Search and Discovery Article #80341 (2013)** Posted November 25, 2013

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1 Niobrara Source Rock Maturity in the Denver Basin: A Study of Differential Heating and Tectonics on Petroleum Prospectivity Using Programmed Pyrolysis* David J. Thul 1,2 and Steve Sonnenberg 2 Search and Discovery Article #80341 (2013)** Posted November 25, 2013 *Adapted from oral presentation at AAPG Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013 **AAPG 2013 Serial rights given by author. For all other rights contact author directly. 1,2 PetroLuminary, LLC, Denver, CO (dthul@petroluminary.com) 2 Colorado School of Mines, Golden, CO (ssonnenb@mines.edu) Abstract The Niobrara Formation of the Denver Basin is an unconventional oil and gas drilling target composed of alternating chalk and marl units. These units act as the source, seal and trap for hydrocarbons generated in the total organic-carbon-rich marl beds of the Niobrara. Organic geochemical data, such as oil-to-source rock correlations, oil biomarkers and gas isotopes, indicate that the fluids accumulated within the reservoirs closely match the source rocks in type and maturity; therefore, this is a system of in-situ generation and accumulation as well as low migration. In a system where migration is minimal, proximity to an effective source rock is a prerequisite for a productive well. With such a prerequisite, play delineation should begin with regional source-rock maturity assessment. Historically, source-rock maturity has been studied through programmed pyrolysis (such as Rock-Eval ), vitrinite reflectance, log interpretation or basin modeling. Recently, a new pyrolysis instrument (the Source Rock Analyzer ) has come to market. With this new addition, questions of data congruence have arisen between the Rock-Eval and the Source Rock Analyser that preclude combining data sets without further study. This work establishes the veracity of the data from the Source Rock Analyzer and compares its results to those of a Rock-Eval instrument, using a suite of 103 source rock samples. The test of data veracity shows that the S2 and Tmax parameters from the Source Rock Analyzer are comparable to those from the Rock- Eval, showing good correlation and a nearly one-to-one relationship. The other parameters, S1 and S3 show similar trends but there is significant scatter in the data. The calculated parameters (hydrogen index, oxygen index, production index, and total organic carbon) are correlative but deviate significantly from a one-to-one relationship.

2 Using the newly understood relationship between SRA and Rock-Eval pyrolysis, regional assessment of the Niobrara shows that the onset of hydrocarbon maturity in the Niobrara is 432 degrees C Tmax and that hydrocarbon expulsion occurs between 438 degrees C and 443 degrees C Tmax. The study also shows that Niobrara production can be predicted by mapping the thermal maturity stages as well as free hydrocarbon anomalies within the basin. References Cited Higley, D.K., 1988, Core porosity, permeability, and vitrinite reflectance data from the Lower Cretaceous J sandstone in 141 Denver Basin coreholes : U.S. Geological Survey Open-File Report , 6 p. Landon, S.M., M.W. Longman, and B.A. Luneau, 2001, Hydrocarbon source rock potential of the Upper Cretaceous Niobrara Formation, Western Interior Seaway of the Rocky Mountain region : The Mountain Geologist, v. 38/1, p Longman, M.W., B.A. Luneau, and S.M. Landon, 1998, Nature and distribution of Niobrara lithologies in the Cretaceous Western Interior Seaway of the Rocky Mountain region: The Mountain Geologist, v. 35/4, p Momper, J.A., 1980, Oil expulsion; a consequence of oil generation: Bulletin of the South Texas Geological Society, v. 20/5, p Rice, D.D., 1984, Relation of hydrocarbon occurrence to thermal maturity of organic matter in the Upper Cretaceous Niobrara Formation, Eastern Denver Basin--Evidence of biogenic versus thermogenic origin of hydrocarbons, in J. Woodward, F.F. Meissner, and J.L. Clayton, (eds.), Hydrocarbon source rocks of the Greater Rocky Mountain area: Rocky Mountain Association of Geologists Guidebook, p Tainter, P.A., 1982, Investigation of stratigraphic and paleostructural controls on hydrocarbon migration and entrapment in Cretaceous D and J sandstone of the Denver basin: Boulder, Colorado, University of Colorado, M.S. Thesis, 235 p.

