Table Of ContentQaJl^u^^i
IP 146 M.Q%:
An Integrated Geologic and
Engineering Study the
of
Lease Aux Vases
Plumfield
Reservoirs, Zeigler Field,
Franklin County,
Illinois
Steve K. Sim, Beverly Seyler, Emmanuel O. Udegbunam
A
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Illinois Petroleum 146
1994
Department of Energy and Natural Resources
ILLINOIS STATE GEOLOGICAL SURVEY
IJMHISTATE^GEOLOGICALSURVEY
3 3051 00004 8797
An Integrated Geologic and
Engineering Study of the
Lease Aux Vases
Plumfield
Reservoirs, Zeigler Field,
Franklin County,
Illinois
Steve K. Sim, Beverly Seyler, Emmanuel O. Udegbunam
Illinois Petroleum 146
1994
ILLINOIS STATE GEOLOGICAL SURVEY
Morris W. Leighton, Chief
Natural Resources Building
615 E. Peabody Drive
Champaign, Illinois 61820-6964
DISCLAIMER
This reportwaspreparedbythe IllinoisStateGeologicalSurvey(ISGS)fora project
sponsored by the State of Illinois and the U.S. Department of Energy (USDOE). It
presents reasonable interpretations ofavailable scientific data. Any opinions, find-
ings, conclusions, or recommendations expressed herein are those of the authors
and do not necessarily reflect the views of the USDOE. Neither the ISGS, any
memberofthe ISGS staff, the Illinois DepartmentofEnergyand Natural Resources
(ENR), nor the USDOE assumes any liability with respect to the use, or for any
damages resulting from the use, ofany information contained in this report. Use of
trademarks and brand names in this reportdoes notconstitute endorsementofany
product bythe ISGS, ENR, or USDOE.
—
Editor E. Anne Latimer
—
Graphic Artist Sandra Stecyk
PrintedbytheauthorityoftheStateofIllinois/1994/1200
printedwithsoybeaninkonrecycledpaper
7
CONTENTS
ABSTRACT
1
INTRODUCTION 2
FIELD HISTORY 3
Production History 3
Pressure Maintenance History 3
Historical Recovery Performance 4
RESERVOIR CHARACTERIZATION 4
Geological Description of Reservoirs at Zeigler Field 4
Depositional processes 5
Bottom-hole pressure surveys 6
Trapping mechanism 7
Diagenesis 7
Reservoir Properties 8
Drill stem test data 8
Original reservoir pressure from drill stem tests 12
Effective in situ permeability and permeability-thickness product 12
Estimated damage ratio 13
Determination of productivity index 13
Trends of Reservoir Data in the Plumfield Lease 15
Hydrocarbon PVT properties 16
Initial water saturations 1
Oil-water contact 17
Estimation of Reserves 20
Geological Modeling 20
RESERVOIR SIMULATION 22
Gridblock Selection and Simulation Technique 22
Initialization ofthe Reservoir Simulation Model 22
History Match 23
Waterflood History in the Plumfield Lease 23
Oil Recovery Factor and Unrecovered Mobile Oil in the Plumfield Lease 26
FUTURE DEVELOPMENT OPPORTUNITIES IN THE PLUMFIELD LEASE 26
SUMMARY AND CONCLUSIONS 27
ACKNOWLEDGMENTS 28
REFERENCES 28
1 681
FIGURES
1 Location ofZeigler Field, Franklin County, Illinois 2
2 Generalized stratigraphic column for southern Illinois 2
3 Well location map of Plumfield and Mack leases, Zeigler Field 4
4 Oil production history of Plumfield lease 5
5 Conceptual geologic model depicts conditions leading to encasement
of reservoirsandbars 5
6 Contour map of net pay in the Plumfield and Mack leases 6
7 Cross section (A-A') of South Plumfield lease shows the convex
geometry ofthe sandstone bar 7
8 Cross section (B-B') ofthe northern part ofthe West Plumfield and
Plumfield leases 8
9 Distribution of bottom-hole pressure in the Plumfield lease in
January 1966 10
10 Distribution of bottom-hole pressure in the Plumfield lease in
January 1967 10
1 Structure map oftop ofthe Ste. Genevieve Limestone Formation 1
12 Hornerplot foranalysis of drill stem test data from the Plumfield
no. 1 well 13
13 Contour map of permeability-thickness (kh) in the Plumfield lease 14
14 Contour map of heterogeneity index in the Plumfield lease 14
