Research On Hydrocarbon Generation Kinetics And Thermal Effect Of Volcanism, Its Application

During the past 40 years volcanic reservoir exploration in China, many researches have been carried out, such as reservoir lithology, facies classification, porosity-permeability characteristics, volcanism on the source rock maturity and the formation mechanism of inorganic hydrocarbon, however, the hydrocarbon generation thermal effect of volcanism has not been studied. It is not only hopeful to provide a technical means for quantitative evaluating the net quantity of hydrocabon generation and the destroyed degree of oil reservior, which is caused by volcanism, but also helpful to recognize the contribution of volcanism to the petroleum exploration and perfect the theory of volcanic petroleum exploration. To achieve this target, the heat capacity model of magmatic intrusion, the heat conduction model and the chemical kinetics model of hydrocarbon generation should be established. Therefore, some chemical kinetic models and thermal conduction models have been established, so do parameters calibation methods. Based on thermal simulation experiments for different types OMs (organic matters) and the relation data between products yields and heating temperatures, comparison researches on different kinetic models, the products yields from different experiments and the hydrocarbon generation kinetic characteristics of different types OMs have been completed, meantime, the stability of kinetic models, the effect of source rock heterogeneity on kinetic parameters and the effects of intrusion dimensions, nature and the time-space range of source rock on country rock maturity and hydrocarbon geneartion thermal effect have been investigated. At last, combined source rock parameters and the above mentioned models, the natural gas resource of Xujiaweizi depression and Yingtai depression have been estimated. The research method and conclusions of this dissertation have important guiding significance to oil-gas resource potential appraisement and quantitative evaluating the net quantity of hydrocabon generation caused by thermal effect of mamatic intrusion. In a summary, the main conclusions and achievements of the dissertation are listed bellow:1. The tempeartue corresponding to C1-5 mass yields decreasing and the inflection point temperature of C2-5 mass yields are different when OM and oil cracking under closed system in the lab, which indicates that there is also the contribution of primary cracking from OM and oil to the methane source, not only the contribution of C2-5 cracking. However, the above two temperature should be colse for pure compund or oil with simpler compositions.2. The termination temperature of methane generation from coal sample under TG-MS experiment is about 850℃(with 10℃/min heating rate), and the corresponding Ro is about 5.3% calculated by extended EasyRo% model. However, the C1-5 mass yields increase all the while even at the end experiment temperature under the closed system experiment (the corresponding Ro is about 4.9% and with 2℃/hour heating rate), which indicates coal sample has gas potential at higher maturity stage. It may be caused by the recombined reaction of C6+ liquid hydrocarbons with kerogen or bitumen under closed environment, which will be formed new products with high thermal stability and the new formed products will generate methane at higher maturity stage. For open system, such as TG-MS experiment and Rock-Eval experiment, this recombined reaction cannot take place because the C6+ liquids are swept off by the carried gas.3. The measured Ro can be fitted by combining the thermal conduction model and the EasyRo% model, and the combined of the two models can be easily used to simulate the temperature fields and maturity evolution history caused by magmatic intrusion in two or three dimensions. The thermal effect scope of the magmatic intrusion is limited and the scope changes with different geological situations. For intrusions with the same thickness, the higher the initial temperature of intrusion, the heavier of the metamorphism degree and the deeper of the scope, however, the X/D ratio is smaller than 3 generally (D corresponds to the intrusion thickness and X corresponds to the distance from the contact surface and to the simulated depth). For intrusions with different thickness, the thicker of the intrusion, the deeper of the scope, and the X/D ratio is smaller than 2 generally.4. The kinetic equation in the overall reaction model is simple but can't well simulate the complicated hydrocarbon generation process. The hydrocarbon generation process may not be fully consistent with the mechanism of consecutive reaction model, but it is appropriate to combine the consecutive reaction model and parallel reaction model to describe the hydrocarbon generation process. However, due to the complexity of the model and thus heavy experiment work in the lab. The Friedman type model is inappropriate from the view of kinetic theory and kinetic parameters. In view of the model application in source rock potential