Volume 28 Number 6

BULLETIN
of the
AMERICAN ASSOCIATION QF
PETROLEUM GEOLOGISTS
JUNE, 1944

CLASSIFICATION OF EXPLORATORY DRILLING

AND STATISTICS FOR 19431
FREDERIC H. LAHEE*
Dallas, Texas

ABSTRACT
A serious need of the petroleum industry is standardization of the definitions and classification
of exploratory wells, for only upon a generally accepted nomenclature can satisfactory estimates be
made of the exploratory effort in the search for new oil and gas reserves. After much discussion and
correspondence, we have prepared a statement of definitions and a classification of exploratory holes
which, we hope, will prove to be suitable for general use. This topic is treated in Part II of the present
report, where numerous explanatory comments are included.
In Part III is our review of exploratory drilling in 1943. This year we are following the proposed
classification (Part II) in referring to "exploratory holes," a term which, however, is analogous to the
word "wildcats," as used in our earlier reports on this subject. On this basis, in 1943, 3,843 explora-
tory holes were drilled as contrasted with 3,212 holes drilled in 1942. The total exploratory footage
drilled in 1943 was 15,122,364 feet as against 12,123,994 feet in 1942. The average depth of hole in-
creased from 3,77s feet in 1942 to 3,935 feet in 1943, for all states covered; and from 4,647 feet to
4,968 feet in the southern states. Again, we have compiled figures on exploratory drilling and on esti-
mated proved reserves in the eleven states of Arkansas, California, Illinois, Indiana, Kansas, Louisi-
ana, Michigan, Mississippi, New Mexico, Oklahoma, and Texas.
From all points of view, as brought out by these statistics, the exploratory effort must be still
further stepped up during 1944.

PART I. INTRODUCTION

In the search for new crude-oil supplies and in the effort to make substantial
additions to partly developed pools, holes3 are drilled either at random or, more
commonly in these modern times, on the basis of technical information (geolog-
ical, geophysical, or both) which is never complete. Such holes are referred to as
"exploratory." They do not include holes drilled within the limits of a developed
pool, or of the developed part of a pool, where such drilling is carried down only
to the known producing formation (or formations) of this pool. Holes of this latter
class are commonly known as "field wells."
1
Presented before the Association at Dallas, March 23,1944. Manuscript received, April 6,1944.
2
Chief geologist, Sun Oil Company.
8
Although "well" is better used for a hole that has been completed as a producer, in the present
paper we are using hole and well synonymously, in conformity with general practice. In some parts of
this paper "test" is used for a hole not completed as a producer.

701
702 FREDERIC II. LAHEE

There are several types of hole of the former class, all of which are exploratory,
but in varying degrees. For example, (a) there are holes which are drilled on geo-
logic structures or in areas which have never before produced oil. (b) There are
holes which are drilled on producing structures, but completely outside of the
then known limits of any pools previously developed on such structures. And (c)
there are holes which, although drilled within the then known boundaries of a
producing pool, are carried on down to greater depths to explore for unknown
possibilities below the deepest producing formation of this pool.
In our reports of the last 4 years, covering information for 1939, 1940, 1941,
and 1942,4 we have included these types of exploratory hole under the general
category of wildcats, but, in the original statistics from which the tabular data
were compiled, we listed holes of type a as "rank wildcats" and holes of types b
and c as "semi-wildcats." Previous to 19395 our figures omitted "semi-wildcats"
of type c, a very small group in those days. We want especially to make these
points clear because recently, in his article on wildcat drilling,6 W. V. Howard
has stated that "Lahee's definition of a wildcat has become successively liberal-
ized so that the increase" [in annual number of wildcats reported as drilled] "may
represent wells added as a result of this liberalization." For the years 1939 to 1942
inclusive, the same basis was used and accordingly the data presented for these
years may be compared, with assurance that they are essentially analogous. Be-
fore 1939 there were some minor changes in our approach with the result that
the totals may not be as closely comparable, but even here the variations amount
to probably less than 5 per cent. Another point which may well be stressed in this
connection is the fact that a large proportion of the statistics which have been
used in these reports 7 was collected and compiled by the same geologists from
year to year, thus lessening the chance for variation in definitions due to the
personal equation. In other words, we believe that our data on wildcatting, as
published by the American Association of Petroleum Geologists in recent years,
and certainly within the last 4 years, are comparable from year to year, and that
they do illustrate, within a very small percentage of error, the trend of explora-
tory effort in the states covered.
With reference to exploratory statistics submitted by different organizations,
it is true that there are unfortunate discrepancies. One can not safely compare
the figures compiled under different auspices, and it is mainly for this reason that
standardization of terms and classifications used in these studies is a necessity.
Toward this end we have prepared, and we herewith present as Part II of this
paper, a classification of exploratory drilling, which we hope will be acceptable
4
See this Bulletin, Vol. 24, pp. 953-58; Vol. 25, pp. 997-1003, 19,38, 1939; Vol. 26, pp. 969-82;
and Vol. 27, pp. 715-729.
6
This Bulletin, Vol. 21, pp. 1079-82; Vol. 22, pp. 645-48, 1231-36; Vol. 23, pp. 789-94.
6
"Wildcat Drilling Has Failed to Keep Up with Increasing Need of Discoveries," Oil and Gas
Jour. (February 17, 1944), pp. 41, 42.
7
For 1939-42, as previously cited.
 EXPLORATORY DRILLING AND STATISTICS TOR 10U 703

