U.S. Department of the Interior

U.S. Geological Survey

 Fact Sheet 2008-3098

 December 2008

Florida Integrated Science Center

Borehole Geophysical Logging Program:

Incorporating New and Existing Techniques in 

Hydrologic Studies

Printed on recycled paper

Overview

The borehole geophysical logging program at the U.S. 

Geological Survey (USGS)-Florida Integrated Science Center 

(FISC) provides subsurface information needed to resolve 

geologic, hydrologic, and environmental issues in Florida. The 

program includes the acquisition, processing, display, interpretation, and archiving of borehole geophysical logs. The borehole 

geophysical logging program is a critical component of many 

FISC investigations, including hydrogeologic framework studies, 

aquifer flow-zone characterization, and freshwater-saltwater 

interface delineation. 

New Borehole Geophysical Logging Capabilities 

in Florida

In addition to acquiring standard borehole-log information 

such as caliper, gamma, spontaneous potential, and electromagnetic induction data (table 1), FISC utilizes new technologies and 

procedures to generate advanced logs. Of particular importance 

are digital borehole imaging and electromagnetic flowmeter logging, both of which are now used to augment existing techniques.

Digital borehole optical televiewers equipped with a highresolution cameras can create detailed, 360-degree images of 

borehole walls and simultaneously collect borehole deviation 

data. The digital borehole images can be used to (1) accurately 

determine the depths for a well completion interval, (2) position 

a recovered core to its proper depth, (3) acquire a high-resolution 

borehole image that serves as a surrogate for intervals having 

no core recovery (Ward and others, 2003), and (4) characterize aquifer pore systems. Fracture and bedding plane orientations can also be determined, because borehole images can be 

oriented to magnetic north. In combination with a new digital 

log acquisition system, a digital borehole image can be acquired 

at relatively high logging speeds (about 3-15 feet per minute, 

depending on desired pixel density). Various log presentation 

software can be used to display these images, as well as standard 

logs on multilog-paper displays up to 36 inches wide. A digital 

copy of the display can be viewed on a computer using nonproprietary software readers.

To address difficulties in accurately quantifying relative transmissivity in aquifer flow zones, FISC is now using 

an electomagnetic flowmeter to accurately measure flow at 

intermediate velocities. Previously, heat pulse flowmeters and 

spinner flowmeters were solely used to measure flow across all 

velocities. Heat pulse flowmeters, however, can only measure 

low-velocity flow and do not generate continuous logs. Spinner 

flowmeters adequately measure high velocity flow and generate 

continuous logs, but quantifying the amount of flow from spinner revolutions is time consuming and difficult. The electromagnetic flowmeter accurately measures medium flow velocities, 

generates a continuous log of flow velocity and direction, and 

can make stationary measurements like the heat pulse flowmeter. 

The logs generated by the electromagnetic flowmeter can help 

show the relative transmissivity of flow zones within a well. A 

fluid meter built into the tool also displays changes in temperature and fluid resistivity, which also aids in the identification of 

flow zones. 

Although most borehole geophysical log acquisition is 

performed from a vehicle, equipment portability also allows 

easy transport to remote well sites, such as those in offshore 

marine or wetland environments. Wells up to 3,200 feet deep and 

greater than 2 inches in diameter can be accommodated, providing access to all major aquifers in Florida, including much of the 

Floridan aquifer system. 

FISC Hydrologic Investigations Employing 

Borehole Geophysical Logging Techniques

Geophysical logs run in exploratory or investigative boreholes can provide valuable hydrogeologic information, especially in areas with poor lithologic and (or) hydrologic control. 

Geophysical logs also can provide much needed information to 

help in determining the correct placement of well completion 

depths or intervals. The acquisition of borehole geophysical logs 

can become the determining factor in solving complex subsurface issues. The following studies highlight new and existing 

techniques used by FISC to resolve geologic, hydrologic, and 

environmental issues.

Hydrogeologic Framework Studies

Partially recovered core samples typically can only be placed 

within a 5- to 10-foot range of core barrel depth. Placement 

of core material or recognition of void space within these poor 

recovery intervals is often difficult using examination of the core 

and standard borehole geophysical methods. With the aid of a 

digital optical borehole image log, a trained user can accurately 
reconstruct core sample depths (Ward and others, 2003) and use 

image log data to aid in pore-type characterization (including 

large cavities) for both intervals with and without recovered core. 

Cunningham and others (2004a, b; 2006a, b) used digital images 

to identify lithology, pore type, and zones of concentrated groundwater flow to show the connection between stratigraphy and the 

development of porosity and permeability within the Biscayne 

aquifer. Further study led to the development of a multilayer, conceptual hydrogeologic framework for the Biscayne aquifer along 

the Everglades-Urban corridor (Lake Belt area) in northwestern 

Miami-Dade County (Cunningham and others, 2006a).

