Polymer red mud-based well killing fluid and application thereof

Abstract

A high density red mud based kill fluid composition includes a neutralized red mud, a polymeric material, and a H2S trapping agent. A method (100) of neutralizing red mud includes providing a red mud slurry (102), adding gypsum to the red mud slurry (104), and providing a neutralized red mud slurry (108). The pH range of the neutralized red mud is 7.5-9.0. A method (300) of treating an acidic well includes injecting a red mud-based kill fluid comprising neutralized red mud, a polymeric material, and a H2S trapping agent into the acidic well (302), curing the red mud-based kill fluid (304), and treating H2S gas and CO2 gas in the acidic well (306). The acidic well contains H2S gas and CO2 gas.

Description

Background Art

[0001] Recent environmental restrictions to reduce highly toxic and harmful H2S and CO2 emissions from isolated acidic petroleum reservoirs have led to the emergence of various green fluid, emulsifier, chemical surfactant, and geopolymers technologies, which are intended for use in mud formulations for hydrocarbon well killing operations. Typically, well killing operations use high-density water-based mud fluids and additives to prevent accidental blowouts from abandoned and depleted wells. In a sour well, the aim is to formulate a high-density well control fluid that can ensure the safety of well completion operations by preventing any formation fluids from entering or a large amount of climate-impacting CO2 and H2S greenhouse gases from being emitted into the environment.

[0002] Unfortunately, traditional high-density water-based well control fluids contain a large amount of free water, which can increase the content of H2S in sulfur-bearing reservoirs or easily cause water block damage to the reservoirs. Therefore, there is a need to develop a low-water or water-free high-density well control fluid formulation for high-temperature and high-pressure (HTHP) acidic reservoirs. Summary of the Invention

[0003] This summary is provided to introduce a series of concepts that will be further described in the detailed description below. This summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used as an aid in limiting the scope of the claimed subject matter.

[0004] In one aspect, embodiments disclosed herein relate to a high-density red mud-based well control fluid composition comprising a neutralized red mud slurry, a polymer material, and an H2S scavenger.

[0005] In another aspect, embodiments disclosed herein relate to a method for neutralizing red mud, which comprises providing a red mud slurry, adding gypsum to the red mud slurry, and providing a neutralized red mud slurry, wherein the pH range of the neutralized red mud slurry is from 7.5 to 9.0.

[0006] In yet another aspect, embodiments disclosed herein relate to a method for treating a sour well, which comprises injecting a red mud-based well control fluid comprising a neutralized red mud slurry, a polymer material, and an H2S scavenger into the sour well, wherein the sour well contains H2S gas and CO2 gas; curing the red mud-based well control fluid; and treating the H2S gas and CO2 gas in the sour well.

[0007] Other aspects and advantages of the claimed subject matter will be apparent from the following description and the appended claims. Brief Description of the Drawings

[0008] Figure 1 is a block flow diagram of a method for neutralizing red mud according to one or more embodiments of the present disclosure.

[0009] Figure 2 is a block flow chart of a method for preparing a red mud-based kill fluid according to one or more embodiments of the present disclosure.

[0010] Figure 3 is a block flow chart of a method for treating an acidic well according to one or more embodiments of the present disclosure.

[0011] Figure 4 is a viscosity curve graph of a red mud-based kill fluid according to one or more embodiments of the present disclosure.

[0012] Figure 5A -C is a photograph of a red mud-based kill fluid according to one or more embodiments of the present disclosure.

[0013] Figure 6A -B is an ESEM image of a red mud-based kill fluid according to one or more embodiments of the present disclosure.

[0014] Figure 7 is an EDS analysis image of a red mud-based kill fluid according to one or more embodiments of the present disclosure.

[0015] Figure 8 is a curve graph of the absorption of H2S and CO2 by a red mud-based kill fluid according to one or more embodiments of the present disclosure. Detailed Embodiments

[0016] The present disclosure generally relates to compositions and methods for well killing operations. Specifically, the disclosed compositions and methods can be used for well killing operations in acidic wells. An acidic well can be any well that produces or is capable of producing acidic gases. As can be understood by those of ordinary skill in the art, the term "acidic gas" can be used to describe a gas contaminated with sulfur or sulfur compounds, particularly a gas contaminated with hydrogen sulfide (H2S). Acidic gases can also include other gases that cause corrosion, such as, for example, CO2. Thus, the compositions and methods for well killing operations disclosed herein can also treat acidic gases.

[0017] The composition according to the present disclosure can include a red mud-based kill fluid. The red mud-based kill fluid can include a neutralized red mud slurry, a polymeric material, and an H2S scavenger. Methods for preparing a neutralized red mud slurry are disclosed herein. The compositions of one or more embodiments can be used to treat acidic gases in an acidic well and to kill the acidic well. In some embodiments, the compositions and methods disclosed herein can simultaneously achieve the treatment and well killing of an acidic well.

[0018] Method for neutralizing red mud

[0019] In one aspect, embodiments of the present disclosure relate to a method for neutralizing waste red mud. Red mud, also known as spent bauxite residue and bauxite tailings, is a highly corrosive waste product generated by the Bayer process, in which alumina is extracted from bauxite. More than 95% of the world's total alumina production is produced by the Bayer process, and for every ton of alumina produced by the Bayer process, approximately 1 to 1.5 tons of red mud are generated. The red mud generated during the extraction of alumina from bauxite is characterized by a high pH value (usually between pH 11 - 14) and high concentrations of soluble ions, and contains little to no organic matter. Due to its high alkalinity, red mud is considered toxic to the environment. However, the present disclosure describes methods and compositions for using waste red mud to address environmental problems encountered in the oil and gas industry.

