RU2823955C1 - Method of cementing casing string in well - Google Patents

Abstract

FIELD: mining.

SUBSTANCE: invention relates to a method for cementing a casing in a well. Method involves successive pumping of a washing spacer fluid and portions of cement mortar, the first portion of cement mortar with density of 1,520–1,640 kg/m³ in a volume which provides filling of the annular space in the well in the interval from mouth to 100 m from the bottomhole. First portion of the cement mortar contains a dry cement mixture, a water loss reducer, an antifoaming agent and water. Dry cement mixture is represented by a mixture with the following ratio of components, wt.pts.: portland cement – 100, lightening inert filler – 10–23, fibrous material – 0.1–0.6, water loss reducer “ПВС-ВР” or “ПВА” – 0.5, antifoaming agent “ПЕНТА-465” or FOBR – 0.05, at a ratio of dry cement mixture to water of 100 wt.pts. to 60 wt.pts. respectively, second portion of cement mortar, forcing through portions of cement mortar, performing process exposure for the time of waiting for hardening of cement mortar. Second portion of the cement mortar is pumped with density of 1,880–1,920 kg/m³ in a volume which provides filling of the annular space of the well in interval of 100 m from the bottomhole. Second portion of the cement mortar contains a dry cement mixture and water at a ratio of the dry cement mixture to water of 100 wt.pts. to 44 wt.pts. respectively, dry cement mixture used is a mixture of backfill portland cement and microcement, with the following ratio of components, wt.pts.: portland cement – 100, cement with particle size of 5 microns – 10–20.

EFFECT: increased efficiency of the method due to improved quality of cementing in wells with residual losses of drilling mud, elimination of filtration of cement mortar after opening of pores of permeable formations and increased tightness of cement lining at contact of cement stone-rock.

1 cl, 2 tbl

Description

The proposal relates to the oil industry, in particular to methods of cementing casing columns in wells.

A method of well cementing is known, which includes the preparation, pumping and squeezing of a cement solution (suspension) into the well (Vadetsky Yu.V. Drilling of oil and gas wells. 4th edition, revised and enlarged. - Moscow: Nedra. - 1978. - P. 387).

A significant disadvantage of standard cement slurries is that they cannot be used to eliminate behind-the-casing flows, shut off formations, seal production columns, and perform water-proofing work, since coarsely dispersed cement slurries cannot be pumped into microgaps, microcracks, and low-permeability areas.

Also known is a method for cementing water influx zones of wells (patent RU No. 2297515, IPC E21B 33/13, published on 20.04.07, bulletin No. 11), which includes lowering a tubing string into the well, installing the open end of the tubing above the water influx zone, determining the specific injectivity, preparing and pumping in a cement slurry, starting with the fraction with a smaller particle size, squeezing the cement slurry, washing the remains of the cement slurry for the time required for the cement slurry to set at a pressure of 0.3-0.5 MPa below the final pressure during squeezing, and leaving it for the time it takes to wait for the cement slurry to harden.

The disadvantage of this method is its low efficiency due to the low penetrating ability of the cement slurry prepared from standard Portland cement and divided into fractions into low-permeability areas. The main disadvantage of standard Portland cement is that most of the slurry (the fraction with the smallest particles in the volume from 50 to 75% of the total) is limited by the size of the sieve with a number of 0.8, which does not allow the cement slurry divided into fractions to penetrate into microgaps, microcracks and low-permeability areas. When squeezing the cement slurry under normal flow and pressure conditions, the main part of the small fraction will move mainly through highly permeable areas, and the fraction following it will settle at the entrance to the pores of the low- and medium-permeability area, which will lead to insufficient coverage of water inflow zones with low and medium permeability. Then, the remaining cement slurry is flushed at a pressure of 0.3-0.5 MPa below the final pressure during squeezing. In this case, quite often a significant portion of the cement slurry, previously absorbed by the water influx zone, is washed out, which negatively affects the success of well cementing and the need to perform repeated work on sealing the production casing with low-viscosity hardening true solutions (synthetic resins or other materials) and, as a result, leads to additional material costs. With a specific injectivity of the water influx zone of more than 2 m³/(h⋅MPa), to achieve the effectiveness of the work, it is necessary to pump in a large volume of cement slurry.

A method of repair and insulation work is also known, which includes pumping a composition based on microcement using the additive - plasticizer Glenium-51 (Storchak V.A., Melehin A.A. Development of compositions of cement mixtures based on microcements // Construction of oil and gas wells on land and at sea. - 2011. - No. 8. - P. 51-53).

