Core Center News: Why a Building Full of Rocks is so Important to Utah

Core Center News: Why a Building Full of Rocks is so Important to Utah

By Michael D. Vanden Berg

Established in 1951, the Utah Geological Survey’s Utah Core Research Center (UCRC) contains the region’s only publicly available and most complete collection of geologic core and cuttings from Utah. Think of it as a geologic library, storing inimitable archives of geologic knowledge for future generations. The current 15,000-square-foot facility was built in 1997 and presently holds core from over 1500 drill holes totaling about 400,000 feet of material (over 75 miles, roughly the distance from Salt Lake City to Logan!), and cuttings from nearly 5000 drill holes representing over 57 million feet of subsurface data (nearly 11,000 miles, almost half way around the Earth!). Most of this material came from oil and gas wells, but some came from metal and potash exploration wells, water/geothermal wells, coal exploration wells, and many others. This collection represents about $5 billion worth of investment in Utah’s natural resources and in many cases is irreplaceable.

The UCRC collection is an invaluable resource for companies looking to develop mineral and energy resources in Utah, most of which are in rural areas of the state. In 2018 alone, the UCRC hosted over 400 visitors from all over the world. Industry professionals often visit the UCRC to examine core and collect sample material for analytical testing. These examinations help them better understand their lease area, reduce exploration costs, and hopefully spur increased development. It is not uncommon for the UCRC to be the first place that a new-to-Utah petroleum company will visit before investing in Utah leases or drilling new wells. The collection is also widely used by the academic community. Professors and students from all over the world come to Utah to examine our core and cuttings for various research projects, the results of which are often published, leading to increased interest and understanding of Utah’s geology.

Furthermore, the UCRC hosts educational workshops (20+ per year) on a wide variety of geologic topics. Outside groups will use our facility and core material to run workshops, or geologists from the UGS will organize custom educational courses for oil companies and university geology students. In the past few years, the UGS has organized workshops for geologists from several international companies including BP, ExxonMobil, Shell, ConocoPhillips, Anadarko, Total (France), Petrobras (Brazil), Equinor (Norway), and Repsol (Spain), as well as more local companies including QEP Resources, Wexpro, Newfield, Finley, Ultra, Berry, Crescent Point, Bayless, Bill Barrett, Axia, Resolute, Rose Petroleum, Fidelity, and many others.

Since the downturn in oil and gas prices in late 2014, several companies have donated large quantities of core/cuttings material to the UCRC as a cost-saving measure. The most significant donation was from Resolute Energy, the former operator of Greater Aneth, Utah’s largest producing oil field located in San Juan County (see Survey Notes, v. 49, no. 2, p. 6–7). This donation consisted of core from over 120 wells, stacked on about 140 pallets requiring six semi-truck loads to deliver the material from Texas. In addition, we have recently received new cores from the Green River Formation in the Uinta Basin, the Moenkopi Formation near the San Rafael Swell, and cores from the Navajo, Entrada, and Dakota Sandstones.

Proposed Expansion

With all the recent donations, the UCRC warehouse is at capacity. The UGS has proposed building an additional 9000 square feet of storage space to accommodate additional donations of core and cuttings. Without access to a secure/modern core center, operators looking to offload their core might opt to dispose of it instead of donating this valuable material. It is of vital importance that the State of Utah offers an option to collect and store this important material and make it available for companies, researchers, and students to use and examine.

In addition, the UCRC is in dire need of an updated and expanded core viewing area. The UCRC currently uses space in the warehouse portion of the facility. This space is not ideal for core examination or for teaching workshops because the area is too small, limiting the amount of core that can be displayed at one time and making examination difficult and inefficient; the area is not climate controlled, becoming too cold in winter and too hot in summer; and the area is within the active warehouse, making safety of guests a concern. With an improved core viewing area, we can provide a more user-friendly environment for core examination, increasing productivity and efficiency. We will also be able to host larger and more professional educational workshops, attracting more visitors to the state.

As the UGS tries to raise the funds necessary to expand and improve the UCRC, we want to emphasize that the facility is not just a warehouse full of rocks, but holds billions of dollars worth of investment in Utah’s natural resources. UGS geologists are dedicated to curating this important collection and fostering its beneficial use for Utah industry and geologic knowledge. If you are interested in seeing thi collection, using it for research, or teaching a core-based geologic workshop, please feel free to contact us at any time. Visit https://geology.utah.gov/?p=5230 for more information.

Importance of the UCRC: Two Case Studies

Metal Exploration
In 1972, AMAX Exploration drilled four deep core holes near the historical Cactus coppergold- molybdenum mine in the San Francisco district, Beaver County, Utah. Although these holes intersected alteration and some mineralization, they were not sufficiently encouraging at the time for AMAX to retain their property position and do further work. Rather than continue storing the core, they chose to donate it to the UGS.