[0020] In such compositions and methods, the red mud can be neutralized so that it is no longer corrosive to the environment. Accordingly, one or more embodiments disclose a method for neutralizing red mud. The method can include mixing waste red mud and gypsum to provide a neutralized red mud slurry. The neutralized red mud slurry can then be used in the compositions and methods for well killing operations disclosed herein.

[0021] Typically, strong acids such as HCl, HNO3, H2SO4, and CH3COOH are used to neutralize red mud on a small scale. However, for large-scale industrial applications in the oil field, the reason for not using strong acids is the high cost of purchasing large quantities of acidic reagents. Thus, it is notable that the method for neutralizing red mud according to the present disclosure does not include strong acids.

[0022] Figure 1 The method for neutralizing red mud is shown and discussed with reference to Figure 1 First, method 100 includes providing a red mud slurry 102. The red mud slurry can be collected from a dump site of any alumina production facility. In one or more embodiments, the red mud slurry includes an aqueous fluid and one or more minerals. The aqueous fluid includes water. The water can be distilled water, deionized water, tap water, fresh water from surface or underground sources, production water, formation water, synthetic seawater, black water, brown water, drinking water, non-drinking water, other water, and combinations thereof, which are suitable for use in a wellbore environment. In one or more embodiments, the water used may naturally contain contaminants such as salts, ions, minerals, organic matter, and combinations thereof, which do not interfere with the neutralization of the red mud slurry.

[0023] In one or more embodiments, the red mud slurry includes water in an amount ranging from about 20 wt% to 40 wt% based on the total weight of the red mud slurry. In a specific embodiment, the red mud slurry contains less than about 40 wt% of water based on the total weight of the red mud slurry.

[0024] As shown above, the red mud slurry may contain one or more minerals. Exemplary minerals that may be present in the waste red mud slurry include, but are not limited to, larnite (Ca2(SiO4)), sodalite ((NaCa)8(AlSiO4)6(CO3SO4)2·2H2O), hematite (Fe2O3), goethite (FeO(OH)), calcite (CaCO3), perovskite (CaTiO3), grossite (CaAl4O7), quartz (SiO2), gibbsite (Al(OH)3), and combinations thereof. The mineral composition of the red mud slurry can be determined by X-ray powder diffraction (XRD). In some embodiments, the elemental composition of the red mud slurry contains one or more elements, including but not limited to Fe, Al, Na, Si, Ca, Ti, S, Zn, Sr, Mg, P, Cr, K, Mn, Ce, Pb, Ni, Th, and combinations thereof. The elemental composition of the red mud slurry can be determined by XRD.

[0025] In one or more embodiments, based on the total weight of the red mud slurry, the red mud slurry includes one or more minerals in a content range of 50 to 70 wt%. For example, one or more minerals may be present in the red mud slurry in a content range from one of the lower limits 50, 52, 54, 56, 58, and 60 wt% to one of the upper limits 60, 62, 64, 66, 68, and 70 wt%, where any lower limit can be paired with any mathematically compatible upper limit.

[0026] The red mud slurry may have a high alkalinity. As will be understood by those of ordinary skill in the art, alkalinity can be measured by pH, where a pH above 7.0 is considered basic or alkaline. In one or more embodiments, the red mud slurry may have a pH in the range of 11.0 to 14.0. For example, the pH range of the red mud slurry can be from one of the lower limits 11.0, 11.5, 12.0, and 12.5 to one of the upper limits 12.5, 13.0, 13.5, and 14.0, where any lower limit can be paired with any mathematically compatible upper limit. In a specific embodiment, the red mud slurry may have a pH in the range of 12.5 to 13.0.

[0027] Then, method 100 includes adding gypsum 104 to the provided red mud slurry. Gypsum, a soft mineral composed of calcium sulfate dihydrate (CaSO4·2H2O), is commonly used as a fertilizer. However, in the present disclosure, gypsum can be used as a neutralizing agent for highly alkaline red mud slurry.

[0028] In one or more embodiments, the gypsum is added to the red mud slurry in the form of a gypsum solution. The gypsum solution can include gypsum and an aqueous fluid. The aqueous fluid includes water, which can be the same water as described for the aqueous fluid of the red mud slurry above. In one or more embodiments, the aqueous fluid of the gypsum solution is the same as the aqueous fluid of the red mud slurry.

[0029] Based on the total weight of the gypsum solution, the gypsum solution may contain gypsum in a concentration range of 5.0 to 25 wt%. For example, in one or more embodiments, the concentration of gypsum in the gypsum solution ranges from one of the lower limits 5.0, 10, and 15 wt% to one of the upper limits 15, 20, and 25 wt%, where any lower limit can be paired with any mathematically compatible upper limit.

[0030] Gypsum can be added to the red mud in an amount sufficient to neutralize the corrosive minerals in the red mud. The red mud is considered neutralized when the pH range of the red mud is from about 7.5 to 9.0. In one or more embodiments, gypsum can be added to the red mud in a molar ratio of gypsum to red mud in the range of about 0.2:1 to about 0.4:1. For example, gypsum can be added to the red mud in an amount such that the molar ratio of gypsum to red mud ranges from one of the lower limits 0.2:1, 0.25:1, and 0.3:1 to one of the upper limits 0.3:1, 0.35:1, and 0.4:1, where any lower limit can be paired with any mathematically compatible upper limit.

