RU2836208C1 - Method for preparation for cementing of wells drilled on drilling mud on hydrocarbon basis - Google Patents

Abstract

FIELD: construction.

SUBSTANCE: invention relates to construction of wells, in particular to methods of preparing wells for cementing, drilled with oil-based drilling mud. Method of preparing wells drilled on a hydrocarbon-based drilling fluid for cementing includes lowering casing pipes into the well, flushing them with drilling fluid, sequential pumping of spacer fluids into the well, their squeezing into the annulus with grouting solution and displacement fluid with their complete displacement from the well and installation of grouting solution in the annular space in the required interval. After running in of the casing string and flushing with oil-based drilling fluid, three spacer fluids are injected into the well: dissolving, displacing and washing fluids.

EFFECT: increase in the volume of dense contact of the cement stone with the enclosing surfaces: casing string – cement stone, cement stone – rock in wells drilled on hydrocarbon-based drilling fluids, due to complete displacement of hydrocarbon-based drilling fluids and achieving maximum adhesion of cement stone with rock and casing from the well.

1 cl, 2 tbl, 3 ex

Description

The invention relates to well construction, in particular to methods for preparing wells for cementing, drilled using hydrocarbon-based drilling mud.

Due to the need to reduce the time for well construction, namely to reduce the time spent on working through unstable clay intervals, hydrocarbon-based drilling fluids (hereinafter referred to as CBF) are actively used. The high inhibiting capacity of CBF and low filtrate recovery allow preventing swelling and shedding of unstable clays. CBF also allows preserving the reservoir properties of the productive formation.

This creates an additional technological challenge: the problem is that the OBM is a viscous, oily and hydrophobic liquid, so it is not possible to effectively displace the OBM and remove the oil film from the well walls and casing pipes with water-based spacer fluids. For the maximum possible displacement of the OBM and removal of the oil film, a comprehensive approach to preparing the well for cementing is required. This is necessary to achieve tight contact of the cement stone with the casing and the well walls, as well as to ensure a tight well lining and minimize the risk of behind-the-casing circulation.

A method for cementing a casing string in a well is known (Deryaev A.R. Method for cementing a casing string in a well drilled with a hydrocarbon-based drilling fluid / Current Research No. 7 (86), 2022, pp. 19-26), drilled with a hydrocarbon-based drilling fluid. The method involves using two compositions as a spacer fluid. The first composition is diesel fuel with the addition of sulfonol and sea water in a weight ratio of (0.5: 0.05: 0.45). The second portion is a 10% aqueous solution of sulfonol, consisting of water (technical, formation or cement mixing fluid) and sulfonol in a weight ratio of (0.9: 0.1).

The disadvantage of this method is the need to mix an aqueous solution of sulfonol and diesel fuel, which are immiscible liquids. According to the studies, the washing capacity of this spacer fluid was 81.3%, which is insufficient for the effective removal of hydrocarbon-based drilling mud residues from the well walls and casing. The adhesion of cement stone to metal/rock after using these spacer fluids is 1.3/0.69 MPa, which is insufficient to create a seal.

Also known is a method for preparing wells for cementing (patent RU No. 2137906, IPC E21B 33/138, published 20.09.1999), which includes installing a metasilicate bath at the well bottom, sequentially pumping the following compositions: a viscoelastic separator, a loosening composition, a waterproofing and fixing composition, and a colmatage composition. As a result, the degree of replacement of the drilling fluid with a viscoelastic separator increases, the permeability of the filter cake decreases, and its resistance to the effects of the cement mortar increases.

The disadvantage of this method is that it is designed for wells drilled with water-based drilling fluid, since the spacer fluids used are prepared on a water basis and may not be compatible with the drilling fluid, the displacement of the drilling fluid by the cement will be partial - the quality of cementation will be low.

