04_3- Mud Erodibility Technology

8/13/2019 04_3- Mud Erodibility Technology

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Mud Erodibility Technology -

Impact on Cementing

Operations


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Beirute Consulting, L.L.C. 2

Large Scale Experiments Have

ShownGelationplusdehydrationof the mud across

permeability is one of the main causes of

mud displacement (removal) problems


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Large Scale Experiments Have

Shown (cont.) Extended shutdowns:very detrimental to

the hole cleaning (circulatable hole) process

Age: of the Partially Dehydrated-Gelled

(PDG) mud: very detrimental

Removal of the PDG:Requires energy


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Vertical Hole - Large Scale

Experiments

PDGFormation

CementCasing


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Inclined Hole - Large Scale

Experiments

PDG and

settled

solids


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7/41Beirute Consulting, L.L.C. 7

Next StepStudy mechanism of mud cake deposition

and erosion with the goal of developing

better means for improved removal



Objectives Build an experimental setup to study the

mechanism of mud deposition and removal

Develop a mathematical model

Recommend procedures for field operations



Model about 20+ ft long



Experimental Procedure Day 1:

Water calibrationin turbulent flow

Mud calibration:2, 4 BPM - No filtrate collected

Mud circulation:1 BPM, 1hrFiltrate collected

Mud circulation:3 and 5 BPMFiltrate collected

Shutdown,18 hrs, 100 psi differential



Experimental Procedure (cont.) Days 2 and 3:

Mud circulation at 1 BPM to near steady-state

Same as above at 2, 3 and 5 BPM

Shutdown with 100 psi differential



Experimental Procedure (cont.) Day 4:

Same as day 2

Spacer fluid pumped

Cement slurry pumped

Model cured for 48 hrs

Later: Model cut in sections

Observations made

Pictures taken


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Tests Results - Example


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PDG Thickness vs. TimePDG Thickness (in)

Rate (bpm) Day 2 Day3 Day5

~1 0.4 0.44 0.415

~2 0.37 0.40 0.41

~3 0.338 0.373 0.402~5 0.335 0.375


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Important Conclusions Rate (wall shear stress) is needed to

remove the PDG

Extremely high ratescan be detrimental

to the PDG removal process

The olderthe PDG, the harder it is to

remove it


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Proposed Mechanism

Opposing Forces: Differential pressure against permeability causes the

deposition of filter cake and PDG

Erosion by flowingfluid tends to removethe PDG

PDG drilling fluid and filter cake are eroded aslong as pressure drop (wall stress)in the

annulus exceeds a certain value

Shear stress at the wall:hydrodynamic forceresponsible for the erosion

Adhesion forces:resistance to erosion


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Proposed Mechanism (cont.) Erosion takes Place for as long as the

shear stress at the wall (point of contact

between the flowing fluid and the static

PDG or filter cake) exceeds the yield

stress of the PDG or filter cake.


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Can the stress of the PDG be inferred from normally

reported mud properties?

Compare

magnitude

of the

values


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Conversion Factor

Wall Shear Stress and Friction Pressure

relationship: = Dex P/4L

Wall Stress (lb/100 ft2) =

300x De(in) x P (psi)/(4 x L (ft))

P (psi) =

Wall Stress (lb/100 ft2) x L (ft)/ (300x De (in))


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Lab Work

Since stress levels of the PDG need to be

measured in the labto be able to design

jobs to effectively erode the PDG. Then:

Develop and test erodibility cell

Test erodibility of muds

Design rates and spacer properties to

erode PDG and filter cake


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Large Scale Test Cell


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PDGs of Different Muds

Over all, PDGs of oil base, MOBM andSOBM have been found to be thinner and

easier to remove that those generated by

water base muds. Levels: ~ 25 lb/100ft2 Worst PDGs are those generated by

poor quality water base muds:poor fluid

loss control, progressive gels, etc. Levels:as high as 100 + lb/100ft2


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Using a Simulator and lab

Measurements to Better Design

Cement Jobs


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Documents

04_3- Mud Erodibility Technology