RU2792473C1 - Structured flush fluid - Google Patents

Abstract

FIELD: oil and gas well construction.

SUBSTANCE: flush fluids used in the process of casing wells to separate drilling and cement slurries, remove clay filter cake and ensure high-quality adhesion of cement stone to the casing string and rocks that form the walls of the well. The structured flush fluid contains a gelling agent, a stabilizer and a weighting agent. Lime is used as a gelling agent, a complex of water-soluble salts containing sodium chloride and/or potassium chloride, ammonium nitrate, sulfate and/or chloride of ns ² np ¹ elements in the form of boron and/or aluminum and/or gallium compounds is used as a stabilizer and sodium tetraborate at their specific ratio, and as a weighting agent - calcium carbonate, and/or barium sulfate, and/or iron oxide (III) at their specific ratio.

EFFECT: creation of a pseudo-plastic structured flush fluid that optimally meets the requirements of well casing under conditions of normal and abnormally high formation pressure (AHFP), which are drilled using polymer-clay loaded drilling mud.

2 cl, 1 tbl

Description

Technical field

The invention relates to the construction of oil and gas wells, namely to buffer fluids used in the process of casing wells for separating drilling and cement slurries, removing clay filter cake and ensuring high-quality adhesion of cement stone to the casing string and rocks that form the walls of the well.

Prior Art

At present, structured buffer compositions are known that ensure the stability of the borehole walls due to the ability to weight with the introduction of a finely dispersed filler: chalk, barite, hematite, etc. To keep the particles of the weighting agent in suspension, the buffer liquid must have a coagulation-type structure with the possibility of reversible destruction and recovery . The structure former is, as a rule, bentonite clay powder, which has the ability to swell in the aqueous phase and form long-range structured suspensions. For example, in patent RU 2154083 published on August 10, 2000, the buffer liquid contains a clay builder, a complex polymer stabilizer based on polyacrylamide and carboxymethylated cellulose, and a weighting agent, which is used as an iron ore concentrate from titanium-vanadium ores. This composition effectively separates the drilling fluid and the cement slurry, but is characterized by insufficient detergent action to remove the clay filter cake from the well walls.

Patent RU 2378313, published on January 10, 2010, describes an invention in which, to create a structured buffer liquid, a clay-free formulation based on ethoxylated cellulose ethers and a post-astifier, which is carboxylates or complexes of melamine or naphthalene resins, is used. The disadvantage of this formulation is the impossibility of its weighting at elevated temperatures, since the polymer matrix significantly loses strength with heating of the system.

From patent RU 2592308 published on 07/20/2016, it is known that to increase the washing ability of the buffer liquid, it is used in combination (sodium tripolyphosphate) together with an aqueous solution of butyl glycol. Similarly, water-soluble polyphosphates (pyrophosphate and / or tripolyphosphate, and / or alkali metal metaphosphate) are used in the composition of the washing buffer liquid in combination with a non-ionic surfactant (ethoxylated alkylphenol with a degree of oxyethylation of 9 - 25), as disclosed in patent RU 2204692, published on 20.05 .2003. In addition, the composition of a water-based washing buffer liquid is also known, described in patent RU 2455334, published on 07/10/2012, in which a composition of hydrochloric acid hydroxylamine and hydroquinone is used as a surfactant. However, a common disadvantage of detergent buffer compositions based on non-ionic and ionic surfactants is the impossibility of introducing a weighting component, but it also does not provide a good separation of cement and drilling fluids, and also does not allow efficient removal of exfoliated mudcake fragments.

A complex powder composition for the preparation of a structured buffer liquid is known from the prior art, disclosed in patent RU 2439118, published on January 10, 2010, in which a powder material based on the composition of a carbon-alkali reagent, carboxymethyl cellulose and a complexone - nitrilotrimethylene phosphonic acid (NTP) is used to prepare viscoelastic structured buffer liquids . The washing effect of this composition is provided by the introduction of NTF. However, the structural properties of such a system significantly depend on the pH level, and, at a pH value of more than 9 (which is typical for cement slurries), the structural properties of the suspension are significantly reduced.

