EA006953B1 - Proppants, method of their manufacture and use - Google Patents

Abstract

Described is the use of kaolin or a mixture of kaolin and bauxite with a content of KO or less than 0.2% by weight for manufacturing a proppant, i.e. an agent for maintaining in a propped condition (keeping from closure) a fracture in a subterranean formation (in oil- and gas-bearing formations).Sintered pellets manufactured from such materials possess increased strength (resistance to crushing) and increased permeability for oil and gas.

Description

The scope of the invention

The present invention generally relates to proppants for oil and gas wells (proppants), and more particularly, to sintered proppants that contain kaolin as a main component, to a method for manufacturing such proppants, and to a method for maintaining a fracture (fracture) in an underground (geological) formation in a wedging state through the use of such proppants.

Prior art

Oil and natural gas are obtained from wells passing through porous and permeable subterranean formations. The porosity of the formation allows it to accumulate oil and gas, and the permeability of the formation allows oil or gas to flow through the formation. The permeability of the formation (reservoir) is essential so that oil and gas can flow to a location from which they can be pumped out of the well. Sometimes the permeability of a formation storing gas or oil is insufficient for cost-effective production of oil and gas. In other cases, during the operation of the well, the permeability of the formation decreases so that further production becomes economically disadvantageous. In such cases, it is necessary to break the formation and keep the gap open (to keep the crack from closing) using a proppant material or proppant. Such a fracturing (fracturing) is usually carried out using hydraulic pressure, and the proppant or proppant are sintered granules that are injected into the fracture using a fluid.

Spherical granules are generally considered the most effective proppants because of their maximized permeability. For this reason, provided that the other properties are the same, spherical or mainly spherical proppants are preferred.

The proppants used recently include alumina (alumina) and silica (silica) in various proportions. It is believed that it is the content of these oxides in the granules that determines the operational characteristics of proppants. Alumina gives proppants the strength that is necessary to maintain the integrity of the granules that experience compressive stresses of up to 10,000 ρκ свыше (over 700 kg / cm ² ) or more depending on the depth of the propped crack. Silicon oxide affects the elasticity of the material, which is crucial for the formation of granules.

As aluminosilicon raw materials for the manufacture of proppants, kaolins or bauxites, or mixtures thereof, are usually used.

Examples of use for the manufacture of kaolin proppants are the patents of the Russian Federation No. 2140874, 2140875 and 2215712, as well as US patents No. 5.030.603. and No. 5.188.175.

Examples of use for the manufacture of bauxite proppants are the patent of the Russian Federation No. 212998, as well as US patents No. 4068718 and No. 4668645.

The patent of the Russian Federation No. 2211198 describes the use of a mixture of kaolin and bauxite for the manufacture of proppants.

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

The higher the proppant crushability, the lower their throughput at the same compressive stresses. So, for lightweight proppants, which mainly relates to the present invention, used at shallow depths, crushability should not exceed 7.4% at a voltage of 7.500 ρκί (7.5 k) and 10% at a voltage of 10.000 ρκί (10 k).

As noted earlier, it is believed that the strength of proppant granules, if we talk about the chemical composition of the raw materials for their manufacture, is determined by the content of aluminum oxides in it. This explains, in particular, the fact that if the feedstock contains a small amount of aluminum oxides, additives are added to it that increase the strength of the granules with a high content of these oxides. So, in the patent of the Russian Federation No. 2140875, which describes the use of kaolin with a low content of aluminum oxides (30-45 wt.%), It is proposed to use, as additives, increasing the strength of the granules, in particular, alumina dust with a content of A1 ₂ O ₃ 99,099 5 wt.%.

SUMMARY OF THE INVENTION

In addition to these oxides, the raw materials used for the manufacture of proppants contain oxides of elements such as iron and titanium, as well as alkaline elements —ΝαΟ, K ₂ O, CaO and MdO. Previously we studied the influence of content T1O ₂ granule strength proppants, wherein it was concluded that increasing it over 0.8 wt.% Does not significantly affect improvement of the strength properties (Patent NO 2,166,079).

The authors of the present invention unexpectedly found that on the crushing ability of proppant granules (strength) and, as a consequence, on their throughput (permeability to oil and gas)

- 1 006953 has a significant effect on the content of potassium dioxide K ₂ O used in their production, namely, the higher it is, the lower the strength of the granules and vice versa.

As shown in the present description below, the strength of the granules made from it depends to a large extent on the content of this particular oxide in the starting kaolin. With an equal content of alumina, the strength will be higher for those granules made of kaolin with a lower content of K ₂ O. Moreover, granules made of kaolin with a lower content of A1 ₂ O ₃ but with a low content of K ₂ O are stronger than granules made from kaolin with a higher A12O3 content, but with a high K2O content.

