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If you were to do a slug-in test where you put in a known volume of water, would there be a point where, say if the formation was extremely permeable, the permeability of the screen itself would be measured?

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High permeability (K) values for rock /sediment would be 1x10+2 to 1x10+5 (darcy) The table below shows permeability values for sand/gravel packs placed around the well screen. Well Screen itself would have even higher K values.

I would say, that well screen itself (not including the sand and gravel pack around the well screen) will not limit the results of slut test results.

Essentially, for the well screen to limit slug test results, you need to place the well into a large cave or min void and the use a very large slug volume if you hope to measure the screen itself.

Note: Permeability values can approach very large values in limestone with caves.

Note: my answer assumes that the well construction materials and methods are known that were used to install the well being tested. I am also assuming the well has a manufactured well screen not a piece of pipe with 3 hack saw cuts to allow water to flow. Not knowing the well configuration, can reduce the accuracy of slug test results.

Permeability of Gravel-pack sands

Source: Petrowiki

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  • $\begingroup$ Could you please clarify your range for sediment permeability? I would say 12 to 15 is a rather limited value, while interpreting the +2 and +5 as exponents would mean a range of 100 to 10,000 (which seems high to me), in which case the gravel pack would be limiting in quite a lot of cases, or am I missing something? To me it seems you don't really answer the core of the question: can the well construction be limiting the slug-in test results? $\endgroup$ – hugovdberg Sep 13 '15 at 21:57
  • $\begingroup$ Yes, well construction can absolutely limit slug test results. Imagine clean gravel bed aquifer and the well is installed with a fine sand pack. Sand pack would lower the permeability. My answer addresses the question: can the well screen itself limit slug test results. My answer is no. Only way I can see the physical screen limiting slug test results would be if well casing is placed into an open void cavern or mine void and even then you would need a very large slug volume in hopes of measuring very high permeability values. $\endgroup$ – Gary Kindel Sep 14 '15 at 19:20
  • $\begingroup$ What if the 'screen' is a number of hack-saw cuts into a PVC pipe - an all too common construction in older wells around here? or if the well is completed by perforating steel casing with cutters from the inside? $\endgroup$ – haresfur Sep 15 '15 at 22:43
  • $\begingroup$ My answer and my comments assume a manufactured well screen (PVC or Steel). Having done hydrogeological consulting, I understand there can be a wide variety of well screens including hand-made screens by cutting or drilling holes into ordinary well pipe. To accuracy assess results from a slug test, you need to know the construction method used to construction the well and well materials must be known. Without this information, slug test results can still be valid but you are likely making assumptions that the well pack and screen are not limiting your results. $\endgroup$ – Gary Kindel Sep 16 '15 at 12:57

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