RU2589881C1 - Viscoelastic composition for temporary isolation of productive formations - Google Patents

Abstract

FIELD: oil and gas industry.

SUBSTANCE: invention relates to process compositions used for completion, development, overhaul and routine maintenance of wells for temporary isolation of productive beds in the process of killing of wells with normal and abnormally low formation pressures. Viscoelastic composition (VEC) includes an aqueous solution of a polymer of polysaccharide nature, carbamide and calcium carbonate as activators of polymer cross-linking, a cross-linking agent -for formation of intermolecular spatial structure, a decomposer - for self-destruction of gel after a given time interval, a water-soluble salt of monovalent metal for increase in density of the composition with the following proportions, MP: biopolymer (xanthan gum) - 0.8-1.3; carbamide (urea) - 0.4-0.6; calcium carbonate (marble chips) - 1.4-2.3; acetic chrome, aqueous solution - 0.4-0.7; ammonium sulfate - 0.025-0.125; fresh water or solution of monovalent metal salts (sodium, potassium) of required density - the rest.

EFFECT: higher technological effectiveness of using the composition due to optimisation of gel formation time, improvement of structural-mechanical and insulating properties, reduction of negative effect of filtrate on productive formation due to reduction of filtration index, controlled time of composition destruction.

1 cl, 3 tbl

Description

The invention relates to the field of oil production, in particular to technological compositions used in completion, development, overhaul and repair of wells for temporary isolation of productive formations in the process of killing wells with normal and abnormally low formation pressures.

Known viscoelastic composition for completion and overhaul of wells [1], containing 1-3% of the reagent based on polysaccharides, alkali metal hydroxide 0.05-0.45%, structure-forming agent - aluminum sulfate or copper sulfate 0.15-0.3% , the destructor is urea monoperoxyhydrate 0.1-0.2% and the rest is water. This composition is used when completing wells and their overhaul as a killing fluid, perforation fluid, fracturing fluid and sand carrier, as well as a viscoelastic separator for well cementing. The known composition, according to the patent holder, provides killing wells while maintaining the permeability of the rocks of the reservoir.

The disadvantage of this composition [1] is its low heat resistance - it loses its physical and mechanical properties at a temperature of 45 ° C, a short time of structure formation (10-40 min), insufficient for delivery of the composition to the installation zone of a viscoelastic composition (hereinafter WCS).

The closest technical solution to the claimed one is a heat-resistant viscoelastic composition for completion and repair of wells [2], consisting of a polysaccharide reagent from the class of galactomannans 0.5-2%, chromium acetate 0.1-0.4%, hydrocarbon-containing reagent 0.5- 3.5%, alkali metal hydroxides 0.1-0.35%, water - the rest.

The disadvantage of this composition [2] is the short time of structure formation (18-45 min at 60 ° C) and its active destruction with the claimed oxygen-containing destructor in an amount up to 5% of the mass. These restrictions lead to difficulties in delivering the composition to the installation interval, as well as to the inability to effectively control the destruction time of the WCS. The consequence of this can be both early structure formation and rapid destruction of the composition with a change in its structural-mechanical and filtration properties and, as a result, contamination of the reservoir.

Alkali metal hydroxide is used in prototype compositions as an auxiliary component (activator) for forming the spatial structure of the gel. However, this imposes certain restrictions on the technology for preparing and delivering the compositions to the well — the compositions quickly thicken and are poorly pumped, or parallel injection of the composition and activator is required to mix them during the injection process.

To eliminate the known drawbacks of the prototype compositions and to improve the processability of use, a WCS was developed for temporary isolation of productive formations containing a polysaccharide polymer, chromium acetate, and also additionally contains urea, calcium carbonate, an aqueous solution of chromium acetate, ammonium sulfate in the following ratio,% wt. .:

- biopolymer (xanthan gum) - 0.8-1.3;

- urea (urea) - 0.4-0.6;

- calcium carbonate (marble chips) - 1.4-2.3;

- chrome acetic acid (50% aqueous solution) - 0.4-0.7;

- ammonium sulfate - 0.025-0.125;

- fresh industrial water or a solution of a monovalent metal salt (sodium, potassium) of the required density - the rest.

The technical result is an increase in the manufacturability of using the composition by optimizing the gel formation time, increasing the structural-mechanical and insulating properties, reducing the negative effect of the filtrate on the reservoir by reducing the filtration rate, and the controlled composition destruction time.

The technical result of the invention is provided by replacing the alkali metal hydroxide with calcium carbonate and urea. Urea creates the alkaline medium necessary for crosslinking the polymer, hydrolyzing at temperatures above 55 ° C. Calcium carbonate has a dual function - it activates the crosslinking of the polymer, creating the necessary alkaline environment in conjunction with urea, and acts as a colmatant.

