Solid-phase-free high-density well killing fluid as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of oil exploitation, and particularly relates to solid-free high-density well killing fluid as well as a preparation method and application thereof. The well killing fluid comprises the following components in parts by mass (total 100 parts): 20-60 parts of potassium formate; 10 to 20 parts of a multifunctional tackifier; the rest is tap water; the molecular structural formula of the multifunctional tackifier is shown in the specification, and m is equal to 1000-10000; n is equal to 200 to 4000; and p is equal to 100 to 2000. The solid-free high-density well killing fluid disclosed by the invention has the advantages of high density, adjustable density, low corrosion rate, good anti-swelling effect and low damage to strata.

Description

Technical Field

[0001] This invention belongs to the field of petroleum extraction technology, specifically relating to a solid-free high-density well control fluid, its preparation method, and its application. Background Technology

[0002] For well workover in high-temperature, low-pressure oil and gas wells, higher requirements are placed on the thermal stability and pressure resistance of the kill fluid, increasing the difficulty of resuming production. Given the current status and existing problems of kill fluids for high-temperature, low-pressure oil and gas wells, it is necessary to conduct research on new kill fluid technologies to enable them to possess good anti-leakage performance and reservoir protection effects.

[0003] High-temperature, low-pressure oil and gas wells experience high downhole temperatures, making conventional kill fluids prone to degradation and solidification under these conditions. This leads to decreased system stability, such as weighting agent sedimentation and abnormal viscosity changes, affecting the kill fluid's ability to plug and balance pressure. This can easily cause downhole accidents such as tubing string obstruction and pump start-up difficulties. Furthermore, high temperatures can damage the colloidal structure of the kill fluid, preventing it from effectively forming a stable liquid column pressure, making it difficult to control formation fluids, and posing risks of well kicks and blowouts.

[0004] Traditional kill fluids often contain solid particles and chemical additives, which can easily cause pore blockage and decreased permeability after entering the reservoir, thus damaging oil and gas reservoir productivity. Furthermore, some kill fluid filtrates are incompatible with formation fluids, leading to secondary damage such as clay swelling and emulsion blockage, resulting in a significant reduction in oil and gas well production.

[0005] CN104212418B discloses a high-density kill fluid, which is composed of sodium formate, attapulgite, ultrafine calcium carbonate, regulators, and water in a specific mass ratio. This kill fluid is mainly used to balance formation pressure during high-pressure oil and gas well modification and workover operations. Compared to using solid-free high-density kill fluids, it significantly reduces costs while protecting the oil and gas reservoir. However, the composition of this invention contains 7.93-19.18% ultrafine calcium carbonate, which can clog the formation to some extent.

[0006] CN116622353B discloses a solid-free kill fluid containing polysaccharides and complex salts, and its preparation method. The fluid comprises the following raw materials in parts by weight: 100 parts water, 20-60 parts complex salts, 1.4-2.2 parts modified chitosan, 1-1.7 parts plant-based alkyl polysaccharide glycosides, 3-5 parts functional polymers, and 0.02-0.04 parts sodium fluorotitanate. This kill fluid exhibits excellent high-temperature resistance; after 16 hours of thermal aging at 180℃, its density, apparent viscosity, shear force, and filtration loss show no significant adverse changes, demonstrating superior high-temperature performance. Although this kill fluid is solid-free and will not clog rock pores, it still causes some damage to the core sample. Summary of the Invention

[0007] This invention addresses the shortcomings of existing technologies by providing a solid-free high-density kill fluid, its preparation method, and its applications. The solid-free high-density kill fluid of this invention has advantages such as high density with adjustable density, low corrosion rate, good anti-swelling effect, and low formation damage.

[0008] The first objective of this invention discloses a solid-free, high-density kill fluid, the composition and mass fraction (total 100 parts) of which are as follows: Potassium formate 20-60 parts; 10-20 parts of multi-functional tackifier; The remaining portion is tap water; The molecular structure of the multifunctional thickener is as follows:

[0009] Where m = 1000 - 10000; n = 200 - 4000; p = 100 - 2000; The molecular weight of the multifunctional tackifier is 500,000-1,000,000.