[0031] In one or more embodiments, gypsum is added to the red mud at ambient temperature and pressure. The reaction between the red mud and gypsum may be exothermic. Therefore, gypsum can be added slowly (e.g., drop by drop) to the red mud to keep the reaction temperature around ambient temperature. In a specific embodiment, the reaction temperature can be kept below 47 °C. Additionally, to maintain the ambient conditions, a reaction vessel containing the red mud for regulating temperature and pressure can be equipped, such as equipped with a chiller or an ice-water bath. For example, on a large scale, the reaction vessel can be an industrial-type stainless steel batch reactor equipped with a circulating ice-water bath to ensure the required conditions. In one or more embodiments, the red mud is stirred during and after the addition of gypsum. The red mud can be stirred for a time in the range of about 3 to about 6 hours. For example, in one or more embodiments, the time for stirring the red mud ranges from one of the lower limits 3.0, 3.5, 4.0, and 4.5 hours to one of the upper limits 4.5, 5.0, 5.5, and 6.0 hours, where any lower limit can be paired with any mathematically compatible upper limit.

[0032] In method 100, after adding gypsum to the red mud and while stirring the red mud, one or more calcium-containing mineral complexes 106 are formed. One or more calcium-containing mineral complexes can be formed by replacing the Na 2+ ions in the red mud with Ca + ions in the gypsum. In one or more embodiments, exemplary calcium-containing mineral complexes that can be formed include, but are not limited to, tricalcium aluminate (Ca3Al2(OH)2), hydrocalumite (Ca3Al2(OH) 12 CaCO3·5H2O), ettringite (Ca3Al2(OH)12 ·3CaSO4·26H2O), and combinations thereof. The following reaction equations (1-3) show the process of forming three exemplary calcium-containing mineral complexes by replacing Na 2+ with Ca + and forming three exemplary calcium-containing mineral complexes.

[0033]

[0034] In a specific embodiment, one or more calcium-containing mineral complexes include all three of tricalcium aluminate, hydrocalumite, and ettringite.

[0035] Finally, in method 100, a neutralized red mud slurry 108 is provided. After the red mud is neutralized and one or more calcium-containing mineral complexes are formed, the reaction can be stirred for a sufficient length of time under ambient conditions. In one or more embodiments, the reaction is stirred for a sufficient length of time to provide a neutralized red mud slurry with high uniformity and a suitable pH value. The sufficient length of time can range from 2.0 to 4.0 hours. For example, to provide a neutralized red mud slurry with desired properties, the stirring time of the reaction can range from one of the lower limits 2.0, 2.5, and 3.0 hours to one of the upper limits 3.0, 3.5, and 4.0 hours, where any lower limit can be paired with any mathematically compatible upper limit.

[0036] As described above, the reaction can be stirred until a neutralized red mud with desired properties is provided. Therefore, during the stirring process, various properties of the reaction can be monitored. Properties such as temperature, pH, uniformity, etc. can be monitored. In one or more embodiments, changes in these properties can indicate the degree of completion of the neutralization reaction. For example, due to the incorporation of gypsum and the reaction with gypsum, the neutralized red mud slurry can exhibit higher uniformity. Similarly, due to the neutralization of alkaline components, the pH of the neutralized red mud slurry may be lower. In a specific embodiment, the pH value of the reaction is monitored and the pH value of the reaction is used to determine the degree of completion of the reaction by indicating the neutralization of the red mud. The pH can be monitored according to methods known in the art.

[0037] In one or more embodiments, when the pH of the reaction is in the range of 7.5 to 9.0, the reaction can be completed and the red mud slurry is neutralized. For example, the pH range of the neutralized red mud slurry can be from one of the lower limits 7.5, 8.0, and 8.5 to one of the upper limits 8.0, 8.5, and 9.0, where any lower limit can be paired with any mathematically compatible upper limit. In a specific embodiment, the pH range of the neutralized red mud slurry can be from 8.5 to 9.0.

[0038] In one or more embodiments, the neutralized red mud slurry prepared according to method 100 can be used on-site without any further purification.

[0039] Kill fluid composition

[0040] In another aspect, embodiments disclosed herein relate to a composition for killing a well in an acidic well. The composition can be a red mud-based well-killing fluid. The well-killing fluid composition can include a neutralized red mud slurry, a polymeric material, and an H2S scavenger. In order to effectively kill a well in an acidic well, such a composition can have a high density and the ability to absorb acidic gases.

[0041] In one or more embodiments, the composition includes a neutralized red mud slurry. The neutralized red mud slurry can be prepared according to the method 100 described above. Thus, the neutralized red mud slurry can include the aqueous fluid and one or more calcium-containing mineral complexes as described previously.

[0042] One or more calcium-containing mineral complexes contained in the neutralized red mud slurry can have weighting agent properties, i.e., they can impart a high density to the slurry. Thus, the red mud-based well-killing fluid composition can include a neutralized red mud slurry in an amount sufficient to provide a suitable density to the composition. Thus, based on the total weight of the well-killing fluid composition, the neutralized red mud slurry can be present in the well-killing fluid composition in an amount in the range of 70 to 98 wt%. For example, in one or more embodiments, the well-killing fluid composition includes a neutralized red mud slurry in an amount ranging from one of the lower limits 70, 75, and 80 wt% to an upper limit of 85 wt%, where any lower limit can be paired with any mathematically compatible upper limit.

