RU2463329C1 - Method of producing silicon-magnesium proppant, and proppant - Google Patents

Abstract

FIELD: oil-and-gas production.

SUBSTANCE: proposed method comprises preparing initial components of charge mix, their grinding with complex sintering additive, charge mix pelletising, annealing and screening of annealed pellets. Note here that said additive represents mix of brucite, colemanite, sodium fluorosilicate and fayalite in amount of 0.4-3.0 % of charge weight based on silicon-magnesium raw stock, at the following ratio of components in wt %: brucite 0.1-1.0, colemanite 0.1-0.6, sodium fluorosilicate 0.1-0.4 and fayalite 0.1-1.0, at total amount of MgO in charge mix making 19-48 wt %. Note here annealing is performed at 1150-1220°C, while main component of said mix represents natural silicon-magnesium raw stock. i.e. serpentinite, olevinite, dunite, both separately and in mix with natural quartz feldspar sand. Proposed silicon-magnesium proppant is produced as described above.

EFFECT: reduced permeability of proppant bench at high pressures at hydrothermal effects.

4 cl, 3 ex, 1 tbl

Description

The invention relates to the oil and gas industry, and in particular to the technology of manufacturing proppants of medium density, intended for use as proppants in oil or gas production by hydraulic fracturing - hydraulic fracturing. Hydraulic fracturing is the process of pumping fluids into an oil or gas-bearing underground formation at sufficiently high speeds and pressures to form cracks in the formation, increasing the flow of fluids from the oil or gas reservoir into the well.

Proppants (proppants) are strong spherical granules that hold hydraulic fractures from closing under high pressure and provide the necessary productivity of oil and / or gas wells by providing a conductive channel in the formation. Various organic and inorganic materials are used as proppants - walnut shells, sand, polymer coated sand, ceramic proppants. Among ceramic proppants in recent years, magnesium silicate proppants are increasingly used. This is due to the cheapness and accessibility of natural raw materials for their production, as well as the fact that existing technologies make it possible to obtain proppants with high strength, sphericity, and roundness at medium density values. At the same time, the known ceramic proppants have several disadvantages, one of which is a significant loss of strength during their operation in hydrothermal conditions under the influence of high pressures, which leads to a drop in the conductivity of the proppant pack.

Thus, reducing the drop in the conductivity of the proppant pack at high (over 6000 psi) pressures is a priority for technologists working to improve the performance of the proppants.

A known method of manufacturing ceramic oil proppants (see RF patent No. 2235702) from a ceramic material, which is used as magnesium metasilicate and / or calcium metasilicate, which is subsequently crushed, granulated to a bulk density of raw granules of at least 1.2 g / cm ³ and fired at a temperature of 1215-1290 ° C. In addition, the crushed metasilicate before granulation is mixed with modifying and sintering additives, for example titanium oxide, zirconium silicate, etc.

The disadvantage of this method is that with an increase in external load in hydrothermal conditions, the conductivity of the proppant pack is significantly reduced. This is due to the fact that despite the introduction of sintering additives into the material, the total amount of glass phase in the sintered granules remains insufficient to prevent hydration in hydrothermal conditions under the influence of high pressures. In addition, at the claimed temperature range for firing the material, a number of polymorphic transformations of magnesium and calcium metasilicates causing microcracking of ceramics cannot be avoided.

The closest in technical essence to the claimed solution is a method of manufacturing ceramic proppants (proppants) of oil wells (see RF patent No. 2235703) from a magnesium silicate material based on forsterite with a content of the latter 55-80%, which is crushed, sintering and modifying additives are introduced, granulated and burn at a temperature of 1150-1350 ° C.

The disadvantage of this method is that with an increase in external load, the conductivity of the proppant pack is significantly reduced. This is explained by the fact that during sintering of granules in the stated temperature range and subsequent cooling, a series of polymophic transformations of magnesium metasilicate occurs in the material, accompanied by volume changes, as a result of which a certain amount of microcracks and pores remain in the granules after firing. This leads to a loss of strength, and consequently, the conductivity of the proppant layer at elevated pressures. In addition, the low content of fluxes in the charge reduces the total amount of glass phase in the calcined proppants, and this, in turn, leads to undesirable hydration of MgO on the surface of the granules under hydrothermal conditions.

The technical problem to which the claimed invention is directed is to reduce the drop in the conductivity of the proppant pack at high (over 6000 psi) pressures under hydrothermal conditions.