In 2016, Alderan Resources acquired a large property in the San Francisco district, including the old Cactus mine. In the course of their due diligence, they discovered that the UGS had the AMAX core. Company geologists visited the UCRC to examine these cores and took samples for new assays. They recognized that the drill core was compatible with their geologic model of the Cactus mine being part of a much larger porphyry copper system, similar to the Bingham Canyon mine. As a result of the promising analyses performed on the core housed at the UCRC, in 2017 Alderan raised about $20 million in an initial public offering, set up an office in Salt Lake City, hired some local senior staff, leased a field office in Milford, hired local support staff, and began an aggressive core drilling program. Their  initial holes in 2017-18, totaling over 14,000 feet, targeted the Cactus mine area and intersected some interesting shallow mineralization. Alderan then raised another $3 million to test additional targets in the district.

Oil and Gas Exploration and Production
When new oil and gas leases are offered or if a company is looking to acquire acreage, potential buyers need to understand the geology and resources available on these lands. Often, prospective buyers send their geologists to the UCRC to examine core and cuttings material from the lands in question to gain a better understanding of the potential investment. For example, in spring 2018, QEP Resources decided to sell their long-held acreage in the Uinta Basin. Soon after the announcement, Middle Fork Energy visited the UCRC to examine our extensive collection of cores from this area. Subsequently, in July 2018, Middle Fork announced that it had purchased QEP’s acreage for $155 million. Several times a year, companies with no current assets in Utah will visit the UCRC to examine core material; most of these companies are doing initial data gathering to determine if they want to invest in Utah resources. UGS geologists are always on hand and available to help educate company representatives on Utah’s natural resource potential.


Survey Notes, v. 51 no. 1, January 2019

Drilling of the PR-15-7c core.

Core Center News: Core Like Never Before: An Unprecedented 1600-foot Core from the Green River Formation in the Uinta Basin

Core Center News: Core Like Never Before: An Unprecedented 1600-foot Core from the Green River Formation in the Uinta Basin

By Michael D. Vanden Berg

In May 2015, the Utah Geological Survey (UGS) had a unique opportunity to team up with French oil company Total SA and the University of Utah to drill a 1600-foot continuous core from the Eocene-age Green River Formation.  Drilling 1600 feet of core is a rare treat and has provided an unprecedented window into the evolution of ancient (55- to 43-million-year-old) Lake Uinta.  Drilled on the far east side of the Uinta Basin, just over the border in Colorado, the PR-15-7c core is destined to become one of the Utah Core Research Center’s (UCRC) prized and most studied acquisitions.

For several years, the UGS-Total-University of Utah partnership has researched the evolution of Lake Uinta, from initial formation to eventual demise, to better understand how paleoclimate relates to sediment deposition in a lacustrine setting.  Also of interest is the potential for these different sedimentary layers to generate (organic-rich zones) or store (porous reservoirs) hydrocarbons.  Not only is this research important for understanding the Uinta Basin’s petroleum system (the most productive in Utah), but it is also applicable to the study of lacustrine systems around the world.

The PR-15-7c core captured nearly the entire Green River Formation.  The well was spudded in the upper Parachute Creek Member and coring began only a couple feet below the surface.  The core is missing the very top of the formation due to limitations on drilling location.  Coring proceeded through the famous Mahogany “oil shale” zone, several organic-rich and organic-lean intervals, into the Douglas Creek Member, through the Carbonate Marker unit, the Wasatch tongue, the Uteland Butte, and finally into the underlying Wasatch Formation.  After transport to the UCRC, the core was slabbed (cut length-wise) for improved viewing of the depositional features.  The next step was to describe the core inch-by-inch in fine detail, making notes on lithology, sedimentary structures, mineralogy, fossils, depositional cycles, etc.  This tedious exercise was performed by University of Utah graduate student Jennifer Morris under the direction of Dr. Lauren Birgenheier.  In addition to the description, we collected over 200 samples spaced evenly down the entire core that were analyzed for total organic carbon (TOC), elemental abundances, mineralogy, and thermal properties.  This important analytical work was performed in partnership with the U.S. Geological Survey in Denver, Colorado.

The first transgression of ancient Lake Uinta, recorded in the Uteland Butte interval at the base of the core, occurred after an extensive period of fluvial deposition (Wasatch Formation).  The Uteland Butte displays evidence that Lake Uinta, at its formation, was a freshwater lake with abundant gastropods and bivalves.  These nearshore deposits also record several shallowing-upward lake level cycles and contain evidence of full or partial exposure (preserved mud cracks and thin coal deposits).  After Uteland Butte deposition, the lake regressed, and the core captures a return to fluvial deposition, recorded in the Wasatch tongue interval.  Shortly thereafter, Lake Uinta experienced another dramatic increase in water depth termed the Long Point transgression, marked in the core by an organic-rich, gastropod-rich, limestone bed.  This transition into a larger, deeper lake continued through the entire 278-foot-thick Carbonate Marker unit, which is composed mostly of organic-rich carbonate mudstones.  Interestingly, the gastropods in the Long Point bed are the last freshwater mollusks found throughout the rest of the existence of Lake Uinta, suggesting that from this point on, the lake was moderately to strongly saline.

