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# Mathematical modeling the processes of behind-casing fluid movement in the wells during waiting on cement

UDK: 622.245.42.001
DOI: 10.24887/0028-2448-2019-5-67-71
Key words: well cementing, isolation of layers, the cement slurry, pore pressure suspensions, backflow
Authors: K.A. Jabarov

In a series of stages of creating insulation in a well in the form of a cement ring, the most critical and least studied is the stage of the beginning of the hardening of the cement slurry behind the casing. It is proved that during this period the pressure of the solution column at the bottomhole decreases and conditions arise for the influx of reservoir fluids into the well and the formation of behind-the-casing flows. It is difficult to simulate these processes in the laboratory, and it is expensive to observe in the well. Therefore, mathematical modeling can be a significant addition to their understanding.

In the article, solutions are given to boundary value problems of an equation describing the process of the fall of the “hydrostatic” pressure of cement slurries in a well with impermeable walls even when the cement mortar column hardens in contact with the permeable formation with a given pressure of fluid. Using the formulas obtained, the pressure distribution curves of the cement slurry over the depth of the well and over time were constructed according to which pressure gradients operating during the waiting on cement period in the annular space of the well were calculated. The criteria for the resistance of cement slurries to the introduction of formation fluid in them to the formation of behind-the-casing flows through hardening cement mortar are formulated. Comparison of pressure gradients acting in the well with the criteria for cement slurry resistibility allows calculating the size of the zones of suffusion fracture of the structure of cement suspensions by formation fluid in the annular space during waiting on cement.

References

1. Letchenko V.K., Casing annular emissions after casing cementing (In Russ.), Azerbaydzhanskoe neftyanoe khozyaystvo, 1954, no. 8, pp. 18–20.

2. Mamedov A.B., Rustambekov A.F., About the true causes of annular emissions after casing cementing (In Russ.), Azerbaydzhanskoe neftyanoe khozyaystvo, 1955, no. 2, pp. 13–14.

3. Malevanskiy V.D., Otkrytye gazovye fontany i bor'ba s nimi (Uncontrolled gas blowout and the emergency response), Moscow: Gostoptekhizdat Publ., 1963.

4. Gayvoronskiy A.A., Farukshin L.Kh., Hydrostatic pressure of cement mortar (In Russ.), Neftyanik, 1963, no. 10, pp. 30–32.

5. Grachev V.V., Leonov E.G., Investigation of the pore and skeletal pressure of the cement mortar during cement setting (In Russ.) Burenie, 1969, no. 3, pp. 17–21.

6. Levayn D.K. et al., Prevention of gas migration in the annulus of a cemented well (In Russ.), Neft', gaz i neftekhimiya za rubezhom, 1980, no. 10, pp. 8–17.

7. Bulatov A.I. et al., The emergence of channels in the annulus of wells after cementing (In Russ.), Gazovaya promyshlennost', 1970, no. 2, pp. 3–6.

8. Shchishchenko R.I. et al., Studying the nature of gas occurrences after casing cementing (In Russ.), Gazovaya promyshlennost', 1965, no. 9, pp. 7–11.

9. Raykevich S.I., Razrabotka sposobov i tekhnologiy povysheniya produktivnosti skvazhin gazovykh i neftyanykh mestorozhdeniy (Development of methods and technologies for increasing the productivity of wells in gas and oil fields); thesis of candidate of technical science, Moscow, 2004.

10. Oskarsen R.T.,Walzel D.,Wright J.W., Recommendations for advanced cementing methods (In Russ.), Neftegazovye tekhnologii, 2010, no. 4, pp. 26–29.

11. Environmental technology in the oil industry: edited by Orszulik S.T., Dordrecht: Springer, 2016.

12. Vidovskiy A.L. et al., Field studies of pressure measurement in the cemented portion of the annular space of wells (In Russ.), Burenie, 1974, no. 7.

13. Cooke C.J. Jr. et al., Field measurements of annular pressure and temperature during primary cementing, SPE 11206-PA, 1983.

14. Dzhabarov K.A., The pressure in the liquid phase of drilling and cement slurries in the well (In Russ.), Izvestiya vuzov “Neft' i gaz”, 1987, no. 7, pp. 26–30.

15. Khadur M.Kh., Formirovanie davleniya tsementnykh rastvorov v skvazhine v svyazi s gazoneftevodoproyavleniyami v period OZTs (The formation of pressure of cement mortars in the well in connection with the gas and oil showings during the WOC time): thesis of candidate of technical science, Moscow, 1991.

