that is, the top and bottom of the illustration, would not be touched by the
injected water, and as a result a bank of unrecoverable oil would be forced
into this untapped area of the reservoir, The unflooded edge area chown in
figure 6 represents 25 percent of the total unflooded volume in pattern 1
only; however, the unflooded edge volume is approximately equal in all of
the flood patterns,

The volumetric efficiency obtained by this pattern at breakthrough was
60.0 percent, However, the test was continued to 117.5 percent of break-
through time, and the final efficiency at this time was 69.7 percent. The
volumetric efficiencies of all patterns or techniques were computed by first
enlarging and then tracing the outline of the copper-zinc ion interface from
the photographic record of the flood. The boundaries of the field (as shown
in all illustrations of these floods) were then added to complete the tracing.
The total area of each pattern was divided into rectangular wits by dividing
the width of the field into 30 equal parts, All unflooded areas in each
rectangle were planimetered and, from the scale determined for each tracing,
converted into unflooded acres, The unflooded volume under a particular
rectangle is the product of the unflooded acres in that rectangle and its
average thickness in feet, These unflooded volumes were totaled to give
the final unflooded volume of the whole pattern. The total acre-feet in
both the 500-foot or 600-foot spacing patterns were computed, and the
volumetric efficiency of a flood pattern was obtained by subtracting the
unflooded volume from the total volume, dividing this flooded volume by
the total volume, and mltiplying by 100,

Although pattern 1 (fig. 6) shows the lowest volumetric efficiency at
break-through, the quantity of electricity, in milliampere-hours, needed to
flood the pattern to break-through was elso very low. The quantity (milli-
ampere-hours) is the product of the total injection rate for all the injection
wells in a pattern illustration and the time required to flood the pattern
experimentally. For example, in the portion of the experimental field
illustrated in figure 6, 10 milliamperes flowed through each of the four
injection wells for a total of 40 milliamperes. Of the 40 milliamperes,
only 20 flowed from the field through the producing well shown in the illus-
tration; the remaining 20 milliamperes flowed through the two producing
wells, which were not included in the composite flood illustratim. The time
required to obtain the flood front at 100 percent break-through time was 4.3
hours, or a total of 860 ma-hr. At 117.5 percent of break-through time,
the pattern had used 101.0 ma-hr,

Pattern 2 (not illustrated) end pattern 3 (fig. 7) are identical, except
that the distance between rows of injection wells in pattern 2 represented
500 feet, whereas the distance between rows of injection wells in pattern 3
represented 600 feet, The producing wells were spaced 106.6 feet from tho
axis of the shoestring, or 213.2 feet apart, whereas the two outer injection
wells were 158 feet from the axis of the sand body. The thickness of the
gelatin field at the position of the center well was 0,094 inch, whereas the
thiclmess of the gelatin field at the position of an outer injection well
was 0,074’inch, Therefore, the center injection well's current or injection
rate was 1,28 times as lerge as an outer well's injection rate, This flood

waah -6-


Recoverable oil was determined by the equation:

-24P(Vg) = OLE (VY X 100,

O.4OP
ory
R = Q.24Vg = 0.16%, x 100;
O49
where,

R = recoverable oil in percent of total oil in
portian of reservoir studied, *

fraction of total reservoir swept by flood
(volumetric efficiency)

fraction of total reservoir not swept by
flood (1 ~ Vg),

<6
a 0

a
0

total pore space in reservoir, barrels.

Fran this equation, ‘the percentage of oll recoverable was determined
for each of the floods investigated. The average area of the four cross
sections shown in figure 2 was 14,023 sq. ft., and the gross volume of a
500-foot pattern was 161.0 acre-feet.

14,023 sq. ft. 0 ft.) = 161.0 acre-feet
5,500 8qe ft. per acre

A 600-foot. spacing contained 193.2 acre-feet of oll-bearing sandstone. The
total volume of o11 in 161.0 acre-feet is equel to:

(7,758 bbl. X (161 ac.-ft.) X (0.217 porosity)
ale . .

(0.49 o12 saturation) = 132,805 bbl.

The 193.2 acre-feet within a 600-foot spacing contained 159,375 barrels of
oil. The volume of oil produced at specific times for the various patterns
is shown in table 2 as theoretical oil recovery fran the pattern in. barrels,
This oil recovery is also expressed TMm an acre and acre-foot basis in the
table.

The quantity, theoretical water injected, was canputed by first
establishing a volume of water injected - milliampere-hour relationship for
each of the patterns. This relatimship was determined by canputing the
volumetric efficiency at various times before the ion interface fram any
individual injection well reached the ion interface fran any other injection
well end, also, at break-through time.

wah -n-


Figure 14. - Composite flood of pattern 10 - spacing 600 feet.




described by Botset.LL/ The position of the wells, either injection or
production, across the width of the field was determined by the cross-sectional
shape of the field (fig. ¥). ‘The trough representing the shoestring sand
was formed in a sheet of plastic 12 inches long, 6 inches wide, and 1/4 inch
thick by using a shaping tool. ‘The field's dimensions were 3/32 inch deep
at the center, 3 inches wide, and 8 inches long. To obtain the curve of the
pbottan of the shoestring, the total depth of 3/32 inch was considered to
equal 15 units. The cross sectio was divided into eight portims of equal
length, four on each side of the center line. At a point me-fourth the
distance from the center to either edge of the field, the curve rose onc-
fifteenth of the total depth; at the second point, three-fifteenths of the
total depth; at the third, seven-fifteenths of the total depth; and at the
fourth, the curve rose the remaining eight-fifteenths of the total depth,
and a shoulder 1/64 inch in depth was provided to insure a void space. between
the gelatin field and the bakelite cover plate.

‘The shape of the electrolytic model field used in these tests was
designed to give a cross-sectimal area comparable to an average cross
section of the oil-producing sand of the Paola shoestring. It must be re-
membered that a smooth, level, upper surface is required of the gelatin field;
therefore, all sand-thickness variations must be campensated in the bottan
curve of the trough.

With the shape of the field thus determined, the cross section of the
field was divided into two equal areas, as well as into three equal areas.
The centroid of the two equally divided areas was determined to be 0,533 inch
fran the center line. Using the three equal areas, the centroid of the
outer two was 0.79 inch fran the center line; the centroid of the center area
was in the exact center of the cross section. These distances represent
106.6 feet and 158 feet, respectively, as the model field was constructed to
a horizontal scale of 1 inch equals 200 feet. Most of the investigations
were made by using well patterns consisting of alternate rowa of two and
three wells in a line perpendicular to the axis of the shoestring. As the
rate of injection through any well was proportional to the thickness of the
reservoir at that point, the distances mentimed above were determined for
expected maximum flooding efficiency.

