RU2257466C1 - Fluid for hydraulic fracturing of formation - Google Patents

Abstract

FIELD: oil and gas production.

SUBSTANCE: fluid contains, wt %: industrial-grade powdered lignosulfonates 26.4-31.7, potassium chloride 4.9-5.9, aluminum sulfate 1.2-1.50, borax 0.4-0.5, formation water 40.3-44.7, and sweet water in proportion to formation water as 1:(1.98-1.99).

EFFECT: improved process parameters due to improved structurally mechanical properties of fluid, raised viscosity thereof, high sand-retention ability, and possibility of controlling lifetime without loss in high technological characteristics.

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Description

The invention relates to the field of oil production, in particular to hydraulic fracturing fluids, and is intended to increase oil recovery developed oil-containing formations. The invention can also be used as a flushing fluid, a fluid for killing a well and a visco-elastic separator.

The invention is recommended for use in oil companies, mainly in injection wells.

Known hydraulic fracturing fluid (hydraulic fracturing) containing the following ingredients, wt.%: Carboxymethyl cellulose (CMC) 1.0-2.5; chromates 1.0-3.0; lignosulfonates 0.2-0.7; salt of perchloric acid 0.75-2.1 and formation water - the rest (see, for example, "Instructions for the technology of deep penetrating hydraulic fracturing" RD 39-0147035-236-89, MNP. M., 1988, S. 16- 17).

The specified fluid is recommended for use in hydraulic fracturing with a bottom temperature of 60-150 ° C.

However, this known liquid has the following disadvantages:

- it has a high filtrate recovery (11-14 cm in 30 min), which under commercial conditions leads to the penetration of the filtrate into the reservoir and its blockage. In this case, the filtrate from the reservoir is practically not displaced and as a result strongly clogs the reservoir;

- it is difficult to pump, and even with a minimum lower limit of the content of ingredients, its pumping ability is only 66 cm / s, which in commercial conditions leads to technological difficulties when using the specified liquid;

the composition of the known fluid includes environmentally unsafe substances - chromates and chlorates, which lead to pollution of groundwater;

- is a multicomponent system, which complicates the process of its preparation, is expensive due to the use of expensive components.

Hydraulic fracturing fluid is also known, comprising the following components, wt.%: Sulphite-alcohol yeast vinasse 31.72-39.76; potassium chloride 3.37-6.92; polyacrylamide 0.05-0.12; surface-active substance of the ML-80 grade 0.03-0.15 and formation water - the rest (RF Patent No. 1710710, class E 21 B 43/26, from 1990).

However, this known liquid also has a high filtrate recovery (4.0-7.0 cm ³ in 30 minutes), and only with the upper limits of the components - 1.2 cm ³ in 30 minutes, therefore, under commercial conditions, the filtrate of this known liquid will penetrate into the pore space of the reservoir, which can lead to blockage.

In addition, the known fluid, despite the low viscosity and static shear stress, is characterized by a lower pumping capacity than water (72.5-73.3 cm / s), which in the field will create technological difficulties when it is injected into the reservoir.

It should also be noted that the composition of the known liquid includes expensive and, in addition, environmentally unsafe substances - the surface-active substance ML-80, which, getting on the surface of the earth, leads to pollution of groundwater, and can also cause allergic reactions in people in the process of preparing this fluid. The scarcity of reagents included in a known fluid, their high cost and the difficulty of preparing a known fluid limit its use in hydraulic fracturing.

Closest to the proposed invention is a hydraulic fracturing fluid containing the following components, wt.%: Technical lignosulfonates modified with hexamethylenetetramine and carbamide 40.98-43.31; potassium chloride 3.70-4.32; aluminum sulfate 0.52-1.03 and produced water - the rest (RF Patent No. 2138633, Cl. E 21 B 43/26, 1998).

The disadvantages of this known liquid are the following:

- life time regulation is not ensured; its properties deteriorate even before the end of the technologically necessary time;

- low viscosity and structural-mechanical properties;

- low sand holding ability;

- the need to modify in the factory the main component - lignosulfonates, which complicates the preparation technology and increases the cost.

The technical result provided by the invention is to improve the technological parameters of the liquid by increasing the structural and mechanical properties, increasing its viscosity, providing high sand-holding ability while at the same time giving the property of adjustable life spans by maintaining high technological properties for the technologically necessary time.

An additional technical result is the preservation of low filtration.

The specified technical result is achieved by the proposed hydraulic fracturing fluid containing technical lignosulfonates, potassium chloride, aluminum sulfate and produced water, while it additionally contains borax and fresh water, as technical lignosulfonates, technical lignosulfonates are powdery, in the following ratio of components, wt.% :

technical powder lignosulfonates 26.4-31.7

potassium chloride 4.9-5.9

aluminum sulfate 1.2-1.5

borax 0.4-0.5

formation water 40.3-44.7

fresh water the rest

moreover, the mass ratio of formation and fresh water is 1.98-1.99: 1, respectively.

The achievement of the specified technical result is ensured by the components included in the resulting hydraulic fracturing fluid, at their stated ratio.

Thanks to the additional introduction of borax in conjunction with other components of the liquid, life time control is ensured, i.e. regulation of the process of fluid “fluidization” for hydraulic fracturing as a result of the structural effect of borax due to the interaction of its hydroxyl groups with active groups of lignosulfonates.

