U.S. Department of Interior

U.S. Geological Survey

Composition of crude oil and natural gas produced from 14 wells in the

Lower Silurian “Clinton” sandstone and Medina Group,

northeastern Ohio and northwestern Pennsylvania

R. C. Burruss

1

and

R. T. Ryder

1

Open-File Report 03-409

This report is preliminary and has not been reviewed for conformity with

U.S. Geological Survey editorial standards and stratigraphic nomenclature.

Any use of trade names is for descriptive purposes only and does not imply

endorsement by the USGS.

1 U.S. Geological Survey, Reston, Virginia 20192
CONTENTS

Page

Introduction........................................................................... 1

Sample Locations.................................................................. 3

Sampling and Analytical Methods................................................ 4

Results.................................................................................. 5

Natural gases.................................................................. 5

Crude oils..................................................................... 7

Preliminary Conclusions.............................................................. 8

Natural gases.................................................................. 8

Crude oils........................................................................ 10

Acknowledgements................................................................... 13

References Cited....................................................................... 13

ILLUSTRATIONS

Page

Figure 1. Map of the Lower Silurian regional oil and gas accumulation

showing the location of the study area and regional cross

sections A-A’ and D-D’............................................ 18

Figure 2. Correlation chart of Lower Silurian and adjoining strata,

northeastern Ohio, northwestern Pennsylvania, and central

Pennsylvania showing the interval of the Lower Silurian

regional oil and gas accumulation................................ 19

Figure 3. Map showing the well locations in Geauga and Trumbull

Counties, Ohio, and Mercer and Butler Counties, Pennsylvania,

where oil and (or) gas was sampled for the investigation...... 20

i
Figure 4. Schoell (1983) diagram showing the isotopic composition

of selected natural gases in the lower Silurian regional oil and

gas accumulation.................................................... 21

Figure 5A. Whole oil gas chromatogram, sample 98OH01B,

#2 Patterson......................................................... 22

Figure 5B. Saturated hydrocarbon fraction gas chromatogram, sample

98OH01B, #2 Patterson........................................... 23

Figure 5C. Aromatic hydrocarbon fraction gas chromatogram, sample

98OH01B, #2 Patterson........................................... 24

Figure 6A. Whole oil gas chromatogram, sample 98OH02A,

#1 Bruno............................................................ 25

Figure 6B. Saturated hydrocarbon fraction gas chromatogram, sample

98OH02A, #1 Bruno.............................................. 26

Figure 6C. Aromatic hydrocarbon fraction gas chromatogram, sample

98OH02A, #1 Bruno.............................................. 27

Figure 7A. Whole oil gas chromatogram, sample 98OH03A,

#2 Grandview-Johnson............................................. 28

Figure 7B. Saturated hydrocarbon fraction gas chromatogram, sample

98OH03A, #2 Grandview-Johnson............................... 29

Figure 7C. Aromatic hydrocarbon fraction gas chromatogram, sample

98OH03A, #2 Grandview-Johnson.............................. 30

Figure 8A. Whole oil gas chromatogram, sample 98OH04A,

#1 Detweiler........................................................ 31

Figure 8B. Saturated hydrocarbon fraction gas chromatogram, sample

98OH04A, #1 Detweiler.......................................... 32

Figure 8C. Aromatic hydrocarbon fraction gas chromatogram, sample

98OH04A, #1 Detweiler.......................................... 33

Figure 9A. Whole oil gas chromatogram, sample 98OH05A,

#2 Hissa............................................................. 34

ii
Figure 9B. Saturated hydrocarbon fraction gas chromatogram, sample

98OH05A, #2 Hissa............................................... 35

Figure 9C. Aromatic hydrocarbon fraction gas chromatogram, sample

98OH05A, #2 Hissa............................................... 36

Figure 10A. Whole oil gas chromatogram, sample 98OH06A,

#2 French........................................................... 37

Figure 10B. Saturated hydrocarbon fraction gas chromatogram, sample

98OH06A, #2 French............................................. 38

Figure 10C. Aromatic hydrocarbon fraction gas chromatogram, sample

98OH06A, #2 French............................................. 39

Figure 11A. Whole oil gas chromatogram, sample 98OH07A,

#3 Griffin........................................................... 40

Figure 11B. Saturated hydrocarbon fraction gas chromatogram, sample

98OH07A, #3 Griffin............................................. 41

Figure 11C. Aromatic hydrocarbon fraction gas chromatogram, sample

98OH07A, #3 Griffin............................................. 42

Figure 12A. Whole oil gas chromatogram, sample 98OH08, #1 Bates... 43

Figure 12B. Saturated hydrocarbon fraction gas chromatogram, sample

98OH08, #1 Bates................................................. 44

Figure 12C. Aromatic hydrocarbon fraction gas chromatogram, sample

98OH08, #1 Bates................................................. 45

Figure 13A. Whole oil gas chromatogram, sample 98PA02, #6 Weber.. 46

Figure 13B. Saturated hydrocarbon fraction gas chromatogram, sample

98PA02, #6 Weber................................................. 47

Figure 13C. Aromatic hydrocarbon fraction gas chromatogram, sample

98PA02, #6 Weber................................................. 48

Figure 14A. Whole oil gas chromatogram, sample 98PA05A, #8 Oris... 49

iii
Figure 14B. Saturated hydrocarbon fraction gas chromatogram, sample

98PA05A, #8 Oris................................................. 50

Figure 14C. Aromatic hydrocarbon fraction gas chromatogram, sample

98PA05A, #8 Oris................................................. 51

Figure 15A. Whole oil gas chromatogram, sample 98PA06A,

#2 Gibson........................................................... 52

Figure 15B. Saturated hydrocarbon fraction gas chromatogram, sample

98PA06A, #2 Gibson............................................. 53

Figure 15C. Aromatic hydrocarbon fraction gas chromatogram, sample

98PA06A, #2 Gibson............................................. 54

Figure 16. Plot of pr/nC17 vs. ph/nC18 for “Clinton”/ Medina oils

and Utica Shale bitumen extracts.............................. 55

Figure 17. Plot of 13C distributions in the saturated and aromatic

hydrocarbon fractions for “Clinton”/Medina oils and

Utica Shale bitumen extracts.................................... 56

Figure 18A. Terpane mass fragmentogram, m/z 191.180, sample

98PA02, #6 Weber................................................ 57

Figure 18B. Sterane mass fragmentogram, m/z 217.1956 sample

98PA02, #6 Weber................................................ 58

iv
TABLES

Page

Table 1. Wells sampled for gas and oil in northeastern Ohio and 

northwestern Pennsylvania........................................ 59

Table 2A. Molecular and isotopic composition of gas samples........... 60

Table 2B. Molecular and isotopic composition of gas samples........... 61

Table 3. Properties of the whole crude oil and crude oil fractions...... 62

Table 4. Properties of the saturated hydrocarbon fraction of the

crude oils............................................................. 63

Table 5. Terpane and sterane compounds identified in the saturate

fraction of the oil in the #6 Weber well......................... 64

v.
Introduction 

The Lower Silurian regional oil and gas accumulation was named by Ryder and 

Zagorski (2003) for a 400-mi-long by 200-mi-wide hydrocarbon accumulation in the 

central Appalachian basin of the eastern United States and Ontario, Canada (Figure 1). 