After the bakelite cover plate was drilled and the wells and trough
were filled with their appropriate gelatin solutions, the cover plate was
securely attached by means of cellophane tape to the sheet of plastic that
contained the electrolytic field. The wells were then placed in their
respective positions in the cover plate; the copper electrodes were inserted,
and a small amount of the appropriate clectrolyte solution was poured into
each well, as shown in figure 4, The current then was applied, and the flow
through the various injection and producing wells was adjusted to previously
computed values. It has been determined that the maximum permissible current
flow through any well in the equimment is 25 milliamperes; a greater current
will cause the formation of a gas bubble or will cause the gelatin to split
in the well tip, breaking the electrical circuit.

The different well arrays and techniques investigated were suggested
by the operators of the Paola shoestring. It is felt that these patterns
and the included data show the effect of well spacing, in both width and
L1/ See footnote 9.

4a -4A-



calculated value unless there exists a conditon of excess by-passing. In
this case the water:oil ratio will be excessive in the carly life of the
water-flooding project.

In evaluating the relative merits of the patterns studied to determine
which would most efficiently and economically water-flood a shoestring sand,
patterns 5, 6, 8, and 10 were elininated from consideration because they haa
either low volumetric efficiacles when they were stopped or the cost per
barrel of oil produced was high.

CONCLUSIONS

The rsults obtained from investigating these patterns and the derived
data show conclusively that wider spacing between rows of water-injection
wells increases the volumetric efficiency both at break-through and, there-
after, within the spacing limits investigated. The volumetric efficiency at
break-through increased 3.1 percent when the spacing was increased 100 feet.
This increase anounted to 9,537 barrels of oil above that which the similar
shorter spacing would theoretically produce at break-through time. Develop-
nent and water costs per barrel of oil produced at break-through were less
by 7-0 cents when the spacing was increased fram 500 to 600 feet.

Although the time needed to flood a longer spacing increases as the
distance between input and output wells increases, the profit obtained by
water-flooding a shoestring with the lmger spacing should more than ca-
pensate the operator for that extra tine.

Of the patterns studied, the pattern and technique shown as pattern 7
(fig. 11) is best suited to water-flood a shoestring’ send most effectively.
This pattem has two stages, the first having alternate rows of two injection
wells and two producing wells across the 600-foot width of the shoestring.
The injection wells in the first stage are 213.2 feet apart; the producing
wells are 316.0 feot apart, or 158 feet fran the axis of the field. When the
two producing wells were converted to injection wells and a central producer
was drilled to initiate the second stage, the pattern took the form of a
modified seven-spot flood pattern.

yah - 18 -
Interior, Bureau of Mines, Pittsburgh, Pa.








A 500-foot spacing in the Paola shoestring contained 161.0 acre-feet
of "pay", which is eaual to 7,011,500 cubic feet of sandstone; a 600-foot
spacing would contain 8,413,800 cubic feet of sandstone. . The following
calculation was made to determine the total barrels of pore volume available
to the injected water in the 500-foot spacing pattern, based on the assump-
tion that 40 percent of the total pore volume would be filled with injected
water; the 2k percent of the pore volume from which oil was recovered and
the 16 percent of the pore volume that initially contained gas:

(7,011,500 cubic feet) 0.217 porosity) y (0.40 pore volume )
x x
of sandstone ) (available to water)
(5.61 cubic feet/barrel)

= 108,484 bbl. of pore volume available to the
injected water, or the effective pore volume,

A comparable calculation for the 600-foot spacing shows 130,181 barrels of
effective pore volume,

Knowing the pore volume into which the injected water could flood and
the volumetric efficiency, the volume of water that had to be injected into
the pattern was determined, This volume of water was divided by the total
milliampere-hours the pattern required to that time. From one to four of
these calculations were made for each pattern and averaged to give the
relationship for each pattern. For example, in pattern 3, which was in-
vestigated using a 600-foot spacing, two photographs that could be used
for this calculation were made of the flood before break-through occurred.
The first photograph was made after 12 minutes had elapsed; the second
photograph after 2) minutes had elapsed, Break-through time occurred in
135 minutes (2.25 hours), as shown in table 2, Pattern 3 had a volumetric
efficiency of 6.52 percent at the time the first picture was made and
12.59 percent when the second picture was made, The volume of water that
had to be injected to attain the 6.52 percent volumetric efficiency was
determined as follows:

(130,181 bbl. of =)

(effective pore volume) X (0.0652) = 8,479 bbl, of water

This volume of water was divided by the total milliampere-hours used
to the time the picture was made. The current was 43,6 milliamperes and
the time was 0.2 hour, therefore:

etl bbl. of water
= 972.3 bbl. of water
3-6 x 0,2)ma-hr. injected per ma-hr.

yay -1-


ELECTROLYTIC MODEL STUDIES AS APPLIED TO WATER-FLOODING

A SHOESTRING SAND
by
William E. Eckard2/ and Jack A. Mason2/

CONTENTS

Introduction and SUMMATY.....cseeceeececcar renee scsceecercens
Acknowledgments.....seeee
Geology of Paola shoestring
Theory of electrolytic model.,.
Experimental procedure........+.
Description of tests....
Discussion of results.
Conclusions. ..cccccecccccccessercseccsecccecscesseesecesseees

TABLES

1. Comparison of patterns 2 and 3....cceeceecceccececcecceee
2. Summary of electrolytic model studies as applied to

water flooding shoestring sandS.,....cccssecccecsecccece
3. Calculated produced water:oil ratio for patterns 2, 3,

BNA Trcccccccccccvccccccssceccsccceeenesesceseceseseees

be Ss
SSUWW Pb HER

13
17

1/ Petroleum engineer, U. S. Bureau of Mines.
2/ Petroleum engineer, Brundred Oil Corp.

Report of Investigations 4778


Figure 13. - Composite flood of pattern 9 - spacing
500 feet.




Pe 21 a1
TM WS
I,

Figure 9. - Composite flood of pattern 5 - spacing

500 feet.


Figure 8. - Composite flood of pattern 4 - spacing
600 feet.








Figure 12. - Composite flood of pattern 8 - spacing
500 feet. .




INTRODUCTION AND SUMMARY ‘

Production of oil from a narrow shoestring sand presents problems unique’
in the oil industry. Especially important, fran both an engineering and an
econanic standpoint, are the limitations imposed upon well patterns and
spacings by the shape of the field. This report comcerns a study of the
Paola shoestring, Miami. and Franklin Counties, Kans., where well density of
0.85 acre per well was not uncamon to insure profitable primary recovery in
@ reasonable time. However, such a great number of wells increased the
operator's investment and reduced his profit considerably.

It was the purpose of this study to investigate various well patterns and
spacings applicable to water-flooding a shoestring reservoir and the effect
of these factors upon recovery of oil and the most profitable operation of
the pool. The designer of well patterns for a shoestring sand should evaluate
carefully the edges of the shoestring, even though they may be considered too
thin to drill. These comparatively thin edges contain large quantities of
recoverable oil; moreover they are resaturated with oil as the pool is water-
flooded, *

Several methods were used in designing the well patterns employed in this
investigation, The first flooding procedure had only me stage - injection
and producing wells were not changed at any time during progress of the flood.
A second method involved converting producing wells to injection wells
when the flood front reached an oil-producing well, or at some other specific
time. A third method included drilling additional producers at some inter-
mediate time in order to tap quantities of oil concentrated by the flood.