In order to destroy the WCS in the well, a destructor, ammonium sulfate (persulfate), is introduced into its composition, which allows the gel to be destroyed to the pumped state after a predetermined time and removed from the well without additional downhole operations (acid treatment, etc.).

The composition density required for work in the well is achieved by using an aqueous solution of sodium or potassium salt instead of fresh water. A polysaccharide polymer and a crosslinking agent are used to form the spatial structure.

Experimentally, the content of the destructor was selected to destroy the WCS to the pumped state, depending on the required time the gel was in the wellbore, in the temperature range 55-75 ° C (see Table 1).

The claimed composition prepared according to the above recipe is characterized by the properties shown in table. 2.

From the patent and scientific and technical literature, we do not know the kill fluid containing the combination of the above components in the proposed quantitative ratio, which allows us to conclude that the proposed solution is new.

A comparative analysis with the prototype allows us to conclude that the inventive viscoelastic composition differs from the known one in that it does not contain alkali, which makes it possible to postpone the time of its crosslinking and simplify the technology of delivering the composition to the well in the installation interval. Also, the composition contains a certain amount of acid-soluble colmatant to reduce filtration into the reservoir and a certain amount of destructor to destroy the composition after a given time. In this case, the WCS stably maintains its viscoelastic properties for a long time, and is resistant to formation temperatures and pressure.

If necessary, to increase the density of the composition, it is possible to use salts of monovalent metals sodium and potassium. It is not allowed to use in order to increase the density of the composition of soluble salts of divalent metals, such as calcium and magnesium. The ions of these metals lead to premature crosslinking of the polymer.

The essence of the invention is illustrated by the following example.

9.6 g of biopolymer and 4.8 g of urea were dissolved in 960 ml of fresh industrial water. After complete dissolution of the polymer, 5 ml of a 50% aqueous solution of chromium acetic acid were introduced and mixed until a uniform color, after which 17 g of medium-sized marble chips were added, mixed until a homogeneous mass was formed.

Other viscoelastic formulations with different ratios of ingredients were prepared in a similar manner.

In laboratory conditions, the claimed composition was determined by the following technological properties: Filtration rate (F, ^cm3 / 30 min) under conditions of high pressure and temperature using a filter press HPHT (High Pressure High Temperature) at a differential pressure of 3.4 MPa and a temperature of 75 ° C; density on the lever scales-densitometer company FANN (d, g / cm ³ ); dynamic viscosity; the destruction time of the compositions depending on the temperature and the amount of introduced destructor; compatibility with formation fluids (oil, saline water).

As the data shown in table 2 show, the claimed viscoelastic composition has low values of the filtration index, the required density, low dynamic viscosity before polymer crosslinking and after destruction of the composition is fully compatible with oil and mineralized water.

Table 3 presents a comparison of the filtration rate and the yield time of the claimed composition with the prototype. From the data of table 3 it can be seen that the prototype composition has a very short structure formation time - polymer crosslinking begins immediately after the addition of the crosslinker due to the presence of alkali in the composition. A very high filtration rate is a consequence of the insufficient degree of crosslinking of the polymer due to the small amount of crosslinking agent. All these disadvantages are deprived of the claimed composition. The formation time at 60 ° C reaches 45-60 min, the amount of crosslinker is sufficient to form a viscoelastic composition with low filtration.

The claimed viscoelastic composition with such property indicators will provide high-quality and effective temporary isolation of the productive formations in the process of killing wells with maximum preservation of the reservoir properties of the productive formation, with subsequent destruction of the composition and its removal from the well.

Information sources

1. RF patent 2116433 "Viscoelastic composition for completion and overhaul of wells", LLC PermNIPIneft;

2. RF patent 2386665 "Heat-resistant viscoelastic composition for completion and repair of wells", LLC PermNIPIneft.

Claims (1)

A viscoelastic composition for temporary isolation of reservoirs containing a polysaccharide polymer of nature, chromium acetate, characterized in that it additionally contains urea, calcium carbonate, an aqueous solution of chromic acetic acid, ammonium sulfate in the following ratio, wt.%:
biopolymer (xanthan gum) 0.8-1.3 urea (urea) 0.4-0.6 calcium carbonate (marble chips) 1.4-2.3 chrome acetic acid (50% aqueous solution) 0.4-0.7 ammonium sulfate 0.025-0.125 fresh process water or salt solution monovalent metal (sodium, potassium) of the required density rest