ABSTRACT
and swab pressure is very important in drilling hydraulics. Most problem in oil wells have been as a result of surge and swab pressures developed from running or pulling of goods in liquid-filled bore hole.
Excessive surge pressures can fracture the geological formation, while excessive swab can result in blowouts. In this work the analysis of steady state, laminar couette flow of non- yield power law drilling fluid model (Herschel-Bulkley) is used to compute the surge and swab in Eccentric annuli.
A slot flow model was first of all developed for a yield power law fluid in a concentric annulus, this model equation formed the basis of this work. And in solving for an eccentric annulus, the mathematical concept of conformal mapping was applied.
A suitable mathematical bilinear function was applied in mapping the original eccentric plane, for a particular eccentricity ratio, to a concentric (zero eccentricity ratio) plane.
By applying a suitable iterative technique, the various pressure values were obtained and plots of dimensionless pressures versus dimensionless flow rate or radii were made.
BACKGROUND OF THESIS
There is much relevance in the study of surge and swab in bottom hole while drilling. A surge is an increase in the bore hole hydrostatic pressure as a result of increasing velocity of the drill string down hole.
This can create a pressure that can fracture the formation, that is, if the resultant hydrostatic pressure exceeds the fracture pressure of the formation. In lowering the drill string in a mud filled hole, great care is taken so that a surge doesn’t occur.
A surge can lead to lost circulation, whereby mud used in drilling is lost into the formation. On the converse, a swab can occur while pulling out the drill string or tubular goods.
As a result of pulling, a partial vacuum is created and as “Nature abhors a Vacuum” formation fluid from the pores of the formation would take up place to replace the vacuum.
This can result to a Kick and if not controlled can result to a blowout, which is an uncontrollable outpour of formation fluid and drilling mud fluid from the hole. As a result of the phenomenon of surge and swab, great care has to be taken to prevent the adverse effects of it.
The question then becomes, what are the best ways surge and swab can be quantified? At what values of pressure is it going to fracture the formation? And also, at what values can a kick occur? And also, at what values of velocity would it be safe to lower or raise tubular goods or drill string?
These questions led to research and computational work resulting in generation of pressure profiles for different fluid models. Plots are also made using dimensionless characteristics.
With these charts it is very easy to read up a particular pressure surge value for a corresponding velocity value, and with such a value, care is taken so as not to exceed such values. These can be applied on the field.
REFERENCES
Adam , T. B et al: Applied Drilling Engineering (1986), Society of Petroleum Engineers,
Richardson Texas.Bird, R. B. et al. Transport Phenomena, (1960), JOHN WILEY & SONS Inc.
Bizanti, M.S.; Felipe, R.E.: “Are Improved Surged Models Needed?” Society of Petroleum
Engineers (1991) SPE 22057.Burkhardt, J.A.: “Wellbore pressure surges produced by pipe movement,” J. Pet. Tech. (June
1961), pp. 595-605.Canon, G.E.: “Changes in hydrostatic pressure due to withdrawing drill pipe from the hole” API
Drill and Prod. Pract. (1934) pp 42-47Chukwu, G.A.; E.F. Blick: “Surge and swab pressure model: Surge and swab pressure from
couette flow of power-law fluids through a concentric annulus,” Pet. Eng. Int’l. (Nov. 1991)Chukwu, G.A.; “Surge and swab pressure computed for couette flow of power-law fluids”, Ph.D.
Dissertation University of Oklahoma, (1989).Chukwu, G. A: “ A Practical Approach for Predicting Casing Running Speed from Couette Flow of
Non-Newtonian Power-Law Fluids” Western Regional Meeting Bakersfield, (1995) Society of
Petroleum Engineers, inc. pp. 263-268.
StudentsandScholarship Team.
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