Research On The Constitutive Model Of Natural Gas Hydrate And The Law Of Reservoir Response

Natural gas hydrates have an important strategic position for the future energy structure.They can solve the increasingly prominent contradiction between economic development speed and energy shortage,and can also alleviate the looming environmental problems,but all must be based on large-scale commercial exploitation.basically.At present,the exploitation methods of natural gas hydrates are still not mature.A large number of scientific research workers with extensive experience in oil and gas exploration engineering and technology want to contribute to the improvement of these methods,but they are subject to the mechanical and thermal forces of natural gas hydrates.The lack of understanding of the response under external disturbances such as mass transfer and chemistry.Accurate description of the deformation and mechanical properties of hydrate deposits is an important prerequisite for the economic and safe development of natural gas hydrate resources.Due to the harsh conditions of field data monitoring and the difficulty of experiment,the theoretical analysis and numerical simulation are effective ways to analyze the mechanical behavior and response law of natural gas hydrate.In order to accurately and accurately describe the response law of natural gas hydrate reservoir under external disturbance,it is necessary to understand the mechanical behavior characteristics of hydrate,establish a constitutive equation suitable for natural gas hydrate sediments and a multi-field coupled mathematical model.Natural gas hydrate deposits are affected by various factors such as effective confining pressure and hydrate content,and thus exhibit two mechanical properties of strain softening and strain hardening.In order to describe its deformation characteristics,based on the statistical damage theory framework,the Weibull distribution is used to describe its micro-element failure probability and the Drucker-Prager criterion is used as the micro-element strength metric to construct the basic constitutive relation of natural gas hydrate sediments.Based on the mixing rate theory and rock pore damage theory,the equivalent elastic modulus model of natural gas hydrate sediments was established.The yield strength model was established based on the Mohr-Coulomb criterion to determine the parameters of the constitutive model to a certain extent.Sex and simplicity.The comparison with the experimental data shows that the model can describe the strain softening behavior of natural gas hydrate deposits under different working conditions,and the parameters are easy to determine,which can be easily applied to the numerical simulation of drilling and mining.The optimization of the drilling process and the optimization of the crushing tool provide a criterion for the analysis and evaluation of the stability of the hole in the fractured hole,which has a certain promoting effect on the economic and safe mining of the non-diagenetic gas hydrate.At present,the theoretical research on natural gas hydrate deposits is mostly regarded as a medium with mature theoretical framework such as composite rock and soil by analogy.In order to make the constitutive model of natural gas hydrate more specific,three-dimensional stress is considered.The role and the internal pores of sediments.The three-dimensional equivalent elastic performance model of natural gas hydrate deposits.The comparison of the equivalent elastic model of natural gas hydrate deposits established by pre-humans compared with frozen soil shows that three-dimensional stress and pore action are considered in three dimensions.The elastic modulus model predicts the elastic modulus of natural gas hydrate deposits better,and has better adaptability under different occurrence conditions and occurrence modes.By summarizing the five transformation and hardening stages of natural gas hydrate deposits under micro-deformation process under load,the constitutive relationship of natural gas hydrate deposits was corrected,and the residual strength model and stress were established by MATLAB software.The porosity model below completes the parameter determination of the modified model.The adaptation of the damage evolution equation established by Weibull distribution function and Harris function to the strain softening law of natural gas hydrate sediment constitutive model under different working conditions is discussed.The results show that the Harris function is under most conditions.The description of the mechanical response of natural gas hydrate deposits has good adaptability,but the Weibull distribution function describes better softening trend under lower hydrate saturation conditions,but both can be used for natural gas hydrate deposition.The establishment of the constitutive model.Natural gas hydrates are harsh in conditions,which cause a series of changes in reservoir physical properties and phase equilibrium under external disturbances.Consider the hydrate decomposition and damage degradation effects of reservoirs during disturbance,based on conservation of mass energy and Darcy.Multi-physics coupling theory such as law establishes a coupled mathematical model of temperature field-seepage field-stress field-damage field(THMD)of natural gas hydrate reservoir,and compares it with the measured value and predicted value of two natural gas hydrate mining processes.The preliminary feasibility of the model was verified.Through the established THMD multi-field coupling model,the effects of temperature and pressure changes on the natural gas hydrate sediment reservoirs were discussed.The response of natural gas hydrate deposits under external temperature and pressure disturbances was explored.The change of physical parameters and the evolution trend of hydrate saturation provide theoretical basis and technical support for future gas hydrate mining schemes and process design,so that decades of accumulated oil and gas drilling experience can be obtained in the development and exploitation of natural gas hydrates.application.