[0010] Another objective of this invention is to disclose a method for preparing the aforementioned solid-free high-density kill fluid, the specific steps of which are as follows: (1) Add isothiazolinone, allyl chloride, sodium sulfite, copper chloride, and ethanol to the reactor, stir, heat under reflux, filter, and distill the filtrate under reduced pressure to obtain a viscous intermediate; the reaction equation of the intermediate is as follows:

[0011] (2) Add deionized water, sodium p-ethylenebenzenesulfonate, and 2-(trifluoromethyl)acrylic acid to the above reactor, stir evenly, purge with nitrogen, add initiator, and keep the reaction at the temperature to obtain a multifunctional thickener; the reaction equation of the multifunctional thickener is as follows:

[0012] (3) Add tap water and potassium formate to the container, stir to dissolve, then add multifunctional thickener, stir evenly to obtain solid-free high-density kill fluid.

[0013] In this invention, preferably, the molar ratio of allyl chloride, sodium p-vinylbenzenesulfonate, 2-(trifluoromethyl)acrylic acid and isothiazolinone is 0.8-1.2 : 0.2-0.4 : 0.1-0.2 : 1.

[0014] Preferably, in step (1), the weight ratio of sodium sulfite, copper chloride, ethanol and isothiazolinone is 0.05-0.1:0.02-0.05:10-20:1.

[0015] Preferably, in step (1), the heating reflux time is 4-12 hours.

[0016] Preferably, in step (2), the weight ratio of deionized water to isothiazolinone is 15-20:1.

[0017] Preferably, in step (2), the initiator is one of potassium persulfate, sodium persulfate, or ammonium persulfate, and the weight ratio of the initiator to isothiazolinone is 0.02-0.1:1.

[0018] Preferably, in step (2), the heat preservation reaction temperature is 50-70℃ and the time is 1-4h.

[0019] The third objective of this invention is to disclose the application of the above-mentioned kill fluid in oil and gas well workover.

[0020] Compared with the prior art, the present invention has the following advantages and beneficial effects: The potassium formate in the kill fluid of this invention can significantly increase the density of the kill fluid. At the same time, the diameter of potassium ions is 266 pm, which is very close to the pore size of clay (280 pm). It is easy to enter the pore space and difficult to release, reducing the entry of water molecules and playing an anti-swelling role, thereby playing an anti-collapse role. The multifunctional viscosity improver in the kill fluid of this invention has the following functions: (1) Viscosity improver, which can increase the viscosity of the kill fluid after dissolving in brine, reduce the filtration loss of the kill fluid, and reduce the damage of the kill fluid filtrate to the formation; (2) Surfactant, which can reduce the surface tension and interfacial tension of the kill fluid, so that the kill fluid filtrate that has invaded the formation can be more thoroughly returned, reducing capillary resistance and reducing water lock damage; (3) Corrosion inhibitor, which forms an isolation protective film on the metal surface, isolating the contact between the corrosive medium and the metal, thereby slowing down the corrosion of oil and casing. The kill fluid of this invention is a solid-free kill fluid with low filtration performance. It can not only avoid the loss of the kill fluid in the formation, but also avoid the damage of the filtrate to the formation.

[0021] The solid-free, high-density kill fluid of this invention has a high and adjustable density, ranging from 1.19 to 1.5 g / cm³ as needed. 3 The corrosion rate of the solid-free high-density kill fluid of the present invention is low, reaching as low as 0.008 mm / year; the anti-swelling rate of the solid-free high-density kill fluid of the present invention is high, reaching as high as 97.3%. Detailed Implementation

[0022] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0023] The technical solution of the present invention will be further described below with reference to specific embodiments: Example 1 Preparation of Multifunctional Tackifier Z1 (1) Add 0.1 mol isothiazolinone, 0.08 mol allyl chloride, 0.575 g sodium sulfite, 0.23 g copper chloride and 115 g ethanol to the reactor, stir, heat under reflux for 4 h, filter, and distill the filtrate under reduced pressure to obtain a viscous intermediate. (2) Add 230g of deionized water, 0.02mol of sodium p-ethylenebenzenesulfonate and 0.01mol of 2-(trifluoromethyl)acrylic acid to the above reactor, stir evenly, purge with nitrogen, add 0.23g of sodium persulfate, keep warm at 50℃ for 4h to obtain multifunctional thickener Z1.

[0024] Example 2 Preparation of Multifunctional Tackifier Z2 (1) Add 0.1 mol isothiazolinone, 0.12 mol allyl chloride, 1.15 g sodium sulfite, 0.575 g copper chloride and 198 g ethanol to the reactor, stir, heat under reflux for 8 h, filter, and distill the filtrate under reduced pressure to obtain a viscous intermediate. (2) Add 221g of deionized water, 0.025mol of sodium p-ethylenebenzenesulfonate and 0.012mol of 2-(trifluoromethyl)acrylic acid to the above reactor, stir evenly, purge with nitrogen, add 0.58g of sodium persulfate, keep warm at 55℃ for 4h to obtain multifunctional thickener Z2.