The closest in terms of essential features is a weighted buffer liquid disclosed in patent RU 2561134, published on August 20, 2015, including clay powder, a stabilizer, a weighting additive and water, while a polymeric stabilizer (Natrosol 250EXR) is used as a stabilizer, and a weighting additive - galena concentrate KG-2.

This weighted buffer liquid has a number of disadvantages:

1. Clay powder used as the main structurant forms a suspension with insufficient pseudoplastic characteristics, which does not allow efficient removal of mudcake fragments and causes poor separation and undesirable mutual mixing of cement and drilling fluids.

2. The composition of the above weighted buffer fluid does not contain detergent surfactants and active coagulants capable of destroying and exfoliating the filter cake from the surface of the wellbore. As a result, the pumping of the weighted buffer liquid does not allow effective removal of the clay cake, which largely remains on the surface of the rocks that form the borehole walls, and prevents the formation of a strong contact with the cement stone due to the implementation of the contraction effect.

3. The weighted buffer fluid has a low affinity for the cement slurry, which destroys the clay slurry, promoting its coagulation and syneresis. In the case of using a buffer composition with a density higher than 1300 kg/m ³ there is a significant thickening of the system in the zone of contact with the cement slurry with separation of the aqueous phase. This violates the hydraulic regime of drilling fluid replacement, leads to an increase in pressure in the annular space and violates the stability of the borehole walls.

Disclosure of invention

The objective of the present invention is to create a structured buffer fluid capable of weighting, which has an effective combination of structural and pseudoplastic characteristics, a pronounced ability to coagulate the removal of a clay filter cake from the well walls, as well as a high affinity for the cement slurry, mixing with which is not accompanied by thickening and degradation of the system. . A sign of the presence of a structure is the existence of a tensile strength under the deformation effect on the buffer liquid. The higher the ultimate strength, the more structured the buffer liquid and the higher its sedimentation stability.

The technical result achieved in the implementation of the claimed invention is the creation of a pseudoplastic structured buffer fluid that optimally meets the requirements of well casing under conditions of normal and abnormally high reservoir pressure (AHRP), which are drilled using polymer-clay weighted drilling fluids.

This technical result is achieved due to the fact that the structured buffer liquid contains a structurant, a stabilizer and a weighting agent and is characterized in that lime is used as a structurant, a complex of water-soluble salts is used as a stabilizer, and calcium carbonate and/or barium sulfate is used as a weighting agent, and/or iron oxide (III) in the following ratio of components, wt.%:

Lime - 2 - 15;

Complex of water-soluble salts - 5 - 40;

Weighting agent - 1 - 70;

Water is the rest.

This technical result is also achieved due to the fact that calcium hydroxide (Ca(OH) ₂ ) or calcium oxide (CaO) is used as lime, and a composition of sodium chloride and / or potassium chloride, ammonium nitrate, sulfate is used as a complex of water-soluble salts. and/or chloride ns ² np ¹ -elements and sodium tetraborate in the following mass ratio, wt.%:

Sodium chloride (NaCl) and/or potassium chloride (KCl) - 5 - 30;

Ammonium nitrate (NH ₄ NO ₃ ) - 5 - 10;

Sulphate and/or chloride ns ² np ¹ elements - 50 - 85;

Sodium tetraborate (Na ₂ B ₄ O ₇ ) - 5 - 10.

In the claimed structured buffer liquid as part of a complex of water-soluble salts, boron and/or aluminum and/or gallium compounds are used as sulfates and/or chlorides of ns ² np ¹ elements.

