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1 Presented by: Dick Drozd Email: Dick.Drozd@WeatherfordLabs.com Source Rock Geochemistry and Thermal Maturity Discussion of the Utica-Point Pleasant in the Northern Appalachian BasinPresented by: Dick Drozd
2 Presentation OutlineWhat are the important elements of a geochemical evaluation and why.Specific geochemical issues with the Ordovician section.Geochemistry of the Utica – Point Pleasant and equivalent units.Implications for exploration.Questions
3 Significant Elements of Source Rock Evaluation Organic RichnessRemaining Potential for GenerationThermal MaturityKerogen TypeAll measurements are made on present-day as- received materialOriginal condition most significant for exploration
4 Total Organic Carbon (TOC) Solid organic material contained within a sample that can be subdivided into kerogen and bitumen.Total organic carbon determined by combustion of samples that have been treated with acid to remove inorganic carbon.Usually reported in units of weight fraction, TOC weight divided by sample weight.
5 Why is TOC Important? TOC provides the carbon for hydrocarbons TOC provides increased porosity with increasing thermal maturationTOC provides adsorptive sites for hydrocarbonsTo retain oil for cracking to gasStorage of adsorbed gas
6 Total Organic Carbon Guidelines Present day organic richness of source rockQualityTOC (wt%)Poor<0.5Fair0.5 to 1Good1 to 2Very good2 to 4Excellent>4Threshold Shale OilThreshold Shale GasThe TOC Myth: “If I have high TOC, I have a good source rock.” (Dembicki, 2009)
7 Programmed Pyrolysis Pyrolysis Temperature-Programmed Pyrolysis A chemical degradation reaction that is caused by thermal energy. (The term pyrolysis generally refers to an inert environment.)Temperature-Programmed PyrolysisA pyrolysis during which the sample is heated at a controlled rate within a temperature range in which pyrolysis occurs.
8 Source Rock Analyzer (SRA) Pyrolysis instrument that uses an FID detector and IR cells to measure:Available Hydrocarbon Content – S1Remaining Hydrocarbon Generation Potential – S2Organic Richness – TOCThermal Maturity – Tmax
9 Parameters MeasuredWith Flame Ionization Detector (FID) - detects hydrocarbons only:Volatile hydrocarbon content – S1Pyrolized hydrocarbons – S2Tmax – Temperature of maximum S2 releaseWith Infrared Detector – detects CO and CO2 only:CO2 generated during pyrolysis – S3Total organic carbon (TOC) – S4
11 Thermal Maturity Challenging to Measure Maturation parameters are indicative of the maximum paleo- temperature that a source rock has reached:VisualVitrinite reflectance (whole rock or kerogen concentrate)Color indices (Conodonts, Zooclasts, bitumen)ChemicalProgrammed Pyrolysis Tmax (chemical)111111
12 Vitrinite Reflectance Vitrinite: a term (from coal petrography) for the jellified remains of higher plant tissues (post-Silurian)With increasing thermal alteration, vitrinite becomes more graphitic (condensed aromatic rings increase) and reflects more lightReflectance (%Ro) tracks kerogen maturityOther maturity measures expressed on vitrinite “scale”
13 Problems Obtaining Ro Maturities Properly identified vitrinite:PrimaryRecycledCavingsMud additivesFactors affecting accurate Ro measurements:Poor polishOxidized vitriniteInclusions (pyrite, bitumen, other macerals)Poor statistics (too few particles)Hunt, 1996, p. 515
14 Calculated %Ro Values from Tmax %VRo from Tmax = ( x Tmax) -7.16Calculated valuesJarvie et al., 2001
15 Issues with Tmax Anything that affects the peak shape will affect Tmax Contamination from drilling mud may alter the S2 peak,with high amounts of indigenous or migrated oil present, the oil part of S2 may exceed the kerogen S2 and Tmax will be too low,at very high maturities, there is no S2 peak (flat) and Tmax is virtually randomdependent on kerogen type.
17 Thermal Maturity Guidelines Vitrinite Reflectance (% Ro) scale for maturity assessmentImmature <0.6% RoOil window % RoWet gas window % RoDry gas generation 1.4-~2.2% RoDry gas preservation ~2.2-~3.2% RoGas destruction >~3.2% Ro (?)171717
18 The TOC Myth: “If I have high TOC, I have a good source rock The TOC Myth: “If I have high TOC, I have a good source rock.” (Dembicki, 2009)Although a good source rock must have high TOC, not all organic matter is created equal.The more hydrogen associated with the carbon, the more hydrocarbon it can generate – particularly liquid hydrocarbons.Thus, we also need an indicator for the amount of hydrogen present in the organic matter (measured present day – projected into the past).KEROGEN TYPEFrom, Dembicki, H. (2009), Three common source rock evaluation errors made by geologists during prospect or play appraisals, AAPG Bulletin, v. 93, p
19 Primary Hydrocarbon Generation Yields Oil vs. GasType I (HI=810)Type II (HI=420)Type III (HI=250)C1C2-C4C5-C14C15+(Not secondary cracked products)Jarvie, unpublished data
20 Kerogen Maceral TypesMaceral composition is determined via petrographic (optical) analyses of pelletized samples or thin sections.Three Primary Maceral Groups.Liptinite: Hydrogen-RichVitrinite: Oxygen-RichInertinite: Carbon-RichNumerous macerals and sub- macerals in each maceral group.Fully characterize Kerogen Type via Maceral Composition and Programmed Pyrolysis.Maceral GroupMaceralsOrganic PrecursorsKerogen TypeLiptiniteAlginite IFresh Water AlgaeIAlginite IIMarine AlgaeIIExiniteSpores (Sporinite), PollenCutiniteLeaf CuticleResiniteResin, Tree SapVitriniteVitrinite, PsuedovitriniteWoody TissueIIIInertiniteSemifusinite, Fusinite, Sclerotonite, etc.Reworked and/or Oxidized Material, CharcoalIV1. The coal mining and coal gas industries describe the organic composition of coal seams (or coal gas reservoir systems) in terms of maceral concentrations.
