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Single Well Tests
tests on individual wells
| Question | Answer |
|---|---|
| Slug test | H2O level in w. displaced away from its static or position (hs). “slug test” raises H2O level & “bail test” lowers H2O. H2O level (h) in w. monitored w/ t as it recovers to its original static position. rate of response used estimate K around well |
| Hvorslev Method | Ho = ho - hs = initial h2o level displacement H(t) = h - hs = water level displacement at t |
| Bouwer-Rice Method | assumes storage is negligible |
| Cooper-Bredehoeft-Papadopulos Method | includes influence of storage for tests on fully penetrating wells in confined aquifers |
| What are some critiques of the CBP method? | storativity estimates have limited reliability assumes: • data from unconfined aquifers or p.p wells should be analyzed w/ caution • errors associated w/ p.p. wells are typically small relative to other sources of error in the test method |
| Kansas Geologigcal Survey Methods | account for affects such as formation storage and partial penetration in both confined & unconfined aquifers |
| What is the procedure for a single well test? | 1. Obtain details of well. 2. raise or lower h2o level, known amount. (fast); slug; bail 3. Monitor the h2o level response. (sec to yrs) 4.Repeat 2 & 3 2 more times 5. Choose method & plot your data 6.find K (or T) and S (if applicable). |
| What are some complicating factors that can affect the interpretation of single well response tests? | underdamped response skin effects filter pack vs. screen size partially submerged screens |
| what is an underdamped response? | For highly permeable materials, the water level in the well may oscillate due to inertial effects. Reliable estimates of aquifer properties can still be obtained |
| what are skin effects? | zone of alteration around well; can influence how the well responds during test & affect interpretation of test results positive or negative |
| positive skin effect | reduction in K around the wellbore • e.g., clay smearing, clogging of filter pack with drilling mud, biofouling |
| negative skin effect | increase in K around the wellbore • e.g., fracturing during drilling |
| what is filter pack vs screen size? | fine-grained materials, wells often constructed w/ sand filter pack around the well screen. High K sand pack respond much quicker than the lower K formation material. Response test partially measures K of sand pack =! true properties of formation |
| what are partially submerged screens? | In unconfined aquifers, the static water level can be located w/in the screened interval or be lowered into the screened interval during testing sand pack will fill or drain at a diff. rate than formation material = multistage water level response |
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