Starting at about 1080 feet in core depth, there is a dramatic change in lithology.  The Douglas Creek Member marks a transition to a more siliciclastic-dominated system with preserved delta channels and distal mouth bar deposits from an expanded influx of sand into the lake brought by significant river systems.  Lake level was fluctuating at this time but is thought to be relatively lower than previous intervals.  In addition, during this time microbialites start to appear, most likely growing in the off-channel lagoons of the deltas.  At about 710 feet in core depth, the lake again returned to a more carbonate-dominated system represented by the Parachute Creek Member.  This upper Green River Formation interval is well known for its alternating organic-rich (R-zones) and organic-lean (L-zones) intervals, the former prized for its “oil shale” development potential.  Overall the lake was growing in size and depth up through deposition of the Mahogany bed, within the Mahogany zone, located at 115 feet in the core.  This bed represents Lake Uinta’s highest level and largest regional extent (and is the most organic-rich), before retreating again during upper Parachute Creek time (only partially captured in this core).

For researchers interested in studying lacustrine sedimentation, Eocene hothouse climate, lacustrine-hosted hydrocarbon systems, and basic basin evolution, the PR-15-7c core is a unique and invaluable resource.  Rarely do geologists get to see a continuous section of rock from the subsurface.  Researchers at the UGS have already used this core several times for core workshops, particularly for Uinta Basin oil and gas operators, to help them understand the different intervals of the Green River Formation and how they relate to hydrocarbon production.  We are only at the very beginning of understanding everything this core has to offer.  We look forward to continued research and collaborations, and to discovering all the secrets hidden within these wonderful rocks.

If you are interested in seeing or studying the PR-15-7c core, or are interested in using the core for a workshop, please contact Michael Vanden Berg at michaelvandenberg@utah.gov or Peter Nielsen, UCRC curator, at peternielsen@utah.gov or 801-537-3359.


Survey Notes, v. 50 no. 2, May 2018

Example of Paradox Formation core from Greater Aneth field well McElmo Creek No. J-15, showing the lower producing reservoir. The environment of deposition of this sample was a reef-like buildup of algae in a shallow, warm sea.

Core Center News: UCRC Receives a Treasure Trove Donation of Greater Aneth Oil Field Cores

Core Center News: UCRC Receives a Treasure Trove Donation of Greater Aneth Oil Field Cores

by Thomas C. Chidsey, Jr.

The Utah Core Research Center (UCRC) has added to its inventory an amazing and scientifically significant collection of cores taken from wells in Utah’s largest oil field, Greater Aneth in the southeasternmost part of the state in the Four Corners area. Cores taken while drilling provide an incredible wealth of information about oil- and gas-producing rocks (reservoirs) that geologists and engineers can use to increase production, reduce risks, and find new reserves. Surprisingly, many fields have no or very few cores, due in part to the high cost of acquisition (as much as $2,500 per foot). In addition, at a time of low oil prices many oil companies are opting to permanently dispose of their cores rather than pay fees for continued storage. This was the case at Greater Aneth field but instead of being disposed, this massive collection of cores was generously donated to the UCRC by the field operator Resolute Energy Corporation of Denver, Colorado. Resolute and Peter Nielsen, UCRC Curator, worked very hard to permanently preserve the Aneth core collection and make it publicly available for study and education by other oil companies, universities, and research organizations.

The Resolute collection consists of cores from 127 wells totaling 24,318 feet—or about 4.6 miles. Prior to this donation, the UCRC had only seven cores from the northwest part of the field and a dense concentration of cores (acquired over many years since the field was discovered in 1956) in the southwest of the horseshoe-shaped field boundary, leaving vast areas of Greater Aneth with no publicly available core coverage. Now the UCRC has cores from an incredible 43 percent of the Greater Aneth wells, especially unusual for such a large field (i.e., 444 active wells). It took six semi trucks to haul the cores from a storage facility in Texas to Utah!

Besides donating the Aneth core, Resolute also provided generous funding to cover most of the shipping and logistical costs. The remaining funds to move the cores were provided by generous donations from the Utah Geological Association, the Rocky Mountain Section of the American Association of Petroleum Geologists (RMS AAPG), and the RMS AAPG Foundation. These organizations also recognized the great importance of preserving this truly remarkable collection for future generations of geologists. Besides the cores, Resolute also donated thin sections (microscope slides made from rocks), drill-hole cuttings, core analyses, core descriptions, and other important data and company reports. Peter Nielsen estimates the approximate cost in today’s dollars to obtain these cores (drill-rig time, special core-drilling equipment, core preparation, etc.), as well as the other donated materials, would be an astonishing $60 million!