The disadvantages of the known method are the short curing time of the microcement-based composition - 2.5 hours, which can lead to its premature curing during repair and insulation work in the well, as well as the low strength of the cement stone.

Also known is a method for cementing water influx zones of wells (RU patent No. 2533997, IPC E21B 33/138, published on 27.11.2014, bulletin No. 33), which includes lowering a tubing string (TU) into the well, installing the open end of the TU above the water influx zone, determining the specific injectivity of the water influx zone in two operating modes of the pumping unit, and, if the specific injectivity is more than 2 m³/(h⋅MPa), a spacer fluid and a water-insulating composition are pumped in succession until a specific injectivity of 0.5-2 m³/(h⋅MPa) is achieved. Then, depending on the specific injectivity of the water influx zone, the total volume of the cement slurry is determined. At the same time, a cement slurry is prepared consisting of a slurry of oil well portland cement in the amount of 35% of the total volume of the cement slurry and a slurry of micro cement in the amount of 65% of the total volume of the cement slurry. With a specific injectivity of the water influx zone of 0.5-2 m³/(h⋅MPa), a spacer fluid, a cement slurry of micro cement, and a cement slurry of oil well portland cement are pumped in succession. Then, the flow rate and injection pressure are increased to the maximum permissible pressure on the production casing and, at such a flow rate, without reducing the pressure, the spacer fluid and the entire volume of the cement slurry of micro cement are squeezed out. Then, the flow rate and injection pressure are reduced to the minimum possible, at which the well continues to receive and the cement slurry of oil well portland cement is squeezed into the water influx zone until zero injectivity is obtained. The pressing is stopped and a technological holding is carried out, then the remains of the cement slurry from the oil well portland cement are washed with a counter pressure equal to the final pressure of pressing the cement slurry from the oil well portland cement into the water inflow zone.

The disadvantage of this method is its low efficiency due to the low penetrating ability of the cement suspension prepared from standard Portland cement and divided into fractions, into low-permeability areas. Other disadvantages include the low quality of casing cementing, failure to achieve tightness of the cement lining and low quality of layer separation.

Also known is a method for cementing a casing string in a well (RU patent No. 2398955, IPC E21B 33/138, published on 10.09.2010, bulletin No. 25), which includes sequential pumping of a washing spacer fluid and portions of cement slurry. In this case, the first and second portions of cement slurry are made of a cement slurry with a density of 1650-1750 kg/ ^m3 with erosive properties, containing a mixture of plugging portland cement and an abrasive material - fine quartz sand with an average grain size of no more than 1 mm in a weight ratio of 100:8 to 100:10, as well as polyvinyl alcohol - PVS-VR in an amount of 0.4-0.6% and a defoamer in an amount of 0.04-0.06% by weight of cement. The third portion is made from the specified cement mortar, which additionally contains calcium chloride in an amount of 2% and sodium chloride in an amount of 1%, by weight of the cement, and with a density of at least 1850 kg/ ^m3 .

The disadvantages include the low quality of cementation, since the last portion does not contain modifying components, and sodium and calcium salts only accelerate the hardening process of the cement stone in the early stages.