for general adoption by the industry. 7 a This classification and the accompanying
definitions are the outcome of a voluminous correspondence and of many confer-
ences with other geologists and petroleum engineers in various parts of the coun-
try. 8 They represent the result of repeated criticisms, suggestions, and revisions,
until, as nearly as seems feasible, the variable factors that apply in different dis-
tricts and under different conditions have been covered. H i e classification is in-
tentionally broad so that it can be applied in any region. We have tried to steer
away from being too specific as to details. If this classification does not seem
exactly to fit the conditions in your local district, bear in mind that the endeavor
has been so to construct it that it will cover all districts. Its practical value rests
on its general applicability and not so much on an itemization of innumerable
minor factors.
One more word before presenting this classification: we earnestly believe
and in this a large majority of geologists, whom we have questioned, agreethat
the main criterion for defining a wildcat should continue to be the degree of risk
of failure involved in the drilling, the degree of hazard in the venture. And we be-
lieve that this criterion should be applied in classifying different types of explora-
tory holes. It is important to realize t h a t the degree of risk depends primarily on
how much is known and how much is unknown of the underground geological
conditions at and near the site of the hole. As we indicated in our earlier definition
of a wildcat, 9 distance is a less significant factor, which can not be stipulated as so
many feet, or so many miles. Therefore, it is our conviction that logical classifica-
tion of exploratory holes properly requires the judgment of a geologist.

P A R T II. CLASSIFICATION OF EXPLORATORY D R I L L I N G FOR PFTROLEUM

A. DEFINITIONS 1 1 1

1. Petroleum defined.
For statistical purposes, as discussed in Part II of this paper, petroleum is de-
fined as including crude oil, natural hydrocarbon gas, and the condensate content
of natural gas, wherever these occur under natural conditions.

2. Occurrence of petroleum.
(a) A pool, as used in the following discussion, is an underground accumulation
of petroleum in a single and separate natural reservoir (ordinarily a porous sand-
7a
This classification was accepted by the Petroleum Administration for War and by the Petroleum
Industry War Council on May 2, 1944.
8
We art grateful, for constructive criticism, to G. C. Gester, A. I. Gregersen, Wm. B. Heroy,
Graham Moody, R. J. Schilthuis, Carleton D. Speed, K. G. Trostel; and especially to Paul Weaver,
Leonard Orynski, Phil Martyn, and Sidney Judson, all members of P. A. YV. Subcommittee on Ex-
ploration for District 3.
9
See this Bulletin, Vol. 27, p. 717 (June, 1943).
10
The definitions given in this paper are for the purpose of reporting exploratory drilling, and
are not to lie construed as legal definitions.
704 FREDERIC II. LAHEE

stone or limestone). It is characterized by a single natural-pressure system so that

production of petroleum from one part of the pool affects the reservoir pressure
throughout its extent. In all directions a pool is so bounded by geologic barriers
(sucli as impermeable strata, geologic structural conditions, and water in the rock
formations) that it is effectively separated from any other pools thai may be pres-
ent in the same district, or on the same geologic structure.
(b) A field may be a single pool, or it may consist of two or more pools, all on,
or related to, the same geologic structure. Where there is more than one pool in
the same field, the several pools are separated from one another through geologic
causes such as synclinal conditions, faulting, pinching-out of reservoir beds, and
changes in porosity and permeability. The pools may occur at several horizons of
different geologic age, separated by relatively impervious strata, and in such cases
they may directly, or only partly, overlap one another in a horizontal sense; or
they may not overlap at all.
Comment.The terms "pool" and "field" are applied herein only where they
are capable of producing oil or gas in substantial quantities, which, in most cases,
means in commercial quantities. These terms are not intended to cover slight ac-
cumulations from which nothing but very small showings can be obtained. (See
comments on "discovery" under 5(c).)
Though a field may include several pools which, by definition, must all be on,
or related to, the same geologic structure, the reverse may not be true. In other
words, all the pools on one major structure do not necessarily constitute one field.
If the structure is large, several fields may be located on it.

3. Classification of drilling.
(a) Development drilling, in the petroleum industry, is the drilling of wells
within, or close to, the limits of a producing (or producible) pool, as these limits
are known at the time of this drilling, the object being to complete such wells in
the "pay horizon" (sand, limestone, et cetera) of the pool.
Comment.The word "producible" is added in parentheses here, and else-
where in this report, to cover the case of a pool, which, temporarily, may not be
producing because its well or wells are shut in.
Development drilling is mentioned in this paper mainly for contrast with
exploratory drilling.
(b) Exploratory drilling is (1) the drilling of wells relatively a considerable
distance outside the limits of developed, or developing, pools as these limits are
known at the time of such drilling; or (2) the drilling of wells within the then
known limits of a pool with the object of searching for new producible formations
above or below the producing (or producible) formation of the pool; or, if there are
two or more superposed pools in the field, above or below the producing (or pro-
ducible) formation of the deepest pool penetrated by this well.
Comment.For a discussion of this subject see (b) (3), (p. 706}.
 EXPLORATORY DRILLING AND STATISTICS FOR 1943 705