Greater Aneth field has produced over 481 million barrels of oil and 437 billion cubic feet of gas from the limestone and dolomite (carbonate rocks) of the Pennsylvanian (308 million years ago) Paradox Formation. (For more details on the geology and UGS studies of Greater Aneth field see articles titled “Cores from Greater Aneth Oil Field: A Trip Back in Time to Utah’s ‘Bahama Islands’ and ‘Florida Keys,’” Survey Notes, v. 48, no. 3, p. 7–8, and “Geological Sequestration of Carbon Dioxide and Enhanced Oil Recovery—the Utah Geological Survey’s Efforts to Reduce Global Warming While Increasing Oil Production,” Survey Notes, v. 39, no. 2, p. 4–7.) Not only is Greater Aneth the largest oil field in Utah, it is the largest field that produces from carbonate rocks in the Rocky Mountain region. Over half of the world’s oil production comes from carbonate rocks. This fact makes the Greater Aneth core collection that much more important in terms of research and training, not only as it pertains to Utah’s oil resources but those throughout the globe. These cores beautifully display a wide variety of characteristics that are critical for understanding carbonate oil reservoirs—depositional environments, changes to the rocks that have occurred since deposition (diagenesis), petrophysical properties (porosity, permeability, etc.), and sea-level cycles, to name but a few. For years, the UGS has used its small set of Aneth cores for numerous industry workshops and student petroleum classes. Now we have a plethora of Aneth carbonate cores to choose from for these teaching activities. Dr. David E. Eby, a prominent carbonate-rock specialist and industry consultant based in Denver, Colorado, stated concerning the new core collection:

Acquisition of the Aneth field core collection is a magical and important addition to the teaching/research collection of the Utah Geological Survey. Academic and industry researchers will, for the first time, have access to a complete core collection from Utah’s largest oil field. This collection will surely be the basis for numerous future student research projects and teaching workshops devoted to classic Pennsylvanian and carbonate reservoirs. Congratulations UGS and Resolute Energy for making this happen!!

Already two graduate students from Brigham Young University (BYU), Provo, Utah, are using the new Aneth core collection for their Master of Science thesis projects. These students are conducting in-depth studies of the depositional environments of the upper and lower Aneth reservoirs and how they fit into various stacked packages of rocks, created over time at small and large scales. Their advisor, Dr. Scott M. Ritter, BYU Department of Geological Sciences, said,

The significance of this donation both for the students involved and for the larger geological community is the integration of data from a variety of related sources to develop a holistic understanding of this remarkable carbonate field. The core and other materials donated by Resolute could profitably occupy an entire research career. I intend to spend much of my remaining career working on Aneth field.

It is our hope that the UCRC can acquire additional sets of these incredibly important cores from other Utah oil and gas fields, especially if they are in jeopardy of heading to a landfill. To geologists, whether in the petroleum industry or a bright young university student, these cores are true “treasure troves” that may hold the keys to future oil and scientific discoveries.

To see the new Greater Aneth oil field core set or schedule a workshop at the UCRC, contact Peter Nielsen, Curator (801-537-3359, email: peternielsen@utah.gov).


Survey Notes, v. 49 no. 2, May 2017

Landsat image of southern Florida and the Bahama Islands.

Core Center News: Greater Aneth Oil Field: A Trip Back in Time to Utah’s “Bahama Islands” and “Florida Keys”

Core Center News: Cores from Greater Aneth Oil Field: A Trip Back in Time to Utah’s Bahama Islands and Florida Keys

By Thomas C. Chidsey, Jr.

Time machines—Homer Simpson made one out of a toaster and Mr. Peabody and his pet boy, Sherman, invented the “Wayback Machine.” If you were to take one of these time machines to southeastern Utah near the Four Corners area and set the dial to 308 million years ago—the middle of the Pennsylvanian Period—transporting you back in time, the region would look very different from the desert landscape of today.

Back then, southeastern Utah was covered by a warm, shallow-marine sea that at times was very salty. Shoals of ooids—rounded sand-size grains composed of concentric layers of calcium carbonate—formed in a high-wave-energy environment on the shallow, lime-mud seafloor or along the beach swash zones. Banks of broken shells, corals, and other skeletal debris also accumulated as coarse sands in the shallows. Currents removed most of the mud from these skeletal and ooid deposits, leaving open pore space between the grains.

Additionally, patches of leafy, seaweed-like algae, called Ivanovia and Kansasphyllum, built up from the sea bottom to the surface in well-circulated, moderate- to low-energy environments, and were occasionally exposed to the atmosphere. These algal buildups or “mounds” can be likened to giant piles of potato chips, each “chip” being an algal leaf or plate, and spaces between the chips being pores. These same types of deposits—ooid shoals, skeletal banks, and algal mounds—can be found today around the Bahama Islands and along the Florida Keys, no time machine required!

