Fluid Flow and Displacement in the Annulus
During a primary cementing job, a sequence of fluids is pumped into the annulus in order to displace the mud and prepare the annulus for cement placement. The factors affecting the mud displacement efficiency are discussed in this chapter. The effects of
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Fluid Flow and Displacement in the Annulus
Abstract During a primary cementing job, a sequence of fluids is pumped into the annulus in order to displace the mud and prepare the annulus for cement placement. The factors affecting the mud displacement efficiency are discussed in this chapter. The effects of pipe eccentricity, breakouts, and irregular wellbore cross-section on the displacement efficiency are demonstrated using a simple kinematic model of annular cementing. In particular, it is shown that breakouts may have a substantial detrimental effect on the displacement efficiency since the displacing fluids might be flowing only in the breakouts. Channelization is also shown to occur when the wellbore has neither breakouts nor washouts, but rather a slightly irregular cross-section, like real wells normally do in sedimentary formations. In this case, viscous instabilities occur for unfavorable mobility ratios. Channelization may in this case be prevented most effectively by increasing the yield stress of the displacing fluid. The effects of well inclination, pipe movement and flow regime are discussed. A brief overview of numerical models of well cementing is provided. Unresolved issues in modelling are summarized.
Keywords Cement Preflush Flow Annulus Eccentricity Mud displacement Displacement efficiency Mobility ratio Model Numerical model
During primary cementing, a sequence of fluids is injected into the annulus in order to displace the drilling mud and prepare the annulus for cement placement. After the interval has been drilled, the well is first circulated in order to bring drill cuttings to surface. The drill string is then pulled out of the hole, while the circulation may continue. Circulation is then stopped, the well is logged, the casing string is run in hole, and the mud circulation is resumed. Mud circulation before logging and after running casing in hole is usually called mud conditioning. It serves to remove gas and solids (cuttings, settled weighting agents such as barite, and filter cake possibly deposited against a permeable formation). Moreover, mud conditioning is intended to break gel if the mud has been static in the well for a long time. According to current industrial recommendations, mud circulation should be carried on as long as it takes to remove solids and gelled mud from the well [1]. Moreover, © The Author(s) 2016 A. Lavrov and M. Torsæter, Physics and Mechanics of Primary Well Cementing, SpringerBriefs in Petroleum Geoscience & Engineering, DOI 10.1007/978-3-319-43165-9_3
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mud conditioning aims to replace the thicker, heavier mud used while drilling the well, with a lighter, thinner mud that is easier to displace during subsequent cementing. Since solids can be scraped off the wellbore walls by running the casing pipe, it may be wise to perform mud conditioning also at intermediate depths as the casing is being run in hole. Thinning the mud during conditioning should, however, not jeopardize its abilit
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