Visualization of Fluid Flow Into a Perforation Tunnel –Jeremy Harvey Philip Kokel David AtwoodJeremy Harvey, Philip Kokel, David Atwood

Outline Introduction Discussion of laboratory apparatus and tests

Axial vs radial flow– Axial vs. radial flow– Open Tunnel Length

Fluorescent Dye FlowCFD di ti– CFD predictions

– Radial Flow– Axial Flow

Simulated Drilling Damage– Simulated Drilling Damage– Permeability Heterogeneity– Stress Frame FlowF t W k d C l i Future Work and Conclusions

Introduction• An efficient flow visualization method has been needed for Section IV testing to answer some fundamental questions

– Where does the flow actually occur in the core? With axial and radial?– Is the flow symmetric?– Is the permeability uniform?

• Several “oil-based solvent” dyes have been identified– Typically available in powdered form which dissolves with OMS– Several colors available allowing for a potential of different optionsA ill b h d fl di l t f t i th d lt• As will be shown, dye flow displacement front is the end result– Displacement front moves over time even for a steady flow (pressure contours and streamlines are not changing)– Can be misleading without proper interpretation– CFD simulation highly encouraged

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Laboratory Testing (Section IV)

Radial Flow

CorePore Pressure(applied along OD and far end of core)

Conventional modelProposed model

• Conventional model: crushed zone impairment (kc/K<1, tc>0) along an otherwise productive tunnel

• Proposed model: partially productive tunnel length with minimal crushed zone impairment (Kc/K=1 0 and/or tc=0)impairment (Kc/K 1.0 and/or tc 0)

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Open Tunnel Length

• Visual observation of the “open” ptunnel length vs. the max DoP (l/L)

• Remarkable correlation with CFE suggesting that the flow is entering th t l l l th l th the tunnel only along the open length and without any crushed zone impairment

• A few outliers (circled) were repeated A few outliers (circled) were repeated with dye flow– l/L moved onto the main trend line– Visual observation of l/L was not

dadequate• Dye flow visualization needed to

confirmed the l/L observation

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CFD Predictions• Displacement front evolves until it reaches

the tunnelDye can be observed at outflow indicating • Dye can be observed at outflow indicating time required to “break-through”

• Stopping flow at break-through does not provide a clear picture of productive lengthprovide a clear picture of productive length– Flow an additional 40% longer

• Longer flow only slightly alters displacement front

• Eventually entire pore volume will be displaced but may take 100s of pore volumesSame as above but with a

shorter open tunnel length

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CFD Predictions• Dye displacement front should match CFD

simulations when actual tunnel geometry and permeability are modeledpermeability are modeled

• This comparison was made with a core with a CFE=1– Brighter region is where dyed OMS has flowedg g y– Entire tunnel is producing

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Radial Flow• Effect of not flowing vertical and stopping flow

too soon can be seen in first two imagesThird image provides a clear boundary that is • Third image provides a clear boundary that is symmetric

• Three tunnels were shot with dynamic underbalance with increasing amplitude

CFE=0.1; l/L=0.1

underbalance with increasing amplitude and/or duration– Increasing open tunnel length is evident with dye– CFE~l/L

CFE=0 61; l/L=0 62CFE=0.61; l/L=0.62

CFE=1; l/L=1

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Axial Flow• Dynamic underbalance tests

– Radial flow during perforation– Axial flow for dye flowDi l t f t ti t d t • Displacement front continues to advance past transition to open tunnel– ~1 pore volume of flow will displace everything– Need to stop flow as soon as dye is detected at Need to stop flow as soon as dye is detected at

outflow to get reliable indication of open tunnel length

• Attempted to make some evaluation of tunnel fill permeabilityfill permeability– Inconclusive; Kfill<=K

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Simulated Drilling Damage• Used 6” length of Carbon Tan (~20 mD) to

simulate drilling damage with 12” of Berea (~120 mD)DUB t ll d h th t t l • DUBs were controlled such that open tunnel length would be a) entirely within the simulated drilling damage and b) extending past the drilling damage

A

p g g• Test A: path of least resistance was through

much lower perm core into open tunnel– No apparent flow through Berea

• Test B: path of least resistance is entirely through Berea into tip of clean tunnel– Tunnel appears to be visibly clean along entire

lengthB length

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Permeability Heterogeneity• Torrey Buff Sandstone• K~0.95 mD• Repeat of identical test with 2670 psi

• Indiana Limestone• K~1.5 mD

• Repeat of identical test with 2670 psi DUB, 98 ms recovery

• Initial test produced CFE=0.93 (no dye flow)Thi d d CFE 0 2• This test produced CFE=0.27

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Permeability Heterogeneity• High Perm Carbonate• K~200 mD; from same formation

with typical perms of 1.5 mDf• Previous dye viz suggests significant

heterogeneity• CFE~1 even though large zone at

base of tunnel without any apparent flow

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Stress Frame Flow

• Predictions for stress frame block flow using CFD• No-flow at square corners? Is this some strange artifact of No flow at square corners? Is this some strange artifact of

the CFD?• 2D pressure gradient would need to be zero

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Conclusions and Future Work

• Dye flow visualization provides an efficient and valuable experimental tool for flow lab testingy p p g• Direct evidence of qualitative measures of flow:

– Flow asymmetry– Permeability heterogeneity

• Direct evidence of quantitative measures of flow:– Open tunnel length– Effect of drilling damage

Other applications yet to be developed– Other applications yet to be developed

• Future uses: drilling damage using drilling and completions fluids– Multiple dye colors: red dye in drilling fluid, blue in pore fluid

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