RU2841103C1 - Method of cementing wells in permafrost intervals - Google Patents

Abstract

FIELD: mining.

SUBSTANCE: invention relates to a method of cementing wells in permafrost intervals. Method includes pumping to pipe space of design volume of grouting mortar and its pumping with direct forcing in one stage. Cementing is carried out using a grouting composition similar to that used during cementing of the direction and/or surface conductor. Dry grouting mixture is prepared during production by successive mixing of components in a mixing unit in accordance with the manufacturer's process chart. Tempering fluid is prepared directly on drilling site by means of introduction of rated number of components into process water. Introduction is carried out with continuous stirring, first at a slow rate, in order to avoid lump formation, introducing a synthetic sulphonated copolymer and stirring until its complete dissolution, then, with interval of 10 minutes, a polycarboxylate superplasticiser, a hardening agent and an antifreeze additive are added. Then the produced mixture is thoroughly stirred during 10 minutes. Then dry grouting mixture of factory readiness is added to the prepared tempering fluid.

EFFECT: higher efficiency of well construction in permafrost conditions.

2 cl, 2 dwg

Description

The invention relates to the oil and gas production industry, namely, to a method for cementing wells in permafrost intervals and a composition for cementing, and can be used to improve the quality of construction of oil and gas wells in permafrost conditions by implementing complex formulation and technological solutions that ensure, during the process of fastening casing strings in the upper intervals, the creation of a thermodynamic barrier and preventing the occurrence of behind-the-casing flows, inter-casing pressures, as well as thawing of the wellhead zone.

State of the art

It is known:

1. The use of a setting accelerator composition for inorganic binders, which comprises at least one water-soluble comb polymer, which comprises structural units of (meth)acrylic acid, maleic acid, polyalkylene glycol vinyl ethers, polyalkylene glycol allyl ethers and polyalkylene glycol ethers of (meth)acrylic acid and particles of calcium silicate hydrate in cementing oil and gas wells in permafrost regions and in the shelf zone, wherein the comb polymer is a copolymer, which on the main chain has side chains comprising polyether functional groups, as well as acid functional groups, and the particles of calcium silicate hydrate are less than 5 μm, preferably less than 1 μm, more preferably less than 500 nm, particularly preferably less than 200 nm and in particular less than 100 nm.

2. Use according to claim 1, wherein the setting accelerator composition is used in the form of a suspension, preferably in the form of an aqueous suspension.

3. Use according to paragraph 1, wherein the setting accelerator composition is used in powder form.

4. The use according to any one of claims 1 to 3, wherein the comb polymer is in the form of a copolymer which can be obtained by radical copolymerization of acidic monomers and polyether macromonomers, wherein the copolymer in total contains at least 45 mol.%, preferably at least 80 mol.%, of acidic monomer and/or polyether macromonomer structural units.

5. The use according to claim 1, wherein the comb polymer has an average molecular weight (Mw) of 5000 to 200000 g/mol, preferably 10000 to 80000 g/mol and in particular 20000 to 70000 g/mol, measured by gel permeation chromatography.

6. The use according to claim 1, wherein the molar ratio of calcium to silicon in the calcium silicate hydrate is from 0.6 to 2.0, preferably from 1.1 to 1.8.

7. The use according to claim 6, wherein the molar ratio of calcium to water in the calcium silicate hydrate is from 0.6 to 6, preferably from 0.6 to 2.0 and in particular from 0.8 to 2.0.

8. The use according to claim 7, wherein the particles of calcium silicate hydrate can be obtained by reacting a water-soluble calcium compound with a water-soluble silicate compound, wherein the reaction is carried out in the presence of an aqueous solution of a water-soluble comb polymer suitable as a plasticizer for hydraulic binders.

9. Use according to paragraph 1, wherein Portland cements, calcium aluminate cements, gypsum, anhydrite, blast furnace slags, granulated blast furnace slags, fly ash, quartz dust, metakaolin, natural and synthetic pozzolans and/or burnt oil shales, primarily Portland cements, are used as inorganic binders.

10. The use according to claim 9, wherein the binders are used in the form of a cement slurry, wherein the water/cement ratio is preferably in the range from 0.2 to 1.0, in particular in the range from 0.3 to 0.6.

