RU2445339C1 - Manufacturing method of siliceous proppant, and proppant - Google Patents

Abstract

FIELD: oil and gas industry.

SUBSTANCE: in manufacturing method of siliceous proppant, which involves charge grinding, granulation and baking of granules, natural highly siliceous sand or its mixture with quartzite in quantity of 1-25% of mass of mixture at SiO₂ content in the charge of not less than 87 wt % is used as charge; grinding is performed to the size of not more than 10 mcm at fraction content of not more than 5 mcm, which is not less than 50 wt %, and calcination - at 1120-1300°C at heating rate of 1000-2500°C/h and cooling rate of 1000-2000°C/h. Siliceous proppant is characterised by the fact that it has been obtained by means of the above method; at that, content of christobalite in calcined granules does not exceed 10 vol %.

EFFECT: decreasing proppant density at maintaining allowable strength values of granules.

3 cl, 2 ex, 1 tbl, 1 dwg

Description

The invention relates to the oil and gas industry, and in particular to a technology for the manufacture of ceramic oil well proppants - proppants used in the intensification of oil or gas production by hydraulic fracturing - hydraulic fracturing.

Ceramic proppants have the best performance compared to other types of proppants - from walnut shells, natural rounded sand, etc. However, for economic reasons, their use is limited, and therefore the search for cheap natural raw materials that provide acceptable performance characteristics of proppants is relevant. Silica ceramic proppants with a low bulk density attract particular attention. As the proppant density decreases, the fracturing fluid used to fill the fracture with proppant can have a lower viscosity, which reduces the cost of the fracturing fluid, and also reduces the likelihood that the fracturing fluid that remains in the reservoirs blocks the flow of gas and oil, reducing well productivity . Reducing the density of the proppant facilitates and reduces the cost of pumping proppant into the well, and the proppant itself can penetrate deeper into the fracture, increasing the productivity of an oil or gas well.

According to US patent RE 34371, publ. 09/07/1993, a light proppant for oil and gas wells is obtained by simultaneously mixing and compacting a mixture of kaolin clay, calcined at a temperature of less than 900 ° C, and silica, from amorphous to microcrystalline, both materials being crushed to a total average grain size of 7 μm or less. The low density proppant, comprising approximately 35-60 wt.% Mullite and approximately 35-60 wt.% Cristobalite, has a specific gravity of less than 2.7 g / cm ³ (2.52-2.59 g / cm ³ ). The disadvantage of this proppant is the increased density, due to the significant content of mullite in the calcined granules. In addition, the need for preliminary firing of kaolin clay complicates and increases the cost of the material production process. A decrease in the density of proppant granules is achieved by high-temperature firing at a temperature of 1300-1500 ° C, at which quartz is converted to cristoballite with corresponding volumetric changes that cause a softening of the ceramic structure. However, in this case, the proppant has lower strength values.

According to US patent No. 6753299, publ. 06/22/2004, proppant is made of a composite siliceous material, including equal by weight amounts of unbaked bauxite, unbaked slate and quartz, held together by a binder formed by wollastonite and talc, in amounts of less than 10% by weight of the named composition. The composition includes alumina in an amount of less than 25% by weight of a given composition and silica in an amount of more than 45% by weight of this composition.

Closest to the claimed invention are a method of manufacturing a siliceous proppant and proppant obtained by this method, according to which grinding is carried out to a size of 15 microns of the components of the mixture, containing, wt.%: Talc - 1-10, wollastonite - 1-10, bauxite - 5- 33, quartz - 10-65 and shale containing potassium oxide - 5-10 and silica 75-90, 10-65, with a total silica content of the mixture - 45-70, a Al ₂ O ₃ - 15-25, granulation and firing of granules at a temperature of 1100-1200 ° C, while the main crystalline phases that make up the calcined proppant are quartz, EMAT, α - Al ₂ O ₃ and anorthite (WO 03/042497, published on 22.05.2003.).

The disadvantage of these proppants is the increased density of 2.623-2.632 g / cm ³ . This is because in order to reduce the sintering temperature and to prevent the phase transformation of quartz into tridymite and cristobalite and the related softening of ceramics, a significant amount of fluxes forming a glass phase with an increased density is introduced into the mixture. The significant disadvantages of the material include the multicomponent composition of the charge.

