RU2081297C1 - Compound for isolation of water inflow to oil and gas wells - Google Patents

Abstract

FIELD: oil and gas industry. SUBSTANCE: compound is as follows, mas.%: sodium silicate, 6-8; polyatomic alcohol, 5-10; electrolyte, 0.4-0.8; wood flour, 2-5; water, the balance. In function of polyatomic alcohol use can be made of glycerine or glycol, and in function of electrolyte - calcium chloride. EFFECT: high efficiency. 2 cl, 1 tbl, 1 dwg

Description

 The invention relates to the oil industry, in particular, to compositions for limiting water inflow in oil and gas wells, to create a waterproof screen and align the injectivity profile of injection wells.

 A known composition for the isolation of permeable zones containing sodium silicate (water glass), lignosulfonate and water (1). The disadvantage of this composition is its low strength and instant coagulation in mineralized water.

 A known composition having as filler dry sawdust or shredded cardboard (2). Sawdust and shredded cardboard are coarse particulate fillers and can only be used to isolate absorption zones.

 The closest solution taken as a prototype is a viscoplastic insulation material containing hypane, water glass, hydrochloric acid, an inert filler, a swelling additive and water (3). The disadvantage of the composition is the short gelation period (10-45 min) and insufficient gel strength. The disadvantage is the completely unjustified inclusion of three polymeric substances (hypane, CMC, sodium silicate), each of which is an independent gelling agent. The presence of all these substances in one composition does not improve its technical and strength properties.

 The objective of the invention is to increase the clogging properties of the composition, increasing the strength of the resulting gel.

 The problem is solved in that the known composition containing sodium silicate, electrolyte and water additionally contains polyhydric alcohol and wood flour in the following ratio of components, wt. sodium silicate 6-8; polyhydric alcohol 5-10; electrolyte 0.4-0.8; wood flour 2-5; water is the rest. In this case, calcium chloride is used as an electrolyte, and glycerol or glycol (ethylene glycol, diethylene glycol, triethylene glycol) is used as a polyhydric alcohol.

 Comparative analysis with the prototype shows that the claimed composition differs from the known introduction of glycerol (glycols), which is a modifier, and wood flour, which allows us to conclude that the proposed technical solution meets the criterion of "novelty."

 Analysis of the known compositions for isolating water inflow into the well showed that the sodium silicate component introduced into the claimed solution is known as "Sodium silicate (water glass). Technical conditions. GOST 13078-81."

However, its use in known compositions does not provide the properties that it exhibits in the claimed solution, namely, obtaining a strong gel in a short time at an elevated formation temperature of 60-80 ^o C and a long shelf life of 4-12 hours at a temperature of 15- 25 ^o C; the possibility of using saline water; an increase in the filtration resistance of washed and fractured zones at the time of pumping the solution and, as a result, an increase in the coverage of the formation by exposure.

 To prevent instant coagulation of sodium silicate when interacting with a solution of calcium chloride prepared on mineralized water ("Calcium Chloride. Specifications. GOST 450-77"), trihydric alcohol or dihydric glycols are introduced into the composition.

 Glycerin is a syrupy liquid without color and odor, has a sweet taste, non-toxic. Industry is produced in large volumes. "Glycerin. Specifications. GOST 6259-75." It is used in various industries, including food.

Physical properties of glycerin: density 1260 kg / m ³ , boiling point 290 ^o C, freezing point of a technical product -25 ^o C, diluted with water in any ratio.

Гликоли спирты, содержащие две группы OH, по своим свойствам похожи на глицерин. Плотность 1161 кг/м², температура кипения 245^oC. Температура замерзания -20^oC, с водой смешивают в любых соотношениях. ("Этиленгликоль. Технические условия. ГОСТ 19710-83"). При взаимодействии с катионами Ca²⁺, Mg²⁺ также образуют гликолята по схеме:

Глицерин и гликоли, образуя слабые комплексные соединения с хлоридом кальция, замедляют его взаимодействие с силикатом натрия и дают возможность регулировать время гелеобразования в интервале 4-12 ч при температуре 20-25^oC.Glycerin interacts with divalent metal cations CA ²⁺ , Mg ²⁺ , Ba ²⁺ , forming compounds with them similar to weak complex compounds. Hydrogen in the hydroxyl groups of glycerol is replaced by a metal, forming glycides. The interaction of glycerol with calcium or magnesium chloride can be described by the reaction scheme:

Glycols alcohols containing two OH groups are similar in their properties to glycerin. Density 1161 kg / m ² , boiling point 245 ^o C. Freezing temperature -20 ^o C, mixed with water in any ratio. ("Ethylene glycol. Technical conditions. GOST 19710-83"). When interacting with cations Ca ²⁺ , Mg ²⁺ also form glycolates according to the scheme:

Glycerin and glycols, forming weak complex compounds with calcium chloride, slow down its interaction with sodium silicate and make it possible to adjust the gelation time in the range of 4-12 hours at a temperature of 20-25 ^o C.

 Glycolates are weak complexones that break down at elevated formation temperatures and contribute to a stronger gel.

 A dispersed medium is introduced into the composition in order to increase the coverage of the formation by exposure. As a dispersed medium using wood flour ("Wood flour. Specifications. GOST 16361-87"). The use of the proposed composition makes it possible to plug fractured and highly permeable zones at the stage of injecting the solution into the formation, increase the filtration resistance and thereby increase the coverage of the formation by exposure. After injection of the solution into the formation at elevated temperature, gelation occurs. The gel includes particles of wood flour in its structure, which clog small fissures and washed areas, while creating a strong insulating screen. This leads to the distribution of filtration flows with the inclusion in the active development of weakly drained low-permeability formations.