11. Use according to item 10 to accelerate the setting of cement slurries.

12. The use of claim 10 for reducing the time it takes for the static gel strength of curable cement slurries to increase from 100 lb/100 ^ft2 (4.88 kg/ ^m2 ) to 500 lb/100 ^ft2 (24.4 kg/ ^m2 ).

13. Use according to item 1 together with other additives used in cementing boreholes, in particular plasticizers, water-retaining agents and/or rheology-modifying additives (see patent RU No. 2598945, IPC C 09 K 8/467, E 21 B 33/138, published 10.10.16, Bulletin No. 15).

The disadvantage of this method is that it is not effective enough to counteract the pressure of underground formations and, thus, does not prevent the uncontrolled appearance of liquids.

A method is known for lining a well with a casing in a section of permafrost rocks with a high ice content, which consists in drilling a wellbore to stable rocks, drilling without flushing the well with drilling mud, lowering a casing consisting of casing pipes with a heat-insulating shell, equipping the casing with centering elements, a column shoe and a channel for monitoring the temperature along the entire length of the casing, while when lowering the casing into the well, small-diameter pipes are secured on the outside of the casing, which form an autonomous channel for cementing the casing, along which the annular space is filled from the bottom to the wellhead with a cementing slurry, while at the same time the casing space is filled with an antifreeze (see RU Patent No. 2662830, IPC E 21 B 33/14, E 21 B 43/10, E 21 B 36/00, published. 07/31/2018, Bulletin. No. 22).

The disadvantage of this method is the insufficient improvement of the well fastening quality and ensuring its operational reliability in the section of permafrost rocks with high ice content.

The closest in technical essence and achieved positive effect and accepted by the authors as a prototype is:

1. A method for cementing a production string of a gas well in permafrost conditions, including pumping a spacer fluid and a cement slurry into the tubular space and squeezing with a squeezing fluid, wherein a three-phase foam is used as the spacer fluid, a lightweight cement slurry with a filler - gas-filled microspheres - is pumped in before the cement slurry, and before it a suspension is fed into the tubular space consisting of a non-freezing liquid, the density of which is higher than the density of the mixing liquid of the said lightweight cement slurry, and gas-filled microspheres treated with wool fat acids in an amount of 0.1-0.4% of their weight, wherein in the said suspension the volume of non-freezing liquid

mass of the specified microspheres, Q _GM = (VV _f )⋅ρ,

where V _f is the volume of non-freezing liquid, ^m3 ;

ρ ₀ - bulk density of the specified microspheres treated with wool fat acids, kg/m;

ρ - density of the specified microspheres, kg/ ^m3 ;

m - the coefficient of grain separation of the specified microspheres - 1.05-1.25;

V is the volume of the annular space from the wellhead to the depth of the permafrost base, ^m3 ;

Q _gm - mass of the specified microspheres, kg,

the said pumping is carried out in the volume necessary to fill the annular space from the well bottom to the roof of the productive formation, the said suspension is pumped in the volume necessary to fill the annular space from the wellhead to the base of the permafrost rocks, and the lightweight cement slurry with gas-filled microspheres is pumped in the volume necessary to fill the annular space from the roof of the productive formation to the base of the permafrost rocks.

2. The method according to claim 1, wherein aluminosilicate, or glass, or polymer gas-filled microspheres are used as gas-filled microspheres (see patent RU No. 2281382, IPC E 21 B 33/13, C 09 K 8/473, published 10.08.2006, Bulletin No. 22).

The disadvantage of this method is the low efficiency of cementing the production well casing in permafrost conditions.

Disclosure of the invention The objective of the proposed invention is to develop a method for cementing wells in permafrost intervals and a composition for cementing, i.e., to develop such formulation and technological solutions that will ensure normal hardening of the cement slurry during the process of fastening casing strings in the upper intervals, the creation of a thermodynamic barrier and the prevention of the occurrence of behind-the-casing flows, inter-casing pressures, as well as thawing of the wellhead zone in permafrost conditions.

