RU2525537C1 - Polymeric composition for highly mineralised water-based weighted drilling fluids - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: polymeric composition for highly mineralised water-based weighted drilling fluids includes hydrolysed cyanoethylated polyvinyl alcohol, which is synthesised by an interaction of acrylonitrile with polyvinyl alcohol in a water-alkaline medium, and oxyethylcellulose with the following ratio of ingredients, wt %: hydrolysed cyanoethylated polyvinyl alcohol 80-90, oxyethylcellulose 10-20.

EFFECT: considerable reduction of the index of high-temperature filtration, optimal structural-mechanical and viscous characteristics of fluids for accident-free drilling of gently sloping and horizontal wells, composed by highly colloidal clayey rocks at high temperatures.

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Description

The invention relates to the drilling of oil and gas wells, and in particular to reagents for the chemical treatment of highly mineralized weighted drilling fluids, water-based, used in the drilling of highly colloidal clay rocks and zones of abnormally high reservoir pressure (AAP).

The assortment of drilling fluid stabilizing agents under conditions of polymineral aggression is not large. In addition to starch, which is characterized by low resistance to thermal and bacterial degradation, the use of ethoxylated cellulose (OEC) is also known (Bulatov A.I., Penkov A.I., Proselkov Yu.M. Handbook for flushing wells. - M .: Nedra, 1984. - S. 61). Sulfacell-2 (grades 400, 800, 2000), manufactured in accordance with TU 2231-013-32957739-01, is used as the OEC. The reagent increases the plastic viscosity of highly mineralized weighted water-based drilling fluids, increasing their bearing capacity, and reduces the penetration of the aqueous phase into the pore space of the productive formations.

A disadvantage of the low viscosity (low molecular weight) modification of hydroxyethyl cellulose (grade 400) is the high rate of high-temperature filtration (Ф at 100 ° C) of highly mineralized water-weighted drilling fluids under conditions of polymineral aggression. The high molecular weight modification of the product (grade 2000) has an acceptable indicator of high-temperature filtration (Ф at 100 ° C), but the plastic viscosity (η _PL ) exceeds the permissible value by more than 5 times, which is unacceptable from the point of view of hydrodynamic resistance when flushing a well.

Closest to the proposed technical solution is an invention in which it is proposed to use hydrolyzed cyanethylated polyvinyl alcohol (CEPS) synthesized by the interaction of acrylonitrile (GOST 11097-86) with polyvinyl alcohol (GOST 10779-78) in an aqueous alkaline medium, as an indicator filtration (Ф at 20 ° C and Ф at 100 ° C) of water-based clay drilling fluids with the content of polyvalent cations up to 10% (AS No. 732357 from 04/17/78, published on 05/08/80).

The disadvantage of CEPS is the high value of the high-temperature filtration index (Ф at 100 ° C) of highly mineralized water-weighted drilling fluids with a content of polyvalent cations of more than 10% (the research results are presented in the table below).

The problem to be solved and the expected technical result is the creation of a polymer composition with a content of polyvalent cations of more than 10%, which ensures a decrease in the high-temperature filtration rate (Ф at 100 ° С) of highly mineralized water-weighted drilling fluids. In this case, the technological parameters of the solutions should be within the following limits:

filtration rate at 100 ° C (Ф at 100 ° C) 3-5 cm ³ plastic viscosity at 20 ° C (η _PL )  50-60 MPa · s dynamic shear stress at 20 ° C (τ ₀ )  60-90 dPa clay moisturizing index (P ₀ )  0.01-0.03 m / h

which in turn makes it possible to ensure the exclusion of differential sticks of the drilling tool, squeezing pressures in the circulation system of not more than 14 MPa and a stable state of the borehole of a minimum diameter (70 mm) to collapse and cavern formation for at least 15 days.

The problem is solved in that the polymer composition for highly mineralized weighted drilling fluids based on water, including hydrolyzed cyanethylated polyvinyl alcohol synthesized by reacting acrylonitrile (GOST 11097-86) with polyvinyl alcohol (GOST 10779-78) in an aqueous alkaline medium, additionally contains hydroxyethyl cellulose (TU 2231-013-32957739-01) in the following ratio of ingredients, wt.%:

hydrolyzed cyanethylated polyvinyl alcohol  80-90 hydroxyethyl cellulose  10-20

The combined use of hydroxyethyl cellulose and hydrolyzed cyanethylated polyvinyl alcohol provides a synergistic effect of reducing the high-temperature filtration rate. A synergistic effect is observed when the total content of the reagents of the polymer composition is within 0.2-0.4% by weight of the volume of the solution, while the maximum effect is achieved when the ratio of hydrolyzed CEPS: OEC = 8-9: 1-2. The synergy of the action is explained by the formation of a mosaic structure of linear low molecular weight cyanethylated polyvinyl alcohol and spiral-shaped macromolecules of high molecular weight hydroxyethyl cellulose, which in the system with the reagent create a stable spatial lattice, eliminating inside and intermolecular “crosslinking” of polyvalent cations. In this case, the plastic viscosity and the high-temperature filtration index of the resulting polymer composition do not exceed the specified limits, which is confirmed by the research results presented below.