The closest method is the preparation for cementing of wells drilled with invert-emulsion drilling mud (patent RU No. 2452849, IPC E21B 33/13, C09K 8/40, C09K 8/467, published 10.06.2012), which includes lowering a casing string into the well and flushing it with invert-emulsion drilling mud, sequentially pumping four spacer fluids into the well: separating-displacing, dissolving, washing and displacing, and subsequent squeezing them into the annular space with a cement slurry and squeezing fluid with their complete displacement from the well and installation of the cement slurry in the annular space in the required interval, while a mixture of invert-emulsion drilling mud with formation water and with an organic solvent in a volume ratio of (4-6):(2.5-5.5):(0.5-1.5), respectively, as a dissolving spacer fluid - a mixture of an organic solvent, tall oil and a 40% aqueous solution of sodium hydroxide in a volume ratio of (9.0-9.6):(0.2-0.5):(0.2-0.5), respectively, as a washing spacer fluid - an aqueous solution of a detergent, additionally possessing the properties of a demulsifier, 0.5-4% mass concentration, as a displacing spacer fluid - lightweight cement mortar with a density of 1.35-1.45 g / cm ³ , wherein the rheological characteristics: plastic viscosity and dynamic shear stress, of the dissolving spacer fluid exceed the rheological characteristics of the previous - separating-displacing, and the subsequent - washing spacer fluids, and the density and the rheological characteristics of the displacing buffer liquid exceed those of the previous one - the washing buffer liquid.

The disadvantages of this method are the multi-component composition and the need to prepare it at the drilling site. Other disadvantages include low cleaning capacity - 75.8%, which is insufficient for effective removal of hydrocarbon-based drilling mud residues from the well walls and casing, and insufficient adhesion of cement stone to metal/rock after using these spacer fluids - 1.2/0.65 MPa, which is insufficient to create a seal.

The technical result is an increase in the volume of tight contact of the cement stone with the enclosing surfaces: casing column - cement stone, cement stone - rock in wells drilled with hydrocarbon-based drilling fluids, due to the complete displacement of hydrocarbon-based drilling fluids and the achievement of maximum adhesion of the cement stone with the rock and the casing column from the well.

The technical result is achieved by a method of preparing wells drilled with hydrocarbon-based drilling mud for cementing, including lowering a string of casing pipes into the well, flushing them with drilling mud, sequentially pumping spacer fluids into the well, squeezing them into the annular space with cementing mud and squeezing fluid with their complete displacement from the well and installing cementing mud in the annular space at the required interval.

What is new is that after lowering the casing string and flushing with hydrocarbon-based drilling mud, three spacer fluids are pumped sequentially into the well: dissolving, displacing and washing, while diesel fuel or a 29-31% aqueous solution of WellFix Spacer OBM is used as the dissolving liquid, consisting of WellFix Spacer OBM concentrate and industrial water in a volume ratio of concentrate to industrial water (0.29-0.31): (0.69-0.71) in a volume of 3-5 m ³ , an aqueous solution of a mixture of SBP-3 powdered buffer in a weight ratio of powder to water of 1: (0.85-0.89) or an abrasive-containing cement mortar ASCR, consisting of quartz sand, Portland cement without additives of increased sulfate resistance PCT-IG-CC-1 is used as the displacing spacer fluid. and industrial water in a mass ratio of quartz sand, plugging portland cement and industrial water (0.97-1.03):(9.97-10.03):(7.67-7.73) or clay drilling mud consisting of bentonite clay powder, soda ash and industrial water in a mass ratio of (1.97-2.03):(0.022-0.028):(7.97-8.03) in a volume of 3-5 ^m3 , as a washing spacer fluid - 9-11% aqueous solution of Winclean OBM 1, consisting of Winclean OBM 1 concentrate and industrial water in a volume ratio of concentrate to water (0.09-0.11):(0.89-0.91) or 4-6% aqueous solution of sulfonol in a mass ratio of sulfonol and water (0.04-0.06):(0.94-0.96) in a volume of 3-5 ^m3 .

To implement the method, use:

Hydrocarbon-based drilling fluid that meets the requirements of GOST 33697-2015;

Diesel fuel according to GOST 305-2013;

WellFix Spacer OBM is a composition of hydrocarbon solvents based on terpenes TU 20.59.59-272-14023401-2020;

Buffer powder mixture SBP-3 is a mixture of a structure-forming agent, weighting agent, viscosity regulator, viscosity reducer and dye according to TU 5717-008-80338612-2007;

Abrasive-containing cement mortar (ACCM), consisting of quartz sand produced in accordance with GOST 22551-2019, and Portland cement without additives with increased sulfate resistance (PTsT-I-G-CC-1, hereinafter referred to as Portland cement), produced in accordance with GOST 1581-2019;

Clay drilling mud consisting of bentonite clay powder, soda ash and industrial water.