The technical result that can be obtained using the proposed invention is to increase the efficiency of well construction in permafrost conditions by minimizing the risk due to insufficient hardening of the cement slurry, the occurrence of undesirable heat exchanger processes leading to thawing of the wellhead and a decrease in the quality of fastening of casing strings in the cryolithozone intervals, as well as by preventing the occurrence of behind-the-casing flows, griffins and/or inter-casing pressures due to the use of a specially developed composition for cementing and an improved cementing technology.

The specified technical result is achieved with the help of:

1. A method for cementing wells in permafrost intervals and a cementing composition comprising pumping a calculated volume of cement slurry into the tubular space and pumping it with direct squeezing in one stage, wherein cementing is carried out using a cementing composition similar to that used for cementing the direction and/or conductor, wherein the dry cement slurry is prepared at the plant by sequentially mixing the components in a mixing unit in accordance with the manufacturer's process chart, and the mixing fluid is prepared directly at the drilling site by introducing the calculated amount of components into process water, the introduction is carried out with continuous mixing, first at a slow pace, in order to avoid lump formation, a synthetic sulfonated copolymer is introduced and mixed until it is completely dissolved, then a polycarboxylate superplasticizer, a setting accelerator and an antifreeze additive are added at 10-minute intervals, after which the resulting mixture is thoroughly mixed for 10 minutes, then 100% of the prepared mixing fluid is introduced into the prepared dry cement mixture of factory readiness, while the cement slurry has the following component composition, mass %:

- Politsem Gips - Gips G-18 - high-strength separated gypsum binder for special purposes for cement slurries - 38.37-45.35;

- Ultracement-5 - micronized oil well portland cement - 6.98-17.44;

- PCT-1-50 - standard Portland cement without additives for low and normal temperatures - 1.39-10.46;

- DR-50 - expanding additive (SABV - sulfoaluminate belite binder) - 4.88-6.98;

Hollow glass microspheres - heat-insulating additive (gas-filled glass granulate) - 3.49-10.46;

- Politsem Plast-1 - polycarboxylate superplasticizer - 0.14-0.7;

- Policem Gasblock - sulphonated synthetic copolymer - 0.007-0.014;

- Monoethylene glycol is a polyhydric alcohol - 3.1-5.23;

- Calcium nitrite-nitrate-chloride (NNHC) or Calcium nitrite-nitrate (NNK) or Calcium nitrate (NK) or Calcium nitrite-nitrate + Calcium formate, which does not contain chlorides and/or neutralizes their aggressive action, a setting accelerator, a mixed-type corrosion inhibitor for casing metal - 0.7-1.39;

- Fresh technical (tap) water - the rest is 23.72-28.25.

2. Method of cementing wells in permafrost intervals and composition for cementing according to paragraphs. 1., wherein cementing is carried out through drill pipes when fastening casing columns with a diameter of 324 mm or more, wherein the shoe of the cemented column is equipped with a special device for sealing, wherein the dry cementing mixture is prepared at the plant by sequentially mixing the components in a mixing unit in accordance with the manufacturer's process chart, and the mixing liquid is prepared directly at the drilling site by introducing the calculated amount of components into process water, the introduction is carried out with continuous mixing, first at a slow pace, in order to avoid lump formation, a synthetic sulfonated copolymer is introduced and mixed until it is completely dissolved, then a polycarboxylate superplasticizer, setting accelerator and antifreeze additive are added at intervals of 10 minutes, after which the resulting mixture is thoroughly mixed for 10 minutes, then a dry cementing mixture of factory readiness is introduced into the prepared mixing liquid, wherein the cementing slurry has the following component composition, mass %:

- Politsem Gips - Gips G-18 - high-strength separated gypsum binder for special purposes for cement slurries - 38.37-45.35;

- Ultracement-5 - micronized oil well portland cement -6.98-17.44;

- PCT-1-50 - standard Portland cement without additives for low and normal temperatures - 1.39-10.46;

- DR-50 - expanding additive (SABV - sulfoaluminate belite binder) - 4.88-6.98;

Hollow glass microspheres - heat-insulating additive (gas-filled glass granulate) - 3.49-10.46;

- Politsem Plast-1 - polycarboxylate superplasticizer - 0.14-0.7;

- Policem Gasblock - sulphonated synthetic copolymer - 0.007-0.014;

- Monoethylene glycol is a polyhydric alcohol - 3.1-5.23;

- Calcium nitrite-nitrate-chloride (NNHC), or Calcium nitrite-nitrate (NNK), or Calcium nitrate (NK), or Calcium nitrate-nitrate + Calcium formate, a chloride-free and/or chloride-neutralizing setting accelerator, mixed-type casing metal corrosion inhibitor - 0.7-1.39;

- Fresh technical (tap) water - the rest is 23.72-28.25.