On a model drilling fluid with a polyvalent cation content of more than 10 wt.%, Which is a mass concentration of 0.25% XG Polimer biopolymer solution (TU 2235-003-97176409-09), treated with 4% chalk MTD-1 (TU 5743 -001-53346358-98) and weighted with Unisalt-A complex salt additive (TU2458-002-60370134-2011) up to a density of 1.56 g / cm ³ , according to filtration indices (Ф at 20 ° C and Ф at 100 ° C) The stabilizing effect of the new polymer composition was evaluated. Rheological parameters (plastic viscosity - η _PL , mPa · s and dynamic shear stress - τ ₀ , dPa) of highly mineralized water-weighted drilling mud were determined using a Fann 35 S viscometer. Structural and mechanical parameters (static shear stress - СНС _1/10 , dPa) were determined on the device SNS-2.

Filtering display (P at 20 ° C, ^cm3 / 30 min) was evaluated using a filter-press at a pressure differential of 0.7 MPa. Display high filtration (O at 100 ° C, ^cm3 / 30 min) was estimated using high pressure filter press at high temperature and pressure drop of 3.45 MPa and a temperature of 100 ° C. Clay moisturizing index (P ₀ , cm / h) was determined in accordance with RD 39-2-813-82.

Studies have shown that the addition of Sulfacell-2 grade 400 to a model solution of the order of 0.2-0.6% leads to a significant increase in plastic viscosity (η _PL ) and dynamic shear stress (τ ₀ ) (table 1). At the same time, the reagent well reduces the rate of high-temperature filtration (Ф at 100 ° C) of a highly mineralized weighted drilling fluid based on water. Table 1 also presents the results of processing the model solution with hydrolyzed cyanethylated polyvinyl alcohol in an amount of 0.2-0.4 wt.% Of the volume of highly mineralized weighted drilling fluid on an aqueous basis. With an increase in the concentration of CEPS, a decrease in the high-temperature filtration index (Ф at 100 ° C) is observed to a lesser extent than with Sulfacell-2 grade 400, while the dynamic shear stress (τ ₀ ) also decreases.

Table 1 Filtration and rheological parameters of a model drilling fluid with stabilizing additives introduced separately Additive,% F at 20 ° C, ^cm3 / 30 min F at 100 ° C, ^cm3 / 30 min η _pl at 20 ° C, MPa · s τ ₀ at 20 ° C, dPa Sulfacell-2 grade 400 0 14.6 32 55 96 0.05 10.5 23 57 104 OD 8.3 15.0 69 145 0.2 4.6 9.7 75 234 0.4 2.0 6.2 88 > 300 0.6 1,2 4.8 102 > 300 CEPS 0.05 13.3 24 53 96 0.1 7.4 12.7 55 74 0.2 3,1 10,4 57 56 0.4 1.3 7.9 68 53

When the solution is treated with the same amounts of Sulfacella-2 grade 400 and hydrolyzed CEPS in the form of the inventive polymer composition, the filtration rates at 20 and 100 ° C (Ф at 20 ° C and Ф at 100 ° C) decrease significantly more (table 2), and rheological parameters (plastic viscosity - η _PL and dynamic shear stress - τ ₀ ), affecting the hydrodynamic resistance of the circulation of highly mineralized water-weighted drilling fluids in the well, vary slightly. With the ratios of the components: hydrolyzed CEPS: Sulfacell-2 from 9: 1 to 8: 2, a synergistic effect is observed due to the mechanism of complex conformation of the product in the salt solution. When the content of Sulfacell-2 grade 400 in the composite reagent is less than 10% or more than 20%, a synergistic effect is not observed. In addition, the individual additive Sulfacell-2 grade 400 in an amount of 0.2% wt. (see table 1) does not provide an additional significant result.

table 2 Filtration and rheological parameters of a model drilling fluid with stabilizing additives, introduced together (the content of the polymer composition in the solution of 0.2% wt.) The ratio of components in the polymer composition F at 20 ° C, ^cm3 / 30 min. F at 100 ° C cm ^3/30 min η _pl at 20 ° C, MPa · s τ ₀ at 20 ° C, dPa Sulfacell-2 grade 400 CEPS 0.5 9.5 3,1 5.3 57 60 one 9 1.9 2.9 45 66 2 8 1,6 2,3 48 84 3 7 2.7 5,0 60 106 5 5 3.0 5,6 78 183 7 3 3.6 6.9 88 222

As can be seen from table 2, a change in the ratio of components outside the optimal region leads either to a rapid increase in rheological parameters (plastic viscosity - η _PL and dynamic shear stress - τ ₀ ), which negatively affects the well wash hydraulics, or reduces the effect of the reagent on the high-temperature filtration rate solution (Ф at 100 ° C). With the ratios of hydrolyzed CEPS: Sulfacell-2 from 9: 1 to 8: 2, a decrease in the high-temperature filtration index (Ф at 100 ° C) of the weighted water-based biopolymer drilling mud is significant in relation to the action of both products separately. In addition, with the specified ratio of the components, the plastic viscosity η _PL and the dynamic shear stress τ ₀ remain within acceptable limits.

