Research Papers

Annular Pressure Reduction During Primary Cementing

[+] Author and Article Information
Desheng Zhou

 College of Petroleum Engineering, Xian Petroleum University, Xian, Shanxi 710065, ChinaDesheng@xsyu.edu.cn

Andrew K. Wojtanowicz

 Craft and Hawkins Department Petroleum of Engineering, Louisiana State University, 3516 CEBA, Baton Rouge, LA 70803awojtan@lsu.edu

J. Energy Resour. Technol 133(3), 031003 (Sep 06, 2011) (8 pages) doi:10.1115/1.4004809 History: Received March 15, 2007; Revised July 28, 2011; Published September 06, 2011; Online September 06, 2011

Annular pressure reduction during cementing is a major factor causing annular gas flow. It has been widely accepted and proven experimentally that the pressure reduction phenomenon results from the shear stress opposing downward motion of slurry undergoing volume reduction. The models that have been proposed to describe this process are based on the gel strength and shear stress developments in time and ignore system compressibility. They explain the pressure reduction process observed in the lab where compressibility of the system is very small. However, the models cannot explain the pressure reduction patterns observed on the field where compressibility is significant and the time-dependent effects of cement slurry volume loss significantly contributes to the process. The paper presents a mathematical model combining the effects of gel strength, volume reduction, and compressibility of cement slurry to describe pressure loss in the annular cement column. Results from the model, shown in the paper, compare very well with the data from the laboratory and field tests. Also, the simulated results explain discrepancies between the pressure loss patterns observed in the lab and field tests.

Copyright © 2011 by American Society of Mechanical Engineers
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Figure 1

Patterns of lab-measured pressure reductions during cement setting; pattern 1—[2], pattern 2—[2,21-22], and pattern 3—[2,23]

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Figure 2

Pressure reduction in time from models; pattern 1—shear-stress model [7]; pattern 2—compressibility [2], gel-strength [3-4], shear-stress [8-9,18], and Darcy flow [12] models.

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Figure 3

Field measured pressure reduction [13]

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Figure 4

Components of annular compressibility effects: wellbore contraction and casing expansions due to slurry pressure reduction and geothermal heating, and slurry expansion due to geothermal heating

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Figure 5

Comparison of calculated pressures (average compressibility model) with field measured data by Cooke [13]

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Figure 6

Depressurized (trapped pressure) slurry column

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Figure 7

Calculated depressurized section length versus time for five slurries




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