Lithologic and Petrophysical Characterization of the Upper Silurian Interlake Group, Nesson Anticline Area, North Dakota and Eastern Montana

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1 AAPG 2018 ACE101:Bridging Fundamentals and Innovation Theme 2: Carbonates of Western North America Salt Lake City, UT May 20-23, 2018 Lithologic and Petrophysical Characterization of the Upper Silurian Interlake Group, Nesson Anticline Area, North Dakota and Eastern Montana Richard Inden 1, Alan P. Byrnes 2, late Robert Cluff 3, Suzanne Cluff 3 1-LSSI, Ltd.; 2- Whiting Petroleum Corp.; 3 The Discovery Group Denver, Colorado USA

2 Forward-Looking Statements This presentation includes forward-looking statements that Whiting Petroleum Corporation (the Company ) believes to be forward-looking statements within the meaning of the Private Securities Litigation Reform Act of All statements other than statements of historical fact included in this presentation are forward-looking statements. These forward looking statements are subject to risks, uncertainties, assumptions and other factors, many of which are beyond the control of the Company. Important factors that could cause actual results to differ materially from those expressed or implied by the forward-looking statements include the Company s business strategy, financial strategy, oil and natural gas prices, production, reserves and resources, impacts from the global recession and tight credit markets, the impacts of state and federal laws, the impacts of hedging on our results of operations, level of success in exploitation, exploration, development and production activities, uncertainty regarding the Company s future operating results and plans, objectives, expectations and intentions and other factors described in the Company s Annual Report on Form 10-K for the year ended December 31, Whiting s production forecasts and expectations for future periods are dependent upon many assumptions, including estimates of production decline rates from existing wells and the undertaking and outcome of future drilling activity, which may be affected by significant commodity price declines or drilling cost increases.

3 Acknowledgements When this work was done Robert Cluff was with us and he was a principal investigator in this study. We miss him. Described & sampled 8000 ft from 85 cores North Dakota Geological Survey. Former Shell Oil Company core facility. USGS Core facility in Denver, Colorado.

4 General Outline 1. Stratigraphy & Depositional Setting 2. Type depositional cycles 3. Lithofacies properties 4. Reservoir/Nonreservoir key comparisons 5. Wireline analysis challenges 6. Well performance & bypassed pay question 7. Conclusions

5 Williston Basin and Silurian Interlake Interval Interval Thick Upper Interlake Lower Interlake Salsbury Putnam Stonewall-Gunton Stoney Moutain Sh Study Area Vertical well EUR (BO) Nesson Anticline Subsea Structure Contour Top Red River

6 Ashern GR-CAL marker Upper Interlake Lower Interlake Upper Interlake Cycles Lower Interlake Cycles Cycle Distribution Highfrequency 3-50 thick cycles Putnam Salsbury Stonewall Gunton Stoney Mtn Sh Red River Salsbury Stonewall Gunton Cycles

7 Depositional Setting & Lithofacies (from Blakey, intracratonic basin Upper Interlake Arid Lower Interlake Temperate Stoney Mt. Arid Putnam Upper < GR GR > Reservoir Lithofacies Supratidal Intertidal Subtidal High Subtidal Restricted Normal Marine Marine brecciated dol mudstn - fenestral algal bndstn - bedded blackened algal boundstone fenestral - blackened bedded - lithoclastic blackened caliche - algal boundstones intraclast packstone laminated algal boundstone bedded - laminated pellet packstone bedded pellet packstone bedded, laminated fossil- pellet packstone nodular coral bedded mudwackestone packstone, reef stromatoporoid boundstone nodular bedded, borrowed, bioturbated crinoid mudwackestone nodular bedded, borrowed, bioturbated crinoid mudwackestone Non-Reservoir Lithofacies mudtones/wackestone & cemented reservoir lithofacies

8 Modern Analog Andros Island Perry Roehl AAPG 1967 west Andros Island Aerial view tidal flats tidal flats rooted/burrowed tidal flats dessicated mudrocks blackened algal mats

9 Lower Interlake Type Depositional Cycles Open Marine Restricted Marine 6-50 Brecciated mudstone soil Laminated algal boundstone (908) Bedded-laminated pellet packstone Fossil-pellet pckstn Nodular (222) bedded (236) mudstone Coral- Stromatoporoid packstone & boundstone (649/959/999) Nodular (222) bedded (236) mudstone Unique sets of facies arranged in distinct, repetitive cycles that do not vary significantly laterally. Diagenesis (primarily early) strongly influenced each cycle and varies laterally and vertically among adjacent cycles 5-15 Mudstone soil (968) Massive mudstn (202) Laminated algal boundstone (908) Brecciated mudstone (948) Laminated algal boundstone (908) Bedded-laminated pellet packstone ( ) Fossil-pellet pckstn ( ) Laminated algal boundstone (908)

