Oil-based drilling fluid flushing fluid system for well cementation engineering of shale oil-gas well and preparation method of oil-based drilling fluid flushing fluid system

Abstract

The invention discloses an oil-based drilling fluid flushing fluid system for well cementation engineering of a shale oil-gas well. The oil-based drilling fluid flushing fluid system comprises the following components in parts by weight: 1-50 parts of a nonionic surfactant, 1-50 parts of an anionic surfactant, 0.1-20 parts of a tackifier, 0.1-20 parts of a retarder and 100 parts of water, wherein the nonionic surfactant is obtained by compounding main raw materials including fatty alcohol-polyoxyethylene ether, fatty acid polyoxyethylene alkyl ester and polyoxyethylene alkylamine; and the anionic surfactant is obtained by compounding the main raw materials of triethanolamine alkylbenzene sulfonate, dodecylbenzene sulfonate and fatty acid salt. The flushing fluid system disclosed by the invention is high in flushing efficiency and good in flushing effect on the oil-based drilling fluid, has good emulsifying, dispersing and decontamination effects, and can be used for effectively cleaning an oil film and residual oil; and the related manufacturing process is simple, convenient to operate and wide in applicable temperature range, can be widely applied to oil well cementing engineering, and has great economic and popularization values.

Description

Technical Field

[0001] The present invention belongs to the technical field of oil and gas drilling engineering, and particularly relates to an oil-based drilling fluid flushing fluid system for shale oil and gas well cementing engineering and a preparation method thereof. Background Art

[0002] After drilling construction with oil-based drilling fluid, a dense mud cake and oil film will be formed on the wellbore wall and casing wall of the construction section. If these mud cakes and oil films are not removed, gaps and gas channeling channels will be formed during the cementing process, which will seriously affect the bonding strength of the cement sheath at the two interfaces, and even cause annulus pressure after fracturing of shale gas wells. To fully ensure the cementing quality, a large amount of efficient flushing fluid is required to fully flush the oil-based mud cake on the wellbore wall and the oil-based drilling fluid adsorbed on the upper casing wall, realizing the inversion of the interface from oil wetting to water wetting, and then carrying out cementing construction.

[0003] Patent CN106367050A discloses a high-temperature-resistant flushing fluid for high-density oil-based drilling fluid and a preparation method thereof. The flushing fluid includes 2-25% of coconut oil fatty acid diethanolamide, 2-20% of triethanolamine alkyl benzene sulfonate, 0.1-15% of ethylene glycol monobutyl ether, 0.5-10% of maleic acid-acrylic acid copolymer, and the balance is water; the flushing efficiency of the flushing fluid for high-density oil-based drilling fluid can reach more than 90%; it has strong high-temperature resistance and stable performance at 190°C; it has good compatibility with cement slurry and oil-based drilling fluid. Patent CN110846013A discloses a cementing flushing fluid for oil-based drilling fluid, which includes fresh water, non-ionic surfactant I, non-ionic surfactant II, normal salt co-solvent and acid salt co-solvent; non-ionic surfactant I adopts fatty alcohol polyoxyethylene ether non-ionic surfactant, and non-ionic surfactant II adopts nonylphenol polyoxyethylene ether non-ionic surfactant; non-ionic surfactant II has good emulsifying performance, and the hydrophilic end is easily adsorbed on the oil-water interface, casing and wellbore surface; non-ionic surfactant I is used as the main agent of the flushing fluid, which has good wettability, foaming property, detergency and emulsifying power, and has higher degreasing ability.

