西气东输盐穴储气库库容及运行模拟预测研究

FORECAST STUDY ON THE SALT CAVERN STORAGE CAPACITY AND ITS OPERATION IN THE PROJECT OF "WEST-TO-EAST GAS PIPELINE"

掌握盐穴储气库的库容量和运行过程中的状态变化是合理制定盐穴储气库调峰方案的基础。在溶腔体积一定时,通过气体状态方程可求出单个溶腔的库容量,但需充分考虑溶腔的最大压力和温度对库容及工作气量的影响。在气库的注采过程中,天然气的不断压缩和膨胀并在井筒和地层中产生热交换,引起井筒和溶腔内的温度和压力变化。该变化过程遵循能量守恒和质量守恒定律,可建立相应的数学模型对溶腔和井口的温度压力进行预测。对西气东输盐穴储气库单腔运行过程的模拟发现,溶腔投入运行后的首个注采周期是温度、压力变化最剧烈的阶段,且单腔的工作气量并非一成不变,它与溶腔同一周期的采气时间长短成负相关关系,开采周期越长,溶腔温度变化越平稳,能采出的工作气量也越多;反之,则工作气量越少。因此在制定盐穴储气库调峰方案时,应尽量避免单个溶腔的强注强采而导致溶腔温度压力的剧烈变化,从而最大限度地提高单腔工作气量,发挥储气库的最大调峰能力。

It is fundamental for scheming on the peak-shaving plan of salt cavern storage capacity to have both the storage capacity and the state changes during its operation well under control. At a certain volume, single cavern storage capacity can be obtained by the equation of gas state, meanwhile the effects of the storage capacity and working gas capacity by the maximum pressure and temperature should be put into full consideration. In process of gas injection and withdraw, natural gas is compressed and swelled continuously, at the same time heat exchange happen between the wellbore and the formation layer, which results in the change of temperature and pressure in the wellbore and the cavern. The process of the change obeys conservation of mass and energy, which can be predicated by the corresponded mathematical model. Through the simulation on the operation process of the single storage salt cavern in 'West-to-East Gas Pipeline', it is found that the first injection/production circle is the fantastical stage for the change of the temperature and pressure after the cavern is put into production. Working gas volume is determined by operation pressure. Different withdraw time results in different temperature transformation in single cavern and it influences cavern pressure which determines working gas volume. The longer circle time the gas is extracted, the more stable temperature of cavern will be and so the more working gas can be produced, vice versa. Therefore while setting down the plan of peak-shaving for the salt cavern storage, it is suggested the force injection/production should be avoided because this may result in intense variety of temperature and pressure of the cavern, only in this way, the working gas capacity of the single cavern will be improved to the highest level and the maximum peak-shaving ability of the storage will be taken into full use.