The Cole Creek Field is located in the southwestern margin of Powder River Basin, Natrona and Converse Counties, Wyoming. The objectives of this study were:
- To review existing geologic and engineering studies on the Second Frontier, Dakota, and Lakota formations in the Cole Creek Field;
- To provide an assessment of the Original Oil in Place (OOIP) and remaining oil in place for each formation; and
- To estimate the recovery potential of each formation under water flood and CO2 injection processes.
This study included the creation of a database for the Cole Creek Field, the review of the field geology, the analysis of the production and pressure data, the estimation of OOIP for each formation by means of volumetric and material balance calculations, and the estimation of waterflooding and CO2 injection recovery potentials using analog fields, NITEC's knowledge of the area, and the results from nearby studies. Reservoir simulation was not used in this study.
The production and pressure data was gathered from multiple sources, digitized, and a database with basic well data, production and pressure data was created. The basic well data was gathered from the Wyoming Oil and Gas Conservation Commission (WOGCC) database. The production and injection data was obtained from two sources: an existing report provided by Ameriwest (Borah-Borah Petroleum, Inc., August 2000) and the WOGCC. Corrections and additions to the basic well data and the production data were made based on information obtained from Ameriwest and data consistency controls. The well files were carefully reviewed to collect available pressure data and gas/oil ratio (GOR) data; the pressure data was quality controlled and corrected to datum level in each reservoir.
A review of previous geologic analyses concerning the Cole Creek Field was performed. Available data included several geologic reports, structure and sand maps, core analyses, etc. particularly concerning the Shannon, Second Frontier, Dakota, and Lakota Formations, the main producing horizons in the field (Gene R. George, April 1989; Borah-Borah, August 2000; McCutcheon, March 2000, August 2000, January 2001). As a general statement, the quality and thoroughness of the previous work evaluated was outstanding and was considered adequate to serve as a basis for the volumetric calculations. In addition to reviewing the previous work, net sand isopach maps were drawn for the Second Frontier and Dakota formations.
The production, injection and pressure data in the Second Frontier, Dakota, and Lakota
Formations were analyzed. This analysis indicated the presence of compartmentalization in
the Dakota Formation. The Dakota reservoir was subdivided into two main compartments:
North (region 1 in Figure I-1) and South (regions 2, 3, and 4 in the figure). The Dakota net
pay map and oil production bubbles are also displayed in the figure.
Figure I-1: Identification of Production Regions and Compartments in Dakota.
The analysis of the pressure and production data also revealed some inconsistencies in the
Dakota water injection and production data. Some adjustments were made to the original
water injection data, but more corrections are needed if full data consistency is pursued.
Two methodologies were used to estimate the OOIP: volumetrics and material balance. The
final estimates of the most likely OOIP and probable range of OOIP occurrence were based
not only on the volumetric and material balance calculations, but also on engineering and
geologic judgment.
Volumetrics
The maps reviewed and generated during the geology evaluation were used in the volumetric
calculation of OOIP of the Second Frontier, Dakota, and Lakota formations. The results of
the volumetric calculations are presented in Table I-1. The Dakota volumes are reported by
sub-dividing the reservoir in two different ways: by facies (Valley Fill and Strandplain) and
by compartment (South and North).
Table I-1: Results of the Volumetric Calculations.
Material Balance
Two material balance models were run in the Dakota formation (one for each compartment)
while one material balance model was run in each of the other formations studied: Second
Frontier and Lakota. The material balance OOIP estimations are presented in Table I-2.
Table I-2: Original Oil in Place Estimations from Material Balance.
Original Oil in Place Final Estimates
The final estimation of the most likely OOIP and the probable range in each formation was
based on the volumetric calculations and the material balance results. Also, geologic and
engineering judgment was used to weigh the conclusions from production analysis, the
uncertainty of the material balance/volumetric estimations, the quality of the data, and the
limitations in data availability. Table I-3 presents a summary of the OOIP final estimates.
The most likely estimates were later used in all recovery factor calculations.
Table I-3: Original Oil in Place Final Estimates.
The potential oil recovery from water flooding and CO2 injection in each formation was
estimated using NITEC's knowledge of primary and water flood recoveries from fields in the
region, relevant data collected from publicly available sources, and reports provided by the
client. A summary of the expected primary, secondary, and CO2 recoveries is presented in
Table I-4.
Table I-4: Summary of Primary, Secondary and CO2 Injection Recovery Potentials.
Second Frontier formation
 Second Frontier Structure Map |
 Second Frontier Net Pay Map |
Dakota formation
 Dakota Structure Map |
 Dakota Net Pay Map |
Lakota Formation
 Lakota Structure Map |
 Lakota Net Pay Map |
ø: porosity (fraction)
a: formation factor constant (Archie)
Bo: formation volume factor (RB/STB)
fasl: feet above sea level
fbsl: feet below sea level
GOR: gas/oil ratio (SCF/STB)
K: Permeability (md)
m: cementation factor
N: original oil in place (STB)
Np: cumulative oil production (STB)
NTG: net-to-gross ratio (fraction)
OOIP: Original Oil in Place (STB)
P: pressure (psig, psia)
PHI: porosity (fraction)
qo: oil rate (STB/D)
Rs: dissolved gas/oil ratio (SCF/STB)
Rw: formation water resistivity (ohm-m)
Sw: water saturation (fraction)
WGA: Wyoming Geological Association
WPA: Wyoming Pipeline Authority
WOC: Water-Oil Contact
WOR: water/Oil ratio (fraction)
WOGCC: Wyoming Oil and Gas Conservation Commission