4. Classification of wells at time of commencement of drilling.

(a) Under the head of development drilling may be listed field wells.
A field well is a well drilled with the object of further exploiting the "pay hori-
zon" of a pool within the area which has already been essentially-provedfor produc-
tion in this pool. Such a well may be inside the pool as already outlined by producing
(or producible) wells, or it may be a relatively short distance outside these limits.
Comments.Under this definition an edge well, that is, a well knowingly
drilled close to the recognized productive boundary of a pool, is a "field well,"
and this is true whether this edge well is completed as a producer (within the pool)
or is abandoned as a dry hole (just outside the boundary of the pool).
After discovery of a new pool (or a new field), the second well, and subsequent
wells, should all be called field wells if they meet the requirements of the defini-
tion as above stated.
"Field well" may be applied to a well within a field consisting of a single pool;
or in a field consisting of two or more pools, but in the latter case the objective
must be the producing formation of that pool within the boundaries of which, or
close to the boundaries of which, this well is located.
On a structure of moderate relief, where the producing formation blankets the
entire structure, and where through subsurface mapping the contours on this for-
mation can be mapped with a fair degree of correctness, a hole drilled on an unde-
veloped part of the structure, but considerably above edgewater level, may be
called a field well, because its chances of production are very good. Note that in
this case the underground conditions are definitely known as contrasted with
what is known affecting an outpost well (described later).
(b) Under the heading of exploratory drilling we may list these classes of wells:
wildcat wells (including new-field wildcats and new-pool wildcats), outpost wells,
deeper-pool tests, and shallower-pool tests.
(1) A wildcat well (or simply wildcat) is a well located relatively a considerable
distance outside the limits of producing (or producible) pools as these limits are
known at the time of its drilling. A new-field wildcat is a hole drilled on a geologic
structure or in a geologic environment where petroleum has not yet been dis-
covered. A new-pool wildcat is a hole drilled on a structure, or in a geologic envi-
ronment, where other pools have been found, but where the complexities in the
underground geologic conditions are so great that searching for a new pool is very
hazardous. As suggested in these names, the objective of a new-field wildcat is
discovery of a new field, and the objective of a new-pool wildcat is discovery of a
new pool in a field already discovered. (See "Comments" following the next para-
graph.)
(2) An outpost well (or outpost) is a hole drilled with the thought that it will
probably extend, by a considerable distance, a pool already partly developed. Its
original objective is the producing formation of this pool, although it may be
completed or abandoned at a higher, or at a lower, stratigraphic horizon. It is
 706 FREDERIC H. LAHEE

far enough from the limits of the pool, as known at the time when its drilling is
started, to make its outcome uncertain, but it is not far enough from these limits
to be designated a wildcat. If it is successful in its original object, it will add ma-
terially to the productive area of the pool. It may be dry.
Comments.As we have pointed out before, the element of risk of failure to
find oil is an important factor in classifying wildcats and outposts. Therefore,
where geological conditions are simple and easy to anticipate and where, for this
reason, a well is likely to find production, the distance of a wildcat measured from
the known limits of the nearest pool (not from any other drilling well), will be
greater than where geological conditions are complicated and failure is not un-
likely. Where pools are known to be large and geological conditions simple, a hole
located two or three miles from the nearest productive area may be classed as an
outpost. Where conditions are complicated, as on a salt dome, or in an area char-
acterized by faulting or by lensing or shaling sands, a hole drilled just outside the
known actual edge of a pool, and on the same structure as that on which this pool
is located, is essentially a wildcat, for it is exploring for unknown possibilities
under complex geological conditions. On the other hand, if a hole is drilled along
strike several locations from production on a salt dome, it may better be called an
outpost, unless faulting is believed too greatly to diminish the chance of extend-
ing the known producing area in that direction.
Obviously the definition of wildcat or outpost must be applied when a hole is
started and not after its completion. For example, nothing learned during the
drilling of a wildcat nor after its completion or abandonment can alter the degree
of risk which was taken in the original venture of locating and drilling the hole.
If two holes are started as wildcats in the same area, they are still wildcats, even
if one of them happens to discover production before the other is completed.
(3) A deeper-pool test is a well located within the known limits of a pool and
drilled with the object of searching for new producible formations below the pro-
ducing (or producible) formation of the pool; or, if there are two or more overlap-
ping pools, below the producing (or producible) formation of the deepest pool
penetrated by this well.
Comment.In nearly all cases "below," as used in this definition, means both
"stratigraphically below" and "at a greater depth"; but under very rare condi-
tions, such as overthrust faulting, the producing formation of the pool might be
stratigraphically older, though shallower, than the deeper prospects sought in
the "deeper-pool test."
Under certain conditions of complicated geology, within a field that includes
two or more pools at different stratigraphic levels and not superposed one above
another, "deeper-pool test" may be applied to a hole located within the producing
area of a higher pool, but considerably outside the producing area of a lower pool,
if the objective of this well is below the pay zone of the pool within which it is
located. For this classification such a hole should be far enough from the edge of
the deeper pool to be designated a wildcat if there were no higher pool.
 EXPLORATORY DRILLING AND STATISTICS FOR 1943 707

There has been much question about how to discriminate between (1) a well
drilled from the surface with the object of searching for unknown prospects below
the deepest known pay zone penetrated by the well, and finally completed as the
discovery well of a new deep pool, or abandoned at its total depth as a dry deeper-
pool test; (2) a well similarly drilled but, after failing to discover deep oil, plugged
back and completed in the pay zone of the deepest pool within the confines of
which it was located; and (3) a field well which, after producing for some time
(days, months, or years) from the known pay of the pool, has then been deepened
to explore underlying unknown possibilities. In order to simplify the statistical
study of these three varieties of hole, we list all as deeper-pool tests but in each
case we assign as exploratory footage only the footage below the pay zone of the
deepest previously known pool penetrated by this well.
(4) A shallower-pool test is a well located within the known limits of a pool and
drilled with the object of searching for new producible horizons above the produc-
ing (or producible) formation of the pool; or, if there are two or more overlapping
pools at the site of the well, above the deepest of these pools.
Comments.Wildcatsboth those exploring for new fields and those explor-
ing for new poolsare holes drilled considerably outside the limits of producing
areas, in a lateral sense, that is, as would be obvious on a map. On the other hand,
deeper-pool tests and shallower-pool tests are exploratory in a vertical sense since
they are drilled to search for deeper or shallower new pools respectively above or
below a known and partly or wholly developed pool. It is true that a shallower-
pool test penetrates a stratigraphic section at least partly known, but it is defi-
nitely exploring for petroleum and commonly for structure. Our reason for relating
both the shallower-pool and deeper-pool tests to the deepest producing formation
in an area of two or more superposed pools is that this greatly simplifies the defi-
nition. It is much better to do this than to attempt to discriminate between such
tests which might be exploring at various levels where there are several overlap-
ping pools in one field.

