American Oil and Gas Reporter - September 2017 - 42

SpecialReport: Geophysics & Reservoir Evaluation
The objective was to better understand
if a viable and economic Wolfcamp play
could be extended onto the Eastern Shelf
environment. It was essential to investigate
and define the presence of the main petroleum system play elements-namely
source rock quality and potential, reservoir
thickness and quality, and ultimately, the
presence of contained hydrocarbons.
For this project, the Wolfcamp was
divided into five sub-formations: A, B,
Middle B, C and D, per standard industry
nomenclature. Figure 1 highlights the integrated approach used on the project.
The integrated evaluation utilized wireline
logs from 64 wells, cuttings samples collected from recently drilled wells and

public sources, geochemical data collected
from drill cuttings and analyzed at stateof-the-art geochemistry laboratories, and
the two 3-D seismic volumes acquired in
the northern and southern areas of TriGeo
Energy's Sterling County leasehold.
A team of geochemists, petrophysicists,
reservoir geologists and geophysicists
worked in tandem with the operator to
evaluate, integrate and interpret these
datasets to better understand the Wolfcamp
play's occurrence, distribution, thickness
and quality within the study area.
Forty of the 64 total wells were utilized
to generate five correlation panels (three
east-to-west and two north-to-south) across
the study area to construct a thickness

FIGURE 1
Integrated Workﬂow Applied to Source Rock
And Reservoir Evaluation of Wolfcamp Formation

Regional
Correlations
-40 wells
-5 correlation lines

Organic
Geochemistry
(source rock)
- TOC: 188
- Rock-Eval: 144
- %Ro: 13

Thickness Mapping

Maturity
Richness
Burial/Thermal History

Petrophysics
- Advanced: 3
wells
- Basic: 3 wells

Geochemical Evaluation
Reservior
Characterization
- 2 SEM samples

Lithology
Porosity
Sw
Pay
Brittleness (YM-PR)
OOIP

3-D Seismic

Geobodies

FIGURE 2
Oxygen Index versus Hydrogen Index for Evaluated Wells
Well Locations

Type I

1,000
900

Hydrogen Index (mgHC/g TOC)

800

Type II

700
600
500

Well A
Well B
Well C
Well D

400
300
200

Type III

100
0

0

20

40

60 80 100 120 140 160 180 200
Oxygen Index (mgCO2/g TOC)

42 THE AMERICAN OIL & GAS REPORTER

map of the Upper, Middle and Lower
Wolfcamp formations. In two of the eastto-west correlation lines, public domain
wells in bordering Glasscock County,
Tx., west of the study area, were incorporated to assess the potential continuity
of the Wolfcamp formation's occurrence
in Sterling County. This mapping process
generated a gross thickness map of the
Wolfcamp B, recording a thickness as
great as 1,500 feet within the study area,
similar to thicknesses observed in Glasscock County.
The southern edge of the "Glasscock
Nose" also was identified, with the apparent thinning of the Wolfcamp B in the
northern part of the study area. The newly
defined Wolfcamp A, B, Middle B, C
and D tops, along with the recorded thickness data, were used to select sample intervals for geochemical analyses and to
isolate intervals for further petrophysical
interpretation.

To evaluate the petroleum system,
geochemical analyses were performed
on 108 cuttings samples collected from
two newly drilled TriGeo Energy wells
along with an additional 80 cuttings
samples from two public domain wells.
The geochemical analyses included total
organic carbon (TOC) determination,
pyrolysis and organic petrography (percentage of vitrinite reflectance). The
geochemical analyses of these samples
provided insight into the source rock
quality across the study area, and through
1-D petroleum systems modeling, allowed the thermal evolution of the Wolfcamp formation to be evaluated within
TriGeo Energy's Sterling County acreage
position.
Overall, the organic properties of the
entire Wolfcamp formation at each well
location showed poor to fair hydrocarbon
generation ability because of low kerogen
quality and maturity levels. The recorded
TOC values ranged from 0.43 to 3.17
weight percent (wt%), with the Wolfcamp
A averaging 1.27, the Wolfcamp B aver-
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