The dominant reservoirs in this regional accumulation are the “Clinton” sandstone, 

Medina Group sandstones, and Tuscarora Sandstone of Early Silurian age (Figure 2). 

The basin-center gas (continuous) part of this regional Silurian accumulation contains an 

estimated 30 trillion cubic feet (TCF) of recoverable gas and covers an area that extends 

across western Pennsylvania, eastern Ohio, and western West Virginia (Gautier and 

others, 1995; Ryder, 1998). This part of the accumulation occurs in rocks of low 

permeability, usually 0.1 millidarcies (md) or less, downdip of more permeable, watersaturated rocks. A conventional part of the accumulation with hybrid features of a basincenter accumulation lies updip from the basin-center gas (Ryder, 1998; Ryder and 

Zagorski, 2003). This hybrid-conventional part of the regional accumulation follows a 

pre-1980s production trend that extends from Ontario, Canada, through western New 

York, northwestern Pennsylvania, and central Ohio (Figure 1). 

In the basin-center part of the regional accumulation, individual wells ultimately 

produce on the order of 50 to 450 million cubic feet (MMCF) of natural gas. In addition 

to gas, many wells produce variable amounts of brine and crude oil. The gas-to-fluid 

ratio is variable but generally high, on the order of 50,000 to 500,000 standard cubic feet 

(SCF) of gas per barrel of oil or brine. The amount of oil and brine produced affects the 

economics of individual wells because of the cost incurred to dispose of the brine or the 

1
value added through the sale of oil. In general, the best gas producers are those wells that 

produce the least oil and brine. 

We are investigating the geochemistry of the gas and co-produced oil to better 

understand the origin of the hydrocarbons within the Lower Silurian regional 

accumulation. This report documents 12 gas samples and 11 oil samples from 14 wells 

producing from the “Clinton” sandstone and Grimsby/Whirlpool Sandstones in 

northeastern Ohio and northwestern Pennsylvania. The samples from Ohio were 

collected in Geauga and Trumbull Counties and those from Pennsylvania were collected 

in Butler and Mercer Counties. This investigation supplements a previous data set of 10 

oil samples and 3 gas samples collected from the “Clinton” sandstone in Trumbull 

County (Barton, Burruss, and Ryder, 1998; Burruss and Ryder, 1998). 

Other published analyses of crude oils and natural gases from Silurian-age 

reservoirs in the Appalachian basin include those by Barker and Pollock (1984), Cole, 

Drozd, and others (1987), Drozd and Cole (1994), Jenden, Drazan, and Kaplan (1993), 

Laughrey and Baldassare (1998), Obermajer, Fowler, and Snowdon (1998), and Powell, 

Macqueen, and others (1984). Cole, Drozd, and others (1987) recognized two groups of 

oils in Silurian reservoirs in Ohio. One group of oil, they suggested, was generated from

marine black shale of Devonian age and the other group was generated from marine 

black shale of Ordovician age. Most likely, oil in the Lower Silurian “Clinton” sandstone 

was generated from the Ordovician black shale (Drozd and Cole, 1994; Ryder, Burruss, 

and Hatch, 1998). Devonian black shale is a less likely source for the “Clinton” oils 

because the 700-to-1,000-ft-thick Upper Silurian Salina Group, with evaporite beds, is 

located between them (Figure 1). Molecular and isotopic data on natural gas from

2
Silurian reservoirs in western and central Pennsylvania (Laughrey and Baldassare, 1998) 

and western New York (Jenden, Drazan, and Kaplan, 1993) are less diagnostic for 

identifying source rock than geochemical parameters measured in oil samples. However, 

the general conclusion of work to date on “Clinton”/Medina/ Tuscarora gases is that they 

were derived from thermally mature, marine organic matter, probably in strata older than 

the Silurian. 

Sample Locations 

The wells sampled for this investigation follow a northwest-southeast trend that is 

subparallel to the dip of the basin and crosses the approximate boundary between basincenter and hybrid-conventional parts of the Lower Silurian regional accumulation 

(Figures 1, 3). In general, those wells east of Mosquito Creek Lake in central Trumbull 

County are located in the basin-center part of the Lower Silurian regional accumulation 

whereas those wells west of Mosquito Creek Lake are located in the hybrid-conventional 

part (Figure 3). All wells sampled are within 5 miles of cross section D-D’ that shows 

the stratigraphic and depositional character of the “Clinton” sandstone and Medina Group 

(Keighin, 1998) (Figure 3). Cross section A-A’ (Ryder, 2000), which connects with 

cross section D-D’ in Mercer County, is located 5 to 10 miles from the wells sampled in 

southeastern Mercer and northwestern Butler Counties (Figure 3). Also located in Figure 

3 are 10 wells in Trumbull County for which oil and gas analyses have been reported by 

Burruss and Ryder (1998). Selected information on the wells sampled for this 

investigation is listed in Table 1. 

3
Sampling and Analytical Methods 

Most oil and gas samples were obtained, with the assistance of operating 

company field personnel, from the wellhead or the oil and gas separator of individual 

wells. One oil sample was taken from the stock tank at the well site. Gas was sampled at 

the pressure gauge port on the production tubing using evacuated stainless steel cylinders 

supplied by Isotech Laboratories, Inc. Oil was sampled, where possible, at the drain for 

the fluid-level sightglass on the oil and gas separator. The oil is initially saturated with 

gas at the separator pressure and foams from exsolution of the gas as it exits the 

sightglass drain. One oil sample was bailed from the stock tank. 

All samples were analyzed by standard methods. Natural gas samples were 

analyzed at Isotech Laboratories, Inc., Champaign, Illinois, for molecular composition by 

gas chromatography and for stable isotopic composition by isotope ratio mass 

spectrometry. Carbon isotopic composition was determined for methane (C1), ethane 

(C2), propane (C3), and iso-butane (C4). Also, hydrogen isotopic composition was 

determined for methane and nitrogen isotopic composition was determined for molecular 

nitrogen. Carbon isotope ratios are reported in standard per mil deviation relative to the 

Peedee belemnite standard (PBS), and hydrogen isotope ratios are reported relative to 

standard mean ocean water (SMOW) for both gases and oils. Nitrogen isotope ratios are 

reported relative to atmospheric nitrogen. 

Crude oils were analyzed by the U.S. Geological Survey (Denver, Colorado). 

API gravity of the oils was determined gravimetrically. Oils were fractionated by 

dilution in n-heptane to remove asphaltenes. A concentrate of the solution was further 

fractionated by column chromatography on silica gel by selective elution with heptane, 

4
benzene, and benzene-methanol (1:1 v/v) to collect the saturated hydrocarbon, aromatic 

hydrocarbon, and resin (nitrogen-, sulfur-, and oxygen- [NSO] compounds) fractions, 

respectively. The carbon stable isotope composition of an aliquot of the saturated and 

aromatic hydrocarbon fractions was determined on a Micromass Optima isotope ratio 

mass spectrometry system. 

