RU2521989C1 - High-strength magnesium silicate proppant obtaining method - Google Patents

Abstract

FIELD: oil and gas industry.

SUBSTANCE: high-strength magnesium silicate proppant obtaining method that includes milling of the source mixture, its granulating and annealing of the obtained granules, milling of the source mixture with MgO content equal to 24-28 wt % is made up to the particle size of 8 mcm and less, and granulation process is made with water with added sodium or potassium salt of naphthalenesulphonic acid polymethylene or polycarboxymethylene of a sulphonic acid in quantity 0.02-0.07% of the mixture weight in terms of solid matter. The invention is developed in the secondary claims.

EFFECT: obtainment of a high-strength proppant of a medium density.

3 cl, 2 ex, 2 tbl

Description

The invention relates to the oil and gas industry, and in particular to the technology of manufacturing ceramic proppants intended for use as proppants in oil or gas production by hydraulic fracturing - hydraulic fracturing.

Hydraulic fracturing is the process of injecting fluids into an oil or gas-bearing underground formation at sufficiently high speeds and pressures, as a result of which the formation cracks. To keep the crack open after relieving the burst pressure, a proppant (proppant) is used that mixes with the injected fluid. The use of hydraulic fracturing increases the flow of fluids from an oil or gas reservoir into the well by increasing the total contact area between the reservoir and the well, and also because the proppant layer in the fracture has higher permeability than the permeability of the formation.

Modern materials, widely used for fixing cracks in the open state, can be divided into two types - quartz sands and synthetic proppants. The physical characteristics of proppants that affect the conductivity of a crack include parameters such as strength, particle size distribution, the presence of impurities, acid solubility, granule shape (sphericity and roundness), and density.

The first and most commonly used material for fixing cracks are sands, the density of which is approximately 2.65 g / cm ³ . Sands are usually used for hydraulic fracturing, in which the compressive stress does not exceed 40 MPa. In addition, sand is increasingly used, the grains of which have a special polymer coating on the surface, which increases strength and prevents proppant particles from being removed from the fracture. In the late 70s, with the creation of new medium-strength and high-strength synthetic proppants, an increase began in the field of hydraulic fracturing in gas and oil fields confined to dense sandstones and limestones located at great depths.

Medium-strength are ceramic proppants with a density of 2.7 - 3.3 g / cm ³ used with a compression stress of up to 69 MPa. Heavy-duty proppants with a density of 3.3 - 3.8 g / cm ³ are used at compression stresses up to 100 MPa. Lightweight proppants with a density of 2.55 g / cm ³ or less are also produced and used.

Among the synthetic proppants that are widely used in hydraulic fracturing operations, ceramic proppants made from natural aluminosilicate raw materials and possessing the necessary technical characteristics have been leading for decades. The world's largest producer of aluminosilicate proppants is CARBO Ceramics. In this regard, the classification of proppants by density and strength proposed by the company is considered generally accepted among consumers. The company's product line is represented by high-strength and high-density proppants (density - 3.56 g / cm ³ , bulk density - 2.0 g / cm ³ ), medium-strength and medium-density proppants (density - 2.7 g / cm ³ , bulk density - 1 , 56 g / cm ³ ) and lightweight proppants (density - 2.55 g / cm ³ , bulk density - 1.4 g / cm ³ ), which do not have outstanding strength characteristics, but have a low density. A similar line of aluminum-containing proppants is offered by manufacturers of the PRC and Brazil. Thus, hardening of known proppants and transferring them to high-strength discharge is achieved solely due to a significant increase in the density of the material with its transition to the category of high-density proppants by changing the chemical composition of the charge associated with an increase in the Al ₂ O ₃ content.

In the last decade, magnesium silicate proppants, manufactured from natural raw materials based on serpentinite, olivinite, dunite, both independently and in the form of a mixture with natural quartz-feldspar sand, have gained increasing consumer confidence. These proppants on the market are mainly represented by medium-dense and medium-strength granules ForeProp and ForesMgLight (density - 2.7 g / cm ³ , bulk density - 1.54 - 1.56 g / cm ³ ).

