1. 1
Group Field Study
Provided by
Well Watchers
Preston Rich
Edward O’Shea
Sean Burroughs
Chris Strong
Cassidy Kohl
December 5th, 2014
1.0 Overview
This report includes the results of log analyses taken from five different wells in the county of
Sweetwater, in the southern part of Wyoming. The wells are located in the Greater Green
River Basin and encompass three different fields. These fields include the Two Rim, the Wells
Bluff, and the Wild Rose field. They are all in relatively close proximity to each other and
share the same reservoir characteristics. The target formations associated to these well are
the Almond and Ericson formation, which are a sub­group of the Mesaverde formation. The
majority of the wells were gas producing wells, that also produced some volumes of oil. One
of the wells was not producing. Log analysis determined that the lithology was predominantly
quartz and calcite rich sandstone with sections of shale. The well had slight deviation and
were treated with hydraulic fracturing stimulation. All of the perforations were carried out
similarly with some differences to accommodate the conditions of each respective well. The
oil found in this basin is considered to be sweet oil with an API gravity range of 38­44 degrees
API. Core analysis of 96 cores from the Delaney field determined the average permeability to
be 1.3 md and the average porosity to be 14.2%.
2.0 Geology
The lithology in the Two Rim Field is mostly comprised of sandstone, shale, coal, and
siltstone. The target layer for our wells was the Mesaverde layer specifically is primarily
composed of sandstone with a secondary rock type of shale (USGS.gov). Research also
determined the presence of coal and other conglomerates. Based on log analysis, it was
determined that the composition of the sandstone was calcite and quartz with sections of
shale. The porosity that was determined from the log analysis was found to be about 10% for
all the wells.

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2.1 Basin
Our wells are located in the Greater Green River Basin. The majority of the Greater Green
River Basin is located in the southern part of Wyoming and also emcompasses the north
western part of Colorado and a small part of Utah. The Greater Green River basin has a total
of 281 fields, in which it is estimated to have 2.3 million barrels of oil and 347.3 million barrels
of natural gas liquids. The total petroleum system is composed of three continuous gas
assessment units. These three units are the Almond Continuous Gas Assessment Unit, the
Rock Springs­Ericsson Continuous Gas Assessment Unit, and the Mesaverde Coalbed Gas
Assessment Unit.
2.1.1 Field
Our wells are located in the Two Rim, Wells Bluff and Wild Rose fields, which are south west
of Rawlins in Wyoming. All of these fields target the Mesaverde formation, are all sandstone,
and are all gas producers. The differences in the fields can be seen in average porosity,

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ranging from 9% in the Wild Rose to 14% in the Delaney Rim while the permeabilities range
from .07md in the Wild Rose to 1.3md in the Delaney Rim. (Data from
archives.datapages.com)
2.1.2 Basemap
The wells are all located in Township 18N, Range 95W, a township in south­central Wyoming.
The wells in this analysis are no more than five miles apart with the two closest being on the
same pad only 20ft apart.

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*Images found through Google Earth

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Well Location
Well Name Latitude Longitude
23­10D DELANEY RIM 41.524216 ­108.073767
23­160D DELANEY RIM 41.52418 ­108.073807
27­150D DELANEY RIM 41.505866 ­108.100405
15­50D TWO RIM 41.53906 ­108.094197
33­6 MAST 41.563416 ­108.144937
2.2 Stratigraphic Column
As seen in the picture below since the wells are located in the Green River Basin, to reach the
Mesaverde target formation, the wells need to be drilled through the the Wasatch, the Fort
Union, and the Lance formations. The wells will be producing from the target formation; the
Mesaverde formation.

