Determining Wellbore Pressures in Cement Slurry Columns

Abstract

Determining Wellbore Pressures in Cement Slurry Columns Michael Prohaska; Michael Prohaska Mining U. Leoben Search for other works by this author on: This Site Google Scholar D.O. Ogbe; D.O. Ogbe U. of Alaska Fairbanks Search for other works by this author on: This Site Google Scholar M.J. Economides M.J. Economides Mining U. Leoben Search for other works by this author on: This Site Google Scholar Paper presented at the SPE Western Regional Meeting, Anchorage, Alaska, May 1993. Paper Number: SPE-26070-MS https://doi.org/10.2118/26070-MS Published: May 26 1993 Cite View This Citation Add to Citation Manager Share Icon Share Twitter LinkedIn Get Permissions Search Site Citation Prohaska, Michael, Ogbe, D.O., and M.J. Economides. "Determining Wellbore Pressures in Cement Slurry Columns." Paper presented at the SPE Western Regional Meeting, Anchorage, Alaska, May 1993. doi: https://doi.org/10.2118/26070-MS Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex Search Dropdown Menu nav search search input Search input auto suggest search filter All ContentAll ProceedingsSociety of Petroleum Engineers (SPE)SPE Western Regional Meeting Search Advanced Search AbstractThis work discusses the major factors affecting the pressure drop in the cemented annulus which are filtration from the wellbore into permeable layers, shrinkage of the slurry due to hydration, and changes in the rheological properties of the slurry. A model for determining wellbore pressures in cement slurry columns is presented. It accounts for the depth-dependent or placement history dependent behavior of the gel strength evolution. Experiments conducted in the laboratory demonstrate that static gel strength development is a function of temperature, pressure and shear rate. Results show that large differences in wellbore pressures can be obtained when the depth-dependent characteristics of gel strength are neglected in wellbore pressure loss calculations.IntroductionThe main purpose of cementing oil wells is to maintain proper hydraulic isolation among the various permeable layers. The integrity of the cemented annulus is compromised when formation fluids are allowed to enter the annulus. As the cement sets, its ability to transmit hydrostatic pressure diminishes. Fluid loss from the slurry to a permeable layer can lead to volume reduction, and, if the reduction is not compensated for, the cement pore pressure declines. As the cement gel strength develops, it becomes harder for any volume reduction to be compensated for, and therefore, volumetric shrinkage and the continuation of fluid loss to permeable layers may lead to a cement pore pressure decline (Chenevert and Jin, 1989). When the hydrostatic pressure of the slurry falls below the formation pressure, gas can enter the cement matrix. A more comprehensive discussion dealing with the problem of gas migration/invasion during oil well cementing was given by Beirute and Cheung (1989) and Sutton and Ravi (1989).Predicting the pressure behavior of cement slurries is an important task during well cementing. Several pressure drop predictive models have been presented. The basic model which accounts for gel strength development and filtrate loss was introduced by Sabins et al. (1982), and later by Sutton and Ravi (1989), and Beirute and Cheung (1989). Chenevert and Jin (1989) developed a more detailed pressure drop model to account for the gelation properties of the slurry, and the downward movement of the column due to shrinkage and fluid loss. In the Chenevert and Jin model the wall shear stress of a slurry element is determined as a function of gel strength and displacement and it is used instead of the static gel strength to calculate wellbore pressures. Recently, Daccord et al. (1991) expanded the Chenevert and Jin model to include the mass conservation of the slurry. The Daccord et al. model calculates density changes in the slurry as a function of compressibility, chemical shrinkage and fluid loss. In this paper, an improved model for predicting wellbore pressure is presented in which the depth-dependent or placement history - dependent behavior of gel strength development is included.P. 407^ Keywords: compressibility, pressure loss, gel strength development, reduction, shear rate, casing and cementing, bottom element, upstream oil & gas, wellbore pressure, procedure Subjects: Wellbore Design, Casing and Cementing, Wellbore integrity, Cement formulation (chemistry, properties) This content is only available via PDF. 1993. Society of Petroleum Engineers You can access this article if you purchase or spend a download.