5. Results of drilling.
As results of drilling we may designate wells as dry holes, as extension wells,
or as discovery wells.
(a) Any holeeven a well drilled within the known boundaries of a pool as a
"field well"may be abandoned as dry. However, the chances are that field wells
will produce, or be producible; and although the risk is greater, outpost wells have
a fair chance of success; but wildcats, according to statistics, have less than one
chance in five or six of discovering oil or gas "in substantial quantities."
(b) Any well which is located as an outpost well or as a wildcat will be classi-
fied as an extension well (as a result of its drilling), if it extends the productive (or
producible) area of a pool (Table I); but this classification can not logically be ap-
plied until after the fact is demonstrated, and such demonstration may require
the drilling of several intermediate wells.
708 FREDERIC H. LA NEE

(c) Any wildcat, outpost, deeper-pool test, or shallower-pool test, which dis-
covers a new pool of petroleum,11 is a discovery well.
Comments.Discovery, then, as applied to oil and gas, is the finding of a
previously unknown or unproved pool of petroleum. For the first pool on a geo-
logic structure we may speak of discovery of a pool or discovery of a field, since
this first pool may also be called a field; but where there are several pools in one
field, there can be only one field-discovery well on this structure, that is, the well
that was completed as a producer in the first pool found. Thereafter the wells dis-
covering new pools on this same structure are pool-discovcrv wells; they are not
field-discovery wells.
In some places a wildcat, drilled some distance from production, is at first
erroneously credited with discovery of a new pool. Subsequently, through the
drilling of additional wells, it is shown to be an extension well of a pool previ-
ously known. Such a well, although it must obviously be removed from the cate-
gory of discovery wells when the fact is proved, is nevertheless due full credit as a
wildcat, based on factors of distance and risk at the time its drilling was under-
taken.
It commonly happens that the discovery well on a structure, or a well drilled
subsequently in the course of development of the field, penetrates more than one
formation which is capable of producing oil or gas in substantial quantities, (len-
erally the well will be completed in only a single formation. If the well is the dis-
covery well of the field, the formation in which it is completed thus becomes the
initial pool of the field. Other potentially productive formations penetrated,
either above or below the formation in which the well was completed, would not
be considered technically as "discovered" until a well has been completed as a
producer from each of them. Even if the evidence of the presence of petroleum in
such a formation were practically conclusive, a well producing, or so completed
that it could produce, from this formation would be required to constitute a new
discovery. This distinction is essential even though, from the interpretation of
electrical logs, from core samples, and even from drill-stem tests, it may seem
almost certain that the formation is capable of production. If the discovery well
of a field were completed and producible from two formations, such a dual com-
pletion would, of course, be the discovery well of two pools. The discovery well
of a new pool or ''pay zone" is, accordingly, not necessarily the first well that
penetrated the "pay zone" and found evidence of petroleum in it, but the first
well to produce substantial quantities of oil or gas from it.
(d) The date of discovery of a pool is the date on which the discovery well of
the pool is completed as a producer of petroleum. For a field this would be the date
of discovery of the first pool in the field. If the first well completed in a pool hap-
pened to be in the gas cap of an oil pool, this would still be the discovery well of
the pool as a whole, including both gas and oil.

11
See foregoing definitions of "pool" and "petroleum."
 EXPLORATORY DRILLING AND STATISTICS FOR 1943 709

B. STATISTICS ON EXPLORATORY DRILLING

In order that the statistics of exploratory drilling may be as consistent as

possible between different areas and in order that those in successive years may
be as nearly comparable as possible, the foregoing definitions have been sug-
gested for general adoption. In applying these definitions there is bound to be
some question in a few border-line cases, but for the most part classification
should be made without difficulty.
Table I is a summary presentation of the classifications described in the fore-
TABLE I
CLASSIFICATION OF EXPLORATORY WELLS

going pages. To some extent it is briefly explanatory. By following its designa-

tions, statistics can be recorded in several ways. Table II is a suggestion for tabu-
lating statistics. In it the main columns correspond with groups 1, 2 a, 2b, 2c, and
3 in Table I. Under each of these are three subheadings, "successful," "failure"
and "total." (The first two could be headed "producer" and "dry," if preferred.)
Under "successful," the kind of producer (oil, gas, or condensate) is indicated,
and in this column under each major heading, may be shown the fact whether
the producer was a discovery well or an extension well (as proved by the drilling)
by the letters "d" and "e," respectively, against the recorded data. As for these
data, the number of holes or the exploratory footage, or both, can be shown.
Attention is again called to the differences between sections 4 and 5 in the
foregoing text. Bear in mind that preliminary classification is based on the degree
 TABLE I I

TABULATION OF STATISTICS ON EXPLORATORY WELLS

1 2 3
NEW- POOL TESTS

STATE 2t
b
OR * SHALLOWER-POOL TESTS DEEPER-POOL TESTS NEW-POOL WILDCATS
DISTRICT
F
T A SUCCESSFUL "A
SUCCESSFUL SUCCESSFUL T T
0 SUCCESSFUL T
0 S
'L 'L o 'L 'L