The electrolytic model tests indicated that the volumetric flood
efficiencies of the well pattéims. investigated renged fran 60 to 96 percent.
The most efficient flooding technique was a two-stage operation, the second
stage being a modified "7-spot" pattern; development and water costs were
only 19 cents per barrel of oil recovered by the operation. Well patterns
600 feet in length were 3 percent more efficient than the 500-foot patterns,

ACKNOWLEDGMENTS

This eleotrolytic-model investigation was made by the Bureau of Mines in
cooperation with the Brundred Oil Corp. under the general supervision of
R. A. Cattell, chief, Petroleum and Natural Gas Branch, Bureau of Mines,
Washington, D. C., and Sam S, Taylor, supervising engineer, Buréau of Mines,
Petroleum Field Office, Franklin, Pa., and under the direct supervision of
E. M. Tignor, petroleum engineer, Bureau of Mines, Franklin, Pas, and”
R. B. Bossler, Brundred Oil Corps » O1L City, Pa.

dak -1-


16.

17.

4114

ILLUSTRATIONS

Paola shoestring oil field, Miami and Franklin
Counties, Kans., showing location of cross sections
Cross sections A-A', B-B', C-C', and D-D' of oil-
producing formation, Paola shoestring, Miami and
Franklin Counties, Kans. ..ccececcsecerecccceeseeee
Electrolytic model apparatuS.....ccccccceeccsccsceeee
End view of gelatin field used in electrolytic model
study of a shoestring sand, showing machined plate
of plexiglas, bakelite cover plate, plastic wells,
and copper electrodes.......
Well array used in investigating pattern l......
Composite flood of pattern 1 - spacing 500 feet......
Composite flood of pattern 3 - spacing 600 feet. .
Composite flood of pattern 4 - spacing 600 feet...
Composite flood of pattern 5 - spacing 500 feet.
Composite flood of pattern 6 - spacing 500 feet......
Composite flood of pattern 7 - spacing 600 feet...
Composite flood of pattern 8 - spacing 500 feet.
Composite flood of pattern 9 - spacing 500 feet.
Composite flood of pattern 10 - spacing 600 feet
Volumetric efficiency - cumulative input relation-
ships of three patterns investigated irl the elec-
trolytic model study of water-flooding a shoestring
SANG. cee eeeeeee reece cece eescerecesaceresesceeeeeees
Development and water costs - volumetric efficiency
relationships of six patterns investigated in the
electrolytic model study of water-flooding a shoe-
StVing SANA. cee ececcccceccrccecccccecccccssceeceee
Volumetric efficiency - water:oil ratio relation-
ships of three patterns investigated in the elec-
trolytic model study of water-flooding a shoestring

SODA. cece eve veccccccccccc ccc sersceessccecsecsesses

-ii-

Follows
page

2

hea)

DODDDDONNE EE

14

16

16


length of the shoestring, on water-flooding a shoestring sand.. The distance
along the axis of the reservoir between rows of injection wells in all of the
tests represented either 500 or 600 feet; throughout this report this dis+
tance is referred to as spacing.

All these tests can be classified as follows:

1. Input rates proportional to the thickness of the gelatin at the
well location.

2. Input rates proportimal to the thickness of gelatin as given
above, but with some producers converted to injection wells when the flood
frot reached them, or at other longer times.

3. Similar to 2 above, but also including delayed drilling to tap
unflooded volumes in the central portion of a pattern.

Before describing each pattern, it should be made clear that all these
floods are through a medium which represents uniform porosity and perme-
ability, and the input and output fluids are of identical viscosities and
identical densities. The variation of viscosity and density of the fluids
involved in actual water-flooding operations usually does not introduce
errors of great magnitude when compared to a study of this type.

DESCRIPTION OF TESTS

Figure 5 shows all the well positions used in flooding pattern 1. A
small triangle is used to represent the position of an injection well, A
small circle represents a producing well's position. Figure 6 shows positions
of the flood front at various times during the test of pattern 1. In figure 6
and subsequent flood-front illustrations, only the area between two rows of
injection wells is shown. It is known that the current flow lines are
slightly distorted near the outer line of wells in an electrolytic model study
of this type Fancher analyzed this phenomenon in discussing some of the work
of Kelton.t2/ Therefore, to insure a true picture of the flood's progress,
only the central portion of the flood, where the flow lines are analogous to
field conditions , is included in this report. The flood-line designations
denote percentage of "break~through" time. For.the purpose of this paper,
this time is defined as the time at which the flood ’front reaches a producing
well, Breakthrough time in the producing well.is shown as the 100-percent
line.

Pattern 1 (fig. 6) cosists of four injection wells and one central
producer. The longitudinal scale distance between the rows of two injection
wells is 500 feet, and the transverse distance between injection. wells is
316 feet. As shown by these experiments, the outer edges of the shoestring,

ie/ Keltm, F. C., An Electrolytic-Model Study of Cycling in the Grapeland
Field, Houston County, Tex., sec. 9-A: Supplement to Secondary Recovery
of Oil in the United States - 1942, Am. Petrol. Inst., 1943, pp.
199-205. :

4k -5-


RUE

R22E

Figure 1. - Paola shoestring oil field, Miami and

Franklin Counties, Kans., showing lo-
cation of cross sections.

oe 2 7 wm mM

“—~Terganial and verFca] ak, eF ——

Figure 2- Cross sections Al’ 88: CC and 0-0 of oil prociacing formation, Reols Shoestring, Miami and Frsrktin
Counties, kansas

Figure 2. - Cross sections A-A', B-B', C-C', and D-D'
of oil-producing formation, Paola shoe-
string, Miami and Franklin Counties, Kans.


pattern and rate of injection produced a volumetric efficiency at break-
through of 73.0 percent, with rows of injection wells scaled at 600 feet
apart, and 70.8 percent when the distance between rows of injection wells
represented 500 feet. The volumetric efficiencies at other percentages of
break-through time are shown in table l.

TABLE 1. - Comparison of patterns 2 and 3

Volumetric efficiency, percent.:
Status of flood Represented distance between rows of
front, percent of injection wells
break-through time 500 feet 600 feet
LOO secscccceece 70.8 13.0
- 82.9
83.8 8 7)
: 917
- 92.9
90.3 -
eeeeee| 91.5 93.9
| 93-3 -
ZO oevesecerece 93-7 =

The 500-foot spacing of this flood used an amount of electricity equal
to 76.3 ma-hr. at break-through, whereas the 600-foot pattern used 98,1
ma-hr., or a 3.1 percent increase in volumetric efficiency with a 28.6 per-
cent increase in the total ma-hr. used. .