Soda ash according to GOST 5100-85;

Bentonite clay powder according to TU 2164-005-01424676-2014;

Winclean OBM 1 is a composition of anionic and non-ionic surfactants, mono- and polyglycol alcohols according to TU 20.59.59-001-65607606-2023;

Sulfonol is a mixture of isomers of sodium salts of alkylbenzene sulfonic acids according to TU 20.41.20-135-07510508-2020;

An aqueous solution of Portland cement according to GOST 1581-2019 is used as a cement slurry.

Technical water with a density of 1-1.05 g/ ^cm3 .

The method of preparing wells drilled with hydrocarbon-based drilling mud for cementing is carried out as follows.

The method involves lowering a string of casing pipes into the well and flushing them with hydrocarbon-based drilling fluid (HBD). After flushing, pre-prepared buffer fluids are pumped into the well sequentially: dissolving, displacing and washing. After pumping the buffer fluids, they are squeezed into the annular space by pumping in the cement slurry and the displacement fluid, completely displacing them from the well and installing the cement slurry in the annular space.

Diesel fuel or a 29-31% aqueous solution of WellFix Spacer OBM, consisting of WellFix Spacer OBM concentrate and industrial water in a volume ratio of concentrate to industrial water (0.29-0.31):(0.69-0.71) in a volume of 3-5 ^m3 , are used as a dissolving liquid. Diesel fuel and WellFix Spacer OBM aqueous solution are hydrocarbon solvents, the use of which allows for the destruction of hydrocarbon bonds in OBM, liquefaction of OBM and effective removal of OBM from the walls of the casing and rock.

An aqueous solution of a powdered buffer mixture (SBP-3) with a density of 1.3±0.03 g/ ^cm3 in a powder to water weight ratio of 1:(0.85-0.89) or an abrasive-containing cement mortar (ACCM) with a density of 1.47±0.03 g/ ^cm3 consisting of quartz sand, Portland cement and industrial water in a weight ratio of quartz sand, Portland cement and industrial water (0.97-1.03):(9.97-10.03):(7.67-7.73), respectively, or a clay drilling mud with a density of 1.27±0.03 g/ ^cm3 consisting of bentonite clay powder, soda ash and industrial water in a weight ratio of (1.97-2.03):(0.022-0.028):(7.97-8.03), respectively, in a volume of 3-5 ^m3 . SBP-3 has a plastic viscosity of (35-37 mPa s) and dynamic shear stress (DSS) (95-98 dPa), an aqueous solution of ASCR has a plastic viscosity of (39-41 mPa s) and dynamic shear stress (105-107 dPa), a clay drilling fluid has a plastic viscosity of (33-35 mPa s) and dynamic shear stress (92 dPa), which is higher than the plastic viscosity (30.7 mPa s) and DSS (87 dPa) of the hydrocarbon-based drilling fluid used, which allows for the effective displacement of OBM and dissolving spacer fluid.

As a cleaning buffer liquid – 9-11% aqueous solution of Winclean OBM 1, consisting of Winclean OBM 1 and industrial water in a volume ratio of concentrate to water (0.09-0.11):(0.89-0.91) or 4-6% aqueous solution of sulfonol in a weight ratio of sulfonol and water (0.04-0.06):(0.94-0.96) in a volume of 3-5 ^m3 . Winclean OBM 1 consists of anionic and non-ionic surfactants, mono- and polyglycol alcohols; sulfonol is a mixture of isomers of sodium salts of alkylbenzene sulfonic acids, which has wetting, washing and emulsifying properties. These components allow to effectively remove the oil film of the OBM and the remains of previous buffer liquids.

After pumping in the buffer fluids, they are forced into the annular space by pumping in the cement slurry and the displacement fluid, completely displacing them from the well and installing the cement slurry in the annular space.

An aqueous solution of Portland cement manufactured according to GOST 1581-2019 in a mass ratio of Portland cement to water (1-0.43):(1-0.45) is used as a plugging solution. Water with a technical density of 1.0 g/ ^cm3 to 1.05 g/ ^cm3 is pumped in as a squeezing fluid.

Thanks to such a set of operations, their sequence and a specific formulation of the used buffer fluids, maximum displacement of the OBM from the well is ensured, the oil film is removed from the contacting surfaces, tight contact of the cement stone with the surfaces of the casing pipes and the rock is achieved, high adhesion of cement-rock, cement-rock is ensured and the risk of behind-the-casing circulation is minimized.