The closest method is for cementing a casing string in a well (RU patent No. 2720025, IPC E21B 33/14, C08K 8/467, C04B 14/38, published on 23.04.2020, bulletin No. 12), which includes the sequential injection of a washing spacer fluid and portions of cement slurry, with two portions of cement slurry being pumped in succession, the first portion of cement slurry is pumped in with a density of 1520–1640 kg/ ^m3 in a volume that ensures filling the annular space in the well in the interval from the wellhead to 100 m from the bottomhole, while the first portion of cement slurry contains a dry cement mixture, a fluid loss reducer - PVS-VR or PVA, a defoamer - PENTA-465 or "FOBR" and water, as a dry For the cement mixture, a mixture of Portland cement, a lightweight inert filler - foamed glass microgranules of fractions 0.1-1.5 mm or fine-porous spherical foam ceramic granules of the same fraction, and fiber with a fiber size of 3-6 mm and a diameter of 22-35 μm is used in the following ratio of components, parts by weight: Portland cement - 100, a lightweight inert filler - foamed glass microgranules of fraction 0.1-1.5 mm or fine-porous spherical foam ceramic granules of the same fraction - 10-23, fiber - 0.1-0.6, water loss reducer PVS-VR or PVA - 0.5, defoamer PENTA-465 or "FOBR" - 0.05, while the ratio of dry cement mixture to water is 100 parts by weight to 60 parts by weight. h., respectively, then the second portion of cement mortar with a density of 1585–1590 kg/ ^m3 is pumped in a volume that ensures filling the wellbore annular space in the interval of 100 m from the bottomhole, while the second portion of cement mortar contains a dry cement mixture, a setting accelerator - calcium chloride and water, a mixture of Portland cement, a lightweight inert filler - foamed glass microgranules of fractions of 0.1–1.5 mm or fine-pored foam ceramic spherical granules of the same fraction, and fiber with a fiber size of 3–6 mm and a diameter of 22–35 μm is used as a dry cement mixture. h.: Portland cement - 100, lightweight inert filler - foamed glass microgranules of fraction 0.1-1.5 mm or fine-pored foam ceramic spherical granules of the same fraction - 10-23, fiber - 0.1-0.6, setting accelerator - calcium chloride - 1-4, while the ratio of dry cement mixture to water is 100 wt. h. to 50 wt. h., respectively.

The disadvantage is the low density of the second portion of cement slurry, which worsens the degree of substitution of the drilling mud, the presence of spherical granules in the second portion, which can be destroyed during the pumping of the cement slurry, which will entail premature stop and affect the quality of cementing. Another disadvantage is the low bending strength at the age of 48 hours and low adhesion of the lightweight cement slurry to the rock and casing metal, which reduces the degree of tightness of the cement lining.

The technical objectives are to increase the efficiency of the method by improving the quality of cementing in wells with residual absorption of drilling mud, eliminating filtration of cement mortar after opening the pores of permeable formations, and increasing the tightness of the cement lining at the contact between cement stone and rock.

The technical problems are solved by cementing the casing in the well, including the sequential injection of a washing spacer fluid and portions of cement slurry, the first portion of cement slurry with a density of 1520–1640 kg/ ^m3 in a volume ensuring filling of the annular space in the well in the interval from the wellhead to 100 m from the bottomhole, wherein the first portion of cement slurry contains a dry cement mixture, a fluid loss reducer – PVS-VR or PVA, a defoamer – PENTA-465 or “FOBR” and water, as a dry cement mixture – a mixture of Portland cement, a lightweight inert filler – foamed glass microgranules of fractions 0.1–1.5 mm or fine-pored foam ceramic spherical granules of the same fraction, and fiber with a fiber size of 3–6 mm and a diameter of 22–35 μm at the following ratio of components, wt. h.: Portland cement - 100, lightweight inert filler - foamed glass microgranules of fraction 0.1-1.5 mm or fine-pored foam ceramic spherical granules of the same fraction - 10-23, fiber - 0.1-0.6, water loss reducer PVS-VR or PVA - 0.5, defoamer PENTA-465 or "FOBR" - 0.05, with a ratio of dry cement mixture to water of 100 parts by weight to 60 parts by weight, respectively, the second portion of cement mortar, squeezing portions of cement mortar, carrying out technological curing while waiting for the hardening of the cement mortar.

What is new is that the second portion of cement slurry is pumped in with a density of 1880–1920 kg/ ^m3 in a volume that ensures filling the wellbore annular space within an interval of 100 m from the bottomhole, while the second portion of cement slurry contains dry cement mixture and water with a ratio of dry cement mixture to water of 100 parts by weight to 44 parts by weight, respectively, a mixture of Portland cement and cement with a particle size of 5 microns is used as the dry cement mixture with the following ratio of components, parts by weight:

Portland cement 100 cement with a particle size of 5 microns 10–20

To implement the method, use:

Portland cement for oil wells grades PTsT I-50 or PTsT I-G-CC-1 – GOST 1581-2019.

Lightweight inert filler - foamed glass microgranules of fractions 0.1-1.5 mm, manufactured according to TU 5914-001-53933176-2011. They are a highly porous cellular inorganic heat-insulating material. The cells have a spherical or hexagonal shape, their size can be from fractions of a millimeter to several centimeters. The color of the material is usually greenish-gray.

Lightweight inert filler - fine-pored foam ceramic spherical granules of fractions 0.1-1.5 mm, produced according to TU 5712-001-14851799-2014.

The use of any of the above as a lightweight inert filler leads to the same technical result.