Examples of the preparation of polymer compositions in the laboratory.

Example 1. 1.25 g of hydroxyethylated cellulose (Sulfacell-2 grade 400) (Sulfacell-2 and CEPS ratio 1: 9) was added to 45 g of hydrolyzed cyanethylated polyvinyl alcohol (25% concentration) and stirred on a laboratory stirrer for 10 minutes.

Example 2. To 40 g of hydrolyzed cyanethylated polyvinyl alcohol (25% concentration), 2.5 g of ethoxylated cellulose (Sulfacell-2 grade 400) (Sulfacell-2 and CEPS 2: 8 ratio) were added and stirred on a laboratory stirrer for 20 minutes.

The polymer compositions prepared according to examples 1 and 2 were tested on a model highly mineralized weighted drilling fluid, water-based in comparison with the prototype, also prepared on a model drilling fluid.

As a model weighted water-based drilling mud with a content of polyvalent cations of more than 10% wt. A 0.25% solution of the XG Polimer biopolymer, treated with 4% chalk MTD-1 and weighted with Unisalt-A complex salt additive to a density of 1.56 g / cm ^{3, was} used in mass concentrations. Additives of the reagents prepared according to examples 1 and 2 (solution No. 1 and solution No. 2, respectively) were 0.2 and 0.4%.

According to the description of the prototype, the optimal total addition of hydrolyzed CEPS is from 2 to 3% when introduced into a mineralized clay solution. In highly mineralized weighted water-based drilling fluids, reagent additives are limited to a concentration of 0.2-0.6%. Therefore, the procedure for preparing the solution according to the prototype was as follows: in a model weighted drilling fluid, water-based with a content of polyvalent cations of more than 10% wt hydrolyzed CEPS in the amount of 0.2 and 0.4% was added.

A comparison of rheological (plastic viscosity - η _PL and dynamic shear stress τ ₀ ) filtration (Ф at 20 ° C and Ф at 100 ° C) indicators and indicators of the moisturizing ability of clays (П ₀ ), obtained polymer compositions with the prototype, are shown in table 3 .

Table 3  Comparison of the parameters of a model drilling fluid without additives with solutions with an introduced prototype and with the introduced polymer compositions Name of solution Conc. reagent,% wt. Technological parameters η _pl , MPa · s τ ₀ , dPa CHC _1/10 , dPa F at 20 ° C, ^cm3 / 30 min F at 100 ° C, ^cm3 / 30 min P ₀ , m / hour Model r-op - 55 96 12/18 14.6 32 0.013 P-op with prototype 0.2 57 56 14/18 3.0 10,4 0.012 P-op with prototype 0.4 68 53 9/15 1.3 7.9 0.011 Solution No. 1 0.2 55 66 15/18 2,5 3.6 0.012 Solution No. 1 0.4 62 96 18/24 1,1 2,8 0.010 Solution No. 2 0.2 56 84 15/18 2,4 2.9 0.010 Solution No. 2 0.4 64 126 18/24 0.9 2,3 0.008

From table 3 it is seen that the performance of solutions No. 1 and No. 2 with the introduction of the polymer composition of 0.2% wt. remain within acceptable limits. The plastic viscosity of solutions No. 1 and No. 2, respectively, is 55 and 56 MPa · s, the dynamic shear stress is 66 and 84 dPa. The difference between the static shear stress of solutions No. 1 and No. 2 for 1 and 10 minutes is 3 dPa, which is comparable to the prototype (at a concentration of hydrolyzed CEPS 0.2% wt.) - 4 dPa. The filtration rate of solutions No. 1 and No. 2 at 20 ° C, respectively 2.5 and 2.4 cm ³ for 30 min, the filtration rate at 100 ° C - 3.6 and 2.9 cm ³ for 30 minutes, which is significantly lower than high-temperature filtration of a model solution of 32 cm ³ and a solution with a prototype (at a concentration of hydrolyzed CEPS 0.2% wt.) - 10.4 cm ³ . The moisturizing index of clay of solutions No. 1 and No. 2, respectively, is 0.012 and 0.010 m / h.

Claims (1)

A polymer composition for highly mineralized weighted water-based drilling fluids, including hydrolyzed cyanethylated polyvinyl alcohol synthesized by reacting acrylonitrile with polyvinyl alcohol in an aqueous alkaline medium, characterized in that it additionally contains hydroxyethyl cellulose in the following ratio of ingredients, wt.%:
hydrolyzed cyanethylated polyvinyl alcohol 80-90 hydroxyethyl cellulose 10-20.