Raymond’s Folly — The Codell Play of the Denver Basin

By: RAYMOND PIERSON  |  Certified Petroleum Geologist

The present day Cretaceous Codell oil and gas development in the central portion of the Denver Basin Colorado USA is the result of the successful geological work conducted by Raymond M. Pierson in the early 1980’s.

Raymond’s Early Studies:

As a student at the University of Northern Colorado (UNC) during 1978-80, Raymond was looking at outcrops of the lower Cretaceous along the foothills east of Loveland Colorado. It was there he came across the Fort Hays Limestone and a series of silty sandstones and shales at the base. The sandstone at the base of a deep marine cold-water limestone indicated an unconformity, which was what motivated him to collect a sample. While collecting a sample of the sandstone, he smelled the occurrence of hydrocarbons. From that he knew the rock was the Codell sandstone.

Raymond started correlating from outcrop to the subsurface and across the Loveland field into the deeper portions of the basin in the heart of the Wattenberg field. He used resistivity and density logs from previously drilled wells. The wellbore signature of the Codell in open-hole logs indicated a high gamma-ray, high density porosity and low neutron porosity. When the two are combined they yield the conventional gas-effect cross-over. The resistivity was low and was similar to the Carlile shale below. Also noted was the caliper log. It seemed to indicate a wash-out.

Raymond asked a petrophysicists about this. He was informed the high porosity was probably due to the washout plus the density tool not reading correctly. Initial mapping of the gross Codell thickness indicated it covered many townships and extended throughout the Wattenberg field area and beyond.

It was later determined that the wash out was caused by the differential pressures between the reservoir and the hydrostatic mud column. The reservoir was highly over pressured at 4500 psi while the mud column, at reservoir depth, was near 3200 psi. The differential pressure in favor of the reservoir at 1300 psi caused the Codell, in a highly microfractured state, to disintegrate. Had the permeability been greater, the wells would have blown out. The “J” sandstone at depth had an initial reservoir pressure of about 2750 psi.

After Graduating, Raymond Continued to Investigate:

After graduating from UNC, Raymond went to work for Cities Service Company in Denver and was permitted to continue working on the Codell investigation. Continued correlation indicated the Codell pinched out, going updip and east from the Basin axis at the Codell horizon, which more or less parallels highway 85 going north from Brighton to Greely Colorado. This data indicated a stratigraphic pinch out type trap in the updip direction. The perfect setting for creating a big field. Further correlation to the west indicated a more-or-less full section of the eroded section existing all the way to outcrop along the Front Range.

City Service Needs a Core:

Conventional log analysis indicated the Codell was more-or-less a hundred percent water saturated. To understand the rock, Cities Service needed a core. But the company was not active in the Denver Basin. Thus, to obtain a core for analysis, an independent named Centennial Petroleum was contracted. Cities offered to cover all costs associated with rig time and vendors if Centennial would agree to stop their drilling operations and core the Codell at a depth determined by Cities Service. Centennial agreed and a whole core of the Codell sandstone was obtained from their Futhey #2 well in Boulder County Colorado.

Bob Colby Initiates Further Studies:

In July 1981, the core was sent to the Cities Service Research laboratories in Tulsa Oklahoma and then on to Core Labs. Meanwhile, Centennial drilled their Futhey #1 well to the targeted “J sandstone for completion. One of the requested studies on the Codell core was initiated by Bob Colby, the petrophysicist working with Raymond on the project. He wanted the true A (tortuosity factor,​ ​related to the length of the electrical path through the rock), M (cementation exponent)​, and N (saturation exponent)​ ​for the formation resistivity factor at various brine saturates, as well as core porosity and permeability.

With these parameters, Bob felt that log analysis would be more descriptive than just using an Archie’s type water saturation calculation. When Bob began his log analysis on the Codell he asked Raymond what the file name should be for storage. Raymond left that up to Bob who jokingly named the file “Raymond’s Folly”.

Centennial Requests the Core Results:

A few months passed and Centennial petroleum called Raymond and expressed interest in the core results. Centennial’s Futhey #1 “J” sandstone well had experienced mechanical completion difficulties resulting in tubing and a packer being stuck in the hole. If there was potential in the Codell, then Centennial wanted to attempt a completion rather than junking and abandoning the well. The core results had arrived a few weeks prior to Centennial’s call. The results included some surprises. Bob Colby had already begun using the new A, M, and N values to recompute the water saturation calculations from selected logs across the basin.

The core results included the following:

  • The core of the Codell sandstone was ninety percent quartz, fine grained silt and sand, and heavily bioturbated.
  • Clays appeared to be dominantly montmorillonite, illite, smectite and chlorite.

3) The clay minerals, bioturbated into and mixed with the terrigenous grains, had reduced the permeability to less than 0.01 millidarcies, a level almost too low to measure.

4) The individual quartz grains were observed to contain ‘anastomizing fractures’ which is what results when you drop a heated glass marble into cold water. The marble fractures but does not fall apart. Some tectonic event combined with frictional heat was the suggested cause. Such an event would generate enough heat and stress to cause the anastomizing fractures.

5) The A, M and N values at various saturates from the core were determined to vary. The sample saturated with the lower salinity brine exhibited a lower formation factor than the sample saturated with a higher salinity brine. Hence, it was concluded that fresh-water drilling fluids affected the true resistivity observed in open hole well logs. This impact was attributed to the “conductive solids” and the Cation Exchange Capacity of the rock matrix.

6) In addition, hydrocarbons were present in the Codell core.

Log analysis confirmed the density-neutron gas effect cross-over was real.