[0043] In one or more embodiments, the red mud-based well-killing fluid composition includes a polymeric material. The polymeric material can be any polymeric material known in the art that can be used as a fluid loss control agent, such as, for example, starch, xanthan gum, and carboxymethyl cellulose. In one or more embodiments, the polymeric material is a polysaccharide. The polysaccharide can be included in the well-killing fluid composition in the form of a powder, such as a microcrystalline powder. The polysaccharide can be cellulose. Without being bound by any theory, the free hydroxyl groups located in the cellulose ring structure and the β-1,4-glycosidic bond-linked D-glucopyranose units present in its polymer backbone can provide enhanced viscosity and fluid loss control properties to the red mud-based well-killing fluid. Those of ordinary skill in the art will understand that cellulose is mainly derived from cotton fibers and wood. However, cellulose is present in, and may be derived from, various other plant fibers, such as corn cobs or corn stalks, soybean hulls, sugarcane stalks, oat hulls, rice husks, wheat straw, beet pulp, and bamboo, among others. In one or more embodiments, the polymeric material is cellulose derived from a fiber other than cotton fiber or wood. In a specific embodiment, the polymeric material is corn-based cellulose.

[0044] The polymeric material can be included in the red mud-based kill fluid in an amount sufficient to impart an appropriate viscosity to the kill fluid. In one or more embodiments, based on the total weight of the kill fluid composition, the polymeric material can be included in the kill fluid composition in an amount of 1.0 to 20 wt%. For example, in one or more embodiments, the amount of the polymeric material included in the kill fluid composition ranges from one of the lower limits of 17, 18, and 19 wt% to one of the upper limits of 18, 19, and 20 wt%, wherein any lower limit can be paired with any mathematically compatible upper limit. In another embodiment, the range of the polymeric material is 13.5 to 15 wt%.

[0045] In one or more embodiments, the red mud-based kill fluid composition includes an H2S scavenger. Any compound known in the art that exhibits H2S absorption, neutralization, and / or conversion can be used as the H2S scavenger in the present composition. Suitable H2S scavengers include, but are not limited to, silver nitrate, sodium hydroxide, ferric chloride, ferrous sulfate, zinc acetate, and copper sulfate. In one or more specific embodiments, the H2S scavenger is zinc acetate.

[0046] An amount of the H2S scavenger sufficient to give the kill fluid suitable H2S absorption properties can be included in the red mud-based kill fluid. In one or more embodiments, based on the total weight of the kill fluid composition, the red mud-based kill fluid includes the H2S scavenger in an amount ranging from 1.0 to 9.0 wt%. For example, in one or more embodiments, the amount of the H2S scavenger included in the red mud-based kill fluid composition ranges from one of the lower limits of 1.0, 2.0, 3.0, 4.0, and 5.0 wt% to one of the upper limits of 5.0, 6.0, 7.0, 8.0, and 9.0 wt%, wherein any lower limit can be paired with any mathematically compatible upper limit.

[0047] Kill fluid properties

[0048] As described above, the red mud-based kill fluid composition can have various properties capable of simultaneously performing well killing and treating acidic gases in the well. For example, the kill fluid composition in one or more embodiments can be formulated to have a specific density, viscosity, H2S absorption property, and CO2 absorption property, etc.

[0049] In one or more embodiments, the red mud-based kill fluid has a high density. As previously mentioned, one or more calcium-containing mineral complexes can act as weighting agents to impart such a high density to the kill fluid. The density of the kill fluid may be high enough to generate a hydrostatic pressure sufficient to cut off the fluid flowing into the well at the inflow point of the wellbore. Thus, the kill fluid can form a plugging layer in the wellbore.

[0050] The density range of the red mud-based kill fluid composition can be from 11 to 15 pounds per gallon (ppg). For example, in one or more embodiments, the density range of the kill fluid is from one of the lower limits 11, 11.5, 12, 12.5, and 13 ppg to one of the upper limits 13, 13.5, 14, 14.5, and 15 ppg, where any lower limit can be paired with any mathematically compatible upper limit. Similarly, the red mud-based kill fluid composition may have a high specific gravity. The specific gravity range of the kill fluid can be from 1.2 to 1.8 g / cm 3 . For example, in one or more embodiments, the specific gravity range of the kill fluid is from one of the lower limits 1.2, 1.3, 1.4, and 1.5 g / cm 3 to one of the upper limits 1.5, 1.6, 1.7, and 1.8 g / cm 3 , where any lower limit can be paired with any mathematically compatible upper limit.

[0051] In one or more embodiments, the red mud-based kill fluid composition has a high viscosity. As previously mentioned, the high viscosity of the kill fluid can be achieved through the presence of a polymeric material. The kill fluid composition can have a high viscosity to minimize fluid loss in the well.

[0052] In one or more embodiments, the viscosity of the red mud-based kill fluid measured by a rotational viscometer can range from 30 to 70 millipascal-seconds (mPa·s). For example, in one or more embodiments, the viscosity range of the kill fluid composition can be from one of the lower limits 30, 35, 40, 45, and 50 mPa·s to one of the upper limits 50, 55, 60, 65, and 70 mPa·s, where any lower limit can be paired with any mathematically compatible upper limit. In one or more embodiments, the viscosity of the red mud-based kill fluid increases with increasing temperature. For example, the kill fluid may have a viscosity of approximately 30 millipascal-seconds (mPa·s) at 70 °C, and the viscosity may increase to approximately 60 mPa·s at 125 °C. Therefore, the red mud-based kill fluid may exhibit a high viscosity under reservoir conditions such as high temperature and high pressure.

[0053] In one or more embodiments, the red mud-based kill fluid composition has a sufficiently neutral pH. A sufficiently neutral pH may not be alkaline or acidic and may thus be rather inert. According to the present disclosure, a suitable pH range that can be considered sufficiently neutral can be from 7.5 to 9.5. Therefore, in one or more embodiments, the pH range of the kill fluid composition is from one of the lower limits 7.5, 8.0, and 8.5 to one of the upper limits 8.5, 9.0, and 9.5, where any lower limit can be paired with any mathematically compatible upper limit. In a specific embodiment, the pH range of the red mud-based kill fluid can be from 8.0 to 8.5.

