely approximate the mechanics of the 'stick-peel-crack' tests used to measure axial tensile force in solid mechanics, which is proportional to the adhesive energy and work of adhesion (Kendall, Science. 1994, 263, 1720-1725), we positioned the injection needle 1.5-3 mm below the surface and then outfitted the injection tubing with two pin valves. These two pin valves in sequence allowed for the precise control of captive C0 ₂ droplet flows into and out of the pressure cell by regulating the relative pressure of the pure C(¼ in the space between the valves and the pressure in the vessel. N ₂ control experiments were conducted under identical conditions on phlogopite and silica surfaces. Adhesion was determined based on the tendency of a C(¾ droplet to stick to the mineral surface under tensile force created by the pressure difference between the injection needle and the pressure vessel. Irregular contact lines and increased wettability were also common qualitative characteristics of adhered droplets. Table 1 explores the relationship between adhesion, ionic strength, and pressure. Table 2 explores the relationship between adhesion, mineral composition, roughness, and pressure. Experiments for Table 3 were performed at an ionic strength of 1.5 M NaCl. The error range in Tables 2 and 3 represent one standard deviation, and it should be noted that negative percentage is not realistic.

Table 3