So what happened to these marine deposits in Utah since Pennsylvanian time? A lot! They were (1) sealed, top and bottom, by organic-rich marine muds and layers of evaporites (anhydrite and/or salt); (2) lithified (compressed and cemented into the carbonate rock limestone) and preserved as layers in southeastern Utah’s Paradox Formation; (3) buried thousands of feet below sea level and heated for millions of years, causing the contained organic material to “cook” into oil and migrate into the pores that still existed between the ooids, skeletal grains, and algal plates, where it became trapped and stored; and (4) uplifted back up thousands of feet to their current depth (from 7,000 feet below the ground to surface outcrops seen along the San Juan River Canyon).

Along the way, some of the rocks and pores within them underwent changes called diagenesis. Mineral-bearing fluids altered some limestone to a rock called dolomite (a magnesium-calcium carbonate). In other instances, pores were plugged with various minerals and tar-like “dead” oil called bitumen, whereas new pores were created by fresh water dissolving ooids, skeletal grains, and algal plates.

Why is this all so important? Sixty years ago Texaco Inc. drilled a wildcat well in southeastern San Juan County, the No. 1 Navajo C, into the porous, marine limestone rocks of the Paradox Formation and discovered Greater Aneth oil field—the largest oil field ever found in Utah. Greater Aneth has produced over 479 million barrels of oil as of January 1, 2016. The field still has 445 active wells, which produce over 11,000 barrels of oil per day, and should continue to be a major contributor to Utah’s oil production for many years to come. Dozens of similar but smaller fields have since been discovered and produce oil throughout this region of Utah referred to as the Paradox Basin.

The Utah Core Research Center (UCRC) has an incredible collection of cores taken from wells in Greater Aneth and surrounding fields that produce from the Paradox Formation, generously donated by the various oil field operators and petroleum exploration companies over the years. Once slabbed (cut in half), these cores show, up close and personal, all the various environments of deposition (ooid shoals, skeletal banks, algal mounds, etc.) that existed during Pennsylvanian time in southeastern Utah. They also show the diagenetic changes that have occurred over the millions of years since and how those events affect oil production. Additionally, the rocks in cores indicate sea level fluctuations and cyclicity, important factors in understanding differences in oil production from one well to another and identifying new drilling locations.

The characteristics of the Paradox Formation observed in the Aneth field cores provide outstanding teaching tools for geology students. Professional industry geologists also use these cores to help search for potential new oil fields in Utah or better understand how to recover more oil from existing fields. The cores are also used to help explore for similar fields elsewhere in the world, especially where cores are not available.

For example, Greater Aneth cores have been used in several major Utah Geological Survey (UGS) studies designed to increase production from other nearby fields, reduce drilling risks, and lead to new discoveries. Greater Aneth was also a focus of a major UGS field characterization project to enhance oil production from this very mature field by injecting carbon dioxide gas into the porous rocks to force remaining oil out, thus extending the life of the field (see article titled “Geological Sequestration of Carbon Dioxide and Enhanced Oil Recovery— the Utah Geological Survey’s Efforts to Reduce Global Warming While Increasing Oil Production,” 2007 Survey Notes, v. 39, no. 2, p. 4–7).

The great British geologist, Sir Charles Lyell, in his three-volume Principles of Geology, published in 1830–33, popularized one of the first concepts of modern geologic thought, “The present is the key to the past.” I would add that the Paradox Formation cores at the UCRC from Aneth and other fields are keys to understanding Utah’s geological past.

To see the Greater Aneth oil field core set or schedule a workshop at the UCRC, contact Peter Nielsen, Curator (801-537-3359, peternielsen@utah.gov).


Survey Notes, v. 48 no. 3, September 2016

Modern sand dune in Coral Pink Sand Dunes State Park, Kane County; photo by Michael Vanden Berg.

Core Center News: Cores from Central Utah’s Covenant Field – Oil-Bearing Ancient Sand Dunes

Core Center News: Cores from Central Utah’s Covenant Field – Oil-Bearing Ancient Sand Dunes

By Thomas C. Chidsey, Jr.

Great Sand Dunes in Utah’s Past

Around 200 million years ago, Utah was covered by a great “sea” of sand much like the modern Sahara. Huge sand dunes reached hundreds of feet in height. The winds were generally out of the north and northwest. Locally where the water table was high, small ponds or oases formed and were surrounded by vegetation that attracted various kinds of dinosaurs and other reptiles.

Following a 10-million-year period of erosion (or non-deposition), a shallow marine sea transgressed into central Utah from the southwest about 175 million years ago. The eastern shore was marked by tidal flats and coastal sand dunes similar to those found today along the coast of Namibia in southwestern Africa. These coastal dunes were not quite as large as the earlier desert dunes and the wind was dominantly out of the northeast.

