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Experimental Study of Formation Damage during Underbalanced-Drilling in Naturally Fractured Formations

Salimi, Siroos; Ghalambor, A
Journal article, Peer reviewed
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URI
http://hdl.handle.net/11250/2358230
Date
2011
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  • Institutt for geovitenskap og petroleum [1835]
  • Publikasjoner fra CRIStin - NTNU [19736]
Original version
Energies 2011, 4(10):1728-1747   10.3390/en4101728
Abstract
This paper describes an experimental investigation of formation damage in a

fractured carbonate core sample under underbalanced drilling (UBD) conditions. A major

portion of this study has concentrated on problems which are often associated with UBD

and the development of a detailed protocol for proper design and execution of an UBD

program. Formation damage effects, which may occur even if the underbalanced pressure

condition is maintained 100% of the time during drilling operation, have been studied. One

major concern for formation damage during UBD operations is the loss of the underbalanced

pressure condition. Hence, it becomes vital to evaluate the sensitivity of the

formation to the effect of an overbalanced pulse situation. The paper investigates the effect

of short pulse overbalance pressure during underbalanced conditions in a fractured chalk

core sample. Special core tests using a specially designed core holder are conducted on the

subject reservoir core. Both overbalance and underbalanced tests were conducted with four

UBD drilling fluids. Core testing includes measurements of the initial permeability and

return permeability under two different pressure conditions (underbalanced and

overbalanced). Then the procedure is followed by applying a differential pressure on the

core samples to mimic the drawdown effect to determine the return permeability capacity.

In both UBD and short pulse OBP four mud formulations are used which are: lab oil, brine

(3% KCL), water-based mud (bentonite with XC polymer) and fresh water. The return

permeability measurements show that a lab oil system performed fairly well during UBD

and short OB conditions. The results indicate that a short overbalance pressure provides a significant reduction in permeability of the fractured formations. In most tests, even

application of a high drawdown pressure during production cannot restore the initial

permeability by more than 40%.
Publisher
MDPI
Journal
Energies

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