appraisement and the kinetic parameters optimization effect, the parallel first-order reaction model with a discrete distribution of activation energies is the best model for describing the hydrocarbon generation process.5. Apparent activation energy increase gradually with the increasing pre-exponential factor and the order of apparent activation energy from high to low for different types OMs is EII2-III, EI and EII1.6. Based on hydrocarbon generation characteristic described by SFF model, the pre-exponential factors change from low to high, an extreme value for residual errors occurs. And with the increasing pre-exponential factor, the distribution shape of activation energies are nearly the same, but the values of activation energies move toward to higher integrally. The average activation energies increase about 12kJ/mol for ten times increasing of pre-exponential factor, and the temperature corresponding to TR0.5 is higher, but the net increasing value change to small when extrapolating using a simple geological heating rate (3.3℃/Ma).7. The TR ratios obtained from experiment and the relationship of reaction fraction vs. activation energy reveal that the types of compound structures and chemical bonds of lacustrine facies type I OM are relative homogeneous, which with one dominating activation energy. And types of chemical bonds of lacustrine facies type II1 OM and the terrestrial type III OM is relative complex, which with a broad activation energy distribution. And the reaction fraction of the preponderant activation energy drops with the decrease hydrogen index. The study of the impact of activation energy distribution spaces on the geological extrapolation shows that different spaces have little effect to the hydrocarbon transformation ratio. Therefore, the parallel first-order reaction model with proper number activation energies can be better used to describe the hydrocarbon generation process. The geological extrapolation results of 18 samples kinetic parameters show that, the distribution range of hydrocarbon generation rate for different types of organic matter have different distribution profiles, of which type I organic matter features a narrow and smooth generation curve and types II1 and II2-III span over a wide range whilst type II2- III has many peaks and fluctuates frequently. Distribution width of hydrocarbon generation rate has relationship with its kinetic parameters, namely, the narrower the activation energies distribution is, the narrower the hydrocarbon generation rate distribution is, the smoother the hydrocarbon generation curve is, and vice versa.8. The comparison and analysis between MFF model and SFF model shows that MFF model can avoid miscalculating the hydrocarbon generation potential (reaction ratio) in the low and high evolution stages, which appears in SFF model.9. The heterogeneity of source rock has influence on oil-gas resource appraisement when using the hydrocarbon generation kinetic method, however, it can be avoid by combining the MFF model and the weighted averaged kinetic parameters for more samples. Meantime, it is recommended to confine the kinetic parameters using geological data, such as S1, Tmax and S1+S2 et al.10. The thermal effect of maturity and hydrocarbon generation caused by magmatic intrusions are different for OMs with different initial maturities, though intrusions with the same conditions. For example, thermal effect increases with the increasing initial maturity of OM if the vitrinite reflectance is smaller than 0.9%, but the thermal effect decreases with the increasing initial maturity of OM if the vitrinite reflectance is bigger than 0.9%. Therefore, intrusions with the same initial conditions can cause different metamorphism degrees. Before the hydrocarbon generation, the later the emplacement of intrusion, the greater the thermal effect of hydrocarbon generation, and vice versa.11. Analyzing results of maturity and geochemical index for mudstone near intrusions of Longshen1 well indicates that with the decreasing distance from contact surface, the maturity increases from 1.6% to 2.1%, the Tmax increase gradually, the H/C, O/C and TOC values decrease gradually and the chloroform bitumen"A"increases firstly then decreases. Between two intrusions the Tmax values takes on"V"shape, and so do TOC values. The HI and S2 values change as above mentioned rule.12. The research results of thermal effect for intrusions of Longshen1 well show that the gas generation TR increases quickly in the metamorphism range, for example it can be increase from 0 to 80% during a short period. It also shows that combining the kinetic model, burial model, thermal conduction model and normal thermal model can be a useful tool to describing the hydrocarbon generation process.13. The natural gas generation amount is 5.1×1012m3,and resource quantity is 1072×108~1608×108m(3the corresponding range of migration and accumulation coefficient is from 1.6% to 2.4%)for Yingtai depression. And the natural gas generation amount is 33.75×1012m3,and resource quantity is 5020×108~7530×108m3for Xujiaweizi depression.