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2.3 Well Cross­Section
The wells across the field exhibited a large variation in their gamma ray logs which made
them difficult to correlate, but by using the data available on the Wyoming Oil and Gas
Conservation Commission’s website (wogcc.state.wy.us) the logs were able to be correlated
based on the tops of the Fort Union, Lance, Lewis, and Mesaverde formations.
3.0 Multi­well Petrophysics
While comparing all of the wells the largest discovery was that the petrophysics of the wells
can and does vary widely. Though all of these wells were targeting the same formation the
depths for the different formations was radically different. For example The top of the Lewis
formation in DELANEY RIM 23­160D is at a depth of 9,034 ft while the TWO RIM 15­60D hits
the Lewis formation at 8,362 ft, a difference of more than 650 ft. While there is a lot of
confidence on the depth data for the top of each formation (as it was provided by the
Wyoming Oil and Gas Conservation Commission) but when comparing the gamma ray logs
across the wells the logs did not necessarily look similar to one another even though they
were breaching the same formation and they could vary widely between the tops of the
formations. This wide change in gamma ray suggests a wide variation in the composition
across the Basin.

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4.0 Drilling
4.1 Typical Well Design
With the exception of the 33­6 Mast well, which was drilled vertically, the other four wells are
all S­shaped wells. Each well has a very shallow kick­off point with surface casing run to
around 1,500 feet TVD. The Delaney Rim 27­150D and 23­160D build to 250
. The Delaney
23­10D and Two Rim 15­60D build to 200
before holding a slant. The Two Rim well begins to
drop at 3,300 feet, while each of the Delaney’s hold their slant to around 6,300 feet before
dropping. Each well (including 33­6 Mast) is drilled to a TVD around 11,200 feet TVD. Due to
the short slant of the Two Rim well, it has a much shorter departure at TD than the other three
S­shaped wells. Each of the Delaneys have similar, yet different departures at TD due to
differing drop gradients. Examples of one of the Delaneys as well as the Two Rim well may be
seen below.
Delaney Rim 23­160D Two Rim 15­60D
Each of the 5 wells have the same sizes of casing, but their depths differ slightly. All 5 begin
with a 8­⅝”, 28 ppf J­55 casing in an 11” hole to between 1,057 and 1,544 feet. The Two Rim
well begins its intermediate casing as a 4.5”, 13.5 ppf P­110 casing run in a 7­7/5” hole.
However, at 9,041 feet, the hole size is increased to 7­⅞”, matching the other 4. Intermediate

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casings are run to between 11,017 and 11,991 feet. The 33­6 Mast well utilizes a 14”
conductor to 40 feet in addition to its surface and intermediate casings.
4.2 Drilling Challenges
Each of the directional wells experienced deviation from the original well trajectory plan. In the
wellbore trajectory images above, the blue lines are the original planned trajectory. The red
lines are the actual trajectory. All four directional wells had sundry reports filled out for
sidetracking. They cement the hole below the planned kickoff point, pressure test it, plug it,
then begin the new sidetracked wellbore.
The Delaney Rim 23­160D experienced a stuck pipe issue while running intermediate casing.
After making a connection, the hydraulic slips wouldn’t disengage and emergency brakes
were activated. After 4­½ hours the problem was fixed and the slips released but the casing,
which had been static for that entire period, would not budge. The driller was instructed to cut
the stuck pipe above where the expected stuck point was, pull out of hole, rig down, and
move to the next well. While drilling the next well, a sidetrack plan was developed to deviate
from the wellbore above the stuck point. The sidetrack plan detailed a new well that began to
deviate about 50 feet below the surface casing shoe and continued on a trajectory that was
similar to the original plan.
5.0 Completion
For each well there were three perforations made in the areas where there was determined to
be a payzone. All of the perforations were done with .32 inch sized holes done at about 76­88
holes per foot for most of the wells. The 27­150D Delaney Rim well was done at 4 holes per
foot. The 15­50D Two Rim well utilized .36 sized holes at 96­294 holes per foot. Hydraulic
fracturing stimulation was done once for all the wells except one, where three hydraulic
fracture stimulations were conducted. The well that had three hydraulic fracture stimulation
was the 27­150D Delaney Rim well.
5.1 Perforations
Perforation overview:
Perforations
23­10D DELANEY RIM Top Perfs (ft.) Bottom Perfs (ft.) Size (in.)
10,853 10,918 0.32

