Study Findings

Recommended Range of KPIs


Addressed efficient milling techniques and suggested pre-job computer modeling to predict achievable plug milling depth and circulating pressure to improve the cleaning operation’s efficiency.

Wiper trip speeds range from 35 to 50 ft/min.


Highlighted the importance of millability tests. The authors highly recommended milling at least two plugs to allow for a more realistic evaluation of a composite plug milling performance.


Indicated the importance of closely analyzing mill bits, motors, and plug designs. The study emphasizes the significance of utilizing a fluid monitoring and controlling system to reduce milling time, Coil tubing fatigue stresses, and cost.

Typical AV = 175 ft/min

Re > 11,500

Linear gels with 25 - 30 cp

AV = 300 ft/min

Return rate of 3 bbl/min

for 2-3/8” CT and 5” casing


Eliminated short rips and produced cleaner wellbores by revising and changing the fluid quality assurance and controls (QA/QC) assessments, the selection of BHA design, and coil tubing selection. The new engineering approach resulted in a significant reduction in time and cost.

AV increased from 143 to 203 ft/min

Short trip decreased from 4 to 1

Time reduced from 72.2 to 25.1 hours

Slick water viscosity decreased by 21%

Reynolds Number increased by 50%


Remodeled downhole design and fluid system and made coil tubing drillout a more effective process by optimizing CT string, using low and high loadings of low shear rate viscosity fluid to effectively clean lateral and vertical sections of the wellbore during POOH, respectively.

Viscosity in the range of 5 to 15 cp provided maximum solids suspension for 2.375” CT and 7” casing at 45˚


Used state-of-the-art bridge plugs to equalize high-pressure formations. When crossflow while perforating risk is present, the flow-through flow plugs (FFTFPs) should only be set where the pressure above is higher than the pressure below. The authors recommended using nitrified fluid when milling composite plugs set above the under pressures zone to reduce the risk of CT stuck incident due to lost circulation.

Circulation rate ranged from 2.1 - 2.7 bbl/min


Utilized non-viscous fluids to better clean the wellbore. The method showed a substantial reduction in time and cost. The authors acknowledged that for a successful cleaning operation, the implementation of new techniques and technology should be proceeded by formal training and communication.

Optimum fluid viscosity of 1 cp Reynolds number ranged from 46,174 to 60,026

Circulation rate range of 3.0 to 3.9 bbl/min)

for 2-3/8” CT and 5.5” casing


Used CT with a larger diameter to improve milling performance. The authors recommended single trips when possible but urged engineers and coil tubing operators to be vigilant of changing well conditions. The study concluded that wiper trips could be reduced but never eliminated due to changing well conditions.

For optimum transport efficiency,

Re > 20,000

AV > 175 ft/min

Fluid viscosities < 4 centipoise

for 2” CT and 4.5” casing


Developed a new milling fluid system and summarized the optimum ranges of penetration rate, set-down force, and differential pressure across positive displacement motor in deep retrograde gas condensate type of reservoirs.

Optimum circulation of 1.2 bbl/min AV of 205 ft/min lifted milling cuttings in annular space between 1.75” CT and 3-1/2” production tubing.


Explained that to reduce drilling time, improve economics, minimize risks, and reduce CT system fatigue, increasing the number of blades by using five to six-blade instead of three-blade PDC bit outperformed the other tested bits. The five- to six-blades bit minimized debris size, reduced stuck pipe risks, motor stall incidents, drillout time, and improved well production.