[0025] Example 3 Preparation of Multifunctional Tackifier Z3 (1) Add 0.1 mol isothiazolinone, 0.09 mol allyl chloride, 0.728 g sodium sulfite, 0.44 g copper chloride and 176 g ethanol to the reactor, stir, heat under reflux for 8 h, filter, and distill the filtrate under reduced pressure to obtain a viscous intermediate. (2) Add 200g of deionized water, 0.03mol of sodium p-ethylenebenzenesulfonate and 0.014mol of 2-(trifluoromethyl)acrylic acid to the above reactor, stir evenly, purge with nitrogen, add 0.49g of ammonium persulfate, keep warm at 60℃ for 2h to obtain multifunctional thickener Z3.

[0026] Example 4 Preparation of Multifunctional Tackifier Z4 (1) Add 0.1 mol isothiazolinone, 0.11 mol allyl chloride, 0.98 g sodium sulfite, 0.56 g copper chloride and 188 g ethanol to the reactor, stir, heat under reflux for 10 h, filter, and distill the filtrate under reduced pressure to obtain a viscous intermediate. (2) Add 208g of deionized water, 0.03mol of sodium p-ethylenebenzenesulfonate and 0.016mol of 2-(trifluoromethyl)acrylic acid to the above reactor, stir evenly, purge with nitrogen, add 0.98g of ammonium persulfate, keep warm at 70℃ for 1h to obtain multifunctional thickener Z4.

[0027] Example 5 Preparation of Multifunctional Tackifier Z5 (1) Add 0.1 mol isothiazolinone, 0.095 mol allyl chloride, 1.04 g sodium sulfite, 0.33 g copper chloride and 230 g ethanol to the reactor, stir, heat under reflux for 12 h, filter, and distill the filtrate under reduced pressure to obtain a viscous intermediate. (2) Add 187g of deionized water, 0.035mol of sodium p-ethylenebenzenesulfonate and 0.018mol of 2-(trifluoromethyl)acrylic acid to the above reactor, stir evenly, purge with nitrogen, add 1.15g of potassium persulfate, keep warm at 60℃ for 3h to obtain multifunctional thickener Z5.

[0028] Example 6 Preparation of Multifunctional Tackifier Z6 (1) Add 0.1 mol isothiazolinone, 0.105 mol allyl chloride, 1.08 g sodium sulfite, 0.48 g copper chloride and 214 g ethanol to the reactor, stir, heat under reflux for 12 h, filter, and distill the filtrate under reduced pressure to obtain a viscous intermediate. (2) Add 173g of deionized water, 0.04mol of sodium p-ethylenebenzenesulfonate and 0.02mol of 2-(trifluoromethyl)acrylic acid to the above reactor, stir evenly, purge with nitrogen, add 0.84g of potassium persulfate, keep warm at 65℃ for 2h to obtain multifunctional thickener Z6.

[0029] Example 7 Preparation of Kill Fluid M1 Add 70g of tap water and 20g of potassium formate to the reactor, stir to dissolve, add 10g of multifunctional thickener, stir evenly, and obtain solid-free high-density kill fluid M1.

[0030] Example 8 Preparation of Kill Fluid M2 Add 63g of tap water and 25g of potassium formate to a container, stir to dissolve, add 12g of multifunctional thickener, stir evenly, and obtain solid-free high-density kill fluid M2.

[0031] Example 9 Preparation of Kill Fluid M3 Add 56g of tap water and 30g of potassium formate to a container, stir to dissolve, add 14g of multifunctional thickener, stir evenly, and obtain solid-free high-density kill fluid M3.

[0032] Example 10 Preparation of Kill Fluid M4 Add 44g of tap water and 40g of potassium formate to a container, stir to dissolve, add 16g of multifunctional thickener, stir evenly, and obtain solid-free high-density kill fluid M4.

[0033] Example 11 Preparation of Kill Fluid M5 Add 32g of tap water and 50g of potassium formate to a container, stir to dissolve, add 18g of multifunctional thickener, stir evenly, and obtain solid-free high-density kill fluid M5.