[0004] The change of temperature will affect the performance of both oil-based drilling fluid and flushing fluid, mainly reflected in: the decrease of temperature will increase the plastic viscosity of oil-based drilling fluid, and the formed mud cake is difficult to clean under relatively high temperature conditions; at the same time, temperature is one of the important influencing factors for the cleaning efficiency of the flushing fluid. The increase of temperature promotes the improvement of the cleaning efficiency of the flushing fluid, while the decrease of temperature reduces the dispersion effect of the flushing fluid. Relying only on the wetting inversion effect will cause the cleaning efficiency to decrease, thus affecting the flushing effect of the upper section interface and the cementing quality. Therefore, there is an urgent need to develop an oil-based drilling fluid flushing fluid for cementing with excellent comprehensive performance, wide temperature range and suitable for shale oil and gas development. Summary of the Invention

[0005] The main object of the present invention is to provide an oil-based drilling fluid flushing fluid system in view of the problems and deficiencies existing in the prior art. This system is used to dilute and disperse the oil-based drilling fluid, improve the interfacial wetting state, can effectively broaden the applicable temperature range, and can play a weighting role to meet the purpose of stabilizing the oil and gas layers, and is applicable to fields such as the cementing engineering of shale oil and gas wells.

[0006] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0007] An oil-based drilling fluid flushing fluid system for the cementing engineering of shale oil and gas wells, each component and its weight parts include: 1-50 parts of non-ionic surfactant, 1-50 parts of anionic surfactant, 0.1-20 parts of thickener, 0.1-20 parts of retarder, and 100 parts of water; among them, the non-ionic surfactant is compounded from fatty alcohol polyoxyethylene ether, fatty acid polyoxyethylene alkyl ester, and polyoxyethylene alkylamine as the main raw materials; the anionic surfactant is compounded from triethanolamine alkyl benzene sulfonate, dodecyl benzene sulfonate, and fatty acid salt as the main raw materials.

[0008] In the above solution, in the non-ionic surfactant, the mass ratio of fatty alcohol polyoxyethylene ether, fatty acid polyoxyethylene alkyl ester, and polyoxyethylene alkylamine is 0.5-2:1:0.5-2.

[0009] Further, the general formula of the fatty alcohol polyoxyethylene ether is R1O(CH2CH2O)nH, R1 is a saturated hydrocarbon group of C n -C 12 -C 18 , n = 10-20; the general formula of the fatty acid polyoxyethylene alkyl ester is R2COO(CH2CH2O)nH, R2 is a saturated hydrocarbon group of C1-C 18 -C 12 -C, n = 8-20; the general formula of the polyoxyethylene alkylamine is R3N(CH2CH2OH)2, R3 is a hydrocarbon group of C6-C

[0010] In the above solution, in the anionic surfactant, the mass ratio of triethanolamine alkyl benzene sulfonate, dodecyl benzene sulfonate, and fatty acid salt is 0.5-2:1:0.5-2.

[0011] Further, the alkyl carbon number of the triethanolamine alkyl benzene sulfonate is 12-18.

[0012] In the above solution, the thickener is xanthan gum or attapulgite; among them, the relative molecular mass of xanthan gum is more than 1 million; the average particle size of attapulgite is below 1μm, and the maximum particle size is below 50μm.

[0013] In the above solution, the retarder is a solution formed by one or more of sodium gluconate, citric acid, organic phosphonate, etc., and its concentration is 15-20 wt%.

[0014] It can be used directly by adding water (solvent) to the oil-based drilling fluid flush fluid system (main agent) for the cementing engineering of shale oil and gas wells described in the present invention. The preparation is simple and suitable for on-site operations.

[0015] The flush fluid provided by the present invention is used to clean the drilling fluid. Especially, it can still effectively clean the drilling fluid under the oil-based drilling fluid, achieving the purpose of effectively cleaning the oil film and wetting the interface. Using this flush fluid in shale gas horizontal wells can greatly improve the qualification rate of cementing. Even for the oil-based drilling fluid that is the most difficult to clean in on-site applications, using the flush fluid provided by the present invention also has a very good flushing effect.

[0016] The preparation method of the above oil-based drilling fluid flush fluid system for the cementing engineering of shale oil and gas wells includes the following steps: successively add water, non-ionic surfactant, anionic surfactant, viscosity increasing agent and retarder under stirring conditions, and carry out heating and stirring treatment to obtain the drilling fluid flush fluid system.

