EA008825B1 - Proppants and method for producing thereof - Google Patents

Abstract

A method is disclosed for producing agents propping fractures in subterranean formations (proppants) comprising a mixture of kaolin clay and bauxite of different bauxites, wherein said mixture is subjected to calcination but not initial kaolin clay and bauxites.

Description

The present invention relates generally to the creation of propping agents (proppants), which are used to keep open fractures from closure in subterranean formations located in the zone of oil, gas and geothermal wells. More specifically, the present invention relates to the use of small (light) and average weight proppants in the operations of cracking and keeping open cracks from closing.

Background to the invention

In oil, gas, and geothermal wells, it often becomes necessary to stimulate product flow in order to achieve cost-effective well flow rates. For example, a new well may have an unacceptably low flow rate due to the low permeability of the formation or collapse around the wellbore. The technology that is often used to stimulate such a well is to inject fluid into the well until pressure rises to a level sufficient to fracture the formation, which leads to the formation of fractures in the formation. These cracks allow the product to be transported into the well at a significantly higher flow rate. This technology is called fracturing or hydraulic fracturing and has been practiced for over 50 years.

It is also known that after a formation (formation) fracture, it is necessary to keep the newly formed fractures from closing in order to create a continuous flow of gas or oil. Otherwise, the cracks will close under the influence of the rock closing pressure. The technology used to keep a fracture from closing is to inject a fluid suspension containing solid powdered material into a fractured formation.

The powder material used, called the propping agent, must be of sufficient strength to withstand the rock clamping pressure (stress causing the crack to close) acting on the crack. The usual type of destruction of a weak proppant is its fragmentation under the influence of compressive stress on small particles that can plug up cracks created during the process of cracking. Since rock-clamping pressure is usually proportional to depth, proppants that use in deeper cracks should be stronger than those suitable for use at shallower depths.

Ripping fillers are usually classified according to three gradations: light weight wedging fillers (B \ UR). intermediate grading proppants (ΙΡ) and high strength proppants (Η8Ρ). Lightweight wedging fillers are suitable for use in a range of stresses that cause a crack to close, ranging from less than 1000 ρκί (pounds per square inch) to approximately 8000 ρκί, intermediate wedging fillers are suitable for stresses up to approximately 10,000 ρκί, and wedging fillers high strength can be used at stresses above 12000 ρκί.

Lightweight proppants are used to take into account the stresses withstand without critical stress destruction at depths not exceeding 3.5 km. The average weight proppants can be used at depths of up to 4.4 km.

Although at such stresses and depths natural wedging agents can be used, for example sand, which has been taking place for a long time, artificial wedging agents are now considered as more preferred, although naturally they have a higher cost.

Spherical granules of the same size are usually considered the most effective proppants for maximum throughput (see, for example, US Pat. No. 4,623,630). In accordance with the standard of the American Petroleum Institute (ΑΡΙ) it is required that the size ranges of the particles (granules) of the proppants are within fairly narrow defined boundaries. For example, particle size ranges should be defined according to cell size designations like 40/70, 30/50, 20/40, 16/30, 16/20, and 12/18. The first number in this designation refers to the size of the cell of the standard (for the USA) largest (top) screen, and the second number to the size of the smallest (bottom) screen, while 90% of all granules are required to be held between the top and bottom sith

There are two interrelated characteristics of proppants, which basically determine their quality: crush strength (or its opposite characteristic — crushability under compressive stress) and their throughput (permeability to liquid and gas).

The higher the crushability of proppants, the lower their throughput at the same compressive stresses. So, for lightweight proppants, crushability should not exceed 7% at a voltage of 7500 ρκί (7.5 k) and 10% at a voltage of 10,000 ρκί (10 k). For proppants, the crushability should be less than 5% at a voltage of 10,000 ρκί (10 k) and 7% at a voltage of 12,500 ρκί (12.5 k).