A line-drive flood, pattern.4, is show in figure 8 The position of
the outer line of wells, eithor production or injection, parallel to the axis
of the field, was moved out toward the edges of the gelatin field to ascertain
what effect a wider well spacing across the width of the shoestring would
have on the unfloodable edges. The distance between these well positims and
the axis of the field was 1.04 inches. This scaled distance would be 208 feet
from the axis of the field, or 92 feet from the edge of the producing horizon.
The spacing between rows. of injection wells was scaled at 600 feet. ‘this
flood pattern contains six injection wells and three producing wells. Break-
through occurred in all producing wells at the same time. At break-through,
the volymetric efficiency of this line drive was 61.7 percent; at 121 percent
of break-through, 69.8 percent; at 145 percent of break-through, 73.3 per-
cent;,and at 162 percent of break-through, 81.1 percent, ‘he. totel amomt
of electricity used was 154.8 ma-hr. No apparent increase in volumetric
efficiency was obtained, nor were more of the edges of the gelatin field
flooded by increasing the well spacing across the width of the shoestring,

. The renaining patterns investigated were changed after break-through had
taken place; this change is thought of as changing the stage. A stage is a
pattern arrangement until break-through has taken place. The position of the
flood front during these different stages and the changes fron producing to
injection wells are shown in different lines; that is, the first stage as

a solid line; second stage, dotted line; third stage, long-and-short dashed
line.

yy -7T-


Bureau of Mines
Report of Investigations 4778

ELECTROLYTIC MODEL STUDIES AS APPLIED
TO WATER-FLOODING A SHOESTRING SAND

By WILLIAM E. ECKARD AND JACK A. MASON

United States Department of the Interior— March 1951

/metadc38559






Figure 3. - Electrolytic model apparatus.






at any time, The deviation of the flood-pattern curves from this line
represents the amount of water being produced, because total fluid pro-
duction equals total fluid injection.

The error, which is primarily human, introduced into the data by the
calculations for both the volumetric efficiency and the cumulative input,
is shown by the difference between the data at break-through and the
straight line. The points should fall on the line; this error averages
2,8 percent for the three patterns shown, pattern 7 being largest, having
4,4 percent error at the break-through point.

To compare the efficiency of the two spacings, patterns 2 end 3 may be
compared, because the transverse distance of thé well positions in both
patterns was equal, It can be noted that the efficiency at break-through
increased 3.1 percent when the spacing was increased 100 feet (patterns 2
and 3, fig. 15). The 600-foot pattern theoretically would have recovered
2.9 percent more oil at break-through than the 500-foot spacing would be
expected to recover with the use of 18.6 percent more water. The points
that represent. the same percentage of break-through time in patterns 2 end
3 (table 1) may be compared in figure 15, In all cases, the 600-foot
spacing increased the volumetric efficiency at specific times,

Musket'«3/ mathematical analysis of the efficiency of the staggered
line drive has shown an increase in percent of total volume flooded at
break-through time if the spacing is lengthened, Although the well pattern
Imown as pattern 3 (fig. 7) is not a staggered line drive, it is quite
similar in many respects and may be considered as a modified form of the
staggered line drive.

The relative merits of patterns 7 and 3 should be compared, as they
show the best possibilities of water-flooding a shoestring reservoir,
Pattern 7 (fig. 11) in its final stage has the same well positions as
pattern 3, but the type cf well in that position has been changed. Figure
15 shows that the first stage of pattern 7 was not as efficient as pattern
3, but when the second stage of pattern 7 had beon initiated, the volume of
the pattern that was swept by the same amount of injected water was far
greater than that swept by pattern 3, For example, when the cumulative in-
put had equaled 140 percent of the effective pore volume in both patterns,
pattern 7 had flooded 3.0 percent more of the pattern's volume, .This means
that more of the reservoir volume would have been exposed to the injected
water for a longer period of input time in pattern 7 than in pattern 3;
although the evidence indicates that all the patterns, with their different
techniques, would eventually reach an efficiency of approximately 96.0 per-
cent if they were continued to their appropriate amount of input time.

The other patterns (1, 4, and 9) from which enough data were obtained
to plot into the form shown in figure 15 have been eliminated, either for
low volumetric efficiencies or excessive costs.

15/ Muskat, M., The Flow of Homogeneous Fluids Through Porous Media:
Second edition, J, W. Edwards, Inc., Ann Arbor, Mich., 19h6,
p. 594, sec, 9.28,

yy -15 -


Figure Il. - Composite flood of pattern 7 - spacing 600 feet.


Cooperation of the management of the Brundred Oil Corp, in furnishing
the field data relative to the Paola shoestring, which made this investiga-
tion possible, is gratefully acknowledged, Special acknowledgment is made
to W. Js Brundred, L. L. Brundred, B, F,. Brundred, and R. B. Bossler, of the
operating corporation,

Acknowledgment is made for constructive criticism of the report by
H. G. Botset, head, Petroleum Engineering Department, University of Pitts-
burgh, Pittsburgh, Pa.; W. J. Brundred, president, Brundred Oil Corp.;
R. B. Bossler, chief production engineer, Brundred Oil Corp., and consulting
petroleum engineer, Bureau of Mines, Oil City, Pa,; Sam S, Taylor, supervis-
ing engineer, Bureau of Mines, Franklin, Pa,; and E, M. Tighor, petroleum
engineer, Bureau of Mines, Franklin, Pa.

The illustrations used in the report weré prepared by the Graphic Serv-
ices Section, Central Experiment Station, Bureau of Mines, Pittsburgh, Pa.

GEOLOGY OF PAOLA SHOESTRING

The location and shape of the Paola shoestring are shown in figure l.
This pool is 8 miles long but varies in width, thickness, and shape through-
out its length. The sandstone has a minimum width of approximately 300 feet
and a maximum width of 600 to 700 feet, The reservoir rock of the Paola
shoestring is either a sand-filled river chamel or a shore feature as
described by Base.3/ The productive sand-body is the Squirrel sand in the
Cherokee group of Pennsylvanian age, as mentioned by Newell and Jewett.
Figure 1 also shows the location of the cross sections shown in figure 2,

Generally, the oil-bearing formation, which is approximately 700 feet
below the surface of the ground, is thickest in the center and thins out
toward both edges umtil it disappears, Some cross sections (fig. 2) show a
thickening toward one edge, whereas others show a thin portion in the middle
of the cross section and greater amounts of sandstone on both edges, The
thickness of the sandstone reservoir. ranges fram 18 to 60 fect along the
axis of the shoestring.

At the bottom of the producing formation, a zone of black micaceous
sandstone from 6 inches to 12 feet in thickness sometimes is found. A high
saturation of asphaltic substance is found in this black sandstone; but the
asphelt-saturated sandstone is nearly impermeable, and the oil content is not
recoverable by water flooding, This black sand is not separated from the oil
sandstone by shale or other type of break, In the cross sections of the
shoestring (fig. 2), this black sand has been omitted.

Analyses of core samples from 10 wells indicate average field conditions,
as follows: porosity, 21,7 percent; permeability, 50 md; oil saturation,
49 percent; water saturation, 35 percent; oil content, 820 barrels per

3/ Bass, N. W., Origin of Shoestring Sands in Greenwood and Butler Counties,
Kans,: State Geological Survey of Kansas Bull. No. 23, Univ. of Kans.
Bull, vol. 37, No. 18, Sept, 15, 1936, p. 87.

a/ Newell, N. D., and Jewett, J, M., The Geology of Johnson, Miami, and
Wyandotte Counties, Kans,: State Geological Survey of Kansas Bull,
No, 21, Univ. of Kans. Bull, vol. 36, No, 10, May 1935, p. 14.