OIL GAS COND*

u \ OIL GAS COND.
U
R
T
A
L OIL GAS COND.
U
R
T
A
L OIL G A S COND*
u
R
T
A
L OIL
R L E E E
E

TOTALS

TOTAL NEW-POOL TESTS ( 2 a + 2b+ 2c ) *

COND.= CONDENSATE OR DISTILLATE

 EXPLORATORY DRILLING AND STATISTICS FOR 1943 711

of risk of failure as estimated when drilling of the hole is commenced, and this risk
is contingent on how much is known of underground geological conditions when
drilling is started. Also remember that preliminary classification of a well, made
before the well is completed, can not logically include reference to discovery or
extension. Thus, classifications under column A in Table I are fixed and must not
be changed. On the other hand, classifications under column B may have to be
changed as more information becomes available.
In compiling statistics for study of both the exploratory effort and the results
of this effort, all five types of exploratory holes should be separately treated. We
refer to the types labeled 1, 2a, 2b, 2c, and 3 in Table I. Unless the data are thus
broken down, misinterpretations of the tabulated statistics are inevitable. Fur-
thermore, when thus broken down, the data can then be combined by each
statistician according to his own purpose in studying these data. For example,
if his object is merely to classify newly discovered reserves, he can group under
headings 1, 2, and 3, all three subclasses of 2 being combined (see Table II). Or
he can group the data under outposts (1), tests exploring above or below known
pools (2a plus 2b), and wildcats (2c plus 3). For purposes of measuring the ex-
ploratory effort, especially from the technical point of view, there is a real
significance in considering both groups of wildcats (2c and 3) together.
To each wildcat, shallower-pool test, and outpost well, its total footage is to
be assigned and listed; but, as already explained, each deeper-pool test is to be
credited with only that footage which was drilled below the "pay zone" of the
deepest pool within the limits of which it was drilled. In no case should footage
penetrated in sidetracking, or in redrilling of a lost hole, be included in the total
footage of any hole.
A hole temporarily abandoned should not be listed in one year's record, and
then again in succeeding years, each time it is drilled a little deeper. As far as
can be determined, it should be listed only when it has been permanently aban-
doned. Where, after a long lapse of time, a hole recorded as permanently aban-
doned, is cleaned out and drilled deeper, it should be so designated as an exception
in the later listing, and only the additional footage drilled should be assigned to
it as of the year during which it was thus deepened.

PART III. STATISTICS ON EXPLORATORY DRILLING IN 194312

Except where otherwise designated, the statistics recorded in Part III of this
paper are similar to those used in our reports for 1939 to 1942 inclusive. In other
words, we include wildcats (both new-field wildcats and new-pool wildcats),
12
For the kind assistance and coSperation of the following gentlemen, the writer is especially
grateful: A. P. Allison, A. H. Bell, J. E. Billingsley, Kendall E. Born, D. H. Cardwell, R. J. Cullen,
M. H. Funk, G. C. Gester, D. C. Harrell, P. Hastings Keller, Edward A. Koester, Chas. S. Lavington,
Geo. D. Lindberg, A. M. Lloyd, W. S. McCabe, Graham B. Moody, D. J. Munroe, Geo. W. Myers,
Tack A. Parker, Chas. H. Row, Glenn C. Sleight, Lee C. Smith, W. T. Teare, Paul Weaver, and
E.B.Wilson.
 712 FREDERIC H. LAHEE

FIG. I

TOTAL:
SE. NEW MEXICO 287 (1,546,956)
1,369 (6,680,512;
ONE PRODUCER FOOT
FOR EVERY
V" 4.32 FEET DRY

TEXAS RAILROAD COMMISSI

FIG. 2
 EXPLORATORY DRILLING AND STATISTICS FOR 1943 713

outpost wells, and deeper-pool tests. For the first two groups we use the total
footage drilled in each hole, whether a producer or a dry hole, but in the case of
the deeper-pool tests we include only the footage drilled below the deepest pro-
ducing formation penetrated by the well. These 1943 figures may be consistently
compared with those published in our reports of 1939 to 1942.13
On the maps (Figs. 1 and 2), numbers in parentheses indicate total footage
drilled; figures preceding parentheses indicate the number of holes drilled; figures
above the cross line are for producing wells, that is, oil, oil and gas, distillate and
gas, and gas; and figures below the cross line are for dry holes.
In the states covered in this review, as shown in Figure 1, and listed in Table
III, during 1943 a total of 15,122,364 feet was drilled in 3,843 exploratory holes,
divided as follows.
Feci
655 producers 2,741,303
3,188 dry holes 12,381,061
This means that 17.0 per cent of the holes drilled, and 18.1 per cent of the footage
drilled were successful in 1943. One producer foot was drilled for every 4.51 feet
of dry hole. One successful well was drilled for every 4.88 dry holes. The average
depth of hole was 3,935 feet.
In the southern states district (Fig. 2), in 1943, a total of 8,227,468 feet was
drilled in 1,656 holes, divided as follows.
Fed
287 producers 1,546,956
1,369 dry holes 6,680,512
In this area, then, 17.3 per cent of the holes drilled, and 18.8 per cent of the foot-
age drilled were successful. One producer foot was drilled for every 4.32 feet of dry
hole. One successful well was drilled for every 4.73 dry holes. The average depth
of hole was 4,968 feet. For comparison with statistics for this same area in 1938,
1939,1940, i94r, and 1942, see Table IV.
Selection of the location for a wildcat well may be based on geology (surface
geology, subsurface geology, trend along known structural or stratigraphic condi-
tions, local or regional, or shallow exploratory drilling); or it may be based on
geophysics (exploration by seismograph, torsion balance, gravity meter, magne-
tometer, et cetera); or it may be based on some non-technical suggestion or re-
quirement, such as "creekology," "hunch," "doodlebug," promotion, lease obli-
gation, reported showing of oil or gas in holes previously drilled, el cetera. In
many cases the reason for choosing the location can not be ascertained.
In Table V are listed the reasons for drilling the exploratory holes in 1943, us-
ing the best information available from men familiar with such statistics, each in
his own state or district. According to these figures, 626 exploratory holes drilled
13
Bull. Amer. Assoc. Petrol. Geol., Vol. 24, pp. 953-58; Vol. 25, pp. 997-1003, 1938, 1939; Vol.
26, pp. 969-82; and Vol. 27, pp. 715-29.
7M FREDERIC H. LAHEE

on technical advice (geology and/or geophysics) were successful (oil or gas),

and 2,616 were dry; 23 holes, located for non-technical reasons, were producers,
and 500 were dry; 6 producers and 72 dry holes were located for reasons unknown.