15 Cumulative distribution function of permeability in the Plumfield no. 2 well 15
16 Variation of solution gas-oil ratio with saturation pressure as determined
by experimental PVT measurements ofgas-crude oil mixtures from the
Aux Vases Formation, Zeigler Field 18
17 Variation of oil formation volume factorwith saturation pressure
as determined by experimental PVT measurements of gas-crude oil
mixtures from the Aux Vases Formation, Zeigler Field 1
18 Comparison of core-derived watersaturation values with calculated
values 19
19 Relationship between capillary pressure and watersaturation in the
Plumfield lease as determined by Leverett (J) function forvarious
permeability values 19
20 Comparison of core-derived permeability values with those determined
SGM™
by 21
21 Permeability distribution of the cross section (C-C') of West Plumfield
and Plumfield leases 22
22 Comparison of simulated values for oil production rates and watercuts
forthe South Plumfield no. 2 well with actual values through time 24
23 Comparison between observed and calculated field pressure atthe
Plumfield no. 2 well 24
24 Relationship between permeability-thickness (kh) and cumulative oil
production of Plumfield lease 25
25 Comparison of historical and alternative (predicted) waterflood oil
recovery performance 25
TABLES
1 Nomenclature used in the report 3
2 Drill stem test ofthe Plumfield no. 1 well 12
3 Average permeability and porosity of some producing formations in the
United States 1
4 Original oil in place (OOIP) as a function of oil-water (OWC) elevation
and rock permeability 20
ABSTRACT
The number of well abandonments in Illinois since 1987 has increased threefold.
One reason for the increase is difficulties encountered in waterflooding small
heterogeneous reservoirs. This study describes the development strategies used
in a successful waterflood project in the Plumfield lease atZeigler Field in Franklin
County, Illinois. These strategies could be applicable to similar reservoirs.
The Plumfield lease produced approximately2 million barrels ofoil during the past
29 years. The reservoir zone is in the Mississippian Aux Vases Formation and
comprises three slightly overlapping and narrowly connected offshore marine
sandstone bars.
Reservoir management strategies used at the Plumfield lease included obtaining
cores from almost every well, bottom-hole pressure surveys, and production and
injection surveillances. Bottom-hole pressure surveys and production and injection
surveillances were used to locate permeability barriers, essential knowledge for
optimum placement of water injectors in the field. The extensive core analyses
showedwhetherreservoirintervalsexisted, andthe reservoirporosity, permeability,
and residual fluid saturations. Data from the core analyses were very important in
defining flow units within the reservoirs in the Plumfield lease.
The waterflood performance of the Plumfield lease at Zeigler Field was evaluated
using an integrated three-dimensional geologic and reservoir simulation model. A
two-layer model was used to characterize the distribution of porosity, permeability,
and fluid saturations in the reservoirs. Estimates from reservoir analyses showed
MMSTB
thatthe Plumfieldleasecontained4.56 (millionstocktankbarrels),ofwhich
43.07% was produced between June 1963 and February 1992. Simulation of
anotherreservoirmanagementscenario inwhichwaterinjectorswere placed atthe
onsetofoilproductionshowedarecoveryof 1.05% moreoilthanthehistoricalcase.
The predicted ultimate oil recovery factorwithoutwaterflood was 23%.
Reserve calculations indicatethatabout57%ofthe original oil in place (OOIP) was
bypassed atthe Plumfield lease and that 14% ofthe remaining OOIP is moveable.
The results of the reservoir simulation indicate the bulk of the recovered oil was
produced from the upper, more permeable sand.