Lid -2-




Four injection and four producing wells were used in the first stage of
pattern 9; the composite flood is show in figure 13. The second stage of
the pattem contained eight injection and one producing well. All the well
positions along the outer edges of the shoestring are located 158 feet from
the axis of the field, whereas 500 feet along the axis of the field separates
the injection wells in the first stage. Break-through in the first stage for
the pattern was considered to be the time of arrival of the ion interface at
those producing wells that were 250 feet from the injection wells. This
pattern was flooded until 168 percent of break-through time before the second
stage of the flood was started. The second stage of the pattern was initiated
by changing four producing wells to injection wells and drilling a central
producer. This stage of the flood was. continued until the copper ions had
replaced the zinc ions in the central portion of the field. The position of
the flood front along the edge of the sand body at this time is shown as the
100 percent break-through-time line in the second stage of figure 13. When
the central portion of the shoestring was completely colored by the injected
ions, patter 9 had flooded 86.9 percent of the total volume, During the
first stage of this pattern, 60.6 percent of the total volume was flooded
at 100 percent of break-through time; 69.8 percent of the volume was flooded
at 125 percent of break-through time; and at 168 percent of break-through,
76.7 percent of the total volume was flooded. The quantity of electricity
uséd in both stages of the test was 193.2 ma-hr.

The flooding technique used in pattern 10 (fig. 14) has three stages.
This technique has many detrimental economic factors in its completion but
was investigated to examine the possibility of increasing the flooded volume
of the field by using more than two stages. The first and second stages of
this flood are shown as in the preceding composite flood illustrations; the
third stege of this flood is shown as a long-and-short dash line. The
distance between rows of injection wells in the third stage was 600 feet;
158 feet separated the wells.on the outer edges of the shoestring from the
axis of the field. Four injection and four producing wells were used in the
first stage; six injection and two producing wells were used in the second
stage; eight injection and one producer, which was added at conversion time,
were used in. the third and final stage of this flood pattern.

Break-through in the first stage was considered to have taken place when
the ion flood front reached those producers that were positioned on the axis
of the field, even though the injected ions had not reached those producers
that were 300 feet from the injection wells. The two producing wells that
experienced break-through then were converted to injection wells, and the
flood continued until it broke into the producers parallel to the axis of
the field. At this stage in the flood the producer shown in the center of
the illustration was inserted in the cover plate, end all other wells show
were converted to injection wells. This flooding pattem and technique show
a volumetric efficiency.of 87.9 percent at the time when the center of the
pattern was completely flooded. +: The flood front at this time is shown es the
100 percent break-through-time line of the third stage. This flood required
144.8 ma-hr. to attain the above volumetric efficiency.

4h -9-


DISCUSSION OF RESULTS

The results obtained by Wyckoff and BotsetL3/ fran the use of the
electrolytic model on simple floods. have been proved to have an accuracy of
95 to 98 percent when compared with results obtained by mathanatical analysis
for simple floods. Therefore, the results of this study are assumed to be
within that limit of accuracy. Pattermms 2 and 3 were investigated for re-
producibility. At break-through time, pattern 2 showed volumetric efficiencies
of 69.8 percent end 70.8 percent, whereas pattern 3 showed 71.7 percent and
73.0 percent volumetric efficiency, or an average variation of 1.6 percmt.
These results show that eny pattern or technique may be reproduced with good
accuracy, and it is logical to assume the results obtained from this study
are within the accuracy of the electrolytic model.

The amount of oil that could be produced by water-flooding a reservoir
that has the characteristics of the Paola shoestring can be determined from
the volumetric efficiencies and pertinent core-analysis deta. However, it
has been mentioed previously in this report that the thin edges of a shoe-
string reservoir will not be swept by a water flood, although this unflooded
volume contains an appreciable quantity of oil. ‘The pressure distributim
established by the water flood would force a portim of the theoretically
recoverable oil from the flooded portia of the reservoir into these edges.
The oil saturation of the unflooded volume would be increased, and the void
spaces in this portio of the reservoir would be campletely filled. The
operators of the Paola shoestring have found this phenanenm to occur in the
field. One old, abandoned, but improperly plugged primary production well
in the thin edge area of the shoestring flowed oil to the surface of the
ground after water had been injected into the sand; the oil forced into
these edges mast have moved into this area from the portion of the sand that
had been swept by the water flood.

The ges-filled portio of the Paola shoestring amamnted to 16 percent
of the total porosity before the water-flooding operation started, and the
authors have assumed this 16-percent void space to be resaturated with oil,
end the liquid saturation of the unflooded portim of the shoestring to
be increased to 100 percent during the water-flooding operation. If the
liquid saturation of the unflooded volume of sand is not increased to 100
percent, more oil will be recovered than is computed in this report. It is
further assumed that the residual oil saturation at the end of the flood will
be 25 percent in the flooded portion of the field; consequamtly, the oil
recovered amounted to 24 percent of the pore space in that portion of the
field. An equation for determining recoverable oil has been derived from
these assumptions and pertinmt core data; a summary of saturation conditions
is listed below.

Fraction of

porosity
Oil saturation at start of flLOOdssececseecceees O49

Water saturation at start of flood. eee . 3D
Gas saturation at start of fl0ods..eceeees . 16
Qil saturation of flooded portim of reservoir

at end Of FLO scceevecvcascecccevecvccsscses 225
Oil removed from flooded portion of reservoir.. ook

137° See footnote 6.
way - 10 -



TABLE 3. ~ Calculated produced water:oll ratio for
patterns 2, 3, and 7

Status of flood front,
Volumetric | percent of break- Theoretical produced
Pattern efficiency throygh time water:oil ratio
2 70.8 100 0.00
83.8 ! 150 260
90.3 200 1.12
91.5 250 1.79
9303 300 2.38
9367 350 3.04
3 73.0 100 00
82.9 . 125 18
Hy 8763 150 46
G17 175 68
92.9 198 95
939 250 1.62
7 (first stage) 64.0 100 00
Thek 127.2 ell
82.0 150 oh
86.3 175 45
87.3 200 vo)
7 (second. stage) 92.6 100 60
935.6 200 60
959 300 +62
94.5 450 65
95.2 600 67
95-4 1,000 78
95-8 2,600 leat
Totalecsscoce 95.8 = 1.2L

