| If the stability of natural gas and the amount and composition of the non-hydrocarbon gases could be predicted in advance of drilling, it would improve economics for deep exploration. The thermal maturation of organic matter is kinetically controlled with higher temperatures and longer periods of time driving the reactions closer to, the equilibrium products of graphite and methane. If the hydrocarbon system and the associated minerals, fluids, and non-hydrocarbon gases have reached equilibrium, thermodynamics could be used to predict the equilibrium composition of the entire system, including hydrocarbon and non-hydrocarbon gases. This dissertation has attempted to determine whether the Madison Formation of the Madden Field, Wind River Basin, central Wyoming, is in thermodynamic equilibrium; at what depth the system changes from kinetic control to thermodynamic equilibrium; and whether thermodynamic modeling can be used to predict the gas composition.; The Madison Formation produces dry gas from approximately 23,000 ft–25,500 ft. During drilling operations Burlington Resources, Inc. cored four wells (BH 1-5, BH 2-3, BH 6-27, and BH 7-34). Some of this core material was obtained and analyzed to determine the diagenetic history (by core and thin section analysis), the mineralogical composition (through petrography, X-ray diffraction, and scanning electron microscopy), the maximum temperature the formation was exposed to (by fluid inclusion microthermometry), and the fluid inclusion gas composition (by mass spectrometry). The information obtained was used to develop kinetic and thermodynamic models, which were then used to determine if the Madison Formation is in thermodynamic equilibrium.; Conclusion. The system is not in thermodynamic equilibrium. Ethane and elemental sulfur were identified in the system, but were not predicted as results of the thermodynamic calculations. Further, although the thermodynamic modeling at a geothermal gradient of 25°C/km came very close to predicting the gas composition of the formation, this geothermal gradient is less than the present day geothermal gradient of approximately 29.2°C/km, which was indicated by the bottom hole temperature of well BH 2-3. The final recommendation is that kinetic and thermodynamic modeling should be combined to more accurately predict the gas compositions of ultra deep reservoirs. |
