United States
Environmental Protection
Agency
Environmental Monitoring
Systems Laboratory
Las Vegas NV89114
Research and Development
EPA-600/S4-84-085 Jan. 1985
&EPA Project Summary
Location of Abandoned Wells
with Geophysical Methods
F. C. Frischknecht, P. V. Raab, and J. Jeffrey van Ee
Mathematical modelling of the
magnetic anomaly induced by steel-
cased wells indicated abandoned wells
could be located with high-sensitivity
aeromagnetic surveys at an altititude of
60 meters with a spacing between
flight lines of 100 meters. The locations
of an estimated 95-98 percent of the
abandoned oil and gas wells in an
Oklahoma test area were identified in
an aeromagnetic survey and substanti-
ated by record and historical
photography searches. Sharp
anomalies resulting from variations in
the near-surface sedimentary rocks
caused difficulty in interpretation of the
aeromagnetic results from a pilot study
in Colorado. A ground magnetometer
was used to locate some of the
abandoned wells to within one or two
meters accuracy. Electrical geophysical
methods were briefly evaluated for the
location of uncased wells, but test
results indicated the methods would be
impractical in locating most abandoned
wells.
This Project Summary was developed
by EPA's Environmental Monitoring
Systems Laboratory, Las Vegas, NV, to
announce key findings of the research
project that is fully documented in a
separate report of the same title (see
Project Report ordering information at
back).
Introduction
The Underground Injection Control
Regulations, promulgated by the
Environmental Protection Agency,
established a minimum radius of review
of V4 mile for proposed injection wells.
This radius can be extended if warranted
by the hydrological properties of the area.
The concern is that abandoned wells near
the injection well could serve as conduits
for the transmission of injected wastes
into an underground source of drinking
water.
In the United States, approximately
500,000 municipal, industrial,
commercial, agricultural, and domestic
wells are used to inject wastes into the
ground, and approximately 5,000 new
injection wells are being constructed
each year. Abandoned wells located near
these injection wells, particularly newer
injection wells, must be located and
properly completed and plugged to
prevent contamination of potable water.
The exact location of many abandoned
are often difficult to determine because
records may be imprecise, incomplete,
antiquated, and difficult to locate. Record
searches can be time consuming and
expensive, and there is always a chance
that a records search will not show an
abandoned well falling within the radius
of review for an injection well. Other
means for locating abandoned wells are
needed.
The primary emphasis in this study was
on the use of aeromagnetic surveys.
Records and historical aerial photo-
graphic searches were also used to
locate candidate test areas and to verify
the correlation of a magnetic anomaly
with an abandoned well. Two ground-
based methods were secondarily
evaluated: electromagnetics and mag-
netometers. Electromagnetic methods
were briefly evaluated for locating aban-
doned wells that had no steel casing and
no magnetic anomaly. However, these
methods quickly proved impractical
because they were time consuming and
too localized for use in large-scale studies.
Further research into these methods was
not pursued.
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Procedures
The United States Geological Survey
(USGS) determined through mathemati-
cal modelling that aircraft flight lines at
100-meter spacings and at an altitude of
60 meters above the ground should be
sufficient to detect wells with some steel
casing. Field measurements, together
with mathematical modelling, indicated
that most wells containing approximately
60 meters or more of 22-centimeter or
larger diameter surface casing could be
detected by a low altitude, high-
resolution aeromagnetic survey. Through
a records search, the University of
Oklahoma's Environmental and Ground
Water Institute identified 24 sections in
four townships around Oklahoma City as
a test area where more than 1 5 wells per
section could be found in rural areas.
The high-resolution aeromagnetic
survey was conducted with the use of a
microwave navigation system that used
transponders on the ground and a real-
time display of the flight-line location in
the aircraft. The radar altimeter and
aircraft orientation sensors were used to
compensate for fluctuations in the
earth's magnetic field from changes in
the altitude and orientation of the aircraft.
3hotographs of the ground were taken
from the aircraft to aid in the
nterpretation of the magnetic data and to
confirm the association of a magnetic
anomaly with an abandoned well.
The Environmental Monitoring System
Laboratory's Environmental Photograph-
ic Interpretation Center conducted an
historical aerial photographic search of
the 24 sections to evaluate another
method for locating abandoned wells
while providing a basis for evaluating the
magnetic technique. Aerial photographs
dating back to the 1930's were examined
for evidence of drilling. The locations of
the past drilling activities were plotted on
recent photographs and maps. The aerial
photographic search together with the
records searches formed the basis for
comparison with the abandoned wells
identified in the aeromagnetic survey.