Gas chromatography of the whole oil, and the saturated and aromatic hydrocarbon 

fractions, was performed with a Hewlett/Packard Model 6890 (HP6890) gas 

chromatograph with a 60 m x 0.32 mm x 0.25 μm DB-1 fused silica capillary column and 

a FID detector. The oven was programmed from 50 to 330°C at 4.5°C/min and held 

isothermal at 330°C for 15 min with helium carrier gas flow at 35 cm/sec. Gas 

chromatography-mass spectrometry (GCMS) of the saturated hydrocarbon fraction of one 

oil was performed with a HP6890-JEOL GCMate system in selective ion monitoring 

mode to identify steranes and terpanes in the fraction. 

5
Results 

Natural gases: The molecular and isotopic composition of natural gas from twelve wells 

is presented in Tables 2A and 2B. All twelve gases are rich in methane, between 76 and 

90 mole %, with low concentrations of hydrocarbons that have more than four carbon 

atoms. All samples contain a trace of helium and 2.01 to 4.55 mole % nitrogen. Eight of 

the twelve wells contain a trace of hydrogen. These gas compositions are consistent with 

gas compositions reported for the “Clinton” sandstone in Ohio by the U.S. Bureau of 

Mines (Moore, 1982).

The carbon isotopic composition of methane, ethane, propane, and n-butane in the 

samples ranges from about 7 to 12 per mil for each component. In eight of twelve wells, 

the carbon isotopic composition of methane, ethane, propane, and n-butane (where 

analyzed) become respectively heavier as normally expected (Chung, Gormly, and 

Squires, 1988) whereas, in four wells, the carbon isotopic composition of methane, 

ethane, propane, and n-butane (where analyzed) show several combinations of reversal in 

the normal trend (see #5 Brown; table 2B). The variation in the hydrogen isotopic 

composition of methane is about 50 per mil and the variation in the nitrogen isotopic 

composition ranges is about 4 per mil. The carbon dioxide content in the samples was so 

low, 0.04 mole % or less, that the carbon isotopic composition of this constituent could 

not be determined. 

Judging from their isotopic location on a Schoell (1983) diagram (Figure 4), 

“Clinton”/Medina natural gases from this study and from Burruss and Ryder (1998) are 

thermogenic in origin. The δ13C methane and δD methane values define a straight line 

that indicates that the gases become isotopically heavier with depth of production (Figure 

6
4). For example, δ13C methane values range from -41.98 in the #2 Patterson well (~3,600 

ft to the gas production) near the northwest end of section D-D’ to –33.97 in the #2 

Mathews well (~6,570 ft) near the southeast end. Isotopic compositions of additional 

Lower Silurian gases from northwestern Pennsylvania (Laughrey and Baldassare, 1998) 

and Lower Silurian gases from New York (Jenden, Drazan, and Kaplan, 1993) also fit the 

trend defined in Figure 4. Natural gases in the basin-center part of the regional 

accumulation are differentiated from natural gases in the hybrid-conventional part based 

on their position relative to the δ13C methane = -37.0 value (Figure 4). 

Crude oils: Bulk parameters and selected molecular parameters of the crude oils are 

listed in Table 3. The API gravity of 8 of the 11 samples is 40° or greater. One of the 3 

exceptions, the No. 6 Weber well with an API gravity of 39.9°, was bailed from the top 

of the stock tank instead of being collected at the separator. The oils are uniformly high 

(84 to 92 wt. %) in saturated hydrocarbons with 12% or less of aromatic hydrocarbons. 

Carbon isotopic compositions of the saturated and aromatic hydrocarbon fractions show 

small ranges of 0.8 per mil and 1.0 per mil, respectively. 

Gas chromatograms of the whole oil, saturated hydrocarbon, and aromatic 

hydrocarbon fractions for samples from the 11 wells are shown in Figures 5A, 5B, 5C, 

respectively, through Figures 15A, 15B, 15C. The saturated hydrocarbon gas 

chromatograms have similar characteristics to “Clinton” oils reported by Cole, Drozd, 

and others (1987). Molecular parameters derived from the gas chromatograms of the 

saturated hydrocarbon fractions are listed in Table 4. All whole-oil gas chromatograms 

of the saturated hydrocarbon fraction, except the one from the #6 Weber well, show a full 

7
spectrum of n-alkanes from n-C10 to n-C30+. The whole oil chromatogram for the sample 

from the #6 Weber well shows depletion in the low carbon number range (<n-C10) 

suggesting evaporative loss of the light ends. Two types of n-alkane distributions and 

one intermediate type are recorded by the saturated fraction gas chromatograms. 

Including the depleted #6 Weber sample, six of the eleven chromatograms show a broad 

spectrum of n-alkanes whose peak heights progressively diminish toward the higher 

carbon numbers (Figure 8B); two chromatograms have a bimodal distribution of nalkanes that peak at about n-C14 and n-C24 (Figure 6B); and three chromatograms show a 

broad spectrum of n-alkanes whose peak heights progressively diminish toward the 

higher carbon numbers but show a secondary peak at n- C24 (Figure 11B). Both types of 

n-alkane distribution show a modest odd-carbon preference and the presence of 

isoprenoids. The pristane/phytane (pr/ph) ratios listed in Table 4 range from 1.31 to 2.01. 

Crude oils from “Clinton”/Medina reservoirs in this study and in Burruss and 

Ryder (1998) are characterized by pr/n-C17 and ph/n-C18 values that vary broadly with 

their depth of production (Figure 16). Major exceptions are sample 14 (#6 Weber) that is 

grouped with oils produced from much shallower depths and sample 6 (#3 Griffin) that is 

grouped with oils produced from much greater depths (Figure 16). Moreover, carbon 

isotopic compositions of the saturated and aromatic fractions of the oils, in general, 

become heavier with depth (Figure 17). Basin-center and hybrid-conventional parts of 

the regional accumulation can be largely differentiated on the basis of trends shown in 

Figures 16 and 17. 

Mass fragmentograms from gas chromatography-mass spectrometry (GCMS) of 

the crude oil samples indicate the presence of biomarkers although many are barely 

8
visible because of their low signal-to-noise ratio. Surprisingly, the best fragmentograms 

are from the depleted oil in the #6 Weber well. Terpane (m/z 191) and sterane (m/z 217) 

fragmentograms of this oil are shown in Figures 18A and 18B, respectively. 