The claimed structured buffer liquid is a freely dispersed colloidal system of microparticles of sparingly soluble hydroxide of ns ² np ¹ elements and lime. The yield strength of this system increases with an increase in the concentration of the components involved in the hydroxide condensation reaction - lime and a complex of water-soluble salts. To create an optimal level of pH = 10.5 - 11.5, the concentration of lime in the buffer liquid should lie in the range of 2 - 15%. At the same time, the concentration of the salt complex is selected in an equimolecular ratio with respect to the alkaline structure-forming agent (lime) and is localized in the range of 5 - 40%. The concentration interval of the weighting agent allows you to vary the specific gravity of the buffer liquid in a wide range: from 1030 kg/m ³ (at a weighting agent concentration of 1% wt.) to 2200 kg/m ³ (at a weighting agent concentration of 70% wt.).

A complex of water-soluble salts is a composition of specially selected products, each of which performs a specific function:

- sodium chloride (NaCl) and/or potassium chloride (KCl): an indifferent electrolyte - an ionic strength regulator that provides primary hydrosol coagulation to create a structure with a long-range order of interaction of colloidal particles;

- ammonium nitrate: a buffer additive that ensures the stabilization of the optimal pH level of the hydrosol dispersion medium;

- sulfate and / or chloride ns ² np ¹ -elements: participates in the condensation reaction of colloidal hydroxide when interacting with lime;

- sodium tetraborate - a non-indifferent electrolyte that provides electrostatic stabilization of colloidal particles of hydroxide ns ² np ¹ -elements.

The lime alkaline buffer may be calcium oxide or calcium hydroxide. At the same time, the effect of calcium oxide and calcium hydroxide is equivalent, taking into account the difference in the molecular weight of the reagents. However, when preparing a buffer liquid in cold water, it is preferable to use calcium oxide, since its hydration is accompanied by an exothermic effect.

The preparation of a structured buffer liquid is carried out as a result of the dissolution of a complex of salts in water, the components of which are introduced in an arbitrary order. After mixing and complete dissolution of the salts, calcium hydroxide is introduced. The mixing time of the buffer liquid after the introduction of calcium hydroxide at a rotation speed of 3000 rpm is 20 - 30 minutes.

The finished buffer liquid is examined by determining the following technological characteristics: gel yield strength and plastic viscosity are determined on a direct-indication rotational viscometer according to GOST 33213-2014 (ISO 10414-1:2008); the wetting angle of the aqueous extract (filtrate) is determined according to GOST 9038-90; the pH level of the suspension is determined according to GOST 33776-2016.

Options for the formulation of a new structured buffer liquid are presented in table. 1.

Recipe 1 is intended for use in well casing technology in the area of normal reservoir pressure and includes the minimum concentrations of lime (2%) and a complex of water-soluble salts (5%) to ensure the yield strength of the system is above 20 dPa, which is sufficient to carry out fragments of a clay cake removed from well walls. The concentration of the solid phase of the weighting agent (calcium carbonate) in this formulation is minimal (1%) - this ensures good wetting of the hydrophilic surface (the contact angle is 58°) and, accordingly, increased penetration of the buffer fluid for effective exfoliation of the clay filter cake formed on the walls of the well (Table 1, Recipe 1).

Formulation 2 includes the maximum concentrations of lime (15%) and a complex of water-soluble salts (40%) to create the necessary structure capable of holding particles of weighting agent (barium sulfate) in suspension. The concentration of barium sulfate in this formulation is 20%, which allows flushing before casing wells in moderate AHRP zones. The yield strength (YP) of this buffer liquid (44 dPa) is almost 2 times higher than the composition according to Recipe 1. A further increase in the concentration of lime (above 15%) and a complex of water-soluble salts (above 40%) is impractical due to an unacceptably high increase in rheological properties of the system that prevent its pumping due to the growth of hydraulic losses. The wetting of the well walls with this liquid is lower compared to Formulation 1 (the contact angle is 65°) due to the higher concentration of the solid phase. With the introduction of a weighting agent, the plastic viscosity of the system also increases up to 6 mPa⋅s compared to Formulation 1 (PV = 1 mPa⋅s) (Table 1, Formulation 2).