STATISTICS ON EXPLORATORY DRILLING AND PROVED OIL RESERVES

IN AREA OF ELEVEN STATES

u _ tt2000 5 6

Si?,*,.',
S-.t

i J. -iU

YEAR DURING WHICH NEW RESERVES WERE ADDED AND EXPLORATORY HOLES WERE DRILLED

FIG. 3

These figures show that 19.3 per cent of the holes drilled on technical advice were
producers as contrasted with 4.4 per cent successful in the case of the holes lo-
cated without technical advice. Therefore, in 1943, locations based on technical
recommendations were nearly 4.4 times as successful as those drilled without
 TABLE I I I . NUMBER OF O I L W E L L S , GAS W E L L S , AND D R Y H O L E S DRILLED AS EXPLO

Oil Producers Gas Producers* Dry

States Number Number

Footage Footage Number Footage
of
Drilled
of Drilled of Holes Drilled
o
Holes Holes

Alabama 0 0 0 0 9 35,777
Arizona 0 0 0 0 1 3,850
Arkansas 5 27,982 0 0 65 306,067
California 44 197,965 13 67,978 194 798,145
Colorado 0 0 r 8,560 10 43,75o
Florida T 11,630 0 0 9 23,494
Georgia O 0 0 0 3 10,037
Illinois I07 274,255 1 1,121 400 928,440
Indiana 6 12,132 0 0 74 134,427
Iowa 0 0 0 0 2 3,799
Kansas 56 198,266 1 1, 266 379 1,416,605
Kentucky (W) 25 42,440 1 790 127 273,577
Louisiana 30 180,245 24 210,916 154 1,068,662
Michigan 24 60,223 8 9,902 236 594,38o
Mississippi 5 40,160 0 0 5i 339,125
Missouri 0 0 0 0 7 12,546
Montana 1 6,040 2 7,805 26 67,136
Nebraska 0 0 0 0 29 84,865
New Mexico 7 25,086 1 9,592 34 H7,334
N o r t h Dakota 0 0 0 0 1 5,359
Ohio (NW) 1 i,479 2 664 2 2,000
Oklahoma 48 211,169 15 53,604 293 1,168,207
South Dakota 0 6 0 0 I 8,000
Tennessee 0 0 3 2,990 4 3,814
Texas 163 752,053 Si 289,292 1,047 4,793.784
West Virginia 1 2, 160 3 7,525 14 72,708
Wyoming 5 26,013 0 0 16 6
5,T73

Totals 529 2,069,298 126 672,005 3,188 12,381,061

* Gas-and-distillate (condensate) wells, of which there were 37 completed in 1943, are included in this column.
t Averages have been recorded here only for states where more than 25 exploratory holes were drilled in 1943.

TABLE IV. COMPARATIVE STATISTICS FOR ALL STATES SHOWN IN FIGU

. -. - Producers Drilled Dry Holes Drilled Total

Number
Holes Footag e Holes Footage Explorato
Holes
Number Per Cent Feet \ Per Cent Number Per Cent Feet Per Cent Drilled

1938 200 13.6 | 984,262 17-4 1,271 86.4 4,667,402 j 8 2 . 6 1,471

161 12.6 779,345 1 14.8 1,113 | 87.4 4,501,669 1 85.2 1,274
187 12.8 910,so6 ; 14-gt 1,279 87.2 5,25i,273t ! 85.it 1,466
258 16.5 1,264,774 18.4 1,305 83.5 5,578,975 1 8 1 . 6 1,565
231 16.-5 * ,289,480 10.6 1,186 j 83.7 5j 2 95j556 80.4 1,417
1943 287 17.3 1,546,956 18.8 i,369 ' 82.7 6,680,512 j 8 1 . 2 ! 1,6s&

* I n this table New Mexico data are from t h e southeastern part of the state only.
f See Bull. Amer. Assoc. Petrol, Geol., Vol. 25, p . 1938, where corrections are mentioned for these figures as they appeared in Table
 TABLE V
BASIS FOR LOCATING EXPLORATORY HOLES DRILLED IN 1943

Geology Geophysics* Geology and S?ttZry Unkno

State Geophysics Non-Technical
Prod. Dry Prod. Dry Prod. Dry Prod. Dry Prod.
Alabama 3 2 2 1
Arizona 1
Arkansas 2 22 1 24 2 14 1
California 39 132 8 24 8 11 1 13 1
Colorado 1 5 1 3
Florida 2 1 7
Georgia 1 2
Illinois 86 280 16 54 6 32 34
Indiana 2 33 2 6 4
Iowa 2
Kansas 40 150 12 59 9 5 161
Kentucky (W) 18 P
25 1 9 5 34 2 S9
70 r
Louisiana 22 19 44 3 37 2
Michigan 32 235 1
Mississippi i 19 1 15 3 11 3
Missouri 2 4
Montana 3 22 2
Nebraska 15 4 3
New Mexico 4 22 3 6 4 1 2
North Dakota 1
Ohio (NW) 1 1 2 1
Oklahoma 23 129 35 89 6 5 69
South Dakota 1
Tennessee 1 2 4
Texas 128 655 5i 193 27 75 7 120 1
West Virginia 4 10 4
Wyoming 4 11 1 1 2 1