Digital optical borehole imagery was used in combination 

with core data to construct stratigraphic sections that show the 

areal extent of macroporous flow zones within the Miami-Dade 

Northwest Well Field (Renken and others, 2005; 2008). Tracer 

tests conducted during 2003-04 at the well field demonstrated the 

continuity of touching-vug flow zones and the potential for rapid, 

long-distance chemical and colloidal transport within the Biscayne 

aquifer (Shapiro and others, 2008; Harvey and others, 2008). Digital optical borehole imagery was used to determine the dimensions 

of macropores, and was also used with core data to develop hydrostratigraphic cross sections to help show the connectivity of macroporosity between wells. Previous studies may have underestimated 

the porosity, as well as the areal extent of macroporosity.

Aquifer Flow-Zone Characterization

Borehole fluid temperature and conductivity logs collected 

during one of the Miami-Dade Northwest Well Field tracer tests 

have been used to illustrate well-to-well tracer movement within 

preferential flow zones (Cunningham and others, 2006b; Renken 

and others, 2008). Observation well borehole fluid temperature 

logs were used to show that a single flow zone constitutes the 

dominant horizon for well-to-well hydraulic interconnection and 

for the migration of most of the tracer mass (fig. 1). The observed 

monotonic increase in temperature with depth shortly after injection 

(1252 hours) suggests that conservative tracers traveling within the 

shallow flow zone approximately 41 feet below land surface arrived 

at the observation well prior to tracers traveling within touching-vug 

pore zones at greater depths (Renken and others, 2008). 

Table 1. Available geophysical logs for use in FISC research.

[cps, counts per second; EM, electromagnetic; FISC, Florida Integrated Science Center; ft/min, foot per minute; gal/min, gallon per minute; PVC, polyvinyl chloride]

Geophysical 

logging tool 

and log type

Tool use Interpretive value 

of log

Borehole deviation Measures deviation of borehole from vertical. Used as input for calculation of true vertical depth.

Borehole fluid

Generates logs of water-quality properties that include 

the following: borehole fluid temperature, resistivity, 

conductivity, specific conductance, salinity, pressure, 

redox, dissolved oxygen concentration, and pH.

Identification of ground-water flow zones penetrated by the 

borehole and sources of incoming water.

Caliper Measures borehole diameter, using mechanical, threearm, or high-resolution acoustic caliper. 

Determination of cavity size and geometry.

Digital, optical and 

acoustic borehole 

image

Televiewer creates digital, optical and acoustic images 

of borehole wall or casing. 

Used to reference core to original depth, detect cavities, faults, 

and fractures, as well as characterize pore systems. Optical and 

acoustic log types can be aligned to magnetic north and exported 

in BITMAP format.

Electromagnetic 

induction

Measures formation conductivity in both cased and uncased wells. Produces a formation resistivity log using 

the inverse relations with conductivity. 

Determination of depth to freshwater-saltwater interface in boreholes. Help identify zones of ground-water flow.

Flowmeter

Measures vertical fluid flow within a borehole. Measures flow under both ambient and pumping conditions. 

Tool choice is based on fluid flow velocity: (1) heat 

pulse flowmeter (units in gal/min) for flows less than 

1.5-0.03 gal/min, (2) spinner flowmeter (units in cps) 

for flows greater than 6.5 ft/min, and (3) EM flowmeter 

(units in gal/min or ft/min) measures a wide range of 

flow velocities (0.01-10.6 gal/min).

Identification of ground-water flow zones penetrated by the borehole and determination of relative transmissivity of flow zones.

Full waveform sonic

Measures acoustic wave travel time through borehole 

fluid and the surrounding rocks. Post processing creates 

compressional, shear, and Stoneley-wave logs. 

Compressional velocity logs are used to create a sonic porosity 

log with either the Raymer-Hunt or Wylie equations. Stoneleywave amplitude log is used to estimate permeability. Additional 

processing yields cement bond logs, as well as logs showing various engineering properties, and synthetic seismic wiggle traces.

Natural-gamma Measures gamma radiation of natural radioisotopes in 

surrounding formation (output is in cps). 

Correlation of lithologic units between wells.

Spontaneous potential and single-point 

resistance

Measures the natural potential that originates from electrochemical differences between borehole and formation 

fluids at lithologic boundaries. Requires an open borehole.