The proposed hydraulic fracturing fluid was tested in laboratory conditions. The following substances were used:

- technical powder lignosulfonates according to TU 2455-002-00281039-00, light brown powder;

- potassium chloride (KCl), chemically pure according to GOST 4568-95, crystalline white powder (technical potassium chloride can be used - a waste product from potash plants);

- aluminum sulfate GOST 3758-75, white powder;

- borax - sodium tetraborate hydrate, GOST 8429-77, a white solid;

- produced water with a density of 1160-1180 kg / m ³ , hardness of 1800 mEq / l, the following composition, mEq / l: cations: Na ⁺ + K ⁺ 3209-3222.92; Ca ⁺² 494.5-1055; Mg ⁺² 191.98-379; Anions: CI ^- 4540.34-4660; SO ₄ ^-2 6.13-11.8; CO ₃ ^-2 1.8-2.88; total mineralization 260 g / l;

- fresh water.

The preparation of the inventive liquid in the laboratory was carried out as follows.

Example 1. To prepare 100 g of liquid, 26.4 g of technical powder lignosulfonates were taken, 22.4 g of fresh water was added, then 44.7 g of potassium chloride-type produced water with a density of 1160 kg / m ^{3 was} added, then 4 were added to this mixture. 9 g of potassium chloride, and then, with stirring, 1.2 g of aluminum sulfate and 0.4 g of borax were additionally added, and after mixing, a hydraulic fracturing fluid of the following composition was obtained, wt.%: Technical powder lignosulfonates (LSTP) - 26.4; potassium chloride 4.9; aluminum sulfate - 1.2; borax - 0.4; formation water - 44.7; fresh water - 22.4.

The inventive liquid with a different content of components was prepared in a similar way.

Example 2. Under field conditions, the proposed liquid was prepared as follows. 28 kg of LFST are loaded into the mixer, then 21.5 liters of fresh water and then 36.1 liters of produced water with a density of 1180 kg / m ³ are fed with a cementing unit. After full loading, mix for 1 hour. The second cementing unit pumps the resulting mixture into a pre-steamed and cleaned container. At the same time, conditional viscosity and density are controlled. After preparing this mixture, the calculated amount of potassium chloride (5.9 kg) is introduced into it. The order of input of potassium chloride is as follows. With one cementing unit CA-320, the mixture is fed into the mixer. After filling it, the calculated amount of potassium chloride is introduced. The second CA-320 produces additional mixing by suction from the mixer and dumping back into the mixer. Mixing time 0.75 hours. Then the second CA-320 treated with potassium chloride mixture is also dumped into a pre-steamed container. Operations are repeated until the entire volume is processed. Then, 1.5 kg of aluminum sulfate and 0.5 kg of borax are sequentially introduced, with each component being introduced similarly to potassium chloride. The mixing time after entering the next component is 0.75 hours.

In the course of laboratory tests, the proposed fluid measured the viscosity at the VBR-1 device, the static shear stress at the SNS-2 device, and the filtration rate at the vacuum unit at ΔР = 0.1 MPa in 30 minutes.

The sand holding capacity of the obtained liquid was determined by measuring the density difference between the upper and lower samples placed in a 100 ml cylinder with a hole at the level of 50 ml of liquid, after sand was introduced into it after 2 hours.

The property of the adjustable life spans of the proposed fluid was judged by the change in its viscosity and structural and mechanical properties over time.

The results obtained during laboratory tests are shown in the table.

The data obtained during the tests show that the claimed hydraulic fracturing fluid has the following advantages over the prototype:

- the viscosity of the proposed liquid is higher by 52-155%;

- structural and mechanical properties are 1.6-6.6 times higher;

- sand-holding ability of the proposed liquid is 3-5 times higher;

- the proposed hydraulic fracturing fluid is characterized by the property of regulating the life time, namely, it retains the technologically necessary parameters for 4-5 days, while the known fluid does not have such a property.

The deviation of the mass ratio of reservoir and fresh water in the proposed fluid (experiment 8) leads to a deterioration in performance.

Due to the improvement of the technological parameters of the proposed fluid, the effectiveness of its impact during fracturing is increased.

The inventive hydraulic fracturing fluid has a wide viscosity range, which allows its successful application in various geological and technical conditions.

Low, almost zero, filtrate recovery of the inventive fluid prevents contamination of the reservoir.

The high pumpability of the inventive fluid allows it to have a high flow rate when carrying out hydraulic fracturing and, as a result, to obtain large fractures, and in combination with high sand holding capacity, high efficiency of the hydraulic fracturing process is provided.

The inventive liquid has high anti-corrosion properties and high inhibitory ability in relation to swelling clay rocks, which prevents clogging of the pore channels.

Due to the property of regulating the life span, the proposed hydraulic fracturing fluid retains high technological properties for a long time, which eliminates the settling of sand in the process strapping during a forced interruption of the hydraulic fracturing process, i.e. warns emergency situations.

The use of the inventive hydraulic fracturing fluid will reduce the time and money spent on hydraulic fracturing due to:

- obtaining a higher initial injectivity (or productivity) of the treated well;

- increase the life of oilfield equipment and increase the overhaul period;

- due to the receipt of large cracks in length and diameter and due to the almost complete restoration of the initial permeability of the formation, an increase in current oil production in production wells is achieved or injectivity in injection wells is increased.

Claims (1)

Hydraulic fracturing fluid containing technical lignosulfonates, potassium chloride, aluminum sulfate and produced water, characterized in that it additionally contains borax and fresh water, and as technical lignosulfonates, technical lignosulfonates are powdery, with the following ratio of components, wt.%: Powdered technical lignosulfonates 26.4-31.7 Potassium chloride 4.9-5.9 Aluminum Sulphate 1.2-1.5 Borax 0.4-0.5 Formation water 40.3-44.7 Fresh Water Else moreover, the mass ratio of formation and fresh water is 1.98-1.99: 1, respectively.