10 Upper Interlake Type Depositional Cycles Above GR marker Below GR marker 5-35 Brecciated mudstone (948) intermixed with Caliche-, blackened-, fenestral-algal boundstones (966/964, 963, 930/938) Intraclast pckstn ( ) Burrowed (282), desiccated (292) mudstone Bedded, laminated mudstone ( ) Intraclast pckstn ( ) Fenestral algal boundstone (930/938) Intraclast pckstn Burrowed (282) desiccated (292) mudstone Intraclast pckstn Lithoclastic blackened caliche crust (964/966) Bedded, blackened algal boundstone Burrowed (282) desiccated (292) mudstone

11 Core Analysis Data Study core analysis 42 wells 200 select analyses NDIC routine core analysis 29 wells ft spacing analyses Routine core analysis data influenced by: Fractures in plugs Plugs cut perpendicular to flow-limiting feature Low net confining stress No Klinkenberg correction

12 Fenestral algal boundstone (930 & 938) 2.54 cm

13 Fenestral algal boundstone (930 & 938)

14 2.54 cm Intraclast packstone (833)

15 Intraclast packstone (833)

16 Desiccated mudstone (292) High-end porosity includes chalkfilled porosity 2.54 cm 3 um

17 Burrowed & rooted mudstone (282) 2.54 cm High-end porosity includes chalk-filled porosity

18 Burrowed & rooted (282) & dessicated (292) mudstone High-end porosity includes chalk-filled porosity

19 Lithoclastic, Blackened Caliche Crust ( ) Bedded, blackened algal boundstone (963) mm mm 2.54 cm cm 964

20 Lithoclastic, Blackened Caliche Crust ( ) Bedded, blackened algal boundstone (963)

21 2.54 cm Skeletal-pellet packstone/grainstone ( )

22 Skeletal-pellet packstone/grainstone ( )

23 Massive. laminated, nodular, bioturbated mudstone ( ) Salt 2.54 cm 2.54 cm

24 Massive. laminated, nodular, bioturbated mudstone ( )

25 Coral-Stromatoporoid/reefal packstone & boundstone (649/959/999) 2.54 cm 2.54 cm

26 Coral-Stromatoporoid/reefal packstone & boundstone (649/959/999)

27 Reservoir/Nonreservoir Reservoir rocks: 100X greater permeability Lower Swi Higher Nonreservoir rocks: Mudstones and cemented reservoir lithofacies Higher Swi and lower

28 Electrical Properties Archie properties indicate that log-calculated properties using standard parameters (a=1, m=2, n=2) estimate saturations within 5% of accurate values Thin-bed resistivity issues create problem for accurate estimation

29 Capillary Pressure Rocks with K < 0.5 md are highly water saturated for all oil column heights Threshold entry pore diameters are consistent with other rocks Nonreservoir rocks have smaller pore sizes (and consequent lower K) Pore size heterogeneity, λ, is high λ = slope log Pc-logSw

30 Wireline log Challenges Porosity distribution of reservoir and nonreservoir rocks is highly similar Salt plugging DEN-NEUT can be problematic SONIC-NEUT more reliable Borehole rugosity is common Fracturing Reservoirs are thin-beds Below standard log resolution Porosity influenced by shoulder Resistivity shoulder is significant and estimated Sw incorrect in reservoir intervals Lithofacies differences are textural Cannot be resolved using standard log suite

31 Vertical Well Production Vertical well estimated ultimate recoveries for analyzed wells exhibit a log-normal distribution with mean = 100 MBO +2.9X (1 sd; ). Initial potential exhibits a poor correlation with EUR

32 Bypassed Pay and Horizontal Potential? Estimated recovery efficiency = 5-35% using EUR, φ>8-10%, Sw from logs BUT if thin reservoir intervals actually have higher oil saturation, So, then RE is much lower implying bypassed pay. High IP, lower EUR, can support interpretation that many fractures are small-scale and drainage is limited. Horizontal wells with longitudinal fractures might be able to contact reservoir beds Increased surface area in high Sw non-reservoir rock is likley to increase watercut

33 Summary Though not a major producing interval in the Williston Basin, the Upper Silurian Interlake is a type example of a common Paleozoic carbonate architecture of thin-bedded boundstone/grainstone/packstone reservoir intervals capping high-frequency cycles contained within a thick, porous, low-permeability, water-saturated wackestone/mudstone. Key reservoir lithofacies comprise: fenstral, blackened algal boundstones. bedded, laminated fossil/pellet packstones. Coral stromatoporoid packstone/reefal boundstones Nodular, bioturbated mudstones/wackestones. Key non-reservoir lithofacies comprise: Massive, burrowed/bioturbated, brecciated mudstone/wackestone Diagenetically altered and cemented reservoir lithofacies Log-normal distributed vertical well production averages 100 MBO+2.9X (1sd) Possibility of bypassed pay. Horizontal technology has the potential to contact isolated reservoir beds and produce significantly greater well contact area but likley will produce significantly more water from non-reservoir intervals.

34 Thank You! Richard Inden 1, Alan P. Byrnes 2, Suzanne Cluff 3 and late Robert Cluff 3 1-LSSI, Ltd. 2- Whiting Petroleum Corp. 3 The Discovery Group Denver, Colorado USA