This result is achieved by the fact that in the method of manufacturing a magnesium silicate proppant, which includes preparing the initial components of the charge, grinding them with a complex sintering additive, granulating the mixture, calcining and sieving the calcined granules, a mixture of brucite, colemanite, sodium silicofluoride and fayalite in the amount of 0.4 - 3.0% by weight of the mixture in the following ratio,% by weight of the mixture:

brucite 0.1-1.0 colemanite 0.1-0.6 sodium silicofluoride 0.1-0.4 fayalit 0.1-1.0

with a total MgO content in the charge of 19-48 wt.%.

Firing proppant is preferable to produce at a temperature of 1150-1220 ° C. In addition, the main component of the charge is the use of natural magnesium silicate raw materials - olivinite, dunite, both independently and as a mixture with natural quartz feldspar sand.

This problem is also solved by the fact that the magnesium silicate proppant obtained in the above manner.

The use of a complex sintering additive is caused by the need to form a sufficient amount of glass phase in the calcined granules in order to smooth out the negative effects of polymorphic transformations of magnesium metasilicate and calcium metasilicate present as an impurity, as well as to prevent surface hydration of MgO / CaO during proppant operation. In addition, lowering the sintering temperature of ceramics avoids higher-temperature phase transitions.

The introduction of a complex sintering additive into the mixture at the grinding stage is due to the need for its thorough averaging and obtaining a mixture of uniform particle size distribution. The composition of the sintering additive is selected in such a way that allows practically avoiding chemical reactions during firing, leading to "loosening" of the microstructure of ceramics. In addition, the components used are available and have a low cost. For magnesium silicate ceramics, the best sintering additives are compounds of calcium, iron, sodium, and the combined presence of B ³⁺ and F ^- ions in the additive stabilizes the glass phase, and the presence of boron oxide also prevents the transition β - 2CaO · SiO ₂ → γ - 2CaO · SiO2 occurring with a significant increase in volume. The presence of brucite in the composition can significantly reduce the porosity of sintered proppant granules due to the fact that when it is decomposed, highly active, reactive magnesium oxide is formed. The authors experimentally found that the introduction into the composition of the mixture for the manufacture of proppant at the grinding stage of the inventive complex sintering additive in an amount of 0.4-3.0 wt.% With the claimed ratio of components allows the formation of an amount of glass phase sufficient to reduce the total porosity and prevent hydration of MgO / CaO in the calcined ceramic . The introduction of this additive in an amount of less than 0.4 wt.% Of the weight of the charge does not significantly affect the conductivity of proppants at high pressures; an increase in the amount of an additive of more than 3.0 wt.% Sharply increases the total amount of glass phase in the calcined granules, resulting in a narrowing of the temperature range of sintering calcination. With a decrease in sintering calcination temperature below 1150 ° C, the proppant granules remain somewhat unfinished and have a low proppant pack conductivity. An increase in the temperature of sintering calcination above 1220 ° C causes the appearance of a large number of cakes and leads to an insufficient increase in the conductivity of the proppant pack.

As the main component of the charge for the manufacture of proppant according to the claimed method, any magnesium silicate raw material is suitable, however, the use of dunites and olivinites is preferable, since these materials practically do not contain chemically bound water and do not require preliminary high-temperature firing to remove it, which degrades the grindability of the material and increases the cost of the final products.

When the content in the charge of MgO in an amount exceeding 48 wt.%, The proppant has low conductivity at high pressures due to the negative consequences due to the low content of glass phase in the calcined product. When the MgO content in the amount of less than 19 wt.%, The proppant has low conductivity due to the fact that at high pressures the destruction of ceramics becomes brittle, avalanche-like in nature, which leads to a sharp drop in the permeability of the proppant layer.

Examples of carrying out the invention.

Example 1

485 g of highly siliceous quartz-feldspar sand dried at a temperature of 150 ° C for 1 hour, 485 g of serpentinite, heat-treated at a temperature of 1000 ° C, as well as 30 g of a complex sintering additive containing 10 g of brucite, 10 g of fayalite, 6 g of colemanite and 4 g of sodium silicofluoride was subjected to joint grinding to a fraction of less than 30 microns. The fractional composition was monitored on a Horiba LA - 300 particle size analyzer. The resulting material was granulated and calcined at a temperature of 1150 ° С. A sample of the calcined proppants of the 20/40 mesh fraction was sent to determine long-term conductivity at various pressures. The measurement results are presented in table 1.