Fiberglass is a micro-reinforcing construction fiber. It is a single-component polypropylene fiber 3-6 mm long and 22-35 µm in diameter, manufactured according to TU 2272-006-13429727-2007 "Reinforcing construction fiber", grade VSM.

Water loss reducer PVS-VR, manufactured according to GOST 10779-78;

PVA Fluid Loss Reducer (BP-08), manufactured by Chang Chun Petrochemical Malaysia, is an emulsifying and stabilizing agent based on polyvinyl alcohol. With low surface tension and the ability to disperse vinyl acetate in water into very fine granules, PVA (BP-08) is used to produce polyvinyl acetate emulsion.

The use of any of the above as a water loss reducer leads to the same technical result.

The PENTA-465 antifoam agent, manufactured according to TU 2257-029-40245042-2002, is a self-emulsifying antifoam concentrate, effectively used in processes accompanied by heavy or moderate foaming, and also prevents excessive foaming when pre-introduced into a composition (formulation);

The defoamer "FOBR", manufactured according to TU 2458-002-65514187-2011, is a defoamer based on organosilicon oligomers with the addition of surfactants. "FOBR" is intended for use as a defoamer in all types of water-based drilling fluids.

The use of any of the above as a defoamer leads to the same technical result.

Microcement, for example, micronized cement of the “ultracement-5” brand according to TU 5739-019-56864391-2020 amend. 1,2.

Water – fresh water with a density of 1000 kg/ ^m3 for the preparation of cement mortars.

A 2% aqueous solution of sodium tripolyphosphate according to GOST 13493-86 or a 0.2% aqueous solution of nitrotrimethyl phosphonic acid according to GOST 6318-77 is used as a washing buffer liquid.

For example, industrial fresh water or mineralized formation water with a density of 1.05-1.16 g/ ^cm3 is used as a squeezing fluid.

The essence of the method

The method of cementing casing strings includes lowering the casing string to the drilled bottom of the well, sequentially pumping in a cleaning spacer fluid and two portions of cement mortar. A 2% aqueous solution of sodium tripolyphosphate or a 0.2% aqueous solution of nitrotrimethyl phosphonic acid is used as a cleaning spacer fluid. Then two portions of cement mortar are sequentially pumped in.

The first portion of cement mortar with a density of 1520-1640 kg/ ^m3 in a volume that ensures filling the annular space in the well in the interval from the wellhead to 100 m from the bottomhole, while the first portion of the cement mortar contains a dry cement mixture, a fluid loss reducer - PVS-VR or PVA, a defoamer - PENTA-465 or "FOBR" and water, a mixture of Portland cement, a lightweight inert filler - foamed glass microgranules of fractions of 0.1-1.5 mm or fine-pored foam ceramic spherical granules of the same fraction and fiber with a fiber size of 3-6 mm and a diameter of 22-35 μm is used as a dry cement mixture.

Portland cement 100 lightweight inert filler - foamed glass microgranules of fractions 0.1-1.5 mm or fine-pored spherical ceramic foam granules of the same fraction 10-23 fiberglass 0.1-0.6 water loss reducer PVS-VR or PVA 0.5 antifoam agent PENTA-465 or "FOBR" 0.05,

in this case, the ratio of dry cement mixture to water is 100 parts by weight to 60 parts by weight.

The second portion of cement slurry is pumped in with a density of 1880–1920 kg/ ^m3 in a volume that ensures filling of the wellbore annular space within 100 m from the bottomhole. The second portion of cement slurry contains dry cement mixture and water with a ratio of dry cement mixture to water of 100 parts by weight to 44 parts by weight, respectively; a mixture of oil well portland cement and cement with a particle size of 5 microns is used as the dry cement mixture with the following ratio of components, parts by weight:

Portland cement 100 cement with a particle size of 5 microns 10–20

After pumping the second portion of cement slurry, the first and second portions of cement slurry are pressed into the wellbore annular space by pumping the displacement fluid. For example, process water or mineralized formation water with a density of 1.05-1.16 g/cm ³ is used as the displacement fluid. Then the casing is left to wait for the two portions of cement slurry to harden for at least 48 hours.

Pumping the first portion of cement mortar with a density of 1520-1640 kg/ ^m3 with a dry cement mixture to water – 100 parts by weight to 60 parts by weight, respectively, ensures a reduction in hydrodynamic pressure during cementing and allows lifting the cement to the wellhead without loss of circulation.