Future development opportunities at Plumfield should include improvement of
sweep efficiency with polymers or cross-linked polymers and use of microbial
enhanced oil recoverytechniques. Targeted infill drilling, as part ofan improved oil
recovery project, should also be considered if economically feasible. Field-wide
tracertests or othertests to define flow units are strongly recommended to identify
various scales of heterogeneities not detected by previous reservoir management
programs in the field. The information gathered will provide a better understanding
of the reservoir architecture and show the best ways to recover the remaining oil
through improved recoverytechniques.
Oil recovery during waterflood in this lease is relatively high for the Aux Vases
Formation and attributable to the good reservoir management practices by the
operator.
INTRODUCTION
Zeigler Field is in the southern half of Franklin County, in the south-central part of
the Illinois Basin (fig. 1). Although Zeigler Field consists of several leases, onlythe
Plumfieldleaseisconsideredinthisstudy. Sinceitsdiscoveryin 1963,thePlumfield
lease hasproducedcloseto2millionbarrelsofoilfromthe MississippianAuxVases
Formation sandstone reservoirintervals (fig.2).The reservoircovers500acresand
contains 30 productive wells on a 10-acre spacing. The Plumfield reservoir is near
the end of the waterflood recovery stage. Most of the wells in this reservoir have
been abandoned since the mid-1970s because oftheir high watercuts.
Fraileys
Beech Creek
Cypress
cd
O
Ridenhower
<
Bethel o_
0-
^Downeys Bluff CO
CO
Yankeetown CO
CO
-?-
Renault
c
Aux Vases
CO
Figure 1 Location ofZeigler iC_D_
Field, Franklin County, Illinois. CD
E
3
Figure 2 right Generalized strati- Ste. Genevieve
graphic column for upper Mississip-
pian rocks in southern Illinois.
Nearlyallthewellswerecoredduringdrilling. Porosityandpermeabilityvalueswere
determined for more than 90% of the core samples. Spontaneous potential (SP)
resistivity logs were also available for most wells. Oil and water production data,
as well aswater injection data, were recorded monthlyforeach well. Five pressure
surveys of the oil-producing wells in the Plumfield lease were performed between
January 1966 and January 1969.
Fields that produce from the Aux Vases Formation are noted for poor oil recovery
during waterflood. Poor oil recovery is generally caused by reservoircompartmen-
talization and heterogeneity. The Plumfield lease, a combination of the West
Plumfield, Plumfield, and South Plumfield leases, has a relatively high waterflood
oil recovery factor despite compartmentalization and heterogeneity. This success
is attributed mainlyto prudent reservoir management bythe operator. Bygathering
the necessary laboratory and field information during developmentofthe lease, the
operatorwasableto maketimelyreservoirmanagementdecisionstoanticipateand
overcome problems caused by reservoir heterogeneity.
This study uses the Plumfield reservoirto demonstrate the value of acquiring and
using geological, engineering, and field data for reservoir management. The abun-
dant core analyses from Plumfield provided useful information for constructing an
integrated geological and engineering reservoir model. Simulation shows that the
operator's careful management of the Plumfield lease resulted in a cumulative oil
recoveryfarabovetheaverageformostAuxVases reservoirs. The studyalso uses
the model to (1) estimate the oil recovery factors to date and the amounts of
remaining OOIP (table 1) and unrecovered mobile oil, and (2) evaluate future
development opportunities for the Plumfield lease.
Table 1 Nomenclature used in the report.