The composition of artificial proppants used recently, usually includes alumina (aluminum oxide) and silica (silicon oxide) in various proportions. It is believed that the content of these oxides in the granules mainly determines the performance characteristics of proppants. Aluminum oxide gives proppants strength that is necessary to maintain integrity.

- 1 008825 of granules that experience compressive stresses when used, silicon oxide affects the elasticity of the material, which is crucial for the formation of granules.

Widely used alumino-silicon raw materials for the manufacture of proppants are kaolin (kaolin clay) (US patent number 5030603 and number 5188175, patents of the Russian Federation No. 2140874, 2140875 and 2215712).

A typical method for making kaolin granules includes the following steps:

a) the enrichment of kaolin clay natural location,

b) drying the clay,

c) clay calcination,

g) grinding of calcined clay,

d) granulation

e) sorting raw granules,

g) roasting (sintering) of granules,

h) sorting the sintered pellets.

Also known is the use as a source of raw materials for the manufacture of bauxite proppants (see, for example, US Pat. Nos. 4,068,718 and 4,668,645 and the Russian Federation No. 2129987). Bauxite is characterized by a higher (by 10% or more) content of A1 ₂ O ₃ than kaolin, and is more expensive raw material than kaolin clay and is used, as a rule, for the manufacture of high-strength proppants.

Finally, it is common to use kaolin and bauxite mixtures, including for the manufacture of lightweight proppants. In this case, bauxite is considered as a hardening additive to kaolin (US Patent No. 4427068 and Russian Federation Patents No. 2140875 and No. 2211198)

The known process of making proppants using a mixture of kaolin and bauxite, disclosed in these patents, includes the following steps:

calcining (roasting) kaolin and bauxite;

mixing baked kaolin and bauxite;

grinding the mixture of calcined kaolin and bauxite to a given particle size;

obtaining granules from the ground mixture;

drying of the obtained granules and sintering and classification of granules (selection of granules of a given size).

In the patent of the Russian Federation No. 2140875 it is indicated that it is possible to use not only calcined, but also raw, unbaked bauxite, before it is mixed with kaolin, but calcining of the latter is considered in this patent as an indispensable condition for carrying out the invention.

Summary of Invention

The present invention is the creation of a method of manufacturing proppants of small and medium weight with less cost to manufacture them.

Another object of the invention is to obtain proppants with lower costs, but with ensuring the necessary strength of the granules.

The solution of these problems is ensured by the possibility of changing the technology for manufacturing proppant granules described above, which consists in mixing kaolin and bauxite (in the manufacture of lightweight proppants) or two different bauxites (in the manufacture of medium-weight proppants) roasting), and before calcining, a mixture of kaolin and bauxite or bauxite is already subjected to calcination.

Reducing the cost of manufacturing the final product by the method according to the present invention is explained as follows.

When using calcined kaolin and bauxite as raw materials, which themselves are naturally more expensive than raw material, the process of making ready-made pellets from them can be separated in time from the process of firing (for example, when the proppant manufacturer does not have its own raw material and purchases it) during which the calcined kaolin and bauxite are stored and / or transported. At the same time, the effect of calcination, which consists, in particular, in reducing the content of free and chemically bound water in them, is reduced, which may affect both the subsequent stages of the process of manufacturing granules and their quality. When using raw, uncalcined kaolin and bauxite as the starting material, this disadvantage is eliminated.

An obvious advantage of the method according to the present invention is also a reduction in the number of pieces of equipment used (one furnace for calcining a mixture of kaolin and bauxite or a mixture of two bauxites instead of two furnaces for their separate calcination), which also reduces the cost of production.

Other characteristics and advantages of the invention will be clear from the subsequent detailed description of it and embodiments of the invention.

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DISCLOSURE OF INVENTION

In accordance with the present invention, a method for making lightweight proppants includes the following steps:

the provision of kaolin and bauxite as a raw material;

preparing a mixture of raw kaolin and raw bauxite; calcining a mixture of raw kaolin and raw bauxite;

grinding the calcined mixture of kaolin and bauxite to a given particle size;

obtaining granules from the ground mixture;

drying the resulting granules and sintering and classification of the granules.