The washing capacity of the dissolving, displacing and washing buffer liquids was determined using the following method. A dry and clean cylinder from the Ofite 800 viscometer is weighed (the mass of the dry and clean cylinder is thus determined). Then the cylinder is placed in the OCB (the OCB properties are presented in Table 1) and rotated for 10 minutes at a rotation speed of 200 rpm, and left to drain for 2 minutes. The cylinder with the OCB film is weighed (the mass of the cylinder with the OCB film is thus determined). After this, the viscometer cylinder is placed in the dissolving buffer liquid for 5 min at a cylinder rotation speed of 200 rpm, then placed in the displacing buffer liquid for 5 min at a cylinder rotation speed of 200 rpm, after which the cylinder is placed in the washing buffer liquid for 5 min at a cylinder rotation speed of 200 rpm, the remainder of the buffer liquids drains for 2 min. Then it is weighed (the mass of the OBM residues with the cylinder is determined). The washing capacity of the buffer liquids in percent is determined by the difference in the masses of the clean cylinder, the cylinder with the OBM film and the washed cylinder.

The adhesion of cement stone to metal is determined using the following method. A clean and dry pipe (inner diameter 50 mm, height 100 mm) is immersed in the OBM for 1 hour, which is mixed using a stirrer rotating at 350 rpm, simulating the circulation of the OBM in the well. Then the pipe is removed from the OBM with metal tongs and kept still for 2 minutes to allow the OBM to drain from the metal. Then the pipe is placed in a dissolving buffer liquid, which is mixed using a stirrer rotating at 350 rpm, simulating the circulation of the buffer composition in the well. After 5 minutes of mixing, the branch pipe is removed from the dissolving buffer liquid and placed in the displacing buffer liquid for 5 minutes, also with circulation created using a stirrer at a frequency of 350 rpm, then the branch pipe is placed in the washing buffer liquid with circulation created using a stirrer at a speed of 350 rpm. After this, the bottom is attached to the lower part of the branch pipe and Portland cement is poured into the branch pipe. Then the branch pipe is placed in a wet storage chamber for 48 hours. After this, the bottom of the branch pipe is removed and the branch pipe is installed on a hydraulic press on special spacers (from below) and a punch is installed (from above) so that the effect of the hydraulic press falls on the cement stone. During operation of the hydraulic press, when breaking the cement stone from the metal, the maximum breaking force is recorded. The adhesion value is calculated as the ratio of the maximum breaking force to the contact area of the cement stone with the branch pipe surface.

The adhesion of cement stone to rock is determined using the following method. A cylindrical rock sample (diameter 30 mm, height 60 mm) is prepared. The rock sample is immersed for 1 hour in the OBM, which is stirred using a stirrer rotating at 350 rpm, simulating the circulation of the OBM in the well. The sample is then removed from the OBM with metal tongs and left at rest for 2 minutes to allow the OBM to drain. The sample is then placed in a dissolving buffer liquid, which is stirred using a stirrer rotating at 350 rpm, simulating the circulation of the buffer composition in the well. After 5 minutes of stirring, the sample is removed from the dissolving buffer liquid and placed in the displacing buffer liquid for 5 minutes, also with circulation created using a stirrer at a frequency of 350 rpm, then the sample is placed in the washing buffer liquid with circulation created using a stirrer at a speed of 350 rpm. After that, the rock sample is placed in a cylindrical vessel, lubricated with oil and filled with Portland cement so that on each side of the cylindrical sample there is cement stone at a distance of 1-1.5 cm along the entire length of the sample. The ends of the rock sample must be clean and have no contact with Portland cement. Then the sample is placed in a wet storage chamber for 48 hours. After that, the sample with the cement stone is removed from the cylindrical vessel. Next, the sample with the cement stone is placed on a hydraulic press on special spacers (from below) and a punch is installed (from above) in such a way that the cement stone rests on the spacers, and the punch impacts the rock sample. When the hydraulic press is operating, when the cement stone is pulled off the rock sample, the maximum breaking force is recorded. The adhesion value is calculated as the ratio of the maximum breaking force to the contact area of the cement stone with the surface of the sample.

For testing, a hydrocarbon-based drilling fluid is used, the properties of which are presented in Table 1. Table 2 presents the results of laboratory tests of dissolving, displacing and washing buffer fluids.