Preliminary Conclusions 

Natural gases: The striking distribution of δ13C methane vs. δD methane compositions is 

clearly a function of the thermal maturity of the gases (Figure 4). In addition, given the 

orderly increase toward heavier isotopes with depth, there appears to have been very little 

mixing of the gases in the “Clinton”/Medina reservoirs after entrapment. Also, these data 

imply a common source rock for the gases. Several explanations are possible for the 

isotopic distributions shown in Figure 4. First, gases may have been introduced to 

Lower Silurian reservoirs from a distant source, became trapped, and then thermally 

modified, in situ, as the reservoirs gradually achieved maximum burial. Secondly, gases 

may have been introduced from a local source rock and then trapped before it was 

allowed to migrate laterally. In these two models, the gases had minimal mobility during 

late-stage basin uplift. A third model suggests that the isotopic character of the gases is a 

late-stage, leakage/fractionation phenomenon whereby the volume of the escaped gas is 

directly related to the thickness of overburden. Therefore, isotopic compositions would 

be heaviest in gases having the greatest overburden thickness. 

Furthermore, conodont alteration index (CAI) isograds for Middle Ordovician 

carbonate rocks (Repetski and others, 2002; J.E. Repetski and R.T. Ryder, unpubl. data) 

show a consistently lower thermal maturity value, for a given locality, than that of the gas 

(Jenden, Drazan, and Kaplan, 1993) (Figure 4). Figure 4 suggests that gases in the 

9
“Clinton”/Medina were derived from source rocks having thermal maturity values about 

1 to 1.5 vitrinite reflectance equivalence (VRE) (Nöth, 1991) greater than the thermal 

maturity of the underlying Middle Ordovician strata based on CAI isograds. A similar 

discrepancy occurs when the thermal maturity of the gases are compared with the thermal 

maturity of the overlying Lower/Middle Devonian strata based on CAI isograds and 

vitrinite reflectance (Ro%) isoreflectance lines. 

The fact that these gases have a significantly higher thermal maturity than the 

underlying Ordovician and overlying Devonian strata suggests that they migrated from

deeper in the basin. Moreover, a Utica Shale source rock is favored over a Devonian 

shale source rock because of the shorter migration distance (25 to 50 mi vs. >100 mi) that 

the Utica requires to account for the observed thermal maturity of the gases. Although 

these data are most consistent with model 1 for the origin of the gases (medium-range 

migration with isotopic signatures being set during maximum burial), model 3 (mediumrange migration with isotopic signatures being set during late-stage uplift and erosion of 

the basin) cannot be rejected. Methane δ13C > ethane δ13C values observed in several 

natural gases in this study (Table 2B) may have resulted from the mixing of mature and 

post-mature gases (Jenden, Drazan, and Kaplan, 1993; Laughrey and Baldassare, 1998); 

however, diffusive leakage of gas through overburden rock (as permitted in model 3) 

may be an alternate explanation (Laughrey and Baldassare, 1998). 

Crude oils: The majority of n-alkane distributions for whole-oil gas chromatograms in 

this investigation (Figures 6A-13A and 15A) show: 1) a broad spectrum of n-alkanes 

ranging from n-C10 through n-C35, 2) modest odd-carbon preference in the n-C15 through 

10
n-C19 range, and 3) the presence of isoprenoids pristane and phytane. The major 

exception to the rule is the oil from the #6 Weber well (Figure 13A) which has an 

incomplete spectrum of n-alkanes (n-C10 and n-C11 are nearly depleted) and lacks oddcarbon predominance in the n-C15 through n-C19 range. As noted earlier, the 

characteristics of the #6 Weber oil were probably caused by evaporative loss during 

sampling and storage. 

The oils analyzed in this investigation have the same basic composition as other 

oils from the “Clinton” reservoir in Ohio (Cole, Drozd, and others, 1987; Burruss and 

Ryder, 1998) and oils from Cambrian/Ordovician reservoirs in Ohio (Cole, Drozd, and 

others, 1987; Ryder, Burruss, and Hatch, 1998). These basic similarities suggest a 

common source rock, probably the Middle Ordovician Utica Shale, for the “Clinton” and 

Cambrian/Ordovician reservoirs (Cole, Drozd, and others, 1987; Ryder, Burruss, and 

Hatch, 1998). Geochemical and geological evidence are much less convincing for other 

source rocks such as the Lower/Middle Devonian black shale and Silurian 

shale/carbonate units (Ryder and Zagorski, 2003). 

CAI isograds for Middle Ordovician carbonates gradually increase eastward 

across the study area from 1.5 to 2.0 (VRE 0.5 to 1) (Repetski and others, 2002; J.E. 

Repetski and R.T. Ryder, unpubl. data). These isograds are indicative of the “window” 

of oil and wet gas generation and preservation and, thus, are permissive of local 

derivation of the oils from the Utica Shale. Also, local oil derivation from the Utica is 

suggested by the similarity of carbon isotopic distributions in Utica Shale extracts from

Coshocton County, Ohio (Figure 3) (depth = 5,600-5,700 ft) and “higher” maturity oils 

from “Clinton” reservoirs (Figure 17). Moreover, the general eastward (basinward) 

11
increase in thermal maturity of the oils, based on pr/n-C17 vs. pr/n-C18 (Figure 16) and 

carbon isotopic distributions (Figure 17), suggests that minimal lateral migration of oil 

had occurred before entrapment. 

Oil from the #6 Weber well is anomalous because it is geochemically associated 

with “lower” maturity oils (Figure 16) and is geologically associated with the CAI 3 

isograd (VRE 2.25) (Repetski and others, 2002) that signifies the “window” of dry gas 

generation and preservation. Either this oil was introduced from a lower maturity source 

rock such as the overlying Devonian black shale or was locally preserved in a relatively 

high thermal regime that favored the generation and preservation of dry gas. In contrast, 

oil from the #3 Griffin well at a depth of about 3,900 ft is geochemically associated with 

“higher” maturity oils whose depth of production is approximately 1,000 ft greater 

(Figures 16 and 17). Possibly this oil migrated into the vicinity of the #3 Griffin well 

from deeper in the basin, or from a more mature secondary phase of generation that 

occurred beneath the well, and was trapped next to the lower maturity oil. Additional 

evidence for the mixing of different several oil types — either caused by a different 

source rock or thermal maturity regime — is suggested by the bimodal n-alkane 

distributions noted in several oils (see Figure 6B). 

The following sequence of events represents one scenario for the origin of the 

oils: 1) oil generation from the Utica Shale, 2) vertical migration of the oil into the 

overlying “Clinton”/Medina reservoir, 3) probable entrapment of the oil before 

significant lateral migration had occurred, and 4) local mixing of oils from disparate 

thermal regimes during late-stage basin uplift and erosion. This scenario suggests that 

12
Acknowledgements

Rick Liddle, Range Resources, Inc. (now Great Lakes Energy Partners), and 

Frank Carolas, Atlas Resources, Inc., enthusiastically gave permission and made

arrangements for us to sample the wells. Assistance with field sampling was kindly and 

patiently provided by Earl (Pep) Horning, John Frederick, and Dave Smallwood, Range

Resources, Inc. (now Great Lakes Energy partners), and Pete Burns, Atlas Resources,

Inc.

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Ontario, Canada: Bulletin of Canadian Petroleum Geology, v. 46, p. 350-378.

15
Powell, T. G., Macqueen, R. W., Barker, J. F., and Bree, D. G., 1984, Geochemical

character and origin of Ontario oils: Bulletin of Canadian Petroleum Geology, v. 32, p.