Accordingly, the method of manufacturing proppants of average weight includes the following steps: provision of two types of bauxite as feedstock;

preparation of a mixture of bauxite;

calcining a mixture of raw bauxite;

grinding the calcined bauxite mixture to a given particle size;

obtaining granules from the ground mixture;

drying the resulting granules and sintering and classification of the granules.

It is advisable to grind raw kaolin and bauxite before mixing to the size of pieces <3 microns, and kaolin to further dry it to a free water content of 5-10 wt.%.

The calcination of a mixture of raw kaolin and raw bauxite or raw bauxite is carried out at temperatures in the range of 900-1200 ° C, for the time required to remove chemically bound water until its content is 3-5 wt.%.

As indicated above, the essence, the main feature of the method according to the invention lies precisely in the joint, rather than separate, calcination of various raw materials in the case of the manufacture of proppants from their mixture. This feature is unexpected for specialists in view of the existing (and reasonable) opinion among them that, due to the different chemical composition of kaolin and bauxite, the temperature regimes of their calcination should be different. So, in the patent of the Russian Federation No. 2211198 it is substantiated that the optimal firing temperature of kaolin is 1400-1500 ° C, and the optimum firing temperature of bauxite is either 1250-1300 ° C (with an Al ₂ O ₃ content _of more than 65%), or 1600-1650 ° C (with smaller values of the content of A1 ₂ O ₃ ), that is, it in any case does not coincide with the firing temperature of kaolin.

The authors of the present invention, it was found that the necessary strength of proppants can be achieved with the joint calcination of kaolin and bauxite or various bauxites, that is, at the same temperature, and even at lower temperatures of 900-1200 ° C. This is confirmed by the following examples of carrying out the invention.

Example 1. Used kaolin and bauxite of the following chemical composition (wt.%):

Kaolin - A1 ₂ O ₃ - 43.63; 81O ₃ - 53.41; ΤίΟ ₂ - 1.12; Re ₂ O ₃ - 1.15; K ₂ O - 0.36; Na ₂ O - 0.07; CaO - 0.13; MDO - 0.12.

Bauxite - A1 ₂ O ₃ - 55.06; 8JO ₂ - 40.81; T1O ₂ - 2.41; Re ₂ O ₃ - 1.24; K ₂ O - 0.14; Na ₂ O - 0.03; CaO - 0.20; MDO - 0.09.

Kaolin and bauxite were ground in a rotating shredder to a lump size of less than 3 microns. In addition, the kaolin was dried in a drum dryer to a free moisture content of less than 10%.

After that, kaolin and bauxite were mixed in the ratio of 39% kaolin and 61% bauxite, and a mixture of the following composition was obtained, wt%: A1 ₂ O ₃ - 50.40; 81O ₂ - 46.10; T1O ₂ - 1.90; Re ₂ O ₃ - 1.04; K ₂ O - 0.24; Na ₂ O -0.05; CaO - 0.15; MDO - 0.10.

The resulting mixture was subjected to calcination at a temperature of 1050 ° C until the content of chemically bound water is less than 5%.

From this mixture were obtained using the Erich mixer granules, which were dried to a free water content of less than 6%, and then subjected to sintering at a temperature of 1500 ° C. The obtained granules with a size of 20/40 were subjected to the crush strength test according to the method of the American Petroleum Institute under a load of 10,000 rya (10k). The fraction of destroyed granules was 4.2% by weight, with 10% acceptable for lightweight proppants.

Example 1a (comparative).

For comparison, a mixture was prepared from the already calcined kaolin and bauxite of the following composition (% weight):

Kaolin-A1 ₂ O ₃ - 42.16; 8U ₂ - 54.23; T1O ₂ - 0.76; Re ₂ O ₃ - 1.14; K ₂ O - 0.54; CaO - 0.07; Md - 0.10.