The question now arises as to when 200 percent of break-through tine
occurs in the first stage of pattern 7, or when, during the progress of the
water flood, the operator should change his producing wells to injection
wells as shown in pattern 7 (fig. 11). Assuming an injection rete of 2
barrels of water per foot of sand per injection well per day, and with the
pertinent core data, the time scale for this flood was determined. The
average sand thickness (23.4 feet) was calculated fram the cross-sections
shown in figure 2. The established injection rate was 93.6 barrels of water
injected into the pattern per day. Fraa table 2, 79,790 barrels of water was
required to flood the pattern to break-through; therefore, 852 days, or 2.4
years, theoretically would be needed for break-through to occur in the first
stage of flood pattern 7. Theoretically, then, 4.6 years would be the time
required before changing the wells. The pattern should then be flooded wntil
the operator realizes no profit fran the water-flooding operation. In field
operations the break-through time should not be greatly different fran the

yaad -17-








VOLUMETRIC EFFICIENCY, PERCENT

100

Pattern No. 3-600’ spacing
p—tar ----4------}----- L-—---{-____]
30 Zs © | O-— Pattern No. 2-500’ spacin,
A Fate No. 7-600’ spacing
4
ZF
80 Y VA
iN
70
nf
60
60 100 140 180 220 260

CUMULATIVE INPUT, PERCENT OF EFFECTIVE PORE VOLUME

Figure 15. - Volumetric efficiency-cumulative input relationships of three patterns investigated
in the electrolytic model study of water-flooding a shoestring sand.


Canparable calculations were made for the other two pictures (one at
24 minutes and the other at break-through time). The average of these three
values equaled 961.3 bbl. of water injected per ma~nr. No explanation can
be given for the variation between these individual calculations for any
one pattern. The quantity, barrels of water per ma-hr., varied slightly
between patterns, probably because the minute variations in the volume of
water that evaporated while boiling the gelatin field solution for each
investigation is reflected in the above relatimship, although very little
error is induced because the unit volume of gelatin flooded by the unit
quantity of electricity in any pattern is a functim of the thickness of the
gelatin field.

The theoretical volumes of water injected into each pattern at specific
times and volumetric efficiencies is shown in table 2. Fran the total volume
of the pattern available to the injected water, the cumlative input, in
percent of effective pore volume, was calculated.

The various well arrays have been studied to determine which well
pattern or flooding technique would be most profitable to the field operator,
In any econamic study of water-floading projects, consideration must be given
to the development costs and operating expenses. As all producing wells in
the Paola shoestring are equipped to flow, the estimated cost of an injection
or a producing well in this area is approximately $2,000. It is estimated
that $115 would be needed to covert a flowing producer to an injection well.
The development costs per pattern reported in table 2 include mly well-
completion and well-conversion costs.

Injection water costs also were considered and calculated by Yuster tal!t/
equation for determining the delivered cost of water to an injectio well
per barrel - in. which D, the cost in dollars per barrel injected, is equal
to 0.012 + 0.00000445 P; where P is the wellhead injectim pressure. Using
an injectio pressure of 720 p.sei., the cost per barrel of water injected
in any of the pattorns studied is equal to $0.0152, and water cost per
pattern is show in table 2.

The pre-eminence of any pattern or technique studied can be determined
fran the volumetric efficiency at specific times, the water costs derived
frau the quantity of electricity used, and the volumetric efficiency, as wall
as the costs of canpleting and converting the wells in a pattern. The develop
nent and water costs per barrel of oil produced are given in table 2. The
500-foot spacing cmtained 6.89 acres, whereas the 600-foot spacing contained
8.26 acres; the development costs per acre are also given in the table.

Figure 15 shows the relationship between volumetric efficiency and the
cumulative input in percent of effective pore volume for patterns 2, 3, and
7. The spacing used on patter 2 was 500 feet, whereas patterns 5 and 7
were flooded, using a 600-foot spacing.

Of all the patterns investigated, only the three most promising were
enalyzed by the graphic-form method shown in figure 15. The volumetric
efficiency at break-through time is shown in the lower left corner of the
graph. The straight line m the graph represents the total cumulative input

i4/ Yuster, S. T., Water Flood Spacing: " Producers Monthly, vol. 12, No. 1,

Nov. 1947, p. 18. .
ome -~ 1h -



Liu

NN N

EI
x
=z Electro re
solution
Gelatin
solution Zi"

—_
4 Plexiglas
y

°
L

Figure 4. - End view of gelatin field used in electro-
lytic model study of a shoestring sand, show-
ing machined plate of plexiglas, bakelite
cover plate, plastic wells, andcopper elec-

trodes.
Aa Aa
° fe} °
4a Aa

Figure 5. - Well array used in investigating pattern |.




Figure 6. - Composite flood of pattern | - spacing
500 feet.


ELECTROLYTIC MODEL STUDIES AS APPLIED
TO WATER-FLOODING A SHOESTRING SAND

By WILLIAM E. ECKARD AND JACK A. MASON

* * * « « «* « « « Report of Investigations 4778

UNITED STATES DEPARTMENT OF THE INTERIOR
Oscar L. Chapman, Secretary
BUREAU OF MINES
James Boyd, Director

Work on manuscript completed February 1950. The Bureau of Mines will welcome reprinting
of this paper, provided the following footnote acknowledgment is made: “Reprinted from
Bureau of Mines Report of Investigations 4778,”

March 1951




Pattern 5 (fig. 9) shows the first-flood pattern employing more than me
stage of flooding. This pattern cmtained four injection wells and two
producers in the first stage. The flood front in this first stage is shown
as a solid line. The second stage was initiated when the two producing wells
on the axis of the shoestring experienced break-through. These two wells
then were converted to injectio wells, and e single central producer was
drilled midway between the rows and on the axis to drain the central portion
of the patterns This is the first flood pattern using a delayed drilling
prosedures

The second-stage flood pattern thus cotained six injectim wells and
one producing well, and the distance between rows of injectio wells was
500 feet. An injection well and a producer in the first stage were spaced
158 feet apart. The second stage of the flood:was continued until 164 per-
cent of break-through; at this time the flood attained e volumetric efficiency
of 82.6 percent, using an amount of electricity equal to 102.2 ma-hr.

In pattern 6 (fig. 10), the first stage has-been reversed slightly fran
the previous well pattern (fig. 9), in that two injection wells in the
pattern were used with five producing wells. Whe the-four outer producing
wells experienced break-through, they were converted to injection wells, ond
the flood continueds The distance between injectim wells across the shoe-
string in the second stage is 158 fect, and 500 feet separate rows of in-
jection wells. This flood was cmtinued until 237 percent of break-through
time and attained a volumetric efficiency of 76.6 percent, using 122.7 -
ma-hre

Pattern 7 (fig. 11) shows a flood pattern using four injection wells and
two producing wells in the first stage. Along the axis of the shoestring
in the first stage, the distance between rows of injection wells was 600
feet; the distance between injection wells was 213.2 feet; and the two pro-
duction wells in the first stage were spaced 316 feet apart. ‘The first stage
of this pattern was continued until 200 percent of break<through time, At
this time the producing wells were cmverted, as show, to input status, and
e central producer was drilled to drain the central portion of the pattern,
making a pattem of six injection wells and one producing well. After can-
verting to the second stage, the injection was continued until 2600 percent
of break-through time in this stage; break-through time was 6 minutes in this
stage, as compared with 2.2 hours in the first stage of this pattern, In
the first stage of the test shown in figure 11, the pattern showed e vol-
umetric efficiency of 64,0 percent at 100 percent of break-through, 82.0 per-
cent at 150 percent of break-through, end 87.3 percent at 200 percent of break-
through. At the close of the second stage, the volumetric efficiency of
this flood was 95.8 percent, using 234.8 ma-hr.