Brief description of drawings and other materials

Fig. 1 shows a method for cementing wells in permafrost intervals and a composition for cementing, a composition for cementing, a table.

Fig. 2, also, shows a graph of laboratory testing of the cementing composition.

Implementation of the invention

The method of well cementing in permafrost intervals and the cementing composition provide, firstly, resistance to freezing at temperatures down to -10°C, secondly, the absence of the thawing effect at the "cement slurry - permafrost" contact during pumping and hardening, and thirdly, the creation of a thermodynamic barrier preventing the occurrence of undesirable heat exchange causing thawing of the wellhead zone during well development and operation. The thermal conductivity coefficient of the resulting cement stone can reach 0.15 W / m⋅K. The increase in temperature of the complex cementing mixture during hardening does not exceed 4 degrees. Freezing resistance of the cementing composition during mixing and pumping, and most importantly, during cement hardening is ensured by introducing an antifreeze additive into the formulation. Frost resistance of the cementing composition determines the parameters of its thickening, setting and strength gain of the cement stone under sub-zero temperatures. In case of insufficient frost resistance of the cement slurry, it freezes before or during the setting process, while the formation and gain of strength of the cement stone either does not occur or occurs partially. In such a situation, after the well is put into operation, due to the resulting heat exchange, the frozen cement slurry thaws and separates into solid and liquid phases. As a result, the cement ring behind the column is not formed, the lining is not tight, and in the upper part of the zone of stratification of the thawed cement slurry, under the action of longitudinal bending, the casing loses stability. Minimizing the heating temperature of the cement slurry during thickening and hardening is of key importance in terms of preventing the occurrence of behind-the-casing flows and ensuring the tightness of the casing lining in the permafrost intervals. The heat released during the hydration of traditionally used cement slurries determines the effect of thawing of ice formations of the cryolithozone at the contact "rock-cement slurry", which, even under conditions that ensure hardening and formation of a cement ring with specified strength parameters, creates prerequisites for the formation of conductive channels of high permeability and length in the annular space of cemented wells in permafrost zones. The formation of these channels determines the leakage of the casing support and the occurrence of behind-the-annular migration of formation fluid, inter-annular pressures, griffins, etc. The proposed invention ensures the minimization of temperature fluctuations in the process of thickening of the cement slurry and hardening of the cement stone.

The mechanism for implementing the effect of minimizing temperature fluctuations is due to the specific nature of the interaction during hydration of the cement composition, namely the ability of the polyhydric alcohol included in the formulation to initially bind a certain volume of water and gradually release it during hydration of the cement composition. In this case, the process of releasing bound water occurs discretely, as a result of which the linear intensity of temperature growth during hydration has minimal values due to the slowdown of convective heat exchange with the external environment, which has a negative temperature. A decrease in the rate of heat release ensures its smooth absorption, without reaching the temperature values that cause active melting of cryolithozone rocks.

The effect was studied in the process of complex laboratory research of thickening and hardening of the developed cement slurry. The data of laboratory testing of the developed cement slurry on studying the kinetics of consistency gain under conditions of reduced temperature of +5°C show that temperature fluctuations during thickening of the pre-cooled cement slurry did not exceed the limit of ±3°C. Creation of a thermodynamic barrier isolating undesirable thermal impact on cryolithozone rocks during well development and operation is ensured by reducing the thermal conductivity of cement stone by introducing heat-insulating materials into the cement slurry and/or aeration of the cement slurry directly during pumping during the casing process. Hollow glass microspheres or other materials allowing the formation of distributed air-filled cavities in the structure of cement stone are used as a heat-insulating additive. In addition, the proposed method of well casing in permafrost conditions provides for physical and chemical aeration of the cement slurry, implemented by introducing a foaming agent into the formulation and using aerating technical means during cementing. Aeration of the cement slurry can be used both as the main and auxiliary solution, ensuring the creation of a heat-insulating barrier in the structure of the cement stone. Aeration also allows imparting hydromechanical elasticity to the cement slurry due to the energy of the compressed gas phase during injection, which allows significantly improving the quality of cementing due to increased adhesion of the cement ring on the contacts, especially under the condition of conducting OZC under pressure.