°API = oil degree API gravity PI = productivity index
bbl = barrel psia = pounds persquare inch absolute
BOPD = barrels of oil perday psig = pounds per square inch gauge
Bg = gas formationvolume factor (cf/scf) PVT = pressure-volume-temperature
B = oil formation volumefactor(rb/stb) q = flow rate (bbl/day)
CDF = cumulative densityfunction Rc = resistivity ofadjacent shale bed (ohm-m)
cf = cubic feet Rs = solution gas-oil ratio (scf/stb)
cp = centipoise Rt = formation resistivity (ohm-m)
DST = drill stem test rb = reservoir barrel
EDR = estimated damage ratio ROIP = remaining oil in place
GOR = gas-oil ratio Sw = watersaturation (%)
h = net pay thickness (ft) scf = standard cubic feet
J(SW) = LeverettJ function SP = spontaneous potential
k = permeability (md) stb = stocktank barrel
In = natural logarithm T = temperature (°F)
md = millidarcy tp = cumulative flowing time (days)
OOIP = original oil in place Tr = reservoirtemperature (°F)
P = pressure (psia) Vdp = Dykstra-Parson heterogeneity index
Pc = capillary pressure (psia) VSh = volumeof shale
Pi = initial pressure (psia) W(r,R) = weighing function
P = bubble-point pressure (psia) u. = viscosity (cp)
Pwi = well flow pressure (psia) = porosity (%)
Pws = shut-in bottom-hole pressure (psia) <t>
FIELD HISTORY
Production History
Thediscoverywellinthe Plumfieldlease, Plumfieldno. 1 (P1,fig. 3),wascompleted
inthespringof1963byGallagherDrillingCompany. ProductionbeganinJune 1963
atan initial rateof237 barrelsofoil perday (BOPD). During thefollowing 6 months,
eightmorewells (P2-P7, P9, P10)weredrilledandcompleted. Thetotal production
rate ofthe ninewells in December 1963was571 BOPD (event 1, fig. 4). Morewells
were developed during 1964 in the West Plumfield and South Plumfield leases. By
December 1964, 27 wells were producing at the rate of 645 BOPD. At peak
production in the studyarea, 30oil-producing andwaterinjection wellswereactive.
Pressure Maintenance History
By the spring of 1965, the pumping rate at the Plumfield no.1 (P1) well had
decreasedfromtheinitialrateof237BOPDto 11 BOPD. Reservoirpressuredecline
was precipitous, falling below 50 psig (pounds per square inch gauge) from an
original reservoir pressure of about 1250 psig.
The injection of water started in February 1965 when four of the lower producers,
West Plumfield no. 3 (WP3), West Plumfield no. 10 (WP10), Plumfield no.12 (P12)
and Plumfield no. 20 (P20), were converted intowaterinjectors (event 3, fig. 4). As
a result, the declining field production rate and declining pressure were reversed.
As more oil producers were shut in because of excessive water cut, some were
convertedintowaterinjectors. By 1979,onlysixwells, producingatotalof28 BOPD,
continued to pump oil (event 7, fig. 4).
R 1 E R2E
P-Plumfield
WP-WestPlumfield
SP-South Plumfield
M - Mack
•
Oilwell
\
Waterinjector
-y-
Drywell
-w- Drywell (oil show)
Figure 3 Well location mapof Plumfield and Mack leases, Zeigler Field. Lines ofcross sections A-A', B-B', and
C-Care shown.
No peripheral water injectors were placed at the east end of the reservoir. The oil
bank was swept eastward toward the stratigraphic pinch-out. This strategyworked
well, as reflected bythe high total oil production and delayofwaterbreakthrough in
the eastern peripheral wells, Plumfield no.1 (P1) and Plumfield no. 9 (P9) (fig. 3).
Historical Recovery Performance
AsofFebruary 1992,thetotaloilrecoveredfromthe Plumfieldleaseswas 1,963,955
barrels. Given an estimated OOIP of 4.56 MMSTB (see section on Estimation of
Reserves), the ultimate recovery factor to February 1992 was calculated to be
43.07% of OOIP.
RESERVOIR CHARACTERIZATION
Geological Description of Reservoirs at Zeigler Field
Depositionalprocesses, mineralogy,anddiagenesisaffectedthegeometry,volume,
connectivity, and composition of the Aux Vases Sandstone reservoirs at Zeigler
Field. Brief discussions of these geologic characteristics and their effects on
reservoir behavior follow. A detailed geologic description of Zeigler Field is pre-
sented in Seyler (in preparation).