299-312.

Repetski, J. E., Ryder, R. T., Harper, J. A., and Trippi, M. H., 2002, Thermal maturity

patterns (CAI and %Ro) in the Ordovician and Devonian rocks of the Appalachian basin

in Pennsylvania: U. S. Geological Survey Open-File Report 02-302, 57 p.

Ryder, R. T., 1998, Characteristics of discrete and basin-centered parts of the Lower

Silurian regional oil and gas accumulation, Appalachian basin: Preliminary results from

a data set of 25 oil and gas fields: U.S. Geological Survey Open-File Report 98-0216, 71

p.

Ryder, R. T., 2000, Stratigraphic framework and depositional sequences in the Lower

Silurian regional oil and gas accumulation, Appalachian basin: From Jackson County,

Ohio, through northwestern Pennsylvania, to Orleans County, New York: U.S.

Geological Survey Miscellaneous Investigations Map I-2726, 2 sheets, pamphlet, 8 p.

Ryder, R. T., Burruss, R. C., and Hatch, J. R., 1998, Black shale source rocks and oil

generation in the Cambrian and Ordovician of the central Appalachian basin, USA:

American Association of Petroleum Geologists Bulletin, v. 82, p. 412-441.

16
Powell, T. G., Macqueen, R. W., Barker, J. F., and Bree, D. G., 1984, Geochemical

character and origin of Ontario oils: Bulletin of Canadian Petroleum Geology, v. 32, p.

299-312.

Repetski, J. E., Ryder, R. T., Harper, J. A., and Trippi, M. H., 2002, Thermal maturity

patterns (CAI and %Ro) in the Ordovician and Devonian rocks of the Appalachian basin

in Pennsylvania: U. S. Geological Survey Open-File Report 02-302, 57 p.

Ryder, R. T., 1998, Characteristics of discrete and basin-centered parts of the Lower

Silurian regional oil and gas accumulation, Appalachian basin: Preliminary results from

a data set of 25 oil and gas fields: U.S. Geological Survey Open-File Report 98-0216, 71

p.

Ryder, R. T., 2000, Stratigraphic framework and depositional sequences in the Lower

Silurian regional oil and gas accumulation, Appalachian basin: From Jackson County,

Ohio, through northwestern Pennsylvania, to Orleans County, New York: U.S.

Geological Survey Miscellaneous Investigations Map I-2726, 2 sheets, pamphlet, 8 p.

Ryder, R. T., Burruss, R. C., and Hatch, J. R., 1998, Black shale source rocks and oil

generation in the Cambrian and Ordovician of the central Appalachian basin, USA:

American Association of Petroleum Geologists Bulletin, v. 82, p. 412-441.

17
Figure 1. Map of the lower Silurian regional oil and gas accumulation showing the

location of the study area and cross sections A-A' and D-D'.

	 	 	 	 	

18
Figure 2. Correlation chart of Lower Silurian and adjoining strata, northeastern Ohio. northwestern Pennsylvania,

and central Pennsylvania, showing the interval of the Lower Siurian regional and gas accumulation.

19
Figure 3. Map of the study area in northeastern Ohio and northwestern Pennsylvania showing well locations in Geauga and Trumbull Counties, Ohio,

and Mercer and Butler Counties, Pennsylvania, where oil and (or) gas was sampled for this ivnestigation and the Burruss and Ryder (1998) investigation.

20
Figure 4. Schoell (1983) diagram showing the isotopic composition of selected natural gases in the Lower 

Silurian regional oil and gas accumulation. A scale devised by Jenden and others (1993) for estimating the 

approximate vitrinite reflectance (%Ro) of the source rock that generated the gas is attached to the right side 

of the diagram. Also shown are the CAI thermal maturity values for Middle Ordovician carbonate rocks located 

near the proposed Middle Ordovician Utical Shale source rock. 

CAI - Conodont alteration index; VRE - Vitrinite reflectance equivalence based on Nοth (1991); BC - Basin-center 

part of the regional accumulation; HC - Hybrid-conventional part of the regional accumulation.

21
10 20 30 40 50 60 70

R etention Time, minutes

5A: Whole oil gas chromatogram, sample 98OH01B, #2 P atterson. S elected peak identifications: n-CX, normal alk

s the carbon number; pr, pristane; ph, phytane.

Whole oil

#2 P atters on

AP I gravity: 42.8

pr

ph

n-C17

methylcyclohexane

n-C10

n-C30

7
pr

ph

0 20 30 40 50 60 70

R etention Time, minutes

e 5B : S aturated hydrocarbon fraction gas chromatogram, sample 98OH01B, #2 P atterson.

S aturated hydrocarbons

#2 P atters on

AP I gravity: 42.8
0 20 30 40 50 

R etention Time, minutes

re 5C: Aromatic hydrocarbon fraction gas chromatogram, sample 98OH01B, #2 P atterson.

Aromatic hydrocarbons

#2 P atters on

AP I gravity: 42.8
10 20 30 40 50 60 70

R etention Time, minutes

6A: Whole oil gas chromatogram, sample 98OH02A, #1 Bruno. S elected peak identifications: n-CX, normal alka

s the carbon number; pr, pristane; ph, phytane.

Whole oil

#1 B runo

AP I gravity: 41.4

pr

ph

n-C17

methylcyclohexane

n-C10

n-C30

7
0 20 30 40 50 60 7

R etention Time, minutes

re 6B : S aturated hydrocarbon fraction gas chromatogram, sample 98OH02A, #1 Bruno.

S aturated hydrocarbons

#1 B runo

AP I gravity: 41.4

pr

ph
0 20 30 40 

R etention Time, minutes

e 6C: Aromatic hydrocarbon fraction gas chromatogram, sample 98OH02A, #1 Bruno.

Aromatic hydrocarbons

#1 B runo

AP I gravity: 41.4
10 20 30 40 50 60 70

R etention Time, minutes

7A: Whole oil gas chromatogram, sample 98OH03A, #2 Grandview-Johnson. S elected peak identifications: n-C

where X is the carbon number; pr, pristane; ph, phytane.

Whole oil

#2 Grandview-J ohns o

AP I gravity: 40.7

pr

ph

n-C17

methylcyclohexane

n-C10

n-C30

7
0 20 30 40 50 60 7

R etention Time, minutes

re 7B : S aturated hydrocarbon fraction gas chromatogram, sample 98OH03A, #2 Grandview-Johnson.

S aturated hydrocarbons

#2 Grandview-J ohns on

AP I gravity: 40.7

pr

ph
0 20 30 40 

R etention Time, minutes

e 7C: Aromatic hydrocarbon fraction gas chromatogram, sample 98OH03A, #2 Grandview-Johnson.

Aromatic hydrocarbons

#2 Grandview-J ohns on

AP I gravity: 40.7
10 20 30 40 50 60 70

R etention Time, minutes

8A: Whole oil gas chromatogram, sample 98OH04A, #1 Detweiler. S elected peak identifications: n-CX, normal a

s the carbon number; pr, pristane; ph, phytane.

