Proppant and method of production

The present invention relates generally to oil and gas industry, more particularly, to production of proppants, the ceramic granulated propping agents used for hydrofracturing treatment of carbonaceous formations aimed to stimulation of oil and gas production from wells.

For hydraulic fracturing treatment, the proppant is mixed with hydrofracturing fluid and the resulting system is pumped into the recently developed fracture in the formation. After the process is completed, the proppant is deposited in the fracture. It plays a dual role: on one hand, it prevents the closuring of fracture walls; on another hand, proppant particles create a porous structure for better transport of hydrocarbon fluid to the wellbore.

The key properties of proppant are strength, particulate size, chemical resistance, density, and permeability of the structure for agglomerates of proppant particles. Properties of proppant dictate the choice for proper treatment task. In turn, proppant properties depend mainly on the phase composition of input materials and the structure formed after proppant production procedure. The proppant production comprises the stages of grinding and mixing of input raw materials, pelletizing, drying and firing of granules at high temperatures. Traditional components for proppant production are different types of kaolin and bauxites.

A method is disclosed in patent US4,894,285, when a proppant with density 2.75-3.4g/cm ³ (and operable at the pressure of 2,000 - 10,000 psi) is fabricated from a mixture of bauxites and clays with the following firing at the temperature 1350 - 1550 ⁰ C.

A method is disclosed in patent US4,921 ,821 fro fabrication of proppant with the density below 3.0 g/cm ³ ; fabrication includes palletizing and further firing of clays.

The invention US5, 120,455 describes the method of proppant production with the density below 3.0 g/cm ³ and pack permeability more than 100,000 mdarcy at the pressure of 10,000 psi made from materials including aluminum oxide in the amount from 40 to 60 %.

The invention US5,188,175 discloses the method of production of proppant with the density 2.2-2.60 g/cm ³ and packing permeability exceeding that of sand; the proppant is fabricated from raw materials including 25 - 40 wt % alumina.

The process of making a proper phase composition and proppant structure from traditional materials is described in technical literature. The key properties of proppant depend mainly on phase composition, more specifically, presented crystals of corundum and/or mullite, and/or aluminosilicate glass.

The distinguishing feature of the disclosed proppant from known in art is that the phase composition includes at least one of listed phases: boron glass, aluminum borate, and chemical compounds, solid solutions and eutectic mixes of borates and aluminum silicates with optical constants different from that for mullite and corundum. These phases in proppant composition are essential for key properties of proppant, but the presence of corundum or mullite phases in the phase composition is not very significant from the point of view of material/product properties.

The process of new-composition proppant fabrication starts from grinding and mixing of input components; the first component must include aluminum or magnesium, the second component includes the element of boron. The next step is making of granules of desired size by wet or dry method, then the granules are dried at the temperature up to 200 ⁰ C and fired at temperatures in the range from 200 to 1550 ⁰ C. The goal of introducing boron-bearing components is to shift the process of

phase formation from traditional aluminosilicates to the phases mentioned above; this is done for lower energy consumption and attaining a higher proppant strength.

The disclosed method can be explained with the following examples. Proppant properties with the sizes 12/18 are summarized in the Table 1.

Example 1.

The technical-grade alumina with the aluminum oxide content above 98% is mixed and grinded with boric acid down to the alumina particle size of 10 microns. The mix includes 162 kg of alumina and 29 kg of boric acid. The grinded mixture is granulized by dry method. The granules with the size of 0.2 - 2 mm were dried at 150 - 200 ⁰ C, screened into fractions and fired at the temperature of 1200 - 1550 ⁰ C and then the product fractions were selected. The main phase of proppant after firing is crystalline aluminum borate.

Example 2.

Bauxite is thermally treated to remove the chemically bound water and bauxite comprises at least 68 - 72 % of alumina. Then it is grinded together with boric acid to the size of bauxite particles of 15 microns. The mix includes 170 kg of alumina and 19 kg of boric acid. The grinded mixture is granulized by dry method. The granules with the size of 0.2 - 2 mm were dried at 150 - 200°C, screened into fractions and fired at the temperature of 1100 - 1400°C and then the product fractions were selected. The main phase of proppant after firing is crystalline aluminum borate.

Example 3.

Kaolin with content of alumina about 40 - 45 % is mixed in water with sodium tetraborate into stable water slurry. The mixture has 170 kg of clay and 19 kg sodium

tetraborate. The slurry is dispersed through a nozzle for production of granulate. These granulate with the size of 0.6 - 1.4 mm is dried at the temperature of 150 - 200 ⁰ C, screened into fractions and fired at the temperature of 800 - 1250 ⁰ C, and then the product fractions are selected. The phase composition of material is presented by a continuous sequence of solid solutions of aluminum borate and mullite, as well as aluminoboratesilicate glass.

Example 4

Bauxite is thermally treated to remove the chemically bound water and bauxite comprises at least 60 - 72 % of alumina. Then it is mixed with natural bauxite and colemanite and grinded down to the average size of bauxite particles about 15 microns. The mixture comprises 142 kg of heat-treated bauxite, 10 kg on untreated bauxite, and 38 kg of boric acid. The mixture is granulated by dry method for 2 minutes taking water as temporary technical binder in the amount of 4 % wt. and the rotation speed for pelletizer shaft is up to 30 m/s. These granulate with the size of 0.2 - 2 mm is dried at the temperature of 150 - 200° C, screened into fractions and fired at the temperature 1100 - 1400 ⁰ C, and then the product fractions are selected. The phase composition of material is presented by aluminum borate and solid solutions of aluminum borate and mullite.

Example 5

Natural bauxite with the alumina content above 60 - 72 % is grinded down to the average size of bauxite particle of 15 microns, and then mixed with bentonite clay and boron oxide. The mixture comprises 130 kg of heat-treated bauxite, 20 kg o clay and 45 kg of boric acid. The mixture is granulated by dry method for 2 minutes taking water as temporary technical binder in the amount of 4 % wt. and the rotation speed for pelletizer shaft is up to 30 m/s. These granulate with the size of 0.2 - 2 mm is dried at the temperature of 150 - 200° C, screened into fractions and fired at the temperature 1100 - 1400 ⁰ C, and then the product fractions are selected. The

phase composition of material is presented by aluminum borate and solid solutions of aluminum borate and mullite.

Table 1