3 Niobrara Source Rock Maturity in the Denver Basin: A Study of Differential Heating and Tectonics on Petroleum Prospectivity Using Programmed Pyrolysis David J. Thul 1,2 Steve Sonnenberg, PhD 2 1 PetroLuminary, LLC 2 Colorado School of Mines

4 Outline Niobrara Fm. in the Denver Basin Previous Maturity Studies Rice, 1984 Higley, 1988 Landon, 2001 Understanding the COMB Trend New Analytical Results Burial History Modeling Results Niobrara Regional Interpretation Conclusions

5 Niobrara Fm.

6 Motivation-Niobrara Maturity Outside of COMB, Maturity approx. linear with depth New Cuttings Pyrolysis Historical Cuttings Pyrolysis (Avg) Outside of COMB Pyrolysis (Avg) NE Weld County, Moderate T-Grad. COMB Trend Near Wattenberg, High T-Grad El Paso, N. Laramie, S. Goshen Counties, Low T-Grad

7 Study Area Converse Dawes Albany Platte Wyoming Goshen Sioux Scotts Bluff Banner Sheridan Box Butte Morrill Garden Nebraska Cherry Grant Hooker Arthur Laramie Kimball Deuel Keith Sedgwick Perkins Logan Jackson Larimer Weld Phillips Chase Hayes Morgan Dundy Grand Boulder Broomfield Gilpin Denver Clear Creek Summit Jefferson Adams Arapahoe Washington Yuma Park Douglas Elbert Colorado Kit Carson Sherman Chaffee Teller El Paso Wallace Logan Kansas Saguache Alamosa Fremont Custer Costilla Huerfano Pueblo Crowley Miles Otero Comb_Axis Bent Study Area Kiowa Prowers COGCC Wattenberg Field Greeley Wichita Hamilton Kearny COGCC Fields (Niobrara Stanton Grant Las Animas Baca Production)

8 Basement Structure Converse Dawes Albany Platte Wyoming Goshen Sioux Scotts Bluff Banner Sheridan Box Butte Morrill Garden Nebraska Cherry Grant Hooker Arthur Laramie Kimball Deuel Keith Sedgwick Perkins Logan Jackson Larimer Weld Phillips Chase Hayes Grand Boulder Broomfield Gilpin Denver Clear Creek Summit Jefferson Park Teller Chaffee Douglas Morgan Washington Adams Arapahoe Elbert El Paso Colorado Yuma Kit Carson Dundy Sherman Wallace Logan Kansas Saguache Alamosa Fremont Custer Costilla Huerfano Pueblo Crowley Otero Las Animas Miles Greeley Wichita Kiowa Hamilton Kearny Bent Prowers Basement Structure Study Area Baca Stanton Grant

9 Previous Maturity Studies

10 Area of Mature Source Rock Converse Dawes Albany Platte Wyoming Goshen Sioux Scotts Bluff Banner Sheridan Box Butte Morrill Garden Nebraska Cherry Grant Hooker Arthur Laramie Kimball Deuel Keith Sedgwick Perkins Logan Jackson Larimer Weld Phillips Chase Hayes Morgan Dundy Grand Boulder Broomfield Gilpin Denver Clear Creek Summit Jefferson Adams Arapahoe Washington Yuma Park Douglas Elbert Colorado Kit Carson Sherman Chaffee Teller El Paso Wallace Logan Kansas Saguache Alamosa Fremont Custer Costilla Huerfano Pueblo Crowley Otero Las Animas Miles Greeley Wichita Kiowa Hamilton Kearny Bent Prowers Rice, 1984 Niobrara Maturity Extent Comb_Axis Study Area Stanton Grant Baca Rice, 1984

11 R o of the Dakota Fm. Converse Albany Jackson Park Platte Wyoming Larimer 0.82 Weld El Paso Pueblo Goshen Sioux Elbert 1.05 Colorado Otero 0.32 Logan Morrill Morgan Grand Boulder Washington Broomfield Gilpin Adams Denver Clear Creek 0.9 Arapahoe Summit Jefferson Chaffee Saguache Alamosa Fremont Custer Costilla Teller Douglas Huerfano Scotts Bluff 0.5 Banner Laramie Kimball Crowley Las Animas Miles Dawes Box Butte Nebraska Bent Sheridan Garden Deuel Sedgwick Yuma Kit Carson Cherry Keith Phillips Avg. Reflectance Chase(%) Hayes Kansas Greeley Wichita Kiowa Ro Contours 0.8 Prowers 1.0 Baca Grant Arthur Perkins Dundy Sherman Hooker Higley, 1988 Vitrinite Wallace Logan Comb_Axis Hamilton Kearny Study Area Stanton Grant Higley, 1988