Recipe 3 includes the maximum concentration of weighting agent (iron(III) oxide) and is intended for casing wells at high AHRP. An increase in the concentration of the solid phase of the weighting agent leads to an increase in the rheological properties of the buffer liquid (PV = 8 mPa⋅s and YP = 66 dPa), as compared with Recipes 1,2. The level of pseudoplasticity of this composition (YP/PV = 8.3) remains approximately at the level of Formulation 2 (YP/PV = 7.3) due to lower concentrations of lime (4%) and complex salts (7%). The surfactant properties of this system (contact angle = 66°) are at the level of Recipe 2, which indicates a limited effect of the solid phase of the weighting agent on the wetting ability of the buffer liquid filtrate (Table 1, Recipe 3).

The new structured buffer fluid has the following advantages compared to the closest analogue:

1. The new structured buffer liquid (table 1, examples 1-4) has a minimum value of plastic viscosity (PV) in combination with a high yield strength (YP), the ratio of which for all formulation options is significantly higher than that of the closest analogue, which indicates higher pseudoplastic characteristics. This provides the new buffer fluid with increased carrying and uncoupling abilities, which ensure good transport of rock fragments and mud cake, and also prevent mixing of drilling and cement slurries.

2. The new structured buffer fluid has a lower value of the wetting angle of the hydrophilic surface filtrate, compared with the closest analogue, which indicates its better washing activity in the process of removing filter cake from the well walls (Table 1, examples 1-4) .

3. The new structured buffer fluid has an affinity for the cement slurry: the pH level of the buffer fluid corresponds to the pH of the cement slurry, which leads to their good level of combination without the formation of zones with increased viscosity and mutual coagulation in the annulus. The pH level of the closest analogue is significantly lower compared to the cement slurry, which causes coagulation destruction of the suspension of the prototype upon contact in the mixing zone (table. 1, examples 1-4).

Table 1
Physical and chemical properties of buffer liquids The composition of the buffer liquid, % Plastic viscosity (PV), mPa⋅s Yield strength (YP), dPa YP/PV Contact angle of wetting, deg. pH, units Example 1
Ca(OH) ₂ - 2
Salt complex - 5
(NaCl - 5%; NH ₄ NO ₃ - 5%; AlCl ₃ - 85%; Na ₂ B ₄ O ₇ - 5%)
Weighting agent (calcium carbonate) - 1
Water - the rest 1 23 23 58 10.5 Example 2
CaO - 15
Salt complex - 40
(KCl - 30%; NH ₄ NO ₃ - 10%; BCl ₃ - 50%; Na ₂ B ₄ O ₇ - 10%)
Weighting agent (barium sulfate) - 20
Water - the rest 6 44 7.3 65 11.2 Example 3
Ca(OH)₂ - 4
Salt complex - 7
(KCl - 5%; NH₄NO₃ - 5%; Ga₂(SO₄)₃ - 85%; Na₂B₄O₇ - 5%)
Weighting agent (iron oxide (III)) - 70
Water - the rest 8 66 8.3 66 10.8 Example 4
the closest analogue 25 50 2 85 7.6

Claims (11)

1. A structured buffer liquid containing a structurant, a stabilizer and a weighting agent, characterized in that lime is used as a structurant, a complex of water-soluble salts containing sodium chloride and / or potassium chloride, ammonium nitrate, sulfate and / or chloride ns ² is used as a stabilizer np ¹ -elements in the form of compounds of boron and/or aluminum, and/or gallium and sodium tetraborate, in the following ratio, wt.%: Sodium chloride NaCl and / or potassium chloride KCl - 5-30; Ammonium nitrate NH ₄ NO ₃ - 5-10; Sulfate and / or chloride ns ² np ¹ -elements - 50-85; Sodium tetraborate - Na ₂ B ₄ O ₇ - 5-10, and as a weighting agent - calcium carbonate, and / or barium sulfate, and / or iron oxide (III), with the following ratio of the components of the buffer liquid, wt.%: Lime - 2-15; Complex of water-soluble salts - 5-40; Weighting agent - 1-70; Water is the rest. 2. Structured buffer liquid according to claim 1, characterized in that calcium hydroxide - Ca (OH) ₂ or calcium oxide - CaO is used as lime.