Whole oil

#1 Detweiler

AP I gravity: 43.8

pr

ph

n-C17

methylcyclohexane

n-C10

n-C30

7
0 20 30 40 50 60 7

R etention Time, minutes

re 8B : S aturated hydrocarbon fraction gas chromatogram, sample 98OH04A, #1 Detweiler.

S aturated hydrocarbons

#1 Detweiler

AP I gravity: 43.8

pr

ph
0 20 30 40 

R etention Time, minutes

e 8C: Aromatic hydrocarbon fraction gas chromatogram, sample 98OH04A, #1 Detweiler.

Aromatic hydrocarbons

#1 Detweiler

AP I gravity: 43.8
10 20 30 40 50 60 70

R etention Time, minutes

9A: Whole oil gas chromatogram, sample 98OH05A, #2 Hissa, collected from a separator that also serves the #

lected peak identifications: n-CX, normal alkanes where X is the carbon number; pr, pristane; ph, phytane.

Whole oil

#2 Hiss a

AP I gravity: 42.8

pr

ph

n-C17

methylcyclohexane

n-C10

n-C30

7
0 20 30 40 50 60 7

R etention Time, minutes

re 9B : S aturated hydrocarbon fraction gas chromatogram, sample 98OH05A, #2 Hissa, collected from a separa

lso serves the #1 Hissa well..

S aturated hydrocarbons

#2 Hiss a

AP I gravity: 42.8

pr

ph
0 20 30 40 

R etention Time, minutes

e 9C: Aromatic hydrocarbon fraction gas chromatogram, sample 98OH05A, #2 Hissa, collected from a separato

so serves the #1 Hissa well.

Aromatic hydrocarbons

#2 Hiss a

AP I gravity: 42.8
10 20 30 40 50 60 70

R etention Time, minutes

10A: Whole oil gas chromatogram, sample 98OH06A, #2 F rench. S elected peak identifications: n-CX, normal 

X is the carbon number; pr, pristane; ph, phytane.

Whole oil

#2 F rench

AP I gravity: 43.0

pr

ph

n-C17

methylcyclohexane

n-C10

n-C30

C7
0 20 30 40 50 60 7

R etention Time, minutes

re 10B : S aturated hydrocarbon fraction gas chromatogram, sample 98OH06A, #2 F rench.

S aturated hydrocarbons

#2 F rench

AP I gravity: 43.0

pr

ph
0 20 30 40 

R etention Time, minutes

e 10C: Aromatic hydrocarbon fraction gas chromatogram, sample 98OH06A, #2 F rench.

Aromatic hydrocarbons

#2 F rench

AP I gravity: 43.0
10 20 30 40 50 60 7

R etention Time, minutes

e 11A: Whole oil gas chromatogram, sample 98OH07A, #3 Griffin. S elected peak identifications: n-CX, normal 

X is the carbon number; pr, pristane; ph, phytane.

Whole oil

#3 Griffin

AP I gravity: 33.8

pr

ph

n-C17

methylcyclohexane

n-C10

n-C30

n-C7
0 20 30 40 50 60 7

R etention Time, minutes

re 11B : S aturated hydrocarbon fraction gas chromatogram, sample 98OH07A, #3 Griffin.

S aturated hydrocarbons

#3 Griffin

AP I gravity: 33.8

pr

ph
0 20 30 40 

R etention Time, minutes

e 11C: Aromatic hydrocarbon fraction gas chromatogram, sample 98OH07A, #3 Griffin.

Aromatic hydrocarbons

#3 Griffin

AP I gravity: 33.8
10 20 30 40 50 60 7

R etention Time, minutes

e 12A: Whole oil gas chromatogram, sample 98OH08, #1 Bates. S elected peak identifications: n-CX, normal a

X is the carbon number; pr, pristane; ph, phytane.

Whole oil

#1 B ates

AP I gravity: 42.9

pr

ph

n-C17

methylcyclohexane

n-C10

n-C30

n-C7
0 20 30 40 50 60 7

R etention Time, minutes

re 12B : S aturated hydrocarbon fraction gas chromatogram, sample 98OH08, #1Bates.

S aturated hydrocarbons

#1 B ates

AP I gravity: 42.9

pr

ph
0 20 30 40 

R etention Time, minutes

e 12C: Aromatic hydrocarbon fraction gas chromatogram, sample 98OH08, #1 Bates.

Aromatic hydrocarbons

#1 B ates

AP I gravity: 42.9
10 20 30 40 50 60 7

R etention Time, minutes

e 13A: Whole oil gas chromatogram, sample 98PA02, #6 Weber. S elected peak identifications: n-CX, normal a

X is the carbon number; pr, pristane; ph, phytane.

Whole oil

#6 Weber

AP I gravity: 39.9

pr

ph

n-C17

n-C10

n-C30
0 20 30 40 50 60 7

R etention Time, minutes

re 13B : S aturated hydrocarbon fraction gas chromatogram, sample 98PA02, #6 Weber.

S aturated hydrocarbons

#6 Weber

AP I gravity: 39.9

pr

ph
0 20 30 40 

R etention Time, minutes

e 13C: Aromatic hydrocarbon fraction gas chromatogram, sample 98PA02, #6 Weber.

Aromatic hydrocarbons

#6 Weber

AP I gravity: 39.9
10 20 30 40 50 60 7

R etention Time, minutes

e 14A: Whole oil gas chromatogram, sample 98PA05A, #8 Oris. S elected peak identifications: n-CX, normal al

X is the carbon number; pr, pristane; ph, phytane.

Whole oil

#8 Oris

AP I gravity: 45.5

pr

ph

n-C17

methylcyclohexane

n-C10

n-C30

n-C7
0 20 30 40 50 60 7

R etention Time, minutes

re 14B : S aturated hydrocarbon fraction gas chromatogram, sample 98PA05A, #8 Oris.

S aturated hydrocarbons

#8 Oris

AP I gravity: 45.5

pr

ph
0 20 30 40

R etention Time, minutes

50 

e 14C: Aromatic hydrocarbon fraction gas chromatogram, sample 98PA05A, #8 Oris.

Aromatic hydrocarbons

#8 Oris

AP I gravity: 45.5
10 20 30 40 50 60 7

R etention Time, minutes

e 15A: Whole oil gas chromatogram, sample 98PA06A, #2 Gibson. S elected peak identifications: n-CX, norma

X is the carbon number; pr, pristane; ph, phytane.

Whole oil

#2 Gibs on

AP I gravity: 38.8

pr

ph

n-C17

ylcyclohexane

n-C10

n-C30

n-C7
0 20 30 40 50 60 7

R etention Time, minutes

re 15B : S aturated hydrocarbon fraction gas chromatogram, sample 98PA06A, #2 Gibson.

S aturated hydrocarbons

#2 Gibs on

AP I gravity: 38.8

pr

ph
0 20 30 40 

R etention Time, minutes

e 15C: Aromatic hydrocarbon fraction gas chromatogram, sample 98PA06A, #2 Gibson.