An example of a specific implementation of the method of cementing wells in permafrost intervals and a composition for cementing.

At the stage of preparation for cementing, the necessary geophysical studies and clarifying calculations are carried out to determine the amount of cement slurry, its parameters and injection mode. According to the existing practice of designing well structures, the permafrost intervals are confined to the upper part of the geological section and are covered by isolation, as a rule, by the first two casing strings direction and/or conductor.

The dry cement mixture is prepared at the production site by sequentially mixing the components of items 1-5 of the table in a mixing unit in accordance with the manufacturing process chart. It is packaged and supplied in 1000 kg bags. The mixing fluid is prepared directly at the drilling site by introducing the calculated amount of components of items 6-9 of the table into the process water. The introduction is carried out with continuous stirring. First, the sulfonated synthetic copolymer is introduced slowly, to avoid lump formation, until it is completely dissolved. Then, at 10-minute intervals, the polycarboxylate superplasticizer, setting accelerator and antifreeze additive are added, after which the resulting mixture is thoroughly mixed for 10 minutes.

Technically, the proposed method is implemented as follows. Cementation of the direction is carried out using standard technology. After lowering the casing string, the calculated volume of cement slurry is closed and pumped with direct squeezing in one stage. The content of the heat-insulating additive is selected in a given range based on ensuring the required heat-insulating capacity of the cement stone, as well as the specified rheological and technological parameters of the cement slurry depending on the type of additive used and the engineering and geological conditions of cementing. In this case, the cement composition must gain at least 80% of the specified strength parameters within 16 hours. The total waiting time for cement hardening should not exceed 24 hours.

Cementation of the conductor can be carried out in two ways.

Option 1. Cementation is carried out by direct squeezing in one stage using a cementing solution, similar to that used for direction cementing. This option is the only one in the case when the well design provides for the overlap of cryolithozone intervals with only one column.

Option 2. Cementation of the conductor is carried out through drill pipes and is recommended for use when fastening casing columns with a diameter of 324 mm and more. Cementation through drill pipes allows for effective control of the speed and volume of squeezing, obtaining a specified density at the output and minimizing temporary process losses. When cementing through drill pipes, the shoe of the cemented column is equipped with a special device for sealing.

When using an aerated cement slurry, the wellhead of the line is equipped with a device that ensures the sealing of the annular space between the line and the caisson conductor. After lowering the conductor, the injection manifold is equipped with an ejector for introducing the gas phase into the cement slurry on the flow. The required degree of aeration is determined by calculation based on the results of laboratory studies, and the actual one is selected by the ratio of the flow rates of the aerated cement slurry and the introduced gas phase, taking into account the process parameters of the pumping and compressor equipment, as well as the design features of the ejector used. Pumping begins with pumping a prepared portion of the buffer non-aerated cement slurry with a volume of 0.5 m ³ , followed by connecting the compressor for aeration. Upon completion of pumping the calculated volume of the cement slurry, before the start of squeezing, the caisson is sealed and the drilling fluid is displaced through the caisson branch. When gel cement (non-arid cement slurry) appears at the outlet, the annulus is sealed and further squeezing is carried out with minimum productivity until the "stop" moment is reached. The last portion of cement in the volume of 0.5-1 ^m3 is also pumped without aeration. In this case, the pressure in the annulus is strictly controlled to prevent the occurrence of hydraulic fracturing of rocks in the cemented interval. When the pressure in the annulus of the cemented column reaches 0.8Ppp (80% of the value of the hydraulic fracturing pressure of rocks), bleeding is carried out through the caisson branch. Waiting for cement hardening (WCH) is carried out under pressure. A decrease in the value of the annular pressure below the required repression is not allowed and it is highly desirable to provide a differential drop at a level close to the limit of the maximum possible values for the WCH period.

The proposed invention has the following advantages compared to the prototype and other known technical solutions:

- improving the quality of fastening of casing columns in the upper intervals of the cryolithozone;

prevention of occurrence of behind-the-casing flows and inter-casing pressures;

creation of a thermodynamic barrier preventing thawing of the wellhead section.