Example 2

920 g of olivinite, dried at a temperature of 150 ° C for 1 hour, 76 g of serpentinite, dried at a temperature of 150 ° C for 1 hour, as well as 4 g of a complex sintering additive containing 1 g of brucite, 1 g of fayalite, 1 g of colemanite and 1 g of sodium silicofluoride, was subjected to joint grinding to a fraction of less than 30 microns. The fractional composition was monitored on a Horiba LA-300 particle size analyzer. The resulting material was granulated and calcined at a temperature of 1200 ° C. A sample of the calcined proppants of the 20/40 mesh fraction was sent to determine long-term conductivity at various pressures. The measurement results are presented in table 1.

Example 3

980 g of dunite dried at a temperature of 150 ° C for 1 hour, as well as 20 g of a complex sintering additive containing 5 g of brucite, 10 g of fayalite, 3 g of colemanite and 2 g of sodium silicofluoride, were subjected to joint grinding to a fraction of less than 30 μm. The fractional composition was monitored on a Horiba LA-300 particle size analyzer. The resulting material was granulated and calcined at a temperature of 1220 ° C. A sample of the calcined proppants of the 20/40 mesh fraction was sent to determine long-term conductivity at various pressures. The measurement results are presented in table 1.

Table 1 Properties of granules of magnesium silicate proppant * No. p / p The composition of the charge The content of MgO, wt.% The amount of complex sintering additives, wt.% Applied Pressure, psi. Spend
bridge, mDft one RF patent No. 2235702 (analogue 1) 2000 10844 4000 7493 40,0 2 (TiO ₂ ) 6000 4033 8000 1879 10,000 861 2 RF patent No. 2235703 (analogue 2) 2000 13410 4000 9732 41.1 1 (titanium 6000 5042 concentrate) 8000 2012 10,000 831 3 sand - 485 g, serpentinite - 485 g, brucite - 10 g, colemanite - 6 g, fayalite - 10 g, sodium silicofluoride - 4 g (example 1) 2000 10924 4000 9258 19.1 3.0 6000 7192 8000 4215 10,000 2419 four olivinite - 920 g, serpentinite - 76 g, brucite - 1 g, colemanite - 1 g, fayalite - 1 g, sodium silicofluoride - 1 g (example 2) 2000 11840 4000 9124 47.2 0.4 6000 7002 8000 4052 10,000 2015 5 dunite - 980 g, brucite - 5 g, colemanite - 3 g, fayalite - 10 g, sodium silicofluoride - 2 g (example 3) 2000 12266 4000 10358 48.0 2.0 6000 7230 8000 4009 10,000 1956 6 sand - 485 g, serpentinite - 485 g, brucite - 10 g, colemanite - 6 g, fayalite - 10 g, sodium silicofluoride - 4 g 2000 10756 4000 8123 22.1 0.3 6000 5855 8000 3002 10,000 1054 7 sand - 485 g, serpentinite - 485 g, brucite - 10 g, colemanite - 6 g, fayalite - 10 g, sodium silicofluoride - 4 g 2000 12567 4000 10670 22.1 4.2 6000 5900 8000 2512 10,000 835 * - measurements were taken by FracTech Laboratories (Great Britain).

Analysis of the data in the table shows that the inventive method for the manufacture of magnesium-silicate proppant allows to obtain a product (No. 3-5 tables), which has increased conductivity of the proppant pack under hydrothermal conditions at high (more than 6000 psi) pressures compared with known analogues.

Claims (4)

1. A method of manufacturing a magnesium silicate proppant, including preparing the initial components of the mixture, grinding with a complex sintering additive, granulating the mixture, calcining and sieving the fired granules, characterized in that as the specified additive, a mixture of brucite, colemanite, sodium silicofluoride and fayalite in the amount of 0 , 4-3.0% by weight of the mixture based on magnesium silicate raw materials in the following ratio,% by weight of the mixture:
Brucite 0.1-1.0 Colemanite 0.1-0.6 Sodium silicofluoride 0.1-0.4 Fayalit 0.1-1.0
with a total MgO content in the charge of 19-48 wt.%. 2. The method according to claim 1, characterized in that the firing is carried out at a temperature of 1150-1220 ° C. 3. The method according to claim 1, characterized in that as the main component of the charge using natural magnesium silicate raw materials - serpentinite, olivinite, dunite, both independently and in the form of a mixture with natural quartz field sand. 4. Magnesium silicate proppant, characterized in that it is obtained by the method according to claim 1.