Aromatic hydrocarbons

#2 Gibs on

AP I gravity: 38.8
Figure 16. Plot of pr/n-C17 vs. ph/n-C18 for "Clinton"/Medina oils and Utica Shale bitumen extracts. BC - Basin-center part of 

the regional accumulation; HC - Hybrid-conventional part of the regional accumulation.

55
Figure 17. Plot of δ

13C distributions in the saturated and aromatic hydrocarbon fractions for "Clinton"/Medina

oils and Utica Shale bitumen extracts. BC - Basin-center part of the regional accumulation; HC - Hybrid-conventional

part of the regional accumulation.

56
10 20 30 40 50 60 

R etention Time, minutes

F igure 18A: Terpane mass fragmentogram, m/z 191.180, sample 98PA02, #6 Weber.

Terpanes

#6 Weber

C21 C23 C24 C25

C28a,b

C29a,b

A B

D

E

F

G

H

I

K

L M

N 

Tricyclic terpanes

P entacyclic triterpanes

57
10 20 30 40 50 

R etention Time, minutes

F igure 18B : S terane mass fragmentogram, m/z 217.1956, sample 98PA02, #6 Weber.

S teranes

#6 Weber

1

2

3

5a,b

7a,b 8

10

12

13, 14, 15

16, 17, 18

58
Perforation Depth Sample ID Well Name Operator API number Ohio or Pa.

County/ 

Township or

71⁄2 quad. 

Producing

Formation Top, 

ft 

Bottom,

ft 

Total 

Depth, 

ft. 

Sample Oil Sample 

Point 

98OH01 #2 Patterson Range

Res. 

3405521619 Geagua/

Chester 

“Clinton”sandstone 

3588 3611 3720 gas, oil sightglass

98OH02 #1 Bruno Range

Res. 

3405520490 Geauga/

Claridon

“Clinton”

sandstone 

3795 3844 3993 gas, oil sightglass

98OH03 #2 GrandviewJohnson Range Res. 3405520285 Geauga/ Claridon “Clinton” sandstone 3906 3962 4098 gas, oil sightglass 98OH04 #1 Detweiler Range

Res. 

3405520818 Geauga/

Middlefield

“Clinton”

sandstone 

3943 3979 4150 gas, oil sightglass

98OH05 #2 Hissa Range

Res. 

3405521083 Geauga/

Huntsburg 

“Clinton”

sandstone 

3797 3897 4015 gas, oil sightglass

98OH06 #2 French Range

Res. 

3415522716 Trumbull/

Mesopotamia 

“Clinton”

sandstone 

3723 3878 3950 gas, oil sightglass

98OH07 #3 Griffin Range

Res. 

3415522594 Trumbull/

Bloomfield 

“Clinton”

sandstone 

3754 3862 4047 gas, oil sightglass

98OH08 #1 Bates Range

Res. 

3415522553 Trumbull/

Bloomfield 

“Clinton”

sandstone 

3815 3895 4085 oil sightglass

98PA01 #5 Brown Atlas

Res. 

3708521979 Mercer/

Grove City 

Grimsby/

Whirlpool

62886416

63286426

6582 gas oil not

available 

98PA02 # 6 Weber Atlas 

Res. 

3708521992 Mercer/

Grove City 

Grimsby/

Whirlpool

63556477

63736487

6637 oil stock tank

98PA03 #1 Velisaris Atlas

Res. 

3701921358 Butler/

Grove City 

Grimsby/ 

Whirlpool

65206584

65686594

6714 gas oil not 

available 

98PA04 #2 Mathews Atlas

Res. 

3701921352 Butler/

Barkeyville 

Grimsby

Sandstone 

6564 6574 6775 gas oil not

available 

98PA05 #8 Oris Range

Res. 

3708522239 Mercer/

Sharpsville 

Grimsby/

Whirlpool

4783 4944 5086 gas, oil sightglass

98PA06 #2 Gibson Range

Res. 

3708521263 Mercer/

Sharpsville 

Grimsby

Sandstone 

4958 5021 5180 gas, oil sightglass

59

Table 1. Wells sampled for gas and oil in northeastern Ohio and northwestern Pennsylvania. 
Sample ID 98OH01A 98OH02B 98OH03B 98OH04B 98OH05B 98OH06B

Well Name #2 Patterson #1 Bruno #2 GrandviewJohnson #1 Detweiler #2 Hissa #2 French

Molecular Analysis, mole %Methane 78.03 85.62 88.10 88.17 76.38 87.48Ethane 9.70 6.18 5.30 5.58 10.98 5.59Ethylene nd nd nd nd nd ndPropane 4.82 2.56 2.16 1.93 6.07 2.12iso-Butane 0.60 0.36 0.36 0.28 1.06 0.33n-Butane 1.33 0.73 0.72 0.51 2.01 0.63iso-Pentane 0.30 0.19 0.21 0.14 0.60 0.17n-Pentane 0.30 0.17 0.18 0.12 0.52 0.15Hexanes + 0.22 0.16 0.23 0.11 0.28 0.14Helium 0.14 0.12 0.11 0.10 0.069 0.12Hydrogen 0.013 nd 0.0047 0.0028 0.0044 0.0067Argon nd nd nd nd nd ndOxygen nd nd nd nd nd ndNitrogen 4.55 3.91 2.63 3.04 2.01 3.24Carbon Dioxide nd nd nd 0.02 0.02 0.02Isotopic Analysis, per mil Methane, δ13C -41.98 -39.17 -38.06 -38.76 -39.83 -38.78δD -201.9 -174.1 -167.3 -174.3 -181.9 -174.6Ethane, δ13C -35.26 -33.76 -34.62 -35.12 -35.16 -35.26Propane, δ13C -32.34 -31.10 -30.81 -30.90 -31.18 -31.05n-Butane, δ13C -30.68 nd -29.52 nd nd ndNitrogen, δ15N -4.92 nd -2.98 nd nd nd

60 

Table 2A. Molecular and isotopic composition of gas samples. nd: not detected
Sample ID 98OH07B 98PA01 98PA03 98PA04 98PA05B 98PA06B

Well Name #3 Griffin #5 Brown #1 Velisaris #2 Mathews #8 Oris #2 Gibson

Molecular Analysis, mole %Methane 88.19 94.36 94.25 94.02 89.94 91.74Ethane 5.17 2.37 2.26 2.23 4.58 3.67Ethylene nd nd nd nd nd ndPropane 1.87 0.15 0.14 0.13 1.35 0.87iso-Butane 0.26 0.017 0.015 0.014 0.22 0.13n-Butane 0.51 0.022 0.017 0.017 0.36 0.25iso-Pentane 0.13 0.009 0.0073 0.0070 0.11 0.0780n-Pentane 0.12 nd nd nd 0.089 0.061Hexanes + 0.098 0.015 0.009 0.0087 0.16 0.087Helium 0.11 0.087 0.09 0.087 0.10 0.097Hydrogen nd 0.01 nd nd 0.0024 0.012Argon nd nd nd nd nd ndOxygen nd nd nd nd nd ndNitrogen 3.54 2.92 3.17 3.45 3.08 2.99Carbon Dioxide nd 0.04 0.04 0.03 0.01 0.02Isotopic Analysis, per mil Methane, δ13C -38.75 -34.69 -34.19 -33.97 -36.90 -35.58δD -175.3 -152.3 -153.3 -150.8 -167.3 -159.8Ethane, δ13C -35.58 -39.75 -41.14 -41.15 -35.32 -35.98Propane, δ13C -31.34 -40.17 -42.85 -42.81 -30.61 -30.74n-Butane, δ13C -29.84 nd -38.89 nd nd -29.24Nitrogen, δ15N -1.31 nd -5.14 nd nd -5.00