Claims (22)

1. A method for cementing wells in permafrost intervals, including pumping a calculated volume of cement slurry into the tubular space and pumping it with direct squeezing in one stage, characterized in that cementing is carried out using a cementing composition similar to that used in cementing the direction and/or conductor, wherein the dry cement slurry is prepared at the plant by sequentially mixing the components in a mixing unit in accordance with the manufacturer's process chart, and the mixing fluid is prepared directly at the drilling site by introducing the calculated amount of components into process water, the introduction is carried out with continuous mixing, first at a slow pace, in order to avoid lump formation, a synthetic sulfonated copolymer is introduced and mixed until it is completely dissolved, then a polycarboxylate superplasticizer, setting accelerator and antifreeze additive are added at 10-minute intervals, after which the resulting mixture is thoroughly mixed for 10 minutes, then dry factory-prepared cement mixture, where the cement slurry has the following component composition, mass %: - Politsem Gips - Gips G-18 - high-strength separated gypsum binder for cement slurries - 38.37-45.35; - Ultracement-5 - micronized oil well portland cement - 6.98-17.44; - PCT-1-50 - Portland cement without additives for low and normal temperatures - 1.39-10.46; - DR-50 - expanding additive - SABV - sulfoaluminate belite binder - 4.88-6.98; - hollow glass microspheres - heat-insulating additive - gas-filled glass granulate - 3.49-10.46; - Politsem Plast-1 - polycarboxylate superplasticizer - 0.14-0.7; - Policem Gasblock - sulphonated synthetic copolymer - 0.007-0.014; - monoethylene glycol - polyhydric alcohol - 3.1-5.23; - calcium nitrite-nitrate-chloride - HNHK, or calcium nitrite-nitrate - HNK, or calcium nitrate - NK, or calcium nitrite-nitrate + calcium formate, a setting accelerator that does not contain chlorides and/or neutralizes their aggressive action, a mixed-type casing metal corrosion inhibitor - 0.7-1.39; - fresh industrial water - tap water - the rest 23.72-28.25. 2. A method for cementing wells in permafrost intervals and a cementing composition according to claim 1, characterized in that cementing is carried out through drill pipes when fastening casing columns with a diameter of 324 mm or more, while the shoe of the cemented column is equipped with a sealing device, and the dry cementing mixture is prepared at the plant by sequentially mixing the components in a mixing unit in accordance with the manufacturer's process chart, and the mixing fluid is prepared directly at the drilling site by introducing the calculated amount of components into industrial water, the introduction is carried out with continuous mixing, first at a slow pace, in order to avoid lump formation, a synthetic sulfonated copolymer is introduced and mixed until it is completely dissolved, then a polycarboxylate superplasticizer, a setting accelerator and an antifreeze additive are added at 10-minute intervals, after which the resulting mixture is thoroughly mixed for 10 minutes, then the dry cementing mixture is introduced into the prepared mixing fluid factory-prepared, while the cement slurry has the following component composition, mass %: - Politsem Gips - Gips G-18 - high-strength separated gypsum binder for cement slurries - 38.37-45.35; - Ultracement-5 - micronized oil well portland cement - 6.98-17.44; - PCT-1-50 - Portland cement without additives for low and normal temperatures - 1.39-10.46; - DR-50 - expanding additive - SABV - sulfoaluminate belite binder - 4.88-6.98; - hollow glass microspheres - heat-insulating additive - gas-filled glass granulate - 3.49-10.46; - Politsem Plast-1 - polycarboxylate superplasticizer - 0.14-0.7; - Policem Gasblock - sulphonated synthetic copolymer - 0.007-0.014; - monoethylene glycol - polyhydric alcohol - 3.1-5.23; - calcium nitrite-nitrate-chloride - HNHK, or calcium nitrite-nitrate - HNK, or calcium nitrate - NK, or calcium nitrite-nitrate + calcium formate, a setting accelerator that does not contain chlorides and/or neutralizes their aggressive action, a mixed-type casing metal corrosion inhibitor - 0.7-1.39; - fresh industrial water - tap water - the rest 23.72-28.25.

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