Table 1 – OBM properties

No. Solution parameters Values 1 Density, kg/ ^m3 1315 2 Electrical stability 300 3 Plastic viscosity, mPa⋅s 30.7 4 DNS, dPa 87 5 SNS _10/10 , dPa 27/29 6 Calcium carbonate content, kg/ ^m3 622.2 7 Hydrocarbon content, % 52 8 Water content, % 28 9 Carbohydrate/water ratio, % 65/35

Table 2 – Cleaning ability and adhesion value to metal and rock of the proposed buffer liquids

p/p Solvent buffer liquid Displacement buffer fluid Washing buffer liquid Washing capacity, % Adhesion of cement stone to metal/rock, MPa 1 Diesel fuel An aqueous solution of a powdered buffer mixture, with a powder to water ratio of 1:0.85 9% aqueous solution of WinClean OBM 1, with a concentrate to water ratio of 0.09:0.91 89.5 1.48/0.8 2 Diesel fuel An aqueous solution of a powdered buffer mixture, with a powder to water ratio of 1:0.87 10% aqueous solution of WinClean OBM 1, with a concentrate to water ratio of 0.1:0.9 90 1.49/0.81 3 Diesel fuel An aqueous solution of a powdered buffer mixture, with a powder to water ratio of 1:0.89 11% aqueous solution of WinClean OBM 1, with a concentrate to water ratio of 0.11:0.89 90.3 1.49/0.82 4 Diesel fuel Abrasive-containing cement mortar with a mass ratio of quartz sand, Portland cement and industrial water (0.97:9.97:7.67) 4% aqueous solution of sulfonol, with a ratio of sulfonol to water of 0.04:0.96 91.4 1.44/0.79 5 Diesel fuel Abrasive-containing cement mortar with a mass ratio of quartz sand, Portland cement and industrial water (1:10:7.7) 5% aqueous solution of sulfonol, sulfonol to water ratio 0.05:0.95 92.3 1.45/0.8 6 Diesel fuel Abrasive-containing cement mortar with a mass ratio of quartz sand, Portland cement and industrial water (1.03:10.03:7.73) 6% aqueous solution of sulfonol, sulfonol to water ratio 0.06:0.94 92.5 1.46/0.79 7 29% aqueous solution WellFix Spacer OBM, ratio of concentrate to technical water 0.29:0.71 Clay drilling mud, with a mass ratio of bentonite clay powder and soda ash and industrial water (1.97:0.022:7.97) 9% aqueous solution of WinClean OBM 1, with a concentrate to water ratio of 0.09:0.91 91.5 1.47/0.81 8 29% aqueous solution WellFix Spacer OBM, ratio of concentrate to technical water 0.29:0.71 Clay drilling mud, with a mass ratio of bentonite clay powder and soda ash and industrial water (2:0.025:8) 10% aqueous solution of WinClean OBM 1, with a concentrate to water ratio of 0.1:0.9 91.88 1.45/0.82 9 29% aqueous solution WellFix Spacer OBM, ratio of concentrate to technical water 0.29:0.71 Clay drilling mud, with a mass ratio of bentonite clay powder and soda ash and industrial water (2.03:0.028:8.03) 11% aqueous solution of WinClean OBM 1, with a concentrate to water ratio of 0.11:0.89 92.02 1.47/0.81 10 30% aqueous solution WellFix Spacer OBM, ratio of concentrate to technical water 0.3:0.7 An aqueous solution of a powdered buffer mixture, with a powder to water ratio of 1:0.85 9% aqueous solution of WinClean OBM 1, with a concentrate to water ratio of 0.09:0.91 95.4 1.52/0.84 11 30% aqueous solution WellFix Spacer OBM, ratio of concentrate to technical water 0.3:0.7 An aqueous solution of a powdered buffer mixture, with a powder to water ratio of 1:0.87 10% aqueous solution of WinClean OBM 1, with a concentrate to water ratio of 0.1:0.9 96.77 1.53/0.85 12 30% aqueous solution WellFix Spacer OBM, ratio of concentrate to technical water 0.3:0.7 An aqueous solution of a powdered buffer mixture, with a powder to water ratio of 1:0.89 11% aqueous solution of WinClean OBM 1, with a concentrate to water ratio of 