Pumping the second portion with a density of 1880-1920 kg/ ^m3 containing Portland cement and cement with a particle size of 5 microns in a ratio of 100 parts by weight to 10-20 parts by weight ensures the most complete displacement of the drilling mud by the cement slurry due to the higher density of the latter, as well as the most dense contact at the cement stone-rock boundary due to the presence of finer ground particles in the cement structure. Since the cement slurry contains finer ground particles that can penetrate into the pores of the rock, a denser and more hermetic contact is created at the cement stone-rock boundary. This also improves the adhesion of the cement stone to the metal of the casing pipes and the rock.

The method of cementing the casing column is carried out in the following sequence.

After the final work (wellbore boring, geophysical surveys) is completed, the casing is lowered to the drilled well bottom. The cement warehouse prepares the calculated amount of dry cement mix required to prepare two batches of cement slurry, taking into account the well depth and casing diameter. After that, the finished dry cement mix is loaded into cement trucks and sent to the drilling rig.

Before cementing the casing in the well, directly at the drilling site, the dry cement mixture is transferred from the cement trucks to the cement mixing machines. Simultaneously with the transfer of the dry cement mixture, technical water is collected in the bunkers of the cementing units in the amount of 60 parts by weight per 100 parts by weight of the dry cement mixture and in the amount of 44 parts by weight per 100 parts by weight of the dry cement mixture to prepare two portions of the cement mortar.

Next, prepare the mixing water for the first portion of the cement mortar by adding 0.5 parts by weight of a water loss reducer and 0.05 parts by weight of a foam suppressor based on the weight of the Portland cement to the process water by stirring for 0.5-1 hour.

The first and second portions of cement slurry are prepared using a cement mixing device of a cement mixing machine. The density of the first portion of cement slurry at the outlet of the cement mixing device into the process tank "vat" is controlled by the operator using a hydrometer within the range of 1520-1640 kg/ ^m3 , the density of the second portion of cement slurry is 1880-1920 kg/ ^m3 . A cementing head with a squeeze-out separating plug installed in it is installed on the casing pipe column, connected with cementing hoses or high-pressure pipes to the cementing units. The washing spacer liquid is pumped in an amount of, for example, 6-9 ^m3 into the casing pipe column using a cementing unit. Without interrupting the technological process, using a cementing unit, the first and then the second portion of cement slurry are sequentially pumped into the casing pipe column after the washing spacer liquid into the well. The first portion of cement slurry is pumped in a volume that ensures filling the annular space in the well in the interval from the wellhead to 100 m from the bottom, the second portion of cement slurry is pumped in a volume that ensures filling the annular space of the well in the interval of 100 m from the bottom.

After pumping the second portion of cement slurry, the separating squeeze plug is released on the cementing head. By pumping technical fresh water or mineralized formation water with a density of 1.05-1.16 g/ ^cm3, the first and second portions of cement slurry are squeezed into the wellbore annulus until the "STOP" moment is reached. Then the casing string is left to wait for the hardening of two portions of cement slurry for at least 48 hours. After that, the cementing quality is assessed using geophysical studies.

Table 1 shows the recipes for the portions of cement mortar for the method of cementing the casing in the well.

Table 1 - Recipes of cement mortar portions for the method of cementing the casing in the well

Item No. First portion of cement mortar Second portion of cement mortar Dry cement mixture, wt. parts Water loss reducer, wt. h. Defoamer, wt. h. Water, wt. Dry cement mixture, wt. parts Water, wt. Portland cement Lightweight inert filler Fiberglass PVS-VR PVA PENTA-465 FOBR Portland cement Cement with a size of 5 microns Foamed glass microbeads Fine-pored ceramic foam spherical granules 1 2 3 4 5 6 7 8 9 10 11 12 13 1 100 15 - 0,1 0.5 - 0.05 - 60 100 20 44 2 100 20 - 0,1 0.5 - 0.05 - 60 100 20 44 3 100 10 - 0.3 0.5 - 0.05 - 60 100 20 44 4 100 20 - 0.3 0.5 - 0.05 - 60 100 15 44 5 100 23 - 0.3 0.5 - 0.05 - 60 100 15 44 6 100 15 - 0.4 0.5 - 0.05 - 60 100 15 44 7 100 15 - 0.6 0.5 - 0.05 - 60 100 10 44 8 100 - 15 0,1 - 0.5 - 0.05 60 100 10 44 9 100 - 20 0,1 - 0.5 - 0.05 60 100 10 44 10 100 - 10 0.3 - 0.5 - 0.05 60 100 - 44 11 100 - 20 0.3 - 0.5 - 0.05 60 100 - 44 12 100 - 23 0.3 - 0.5 - 0.05 60 100 - 44 13 100 - 15 0.4 - 0.5 - 0.05 60 100 - 44 14 100 - 15 0.6 - 0.5 - 0.05 60 100 - 44