16. Dzhabarov K.A., Metody opredeleniya porovogo davleniya i neftegazoizoliruyushchey sposobnosti tsementnykh rastvorov (Methods for determining pore pressure and oil and gas insulating ability of cement mortars), Moscow: Publ. of VNIIEgazprom, 1991, 24 p.

In a series of stages of creating insulation in a well in the form of a cement ring, the most critical and least studied is the stage of the beginning of the hardening of the cement slurry behind the casing. It is proved that during this period the pressure of the solution column at the bottomhole decreases and conditions arise for the influx of reservoir fluids into the well and the formation of behind-the-casing flows. It is difficult to simulate these processes in the laboratory, and it is expensive to observe in the well. Therefore, mathematical modeling can be a significant addition to their understanding.

In the article, solutions are given to boundary value problems of an equation describing the process of the fall of the “hydrostatic” pressure of cement slurries in a well with impermeable walls even when the cement mortar column hardens in contact with the permeable formation with a given pressure of fluid. Using the formulas obtained, the pressure distribution curves of the cement slurry over the depth of the well and over time were constructed according to which pressure gradients operating during the waiting on cement period in the annular space of the well were calculated. The criteria for the resistance of cement slurries to the introduction of formation fluid in them to the formation of behind-the-casing flows through hardening cement mortar are formulated. Comparison of pressure gradients acting in the well with the criteria for cement slurry resistibility allows calculating the size of the zones of suffusion fracture of the structure of cement suspensions by formation fluid in the annular space during waiting on cement.

References

1. Letchenko V.K., Casing annular emissions after casing cementing (In Russ.), Azerbaydzhanskoe neftyanoe khozyaystvo, 1954, no. 8, pp. 18–20.

2. Mamedov A.B., Rustambekov A.F., About the true causes of annular emissions after casing cementing (In Russ.), Azerbaydzhanskoe neftyanoe khozyaystvo, 1955, no. 2, pp. 13–14.

3. Malevanskiy V.D., Otkrytye gazovye fontany i bor'ba s nimi (Uncontrolled gas blowout and the emergency response), Moscow: Gostoptekhizdat Publ., 1963.

4. Gayvoronskiy A.A., Farukshin L.Kh., Hydrostatic pressure of cement mortar (In Russ.), Neftyanik, 1963, no. 10, pp. 30–32.

5. Grachev V.V., Leonov E.G., Investigation of the pore and skeletal pressure of the cement mortar during cement setting (In Russ.) Burenie, 1969, no. 3, pp. 17–21.

6. Levayn D.K. et al., Prevention of gas migration in the annulus of a cemented well (In Russ.), Neft', gaz i neftekhimiya za rubezhom, 1980, no. 10, pp. 8–17.

7. Bulatov A.I. et al., The emergence of channels in the annulus of wells after cementing (In Russ.), Gazovaya promyshlennost', 1970, no. 2, pp. 3–6.

8. Shchishchenko R.I. et al., Studying the nature of gas occurrences after casing cementing (In Russ.), Gazovaya promyshlennost', 1965, no. 9, pp. 7–11.

9. Raykevich S.I., Razrabotka sposobov i tekhnologiy povysheniya produktivnosti skvazhin gazovykh i neftyanykh mestorozhdeniy (Development of methods and technologies for increasing the productivity of wells in gas and oil fields); thesis of candidate of technical science, Moscow, 2004.

10. Oskarsen R.T.,Walzel D.,Wright J.W., Recommendations for advanced cementing methods (In Russ.), Neftegazovye tekhnologii, 2010, no. 4, pp. 26–29.

11. Environmental technology in the oil industry: edited by Orszulik S.T., Dordrecht: Springer, 2016.

12. Vidovskiy A.L. et al., Field studies of pressure measurement in the cemented portion of the annular space of wells (In Russ.), Burenie, 1974, no. 7.

13. Cooke C.J. Jr. et al., Field measurements of annular pressure and temperature during primary cementing, SPE 11206-PA, 1983.

14. Dzhabarov K.A., The pressure in the liquid phase of drilling and cement slurries in the well (In Russ.), Izvestiya vuzov “Neft' i gaz”, 1987, no. 7, pp. 26–30.

15. Khadur M.Kh., Formirovanie davleniya tsementnykh rastvorov v skvazhine v svyazi s gazoneftevodoproyavleniyami v period OZTs (The formation of pressure of cement mortars in the well in connection with the gas and oil showings during the WOC time): thesis of candidate of technical science, Moscow, 1991.

16. Dzhabarov K.A., Metody opredeleniya porovogo davleniya i neftegazoizoliruyushchey sposobnosti tsementnykh rastvorov (Methods for determining pore pressure and oil and gas insulating ability of cement mortars), Moscow: Publ. of VNIIEgazprom, 1991, 24 p.

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