0.11:0.89 96.88 1.53/0.83 13 31% aqueous solution WellFix Spacer OBM, ratio of concentrate to technical water 0.31:0.69 Abrasive-containing cement mortar with a mass ratio of quartz sand, Portland cement and industrial water (0.97:9.97:7.67) 9% aqueous solution of WinClean OBM 1, with a concentrate to water ratio of 0.09:0.91 95.4 1.51/0.81 14 31% aqueous solution WellFix Spacer OBM, ratio of concentrate to technical water 0.31:0.69 Abrasive-containing cement mortar with a mass ratio of quartz sand, Portland cement and industrial water (0.1:10:7.7) 10% aqueous solution of WinClean OBM 1, with a concentrate to water ratio of 0.1:0.9 94.65 1.5/0.79 15 31% aqueous solution WellFix Spacer OBM, ratio of concentrate to technical water 0.31:0.69 Abrasive-containing cement mortar with a mass ratio of quartz sand, Portland cement and industrial water (1.03:10.03:7.73) 11% aqueous solution of WinClean OBM 1, with a concentrate to water ratio of 0.11:0.89 96.05 1.49/0.8 16 29% aqueous solution WellFix Spacer OBM, ratio of concentrate to technical water 0.29:0.71 Clay drilling mud, with a mass ratio of bentonite clay powder and soda ash and industrial water (1.97:0.022:7.97) 4% aqueous solution of sulfonol, with a ratio of sulfonol to water of 0.04:0.96 90.1 1.45/0.76 17 29% aqueous solution WellFix Spacer OBM, ratio of concentrate to technical water 0.29:0.71 Clay drilling mud, with a mass ratio of bentonite clay powder and soda ash and industrial water (2:0.025:8) 5% aqueous solution of sulfonol, sulfonol to water ratio 0.05:0.95 91.65 1.46/0.75 18 29% aqueous solution WellFix Spacer OBM, ratio of concentrate to technical water 0.29:0.71 Clay drilling mud, with a mass ratio of bentonite clay powder and soda ash and industrial water (2.03:0.028:8.03) 6% aqueous solution of sulfonol, sulfonol to water ratio 0.06:0.94 92.37 1.48/0.8 19 30% aqueous solution WellFix Spacer OBM, ratio of concentrate to technical water 0.3:0.7 An aqueous solution of a powdered buffer mixture, with a powder to water ratio of 1:0.85 4% aqueous solution of sulfonol, with a ratio of sulfonol to water of 0.04:0.96 93.4 1.49/0.8 20 30% aqueous solution WellFix Spacer OBM, ratio of concentrate to technical water 0.3:0.7 An aqueous solution of a powdered buffer mixture, with a powder to water ratio of 1:0.87 5% aqueous solution of sulfonol, sulfonol to water ratio 0.05:0.95 95.2 1.52/0.82 21 30% aqueous solution WellFix Spacer OBM, ratio of concentrate to technical water 0.3:0.7 An aqueous solution of a powdered buffer mixture, with a powder to water ratio of 1:0.89 6% aqueous solution of sulfonol, sulfonol to water ratio 0.06:0.94 94.6 1.51/0.81 22 31% aqueous solution WellFix Spacer OBM, ratio of concentrate to technical water 0.31:0.69 Abrasive-containing cement mortar with a mass ratio of quartz sand, Portland cement and industrial water (0.97:9.97:7.67) 4% aqueous solution of sulfonol, with a ratio of sulfonol to water of 0.04:0.96 93.24 1.49/0.8 23 31% aqueous solution WellFix Spacer OBM, ratio of concentrate to technical water 0.31:0.69 Abrasive-containing cement mortar with a mass ratio of quartz sand, Portland cement and industrial water (0.1:10:7.7) 5% aqueous solution of sulfonol, sulfonol to water ratio 0.05:0.95 94.58 1.49/0.8 24 31% aqueous solution WellFix Spacer OBM, ratio of concentrate to technical water 0.31:0.69 Abrasive-containing cement mortar with a mass ratio of quartz sand, Portland cement and industrial water (1.03:10.03:7.73) 6% aqueous solution of sulfonol, sulfonol to water ratio 0.06:0.94 95.91 1.51/0.82