Table 2 presents the results of studies of the physical and mechanical properties of cement mortars and stone for the proposed method (example No. 1-14) and the result for the method using the closest analogue (example No. 15). As can be seen from Table 2, the highest value of the obtained stone bending strength after pumping the second portion is for the closest analogue - 5.03 MPa, and the obtained stone bending strength according to the proposed method varies from 6.5 to 7.9 MPa, which is 1.6 times higher than the values of the closest analogue. This explains the stronger cement lining, resistant to dynamic loads that occur during well development.

Example of the method implementation

After the final work (working the borehole with a depth of 1800 m, diameter of 216 mm, geophysical surveys) a casing column with a diameter of 168 mm was lowered to the drilled bottom of the borehole with a depth of 1800 m and suspended in the rotor table using an elevator. A day before the start of work on cementing the casing column in the borehole, the calculated amount of dry cement mixture required for the preparation of two portions of cement mortar was prepared in the cement warehouse. The total amount of cement mortar was 25.9 m ³ .

To obtain such a volume of cement mortar, 20.7 tons of dry cement mixture were prepared, consisting of: Portland cement PCT II-50 - 100 parts by weight (18 tons), lightweight inert filler (foamed glass microgranules) - 15 parts by weight (2.7 tons), fiber - 0.1 parts by weight (0.018 tons) (example No. 1, Table 1). Then, by repeated repacking from one cement silo to another at the cement mixture plant, the dry cement mixture was brought into an air suspension with uniform distribution of dry additives throughout the volume of the dry cement mixture. After that, the finished dry cement mixture was loaded into cement trucks and sent to the drilling rig. After the final work (wellbore boring, geophysical surveys) was completed, the casing was lowered to the drilled well bottom (1799.5 m) and suspended in the rotor table using an elevator. A cementing head with a squeeze-out separating plug installed in it was installed on the casing string, connected with cementing hoses or high-pressure pipes to the cementing units.

Before the start of the work, directly at the drilling rig, the dry cement mixture was transferred from the cement trucks to the cement mixing machines. Simultaneously with the transfer of the dry cement mixture, technical water was collected in the bunkers of the cementing units for the first portion of the cement mortar (for 18.5 tons of the mixture) in the amount of 60 parts by weight (11.1 ^m3 ) per 100 parts by weight of the dry cement mixture for the first portion of the cement mortar and for the second portion of the cement mortar (for 10 tons of the mixture) in the amount of 44 parts by weight (4.4 ^m3 ) per 100 parts by weight of the dry cement mixture for the second portion of the cement mortar.

Next, mixing water was prepared for the first portion of the cement mortar by adding 0.5 parts by weight (9.25 kg) of a water loss reducer (PVS-VR) and 0.05 parts by weight (0.92 l) of a foam suppressor to the technical water based on the weight of the Portland cement by stirring for 0.5 hours.

Prepared a washing buffer liquid in the cementing unit bunker in the amount of 6 ^m3 . Pumped the washing buffer liquid into the casing string using the cementing unit.

Using a cementing unit and a cement mixing machine, the first and then the second portion of cement slurry were pumped sequentially into the well after the washing spacer liquid, into the casing string. For the first portion of cement slurry, 18.5 tons of dry cement mix and mixing water were simultaneously fed into the cement mixing device. The density of the first portion of cement slurry at the outlet of the cement mixing device into the process tank "vat" was controlled by the operator using a hydrometer within 1620 kg/ ^m3 , the density of the second portion of cement slurry - 1920 kg/ ^m3 . The first portion of cement slurry was pumped in a volume (21 ^m3 ) that ensured filling the annular space in the well in the interval from the wellhead to 100 m from the bottom, the second portion of cement slurry (7 ^m3 ) - in a volume that ensured filling the annular space of the well in the interval of 100 m from the bottom up from the bottom.

