The influence of modified methyl cellulose on the main properties of expanding cementing slurries

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The influence of modified methyl cellulose on the main properties of expanding cementing slurries

Kochkodan Yaroslav Mykhailovych

PhD, Associate Professor, Department of drilling

Ivano-Frankivsk National technical university of oil and gas, Ukraine

Yurych Lidiia Romanivna

PhD, Associate Professor, Department of drilling

Ivano-Frankivsk National technical university of oil and gas, Ukraine

Vovkiv Volodymyr Yaroslavovych

Student

Ivano-Frankivsk National technical university of oil and gas, Ukraine

Summary

modified methylcellulose cementing slurrie

The effect of modified methylcellulose on the main properties of expanding cementing slurries. When cementing low-temperature wells, expanding cementing slurries based on a mixture of Portland cement (70-75% PCT-I) and gypsum alumina cement (30-25% GAC) are used. Expanding cementing slurries provide sealing of the contact of the mud and stone with the casing and the well wall. The research was conducted using standard methods and other non-standard methods. Modified methyl cellulose is an effective filtration reducer for low-temperature. The modified methyl cellulose additive ranged from 0.1 % to 0.5 % by weight of the cement mixture. The addition of modified methyl cellulose practically does not affect the curing time, but effectively reduces the filtration of cementing slurries. The strength of the cement with an increase in the content of modified methyl cellulose increases slightly compared to the cement without the additive. Increasing the content of modified methyl cellulose above 0.2% does not significantly change the cement strength. The linear expansion of the cementing slurry and stone decreases. A significant disadvantage of modified methyl cellulose is a decrease in the spreadability of cementing slurries. Therefore, modified methyl cellulose should be used in combination with viscosity-reducing agents.

Key words: well, expanding cementing slurries, modified methyl cellulose, filtration, spreadability, lineal expansion.

The main purpose of the cementing slurry in well cementing is to form a sealed annular space that prevents - inter-stratal flows and fluid seepages. In an open wellbore, the pressure of the cementing slurry column is usually always higher than the formation pressure, and under the influence of their difference, a significant part of the excess water is filtered into permeable rocks. At the same time, the cementing slurry is sealed, and thickened, its volume decreases, channels may form, and, which is especially unfavorable for the well, the near-wellbore zone is contaminated. At the same time, some of the hydration products of the cementing slurry are filtered out along with the water, which often causes a significant decrease in the permeability of the productive formation [1,6].

The decrease in permeability may be due to the formation of wall fluid layers on the surfaces of sandstone grains or clay material swelling contained in the rock

In addition, a negative change in the cementing slurry volume with simultaneous dehydration and formation of cracks in the wall cake can cause gas seepages, intercasing pressure and formation of mud springs.

To prevent the occurrence of inter-stratal flows and intercasing gas seepages when cementing low-temperature (up to 50°C) wells, expanding cementing slurries based on a mixture of Portland cement (70-75% PCT-I) and gypsum alumina cement (30-25% GAC) are used. They provide sealing of the contact of the mud and stone with the casing and the well wall but do not reduce filtration (water flow). One of the technological measures that regulates the cementing slurry properties in the required direction and improves the quality of cementing is the addition of chemicals

To reduce the water loss of cementing slurry at elevated temperatures (over 50°C), CMC (Carboxymethylcel cellulose), SWL (sulfite waste liquor), hypane, drilling mud powder, latex, etc. are used. Abroad, chemicals based on polymers, latex, and lignin derivatives are used to reduce filtration. Gel cements and their combinations with chemical additives are widely used. At bottomhole temperatures up to 50°C, the drawback of all the proposed formulations for reducing the filtration of cementing slurries is the simultaneous increase in their curing time from 4-5 hours to 24-48 hours. As for expanding cementing slurries, the selection of reagents to reduce filtration was practically not carried out. Therefore, it became necessary to conduct special studies to develop formulations of expanding cementing slurries with reduced filtration for low-temperature wells (up to 50°C).

The research was conducted using standard methods and other non-standard methods. The water-cement ratio was 0.5; the temperature was 20±2°C; the pressure was atmospheric. The research was carried out for a long time. Cement of different batches (PCT-I and GAC) with different storage times prior to the experiment were used as the starting material [4, 5]. The influence of specific chemical agents on the properties of cementing slurry and stone was studied using different batches of cement.

Thus, depending on the chemical and mineralogical composition of the initial cement batches, their storage time from production to use, the physical and mechanical characteristics of cementing slurry and stone may have different values, depending on the cement batch. Therefore, the data obtained have relative values, and for each specific case of cementing, the spreadability and curing time should be checked in industrial laboratories. We studied the effect of modified methyl cellulose (MMC) in order to select the optimal chemical treatment formulation and regulate the main technological properties of cementing slurries.

To reduce the filtration of expanding cementing slurries, the effect of MMC was studied. The MMC agent is a cellulose methyl ester containing 26-33% methoxyl groups. The temperature resistance limit of the agent is 50°C. At higher temperatures, the reagent solution turns into gelatin. When the temperature drops

below 50°C, the agent properties are restored. MMC is an effective filtration reducer for low-temperature (up to 50°C) wells. Since MMC contains non-ionic methoxyl groups that do not interact with clinker minerals, it does not significantly affect the curing time of fluids, which is important for well cementing. This is obviously the reason for the high activity of MMC since due to the lack of chemical sorption on clinker, the concentration of the agent in the dispersion medium does not decrease. The MMC agent was prepared as a 2-3% water solution. The finished agent solution was added to water to prepare a cementing slurry. We have studied the effect of MMC additives on the properties of expanding cementing slurries. The MMC additive ranged from 0.1 % to 0.5 % by weight of the cement mixture.

The results of laboratory studies of the effect of MMC on the properties of expanding cementing slurries are shown in Table 1. As we can see, the addition of MMC practically does not affect the curing time, but effectively reduces the filtration of cementing slurries. Thus, with an increase in the MMC content from 0.1 % to 0.5%, filtration decreases by 9 times for a mixture of 75% PCT + 25% GAC and almost 8 times for a mixture of 75 PCT + 30% GAC.

Table 1

Effect of MMC additive on the cementing slurry properties and stone

Conclusion

The strength of the cement with an increase in the content of MMC increases slightly (by about 10% at an MMC content of 0.2%) compared to the cement without the additive. Increasing the content of MMC above 0.2% does not significantly change the cement strength. The linear expansion of the cementing slurry and stone decreases. Thus, with the addition of 0.5% of MMC, it is almost four times less than without MMC. A significant disadvantage of MMC is a decrease in the spreadability of cementing slurries to 1 3-14 cm after 3 minutes and to 7 cm after 60 minutes. Therefore, MMC should be used in combination with viscosity-reducing agents.

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