Totals 411 1,828 I49t 5451 66$ 243t 23 500 6

* Including geochemistry.
t Of these holes 145 producers (123 wildcats, 22 outposts) and 508 dry holes (473 wildcats, 34 outposts, 1 deeper-pool test) were lo
j Of these holes, 64 producers (43 wildcats, 17 outposts, and 4 deeper-pool tests), and 230 dry holes (202 wildcats, 25 outposts, a
graph and geology.
 EXPLORATORY DRILLING AND STATISTICS FOR 1943 717

such advice. In the southern states area (Fig. 2) 5.4 per cent of the exploratory
holes, located without technical advice, were producers, whereas 18.6 per cent of
the holes located on technical advice were producers.
Comparing last year's figures14 with figures for 1943, we note the following
conspicuous changes.
1. There was a considerable increase in the exploratory effort in most parts
of the country, but in Illinois, Indiana, and Nebraska there was a marked reduc-
tion both in the number of exploratory holes drilled and in the total depth of
these holes.
2. There was a decrease from 5,013 feet to 4,239 feet in the average depth of
the holes drilled in California. It is noteworthy that last year also California
showed no increase in average depth of exploratory hole drilled.15
3. On the other hand, deeper drilling is proved by marked increases in the
average depths of exploratory holes from 3,521 feet to 3,707 feet in Kansas; from
1,736 feet to 2,071 feet in Western Kentucky; from 6,809 f ee t to 7,018 feet in
Louisiana; from 5,276 feet to 6,773 ^ ee t m Mississippi; from 3,154 feet to 3,619
feet in New Mexico; and from 4,309 feet to 4,627 feet in Texas.
As in the past 2 years we are again submitting herewith special tables relating
to the following eleven states: Arkansas, California, Illinois, Indiana, Kansas,
Louisiana, Michigan, Mississippi, New Mexico, Oklahoma, and Texas. In Table
VI are shown statistics on exploratory holes (previously all listed as wildcats,
and so called), and in Table VII are statistics on proved reserves in the area of
these same eleven states.
In Table VII, under A, are recorded the proved reserves as of January 1 in
each of the indicated years, and for the eleven-states area under discussion. Under
B is shown, for each January 1, the net change in estimated proved reserves since
the preceding January 1, allowing for production during that 12-month period.
Under C are the new proved reserves which are directly attributable to wildcat
discoveries made during the year. Under D are the revisions and additions of
estimated proved reserves in fields already discovered in previous years, these
revisions and additions having been made on the basis of new information ob-
tained through development during the year indicated. Under E all the new re-
serves ( C + D ) are totalled for each year.
If, for each year, we divide the newly discovered proved reserves (C, Table
VII) by the number of exploratory holes drilled in that year, or by the total ex-
ploratory footage drilled in that year, we shall have a measure of the degree of
success of exploratory drilling in terms of newly discovered proved reserves (G
and H, Table VII); and if we divide the total new proved reserves (discoveries
plus revisions plus extensions: E, Table VII) by the number of exploratory holes
drilled, or by the total exploratory footage drilled, we shall have a rough measure

14
F. H. Lahee, "Wildcat Drilling in 1942," Bull. Amer. Assoc. Petrol. Geol., Vol. 27, pp. 715-29.
Is
Ibid., p. 721.
 TABLE VI
STATISTICS ON EXPLORATORY HOLES IN AREA OF ELEVEN STATES*

Located on Non-Technical Unknown Basis

Technical Basis Location for Location Totals

Producers Drv Holes Producers Dry Holes Producers Dry Holes Producers Dry Holes
Num- Per Num- Per Num- Per Num- Per Num- Per Num- Per Num-\ Per Num- | Per
ber Cent ber Cent ber Cent ber Cent ber Cent ber Cent ber 1 Cent ber \ Cent
1937 214 16.05 1,119 83-95 17 5.80 276 94.20 48 9 . 21 473 90.79 279 12.99 1,868 87.01
1938 283 '7-93 1,295 82.07 43 7.61 522 92.30 17 4.67 347 95.33 343 13-68 2,164 86.32
1939 216 13-33 1,404 86.67 43 6.15 656 93.85 10 4.85 196 95.IS 269 10.65 i 2,256 89-35
1940 309 15-69 1,660 84-31 35 4-57 73i 95-43 11 8.09 125 91.91 355 12.37 i 2,516 87.63
1941 463 20.17 1,832 79.83 29 3.92 710 96.08 0 0 55 100.00 492 15-92 2,597 84.08
1942 438 18.25 1,961 81.75 21 3.81 530 96.19 n 12.36 78 87.64 470 12.17 2,569 87.83
1943 54 19-23 2,457 80.77 19 4.41 411 95-59 6 9-23 59 go.77 6og 1 7 . 22 2,927 82.78

* This area includes California, New Mexico, Texas, Oklahoma, Kansas, Arkansas, Louisiana, Mississippi, Illinois, Indiana, and M

TABLE VII
STATISTICS ON PROVED RESERVES IN AREA OF ELEVEN STATES*

1937 1938 1939

A. Proved reserves as of J a n . 1 ofj
V year indicated 12,241 000 ' 14,664,035,000 i 16,630,452,000 ! 17,723,393,000 18,226,542,000
B . N e t change in proved reserves
f- since Jan. 1 of previous yr. + 2,422,150,000 + 1 , 9 6 6 , 4 1 7 , 0 0 0 ! 4 - i , 0 9 2 , 9 4 1 , 0 0 0 +503,149,000
C. New proved reserves discovered
* .' during year indicated 8g6,6g2,ooo 805,293,000 337,989,000 , 280,882,000 423,551,000
D . New reserves added through ex-
tensions and revisions of old
1
fields during year indicated 2,739,254,000 2,313,356,000 ,955,507,000 1,505,816,000 1,496,610,000
E . Total new proved reserves added
(C-r-D) I 3,635,946,000 3,118,649,000 2,293,496,000 1,786,698,000 I 1,920,161,000
F . Production during year indicatedi 1,213,796,000 1,152,231,000 ^ S 1,283,490,000 ! 1,329,918,000
G. Newly discovered reserves (C)j
per exploratory hole drilled in
year indicated 417,647 321,217 1 3 3 857 97,834 I37,H5
H . Newly discovered reserves (C)
per foot of exploratory hole
drilled in year indicated 93-6 39-9 28.6 37-7
I. New proved reserves (E) per
exploratory hole drilled in year
indicated 1,693,500 1,243,976 908 3IS 622,326 621,612
J. New proved reserves (E) per foot
of exploratory hole drilled in
year indicated 362.52 2 7 .36 182.07 170.75

