BACKGROUND OF THE INVENTION

Technical Field

The present invention relates to a method of preparing sodium bentonite. In one aspect, calcium bentonite is converted into sodium bentonite by a combination of chemical, thermal and mechanical treatment procedures. The produced sodium bentonite is suitable for but not limited to oil and gas drilling and cementing applications.

Description of the Related Art

The “background” description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description which may not otherwise qualify as prior art at the time of filing, are neither expressly or impliedly admitted as prior art against the present invention.

Drilling fluids play an important role in drilling operations. They are circulated during drilling to carry out and transport the cuttings produced by the drill bit to the surface, and to cool and lubricate the drilling bit, as well as suspending the drilling cuttings during pauses in the drilling operation. Also, they apply hydrostatic pressure on a geological formation to counter the formation pressure and prevent formation fluids from entering the well bore [Bourgoyne Jr. et al. (1986). Applied Drilling Engineering. Soc Pet Eng 2:514; and Hossain et al. (2015), Fundamentals of Sustainable Drilling Engineering, John Wiley & Sons]. Consequently, drilling fluid interacts with the formation to permanently or temporarily alter the pressure or permeability characteristics of the formation leading to a change in well productivity. Fluid loss control additives are added to the drilling fluid to minimize fluid filtrates and solid particle invasion and to reduce damage to the formation. There are many types of fluid loss control additives used in the oil industry such as polymers, clays, lime, starch, and bridging agents such as calcium carbonate [Caenn et al. (2011) Composition and Properties of Drilling and Completion Fluids, six. ed, Composition and Properties of Drilling and Completion Fluids. Elsevier]. To achieve the desired functions, the rheological properties of the drilling fluids are maintained during the drilling operations by selecting and adding appropriate additives to the drilling fluids. Additives such as polymers and clays may be used to change properties of the drilling fluid such as density, viscosity, gel strength, filtration, and pH.

Bentonite is a natural clay containing primarily montmorillonite minerals that are usually formed from weathering of volcanic ash in the presence of water. There are different types of bentonite, each named after the dominant element, such as potassium (K), sodium (Na), calcium (Ca), magnesium (Mg) and aluminum (Al). Na-bentonite expands up to 15 times its volume when wet, and is capable of absorbing an amount of water that is several times its dry mass. Compared to other types of bentonite, Na-bentonite has superior colloidal and absorbent properties which have helped to popularize its use in drilling mud or drilling fluid for oil and gas wells and for treating boreholes for geotechnical and environmental investigations. Na-bentonite is used as a viscofier or lubricant and in water control to reduce filtration loss. Including Na-bentonite in a drilling fluid helps to cool cutting tools, to remove the soil and rock cuttings, to support the borehole and to prevent the borehole from collapsing through the formation of a mud cake. Most high-grade natural Na-bentonite in the United States, which is the world's largest bentonite producer, is produced from the western part of the country in an area between the Black Hills of South Dakota and the Bighorn Basin of Wyoming. In addition to drilling fluid applications, Na-bentonite is also useful as a sealant, providing a self-sealing, low permeability barrier, for example, at the base of landfills.

Bentonite has been used as a drilling fluid additive to maintain the rheological properties of drilling fluid and to enhance the filtration performance thereby minimizing fluid loss into the formation and prevent formation damage [Darley et al. (1988). Composition and Properties of Drilling and Completion Fluids. Gulf Professional Publishing; Lebedenko et al. (1988) Some Considerations on the Aging of Na2CO3Activated Bentonites. Applied Clay Science, Vol. 3(1), pp. 1-10; Al-Homadhi E. S. (2007) Improving Local Bentonite Performance for Drilling Fluids Applications. Paper No. SPE 110951, presented at the SPE Saudi Arabia Section Technical Symposium, Dhahran, May 7-8; Falode et al. (2008) Evaluation of Local Bentonite Clay as Oil Well Drilling Fluids in Nigeria. Applied Clay Science, Vol. 39(1): p. 19-27; Musaab et al. (2017) Effects of Sodium Carbonate Addition, Heat and Agitation on Swelling and Rheological Behavior of Ca-Bentonite Colloidal Dispersions. Applied Clay Science 147, pp. 176-83; and U.S. Pat. No. 9,676,669 (Musaab et al.)]. Bentonite is also used as weighting material when drilling the upper sections of oil and gas wells. In addition, bentonite clay is used in cementing oil and gas wells. It is mixed with cement slurry as physical extender to cement weak formations to prevent fractures and reduce fluid loss into the formation [Michaux et al. (1989) Cement Chemistry and Additives. Oilf. Rev., Vol. 1(1): p. 18-25]. The American Petroleum Institute (API) has established specifications for drilling grade bentonite which are shown below in Table 1.