[0054] In one or more embodiments, when exposed to high temperatures, the red mud-based kill fluid exhibits enhanced stability and crystallinity. The stability of the red mud-based kill fluid can be determined by the mineral composition and gelling properties of the fluid. For example, at 70 °C, the fluid composition can solidify, and at 125 °C, the composition can crystallize. The crystallized composition can be characterized by scanning electron microscopy (SEM) images and energy-dispersive X-ray spectroscopy (EDS) analysis. EDS analysis can provide the elemental composition of the crystallized composition. In one or more embodiments, the elemental composition of the crystallized kill fluid mainly includes C, Ca, Na, Al, Fe, and Zn. Trace elements that may be present in the crystallized composition include, but are not limited to, Si, Ti, O, and Cl.

[0055] As previously mentioned, the kill fluid compositions disclosed herein may be capable of treating acidic gases. In one or more embodiments, the composition can treat the acidic gases generated by the well while killing the well. Alternatively, the composition can first kill the well and subsequently treat any acidic gases in the well. Whether the treatment and well killing are carried out simultaneously or stepwise, after successful well killing, the red mud-based kill fluid can continue to treat the acidic gases for a sufficient length of time.

[0056] Therefore, the kill fluid composition may be capable of absorbing acidic gases including H2S and CO2. In one or more embodiments, the red mud-based kill fluid has a high H2S and CO2 absorption efficiency. The red mud-based kill fluid can have an absorption efficiency that causes the concentrations of H2S and CO2 to gradually decrease over time. For example, the initial concentration range of H2S and CO2 gases in an acidic well can be from about 6 to about 10 wt%. After exposure to the red mud-based kill fluid of one or more embodiments, the concentrations of H2S and CO2 gases in the well can be less than 1 wt%. Therefore, in one or more embodiments, the kill fluid composition can reduce the concentrations of H2S and CO2 gases in an acidic well by about 80 to 100%. For example, the kill fluid composition may be capable of reducing the concentrations of H2S and CO2 gases in an acidic well by an amount ranging from one of the lower limits 80%, 82%, 84%, 86%, 88%, and 90% to one of the upper limits 90%, 92%, 94%, 96%, 98%, and 100%, where any lower limit can be paired with any mathematically compatible upper limit.

[0057] In one or more embodiments, the absorption efficiency increases at high temperatures. The increase in temperature may enhance the nucleation, aggregation, and adsorption properties of the main minerals, thereby forming ionic and covalent bonds with H2S and CO2 through a precipitation process. Further increase in temperature may cause the precipitated salts to solidify and subsequently incorporate into the crystallized red mud fluid.

[0058] Not bound by any theory, the red mud-based kill fluid composition may have high absorption efficiency because it can react with acidic gases through both carbonation and sulfidation reactions from the liquid phase to the gel phase. Thus, in one or more embodiments, the sulfidation and carbonation reactions cause the red mud-based kill fluid to change from the liquid phase to the gel phase and from the gel phase to the solid phase. Such a process may depend on the mineral composition, gelation rate (viscosity), and reservoir temperature. In one or more embodiments, CO2 gas can react with the red mud-based kill fluid composition according to one or more of the following carbonation reactions (4-6):

[0059]

[0060] where M is Ca 2+ , Fe 2+ , Na + or a combination thereof. As shown in carbonation reactions 4-6, in the presence of hydroxide ions, monovalent metals, divalent metals, trivalent metals, and aluminates, harmful CO2 can be converted into various metal carbonates and bicarbonates. According to the present disclosure, such ions and ion complexes can be present in the red mud-based kill fluid composition.

[0061] In one or more embodiments, H2S gas can react with the red mud-based kill fluid composition according to one or more of the following sulfidation reactions (7-9):

[0062]

[0063] where Y is Zn 2+ , Fe 2+ , Na + or a combination thereof, and YO is ZnO, FeO, or a combination thereof. As shown in sulfidation reactions 7-9, in the presence of hydroxide ions, monovalent metals, and divalent metals, harmful H2S can be converted into various metal sulfides. According to the present disclosure, these ions and metals can be present in the red mud-based kill fluid composition.

[0064] The red mud-based kill fluid composition exhibiting one or more of the above properties can be used in kill well operations. Thus, the kill fluid composition in one or more embodiments can provide efficient and effective acidic gas treatment while plugging and killing the well.

[0065] Method for preparing kill fluid composition

[0066] One or more embodiments of the present disclosure relate to a method for preparing the red mud-based kill fluid composition as described above. The method can include providing a solution including a polymer material and an H2S scavenger, and subsequently introducing the solution into a neutralized red mud slurry.

[0067] The method for preparing the red mud-based kill fluid composition is as Figure 2as shown and with reference to Figure 2 is discussed. As Figure 2 shown, method 200 first includes providing a solution 202 that includes a polymeric material and an aqueous fluid. The polymeric material is as described above.

[0068] In one or more embodiments, based on the total weight of the solution, the amount of the polymeric material included in the solution ranges from 10 to 40 wt%. For example, the amount of the polymeric material present in the solution can range from one of the lower limits 10, 15, 20, and 25 wt% to one of the upper limits 30, 32, 35, 37, and 40 wt%, where any lower limit can be paired with any mathematically compatible upper limit.

[0069] As described above, the solution can include an aqueous fluid. The aqueous fluid includes water. The water can be distilled water, deionized water, tap water, fresh water from surface or underground sources, produced water, formation water, natural and synthetic brines, brackish water, natural and synthetic seawater, black water, brown water, gray water, blue water, potable water, non-potable water, other water, and combinations thereof, which are suitable for use in a wellbore environment.