The effectiveness of the proposed composition was investigated in laboratory conditions by determining: gelation time in fresh and mineralized water at a temperature of 20 and 75 ^o C; gel strength index by determining the value of static shear stress.

 For a comparative analysis, solutions were prepared according to the prototype and the proposed solution, presented in the table.

 For the preparation of compositions using technical products: sodium silicate, calcium chloride, glycerin, wood flour, water.

 An example of the preparation of the composition for insulation in the following ratio of components, wt. sodium silicate 6.0; glycerol or glycol 7.0; calcium chloride 0.7; wood flour 5.0; water 81.3.

The solution is prepared in the following sequence: the estimated amount of water needed to prepare the gelling composition is divided into two equal parts and poured into two glasses. A sample of calcium chloride is dissolved in the first glass, then a sample of glycerol (glycol). Sodium silicate is dissolved in a second beaker. A solution of calcium chloride with glycerin (glycol) is poured into the sodium silicate solution with constant stirring, then wood flour is added to the gelling composition and mixed until the components are completely mixed. The finished solution is used to determine the gelation time at a temperature of 20 and 70 ^o C. Prepared for the experiment, the samples are alternately placed in a measuring vessel reotest, where they are kept for the time required to start gelation at 20 or 70 ^o C. The start time of gelation is determined by the change viscosity of the solution. The strength of the gel is determined by the value of the static shear stress at minimum revolutions (0.2 rpm) of the device. The gel formation time is determined by the control robe in a test tube located in the same temperature conditions.

To prepare 1 m ^{3 of the} composition at the well, 100 l of liquid glass with a density of 1420 kg / m ³ , calcium chloride 5 kg, glycol (glycerin) 70 kg, wood flour 50 kg and 820 l mineralized (18 g / l) water will be required.

 The estimated amount of water for the preparation of the composition is divided into two equal parts. 410 liters of water are collected in the first container, then 100 liters of water glass are poured into it. The solution is stirred using the CA-320 aggregate for 1-2 cycles. An electrolyte solution is prepared in a second container. To do this, 410 liters of water, 70 liters of glycerin (glycol) and 5 kg of calcium chloride are collected in a container. The solution is stirred until complete dissolution of calcium chloride. Then, with constant stirring, load 50 kg of door flour. After mixing, the solutions from two containers are simultaneously fed to the wellhead, where they are mixed and pumped into the well using a hydroactivator. After injection of the insulating composition into the formation, the well is left for gelation time (12-24 hours).

 An analysis of the results of laboratory studies showed that in all the experiments listed in the table, the proposed composition has the best gel strength indicators.

 The composition exhibits its positive properties when varying the content of ingredients in the following range: polyhydric alcohol (glycerin) 5-10% wood flour 2-5% sodium silicate 6-8% calcium chloride 0.4-0.8% The minimum glycerol content at which increases the strength of the gel 5% (experiment 11). A glycerol content of more than 10% does not increase the strength of the composition (experiment 13). The addition of wood flour, as a dispersed phase, increases the strength of the gel (experiments 11-17), however, its content in the composition of more than 5% leads to a sharp increase in the viscosity of the solution (experiment 16). An increase in the amount of calcium chloride of more than 0.8% leads to instant coagulation of sodium silicate (experiment 8). A decrease in the content of calcium chloride below 0.4% leads to a decrease in the strength of the gel (experiment 4).

 The presence in the proposed composition of polyhydric alcohol not only increases the strength of the gel (experiment 10), which allows you to vary the gelation time, but also allows the use of produced water to prepare the composition. This circumstance is of great importance, since in the conditions of Western Siberia in winter there is no fresh water.

The drawing shows the gelation time of the compositions prepared on fresh (curve 1) and mineralized (curves 2, 3) water, depending on the content of calcium chloride and glycerol, at a temperature of 70 ^o C, the content of sodium silicate 6%
Comparing the curves 1,2 and 3,4, the drawing shows that the gelation time in the presence of 10% glycerol (curve 3) increases when using produced water for 30-180 minutes and when using fresh water for 40-240 minutes. Analysis of the results of the table shows that the composition of the prototype (experiments 1-3) has a very short gelation time, insufficient for pumping the solution into the reservoir. The proposed composition has a long gelation time at 20 ^o C from 3 to 6 hours, sufficient for insulation work. At a temperature of the formation of 70 ^o C the gel is formed within 0.5-2.5 hours (experiments 10-17).

 A comparison of the strength characteristics of the gel according to the prototype (experiments 1-3) and the proposed composition showed that the strength of the compositions prepared in fresh water (experiments 16-17) exceeds 3 times the strength of the composition according to the prototype, and the strength of solutions prepared in mineralized water is 2 times (experiments 10-15).

 The proposed composition does not have a corrosive effect, is environmentally friendly and when it is prepared under production conditions, and also has the highest strength indicators, which can withstand large pressure drops and increase the duration of the insulation effect.

Claims (2)

 Composition for isolating water inflow into a well containing sodium silicate, electrolyte, water, characterized in that it additionally contains polyhydric alcohol and wood flour in the following ratio of starting components, wt. Sodium Silicate 6 8
Polyhydric alcohol 5 10
Electrolyte 0.4 0.8
Wood flour 2 5
Water Else
2. The composition according to claim 1, characterized in that it contains glycerol or glycol as a polyhydric alcohol.  3. The composition according to claim 1, characterized in that it contains calcium chloride as an electrolyte.

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