To Rocks and Oil

Over millions of years and burial to thousands of feet, the sand grains of both wind-blown (eolian) deposits of ancient dunes were compacted and cemented together to create sandstone—the Early Jurassic Navajo Sandstone and White Throne Member of the Middle Jurassic Temple Cap Formation. The boundary between these two sets of rocks is called an unconformity indicating a significant time gap (like a book missing a chapter). Today these rocks are widely exposed in southern Utah and best observed in Zion National Park where they form the spectacular cliffs of the canyons.

However, where they remained deeply buried in other parts of Utah, the microscopic pore space between the sand grains became a reservoir for oil when certain conditions were met: (1) thick sandstone layers where sealed above by impermeable rocks like shale, (2) compressional forces folded the sandstone and sealed rocks to create a hydrocarbon trap, and (3) nearby organic-rich rocks were present and sufficiently “cooked” to have generated and expelled hydrocarbons into the pore spaces of the folded sandstone.

“The stuff that dreams are made of!”

A petroleum geologist’s job is to locate a spot where all those right conditions occurred and determine how deep to drill to strike it rich. To help, there are two ways to study the Navajo and Temple Cap reservoir rocks up-close and personal: (1) go to locations where they are exposed around the state, and (2) examine cores taken through them from producing oil wells. Such cores are publicly available at a Utah Geological Survey (UGS) facility—the Utah Core Research Center (UCRC), located in Salt Lake City, Utah.

In late 2004, Michigan based Wolverine Gas & Oil Corporation discovered Covenant oil field about 8 miles east of Richfield, Sevier County, in a region referred to as the central Utah thrust belt; the new field was productive in the eolian sandstone beds of both the Navajo and Temple Cap Formations. Since then the field has produced nearly 22 million barrels of oil; averaging 3900 barrels of oil per day. Cores, test data, and other material from the field were generously donated to the UCRC by Wolverine.

What Do Covenant Oil Field Cores Tell Us?

The cores from Covenant field provide an incredible wealth of information about the Navajo and Temple Cap depositional environments and oil reservoirs. Once slabbed (cut in half), the cores often reveal all the major parts of the ancient dunes encountered by the well—the windward dune flank and crest, and the leeward slipface (sometimes even displaying small avalanche deposits) and dune toe representing the base. The cores often show dune wind ripples and cross-bedding, and the reservoir quality (the amount of porosity and permeability [or how well-connected the pores are to each other]) varies with these features.

The cores also show interdunal environments such as playas and oases, or coastal tidal flats in the case of the Sinawava Member of the Temple Cap, represented by mudstone or limestone, which can be barriers to the flow of oil. Some intervals are highly fractured which enhances oil productivity whereas others are oil saturated giving off a distinct petroleum odor—”the smell of money!” Unconformities (depositional gaps) can be recognized in cores by the presence of scoured surfaces, gravel zones, subtle changes in mineralogy, or age-defining microfossils.

Well Logs to Cores

After a well is drilled, the operator sends down a sophisticated package of instruments in a long, skinny torpedo-like container. These instruments measure a variety of reservoir rock properties such as porosity, the conductivity of the fluids within the pores, and the natural radiation of the rocks. The resulting digital data is plotted as a series of depth-related curves, called a wireline or geophysical log, that can be used to determine if the well is a potential hydrocarbon producer and which intervals may produce. These logs are also used to correlate intervals and formations from one well to another within an oil field or regionally.

When cores are available, like those at the UCRC, the data on wireline logs can be matched directly to the actual rocks from the well. Thus one can determine how Navajo Sandstone dune or oasis environments observed in the core, for example, are represented on the log curves. These logs then become templates to identify Navajo and Temple Cap Formation depositional environments and other core-derived information for wells that have no cores—an extremely valuable tool.

Covenant Field Core Research and Workshops

The Covenant cores have been used by Wolverine, professors and students from local universities, and the UGS for research to better understand the field and explore for potential new oil resources in the central Utah thrust belt. Numerous papers based on this research have been published in scientific journals or presented at petroleum geology meetings.

The UGS offers workshops (and field trips) using these cores for industry training and university petroleum geology classes. Geology groups can examine the Navajo Sandstone cores at the UCRC and then visit the same rocks spectacularly exposed in places like the San Rafael Swell of east-central Utah or Zion National Park. During UGS workshops, petroleum geologists and students study the various rock types, environments of deposition, unconformities, and reservoir properties of the cored sections. Students are asked to make recommendations to the “company president and vice president” (i.e., the UGS instructors) as to whether the well could produce oil and from which intervals. These workshops help them prepare for the real world projects they may encounter as future petroleum geologists.

To see the Covenant oil field core set or schedule a workshop at the UCRC, contact Peter Nielsen, Curator (801-537-3359, peternielsen@utah.gov).