[0070] In one or more embodiments, based on the total weight of the solution, the solution includes an aqueous fluid in an amount ranging from 60 to 90 wt%. For example, the amount of the aqueous fluid present in the solution can range from one of the lower limits 60, 62, 65, 67, and 70 wt% to one of the upper limits 75, 80, 85, and 90 wt%, where any lower limit can be paired with any mathematically compatible upper limit.

[0071] The solution can be stirred for a sufficient length of time to achieve a suitable homogeneity. The solution can be stirred according to methods known in the art, such as, for example, using an electric mixer. The sufficient length of time can range from about 30 minutes to about 3 hours. For example, in one or more embodiments, the time for stirring the solution ranges from one of the lower limits 0.5, 0.7, 1.0, and 1.5 hours to one of the upper limits 2.0, 2.5, 2.7, and 3.0 hours, where any lower limit can be paired with any mathematically compatible upper limit.

[0072] Then, method 200 includes adding an H2S scavenger 204 to the solution that includes the polymeric material. The H2S scavenger is as described above. In one or more embodiments, the H2S scavenger is added to the solution such that the amount of the H2S scavenger included in the solution ranges from 5.0 to 20 wt% based on the total weight of the solution. For example, the amount of the H2S scavenger present in the solution can range from one of the lower limits 5.0, 6.0, 7.0, 8.0, 9.0, and 10 wt% to one of the upper limits 10, 12, 15, 17, and 20 wt%, where any lower limit can be paired with any mathematically compatible upper limit.

[0073] In one or more embodiments, a solution comprising a polymeric reagent and an H2S scavenger is stirred for a period of time. The solution can be stirred to uniformly mix the polymeric reagent and the H2S scavenger throughout the solution. In one or more embodiments, the solution is stirred for a time ranging from about 1.0 to about 6.0 hours. For example, the solution comprising the polymeric material and the H2S scavenger can be stirred for a time ranging from one of the lower limits 1.0, 1.5, 2.0, 2.5, and 3.0 hours to one of the upper limits 4.0, 4.5, 5.0, 5.5, and 6.0 hours, where any lower limit can be paired with any mathematically compatible upper limit.

[0074] Finally, method 200 includes mixing the solution with the neutralized red mud slurry 206 to provide a red mud-based kill fluid according to the present disclosure. In one or more embodiments, the neutralized red mud slurry is prepared using gypsum according to the neutralization method (method 100) described previously. Such embodiments may be preferred because the neutralization method does not require the use of corrosive chemicals such as strong acids.

[0075] To provide a red mud-based kill fluid having suitable properties such as, for example, viscosity and density, the kill fluid can be stirred for a period of time. In one or more embodiments, a mechanical stirrer is used to continuously stir the kill fluid. After stirring for a period of 8 to 24 hours, a red mud-based kill fluid having the desired properties can be obtained. For example, in one or more embodiments, the kill fluid composition is stirred for a time ranging from one of the lower limits 8, 10, 12, 14, and 16 hours to one of the upper limits 16, 18, 20, 22, and 24 hours, where any lower limit can be paired with any mathematically compatible upper limit.

[0076] Method for killing and treating acid wells

[0077] In yet another aspect, embodiments of the present disclosure relate to a method of using the above-described red mud-based kill fluid composition. The method can include plugging the bottom section of a well using a pump and pull placement technique.

[0078] Compared to a conventional pump and plug method, the pump and pull technique is an alternative method for improving the placement of kill fluid in deviated and horizontal wellbores. Figure 3Method 300 of using a red mud-based kill fluid in a well killing operation according to pumping and pulling techniques, including the treatment of sour gas, is shown. In method 300, the red mud-based kill fluid in one or more embodiments is injected into well 302. In one or more embodiments, the well is a sour well. The kill fluid can be injected into the well to render the well no longer capable of producing hydrocarbons or other downhole liquids and gases. The kill fluid can be pumped into the well by extending a work string from the bottom to the top of the well to achieve proper mud circulation and displacement.

[0079] In one or more embodiments, the red mud-based kill fluid can be pumped into the well to ensure that the red mud-based kill fluid is adequately placed in the bottom section of the well. Depending on the diameter and depth of the wellbore, the pumping time of the kill fluid can range from about 10 to about 30 minutes. Typically, the red mud-based kill fluid can be pumped for about 15 minutes. After the placement of the kill fluid, the tubing string can be carefully removed from the mud to avoid plugging interference. In one or more embodiments, the pumping and pulling techniques are repeated up to 3 times with the same volume of kill fluid until the entire well section is plugged to prevent sour gas emissions.

[0080] After injecting the red mud-based kill fluid into the well, method 300 includes curing the red mud-based kill fluid 304 in the well. As described above, under reservoir conditions such as high temperature and high pressure, the kill fluid may cure into a plug under reservoir conditions. Thus, once the red mud-based kill fluid is injected into the well and exposed to downhole temperature, the kill fluid may exist in a solid to crystalline phase to plug the well. Therefore, the kill fluid can effectively inhibit the production of the well.

[0081] Finally, in method 300, the sour gas present in the well can be treated 306 after being exposed to the red mud-based kill fluid. In one or more embodiments, H2S and CO2 gases react with the kill fluid through the above-mentioned sulfidation and carbonation reactions (equations 4-9) to form non-toxic metal sulfides, carbonates, and bicarbonates. As described above, the kill fluid can reduce the amount of sour gas in the well by about 80% to 100%.

