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Skin Factor due to Injectivity Decline Injection Well History Analysis and Interpretation . Bedrikovetsky , P., Fonseca, D. R., da Silva, M. J. (North Fluminense State University, Rio de Janeiro ) Furtado, C., Serra de Souza, A.L. & Siqueira, A.G. ( Petrobras, Cenpes ). Injectivity index

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slide1

Skin Factor due to Injectivity Decline

Injection Well History Analysis and Interpretation

Bedrikovetsky , P., Fonseca, D. R., da Silva, M. J.(North Fluminense State University, Rio de Janeiro )

Furtado, C., Serra de Souza, A.L. & Siqueira, A.G.(Petrobras, Cenpes)

slide3

Particle capture kinetics

Deposition at

core inlet

Permeability decline

Inlet plugging at

the transition time

4 deep bed filtration parameters:

λ – filtration coefficient

β – formation damage coeficient

α – critical porosity ratio

kc – external cake formation

Transition time

slide4

Impedance J – reciprocal of II

3 equations:

m(λ,β), ttrans(α, λ)

and mc(kc, λ,β, α)

1 equations is missing !!!

Proposal:

critical porosity ratio α=0.5

Mean α=0.1

  • M. Sharma, S. Pang, K. Wennberg, 1994, SPE 28489 & 1997, SPE 38181
  • Khatib, Z., 1995, SPE 28488

α_β correlation is a missing equation

  • W.M.G.T. van den Broek, Bruin, J.N., Tran, T.K., 1999, SPE 54769
  • Bedrikovetsky, P., Tran, P. , Van den Broek, et.al, 2003, J SPE PF, No 3
  • Da Silva, M., Bedrikovetsky, P., Van den Broek, W.M.G., 2004, SPE 89885
slide6

ASSUMPTIONS OF THE INJECTIVITY IMPAIRMENT MODEL

  • ·Water incompressibility
  • ·Small particle concentration -> the suspension density is equal to water density
  • ·No diffusion
  • ·Linear law for particle capture kinetics
  • ·Constant filtration coefficient
  • ·No particle penetrates after the transition time
  • Incompressible external filter cake
slide8

Injectivity damage parameters as calculated from well history

Sharma, M., Pang, S., Wennberg, K.E., 2000, J SPE P& F

Treatment of 27 routine lab test data

from SPE by the α(β) correlation

Bedrikovetsky, P., Tran, P. , Van den Broek, et.al, 2003, J SPE PF, No 3

slide9

Offshore A, Brazil

  • Contents:
  • Introduction:
  • Analytical model for injectivity impairment accounting for varying Oil-Water mobility
  • Effect of varying O-W mobility
  • Injection well impairment – prediction results
  • Conclusions
1 deep bed filtration of injected particles
1. Deep bed filtration of injected particles

Physics meaning of filtration coefficient

slide13

One Dimensional Deep Bed Filtration:

System of three equations for three unknowns

Mass balance for suspended and retained particles

Particle capture kinetics

Darcy’s law with permeability damage

slide14

1d DBF: System of three equations for three unknowns

Mass balance for suspended and retained particles

Particle capture kinetics

Introduce dimensionless radius, time, rate and concentrations

Darcy’s law with permeability damage

The dimensionless system is:

  • Iwasaky, T., 1937
  • Herzig, J., Leclerc,D. and Goff, P. 1970
  • Sharma M., et.al., 1987, 1994, 1997
slide15

1D injection of particle suspension into a “clean” core

Impedance versus time T, p.v.i.

Skin factor

During constant rate injection into an injection well during T=0.0001 pvi, pressure drop increases 5 times. Calculate the pressure drop increase for T=0.0005 pvi.

slide17

Particle capture kinetics

Permeability decline

Inlet plugging at

the transition time

Deposition at

core inlet

4 deep bed filtration parameters:

λ – filtration coefficient

β – formation damage coeficient

α – critical porosity ratio

kc – external cake formation

Transition time

slide18

M=1

M=1

M=3

M=3

M=25

M=25

Injectivity Increase During Damage-Free Waterflooding

During the particle-free water injection into a reservoir saturated by oil that is less mobile than water, the total mobility ratio increases M times due to displacement of less mobile fluid by more mobile one

The increase happens during (1-5)10-5 p.v.i.

:

slide19

Mass balance for water (Buckley-Leverett)

Darcy’s law for total oil-water flux

Total oil-water mobility accounting for

particle retention in swept zone

Mass balance for suspended

and retained particles

Kinetics of particle retention

Combined Effect of Formation Damage and Mobility Variation on Injectivity Decline

slide20

1

1

4

4

2

5

3

6

2

5

3

6

Impedance curve behaviour for M=1, 3 and 25 for high and low formation damage (curves 1,2,3 and 4,5,6 respectively); a)for time scale 0.01 p.v.i.; b) zoom for time scale 0.00001 p.v.i.

The effect is particularly significant for heavy oil reservoirs and for relatively low

formation damage

If during the short initial waterflooding stage in a heavy oil reservoir the injectivity does not change, the reservoir suffers large formation damage which will cause a significant injectivity decrease

slide21

Well AA016

Offshore A

Brazil

slide22

Well AA013

Offshore A

Brazil

slide23

Well AA002

Offshore A

Brazil

slide26

Well-history-based Injectivity Prediction

with and without varying O_W mobility effect

Shumbera, D. A. et.al, 2003, SPE 84416

Paige, R. W. et al, 1995, SPE 29774

slide27

Conclusions

  • Some injectivity index increase before the injectivity impairment is explained by displacement of more viscous oil by less viscous water from injector vicinity
  • The analytical model for injectivity impairment accounts for particle deep bed filtration, external cake formation and for varying oil-water mobility during waterflood
  • The analytical model allows determination of the injectivity impairment coefficients – filtration and formation damage coefficients, critical porosity fraction and cake permeability - from well injectivity decline curve
  • The injectivity impairment coefficients as obtained from treatment of xxx injectors vary in the same intervals as that obtained from lab coreflood
slide28

Injector A7 data were treated. Prediction. Well fracturing was anticipated

  • Acidification was anticipated in case of well A13.
  • Reservoir B is similar to reservoir A. Well injectivity was predicted.
  • Finally, it was recommended to drill 37 wells instead of 26 wells
  • Horizontal injector N23 data have been treated, and penetration radius 1/ was found to be xxx cm. Acidification was planned based on this radius. It allows to economise xxx cu m of acid
  • Vertical well N13 data have been treated, and penetration radius 1/ was found to be xxx cm. It allows recommending xxx cm depth of perforation instead of xx cm planned before