Results and Discussion
The results of the study show that the
magnetic method is effective in locating
abandoned wells. Depending on the total
area to be surveyed, most agencies or
organizations with the responsibility for
finding wells will require technical assist-
ance in designing and carrying out
magnetic surveys; however, the results of
this study do not indicate that further
research is required before the magnetic
method can be applied in the search for
abandoned wells.
The aeromagnetic results in Oklahoma
agreed well with those obtained by a
records search and by interpretation of
aerial photographs. The aeromagnetic
survey located an estimated 95-98
percent of the abandoned wells. The
exact figure varied from one section to the
other.
Most wells in the Oklahome test areas
produced easily identifiable magnetic
anomalies. In a few cases the anomalies
were small; but, with careful analysis,
most of them were recognized. When
several wells occurred in close proximity,
it was difficult to determine how many
there were from the aeromagnetic
results. Anomalies due to other
manmade features,such as pipelines and
transmission line towers, were a minor
problem in interpreting the aeromagnetic
results.
In considering the application of the
magnetic method in the search for
abandoned wells, the most important
questions are: (1) What size magnetic
anomalies are the casings likely to pro-
duce? (2) How much magnetic
interference will there be from other
manmade sources and from natural
sources? These questions can never be
completely answered in advance, since
each area will be somewhat different
from those already investigated.
However, the test areas in Colorado and
Oklahoma are representative of condi-
tions in many oilfields, and the results
from these studies can be used in plan-
ning and conducting work in other areas.
areas.
Conclusions
The results of this study indicate that it
is very useful to employ three methods,
records search, photo interpretation, and
magnetic surveys, in locating wells. All
three methods should be considered for
use in new areas. However, since each
method has deficiencies, there is the
possibility that in particular areas one or
more of the methods will not be
applicable. Also, in some areas, it is
probable that wells can be located by use
of only one or two of the three methods.
There are a number of different
circumstances in which the use of
magnetic methods to locate abandoned
wells should be considered. Sometimes
it is necessary to physically locate buried
wells which are known from records.
Ground-magnetic methods are most
useful for this purpose. The EPA
regulations require a search for
abandoned wells within a certain
minimum radius of V4 mile, of proposed
new injection wells. Ground or airborne
methods might be used in such a search;
however, if a search is to be made around
the location of several proposed injection
wells in the same general area, airborne
methods will become less expensive.
Finally, a need may arise to search for
sites for injection wells which are the
prescribed distance from an abandoned
well. In such a case, the economics of an
aeromagnetic survey become more
favorable.
Some of the advantages of the
magnetic method in locating casings are:
(1) The method can be readily used to
accurately locate buried casings
where there has been no surface
evidence of the wellfor manyyears.
(2) By use of an aircraft, large areas
can be surveyed rapidly without
need for access to the property.
(3) With the use of a ground
magnetometer, the horizontal
position of a casing can be located
to within one or two meters
accuracy and the results are
immediately available.
Some of the disadvantages of magnetic
methods and problems in their use are:
(1) Wells which do not contain near-
surface casing or other pipes
cannot be detected at all, and it may
be impractical to locate wells con-
taining only a small amount of
casing.
(2) The magnetic method may be
relatively costly compared with
other methods, particularly if the
areas are small and few in number.
(3) In some areas, magnetic disturb-
ances caused by manmade objects,
such as pipelines and steel
buildings or anomalies due to
naturally occurring magnetic
minerals in near-surface rocks,
interfere with the recognition of
anomalies caused by casings.
(4) Most companies and public
institutions having a needtosearch
for abandoned wells will, at least
initially, require technical
assistance from outside their
organization. The method requires
a large initial capital investment
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and the high-resolution aeromag-
netic survey requires extensive
data interpretation by professional
geophysicists or earth scientists.
F. C. Frischknecht andR. V. Raab are with the U.S. Geological Survey, Denver, CO
80225; the EPA author Jeffrey van Ee (also the EPA Project Officer, see below)
is with the Environmental Monitoring Systems Laboratory, Las Vegas, NV
89114.
The complete report, entitled "Location of Abandoned Wells with Geophysical
Methods," (Order No. PB 85-122 638; Cost: $ 10.00, subject to change) will be
available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Environmental Monitoring Systems Laboratory
U.S. Environmental Protection Agency
P.O. Box 15027
Las Vegas. NV 89114
U.S. GOVERNMENT PRINTING OFFICE; 1985 —559-016/7884
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