After pumping the second portion of cement slurry, the separating squeeze plug was released on the cementing head. By pumping technical water, the first and second portions of cement slurry were squeezed into the wellbore annular space until the "STOP" moment was reached. Then the casing was left to wait for the two portions of cement slurry to harden for 48 hours. Afterwards, the cementing quality was assessed using geophysical studies.

Table 2 - Results of studies of the physical and mechanical properties of cement mortars and stone for the method of cementing the casing in the well

First portion of cement mortar Second portion of cement mortar Water-
division,
ml Rasteka-
ability,
mm Density,
kg/ ^m3 The strength of the resulting
stone after 48 h, MPa Water-
division,
ml Rasteka-
ability,
mm Density,
kg/ ^m3 The strength of the resulting
stone after 48 h, MPa Adhesion, kN bend compression bend compression 1 2 3 4 5 6 7 8 9 10 11 12 Method of cementing a casing in a well   1 0.7 210 1602 4.2 9.11 1 220 1899 7.3 34.3 32.8 2 0 206.5 1544 4.05 10.66 2 216 1901 6.9 33.6 33.5 3 1 218 1640 4.01 11 2,2 218 1880 7.8 34.8 33.4 4 0 206 1546 4.17 10.6 2,2 226 1905 7.9 32.5 31.3 5 1.4 200 1545 4.1 9.8 2.4 230 1903 7 28.2 30.2 6 0 202.5 1593 4.14 11.63 2.5 225 1898 6.8 27.9 29.3 7 0 190 1520 4.3 11.8 3.8 236 1910 7.4 29.2 28.2 8 0.7 210 1602 4.2 9.11 3.8 242 1905 7.7 28.8 26.6 9 0 206.5 1544 4.05 10.66 4 254 1915 7.5 28.4 26.7 10 1 218 1640 4.01 11 4.2 240 1916 6.2 26 25.8 11 0 206 1546 4.17 10.6 4.8 260 1920 6.5 24 23.2 12 1.4 200 1545 4.1 9.8 5.6 250 1918 6.7 23.5 24.9 13 0 202.5 1593 4.14 11.63 5.2 245 1905 6.3 24.2 26.8 14 0 190 1520 4.3 11.8 5.4 240 1910 6.8 25.7 25.2 Method according to the closest analogue 15 1.0 218 1640 4.01 11 0 218.5 1589 5.03 14.8 -

The proposed method increases the efficiency of casing cementing by improving the quality of cementing in wells with residual absorption of drilling mud, eliminating filtration of cement mortar after opening the pores of permeable formations, and increasing the tightness of the cement lining at the cement stone-rock contact.

Claims (2)

A method of cementing a casing string in a well, including the sequential injection of a washing spacer fluid and portions of cement slurry, the first portion of cement slurry with a density of 1520–1640 kg/ ^m3 in a volume ensuring filling of the annular space in the well in the interval from the wellhead to 100 m from the bottomhole, wherein the first portion of cement slurry contains a dry cement mixture, a fluid loss reducer – PVS-VR or PVA, a defoamer – PENTA-465 or “FOBR” and water, as a dry cement mixture – a mixture of Portland cement, a lightweight inert filler – foamed glass microgranules of fractions 0.1–1.5 mm or fine-pored foam ceramic spherical granules of the same fraction, and fiber with a fiber size of 3–6 mm, a diameter of 22–35 μm at the following ratio of components, wt. h.: Portland cement - 100, lightweight inert filler - foamed glass microgranules with a fraction of 0.1-1.5 mm or fine-pored foam ceramic spherical granules of the same fraction - 10-23, fiber - 0.1-0.6, water loss reducer PVS-VR or PVA - 0.5, defoamer PENTA-465 or "FOBR" - 0.05, with a ratio of dry cement mixture to water - 100 wt. h. to 60 wt. h., respectively, of the second portion of the cement mortar, squeezing out portions of the cement mortar, carrying out a technological holding period while waiting for the cement mortar to harden, characterized in that the second portion of the cement mortar is pumped in with a density of 1880–1920 kg/ ^m3 in a volume that ensures filling the wellbore annular space in the interval of 100 m from the bottomhole, while the second portion of the cement mortar contains a dry cement mixture and water with a ratio of dry cement mixture to water of 100 parts by weight to 44 parts by weight. respectively, a mixture of oil well portland cement and cement with a particle size of 5 microns is used as the dry cement mixture with the following ratio of components, h. by weight: Portland cement 100 cement with a particle size of 5 microns 10–20