[0017] In the above solution, the temperature used for the heating and stirring treatment is 50-70 °C, and the time is 1-10 h.

[0018] The oil-based drilling fluid flush fluid provided by the present invention can effectively clean the drilling fluid on the annulus casing and well wall and can wet and reverse the oil film, improving the bonding quality between the cement sheath, casing and formation. Moreover, it is not restricted by the environmental temperature and has a wide application range; it provides a guarantee for the long-term and effective development of shale oil and gas in the later stage and has good application and promotion prospects.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0020] 1) The oil-based drilling fluid flush fluid system described in the present invention can be used to clean the oil-based drilling fluid, having a relatively high flushing efficiency and good flushing effect; the flushing efficiency can reach more than 93%.

[0021] 2) The oil-based drilling fluid flushing fluid system of the present invention can effectively clean the oil-based drilling fluid under the synergistic effect of non-ionic surfactants and anionic surfactants, and at the same time has good emulsifying, dispersing and detergency effects, and can well clean the oil film and residual oil. In the present invention, a multi-component composite non-ionic surfactant and anionic surfactant are respectively used, and the non-ionic surfactant and the anionic surfactant are used in combination. The lipophilic group of the non-ionic surfactant inserts into the oil layer shallower at the interface. When forming a mixed micelle with the anionic surfactant, its relatively large hydrophilic group (the polyoxyethylene chain is zigzag in the aqueous solution) inserts deeper into the aqueous phase, and the steric hindrance effect on the formation of the mixed micelle is smaller, and a relatively tight micelle can be formed to improve the interfacial activity. The non-ionic surfactant has good washing, dispersing, emulsifying, wetting and solubilizing properties, which is beneficial to improving the compatibility of the flushing fluid, drilling fluid and cement slurry, and can further improve the flushing effect of the flushing fluid on the oil-based drilling fluid. In addition, by controlling the ratio between the non-ionic surfactant and the anionic surfactant and cooperating with fatty alcohol polyoxyethylene ether, the obtained flushing fluid has a certain plastic viscosity at room temperature. During the transition from high temperature to low temperature, the plastic viscosity of the flushing fluid will "rebound". Under the condition of pumping the flushing fluid at the same displacement, the increase in plastic viscosity will improve the physical shear effect of the flushing fluid on the oil-based mud cake and improve the cleaning efficiency of the flushing fluid, thereby playing a role in improving the interfacial bonding strength.

[0022] 3) The thickening agent used in the present invention has a relatively high molecular weight and a large viscosity in aqueous solution, which is beneficial to the flushing and displacement of the oil-based mud by the flushing fluid, and can further improve the flushing efficiency of the oil-based mud.

[0023] 4) The manufacturing process involved in the present invention is simple and convenient to operate, and can be widely applied to the oil well cementing project, and has great economic and promotional value. Detailed Embodiment

[0024] In order to make the purpose, technical solution and advantages of the present invention clearer, the present invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0025] The test oil-based drilling fluid is the drilling fluid used in the field drilling.

[0026] In the following embodiments, the fatty alcohol polyoxyethylene ether used has the molecular formula C 30 H 62 O 10 (monododecyl nonaethylene glycol ether), with a molecular weight of 582.81; the fatty acid polyoxyethylene alkyl ester has the molecular formula C 24 H 48 O 13, with a molecular weight of 548; the polyoxyethylene alkylamine has the molecular formula C 16 H 35 NO2 (dodecylamine polyoxyethylene (5) ether), with a molecular weight of 273.45.

[0027] The triethanolamine salt of alkylbenzene sulfonic acid used is the triethanolamine salt of dodecylbenzene sulfonic acid; the molecular formula of sodium dodecylbenzenesulfonate is C 18 H 29 NaO3S; the fatty acid sodium is sodium laurate.