Survey Notes, v. 48 no. 2, May 2016

Survey Notes: Core as Teaching Tool

Core Center News: Skyline 16 Green River Formation Core – World Class Lacustrine Teaching Tool

Core Center News: Skyline 16 Green River Formation Core – World Class Lacustrine Teaching Tool

By Michael Vanden Berg

This article is the second in a series of articles planned to highlight exceptional examples of the diverse geologic cores available at the Utah Geological Survey’s (UGS) Utah Core Research Center (UCRC) (see Survey Notes, vol. 46, no. 3). As well as being used for research purposes, these cores, obtained through UGS projects and generous industry donations, are used for teaching geology students and training industry professionals, particularly those who search for oil and gas.

Utah is fortunate in that many of the same rocks captured in subsurface cores housed in the UCRC collection are exposed in canyons, mountains, and plateaus throughout the state. Thus, geology groups and researchers often head to the field to get a broader view of the same rocks they examine at the UCRC. To assist, the UGS offers core workshops and associated field trips, using cores that showcase classic examples of Utah geology to enlighten bright young minds and train the working professional. The Skyline 16 Green River Formation lacustrine (lake) core is one of the most popular training resources at the UCRC.

The beautiful high desert landscape of the Uinta Basin looked very different 50 million years ago, during the Eocene Epoch. Imagine a landscape similar to present-day Great Salt Lake, but with a much larger lake, one that at times filled the entire Uinta Basin in Utah, as well as the Piceance Basin in western Colorado. The evidence for this large Eocene lake, named Lake Uinta, as well as a similar lake in Wyoming named Lake Gosiute, is recorded in the sediments of the Green River Formation.

Utah’s much-talked-about oil shale resources, as well as significant conventional oil and gas reserves, are found within the strata that accumulated in ancient Lake Uinta. Additionally, recently discovered, massive, deep-water offshore Brazil (pre-salt) oil accumulations are interpreted to be in Lower Cretaceous lacustrine carbonates, including possible microbialites. Similar deep-water carbonate reservoirs have also been found off the west coast of Africa. To better understand these new discoveries, as well as other lacustrine oil reservoirs worldwide, geologic researchers have sought out well-known examples of lacustrine rocks, such as the Green River Formation.

In May 2010, the UGS and the University of Utah’s Institute for Clean and Secure Energy teamed up to recover 1000 feet of continuous 4-inch-diameter core from the middle to upper Green River Formation, about 60 miles southeast of Vernal in Uintah County. The core was subsequently slabbed lengthwise, taking care to provide an excellent, unobscured viewing surface. Additionally, the largerthan- typical core diameter allowed for an unusually large “slab” surface that exhibits many of the core’s excellent lacustrine features.

The lower part of the core captured lithified sediments that were deposited near the shore of the ancient lake. Lake levels fluctuated significantly at this time, creating rapid changes in rock types, or facies, preserved in the core. Similar to Great Salt Lake, the nearshore part of Lake Uinta in eastern Utah was probably very flat and broad, meaning a small change in lake water elevation would greatly affect the lake’s overall size and facies distribution. The fluctuations are recorded as roughly 3-foot, shallowing-upward cycles. Often, the part of each cycle representing the shallowest water contains beautifully preserved microbialites including stromatolites, thrombolites, and associated carbonate grains (ooids, pisoids, and oncolites). The extent and characteristics of the microbialite facies within the Green River Formation is particularly important as these rocks have some of the best petroleum reservoir qualities.

Moving stratigraphically higher in the core, the rocks record a gradual transition from nearshore, shallow water (littoral to sub-littoral) to offshore, much deeper water (profundal), and therefore a much larger lake. At a depth of about 460 feet, the core preserves the Mahogany bed. The sediments in this bed contain almost 40 percent preserved organic material, the highest found in the core. This interval of core is interpreted as preserving the lake’s highest level and largest aerial extent. This zone is also prized for containing the largest oil shale resource in the state of Utah.

Following Mahogany-zone time, the lake began to shrink, eventually retreating to a point where it became restricted and hypersaline. At this time, saline minerals began to precipitate in the lake’s bottom sediments and are now preserved in the core. This transformation is somewhat similar to how Pleistocene Lake Bonneville retreated and shrunk into present-day, hypersaline Great Salt Lake.

The Skyline 16 core provides an excellent teaching tool for researchers interested in lacustrine strata and reservoir systems. The entire range of lacustrine environments are preserved and excellently displayed in this core, from deep-lake, laminated, organic-rich oil shales, to shallow-water microbialites and associated carbonate grainstones, to fluvial, deltaic, and mouth-bar siliciclastics, to evaporite deposits. For the full lacustrine experience, UGS geologists can also arrange a trip to Great Salt Lake, which serves as an excellent modern analogue to features preserved in the core, or a trip to the world-class Green River Formation outcrops in the southeastern Uinta Basin.

To see the Skyline 16 Green River Formation core or schedule a workshop/field trip, contact Michael Vanden Berg, Petroleum Section Manager (801-538-5419, michaelvandenberg@utah.gov) or Peter Nielsen, UCRC Curator (801-537-3359,  peternielsen@utah.gov).