As can be seen from the table, the adhesion values of cement stone to metal vary within 1.44-1.53 MPa, the adhesion values of cement stone to rock vary within 0.75-0.85 MPa, which significantly exceeds the adhesion value of the method according to the closest analogue (the adhesion value of the closest analogue is 1.2/0.65 MPa). The test results also show that the values of the washing capacity vary from 89.95% to 96.88%, which significantly exceeds the washing capacity value of the closest analogue (the washing capacity of the closest analogue is 75.8%).

The adhesive force of the cement stone with the enclosing surfaces increases: casing column – cement stone, cement stone – rock, due to the complete displacement of hydrocarbon-based drilling mud and washing away of the oily film. As a result, the tightness of the cement lining is achieved and the risk of behind-the-casing circulation is minimized.

The buffer liquids used in the implementation of the proposed method in field conditions are prepared in the tanks of cementing units as follows:

To prepare the dissolving buffer liquid, the calculated amount of water is collected in the cementing unit tank and WellFix Spacer OBM concentrate is added in the required volume. When using diesel fuel as a dissolving buffer liquid, diesel fuel is pumped into the cementing unit from a fuel tanker.

To prepare the displacing spacer fluid, the calculated amount of water is collected in the cementing unit tank and the calculated mass of SBP-3 or ASCR powder is fed using a cement mixing machine. When using clay drilling mud, a drilling mud preparation unit of the drilling site or a mud unit is used, into which the calculated amount of technical water is collected, the calculated mass of soda ash and bentonite clay powder is introduced sequentially. Using top-drive mixers and a hydraulic funnel, the components are mixed for 1-1.5 hours. Before pumping into the well, the calculated volume of clay drilling mud is pumped into the cementing unit tank.

To prepare the cleaning buffer liquid, the calculated volume of process water is collected in the cementing unit tank and WinClean OBM 1 concentrate or sulfonol powder of the calculated mass is added.

Examples of practical application

1. After drilling a 1000 m interval with a 146 mm diameter bit and lowering a casing string with an outside diameter of 102 mm and a wall thickness of 6.5 mm into the well, the well was filled with hydrocarbon-based drilling fluid (density - 1300 kg/ ^m3 , ratio of the hydrocarbon phase to the water phase - 65/35) in a volume of 12.08 ^m3 . The well was flushed in 2 cycles, which corresponds to pumping 24.16 ^m3 of drilling fluid into the well. After that, prepared spacer fluids were pumped into the well - dissolving, displacing and washing, each of which performs its own purpose. First, 3 ^m3 of dissolving spacer fluid was injected, consisting of WellFix Spacer OBM and industrial water in a volume ratio of (0.29:0.71), respectively. To prepare 3 ^m3 of dissolving spacer fluid, 0.87 ^{m3 of} WellFix Spacer OBM and 2.13 ^m3 of industrial water were mixed. Then, 3 ^m3 of displacing spacer fluid was injected - clay drilling mud, consisting of bentonite clay powder, soda ash and industrial water in a mass ratio of (1.97:0.022:8.03), respectively. To prepare 3 ^m3 of displacing spacer fluid, 650 kg of bentonite clay powder, 7 kg of soda ash and 2.67 ^m3 of industrial water were mixed. After the displacing spacer fluid, 3 ^m3 of flushing spacer fluid consisting of service water and Winclean OBM 1 in a volume ratio of (0.91:0.09), respectively, were injected. To prepare 3 ^m3 of flushing spacer fluid, 2.73 ^m3 of service water and 0.27 ^m3 of Winclean OBM 1 were used. Following this, 8.17 ^m3 of cement slurry consisting of Portland cement and service water in a mass ratio of (1:0.45) were injected. 12240 kg of Portland cement and 5.5 ^m3 of service water were used to prepare 8.57 ^m3 of cement slurry. After this, 6.21 ^m3 of squeezing fluid consisting of service water was injected to displace the spacer fluids from the annulus and place Portland cement in the annulus.

2. After drilling a 2000 m interval with a 146 mm diameter bit and lowering a casing string with an outside diameter of 114 mm and a wall thickness of 6 mm into the well, the well was filled with hydrocarbon-based drilling fluid (density - 1300 kg/ ^m3 , the ratio of the hydrocarbon phase to the water phase is 65/35) in a volume of 29.39 ^m3 . The well was flushed in 2 cycles, which corresponds to pumping 58.78 ^m3 of drilling fluid into the well. After that, the prepared spacer fluids were injected into the well - dissolving, displacing and washing, each of which performs its own purpose. First, the dissolving spacer fluid was injected, consisting of diesel fuel in a volume of 4 ^m3 . Next, 4 ^m3 of displacement spacer fluid was pumped in, consisting of quartz sand, Portland cement and industrial water in a mass ratio of (1:10:7.7), respectively. To prepare 4 ^m3 of displacement spacer fluid, 3.08 ^m3 of industrial water, 400 kg of quartz sand and 4000 kg of Portland cement were mixed. After the displacement spacer fluid, 4 ^m3 of flushing spacer fluid was pumped, consisting of industrial water and Winclean OBM 1 in a volume ratio of (0.9:0.1), respectively. To prepare 4 ^m3 of the flushing spacer fluid, 3.6 ^m3 of technical water and 0.4 ^{m3 of} Winclean OBM 1 were used. Following this, 22.9 ^m3 of the cement slurry consisting of Portland cement and technical water in a weight ratio of (1:0.44) were pumped in. To prepare 13.06 ^m3 of the cement slurry, 18,650 kg of Portland cement and 8.2 ^m3 of technical water were used. After this, 16.33 ^m3 of the squeezing fluid consisting of technical water was pumped in to displace the spacer fluids from the annular space and place Portland cement in the annular space.