Used to infer lithologic changes. Single-point resistance log can be 

used to detect sections of slotted casing in completed wells.
High-resolution heat pulse, electromagnetic, and spinner 

flowmeters are routinely used by FISC scientists to measure 

vertical fluid flow within a borehole over a wide range of flow 

rates and under both ambient and pumping conditions. Borehole 

flowmeter measurements have been used to identify permeable 

flow zones in the Biscayne aquifer (Cunningham and others, 

2004a; 2006a), and assess vertical hydraulic gradients. Flowmeter measurements combined with data from digital borehole 

images and fluid-temperature and conductivity logs can be used to 

accurately evaluate and characterize flow zones within the context 

of a high-resolution conceptual hydrogeologic framework (fig. 2). 

As an example, Cunningham and others (2004b) used ambient 

flowmeter and borehole fluid-temperature and conductivity logs to 

hypothesize sources of ground-water recharge. Data from flowmeter and borehole-fluid logs collected in seven wells along an 

8-mile reach of the L-31 Canal in Miami-Dade County were used 

to identify sections that were consistent with aquifer recharge by 

surface water from Everglades National Park. Horizontal flowmeters were also placed within preferential flow zones of the 

Biscayne aquifer identified by digital borehole images during this 

study (Cunningham and others, 2004b) as part of a continuous 

ground-water monitoring program operated by the South Florida 

Water Management District. The real-time flow data (which 

are still being analyzed) from these horizontal flowmeters show 

variable ground-water flow directions and rates. These data, along 

with data from Cunningham and others (2004b), were later used to 

further hypothesize that nearby ground-water pumpage in excess 

of the permitted allotment was also influencing recharge. 

Freshwater-Saltwater Interface Delineation

Electromagnetic induction logs have been used to obtain 

detailed vertical profiles of the conductivity of the aquifer 

around each well, and used in combination with surfacegeophysical methods and chloride concentration data, to map the 

position of the saltwater interface in southeastern Florida (Hittle, 

1999). Detection and monitoring of the saltwater front through 

induction logging in cased wells over time is an ongoing effort 

by the USGS and State, county, and municipal cooperators. The 

induction logging tool measures the bulk electrical conductivity of rock and pore fluids to delineate lithology, porosity, and 

fluid salinity within open and polyvinyl chloride (PVC)-cased 

boreholes. Within these casings, this logging tool can measure 

changes in the dissolved-solids concentration of pore fluid over 

time. Data collected from USGS monitoring wells as part of 

the ongoing induction logging program indicate that interface 

movement is irregular within the vertical section of the well, and 

possibly related to differential lateral movement of brackish to 

saline water within zones of higher permeability (fig. 3). 

Figure 1. Temporal change in borehole 

temperature caused by the migration of a tracer 

within a touching-vug flow zone at a depth of 

41 feet below land surface in an observation 

well (modified from Renken and others, 2008). 

Tracer injection occurred at 0930 hours. Fluid 

temperature log at 1252 hours was not completed 

because the top of the logging tool was lodged 

against the casing bottom.

Figure 2. Comparison of borehole image, computed vuggy porosity, 

geophysical, and flowmeter logs for the G-3788 test corehole showing 

evidence of water outflow from the borehole into a preferential flow 

zone. Abbreviation μS/cm is microsiemens per centimeter.

22 Degrees Celsius 24

DEPTH, IN FEET BELOW LAND SURFACE

Caliper log

0 20 Inches

Digital

borehole

image

Fluid temperature change

through time

30

35

40

45

50

55

60

65

0930

1252

1433

1538

1640

EXPLANATION

Computed

vuggy

porosity

(percent)

Digital

borehole

image Fluid

conductivity

(μS/cm)

Fluid

temperature

(degrees

Celsius)

Ambient

heat-pulse

flowmeter

(liters per

minute)

500

31.7

Fort Thompson Formation

Biscayne aquifer

Geologic unit

Hydrogeologic unit

DEPTH BELOW LAND SURFACE , IN FEET

Upward outflow

Caliper

(centimeters)

0 100 0 50

29.4

300 -2.0

Downward outflow

32

34

36

33

35

+2.0
References Cited

Cunningham, K.J., Carlson, J.L., Wingard, G.L., Robinson, E., 

and Wacker, M.A., 2004a, Characterization of aquifer heterogeneity using cyclostratigraphy and geophysical methods in 

the upper part of the Biscayne aquifer, southeastern Florida: 

U.S. Geological Survey Water Resources Investigations Report 

03-4208, 66 p. (Also available online at http://sofia.usgs.gov/

projects/aq_heterogeneity/)

Cunningham, K.J., Wacker, M.A., Robinson, E., Gefvert, C.J., and 

Krupa, S.L., 2004b, Hydrology and ground-water flow at Levee 

31N, Miami-Dade County, Florida, July 2003 to May 2004: 

U.S. Geological Survey Scientific Investigations Map I-2846, 

1 pl. (Also available online at http://sofia.usgs.gov/projects/

seep_mgmt/)

Cunningham, K.J., Wacker, M.A., Carlson, J.L., Robinson, E., 

Dixon, J.F., and Wingard, G.L., 2006a, A cyclostratigraphic and 

borehole geophysical approach to development of a three-dimensional conceptual hydrogeologic model of the karstic Biscayne 

aquifer, southeastern Florida: U.S. Geological Survey Scientific Investigations Report 2005-5235, 69 p., plus appendixes. 