[0028] Example 1

[0029] An oil-based drilling fluid flushing fluid system for shale oil and gas well cementing engineering, and its preparation method includes the following steps:

[0030] 1) Add 100 g of water, 50 g of non-ionic surfactant, 20 g of anionic surfactant, 6 g of thickening agent, and 0.5 g of retarder to the container in sequence under stirring conditions. Among them, the non-ionic surfactant used is obtained by mixing fatty alcohol polyoxyethylene ether, fatty acid polyoxyethylene alkyl ester, and polyoxyethylene alkylamine in a mass ratio of 2:1:1; the anionic surfactant is obtained by mixing triethanolamine salt of alkylbenzene sulfonic acid, sodium dodecylbenzenesulfonate, and fatty acid sodium in a mass ratio of 0.5:1:0.5; the thickening agent is xanthan gum with a molecular weight of more than 1 million; the retarder is sodium gluconate solution with a concentration of 18 wt%;

[0031] 2) Then gradually raise the temperature to 50 °C and stir for 1 h to obtain the oil-based drilling fluid flushing fluid system (main sample of the flushing fluid).

[0032] Example 2

[0033] An oil-based drilling fluid flushing fluid system for shale oil and gas well cementing engineering, and its preparation method includes the following steps:

[0034] 1) Add 100 g of water, 40 g of non-ionic surfactant, 20 g of anionic surfactant, 6 g of thickening agent, and 0.5 g of retarder to the container in sequence under stirring conditions. Among them, the non-ionic surfactant used is obtained by mixing fatty alcohol polyoxyethylene ether, fatty acid polyoxyethylene alkyl ester, and polyoxyethylene alkylamine in a mass ratio of 0.5:1:0.5; the anionic surfactant is obtained by mixing triethanolamine salt of alkylbenzene sulfonic acid, sodium dodecylbenzenesulfonate, and fatty acid sodium in a mass ratio of 1:1:0.5; the thickening agent is xanthan gum with a molecular weight of more than 1 million; the retarder is sodium gluconate solution with a concentration of 18 wt%;

[0035] 2) Then gradually raise the temperature to 50 °C and stir for 1 h to obtain the oil-based drilling fluid flushing fluid system (main sample of the flushing fluid).

[0036] Example 3

[0037] An oil-based drilling fluid flushing fluid system for a shale oil and gas well cementing project, and its preparation method includes the following steps:

[0038] 1) Add 100 g of water, 50 g of non-ionic surfactant, 20 g of anionic surfactant, 6 g of viscosifier, and 0.5 g of retarder into a container in sequence under stirring. Among them, the non-ionic surfactant used is obtained by mixing fatty alcohol polyoxyethylene ether, fatty acid polyoxyethylene alkyl ester, and polyoxyethylene alkylamine in a mass ratio of 1:1:0.5; the anionic surfactant used is obtained by mixing triethanolamine salt of alkylbenzene sulfonic acid, sodium dodecylbenzene sulfonate, and sodium fatty acid in a mass ratio of 2:1:1; the viscosifier is xanthan gum with a molecular weight of more than 1 million; the retarder is a sodium gluconate solution with a concentration of 18 wt%;

[0039] 2) Then gradually raise the temperature to 50 °C and stir for 1 h to obtain the oil-based drilling fluid flushing fluid system (main sample of the flushing fluid).

[0040] Comparative Example 1

[0041] A drilling fluid flushing fluid system, and its preparation method includes the following steps:

[0042] 1) Add 100 g of water, 50 g of non-ionic surfactant, 20 g of anionic surfactant, 6 g of viscosifier, and 0.5 g of retarder into a container in sequence under stirring. Among them, the non-ionic surfactant used is obtained by mixing fatty alcohol polyoxyethylene ether and fatty acid polyoxyethylene alkyl ester in a mass ratio of 1:1; the anionic surfactant used is obtained by mixing triethanolamine salt of alkylbenzene sulfonic acid and sodium dodecylbenzene sulfonate in a mass ratio of 1:1; the viscosifier is xanthan gum with a molecular weight of more than 1 million; the retarder is a sodium gluconate solution with a concentration of 18 wt%;

[0043] 2) Then gradually raise the temperature to 50 °C and stir for 1 h to obtain the oil-based drilling fluid flushing fluid system.