The inventors have established quantitative values of the "low" content of K ₂ O, at which the detected effect is manifested: less than 0.2 wt.%, Preferably less than 0.15 wt.% And most preferably from 0.05 to 0.1 wt.% .

The indicated values are significantly lower than those characteristic of kaolins, proposed for use in the prior art. So, in patents KP 2140874 and KP 2140875 it is proposed to use kaolin with a content of K ₂ O of 0.8-0.9%, in the patent Ki 2215712 kaolin with a content of K ₂ O of 0.45-0.91%.

SUMMARY OF THE INVENTION

In accordance with the present invention, proppants are provided, which are sintered, essentially spherical granules made of kaolin with a low K2O content of less than 0.2 wt.%, Preferably less than 0.15 wt.% And most preferably from 0.05 to 0 , 1 wt.%.

The invention also covers proppants made from a mixture of kaolin and bauxite, with kaolin having a low K2O content in the above ranges, while retaining the advantage of using kaolin with a low K ₂ O content - obtaining more durable and permeable granules.

Another aspect of the present invention is a method of making proppants, wherein the starting material used is kaolin with low content of K 2 O or a mixture of kaolin to bauxite in which kaolin has a low content of K ₂ O.

In accordance with the present invention, there is also provided a method for wedging (holding against closure) cracks in oil and gas wells using proppant granules made in accordance with the present invention.

Brief Description of the Drawings

In FIG. 1 shows the relationship between the content of K ₂ O in various kaolins and the strength of sintered granules made from them.

In FIG. Figure 2 shows for comparison a picture of the distribution of strength values of the same granules depending on the content of A12O3 in kaolins.

DETAILED DESCRIPTION OF THE INVENTION

The proppant in accordance with the present invention has the form of solid, substantially spherical (having an average ratio of minimum to maximum diameter of 0.7 and higher) granules made of kaolin or a mixture of kaolin and bauxite, satisfying the condition of low K ₂ O content (less 0.2 wt.%) In kaolin.

Kaolins are clay rocks of sedimentary origin, consisting mainly of the mineral kaolinite (chemical formula A1 ₂ O ₃ -281O ₂ -2H ₂ O).

Kaolin typically has an alumina content of less than about 50%, and a silica content of more than about 45%. All contents shown here are based on the dry weight of the fully calcined material.

Various methods for producing granules may be used, however, the method described in US Pat. No. 4,427,068 and involving the use of an Esch mixer is preferred. Milled to a particle size of about 10 microns, heat-treated for dehydration, kaolin or a mixture of kaolin and bauxite is mixed with a small amount of binder and water. Starch is a preferred binder, however, any other suitable binder material can be used that properly maintains the shape of the raw granule and does not adversely affect the strength of the calcined granule.

An additional powder of dry milled kaolin (kaolin and bauxite) is then added and stirring is continued until essentially spherical granules are formed. The raw granules are then fired (sintered) at a temperature of from 1100 to 1590 ° C. for about 45 minutes to 1 hour in a rotary kiln.

The inventors studied the effect of the content of K ₂ O in kaolin on the strength of sintered granules made from it using various kaolin clays from the state of Georgia, USA as an example. Strength measurement was carried out in accordance with the methodology recommended by the American Petroleum Institute (AP1).

In accordance with this technique, a layer of granules with a thickness of about 6 mm with the test sample is placed in a hollow cylindrical cell. Then a piston is introduced into the cell. After that, a load is applied to the sample using a piston. One minute is required in order to achieve maximum load, which is then stored for two minutes. After this, the load is removed, the sample is removed

- 2 006953 from the cell and sieved to separate crushed material. Its share of the weight of the initial sample is an indicator of strength: the higher it is, the lower the strength.

The invention will now be described with reference to non-limiting examples.

Example 1

For the preparation of granules, kaolin of the following chemical composition was used:

A1 ₂ O ₃ - 45.17, §ίϋ ₂ - 52.65, Τίϋ ₂ - 2.00, Her ₂ O ₃ - 0.81, CaO - 0.17, MdO - 0.12, P ₂ O ₅ - 0.06 and K ₂ O - 0.04. The calcined kaolin (which has undergone heat treatment at a temperature of 500-1000 ° C) was given the shape of spherical granules with a particle size distribution of 18/30, after which the granules were sintered at a temperature of about 1500 ° C. Sintered granules had a particle size distribution of 20/40. The granules prepared in this way were subjected to strength tests at a load of 7.500 ρδΐ (7.5 k) according to the AP1 method described above. The resulting value is 4.0.

Examples 2-16.