The pattern end technique of pattern 8, shown in figure 12, are virtuelly
the same as the preceding investigation, the only exceptions being that the
spacing was 500 feet and the first stage was continued only until bresk-
through time, The pattern was then converted, and injection cmtinued to 186
percent of break-through time in the secmd stage. At this time 89.5 percat
of the total volume was flooded, using 122.9 ma-hr.

an -8-




Figure 16 shows the relationships. between ‘costs (development and water)
and volumetric efficiency. These curves again show the advantage the
operator would obtain by water flooding the shoestring with a 600-foot
spacing. In caiparing patterns 2 and 3, it will be noted that of the costs
studied, a barrel of 011 may bo produced for 7.0 cents less at breek-through
using the wider spacing. The curves of patterns 1, 4, and 9 have been
extrapolated to the form followed by the curves of patterns 2, 3, and 7.

All the curves turn upward in the leter stages of all the floods, because a
unit volume of water becomes less efficient as the flood progresses, and more
water has to be injected to produce the same quantity of oil. The curves
have been temainated at 96.0 percent volumetric efficiency, as it is believed
that this is the maximum volume that could be flooded. At this point, the
cost per produced barrel of oil would increase in a straight-line relationship
The volumetric efficiency at break-through time of each pattern is given

in table 2. The volunetric efficiency at break-through time for pattern 9
does not fall within the limits of the graph in figure 16. It is a coin-
cidence that pattern 2 (500-foot spacing) and pattern 4 (600-foot spacing)
very closely approximate each other on these graphs. The figure shows that
patterns 3 and 7 excell in having low costs at high volunetric efficiencies.

Figure 16 also shows the pre-azinece of pattern 7 over pattern 3,
because the total volume of oil-bearing sandstome exposed to the water is
greater in pattern 7. Therefore, the reservoir oil can be produced at a
cheaper cost per barrel. It is estimated that when 95 percent of the field
has been swept by the injected water, the cost of producing a barrel of oil
would be 3.7 cents less with pattern 7 than with pattern 3. In other words,
less water would be required to produce a similar volume of oil.

The authors have attempted to obtain a quantitative indication of the
produced water:oil ratio. The following calculation was made'with these
assumptions: (1).No formatiom water was moved, (2) the volume of fluid
produced equaled the volune of fluid injected, and (3) no water was produced
until after break-through tine had occurred. The volume of injected water
that had to be produced was calculated fron the total cumulative water input
at the different volumetric efficiencies. The produced water:oil ratio
(table 3) was obtained by dividing this volume of water by the volume of oil
produced, as indicated by the volumetric efficiency. These ratios at different
times during the flood's progress of patterns 2, 3, and 7 are shown in
figure 17, It is realized that the data from which these curves were obtained
are theoretical, and their value lies mly in indicating the trend that the
produced water:o0il ratio should follow; but it is of interest to note the
variations between the three patterns and the effect the second stage of
pattern 7 has upm that pattern's water:oil ratio.

Wah - 16 -




TABLE 2. - Sumary of electrolytic nodel studios as applied to water flooding a shoestring sand

j Theoretical Developaent
Patera Fattem stdtus of | Theoretical | Theoretical | Theoretical | Thearetical | Theoretical | water injected, | Development and water
or | length, | Pattern | Pattern | Length | quantity of | Volumetric | flood, percent | oil recovery, |oil recovery | oil recovery | oil recovery | water injected| percent cost per | Water cost | cost per bbl. | ell density, | Development
technique spacing, | area, | volume, | of test,| electricity,| efficiency, of break- | percent of | from pattern, | from pattern, | from pattern, | into pattern, | of effective | pattern, | per pattern,| of produced | acres per | cost per acre,
Wo. ft. | acres facre-fect| bre. ma-hrs. | percent | through time | ofl in place bbl. bol. per acre | bbl./acre-ft. bel. pore wolune | dollars | dollars | oil, dollars well dollars
1 500 6.89 | 61.0 [4.30 86.0 60.0 100.0 16.3 21,647 3,u2 135 63,029 58.1 + 958 0.321
5.05 101.0 69.7 nrs 22 32,239 45665 200 74,023 68.2 6,000 2,135 +222 2.30 on
2 500 6.09 | wi.o | 1.75 76.3 ‘p.8 100 33,334 4,838 207 79,489 B3 1,208 +306
2.8 14.7 83.8 150 47,810 27 129,494 0.1 jane 1247
3.50 152.6 90:3 200 54, 583 339 158,978 6.5 2,46 1227
4.38 391.0 a5 250 55,78 346 198,984 13.4 3,025 123
5.25 228.9 93.3 300 57,770 359 238, 9.8 3,625 126
33 267.3 3.7 350 58,169 361 278,473 256.7 110,000 4,23 12s 1.38 2,452
3 600 2.26 | 193.2 | 225 98.1 3.0 100 2,871 5 22 94,304 Rk 1,433 +266
2.81 122.5 2.9 15 55,78. é 239 127,759 90.5 1,790 im
3.38 UIb 87.3 150 61518 Tk aa 141,696 108-8 23154 1198
3.94 ime 7 175 61,255 8,u2 38 265,151 226.9 2,510 1186
5 194.0 92.9 198 a, 81316 356 1865492 3.3 2,835, 1387
5.62 245.0 93.9 250 705124 8,490 363 235,519 180.9 10,000 3,580 +194 1.65 1a
4 600 8.26 | 193.2 | 2.65 5.4, 6.7 100 28,209 3,45 Ub 74,012 56.9 1,125 465
3.20 135.2 a8 wi 38,887 43708 201 89,372 68.7 1,358 344
3.78 136.1 B3 ua 13,349 5,28 2a 105,586 ald 1,605 34
4.30 154.8 ai 162 53,390 6,464 76 120,094 9233 12,000 L825 1259 1.38 1,453
5 | Firet stage 500 6.89 | 11.0 | 1.90 23.9 100 22,669 20.9 345
Second stage 3.80 8.3 74,268 68.5 1129
5:70 102.2 82.6 34.8 46,216 6,708 287 96,937 99.4 2,15 1UB 208 1a7e
6 | First stage 500 6.89 | 161.0 | 2.50 30.0 100 29,697 2.2 4s
Second stage 4.50 52.7 91,764 84.6 1,395
Total 6.00 122.7 6.6 237 2 39,709 5,763 2a 121,461 12.0 10,230 Lyeae +304 1.72 1,485
7 | Firet stage 600 8.26 | 193.2 | 2.20 88.0 64.0 100 1.6 31,297 3,762 12 79,790 61.3 1,23 366
2.80 22.0 The 27.2 28.0 3626 5,402 ZL 201,550 78.0 13544 1264,
3.30 132.0 82.0 150 36.3 5,665 eens 283 19,684 91.9 1,819 1220
3.85 154.0 86.3 175 37.8 5203 7,23 32 139,632 207.3 2y122 1205
eho 176.0 87.3 200 38:6 61,518 78 3B 159,579 122.6 25426 1205
‘Second stage on10 2.3 2.6 00 i290 @3n 8,277 354 ¥ 124.2 2,457 1186
0220 ha 3.6 200 3.7 646 8,432 361 163.659 25.7 2,488 283
0,30 6.8 B.9 300 44.0 70,324 8,490 363 165,745 27.3 2,519 11s2
onhs 2 9.5 450 445 77,921 8,586 367 168,828 129.7 2,566 +180
0.60 95.2 600 45.1 ner 8,702 a2 im,s10 Bar 2,63 1178
1.00 5.4 1,000 45.2 2,037 8,721 3D 140,07. 138.3 2,737 1180
260 95.8 2} 600 45.6 256% 2,798 3% 212,893, 163.5 3,236 1186
Total 7:00 95.8 45.6 72,604 3,738 376 212,893 163.5 19,230 3,236 11086 1.65 1,238
8 | First stage 500 6.89 | 161.0 | 2:00 . 100 625704 7.8 953
Second stage 1-90 42.9 33,625 sa
Total 3.90 122.9 89.5 6 dw. 53,659 7,787 333 36,329 #8.8 1,230 1,464 28 1.38 1,485
9 | First stage 500 6a | 11.0 | 2.50 715 60.6 wo we 22,30. 3,238 9 R,28 66.6 1,098 +607
3.20 120.9 69.8 25 2.3 32,222 4,67 200 99,587 82.6 15362 1428
4.20 163.8 6.7 168 3 39,709 5,763 27 121,376 m9 13845, 1360
Second stage 1.40 Bb 21,785 332
Total 5.60 193.2 26.9 38.3 50,864 7,382 316 43,162 132.0 12, 460 2,176 288 1.01 1,008
20 | First stage 600 193.2 | 2.00 39.0 200 29,550 22.7 M9
Second stage 170 68.0 100 51,524 62.3 3
Third stage 1.80 37.8 28,641 435
Total 4.50 whe 87.9 39.2 62,904 T,5hh 393 109,715 84.3 12,460 1,668 27 1.38 1,508