12 Tmax of the Niobrara Fm. Converse 440 Dawes Albany Platte Wyoming Goshen Sioux Scotts Bluff Banner Sheridan Box Butte Morrill Garden Nebraska Cherry Grant Hooker Arthur Laramie Kimball Deuel Keith Sedgwick Perkins 440 Logan Jackson Larimer Weld Phillips Chase Hayes 420 Morgan Dundy Grand Boulder Broomfield Gilpin Denver Clear Creek Summit Jefferson Adams Arapahoe Washington 410 Yuma Park Chaffee Saguache Alamosa Fremont Custer Costilla Teller Douglas Huerfano 430 El Paso Pueblo Elbert Colorado Crowley Otero Las Animas Miles Bent Kit Carson Kiowa Prowers Baca Sherman Wallace Landon et al., 2001 Tmax Contours Tmax (degrees C) Kansas Greeley Wichita Hamilton Kearny Stanton Logan Landon et al., 2001 Control Pts. Comb_Axis Study Area Grant Landon et al., 2001

13 Data Gap as of 2010 Converse Albany Platte Wyoming Goshen Sioux Scotts Bluff Banner Dawes Sheridan Box Butte Morrill Garden Nebraska Cherry Grant Hooker Arthur Laramie Kimball Deuel Keith Sedgwick Perkins Logan Jackson Larimer Weld Phillips Chase Hayes Morgan Dundy Grand Boulder Broomfield Gilpin Denver Clear Creek Summit Jefferson Adams Arapahoe Washington Yuma Park Douglas Elbert Colorado Kit Carson Sherman Chaffee Teller El Paso Wallace Logan Kansas Saguache Alamosa Fremont Custer Costilla Huerfano Pueblo Crowley Otero Las Animas Miles Greeley Wichita Kiowa Niobrara Rock Core Ro Niobrara Rock Cuttings Ro Hamilton Kearny Bent Prowers Niobrara Rock Core Pyrolysis Niobrara Rock Cuttings Pyrolysis Study Area Stanton Grant Baca

14 Understanding the COMB Trend & Niobrara Maturity 70 cuttings analyses 22 locations

15 COMB Trend & Niobrara Maturity New analyses were taken along the ft structure contour (purple diamonds) as well as long the NE-SW COMB Trend (pink diamonds) Converse Dawes Albany Larimer Jackson Grand Boulder Park Teller Chaffee Platte Goshen Wyoming Broomfield Gilpin Denver Clear Creek Summit Jefferson Douglas Banner Laramie Kimball Weld Morgan Adams Arapahoe Elbert Sioux Box Butte Sheridan Scotts Bluff Morrill Garden Colorado Nebraska Deuel Sedgwick Logan Phillips Washington Yuma Kit Carson El Paso 2000 Cherry Grant Hooker Arthur Keith Perkins Chase Hayes Dundy Sherman Wallace Logan Kansas Saguache Alamosa Fremont Custer Costilla Huerfano Pueblo Crowley Otero Las Animas Miles Greeley Wichita Kiowa ft. Structure Samples COMB Trend Samples Hamilton Kearny Bent Prowers Comb_Axis Study Area Top Niobrara Structure Stanton Grant Baca

16 COMB Trend & Niobrara Maturity Along the S-N transect source rock maturity increases through the COMB Trend Along the NE-SW transect shallow samples in the NE have similar maturities to those deeper in the basin

17 COMB Trend & Niobrara Maturity Onset Phase of Oil Generation Inferred COMB Boundaries There is a clear increase in maturity within the COMB boundaries

18 Burial History Modeling R o Modeled : 0.7 E R o : 0.6 Tert. Removal: 1800 ft. Removal Needed: 800 ft. Converse Albany 2000 Platte Wyoming Goshen Sioux Scotts Bluff Banner Dawes Sheridan Box Butte Morrill Garden 2000 Nebraska Cherry Grant Hooker Arthur R o Modeled : 0.63 E R o : 0.76 Tert. Removal: 2200 ft. Removal Needed: 4200 ft. R o Modeled : 0.74 E R o : 0.93 Tert. Removal: 3270 ft. Removal Needed: 5200 ft. Larimer Jackson Grand Boulder Broomfield Gilpin Denver Clear Creek Summit Jefferson Park Teller Chaffee Laramie ^_ ^_ Weld Douglas 2000 ^_ ^_ 4 ^_ 5 Adams Arapahoe Elbert Kimball Morgan Colorado Deuel Sedgwick Logan Phillips Washington Yuma Kit Carson El Paso Keith Perkins Chase Hayes Dundy Sherman Wallace Logan Kansas R o Modeled : 0.63 E R o : 0.59 Tert. Removal: 2360 ft. Removal Needed: 1500 ft. R o Modeled : 0.76 E R o : 1.3 Tert. Removal: 3210 ft. Removal Needed: 7300 ft. Saguache Alamosa Fremont Custer Costilla Huerfano Pueblo Crowley Otero Las Animas Miles Bent Greeley Wichita Kiowa ^_ Burial History Locations Hamilton Kearny Prowers Comb_Axis Top Niobrara Structure Study Area Stanton Grant Baca

19 Niobrara Regional Interpretation 1360 pyrolysis analyses 1370 TOC analyses 220 well locations

20 Niobrara Regional Interpretation The maturation pathway for the Niobrara source rocks is defined by the decreasing HI with increasing Tmax Hydrocarbon generation appears to begin between Tmax values of 430 C and 435 C

21 Niobrara Regional Interpretation The free petroleum and normalized oil content show a sharp increase at a Tmax of 432 C & plateau at Tmax of 438 C. Interpreted as onset of petroleum generation & petroleum expulsion.