Bauxite - A1 ₂ O ₃ - 53.46; 8U ₂ - 42.85; T1O ₂ - 2.33; Re ₂ O ₃ - 0.84; K ₂ O - 0.12; CaO - 0.29; MDO - 0.14.

Kaolin and bauxite were mixed in such a ratio (25% kaolin and 75% bauxite) to ensure that the content of A1 ₂ O ₃ and 81O _{2 is} approximately the same with example 1: it was, wt.%:

A1 ₂ O ₃ - 50.61; 81O ₂ - 45.73; the rest of T1O ₂ is 2.01; Re ₂ O ₃ - 1.09; K ₂ O -0.17; CaO - 0.25; MDO - 0.14.

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From the mixture obtained, in a similar manner to Example 1, granules were made, which, as a result of the strength tests under the load Yc, yielded a crushability value of 6.6%.

Thus, the strength of the granules obtained by the method in accordance with the present invention, that is, using a mixture of raw kaolin and raw bauxite, mixed before calcining, turned out in this example not only to satisfy the requirements for lightweight proppants, for the manufacture of which the method is intended in accordance with the present invention, but also higher than when using a mixture of calcined kaolin and bauxite.

Example 2

Analogously to example 1, granules were made from mixtures of non-calcined kaolin and bauxite other than in examples 1 and 1a, and subjected to preliminary calcination. Data on the chemical composition of the initial kaolin and bauxite and their mixtures are presented in table. one.

Table 1

Example 2 A1 _g O ₃ 31O2 bye ₂ Its ₂ 0z K ₂ O Ma ₂ O Cao MDO Kaolin B1 42.35 54.75 1.12 1.11 0.33 0.08 0.14 0.11 Bauxite B1 55.06 40.81 2.41 1.24 0.14 0.03 0.20 0.09 43% kaolin B1 and 57% bauxite B1 (mixing before calcining, calcining the mixture at 900 ° C) 48.66 47.96 1.67 1.11 0.27 0.07 0.15 0.10 Kaolin B2 43.37 54.16 0.64 0.46 0.52 0.67 0.18 Bauxite B2 53.46 42.85 2.30 0.84 0.12 0.29 0.14 50% kaolin B2 and 50% bauxite B2 (mixing after calcining} 47.95 48.50 1.73 1.21 0.25 0.22 0.14; I

The results of the strength tests of the obtained granules under load Yuk were as follows: the granules manufactured by the method in accordance with the present invention turned out to be, as in Example 1, more durable than those made by a known method, namely their crushability was 6.5 wt.% Against 7.7% for pellets made from a mixture of kaolin and bauxite, subjected to separate calcination.

Example 3. Analogously to examples 1 and 2, granules were made from mixtures of uncalcined and calcined kaolin and bauxite, the data on the chemical composition of which are presented in Table. 2

table 2

Example 3 αι ₂ ο ₃ SIR? bye ₂ Her ₂ O ₃ K ₂ O N 320 Cao MDO Kaolin C1 44.46 52.93 1.28 0.86 0.12 0.11 0.17 0.07 Bauxite C1 56.24 40.09 2.40 0.86 0.08 0.05 0.20 0.08 75% kaolin C1 and 25% bauxite C1 (mixing before calcining, calcining the mixture at 1200 ° C) 48.83 47.92 1.72 1.07 0.10 0.10 0.19 0.08 Kaolin C2 45.01 52.07! 1.44 1.08 0.08 0.08 0.16 0.06 Bauxite C2 55.06 40.81 2.41 1.24 0.14 0.03 0.20 0.09 62% kaolin C2 and 38% bauxite C2 (mixing after calcining) | 48.60 one 48,10 1.78 1.07 0.12 0.07 0.16 0.09

The results of the strength tests of the obtained granules under load Yuk in this example were as follows: although the crushability of the granules made in accordance with the present invention was higher (7.1 wt.%) Than the granules made of a mixture of pre-calcined kaolin and bauxite (4 , 2 wt.%), It nevertheless does not exceed the allowable for lightweight proppants (10%).