* T h i s area includes Arkansas, California, Illinois, Indiana, Kansas, Louisiana, Michigan, Mississippi, New Mexico, Oklahoma, a
on reserves are taken from the published annual reports of the American Petroleum Institute's Committee on Oil Reserves.
 TABLE VIII
D I S T R I B U T I O N O F E X P L O R A T O R Y W E L L S O F 1943 B Y C L A S S E S A N D R E S U L T S O F

A B C*
All Slates Included Southern States Included Eleven States I
in Table III in Table IV in Tables VI a

Number \ Footage Number | Footage Number \

(Oil 302 1,357,809 137 744,728 281 1

Producers < Gas 65 273,546 27 147,574 55
[Gas-distillate 29 273,959 29 273,959 29
Wildcats Total 396 1,905,314 193 1,T66,284 365 1
Dry 2,618 10,514,401 1,209 5,954.078 2,376 9
(Oil 173 648,098 46 251,900 164
Producers 4 Gas 13 60,323 7 4i,759 12
[Gas-distillate 5 34,n8 5 34,n8 5
Outposts
Total 191 743,439 58 327,777 181
Dry 490 1,770,045 132 683,282 472 1

[Oil 54 62,491 28 40,528 50

Producers I Gas ir 25,903 5 8,234 10
[Gas-distillate 3 4,156 3 4,'S6 3
Deeper-
pool Total 68 92,550 36 52,918 63
tests
Dry 80 96,615 28 43,129 79
Total 1jroducers 6SS 2,741,303 287 1,546,956 609 2
Total dry holes 3,188 12,381,061 1,369 6,680,512 2,927 11

* The horizontal totals of Columns C and D equal the items in Column A.

TABLE IX
E X P L O R A T O R Y D R I L L I N G I N 1943 I N N E W Y O R K , P E N N S Y L V A N I A , AND E A S T E

Pennsylvania
New York E
Deep Shallow
No. Footage Footage Footage
Wildcats Productive o 27,127 8
Dry 18 73,696 31,628 19
73,696 58,755

Outposts Productive 2,720 12,433 36,817 19

Dry 17,575 21,752 43,862 25
Total 6 20,29s 5 34,185 25 80,679 44

Deeper-pool tests Productive 0 0 489 7 14,406 0

Dry 0 0 \ 668 2 2,105
Total 0 0 2 16,511 0
1,157 9

Totals Productive 1 2,720 3 12,922 28 78,350 27

Dry 23 91,271 11 64,379 28 77,595 44
Grand total 24 93,99i M 77,3oi 56 155,945 71
720 FREDERIC H. LAHEE

of the degree of success of the exploratory effort (I and J, Table VII). Under G
and H the measure is short. Under I and J, the measure may be too large or to
small. In any case, there is an unavoidable error in estimating rate of discovery,
or degree of success in wildcatting, measured in terms of new reserves; but the
figures obtainable by these methods, as here described, are a significant index. As
shown graphically in Figure 3, they reveal a marked drop in the rate of discovery
from 1937 to 1943, inclusive, and this in spite of a steadily increasing footage
drilled in exploratory holes and an increasing number of exploratory holes drilled
each year. However, worthy of note is the fact that an increase in proved reserves
newly discovered in 1943 resulted from the marked increase in exploratory drill-
ing during that year. The effects of extending the newly discovered areas of 1943
should be observed especially in 1944 and 1945.
Up to this point, in Part III of this paper, the statistics which we have pre-
sented are analogous to those published in our earlier articles. They relate to the
several kinds of exploratory wells, all totalled together, and, although in this
paper we have called these exploratory holes (or wells), in previous years we called
them all wildcats. There are, of course, objections that may be raised to this
system since it fails to discriminate between those holes that are drilled to search
for new fields, on the one hand, and those which are drilled in fields already dis-
covered, on the other hand. The fact is that whatever the classification of an
exploratory test may be, if it is successful it will probably add materially to
crude oil reserves or to natural gas reserves. Therefore, from this point of view all
of these groups of exploratory holes merit consideration.
We are unable now separately to classify new-field wildcats and new-pool
wildcats of 1943, but we can group these together and list the data for wildcats,
outposts, and deeper-pool tests. This we have done for the major groups of states
in Table VIII. Observe that 3,014 of the exploratory holes drilled in 1943 were
wildcats, whereas 681 were outposts and 148 were deeper-pool tests. In other
words 78.4 per cent of all the exploratory holes recorded in this paper for 1943
were of the wildcat class. How much variation there may be in this relation from
year to year is impossible for us to say since we do not possess the data, but for
convenience and probably without introducing too serious an error, we might as-
sume that about 80 per cent would be satisfactory. If this is fair, we may estimate
that the number of wildcats drilled in 1942, under the same definition as that
adopted in the present paper, was somewhere near 80 per cent of 3,212 or about
2,570; which would mean an increase in exploratory drilling of the wildcat class
from approximately 2,570 in 1942 to 3,014 in 1943.
Whether we take the full number of exploratory holes (3,843) drilled in 1943,
or merely the wildcat group of 3,014, both figures are far below P.A.W.'s urgent
request for 4,500 in 1943. There is no question that the exploratory effort must be
still further intensified in 1944.
 EXPLORATORY DRILLING AND STATISTICS FOR 1943 721

APPENDIX

Through the kind cooperation of Fenton H. Finn, data were received on ex-
ploratory drilling in New York, Pennsylvania, and eastern Ohio, but too late
for inclusion in the main body of this paper. This is just as well since data on these
states, having never been received before, have not been included in our earlier
articles. For those persons who may be interested, we record these additional
statistics in Table IX. We wish to point out that all but one of the productive
(successful) exploratory wells in New York, Pennsylvania, and eastern Ohio,
were gas wells. Only one, with a depth of 3,514 feet is reported to have produced
oil, and this was completed as an oil-and-gas producer.