Survey Notes, v. 47 no. 2, May 2015

Survey Notes 46-3

Core Center News: Ferron Sandstone Cores, Excellent Teaching Tools to Spark the Imagination!

Core Center News: Ferron Sandstone Cores, Excellent Teaching Tools to Spark the Imagination!

By Thomas C. Chidsey, Jr.

An Imaginary Journey into Utah’s Geological Past

Take a drive about 70 miles south of Price through the arid Castle Valley in east-central Utah. Then imagine you are on a huge river delta with swamps and marshes of lush vegetation similar to the Mississippi Delta. Silt- and sand-laden streams and rivers meander through the area flowing east to a nearby sea that stretches east as far as Kansas. To the west lies a towering, north-south-trending mountain range (the Sevier orogenic belt)—the source for the sediments that the river system used to form the delta you are on. Dinosaurs are roaming around and reptiles fly in the sky. This is what east-central Utah looked like around 94 to 86 million years ago during the Late Cretaceous Epoch.

This ancient delta’s streams and rivers deposited their loads of sand and silt as point bars, levees, and channel fills where the rivers met the sea or along beaches, barrier islands, and in tidal inlets. Mud accumulated in bays, lagoons, and farther offshore, whereas vegetation in swamps piled up to form peat bogs. Eventually, the sea retreated and environmental conditions changed. The delta was buried by over 8000 feet of sedimentary rocks. Then regional uplift began about 70 million years ago exposing these rocks to the forces of erosion.

The Ferron Sandstone— Analog for River-Dominated Deltaic Oil and Gas Reservoirs Worldwide

Rapid erosion of the Colorado Plateau by the Colorado River and its tributaries over the last 5 million years and continued uplift have, once again, revealed the ancient river delta, which is now beautifully displayed along the west flank of the San Rafael Swell in the rocks known as the Ferron Sandstone—one of the most extensively studied cliffy exposures of rock in Utah. Why is the Ferron so important to geologists? It shows, spectacularly, vertical and lateral changes (the exposed rock belt extends northeast-southwest for over 80 miles) in the deltaic deposits, which serve as a visual analog for similar rocks that produce nearly half the world’s oil and gas hidden deep below the surface. Examples are found in the U.S. Gulf Coast, Alaska, North Sea, and Utah’s own Uinta Basin fields.

The earliest Ferron Sandstone study goes back to 1874, to investigate coal resources in the area. Well over one hundred years and many studies later, the UGS conducted its own major investigation of the Ferron in the 1990s. The project involved two oil companies, three local universities (professors and students from the University of Utah, Brigham Young University, and Utah State University), and several consulting geologists. The goals of the project were to provide petroleum companies better tools and models to apply to their own oil and gas fields, as well as exploration efforts, using the Ferron rock exposures as examples.

A major question, however, was what did the Ferron look like in the subsurface beyond the outcrop cliff face—a critical factor in predicting changes in the rocks in three dimensions. To answer that question, the UGS drilled four core holes and acquired, through donation, five more rock cores collected from shallow wells immediately west of the outcrop belt. These rock cores proved invaluable to the study, which resulted in over fifteen scientific publications.

UGS Ferron Core Workshops for Students and Industry Professionals

The UGS collection of Ferron Sandstone cores stored at the UCRC continues to be invaluable as training materials for students and industry professionals. After the cores were drilled, they were slabbed (cut in half) to remarkably reveal the various rock types and depositional environments seen in the Ferron outcrops—sandstone beds, representing river channels, sand bars, and beaches; siltstone and shale containing shells and burrows of marine and brackish water organisms that lived offshore or in bays; and coalbeds that formed from vegetation in swamps and peat bogs.

The cores also show rock boundaries indicating times with major changes in sea level, critical information when developing oil and gas fields or exploring for new ones. The cores also provide information about oil and gas reservoir quality (pores in the rocks capable of storing hydrocarbons and permeability— the connection between those pores that permits fluids to flow within the rock to a wellbore). Such descriptive reservoir characteristics can be applied to oil and gas exploration and development of similar ancient delta deposits throughout the world.

The UGS annually hosts or conducts numerous workshops (and companion field trips) using the Ferron cores for educational and industry training. Local universities regularly bring their geology students to the UCRC for Ferron core classes. Attendees of UGS-sponsored and industry training groups have come from all over the U.S., as well as Great Britain, Norway, Ireland, France, Argentina, China, and Indonesia, and researchers continue to use the Ferron cores for new studies.

Someone once said, “Oil is not found in the ground, it is found in the minds of geologists!” Geologists, both students and professionals, use their minds to better understand the geologic past and imagine where to find oil and gas, employing tools such as the UGS core set and rock exposures of the Ferron Sandstone.

To see the Ferron Sandstone core set or schedule a workshop at the UCRC, contact Peter Nielsen, Curator. Phone: 801-537-3359 • Email: peternielsen@utah.gov


Survey Notes, v. 46 no. 3, September 2014