TABLE 1API 13A Specification for Drilling Grade BentonitePropertySpecified LimitsViscometer dial reading at 600 rpmMinimum 30Yield point to plastic viscosity ratioMaximum 3Filtration volume at 30 minMaximum 15 cm3Residue after sieved withMaximum 4.0% by weight >75 μm200 mesh (75 μm)MoistureMaximum 10.0% by weight

Generally, there are three main classes of industrial bentonites: sodium, calcium, and artificial sodium activated bentonite [Ahmed et al. (2012) Studies on the Mineral and Chemical Characteristics of Pindiga Bentonitic Clay. Petroleum Technology Development Journal, Vol. 1 (1595-9104), pp. 1-8, January]. In drilling fluids, sodium bentonite is preferred over calcium bentonite because calcium bentonite has poor swelling and dispersion properties [Hassan and Abdel-Khalek, 1998; Dill, 2016; Yan et al., 2016]

Raw natural bentonite without treatment may not be adequate for use as a drilling fluid additive even when it is rich in montmorillonite and/or contains a sufficient amount of sodium. Untreated natural bentonite may not have the appropriate properties to provide the desired function [Bol G. (1986) Bentonite Quality and Quality-Evaluation Methods. SPE Drilling Engineering, Vol. 1(04): p. 288-96.]. Bentonite performance and properties can be improved by several methods and by the inclusion of inorganic additives. Addition of soda ash (sodium carbonate) is well-known process to increase bentonite quality [Karagüzel et al. (2010) Activation of (Na, Ca)-bentonites with Soda and MgO and Their Utilization as Drilling Mud. Applied Clay Science Vol. 48(3), pp. 398-404. April]. Addition of only 2 to 4 wt. % weight can significantly enhance bentonite properties. Sodium content greatly affects the dispersion characteristics of bentonite.

Na/Ca ratio affects physical properties of bentonite [Lebedenko et al. (1988) Some Considerations on the Aging of Na2CO3Activated Bentonites. Applied Clay Science, Vol. 3(1), pp. 1-10]. Ca-bentonite is found abundantly in many parts of the world including the southern part of the United States such as Mississippi and Alabama, and in Saudi Arabia. It has a good absorbent properties, but it is only capable of swelling 2-3 times of its unwetted volume. Researchers and bentonite producers have attempted to utilize local sources of bentonite. Several methods have been developed to purify or treat raw bentonite, such as dry-sieving, wet-sieving, dispersing in hexametaphosphate solutions, sedimentation and mixing with soda ash, but the methods have been found to be time-consuming or have low efficacy.

Al-Homadhi et al. attempt to treat local bentonite with soda ash, extenders and/or additives such as salt and polymers. The final modified bentonite did not satisfy API specifications for evaluation of drilling mud [Al-Homadhi, E. S. “Improving Local Bentonite Performance for Drilling Fluids Applications”, Society of Petroleum Engineers Saudi Arabia Section Technical Symposium, 7-8 May 2007, Dhahran Saudi Arabia—incorporated herein by reference in its entirety].

In Australian Pat. No. AU566345B (incorporated herein by reference in its entirety), magnesium- and/or calcium-containing bentonite are agglomerated by soda ash treatment to produce Na-bentonite for laundry applications. The produced Na-bentonite has not been evaluated for drilling fluid applications.

Chinese Pat. No. CN1061946C (incorporated herein by reference in its entirety) describes a process of producing Na-bentonite from Ca-bentonite by soda ash treatment followed by ion exchange reaction. The produced Na-bentonite also has not been evaluated for drilling fluid applications.

Yildiz et al. activate local Ca-bentonite with soda ash to increase the Na/Ca ratio and disperse the activated bentonite in sodium hexametaphosphate solutions to increase the stability of the suspension. The rheological properties of the activated bentonite were tested at different sodium hexametaphosphate and NaCl concentrations but did not meet the API standards for drilling fluids [Yildiz et al. “The effect of the electrolyte concentration and pH on the rheological properties of the original and the Na2CO3-activated Kutahya bentonite” Applied Clay Science 14(5-6):319-327 (1999)—incorporated herein by reference in its entirety].

Kaufhold et al. activate Mg/Ca-bentonite with sodium carbonate in both dry state and in solution with excessive water with no heating. They conclude that despite the addition of the sodium carbonate in excess (1-5 wt. %), the activation process may be incomplete and partial whether it is conducted in a dry state or a wet state [Kaufhold et al. “Comparison of methods for distinguishing sodium carbonate activated from natural sodium bentonites” Applied Clay Science 86:23-37 (2013)—incorporated herein by reference in its entirety].

