1、 Oct. 04, 2010Gas Generation Kinetics and Determination of Gas Maturity and AgingTongwei Zhang et al.Bureau of Economic GeologyThe University of Texas at Austin Oct. 04, 2010Principle of Petroleum Generation KineticsTheoremspetroleum generation is the result of a large number of chemical reactions l

2、eading from kerogen to liquid and gaseous products of lower molecular weight and to residues of increasing degree of condensationthese reactions are governed by the basic laws of chemical kineticsSedimentary basins as chemical reactorsfeedstockproductsT, P, catalysts, transportSOMpetroleumLack of ac

3、tive process control must becompensated by intelligent analysis and reconstruction of reaction conditions in time and spaceactive process controlOrder of Reactions1st order2nd ordernth orderTTI Approach (empirical)Reaction rate doubles at 10 C temperature increase (”rule of thumb”)Lopatin (1971); Wa

4、ples (1980)Statistical thermodynamics; partition functionsActivated complexEA - activation energy bond energyA - pre-exponential factor (“frequency factor”) probability of bond cleavageArrhenius relationship (semi-empirical)Comparison TTI - Arrhenius ApproachArrhenius diagramKerogen degradation and

5、hydrocarbon generation (activation energy distribution)kerogenoilCO2 ,H2O, etc.carbon residueafter Tissot & Welte (1984)CO2 ,H2O, H2S, etc.gascarbon residuek11k12k1ik1mk21k22k2jk2nActivation energy distributionKinetic isotope effects during natural gas generationIndividual 1st order reaction rate co

6、efficients for 12C and 13C isotopic speciesKinetic isotope effects during natural gas generationAssuming:Isotope fractionation Oct. 04, 2010Gas Geochemistry in Tarim Basin, ChinaTectonic Elements and Gas Fields in the Tarim Basin, ChinaAAA Main Component is Methane in Natural Gases, Tarim BasinConte

7、nts of Ethane and Propane are varied significantly in the Natural GasesNo obvious difference in ethane and propane contents was observed for coal-type gas and oil-type gas in the Tarim basin. So, it is hard to differentiate gas types based on the gas chemical composition Carbon Isotopic Compositions

8、 are Effective Indicators for Gas Origin IdentificationCoal-type gas posses heavier carbon isotopes of ethane and propane compared with oil-type gas.A positive relationship of d13C2 and d13C1 and d13C3 suggests that the thermal genetic gases from organic matter cracking under high temperature and pr

9、essure are a dominant source in the Tarim basin.GOR-isotope quantitative model can apply to the understanding of natural gas formation and gas filling history.Kerogen+Primary Remain GasSecondary C rackingGas/OilPrimary Expelled GasGas/OilGas/OilSecondary Remain GasGas/OilSecondary Expelled Gas Possi

10、ble Scenario of Gas Generation and ModelingFlow Chart for Gas Generation Kinetics Investigationkerogengold-tube pyrolysiskinetics fittingextrapolationImmature sourceGas Yields and Carbon Isotopes MeasurementEa: activation energyAf: frequency factorTiming of gas generation, migration and accumulation

11、Geochemical Properties of Jurassic Coal Selected for SimulationsamplepercentageTOCd13CHI(%)(%)()(mgHC/gTOC)Coal (Ro =0.4%)67.4-24.3238vitrinite42.366.1-24.8157.8fusinite42.368.3-24.632.6semi-fusinite70.4-24.633.7Exinite1074.5-24.8464.2Mathematical Expression forGas Generation Kinetics is the convers

12、ion of CH4, k is rate constant, R is gas mole constant, E is activation energy. E0 is mean activation energy.controls the shape and is activation threshold. controls the width of the distribution. is the gamma function, 01/1. A is the prefactor.Gas Generation From Coal Anhydrous Pyrolysis at Two Dif

13、ferent Heating RatesGas Yield (mg/g TOC)Temperature (C)C1C2C3Activation Energy Distribution of Gas Generation From Jurassic CoalCarbon isotopes of C1,C2, C3 from organic matter thermal cracking under non-isothermal pyrolysisTheoretical basis for carbon isotope fractionation modelCarbon isotope kinet

14、ics model of C1, C2 and C3 generation from organic matter thermal crackingCarbon Isotope Kinetics of Natural Gas GenerationCarbon Isotopes of Gases From Coal Anhydrous Pyrolysis at Two Different Heating Rates13C (, PDB)Temperature (C)C1C2C3The fractionation factor between 13C-12C bond and 12C-12C be

15、comes less with heated temperature decreasing, and this shows that large fractionation exists at lower temperature and small fractionations exists at higher temperature.According to Tang et al, GCA 2000Laboratory pyrolysis data can not be directly compared with geological data. Only through extrapol

16、ation of kinetic gas isotope fractionation, can one use pyrolysis data to predict gas isotope changes with time and temperature.Observed Gas Isotope Fractionations in the Laboratory and Natured13CGeological TemperaturesLaboratory TemperaturesSmaller FractionationLarger FractionationTemperatured13CTe

17、mperatureExtrapolation of kinetic gas isotope fractionation obtained from pyrolysis data is able to predict gas isotope changes with time and temperature under geological condition.Kinetics Parameters of Isotope Fractionations For Basin Modelingd13CC1C2C3Alpha(1)1.021.021.02BetaLow (cal/mol)11010Bet

18、aHigh (cal/mol)858080Eo (kcal/mol)59.461.461.6Sigma (% Eo)22.337.930.9Gamma ()-30.1-21.2-23.0 Oct. 04, 2010Geological Application of GOR-Isotope Model in Tarim BasinTiming of Gas formation and Expulsion Gas filling historyGas thermal maturityGas reserves estimationGas recharging timeBurial Thermal H

19、istory of Jurassic Source Rock in the Tarim BasinTime-Temperature curve of the bottom of Jurassic sourceBurial history curveAccording to Liang et al. 2003Modeling Carbon Isotopes of Expelled Gases from Jurassic Coal Match with Geological Observation of Natural Gases in Reservoirs d13C1, d13C2d13C3,

20、d13C2Carbon isotope model of expelled gases from Jurassic coalThermal Maturity of Coal-type Gas in Tarim Basinsignificant contribution from secondary cracking1.171.351.51.61.832.02Primary gas from kerogen crackingC1/(C2+C3) vs d13C2Gas Reserves Prediction By Gas Geochemistry Isotope ModelExpelled gas amount from the Jurassic coal5001000150020002500Kela 2 Large-size Gas Field Was Probably Charged About 2 mybpRo 2.2%KL2 gas field was charged about 2mybpConclusionsPetroleum and natural gas generation in sedimentary bas