In recent years, in connection with rising energy prices, technologies for the extraction of hydrocarbons from hard-to-reach and non-traditional sources have been developing rapidly. For example, improvements in horizontal drilling technology in combination with hydraulic fracturing have made cost-effective production of shale gas and shale oil. In this regard, in the near future, an increase in demand for high-strength proppant with a minimum density is predicted, since it is the proppant density that determines the transport and location of proppant along the crack. Lightweight proppant is suspended longer in the fluid transporting it, so it can be delivered to a longer distance along the wings of the crack. In addition, the use of low-density proppant allows the use of lighter fluids and lower injection speeds.

Known high-strength bauxite proppant CARBOHSP with a bulk density of 2.0 g / cm ³ (hereinafter, bulk density will be used to characterize the density of the product). Despite the unique strength characteristics, this proppant has one significant drawback - high density. In this regard, difficulties arise during its transportation to the place of hydraulic fracturing.

Also known medium-strength aluminosilicate proppant medium density CARBOECONOPROP (bulk density of 1.56 g / cm ³ ). Known material has a reduced density, however, it has not enough high strength, which does not allow the use of proppant in deep wells with a high closing pressure.

A known method of manufacturing a lightweight magnesium silicate proppant and proppant (RF patent No. 2437913), including heat treatment of a magnesium-containing component - a source of magnesium oxide, its joint grinding with a silica-containing component, granulation of the resulting mixture, firing of the obtained granules and their sieving. The mixture contains (in terms of calcined substance), wt.%: SiO ₂ 64-72, MgO 11-18, natural impurities - the rest, and heat treatment is carried out at a temperature of not more than 1080 ° C. Lightweight magnesium silicate proppant, characterized in that it is obtained by the above method. The proppant obtained in a known manner has a bulk density of 1.42 g / cm ³ , however, the strength of the granules remains not high enough.

The closest in technical essence to the claimed technical solution is a method of manufacturing a magnesium silicate proppant and proppant (RF patent No. 2463329), which includes preparing the initial components of the mixture, grinding them with a complex sintering additive to a fraction of less than 30 microns, granulating the mixture, calcining and sieving the calcined granules. As the specified additives, a mixture of brucite, colemanite, sodium silicofluoride and fayalite is used in an amount of 0.4-3.0% by weight of a mixture based on magnesium silicate raw materials, in the following ratio,% by weight of a mixture: brucite 0.1-1.0 , colemanite 0.1-0.6, sodium silicofluoride 0.1-0.4, fayalite 0.1-1.0, with a total MgO content in the charge of 19-48 wt.%. Moreover, firing is carried out at a temperature of 1150-1220 ° C, and as the main component of the charge using natural magnesium silicate raw materials - serpentinite; olivinite, dunite both independently and as a mixture with natural quartz feldspar sand. Magnesium silicate proppant is characterized in that it is obtained by the above method.

The proppant obtained in this way has a bulk density of 1.52 - 1.7 g / cm ³ depending on the MgO content in the charge, which allows it to be classified as medium density proppant. At the same time, the increased destruction characteristics of the granules do not allow the product to be classified as high-strength proppants. The insufficient strength of the material is partly due to the fact that when granulating the mixture, crushed to a fraction of less than 30 microns, it is not possible to significantly compact the raw proppant granule. As a result, after firing, the proppant granules contain an excessive number of pores. For example, the bulk weight of the proppant containing 24 to 28 wt.% MgO is 1.56 to 1.58 g / cm ³ .

The technical problem to be solved by the claimed invention is directed is to obtain a medium-density (with a bulk density of 1.6-1.64 g / cm ³ ) high-strength magnesium silicate proppant with a slight compaction of the material and without changing its chemical composition.