3. After drilling a 2500 m interval with a 215 mm diameter bit and lowering a casing string with an outside diameter of 178 mm and a wall thickness of 8 mm into the well, the well was filled with hydrocarbon-based drilling fluid (density - 1300 kg/ ^m3 , hydrocarbon phase to water phase ratio - 65/35) in a volume of 80.05 ^m3 . The well was flushed in 2 cycles, which corresponds to pumping 160.1 ^m3 of drilling fluid into the well. After that, the prepared spacer fluids were injected into the well - dissolving, displacing and washing, each of which performs its own purpose. First, the dissolving spacer fluid was injected, consisting of diesel fuel in a volume of 5 ^m3 . Then, 5 ^m3 of the displacing spacer fluid was injected, consisting of SBP-3 and process water in a powder to water weight ratio of (1:0.85), respectively. To prepare 5 ^m3 of the displacing spacer fluid, 4000 kg of SBP-3 and 3.4 ^m3 of process water were mixed. After the displacing spacer fluid, 4 ^m3 of the flushing spacer fluid was injected, consisting of process water and sulfonol in a weight ratio of (0.94:0.06), respectively. To prepare 5 ^{m3 of} the flushing spacer fluid, 5 ^m3 of process water and 319 kg of sulfonol were used. Following this, 28.55 ^m3 of the cement slurry, consisting of Portand cement and process water in a weight ratio of (1:0.43), were injected. To prepare 28.55 ^m3 of cement slurry, 40,780 kg of Portland cement and 17.54 ^m3 of technical water were used. After that, 51.5 ^m3 of displacement fluid consisting of technical water was pumped in to displace the buffer fluids from the annular space and place Portland cement in the annular space.

Thus, the proposed method allows increasing the volume of tight contact of the cement stone with the enclosing surfaces: casing column - cement stone, cement stone - rock in wells drilled with hydrocarbon-based drilling fluids, due to the complete displacement of hydrocarbon-based drilling fluids and achieving maximum adhesion of the cement stone with the rock and the casing column from the well.

Claims (1)

A method for preparing wells drilled with hydrocarbon-based drilling mud for cementing, which includes lowering a string of casing pipes into the well, flushing them with drilling mud, sequentially pumping spacer fluids into the well, squeezing them into the annular space with a cementing slurry and a squeezing fluid with their complete displacement from the well and installing the cementing slurry in the annular space in the required interval, characterized in that after lowering the string of casing pipes and flushing with hydrocarbon-based drilling mud, three spacer fluids are pumped into the well sequentially: dissolving, displacing and washing, wherein diesel fuel or a 29-31% aqueous solution of WellFix Spacer OBM is used as the dissolving liquid, consisting of WellFix Spacer OBM concentrate and industrial water in a volume ratio of concentrate to industrial water (0.29-0.31):(0.69-0.71) in a volume 3-5 ^m3 , an aqueous solution of a mixture of SBP-3 powdered buffer in a powder to water weight ratio of 1:(0.85-0.89) or an abrasive-containing cement mortar ASCR consisting of quartz sand, non-additive plugging portland cement with increased sulfate resistance PCT-IG-CC-1 and industrial water in a weight ratio of quartz sand, plugging portland cement and industrial water (0.97-1.03):(9.97-10.03):(7.67-7.73) or a clay drilling mud consisting of bentonite clay powder, soda ash and industrial water in a weight ratio of (1.97-2.03):(0.022-0.028):(7.97-8.03) in a volume of 3-5 m3 is used as a displacing spacer fluid. ³ , as a washing buffer liquid - 9-11% aqueous solution of Winclean OBM 1, consisting of Winclean OBM 1 concentrate and industrial water in a volume ratio of concentrate to water (0.09-0.11):(0.89-0.91) or 4-6% aqueous solution of sulfonol in a weight ratio of sulfonol and water (0.04-0.06):(0.94-0.96) in a volume of 3-5 ^m3 .