13) Single Well Tests

slug test __ and bail test __

slug raises water level

bail lowers water level

characteristics of single well tests

cheaper, quicker

less personnel and equipment

poor estimation of S

small sample area of aquifer

no pump required

better for high K than low K

can have smearing or clay build up around well screen

what is the hvorslev method

water is added or withdrawn, or adding solid metal (slug) to represent water volume

used to determine K

only applied to below the water table

gravel is used to fill open area between well screen and wall of open hole
R = radius of bore hole/screen, r = radius of standpipe/well opening at surface, L = length of gravel pack

similar to falling head permeameter test

how to do hvorslev method

pick any two values from straight line and place in equation

can also take H/H0 = 1 at t=0 and H/H0 = 0.37 at t=T0 and use time lag equation

time in not logged in this one, it’s displacement or normalized displacement

little t = time elapsed since displacement

overview of bouwer-rice method

same idea as hvorslev

assumes storage is negligible, used for unconfined, adapted for confined

overview on cooper-bredehoeft-papadopulos (CBP) method

includes influence of storage for tests on fully penetrating wells in confined aquifers

critique: cannot use for unconfined or partially penetrating wells

overview of kansas geological survey methods

≥3 slug tests per well, ≥2 initial displacements

be quick when introducing water

summary of single well response tests

all can estimate K or T

all work with confined

all except CBP work for unconfined and partial wells

CBP&KGS estimate S or Ss

Hvorslev and KGS work for anisotropy

procedure for single well test

obtain construction details of well

quickly raise or lower water level by known amount
metal slug, bail water, or pressurize by air injection

monitor water level response, may take few seconds to a year

repeat steps 2-3 at least two more times

choose appropriate analysis method and plot data accordingly (typically H/H0 against t in some fashion

use method to estimate K (or T) and S if applicable

True or false: in two identical wells in different geologic materials, when conducting a slug test, the well with the higher hydraulic conductivity will reach eqlm more quickly than well with lower hydraulic conductivity

true, adding or removing water it will alwayds reach eqlm faster in higher conductivity

what are complicating factors that can affect interpretation of single well response tests

underdamped response

skin effects

filter pack vs screen size

partially submerged screens

how will underdamped response affect single well tests

in high permeable materials, the water level may oscillate due to inertial effects

how will skin effects affect single well tests

zone of alteration around the well = wellbore skin

positive skin effect: reduction in K around wellbore
clay smearing, clogging of filter pack with drilling mud, biofouling

negative skin effect: increase in K around wellbore
fracturing during drilling

how can filter pack vs screen size influence single well tests

in fine-grained materials, wells are constructed with a sand filter pack around well screen

high K sand pack will respond much quickly than the lower K formation material

the test measures the K of the material in the sand pack, which won’t represent true properties of formation
dimensions L and R should be taken from sand pack, not screen

how will partially submerged screen affect single well tests

in unconfined aquifers, static was level can be located within the screened interval or be lowered into the screened interval during testing

we should avoid partial submergence

the sand pack will fill or drain at a different rate than the formation material and result in a multistage water level response

which test should be used for confined, ideal in transient, with S and T provided

theis
cooper jacob
CBP

which test should be used for confined ideal, steady state, only T provided

thiem

which test should be used for confined, leaky, transient state

neuman and witherspoon
hantusch-jacob

which test should be used for unconfined transient state? unconfined steady state?

transient: neumann

steady state: modified theim

which test should be used for confined, ideal, transient state, K provided

hvorslev (short screen well)
CBP
bouwer and rice (top of well screen is deep enough)

which test should be for unconfined, K provided

bouwer and rice
hvorslev (if well screen is some distance below water table)

list of multi-well tests

theis
cooper jacob
CBP
thiem
neumann
hantusch jacob

list of single well tests

hvorslev
CBP
bouwer and rice