This result is achieved by the fact that in the method of manufacturing high-strength magnesium silicate proppant, including grinding the initial charge, granulating and firing the obtained granules, grinding the initial charge containing 24-28 wt.% MgO, is carried out to a fraction of 8 μm or less, and granulation is carried out on water with the addition of the sodium or potassium salt of polymethylene naphthalene sulfonic acid or polycarboxymethylene sulfonic acid in an amount of 0.02-0.07% of the mass of the charge in terms of solid. Pellets are fired in an oxidizing environment. In addition, sintering additives are introduced into the initial charge.

Magnesium silicate proppants, due to the peculiarities of the feedstock used for their manufacture, initially have a lower bulk density compared to the known metal, ceramic-metal and ceramic high-strength proppants.

However, only when the MgO content in the mixture in an amount not exceeding 28 wt.%, The product has a bulk density of less than 1.65 g / cm ³ . An increase in the MgO content in the charge over 28 wt.% Leads to an increase in proppant density, and a decrease in the MgO content in the charge below 24 wt.% Causes a decrease in the mechanical strength of the material.

The hardening of the proppant obtained by the claimed method is achieved by the combined action of two factors: an increase in the grinding depth of the initial mixture to a fraction of 8 μm or less, as well as the introduction of solutions of these salts into the mixture. Fine grinding provides a denser packing of particles during granulation, in addition, the degree of mechanical activation of the surface of the particles increases. In turn, the introduction of a mixture of a solution of salts of polymethylene naphthalene sulfonic acids and polycarboxymethylene sulfonic acids in the claimed amount gives the system thixotropic properties, that is, with an increase in shear rate, the viscosity of the system decreases and the plasticity of the mass increases. Moreover, the process of compaction of the particles of the mixture during granulation becomes more uniform. The high wettability and mobility of the fine particles relative to each other during granulation increases the bulk density of the raw granules and increases the strength of the calcined proppant.

When grinding the mixture to a fraction larger than 8 μm, the proppant breakability increases. With a decrease in the number of declared salts of less than 0.02 wt.%, The effect of the additive is hardly noticeable, an increase in the number of these salts above 0.07 wt.% Does not lead to a further increase in the strength of the material.

Various sintering additives can be introduced into the initial charge, for example, inorganic fluorides, brucite, additives containing oxides of calcium, iron, potassium, and sodium.

Considering the fact that the crushed mixture based on natural magnesium silicate raw materials used for the manufacture of proppant in accordance with the claimed technical solution contains impurities of both oxidized and metallic iron (introduced into the mixture with intensive grinding), it is advisable to burn the granules in an oxidizing atmosphere. In this case, it is possible to reduce the negative effect exerted on the micro and macrostructure of ceramics as a result of the inversion of FeO↔Fe ₂ O ₃ occurring during high-temperature firing.

Examples of carrying out the invention.

Example 1

4 kg of a mixture of high silica quartz feldspar sand, dried at a temperature of 150 ° C for 1 hour and serpentinite, heat-treated at a temperature of 1000 ° C (MgO content in the charge 24 wt.%), Was subjected to joint grinding to a fraction of less than 8 μm. The fractional composition was monitored on a Horiba LA - 300 particle size analyzer. The obtained material was granulated on a laboratory plate granulator, while the polymethylene naphthalene sulfonic acid sodium salt was added to the granulation water at the rate of 0.02% of the charge mass. The granulate was fired at a temperature of 1230 ° C. A sample of fired proppants of the 30/60 mesh fraction was sent to determine the bulk density and destructibility according to the generally accepted methodology of ISO 13503 - 2: 2006. Similarly, samples were prepared with different contents of MgO and the sodium salt of polymethylene-naphthalene sulfonic acid in the mixture. The measurement results are presented in table 1.