61 

Table 2B. Molecular and isotopic composition of gas samples. nd: not detected
Sample ID Well name API 

gravity 

Petroleum Fractions, 

wt. % 

Isotopic Composition, 

per mil 

Sat 

HC 

Aro 

HC 

NSOs Asph Sat HC, δ13C Aro HC, δ13C 

98OH01B #2 Patterson 42.8 84.46 10.72 2.91 1.90 -30.22 -29.74 

98OH02A #1 Bruno 41.4 85.21 12.10 2.58 0.11 -30.08 -29.40 

98OH03A #2 Grandview 

- Johnson 

40.7 85.20 11.08 3.24 0.48 -30.16 -29.37 

98OH04A #1 Detweiler 43.8 86.85 9.04 3.55 0.56 -29.95 -29.01 

98OH05A #2 Hissa 42.8 86.71 8.72 4.08 0.49 -30.17 -29.37 

98OH06A #2 French 43.0 84.40 11.36 3.55 0.70 -30.09 -29.16 

98OH07A #3 Griffin 33.8 88.03 9.26 2.43 0.29 -30.08 -29.23 

98OH08 #1 Bates 42.9 87.36 8.67 3.24 0.73 -30.01 -29.17 

98PA02 #6 Weber 39.9 89.39 2.21 1.20 7.21 -29.60 -28.72 

98PA05A #8 Oris 45.5 91.81 2.84 4.97 0.39 -29.60 -29.00 

98PA06A #2 Gibson 38.8 92.96 4.27 2.37 0.39 -29.47 -28.80 

Table 3. Properties of the whole crude oil and crude oil fractions. Sat HC: saturated hydrocarbons; 

Aro HC: aromatic hydrocarbons; NSOs: Nitrogen, sulfur, oxygen-bearing organics; asph: asphaltenes. 

62 
 

Saturated HC characteristics 

 Sample ID Well name pr/ph pr/n-C17 ph/n-C18 CPI % n-alk Cond. 

index 

98OH01B #2 Patterson 1.33 0.38 0.33 1.07 7.73 9.72 

98OH02A #1 Bruno 1.35 0.41 0.34 0.96 17.93 5.49 

98OH03A #2 GrandviewJohnson 1.36 0.40 0.33 0.99 24.58 7.21 

98OH04A #1 Detweiler 1.36 0.41 0.34 1.00 10.21 9.82 

98OH05A #2 Hissa 1.32 0.36 0.31 0.96 14.92 8.60 

98OH06A #2 French 1.38 0.38 0.32 1.04 17.95 10.81 

98OH07A #3 Griffin 1.31 0.27 0.23 

98OH08 #1 Bates 1.31 0.43 0.38 1.06 6.35 9.51 

98PA02 #6 Weber 1.44 0.40 0.38 1.05 14.93 3.04 

98PA05A #8 Oris 1.94 0.29 0.19 1.03 18.74 8.23 

98PA06A #2 Gibson 2.01 0.28 0.17 1.02 20.40 5.99 

Table 4. Properties of the saturated hydrocarbon fraction of the crude oils. These properties were 

calculated on the basis of peak area from analyses performed on April 1999. pr/ph: pristane/phytane; 

CPI: carbon preference index; % n-alk: % of n-alkanes in total saturate fraction; Cond. Index: condensate 

index defined by Lewan and Buchardt (1989), % n-C11 of n-C10 to n-C30. CPI, % n-alk, and cond. Index 

were not calculated for the #3 Griffin oil sample. 

63
Table 5. Terpane and sterane compounds identified in the saturate fraction of the oil 

from the #6 Weber well. 

 Molecular 

Label Formula Compound 

Tricyclic Terpanes 

C21 C21H38 C21 tricyclic terpane 

C23 C23H42 C23 tricyclic terpane 

C24 C24H44 C24 tricyclic terpane 

C25 C25H46 C25 tricyclic terpane 

C28a C28H50 C28 [22S] tricyclic terpane 

C28b C28H50 C28 [22R] tricyclic terpane 

C29a C29H52 C29 [22S] tricyclic terpane 

C29b C29H52 C29 [22R] tricyclic terpane 

Pentacyclic Triterpanes

A C27H46 18α trisneonorhopane [Ts] 

B C27H46 17α trisneonorhopane [Tm] 

D C29H50 Norhopane [C29] 

E C29H50 18α neonorhopane [C29] 

F C30H52 Hopane [C30] 

G C30H52 17β21α moretane [C30] 

H C31H54 22S homohopane [C31] 

I C31H54 22R homohopane [C31] 

K C32H56 22S bishomohopane [C32] 

L C32H56 22R bishomohopane [C32] 

M C33H58 22S trishomohopane [C33] 

N C33H58 22R trishomohopane [C33] 

O C34H60 22S tetrakishomohopane [C34] 

P C34H60 22R tetrakihomohopane [C34] 

Steranes 

1 C27H48 13β 17α 20S diacholestane [C27] 

2 C27H48 13β 17α 20R diacholestane [C27] 

3 C27H48 13α 17β 20S diacholestane [C27] 

5a C28H50 13β 17α 20S 24-methyldiacholestane [C28] (I) 

5b C28H50 13β 17α 20S 24-methyldiacholestane [C28] (II) 

7a C28H50 13β 17α 20R 24-methyldiacholestane [C28] (I) 

7b C28H50 13β 17α 20R 24-methyldiacholestane [C28] (II) 

8 C28H50 13β 17β 20S 24-methyldiacholestane [C28] or 5α 14α 17α 20S 

 cholestane [C27] 

10 C28H50 5α 14α 17α 20R cholestane [C27] or 13α 17β 20R 24- 

 methyldiacholestane [C28] 

12 C28H50 5α 14α 17α 20S 24- methyldiacholestane [C28] + Dia – C29

13 C28H50 5α 14β 17β 20R 24- methyldiacholestane [C28] 

14 C28H50 5α 14α 17α 20R 24- methylcholestane [C28] 

15 C29H52 5α 14α 17α 20S 24- ethylcholestane [C29] 

16 C29H52 5α 14β 17β 20R 24- ethylcholestane [C29] 

17 C29H52 5α 14β 17β 20S 24- ethylcholestane [C29] 

18 C29H52 5α 14α 17α 20R 24- ethylcholestane [C29] 

 

64