[0034] Example 12 Preparation of Kill Fluid M6 Add 20g of tap water and 60g of potassium formate to a container, stir to dissolve, add 20g of multifunctional thickener, stir evenly, and obtain solid-free high-density kill fluid M6.

[0035] Example 13 The density and corrosion rate of the solid-free high-density kill fluid of the present invention (Examples 7-12) were tested with reference to SY / T 5834-2014 "Performance Indicators and Evaluation Methods of Low Solid Phase Kill Fluid". The test results are shown in Table 1.

[0036] As can be seen from Table 1: (1) The density of the kill fluid of the present invention (Examples 7-12) is 1.19-1.5 g / cm³. 3 between; (2) The well-killing fluid of the present invention (Examples 7-12) has the advantage of low corrosion rate, with corrosion rates reaching 0.016 mm / year and below, and as low as 0.008 mm / year (Example 12).

[0037] Example 14 The test method refers to the centrifugation method of SY / T5971-2016 "Performance Evaluation Method of Clay Stabilizer for Fracturing, Acidizing and Water Injection in Oil and Gas Fields" to test the anti-swelling rate of the solid-free high-density kill fluid of the present invention (Examples 7-12).

[0038] The difference is that the well-killing fluid of this invention was used instead of the 0.5% clay stabilizer solution for testing, and the test results are shown in Table 1.

[0039] Table 1. Test results of density, corrosion rate, and swelling resistance.

[0040] As can be seen from Table 1: The kill fluid of the present invention (Examples 7-12) has the advantage of high anti-swelling rate, with the anti-swelling rate reaching 95.4% or above, and the highest reaching 97.3% (Example 12).

[0041] In summary, the solid-free high-density kill fluid of this invention has the advantages of high density with adjustable density, low corrosion rate, good anti-swelling effect, and low damage to the formation. Therefore, it has broad market application prospects.

[0042] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details of the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

[0043] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not describe the various possible combinations separately.

[0044] Furthermore, various different embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed by the present invention.

Claims

1. A solid-free, high-density kill fluid, characterized in that, The composition and mass components of the kill fluid (total 100 parts) are as follows: Potassium formate 20-60 parts; 10-20 parts of multi-functional tackifier; The remaining portion is tap water; The molecular structure of the multifunctional thickener is as follows: ， Where m = 1000 - 10000; n=200-4000； p=100-2000。 2. The solid-free high-density kill fluid according to claim 1, characterized in that, The molecular weight of the multifunctional tackifier is 500,000-1,000,000.

3. The method for preparing solid-free high-density kill fluid according to claim 1, characterized in that, The specific steps of the preparation method are as follows: (1) Add isothiazolinone, allyl chloride, sodium sulfite, copper chloride and ethanol to the reactor, stir, heat under reflux, filter, and distill the filtrate under reduced pressure to obtain a viscous intermediate; (2) Add deionized water, sodium p-ethylenebenzenesulfonate, and 2-(trifluoromethyl)acrylic acid to the above reactor, stir evenly, purge with nitrogen, add initiator, keep warm and react to obtain a multifunctional thickener; (3) Add tap water and potassium formate to the container, stir to dissolve, then add multifunctional thickener, stir evenly to obtain solid-free high-density kill fluid.

4. The preparation method according to claim 3, characterized in that, The molar ratio of allyl chloride, sodium p-vinylbenzenesulfonate, 2-(trifluoromethyl)acrylic acid and isothiazolinone is 0.8-1.2 : 0.2-0.4 : 0.1-0.2 :

1.

5. The preparation method according to claim 3, characterized in that, In step (1), the weight ratio of sodium sulfite, copper chloride, ethanol and isothiazolinone is 0.05-0.1:0.02-0.05:10-20:

1.

6. The preparation method according to claim 3, characterized in that, In step (1), the heating reflux time is 4-12 hours.

7. The preparation method according to claim 3, characterized in that, In step (2), the weight ratio of deionized water to isothiazolinone is 15-20:

1.

8. The preparation method according to claim 3, characterized in that, In step (2), the initiator is one of potassium persulfate, sodium persulfate, or ammonium persulfate, and the weight ratio of the initiator to isothiazolinone is 0.02-0.1:

1.

9. The preparation method according to claim 3, characterized in that, In step (2), the heat preservation reaction temperature is 50-70℃ and the time is 1-4h.

10. The application of the solid-free high-density kill fluid according to claim 1 in oil and gas well workover.

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