Karagüzel et al. activate local bentonite with 1.5-3 wt. % soda ash and 0.5% MgO without heating or a prior purification step. The combination of soda ash and MgO was found to influence the viscosities, swelling indices and filtration losses to produce an activated bentonite that satisfies drilling mud standards {Karagüzel et al. “Activation of Na, Ca)-bentonites with soda and MgO and their utilization as drilling mud—incorporated herein by reference in its entirety].

Magzoub et al. (2017) and U.S. Pat. No. 9,676,669—both incorporated herein by reference in their entirety—developed a method for producing sodium bentonite from Saudi local calcium bentonite by heating and stirring a suspension of bentonite in soda ash solution for 24 hours. The method is effective in enhancing the rheological and filtration properties of local bentonite. However, this method requires fresh water which adds significant cost to the process, in particular, in arid environment.

Therefore, one object of the present disclosure is to describe a process for producing sodium bentonite by treating calcium bentonite using seawater that eliminates the use of fresh water and reduces the amount of soda ash required for the treatment.

BRIEF SUMMARY OF THE INVENTION

In one aspect, there is provided a method of converting calcium bentonite to sodium bentonite having a Na/Ca molar ratio of at least 2.5. The method comprises mixing calcium bentonite with sea water at final bentonite concentration in the range of 2 wt. % to 15 wt. % of the total weight of the sea water to form a bentonite suspension, adjusting the pH of the suspension in the range of 8.0 to 11.0, and heating to a temperature in the range of 80 to 100° C. and stirring the suspension for a time in the range of 12 to 72 hours to form sodium bentonite and calcium carbonate. Finally the sodium bentonite is filtered and oven dried.

In a preferred embodiment, the sea water is from the Red Sea, the Arabian Gulf, Mediterranean Sea, or a brine outflow from sea water desalination plant.

In another preferred embodiment, the sea water contains at least 12,000 ppm sodium.

In another preferred embodiment, sodium carbonate is added to the suspension,

In another preferred embodiment, the method further comprising stirring the suspension for a time in the range of 10 to 30 minutes prior to add the soda ash.

In another preferred embodiment, the ratio of soda ash/calcium bentonite is in the range of 1:11 to 1:45.

In a more preferred embodiment, the ratio of sodium carbonate/calcium bentonite weight ratio is in the range of 1:15 to 1:23.

In another preferred embodiment, the pH of the suspension is in the range of 8.0 to 11.0.

In a more preferred embodiment, the pH is in the range of 9.0 to 10.0.

In another preferred embodiment, the suspension is heated to about 100° C.

In another preferred embodiment, the suspension is heated continuously for 24 hours.

In another preferred embodiment, the suspension is stirred at a rate in the range of 300 to 600 RPM.

In another preferred embodiment, sodium hydroxide and/or ethylenediaminete-tracetate (EDTA) is added.

In another preferred embodiment, the Ca-bentonite has been purified by at least one method selected from the group consisting of dry-sieving, wet-sieving, dispersion in deionized water with hexametaphosphate, dispersion in deionized water without hexametaphosphate and sedimentation.

In another preferred embodiment of the method, the product sodium bentonite has an apparent viscosity of at least 15 cP.

In another preferred embodiment of the method, the product sodium bentonite has a yield point of no more than 30 lb/100 ft2.

In another preferred embodiment of the method, the product sodium bentonite has a viscometer dial reading of 33-35 lb/100 ft2at 300 rpm and 39-40 lb/100 ft2at 600 rpm.

In another preferred embodiment of the method, the product sodium bentonite has a total filtrate volume in the range of 12 to 15 mL.

A second aspect of the invention is directed to a method of preparing drilling fluids comprising sodium bentonite having a Na/Ca molar ratio of at least 2.5 comprising:

mixing calcium bentonite with sea water to form a suspension at final bentonite concentration in the range of 2 wt. % to 15 wt. % of the total weight of the sea water,

adjusting the pH of the suspension in the range of 8.0 to 11,

heating the suspension to a temperature in the range of 80 to 100° C. with stirring for a time in the range of 12 to 72 hours, filtering and oven drying the product sodium bentonite, and

mixing the sodium bentonite with water in an amount in the range of 1 wt. % to 10 wt. %.

In a preferred embodiment, the method further comprising mixing one or more additive selected from the group consisting of an antiscalant, a thickener, a deflocculant, a lubricant, a buffer, a biocide, and a weighting agent.