Example 2

3880 g of a mixture of high silica quartz feldspar sand, dried at a temperature of 150 ° C for 1 hour, and serpentinite, heat-treated at a temperature of 1000 ° C, as well as 120 g of a complex sintering additive containing 40 g of brucite, 40 g of fayalite, 24 g of colemanite and 16 g of sodium silicofluoride (RF patent No. 2463329) when the MgO content in the charge 28 wt.%, was subjected to joint grinding to a fraction of less than 8 microns. The fractional composition was monitored on a Horiba LA - 300 particle size analyzer. The obtained material was granulated on a laboratory plate granulator, while polycarboxymethylene sulfonic acid sodium salt was added to the granulation water at the rate of 0.07% of the charge mass. The granulate was calcined at a temperature of 1150 ° C in an oxidizing atmosphere. A sample of fired proppants of the 30/60 mesh fraction was sent to determine the bulk density, destructibility and long-term conductivity according to the generally accepted methodology ISO 13503 - 2: 2006. Similarly, samples were prepared with the addition of the potassium salt of polymethylene naphthalene sulfonic acid and the potassium salt of polycarboxymethylene sulfonic acid. The measurement results are presented in tables 1 and 2.

Table 1  - Properties of burnt proppant No. p / p The content of salt additives The MgO content in the mixture, wt.% Bulk weight, g / cm ³ Destructibility at 10000 psi, wt.% 1. The proppant CARBOHSP - - 2.0 0.6 2. Proppant RF patent No. 2463329 - 28 1,58 3.8 3. Example 1 description 0.02 wt.% Sodium salt of polymethylene naphthalene sulfonic acid 24 1,6 1,5 4. Example 1 description 0.05 wt.% Sodium salt of polymethylene naphthalene sulfonic acid 26 1,62 1.3 5. Example 1 description 0.07 wt.% Sodium salt of polymethylene naphthalene sulfonic acid 28 1,63 1,0 6. Example 1 description 0.01 wt.% Sodium salt of polymethylene naphthalene sulfonic acid 23 1,54 3.8 7. Example 1 description 0.09 wt.% Sodium salt of polymethylene naphthalene sulfonic acid 29th 1.65 1,0 8. Example 1 descriptions of grinding to fractions less than 10 microns 0.07 wt.% Sodium salt of polymethylene naphthalene sulfonic acid 28 1,59 1.7 9. Example 2 description 0.07 wt.% Polycarboxymethylene sulfonic acid sodium salt 28 1,64 0.8 10. Example 2 description 0.07 wt.% Potassium salt of polycarboxymethylene sulfonic acid 28 1,64 0.9 11. Example 2 description 0.07 wt.% Potassium salt of polymethylene naphthalene sulfonic acid 28 1,64 0.7 table 2 - Long-term proppant conductivity Closing Pressure, psi Long-term conductivity, mDarcy × ft at 121 ° C Proppant CAKBOHSP Proppant according to US Pat. RF №2463329 Proppant on the claim. way 2000 3270 3210 3498 4000 3233 2830 3388 6000 2791 2210 2733 8000 2343 1983 2298 10,000 1849 1653 1788

Analysis of these tables shows that the magnesium silicate proppant obtained by the claimed method (examples 3-5, 9-11 of table 1), in mechanical strength and long-term conductivity, is comparable with the high-strength aluminosilicate proppant CARBOHSP, while having a lower bulk density, and exceeds the known medium-density magnesium silicate proppants for resistance to compressive stress and long-term conductivity of the proppant pack. Therefore, this product can be classified as a medium dense high strength magnesium silicate proppant. The use of the indicated proppant will simplify and reduce the cost of hydraulic fracturing by using a less dense gel, facilitate the injection, transportation and placement of proppant (proppant) in wells, especially in wells with complex geometry.

Thus, the claimed technical solution allows you to expand the product line of magnesium silicate proppants.

Claims (3)

1. A method of manufacturing a high-strength magnesium silicate proppant, comprising grinding the initial charge, granulating it and firing the obtained granules, characterized in that the grinding of the initial charge containing 24-28 wt.% MgO is carried out to a fraction of 8 μm or less, and granulation is carried out on water with the addition of the sodium or potassium salt of polymethylene naphthalene sulfonic acid or polycarboxymethylene sulfonic acid in an amount of 0.02-0.07% by weight of the mixture, calculated on the solid. 2. The method according to claim 1, characterized in that the firing of the granules is carried out in an oxidizing environment. 3. The method according to claim 1, characterized in that sintering additives are introduced into the initial charge.