Bob Colby and Raymond Pierson Study the Results:

Bob Colby and Raymond Pierson accessed hundreds of “J” sandstone well logs covering the Wattenberg field. At first, Bob used a formation factor of 1.00 / ø^ 1.40 and an Rw of 0.11, but a more accurate formation factor was later determined. The water saturation calculations yielded values of less than twenty percent, field wide. In addition, Bob used the available Sonic logs to calculate Q, or clay content, and found the percent of clay was almost the same value as the water saturation. Therefore, he concluded if water existed, it was bound in the clay minerals and would never be produced. It was concluded that the net pay covered an area no less than six (6) townships wide and eight (8) townships long, roughly equal to 1728 square miles. What was not known was the productivity potential of the Codell.

Futhey #1 Worth Completion:

Based on the core results of the Futhey #2 and the new log analysis, it was recommended to Centennial Petroleum that the Futhey #1 Codell was worth a completion attempt to prevent junking and abandoning the well. The Futhey #1 is located in the NE SE Section 26, Township 1N, Range 69 West, Boulder County, Colorado, and was completed in the Codell interval. After frac treatment, the well tested 262 BBLS of 52° gravity condensate and 1.3MMCFGPD on May 27, 1981. At about the same time, Martin Exploration Management Corporation completed its #1 Ertl, located in the SE NW Section 17, T1N-R69W by commingling the “J” and Codell sandstones. It reported an initial production of 250 BBLS condensate and 1.6MMCFGPD.

It is not known how much oil and gas came from which zones, but these two wells started the development of the Codell. Amoco Production Company’s first Codell completion was a recompletion of an uneconomical “Muddy J”. The well was the Frank Boulter #1, located in the SW ¼ Section 14, T1N-R66W. On December 16, 1981 during a 24 hour test, the well flowed 102 BOPD and 1.05 MMCFGPD. Amoco, with their large acreage position, was in an excellent position to develop the Codell, but never did.

Mapping the Wattenberg Codell:

Raymond later began consulting and putting together an extensive mapping project of the Wattenberg Codell. He contacted Champlin Petroleum Company and requested a farmout of acreage in the Wattenberg field. Champlin, at the time, was under the understanding that all the acreage was held for production by Amoco and or Champlin due to the existing “J” gas wells on 320-acre spacing.

Raymond had read the original farmout agreement between Champlin and Amoco and pointed out to Champlin that the company had retained all the NE quarter sections for itself and committed only the “J” sandstone rights to a 320 acre spaced unit, leaving all other mineral rights to Champlin. Raymond requested a farmout of the Codell-Niobrara minerals in every NE quarter section of every odd-numbered section in the Wattenberg field on the UPRR right-of-way.

Basin Exploration Enters the Picture:

In early 1985, Raymond contacted Basin Exploration Incorporated, a company in Fort Collins, Colorado, and brought to them the basic farmout proposal. Basin met with Champlin and a farmout proposal was drafted in March, 1985. Basin agreed to drill 20 drill-to-earn wells and have a continual drill-to-earn right on the approximately 7,000 net mineral acres in the Wattenberg field. Raymond became the Vice President of Exploration and Production for Basin Exploration.

The Codell Play:

Since that time, thousands of Codell-Niobrara wells have been drilled in the Denver Basin. It is still undergoing heavy development to this very day. In an article that appeared in the business section of the Rocky Mountain News, on Sunday, July 4, 1982, Raymond was quoted saying “I predict that the Codell

will be the largest continuing producing reservoir in the Rocky Mountains.” He was right. Thousands of wells have been drilled in the Codell play, which is now thirty-five (35) years old. Thousands more are scheduled to be drilled. From its beginning, over thirty-six years ago, the Codell was considered a non-typical reservoir, and it has lived up to that expectation.

Map of well density in the Greater Wattenberg area.

Conclusion:

Thus, what began as a study of “Overlooked Oil and Gas in the Loveland Area” at the University of Northern Colorado, Greeley Colorado, in 1978-80, became the Codell play that has endured until this very day. The initial geological interpretation may have seemed bold. But, over time, it has measured up to all the predictions, even though at first it was called “Raymond’s Folly.”

2018 – Colorado produced a total of 177.8 Million Barrels of Oil.

Weld County produced a total of 158.1 Million Barrels of Oil.

Colorado produced a total of 1.87 Trillion Cubic Feet of gas.

Weld County Produced a total of .81 Trillion Cubic Feet of gas.

Therefore Weld County produced 88.9% of all the oil and 43% of all the gas in the State of Colorado. Weld County has over 25,000 wells.

BIO: RAYMOND PIERSON is a Certified Petroleum Geologist through the Department of Professional Affairs of the AAPG (American Association of Petroleum Geologists.)

After serving in the United States Navy in the Gulf of Tonkin during the Vietnam War, he returned to work for Amoco Production Company in the San Juan Basin of New Mexico during the early 1970’s. He graduated from the University of Northern Colorado in Greeley Colorado with a BA in Earth Sciences – Geology in 1980. For the thirty six (36) years since, he worked directly for or consulted to companies such as Cities Service Company, Rocky Mountain Production Company, Basin Exploration Inc., Shell Western Exploration and Production Inc., Aera Energy LLC, El Paso Corporation, and finally Kinder Morgan. He retired in 2013 with a desire to consult and stay active in petroleum geology and relocated to Windsor Colorado. He was the Keynote Speaker at the University of Northern Colorado Spring 2017 Undergraduate Commencement. He is an active partner with Devoy Energy Partners LLC.

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