22 Niobrara Regional Interpretation To eliminate analytical noise in HI (and Transformation Ratio) it is useful to model TR based on Tmax using a sigmoidal function.

23 Niobrara Regional Interpretation From the modeled values, the onset of petroleum generation is 432 C Tmax (TR 0.1) and expulsion occurs at 438 C Tmax (TR 0.25) which agrees with the volumetric-based analysis of Momper, 1980

24 From Crossplots to Maps Onset of HC generation: 432 C First HC expulsion event: 438 C

25 Niobrara Regional Interpretation Using the data and model of HC generation and expulsion, regions of each maturity are delineated. Expulsion maturity occurs in the greater Wattenberg area as well as Adams, Arapahoe, Elbert and Douglas counties. Onset maturity occurs in NE & NW Weld county as well as parts of Wyoming and Nebraska.

26 Niobrara Regional Interpretation Free hydrocarbon anomalies are present in NE Weld County, SE Wyoming and in the western reaches of the basin. The Greater Wattenberg Area, notably, shows no free hydrocarbon anomaly.

27 Niobrara Regional Interpretation Prospect Ranking Definitions Priority Level (Favorability) Maturity S1 1 Expulsion (Tmax > 438) Elevated 2 Expulsion (Tmax > 438) Not elevated 3 Onset ( 432 < Tmax > 438) Elevated 4 Onset ( 432 < Tmax > 438) Not elevated 5 Immature (tmax < 432) Elevated

28 Niobrara Regional Interpretation The highest priority targets are located along the COMB trend with lower priority targets flanking that zone and dispersed throughout the basin.

29 Niobrara Regional Interpretation The highest level prospects are, in all cases associated with higher geothermal gradients. Converse Albany Platte Goshen Wyoming Laramie Sioux Scotts Bluff Banner Kimball Dawes Sheridan Box Butte Morrill Garden Nebraska Deuel Sedgwick Cherry Grant Hooker Arthur Keith Perkins Logan Jackson Larimer Weld Phillips Chase Hayes Grand Clear Creek Summit Park Chaffee Saguache Alamosa Gilpin Boulder Fremont Custer Costilla Broomfield Jefferson Teller Denver Douglas Huerfano El Paso Pueblo Adams Arapahoe Elbert Morgan Colorado Crowley Otero Las Animas Miles Washington Bent Kiowa Yuma Target Type Sherman Kit Carson S1 Only Good Tmax Prowers Dundy Marginal Tmax Marginal Tmax Wallace +S1Logan Kansas Good Tmax +S1 Tempertaure Gradient Degrees F/100 Ft. High : 2.04 Low : 1.12 Comb_Axis Greeley Wichita Hamilton Kearny Study AreaStanton Grant Baca

30 Niobrara Regional Interpretation Most of the established production is inside the two highest exploration target categories. Converse Albany Platte Goshen Wyoming Laramie Sioux Scotts Bluff Banner Kimball Dawes Sheridan Box Butte Morrill Garden Nebraska Deuel Sedgwick Cherry Grant Hooker Arthur Keith Perkins The notable exception is Silo Field which may be due to its favorable structural history. Jackson Grand Park Larimer Clear Creek Summit Chaffee Saguache Alamosa Gilpin Boulder Fremont Custer Costilla Broomfield Jefferson Teller Denver Douglas Huerfano Weld El Paso Pueblo Adams Arapahoe Elbert Morgan Colorado Crowley Otero Las Animas Miles Logan Washington Bent Kiowa Phillips Yuma Kit Carson Kansas Good Tmax +S1 Hamilton Kearny Prowers Niobrara Oil Wells Baca Chase Dundy Sherman Hayes Wallace Logan Target Type S1 Only Marginal Greeley Tmax Wichita Marginal Tmax +S1 Good Tmax Comb_Axis Study Area Stanton Grant

31 Summary Increased heat, not burial history, best explains increased source-rock maturity along the COMB Trend Areas of varying prospectivity can be identified using regional interpretation of pyrolysis datasets. Using a stacked polygon method (a la Tainter, 1982) creates exploration fairways that encircle existing production. Several other areas in the basin appear prospective using this method but more data is needed.