(Also available online at http://pubs.usgs.gov/sir/2005/5235/)

Cunningham, K.J., Renken, R.A., Wacker, M.A., Zygnerski, M.R., 

Robinson, E., Shapiro, A.M., and Wingard, G.L., 2006b, Application of carbonate sequence stratigraphy to delineate porosity, 

preferential flow, and advective transport in the karst limestone

of the Biscayne aquifer, SE Florida, USA, in Harmon, R.S., 

and Wicks, Carol, eds., 2006, Perspectives on Karst Geomorphology, Hydrology and Geochemistry—A Tribute Volume to 

Derek C. Ford and William B. White: Geological Society of 

America Special Paper 404, p. 191-208.

Harvey, R.W., Metge, D.W., Shapiro, A.M., Renken, R.A., 

Osborn, C.L., Ryan, J.N., Cunningham, and Landkamer, L., 

2008, Pathogen and Chemical Transport in the Karst Limestone of the Biscayne Aquifer: 3. Use of microspheres to 

estimate the transport potential of Cryptosporidium parvum

oocysts: Water Resources Research, v. 44, W08431, 

doi: 1029/2007WR006060. 

Hittle, C.D., 1999, Delineation of saltwater intrusion in the 

surficial aquifer system in eastern Palm Beach, Martin, and 

St. Lucie Counties, Florida, 1997-98: U.S. Geological Survey 

Water-Resources Investigations Report 99-4214, 1 sheet.

Renken, R.A., Shapiro, A.M., Cunningham, K.J., Harvey, R.W., 

Metge, D.W., Zygnerski, M.R., Osborn, C.L., Wacker, M.A., 

and Ryan, J.N., 2005, Assessing the vulnerability of a municipal well field to contamination in a karst aquifer: Environmental and Engineering Geoscience, v. 11, no. 4, p. 319-331.

Renken, R.A., Cunningham, K.J., Shapiro, A.M., Harvey, R.W., 

Zygnerski, M.R., Metge, D.W., and Wacker, M.A., 2008, 

Pathogen and Chemical Transport in the Karst Limestone 

of the Biscayne Aquifer: 1. Revised Conceptualization 

of Groundwater Flow: Water Resources Research, v. 44, 

W08429, doi: 1029/2007WR006058. 

Shapiro, A.M., Renken, R.A., Harvey, R.W., Zygnerski, M.R., 

Metge, D.W., 2008, Pathogen and Chemical Transport in 

the Karst Limestone of the Biscayne Aquifer: 2. Chemical 

retention from diffusion and slow advection: Water Resources 

Research, v. 44, W08430, doi: 1029/2007WR006059. 

Ward, W.C., Cunningham, K.J., Renken, R.A., Wacker, M.A., 

and Carlson, J.I., 2003, Sequence-stratigraphic analysis of the 

Regional Observation Monitoring Program (ROMP) 29A test 

corehole and its relation to carbonate porosity and regional 

transmissivity in the Floridan aquifer system, Highlands 

County, Florida: U.S. Geological Survey Open-File Report 

03-201, 34 p., plus appendixes. (Also available online at 

http://fl.water.usgs.gov/Abstracts/ofr03_201_ward.html)

—Michael A. Wacker and Kevin J. Cunningham

For more information, please contact:

Michael A. Wacker

e-mail: mwacker@usgs.gov

Kevin J. Cunningham

e-mail: kcunning@usgs.gov

U.S. Geological Survey 

Florida Integrated Science Center

(FISC—Ft. Lauderdale)

3110 SW 9th Ave., 

Ft. Lauderdale, FL 33315

Figure 3. Comparison of electromagnetic-induction logs 

collected in well G-3702 from April 2000 through May 2007 

along Black Creek Canal in Miami-Dade County (Scott 

Prinos, U.S. Geological Survey, written commun., 2008). An 

increase in conductivity is evident between 40 and 50 feet.

G-3702

Electromagnetic

Induction Logs

0 30 60 90 120

EXPLANATION

DEPTH, IN FEET BELOW LAND SURFACE

BULK CONDUCTIVITY,

IN MILLISIEMENS PER METER

Very slight

declines 2000-

2007, supported

by water quality

samping

4/11/2000

4/05/2001

5/17/2002

5/02/2003

4/26/2004

4/14/2005

4/17/2006

6/13/2007

Large salinity

increase in

June 2007

No change

2000-2007

0

10

20

30

40

50

60

70

80