[0082] Examples

[0083] The reagent-grade chemicals used in the following examples include zinc acetate (ZnOAc) obtained from Sigma-Aldrich. Gypsum (CaSO4·2H2O) minerals from local sources and corn-based microcrystalline cellulose powder were used to reduce the cost of the red mud-based well-killing fluid formulation. The waste red mud (RM) from Ma’aden Saudi Arabian Aluminum Company was collected from the waste dump after alumina recovery during the digestion process. The measured pH of the waste red mud was 12.8 and it contained approximately 39% free water and 61% of one or more minerals. Sub-samples were subjected to heating acid digestion in 10 mL perchloric acid, 10 mL nitric acid, and 2 mL hydrofluoric acid, and the following elemental abundances were revealed by inductively coupled plasma mass spectrometry (ICP-MS): Fe, Al, Na, Si, Ca, Ti, Zn, Sr, Cr, K, Mg, Mn, Ce, Pb, Ni, Th, S, and P. The mineral composition of the waste red mud characterized by powder X-ray diffraction (XRD) showed the following minerals: larnite (Ca2(SiO4)), cancrinite ((NaCa)8(AlSiO4)6(CO3SO4)2·2H2O), hematite (Fe2O3), goethite (FeO(OH)), calcite (CaCO3), perovskite (CaTiO3), grossite (CaAl4O7), quartz (SiO2), and gibbsite (Al(OH)3).

[0084] Red mud neutralization

[0085] The red mud slurry (3.0 L) was poured into a 10-L industrial-type borosilicate glass reactor equipped with a mechanical stirrer, thermostat, pH meter, and recirculating cooler to maintain the reaction at room temperature (about 25 °C). A 15 wt% gypsum solution was added to the red mud slurry with continuous stirring. The red mud slurry was stirred with an electric mixer for 3 hours until a homogeneous solution with a pH of 8.7 was obtained.

[0086] The presence of salts and other ions in the red mud increased the solubility of gypsum during the neutralization process. Additionally, according to the key reactions shown in Equations 1-3, the Ca in gypsum 2+ reacted to displace the Na in the caustic complex + , reducing the pH of the red mud slurry to 8.7 and forming hydro-phase minerals, including: tricalcium aluminate (Ca3Al2(OH)2), calcium aluminate hydrate (Ca3Al2(OH) 12 CaCO3·5H2O), and ettringite (Ca3Al2(OH) 12 ·3CaSO4·26H2O).

[0087] Preparation of red mud-based kill fluid

[0088] Dissolve approximately 515 grams of corn-based microcrystalline cellulose powder in 1.0 L of deionized water. Mix the solution for 1 hour using an electric mixer, and then add 181.5 grams of zinc acetate. After mixing for approximately 2 hours, slowly add the mixture to the neutralized red mud slurry in a borosilicate glass reactor. Then continuously stir the mixture overnight with a mechanical stirrer to produce a slightly red, gel-like, viscous red mud-based fluid that can be pumped as a high-density kill fluid to control the release of acid gas pollutants into the environment.

[0089] Evaluation of the Properties of Red Mud-based Kill Fluids

[0090] In laboratory studies, various properties of the red mud-based kill fluid of the present invention were determined using a Baroid mud balance, a Mettler-Toledo bench pH meter, and a Fann viscometer. The properties, including mud density, specific gravity, pH, and the estimated range of fluid viscosity, are shown in Table 1 below. The range of fluid viscosity was estimated based on the viscosity curve shown in Figure 4 .

[0091] Table 1. General Properties of an Exemplary Red Mud-based Kill Fluid Composition

[0092] Mud properties Density (ppg) <![CDATA[Specific gravity (g / cm 3 )]]> pH Viscosity (mPa·s) Range (repeated) 12.4–12.7 1.49-1.52 7.9–8.3 59.8–60.3 Average value 12.55 1.51 8.2 60.1

[0093] The overall properties of the red mud-based kill fluid formulation of the present invention indicate that the pH, mud density, and the observed specific gravity of 1.51 g / cm 3 to some extent exceed the standard specifications of a reservoir kill fluid with a density of 1.40 g / cm 3 . Although the viscosity of the kill fluid decreases over time, the viscosity of the heated product increases rapidly, reaching an optimal temperature of 125 °C (as shown in Figure 4 ). This observation indicates that the disclosed kill fluid has good rheological properties under reservoir conditions. Therefore, the red mud-based kill fluid formulation can be easily applied to many oil and gas field drilling, workover, and completion operations.

[0094] Upon physical inspection, the exemplary red mud-based kill fluid exhibits unique microstructural and gel-forming characteristics, and its stability, solidification, and crystallization processes are enhanced when heated under high-temperature reservoir conditions. Figure 5A -B shows the change in the crystallinity of the red mud-based kill fluid with increasing temperature. Specifically, Figure 5A shows an exemplary red mud-based kill fluid including a corn-based cellulose polymer reagent at ambient temperature. Figure 5B shows the red mud-based kill fluid after heating to 70 °C, at which point the fluid has slightly solidified, and Figure 5C shows the red mud-based kill fluid after heating to 125 °C, at which point the changes in the microstructure become visible. Through environmental scanning electron microscope (ESEM) images ( Figure 6A and6B ) and the corresponding energy dispersive X-ray spectroscopy (EDS) analysis (in general area analysis mode) were carried out on the kill fluid after heating to 125 °C for further morphological characterization, confirming the presence of C, Ca, Al, Na, Fe, and Zn as the main elements in the crystalline material ( Figure 7 ). However, Si, Ti, O, and Cl were also found as minor elements in the red mud-based kill fluid of the present invention.

[0095] The predominance of these main elements can be attributed to the preservative properties, stability, and enhancing properties of red mud, which exhibits unique mineralogical and density characteristics and can be easily made into sustainable additives for kill or drilling fluids.