23 Kerogen Quality Plot – Barnett Shale Example Samples as measured today, at present maturity!ca. 1.50% VRoca. 1.00% VRoca. 0.85% VRoca. 0.55% VRoca. 0.70% VRo25% 0.70%Ro50% 0.85%Ro75% 1.00%Ro90% 1.50%Ro
24 Estimation of Yields Measured present day: Original: Barnett Shale (Oil)Measured present day:TOCVolatile HydrocarbonsRemaining PotentialKerogen TypeThermal MaturityOriginal:TOCoTotal PotentialKerogen TypePartitioning gas/oil“Magic” is a set of calculations described in the literature but too long for this presentation.Yield a set of yield estimates.MAGIC
25 Utica / Point Pleasant & Equiv. Rocks Early Paleozoic age, therefore no primary Type III organic matter presentMaturity - no vitrinite – Substitute:Zooclasts reflectance (chitinozoans, scolecodonts, etc.) or bitumen reflectanceConodont colorOriginal Kerogen Type – Original hydrogen index (HIo)Primary organic matter marineContribution from reworked/ recycled organic matter likely low,Contribution of oxidized organic matter unknownOver large geographic area & depositional settings variations likely (measured HIo 200 to 650)
30 Point Pleasant Equivalents Utica UndifferentiatedPoint PleasantCollingwoodCobumAntesCobourgLindsay
31 Source Rock – Oil Correlation Two papers in the 1990’s Cole et al and Drozd & Cole examined the petroleum systems in Ohio. Conclusions:Oil in Ohio classified into three familiesGroup 1 found in Cambrian, Ordovician and some Silurian reservoirs, fingerprint characteristics of Early Paleozoic organic matter, and heavy carbon isotopes,Group 2 found in some Silurian and Devonian to Pennsylvanian reservoirs, variable but distinct fingerprint characteristics, and intermediate carbon isotopes,Group 3 found in a few Berea reservoirs similar to Group 2 in fingerprint pattern, but with light carbon isotopic composition.Source-Oil CorrelationGroup 1 oils from Point Pleasant Shale,Group 2 oils from facies of Ohio Shale, hence variable characteristics,Group 3 oils from Sunbury Shale.
35 Comparison of Pt Pleasant to Other Shale Plays TOC (wt%)TOCo (wt%)Maturity (%Ro eq)OhioPt Pleasant1.652.010.84Attractive2.402.800.76MichiganCollingwood1.962.741.44OntarioLindsay5.205.520.696.537.270.744.967.190.832.563.791.23Utica1.001.250.85PA1.762+Barnett (Oil)3.86Eagle Ford (Oil)2.760.98Geneseo/Burkett2.521.19There is some variability in TOC in OH, similar to Collingwood in MI. Average maturity very different.“Selected” samples can have much higher TOC than cuttings.Utica in PA may include Pt Pleasant facies; much more mature.Other shale oil plays.
36 Ongoing ThoughtsOur understanding of the kinetic of the Point Pleasant kerogen is very limited due in part of lack of appropriate samples (low maturity but similar facies to producing area)Therefore, maturity guides may not be as appropriate as we would like.
37 Kerogen Type Determines Timing/Rates of Conversion 0.604304404504604704804200.400.750.951.101.301.50%RoTmax (oC)Type II-OSType IIType IIIType I
38 Ongoing ThoughtsOur understanding of the kinetic of the Point Pleasant kerogen is very limited due in part of lack of appropriate samples (low maturity but similar facies to producing area)Therefore, maturity guides may not be as appropriate as we would like.Product expectation (heavier oil, light oil, condensate, wet gas) is also less certain than preferred.Variation in properties across a play is always an issue when the play is new, because we have yet to fully measure parameters needed to obtain a basic understanding of the detailed rock characteristics.
39 (Richard Stoneburner, COO, Petrohawk Energy) The first step in our successful development of the Eagle Ford Shale play was to “prove the rocks”.(Richard Stoneburner, COO, Petrohawk Energy)
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