In a similar manner, granules of kaolin of a different chemical composition were made and tested for strength.

The obtained data on the strength of granules at a load of 7.500 ρδΐ (7.5 k) and information on the chemical composition of the studied kaolin clays are presented in Table. one.

Table 1

Example one 2 3 4 5 6 7 8 A1 ₂ Oz 45.17 45.93 46.91 45.77 45.00 45.56 46.85 47.16 Re ₂ O ₃ 0.81 0.90 1.15 0.99 0.86 0.86 1.17 1.14 K ₂ O 0.04 0.05 0.06 0.07 0.08 0.09 0.10 0.11 8U ₂ 51.65 50.70 49.21 50.68 51.75 51.08 49.41 48.95 CaO 0.17 0.15 0.26 0.20 0.16 0.11 0.03 0.20 MDO 0.12 0.10 0.14 0.10 0.08 0.07 0.04 0.12 R ₂ O ₅ 0.06 0.06 0.06 0.03 0.06 0.05 0.06 0.06 T1O ₂ 2.00 2.11 2.22 2.16 2.02 2.17 2.34 2.25 7.5K 4.0 4.5 4.3 4.0 4.4 4.0 4.1 4.4 nine 46.26 0.96 0.12 50.11 0.09 0.07 0.05 2.33 4.6 10 45.78 1.19 0.13 50.59 0.09 0.11 0.05 2.07 4.7 eleven 47.07 1.21 0.14 49.08 0.16 0.11 0.06 2.17 4.5 12 45.48 1.13 0.15 50.89 0.10 0.10 0.06 2.10 4.9 thirteen 44.84 1.22 0.16 59.19 0.12 0.09 0.06 2.31 5.2 14 46.50 1.27 0.18 49.36 0.10 0.07 0.06 2.46 5.8 fifteen 46.63 1.24 0.19 49.26 0.10 0.07 0.06 2.45 7.1 sixteen 47.71 1.47 0.21 48.15 0.14 0.11 0.08 2.14 6.0

As can be seen from the table. 1 data, there is a clear pattern: the lower the content of K ₂ O in kaolin, the lower the granularity of the granules, that is, the higher their strength. This clear relationship is shown in FIG. 1: with K ₂ O values equal to 0.05%, the strength is maximum, with an increase in K ₂ O content in the range of 0.05-0.15%, the strength remains at a level close to the maximum, and with a K2O content value of 0.2 % and above, a significant decrease in the strength of the granules is planned.

At the same time, it turned out that no such dependence was found between the Al ₂ O ₃ content and the strength of the granules (in the range of the Al ₂ O ₃ content from 44.5 to 48%), as illustrated in FIG. 2.

This means that the orientation on the value of the content of alumina in kaolin as the only indicator of the strength of the granules may be erroneous, it should be taken into account as an equally important parameter, and the content of K2O in the feed.

The revealed regularities of the dependence of the strength of granules on the content of K ₂ O in the raw materials were also confirmed for granules made from a mixture of kaolin and bauxite.

Example 17

In laboratory conditions, granules were made from a mixture of kaolin A (85%) and bauxite C (15%). Data on the chemical composition used in this and subsequent examples of kaolins and bauxites are given in table. 2. The granules were subjected to strength tests similarly to examples 116, but at a load of 10.000 ρδΐ (10 K). The resulting strength index is 8.4. The content of K ₂ O in kaolin A is 0.11%.

Examples 18-22.

Granules made and tested for strength were made from a mixture of kaolins (A and B) with bauxite (C, Ό, E) at various ratios in the feedstock. The results are summarized in table. 3.

As follows from the data presented in it, with almost the same total content of A1 ₂ O ₃ , the strength of granules made from a mixture of kaolin and bauxite is 1.4 times (for a mixture of kaolins with bauxite E) and 1.7 times (for a mixture kaolins with bauxite C) are higher when using kaolin with a low content of K ₂ O (kaolin A) compared with kaolin with a higher content of K ₂ O (kaolin B).