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10,954 11,035 0.32
11,138 11,170 0.32
23­160D DELANEY RIM Top Perfs (ft.) Bottom Perfs (ft.) Size (in.)
11,485 11,528 0.32
11,614 11,654 0.32
11,750 11,824 0.32
27­150D DELANEY RIM Top Perfs (ft.) Bottom Perfs (ft.) Size (in.)
11,357 11,441 0.32
11,465 11,574 0.32
11,597 11,682 0.32
15­50D TWO RIM Top Perfs (ft.) Bottom Perfs (ft.) Size (in.)
10,888 10,984 0.36
11,006 11,058 0.36
11,088 11,266 0.36
33­6 MAST Top Perfs (ft.) Bottom Perfs (ft.) Size (in.)
No Data No Data No Data
5.2 Stimulation
Stimulation overview:
Completions Frac Treatments
23­10D DELANEY RIM Top Interval (ft.) Bottom Interval (ft.) Treatment
10,853 11,170 6199­509
23­160D DELANEY RIM Top Interval (ft.) Bottom Interval (ft.) Treatment
11,485 11,824 5502­841
27­150D DELANEY RIM Top Interval (ft.) Bottom Interval (ft.) Treatment
11,357 11,441 1408­2961
11,465 11,574 2250­2961
11,597 11,682 2019­2961
15­50D TWO RIM Top Interval (ft.) Bottom Interval (ft.) Treatment
11,088 10,984 4958­2197
33­6 MAST Top Interval (ft.) Bottom Interval (ft.) Treatment

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No Data No Data No Data
5.3 Completion Challenges
The data found for the wells revealed no complications while completing the wells.
6.0 Production
Of the five wells reviewed in this analysis all but one are producing and all that are producing
are producing primarily gas with some volumes of oil.
6.1 Fluid Properties
The resistivity of the water in the Delaney Rim Unit is about .42 ohms at a temperature of 68
degrees fahrenheit with 15,000 pounds per million of Cl. The gas oil ratio was about 6947 scf
per barrel, which was based on production data. The oil found in the Delaney Rim Unit in the
range of 38­44 degree API, and it is considered a sweet. The drive mechanism found in this
well is gas expansion with limited water drive.
6.2 Production Rates
Well Name
Produced Gas
(mcf)
Produced Oil
(bbls)
Produced Water
(bbls)
23­10D DELANEY RIM 85,089 2,595 85,089
23­160D DELANEY RIM 137,183 5,000 8,687
27­150D DELANEY RIM 320,887 911 7,827
15­60D TWO RIM 536,248 15,559 25,269
33­6 MAST No Data No Data No Data
6.3 Production Challenges
All four producing wells have produced gas at a steady rate since they have come online. The
graph below is a typical flow rate for all of the studied wells showing a steady flow with no
large drops in production.

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*Graph from wogcc.state.wy.us
7.0 Summary
The wells analyzed in this report were all drilled in the Greater Green River Basin targeting
the Mesaverde formation, specifically the Almond and Ericson formations (which are within
the Mesaverde). The lithology is heavily mixed between the wells but sandstone composed of
primarily quartz and calcite usually composes the largest percentage of the lithology matrix.
The hydrocarbons recovered from these wells has been primarily gas. While the wells all go
through the same formations the formations vary widely in composition between the wells.
Most of the wells where drilled as S­wells with the casing size the same in every well. All of
the wells were perforated with a perforation density of 66­88 holes per foot. All of the wells
have also been hydraulically fractured. The porosity that was determined for the wells was
found to be approximately between 10% and 15%.
The gas:oil ratio was about (6947 scf gas) : (1 barrel oil) making the produced oil a sweet oil.
Production is fairly consistent in the four operating wells. The primary drive mechanism is gas
expansion, but a limited water drive is present in some localized areas.

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8.0 References
"AAPG Datapages/Archives." : Delaney Rim Unit. N.p., n.d. Web. 01 Dec. 2014.
Petroleum Systems and Geologic Assessment of Oil and Gas in the Southwestern Wyoming
Province, Wyoming, Colorado, and Utah. Denver, CO: U.S. Dept. of the Interior, U.S. Geological
Survey, 2005. USGS. Web. 01 Dec. 2014.
Wyoming Oil and Gas Conservation Commission. N.p., n.d. Web. 21 Nov. 2014.