The technical problem to be solved by the claimed invention is directed is to reduce the proppant density while maintaining acceptable granule strength values.

This result is achieved by the fact that in the method of manufacturing a siliceous proppant, including grinding the mixture, granulating and firing the granules, natural high-silica sand or its mixture with quartzite in the amount of 1-25% by weight of the mixture with the content of SiO ₂ in the mixture is not less than 87 wt.%, Grinding to a size of not more than 10 microns with a fraction content of not more than 5 microns, comprising at least 50 wt.%, And firing at 1120-1300 ° C with a heating rate of 1000-2500 ° C / h and a speed cooling 1000-2000 ° C / h.

The specified result is also achieved by the fact that siliceous proppant obtained by the above method. Moreover, the content of cristobalite in the calcined granules does not exceed 10 volume%.

The granules obtained according to the claimed invention are a low-density high-siliceous ceramic material that does not require additional introduction of alumina and is represented mainly by a single crystalline phase - quartz. Unexpected was the fact that with the claimed firing modes, it is possible to maintain a uniquely high level of crystalline quartz in the material (see Fig. 1). This is due to the high degree of dispersion of the feedstock and the accelerated mode of heating and cooling during sintering firing of granules. It should also be noted that natural impurities - Fe ₂ O ₃ , Na ₂ O, K ₂ O, Al ₂ O ₃ and others, contained in sands and quartzites, change the temperature of polymorphic transformations of SiO ₂ . The preservation of acceptable proppant strength values is due to the dispersion of quartz grains in the glass phase formed during sintering. A crack that develops along the glass phase inside the granule encounters more durable quartz crystals in its path and spends a significant part of the energy around them, thereby increasing the material's resistance to destructive loads. Another technological factor that has a positive effect on the strength of the proppant is rapid cooling, during which the surface of the granules is compressed - hardening by hardening.

When the content of SiO ₂ in the mixture in an amount of less than 87 wt.%, The proppant density increases. A decrease in the rate of heating and cooling of granules below 1000 ° C / h causes a narrowing of the temperature range of sintering firing, as well as an increase in the proportion of cristobalite in ceramics, which leads to a deterioration in the strength characteristics of proppant. An increase in the heating and cooling rates of granules above 2500 ° C / h and 2000 ° C / h, respectively, does not allow for a uniform temperature field along the calcined proppant layer and leads to cracking of the granules. Grinding the material to a fraction of more than 10 microns with a fraction content of not more than 5 microns less than 50 wt.% Causes proppant softening due to the formation of cracks during the phase transformation of quartz. The authors experimentally first established the particle size distribution of the charge, in which the inventive proppant has the optimal combination of strength and density. According to the authors, when the content of the fraction is not more than 5 microns more than 85-90 wt.%, The conversion of quartz to cristobalite will be accelerated due to amorphization of the surface of the quartz grains, and the strength of the proppant will decrease. Excessive grinding turned out to be harmful for another technological redistribution of proppant production - granulation: the sphericity and roundness of granules larger than 0.2 mm becomes unsatisfactory due to their adhesion. At a firing temperature of less than 1120 ° C, the granules remain unburned and have low strength. An increase in sintering firing temperature of more than 1300 ° C causes the formation of cristobalite and a significant number of proppant granule cakes. If the content of cristobalite in the calcined granules exceeds 10 vol.%, The proppant has reduced strength characteristics.

Examples of carrying out the invention.

Example 1

Compositions 1, 2. Highly siliceous sand with a SiO ₂ content _of approximately 87 wt.% Was fed to a laboratory vibratory mill for grinding and crushed to a fraction of 10 μm or less, with a fraction of less than 5 μm being 52 wt.%. The fractional composition was monitored on a Horiba LA-300 photosedimentograph. Then the material was granulated. The raw proppant of the 30/50 mesh fraction was fired at a temperature sufficient to maximize compaction of ceramics with different heating and cooling rates of the granules. Absorbed proppant was used to determine the absolute density (Accupyc 1340 instrument) and pellet breakage, according to the generally accepted method ISO 13503-2: 2006 (E). Additionally, proppant samples were made of sand containing less than 87 wt.% SiO ₂ (composition 2). In addition, the fired granules were subjected to petrographic studies and X-ray phase analysis (XRD) on a DRON-3M diffractometer. The measurement results are shown in table 1.