[0096] Gas absorption test

[0097] Briefly, the absorption test was carried out by slowly pumping 3.5 kg of an exemplary red mud-based kill fluid through a peristaltic pump into a stainless-steel core flooding unit containing a sour petroleum source rock charged with 5.9 wt% H2S and CO2 and 7.1 wt% CO2. Once the unit was completely filled with the red mud-based kill fluid, the temperature and pressure were increased from 0 to 150 °C and from 0 to 1000 psi, respectively. The CO2 absorption peak was monitored using an in-situ filter array spectrometer and the absorption of H2S by the red mud-based kill fluid under reservoir conditions was measured using an in-situ electrochemical analyzer to record the reservoir fluid CO2 and H2S levels in real time.

[0098] Figure 7 The absorption efficiency results of an exemplary red mud-based kill fluid are shown, which is capable of reacting with acid gases through both liquid-to-gel phase carbonation and sulfidation reactions. Based on the steady decline in the acid gas concentration under different temperature and pressure conditions (as Figure 7 shown), it is assumed that the carbonation and sulfidation reactions shown in Equation 4-9 occur in the presence of hydroxide ions, monovalent, divalent, trivalent metals, and residual aluminum in the form of aluminate ([Al(OH4] - ).

[0099] Embodiments of the present disclosure may provide at least one of the following advantages. The red mud-based kill fluid composition according to the present disclosure includes inexpensive and non-toxic components and can be used for kill operations in acid wells. Such a kill fluid composition can reduce the H2S and CO2 gas concentrations in acid wells by at least 80%, while effectively plugging and killing the wells. Therefore, the red mud-based kill fluid can provide a practical and cost-effective solution for the hydrocarbon energy industry to explore undeveloped sour reservoirs, while also alleviating environmental problems associated with acid gas emissions during drilling and workover operations.

[0100] Although only a few example embodiments have been described in detail above, those skilled in the art will readily appreciate that many modifications may be made to the example embodiments without materially departing from the invention. Accordingly, all such modifications are intended to be included within the scope of the present disclosure as defined by the following claims.

Claims

1. A high-density red mud-based kill fluid composition, comprising: Neutralized red mud slurry; Polymer material; And H2S scavenger.

2. The composition according to claim 1, wherein the neutralized red mud slurry comprises water.

3. The composition according to claim 1 or 2, wherein the neutralized red mud comprises one or more calcium-containing mineral complexes selected from the group consisting of tricalcium aluminate (Ca3Al2(OH)2), hydrocalumite (Ca3Al2(OH) 12 CaCO3·5H2O), ettringite (Ca3Al2(OH) 12 ·3CaSO4·26H2O), and combinations thereof.

4. The composition according to claim 3, wherein the one or more calcium-containing mineral complexes are tricalcium aluminate (Ca3Al2(OH)2), hydrocalumite (Ca3Al2(OH) 12 CaCO3·5H2O), and ettringite (Ca3Al2(OH) 12 ·3CaSO4·26H2O).

5. The composition according to any one of claims 1-4, wherein the polymer material is a microcrystalline powder.

6. The composition according to any one of claims 1-4, wherein the polymer material is corn-based cellulose.

7. The composition according to any one of claims 1-6, wherein the H2S scavenger is zinc acetate (ZnOAc).

8. The composition according to any one of claims 1-7, wherein the density range of the composition is 11 to 15 ppg.

9. The composition according to any one of claims 1-8, wherein the specific gravity range of the composition is from 1.2 to 1.8 g / cm 3 .

10. The composition according to any one of claims 1-9, wherein the pH range of the composition is 7.5 to 9.

0.

11. The composition according to any one of claims 1-10, wherein the viscosity range of the composition is 30 to 70 mPa·s.

12. The composition according to claim 11, wherein the viscosity increases with increasing temperature.

13. A method for neutralizing red mud, comprising: Providing a red mud slurry; Adding gypsum to the red mud slurry; And Providing a neutralized red mud slurry, wherein the pH range of the neutralized red mud slurry is 7.5 to 9.

0.

14. The method according to claim 13, wherein the red mud slurry comprises larnite (Ca2(SiO4)), cancrinite ((NaCa)8(AlSiO4)6(CO3SO4)2·2H2O), hematite (Fe2O3), goethite (FeO(OH)), calcite (CaCO3), perovskite (CaTiO3), grossite (CaAl4O7), quartz (SiO2) and gibbsite (Al(OH)3).

15. The method according to claim 13 or 14, wherein the gypsum is added to the red mud slurry at a molar ratio of gypsum to red mud slurry in the range of 0.2:1 to 0.4:

1.

16. The method according to any one of claims 13-15, wherein the neutralized red mud comprises one or more of tricalcium aluminate (Ca3Al2(OH)2), hydrocalumite (Ca3Al2(OH) 12 CaCO3·5H2O), and ettringite (Ca3Al2(OH) 12 ·3CaSO4·26H2O).

17. The method according to claim 16, wherein the neutralized red mud comprises tricalcium aluminate (Ca3Al2(OH)2), hydrocalumite (Ca3Al2(OH) 12 CaCO3·5H2O) and ettringite (Ca3Al2(OH) 12 ·3CaSO4·26H2O).

18. A method for treating an acidic well, comprising: Injecting a red mud-based kill fluid comprising a neutralized red mud slurry, a polymer material and an H2S scavenger into the acidic well, wherein the acidic well contains H2S gas and CO2 gas; Solidifying the red mud-based kill fluid; And Treating the H2S gas and the CO2 gas in the acidic well.

19. The method according to claim 18, wherein treating the H2S gas and the CO2 gas comprises converting the H2S gas and the CO2 gas into one or more of metal sulfides, metal carbonates and metal bicarbonates.

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