[0044] Comparative Example 2

[0045] A drilling fluid flushing fluid system, and its preparation method includes the following steps:

[0046] 1) 100 g of water, 50 g of non-ionic surfactant, 20 g of anionic surfactant, 6 g of thickening agent, and 0.5 g of retarder were successively added into a container under stirring. Among them, the non-ionic surfactant used was obtained by mixing fatty alcohol polyoxyethylene ether and polyoxyethylene alkylamine in a mass ratio of 0.5:1; the anionic surfactant used was obtained by mixing triethanolamine salt of alkylbenzene sulfonic acid and sodium fatty acid in a mass ratio of 0.5:1; the thickening agent was xanthan gum with a molecular weight of over 1 million; the retarder was sodium gluconate solution with a concentration of 18 wt%.

[0047] 2) Then the temperature was gradually raised to 50 °C and stirred for 1 h to obtain an oil-based drilling fluid flush fluid system.

[0048] The performance test results of the flush fluids described in Examples 1 to 3 and Comparative Examples 1 to 2 are compared as follows:

[0049] Wettability test

[0050] The finished products prepared in Examples 1 to 3 and Comparative Examples 1 to 2 were diluted with water to 30 wt%. Three clean metal sheets were immersed in the oil-based drilling fluid for 5 h and then the contact angle was measured with an instrument. The five metal sheets were cleaned with the dilution solutions of Examples 1 to 3 and Comparative Examples 1 to 2 for 10 min respectively, and then the contact angle was measured, as shown in Table 1.

[0051] Table 1 Contact angle test results of the diluted flush fluids obtained in Examples 1 to 3 and Comparative Examples 1 to 2

[0052] Oil-based drilling fluid Example 1 Example 2 Example 3 Comparative Example 3 Comparative Example 4 Contact angle 82 7 10 5 11 13

[0053] Flushing efficiency test

[0054] The finished products prepared in Examples 1 to 3 and Comparative Examples 1 to 2 were diluted with water to 30 wt%, and then the flushing efficiency was evaluated according to the industry standard SY / T5757+2000 "Usage Method of Preflush Fluid for Cementing in Oil and Gas Wells". Among them, the rotation speed was 1400 revolutions per minute and the flushing time was 5 minutes; the density of the oil-based drilling fluid used was 1.45 g / cm³. The specific test results are shown in Table 2.

[0055] Table 2 Flushing efficiency test results of the diluted flush fluids obtained in Examples 1 to 3

[0056]

[0057] Flushing rate = (G1 - G2) / (G1 - G0) × 100

[0058] Compatibility test

[0059] Taking the flushing fluid system of Example 1 as the test object, first prepare the flushing fluid. Evaluate the compatible rheology according to the industry standard SY / T5374-2000 "Usage Method of Preflush Fluid for Cementing in Oil and Gas Wells". The drilling fluid / flushing fluid is mixed at volume ratios of 95 / 5(1), 75 / 25(2), 50 / 50(3), 25 / 75(4), and 5 / 95(5). Use a six-speed viscometer to measure the rheology and compare it with the drilling fluid without the flushing fluid. The test temperature is 60°C.