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Example 4. Similar to the previous examples, granules were made from mixtures of two uncalcined (in accordance with the present invention) and calcined bauxite, data on the chemical composition of which are presented in Table. 3

Table 3

Example 4 A1 ₂ O ₃ 5Yu ₂ bye ₂ Its ₂ 0z K ₂ O Pa ₂ O Cao MDO Bauxite ϋ1 74.36 18.38 4.26 2.25 0.37 0.14 0.22 Bauxite E1 87.38 6.95 3.73 1.60 0.09 0.05 0.10 0.10 70% bauxite ϋ1 and 30% bauxite E1 (mixing before calcining, calcining the mixture at 1000 ° C) 79.05 14.19 3.90 2.10 0.30 0.14 0.17 70% bauxite 01 and 30% bauxite E1 (mixing after calcining) 78.05 14.50 4.16 1.93 0.37 0.16 0.18

The results of the strength tests of the obtained granules under the load Yuc were as follows: the strength of the granules made in accordance with the present invention was close to the strength of the granules made in a known manner, that is, from previously separately calcined bauxite (crushability of the granules was 3.4 and 2.4 % respectively).

Example 5. Analogously to example 4, granules were made from mixtures of two uncalcined (according to the invention) and calcined bauxite, data on the chemical composition of which are presented in Table. four.

Table 4

Example 5 ΑΙ2Ο3 5Yu ₂ bye ₂ Her ₂ O _e K ₂ O Νθ ₂ Ο Cao MDO Bauxite E1 79.28 7.96 4.52 4.95 0.02 0.04 3.02 0.18 Bauxite C1 72.51 19.94 4.13 2.43 0.34 0.16 0.20 0.23 25% bauxite E1 and 75% bauxite Θ1 (mixing before calcining) 75.12 16.32 4.15 3.01 0.27 0.12 0.77 0.21 70% bauxite E1 and 30% bauxite (31 (mixing after calcining) 75.05 16,34 4.15 3.04 0.27 0.12 0.77 0.21

The results of the strength tests of the obtained granules under the load Yuc were as follows: the strength of the granules made in accordance with the present invention slightly exceeded the strength of the granules made in a known manner from previously calcined bauxite (crushability of the granules was 2.5 and 2.8%, respectively).

Claims (6)

1. A method of manufacturing proppants, which includes the following successive steps: providing kaolin and bauxite as feedstock; preparing a mixture of raw kaolin and raw bauxite; calcining a mixture of crude kaolin and crude bauxite; grinding a calcined mixture of kaolin and bauxite to a predetermined particle size; obtaining granules from the crushed mixture; drying the obtained granules; and sintering and classification of granules. 2. The method according to claim 1, wherein the raw kaolin is ground to a piece size <3 μm and dried to a free water content of 5-10 wt.% Before mixing it with raw bauxite. 3. The method according to π. 1, in which the raw bauxite before mixing it with raw kaolin is crushed to a piece size <3 μm. 4. A method of manufacturing proppants, which includes the following successive steps: the provision of two types of bauxite as a feedstock; preparation of a mixture of bauxite; -5008825 calcination of a mixture of crude bauxite; grinding a calcined bauxite mixture to a predetermined particle size; obtaining granules from the crushed mixture; drying the obtained granules; and sintering and classification of granules. 5. The method according to claim 1 or 4, in which the calcination of a mixture of crude kaolin and crude bauxite or a mixture of raw bauxite is carried out at a temperature of 900-1200 ° C for the time required to remove chemically bound water to its content in the amount of 3-5 weight .%. 6. The proppant, representing the granules obtained by the method according to any one of claims 1 to 5.