Example 2

Compounds 3-5. Highly siliceous sand with a SiO ₂ content _of approximately 87 wt.% With the addition of quartzite in the amount of 5, 15 and 25 wt.% Was fed to the grinding laboratory vibrator and ground to a fraction of 10 μm or less, and the fraction content of less than 5 μm was 55 wt.% . The fractional composition was monitored on a Horiba LA-300 photosedimentograph. Then the material was granulated. The raw proppant of the 30/50 mesh fraction was fired at a temperature sufficient to maximize compaction of ceramics with different heating and cooling rates of the granules. Absorbed proppant was used to determine the absolute density (Accupyc 1340 instrument) and granule disintegration according to the generally accepted method ISO 13503-2: 2006 (E). The calcined granules were subjected to petrographic studies and X-ray phase analysis (XRD) on a DRON-3M diffractometer. The measurement results are shown in table 1, the XRD data in Fig. 1.

Table 1 Properties of pellets of calcined proppant (FR. 30/50 mesh). No. p / p Structure The content of SiO ₂ , wt.% Heating rate, ° C / h Cooling rate, ° C / h The absolute density of the granules of proppant, g / cm ³ Destructibility,% at 7500 psi one Prototype Poppant 45-70 There is no data There is no data 2.623-2.632 There is no data 2 Composition 1 87.1 1000 1000 2.3-2.4 8.4 high siliceous sand Natural impurities - the rest 3 Composition 2 86.0 1500 1500 2.45-2.5 9.0 high siliceous sand Natural impurities - the rest four Composition 3 89.7 1000 1000 2.27-2.3 5.9 sand - 95 wt.% Natural impurities - the rest quartzite - 5 wt.% 5 Composition 4 90.84 2500 2000 2.16-2.18 7.5 sand - 85 wt.% Natural impurities - the rest quartzite - 15 wt.% 6 Composition 5 92.46 1500 1500 2.1-2.11 10.0 sand - 75 Natural wt.% impurities - the rest quartzite - 25 wt.% 7 Composition 4 90.84 980 980 2.05-2.08 18.3 sand - 85 wt.% Natural impurities - the rest quartzite - 15 wt.% 8 Composition 4 90.84 2600 2100 Cracking of granules is observed sand - 85 wt.% Natural impurities - the rest quartzite - 15 wt.%

The phase of cristobalite is difficult to identify and has some peak displacement relative to the data of the XRD file cabinet. Perhaps this is due to the low cristobalite content or the fact that this phase is poorly formed in the analyzed high-silica ceramics. The determination of the quantitative content of the quartz phase in the inventive proppant causes technological and methodological difficulties due to the small grain size, however, in our opinion, the proportion of the quartz phase exceeds 70 vol.%.

Analysis of the data in the table and figure shows that the inventive method for the manufacture of siliceous proppant and proppant allows to obtain a product (No. p / p - 2, 4, 5, 6), which has a lower density compared to known analogues and has acceptable strength characteristics.

Claims (3)

1. A method of manufacturing a siliceous proppant, including grinding the mixture, granulation and firing of granules, characterized in that the mixture is used natural high-silica sand or its mixture with quartzite in an amount of 1-25% by weight of the mixture with a SiO ₂ content of not less than 87 wt.%, grinding to a size of not more than 10 microns with a fraction content of not more than 5 microns, comprising at least 50 wt.%, and firing at 1120-1300 ° C with a heating rate of 1000-2500 ° C / h and cooling rate 1000-2000 ° C / h. 2. Siliceous proppant, characterized in that it is obtained by the method according to claim 1. 3. Silica proppant according to claim 2, characterized in that the content of cristobalite in the calcined granules does not exceed 10 vol.%.

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