- 3 006953

table 2

Material ΑΙ2Ο3 5ΪΟ2 TU2 Her2OZ K2O CaO MDO Kaolin A 44.78 52.64 1.40 0.81 0.11 0.16 0.05 Kaolin B 41.55 55.57 1.06 1.14 0.40 0.16 0.13 Bauxite C 89.65 5.44 3,58 1,07 0.09 0,07 0.10 Bauxite ϋ 75.80 14.04 4.45 5.03 0.32 0.19 0.17 Bauxite E 75.00 17.90 4.23 2.10 0.36 0.15 0.21

Table 3

Examples Product Bulk density g / ss ABC SK weight% ΑΙ2Ο3 8U2 TU2 Her2OZ K2O CaO MDO Mixtures of kaolin A and B with bauxite C 17 85% kaolin A + 15% bauxite C 20/40 1.51 2.77 8.4 52.03 44.66 1.74 1,08 0.08 0.12 0,07 eighteen 79% kaolin B + 21% bauxite C 20/40 1.45 2.70 I 14.0 52,44 44.03 1,69 1.23 0.34 0.15 0.13 Mixtures of kaolin A and B with bauxite ϋ nineteen 76.9% kaolin A + 23.1% bauxite ϋ 20/40 1,53 2.82 9.1 52.01 43.52 2.07 1.97 0.17 0.17 0.09 twenty 68.4% kaolin B + 31.6% bauxite ϋ 20/40 1.51 2.81 9.9 52,20 43.17 1,67 1.75 0.50 0.53 0.18 Mixtures of kaolin A and B with bauxite E 21 73.5% kaolin A + 26.5% bauxite E 20/40 1,54 2.82 10.1 52.22 43.80 2.06 1.46 0.21 0.16 0.09 22 65.2% kaolin B + 34.8% bauxite E 20/40 1,50 2.76 14.0 52.24 43.26 2.07 1.68 0.45 0.16 0.14

Despite the fact that a preferred embodiment of the invention has been described, it is clear that those skilled in the art can make equivalent changes and additions to it that do not go beyond the scope of the following claims. So, presented in the examples, the ratio of the content of kaolin and bauxite in the mixture does not in any way limit the scope of the invention indicated in them.

Claims (15)

CLAIM 1. Agent for wedging cracks in the underground formation, which is a sintered, essentially spherical granules made of kaolin, and kaolin contains K ₂ O in an amount of less than 0.2 wt.%. 2. Agent for wedging cracks according to claim 1, made of kaolin, in which the content of K ₂ About is less than 0.15 wt.%. 3. The agent for wedging cracks according to claim 1, made of kaolin, in which the content of K ₂ About is from 0.05 to 0.10 wt.%. 4. A method of manufacturing an agent for wedging cracks in an underground formation, comprising the following steps: a) heat treatment of pre-crushed aluminosilicate raw materials, ensuring its dehydration; b) mixing the heat-treated aluminosilicate raw materials with a binder and water; C) the formation of the specified mixture, essentially spherical granules; and g) sintering of the obtained granules, and kaolin with a K2O content of less than 0.2 wt.% is used as feedstock. 5. The method according to claim 4, in which kaolin is used with a K ₂ O content of less than 0.15 wt.%. 6. The method according to claim 4, in which kaolin is used with a K ₂ O content of from 0.05 to 0.10 wt.%. 7. A method of retaining from closing a crack in an underground formation formed by hydraulic fracturing, which consists in pumping a fluid containing sintered substantially spherical granules made of kaolin with a K ₂ O content of less than 0.2 wt.%, Preferably less than 0.15 wt.%, most preferably from 0.05 to 0.10 wt.%. - 4 006953 8. Agent for wedging cracks in an underground formation, in particular in oil and gas formations, which is a sintered essentially spherical granule made from a mixture of kaolin and bauxite, and kaolin contains K ₂ O in an amount of less than 0.2 wt.% . 9. The agent for wedging cracks according to claim 8, wherein kaolin contains K ₂ O in an amount of less than 0.2 wt.%. 10. Agent for wedging cracks according to claim 8, wherein kaolin contains K ₂ O in an amount of from 0.05 to 0.1 wt.%. 11. A method of manufacturing an agent for wedging cracks in an underground formation, comprising the following steps: a) heat treatment of pre-crushed aluminosilicate raw materials, ensuring its dehydration; b) mixing the heat-treated aluminosilicate raw materials with a binder and water; C) the formation of the specified mixture, essentially spherical granules; and g) sintering of the obtained granules, moreover, a mixture of kaolin and bauxite is used as feedstock, while the content of K ₂ O in kaolin is less than 0.2 wt.%. 12. The method according to claim 11, in which kaolin is used with a K ₂ O content of less than 0.15 wt.%. 13. The method according to claim 11, in which kaolin is used with a K ₂ O content of from 0.05 to 0.10 wt.%. 14. A method of retaining from closing a crack in an underground formation formed by hydraulic fracturing, which consists in injecting a fluid containing sintered substantially spherical granules made of a mixture of kaolin and bauxite into said crack, wherein kaolin contains K ₂ O in an amount of less than 0 , 2 wt.%, Preferably less than 0.15 wt.%, Most preferably from 0.05 to 0.10 wt.%. 15. The method according to 14, in which the underground formation is an oil or gas reservoir.