Reservoir Sensitivity Of The Niutitang Formation Shale And Variability Effect Of Gas Content In The Cengong Block,Guizhou Province

To explore shale reservoir sensitivity and gas content variability,various approaches,including simulation experiments,statistical induction,theoretical analysis and geological synthesis,were used to study the reservoir physical properties and temperature-pressure effects on both pore-fracture-porosity-rock mechanics and gas content.Further,the effects of pore structure,reservoir physical properties,rock mechanical properties,and temperature-pressure on gas content are discussed.Main findings in this dissertation are as follows.(1)Based on the multi-scale quantitative study in shale gas reservoir,the main influence parameters of shale gas content variability are determined.The main influence parameters include TOC,quartz,pore structure,reservoir pressure,temperature,and effective stress.Organic matters are the material basis of gas generation and provide storage spaces for shale gas.The quartz develops a certain amount of pores and has a protective effect on other pores.The pore structure affects the gas phase and thus controls the gas-bearing structure.Pressure,temperature and effective stress are external factors that change the gas state and shale reservoir physical properties(2)Based on the low-field nuclear magnetic resonance with overburden pressure,porosity and permeability tests,and rock mechanics experiments in formation conditions,relationships among shale free gas content,reservoir physical properties,and acoustic-rock mechanics are found out.Results show that free gas content presents three stages of the rapid increase,high-value stability and slow decrease.Reservoir physical properties present the sensitive,transitional,and stable areas,respectively.Simultaneously,acoustic-rock mechanical parameter changes present three different stages.(3)Based on the isotherm adsorption experiments,gas state equation and the temperature-pressure sensitivity effects of methane solubility,the sensitivity change law of gas content under the reservoir conditions is manifested.In the formation conditions,the adsorbed gas content changes rapidly and then increases to the highest value and then slowly decreases.The temperature sensitivity first increases and then decreases,and the pressure sensitivity constantly decrease.The change law of free gas content and its temperature-pressure sensitivity are similar to those of adsorbed gas,and its sensitivity to effective stress can be quantitatively characterized by pore compression coefficients.Langmuir model can be used for the calculation of dissolved gas content.The change sensitivity of dissolved gas content increases with the increase of salinity and the calculation result of the model needs to consider the solubility correction coefficient.(4)Based on the discussion of the mineral composition,organic carbon content,pore structure,external conditions,and their effects on gas content,the control mechanism of the gas content variability effect in Cengong block is revealed.The pores smaller than 100 nm and larger than 10 nm are the storage spaces for adsorbed gas and free gas,respectively,and they are also main contributors of the specific surface area and pore volume,respectively.Main pore types are organic matter pores and quartz dissolution pores.The pore specific surface area and methane adsorption capacity are positively correlated with TOC content.The gas content under the combined effect of the reservoir pressure,temperature and effective stress is in the high-value range.Conclusions in this study are positive to promote the further revealing of the shale gas occurrence mechanism,enhance the scientificity of shale gas favorable area/stratum selection,innovate the methods of hydrocarbon resource evaluation,and develop a better understanding of the geological conditions and distribution of deep energy minerals.