[0060] Table 3 Compatibility Test Results of the Diluted Flushing Fluid Obtained in Example 1

[0061] Number Oil-based drilling fluid / rinsing fluid Reading of a Fann viscometer AV PV 1 100 / 0 74 / 45 / 31 / 20 / 8 / 7 37 30 2 75 / 25 70 / 42 / 30 / 18 / 6 / 5 35 28 3 50 / 50 60 / 39 / 27 / 18 / 7 / 6 30 21 4 25 / 75 59 / 38 / 26 / 17 / 7 / 6 29.5 21 5 5 / 95 35 / 23 / 17 / 10 / 3 / 2 17.5 12

[0062] As can be seen from Tables 1, 2, and 3, the flushing fluid system of the present invention has good compatibility with the drilling fluid, can clean the oil-based drilling fluid in a short time, and has a high flushing efficiency. After flushing the second interface of the cementing, it is hydrophilic and has good wetting reversal performance, providing a suitable environment for the cement slurry bonding, and can greatly improve the cementing quality.

[0063] The present invention is not limited to the above embodiments. For those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements are also regarded as within the protection scope of the present invention. The content not described in detail in this specification belongs to the prior art well-known to those skilled in the art.

Claims

1. An oil-based drilling fluid flushing fluid system for shale oil and gas well cementing engineering, characterized in that: The components and their weight proportions include: 1-50 parts of nonionic surfactant, 1-50 parts of anionic surfactant, 0.1-20 parts of viscosity enhancer, 0.1-20 parts of retarder, and 100 parts of water; wherein the nonionic surfactant is compounded with fatty alcohol polyoxyethylene ether, fatty acid polyoxyethylene alkyl ester, and polyoxyethylene alkylamine as main raw materials; and the anionic surfactant is compounded with alkylbenzenesulfonic acid triethanolamine salt, dodecylbenzenesulfonate, and fatty acid salt as main raw materials.

2. The oil-based drilling fluid flushing fluid system according to claim 1, characterized in that: In the nonionic surfactant, the mass ratio of fatty alcohol polyoxyethylene ether, fatty acid polyoxyethylene alkyl ester and polyoxyethylene alkylamine is 0.5-2:1:0.5-2.

3. The oil-based drilling fluid flushing fluid system according to claim 1, characterized in that: The general formula of the fatty alcohol polyoxyethylene ether is R1O(CH2CH2O) n H, R1 is C 12 -C 18 Saturated hydrocarbon group, n = 10-20; the general formula of fatty acid polyoxyethylene alkyl ester is R2COO(CH2CH2O) n H, R2 is C1-C 18 The general formula of polyoxyethylene alkylamine is R3N(CH2CH2OH)2, R3 is C6-C 12 saturated hydrocarbon group.

4. The oil-based drilling fluid flushing fluid system according to claim 1, characterized in that: In the anionic surfactant, the mass ratio of alkylbenzenesulfonic acid triethanolamine salt, dodecylbenzenesulfonic acid salt and fatty acid salt is 0.5-2:1:0.5-2.

5. The oil-based drilling fluid flushing fluid system according to claim 1, characterized in that: The carbon number of the alkyl group of the alkylbenzenesulfonic acid triethanolamine salt is 12-18.

6. The oil-based drilling fluid flushing fluid system according to claim 1, characterized in that: The viscosity increasing agent is xanthan gum or attapulgite.

7. The oil-based drilling fluid flushing fluid system according to claim 6, characterized in that: The relative molecular mass of the xanthan gum is more than 1 million; the average particle size of the attapulgite is less than 1 μm, and the maximum particle size is less than 50 μm.

8. The oil-based drilling fluid flushing fluid system according to claim 7, characterized in that: The retarder is a solution formed by one or more of sodium gluconate, citric acid, and organic phosphonate.

9. The method for preparing the oil-based drilling fluid flushing fluid system for shale oil and gas well cementing engineering according to any one of claims 1 to 8, characterized in that: The method comprises the following steps: adding water, nonionic surfactant, anionic surfactant, viscosity enhancer and retarder in sequence under stirring conditions, and performing heating and stirring treatment to obtain the drilling fluid flushing fluid system.

10. The preparation method according to claim 9, characterized in that The heating and stirring treatment is performed at a temperature of 50 to 70° C. and for a time of 1 to 10 hours.

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