sue -B-


Figure 10. - Composite flood of pattern 6 - spacing
500 feet.


acre-foot. The oil at both ends of the shoestring has an API gravity of 32
degrees, but near the central part the gravity drops to 28 degrees, This
low-gravity oil in the center of the shoestring may be a result of vertical
faulting, of which direct evidence has been obtained by means of & diamond
cores

THEORY OF ELECTROLYTIC MODEL

The statement of the analogy between the flow of liquids in rocks and
the flow of, electricity in sheet conductors was first published by C. S.
Slichter in the 19th Annual Report of the U. S. Geological Survey, 1897-1898,
p. 303. In this report he wrote: "I find the problem (of the movements of
water in soils and rocks) is capable of mathematical treatment, and I show
that the question is analogous to a problem in the conduction of heat or
electricity or to any other problem involving the transfer of emergy."

_The theory of the electrolytic model as applied to oil-field problems
has been presented by Muskat and Wyckoff ny, Wyckoff and Botset,

6
Swearingen Hurst and McCarty, 8/ and Botset.2/ Horner and Brucelo/ have
recently presented the analogy bétween the flow of electricity in-a homo-

geneous conductor and the flow of a fluid in a hamogeneous: porous medium.
In brief, the principle of operation of the model used in this investigation
is the transference of positive copper ammonium ions in a copper ammonium
chloride solution fron the positive terminal of direct current to the
negative terminal through a gelatin field containing zinc ammonium chloride
ions, As the blue copper ammonium ios move under the influence: of the
potential applied through the field, they displace the colorless zinc -
ammonium ions and fom a camtinually expanding pattern about the positive
injection well, As the current continues to flow, the ions follow the
steamlines set up by the applied potential and form a pattern that conforms
to the volume of the reservoir that would be flooded by injected water, A
photographic’ record is made at various stages of the flood's progress.

EXPERIMENTAL PROCEDURE

The equipment (fig. 3) and procedure used for investigating the different
well arrays used in this investigation were essentially identical to those

5/ Muskat, M., and Wyckoff, R. D., A Theoretical Analysis of Water Flooding
ing Networks: Trans. A.I.M.E., vol. 107, 1934, pe. 62.

6/ Wyckoff, R. D., and Botset, H. G., An Experimental. Study of the Motion
of Particles’ in Systems of Complex Potential Distribution: Physics,
vol. 5, 1934, pe 265- . 7

u Swearingen, J. S., Predicting Wet Gas Recovery in Re-cycling Operations:
Oil Weekly, vol. 96, No. 3, Dec. 25, 1939, pe 30.

e/ Burst, W., and McCarty, G.M., The Application of Electrical Models to
the Study of Re-cycling Operations .in Gas-Distillate Fields: Drilling
and Production Practice, 1941, p. 228. .

9/ Botset, H. G., The Electrolytic Model and its Application to the Study
of Recovery Problems: Pet. Tech., T.P. 1945, Nov. 1945.

10/ Homer, W. L., and Bruce, W. A., Electrical Model Studies of Secondary
Recovery, che 14; Secondary Recovery in the United States, 2d ed.,
Am. Petrol. Inst., 1950, pp. 195-203. :

yh -3-


Oot

“pues Gul4zsa0ys e Bul poo[4-sazeM Jo Apnys japow 91340439919 94} UI pozebIzsSeAU!
Susazzed XIS JO Sdiysuolzejas ADUGIDI¥Ja D/4}9WN|OA-S}SOo 4azeM puke ZUaWdO[aAeq - *9| a4nB14

ANIOUAd ‘AONZIOISS3 DIYLIWNIOA,
06 08

o£

09 os

Burseds ,009-

pret

€ ‘ON Wayeg

7SY

i oR
«t—~_|

Buloeds ,QOG-T ‘ON Wayeg

Jf

Cauoea 00S- Z ‘ON Wayeg

-7 ma

S

N

Ns

.

‘

.
1 Suiseds ,009- ON Wayeg Dy yy

\

Bureds ,009-/ ‘ON Wayeg

Buioeds ,00G-6 ‘ON Wayeg

ST

se

sy

ss'0

SUV7100 “110 3O T3uuvE Yad LSOD Y3LVM GNY LNSWdO13A30


VOLUMETRIC EFFICIENCY, PERCENT

100

90 Fattern No. 2-500" spacing
ee Pattern No. 3-600" spacing
‘; Pattern No. 7-600’ spacing
°
80
70
ay
60
0 1 2 3 4 5

THEORETICAL PRODUCED WATER-OIL RATIO

Figure 17. - Volumetric efficiency-water:oil ratio relationships of three patterns investigated
in the electrolytic model study of water-flooding a shoestring sand.