Theoretical study of skin effect on multilevel slug tests in highly

permeable aquifer

指導教授 : 陳家洵 老師報告者 : 謝頤祥報告日期 : 2011.06.09

Damaged Zone Around a Well

Damaged zone

Damaged zone

What is Skin Effect?

• A damaged zone caused by drilling mud invasion is less permeable than the native aquifer;

Kskin < Kaquifer as for “positive” skin.

• A damaged zone caused by overdevelopment is more permeable than native aquifer;

Kskin > Kaquifer as for “negative” skin.

• Neglecting the skin effect results in over- or under-estimate of aquifer hydraulic conductivity.

(I) Finite Thickness Skin Zone, K1, SS1, and r1

ls, test interval lengthb, aquifer lengthrw, radius of wellr1, radius of skin

(II) Infinitesimal Thickness Skin Zone, Skin Factor (Sk)

ls, test interval lengthb, aquifer lengthrw, radius of well

Skin Effect

Positive Skin : Negative Skin :

SS1 Sensitivity in Confined Aquifer

SS1 Sensitivity in Confined Aquifer

SS1 Sensitivity in Unconfined Aquifer

SS1 Sensitivity in Unconfined Aquifer

Same Results from Two Models (Confined Aquifer with Positive Skin)

Same Results from Two Models(Confined Aquifer with Negative Skin)

Same Results from Two Models (Unconfined Aquifer with Positive Skin)

Same Results from Two Models (Unconfined Aquifer with Negative Skin)

Conclusions

• The influence of SS1 is negligible as skin zone thickness is relatively small.

• Infinitesimal skin approach is valid for both positive and negative skin effects, and can replace the finite thickness model.

Future Work

• To investigate partially penetrating effects under negative skin on MLST response.

• To estimate the skin factor from field pumping tests.

Thanks you for your attention