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通常人们普遍认为气井开采过程中稳定产能方程系数是基本不变的，并由此来确定不同地层压力下的无阻流量，甚至采用原始地层压力下的稳定产能方程预测废弃条件等。事实上，随着地层压力的下降，与产能方程系数密切相关的多项参数如天然气偏差系数，粘度，气层渗透率，有效厚度等都是变化的，只不过渗透率，有效厚度的变化甚微，相比之下可以忽略不计；但天然气偏差系数和粘度的变化却不容忽视，两者之乘积不断变小，由此引起气井二项

INFLUENCE OF FORMATION PRESSURE DECREASE ON THE PRODUCTIVITY EQUATION AND OPEN-FLOW CAPACITY OF GAS WELL

??It is generally thought that the factors in stable productivity equation are unchanged in the process of production in gas well.From this,the open-flow capacities under different formation pressures were acquired and the abandonment condition was predicted even by use of the stable productivity equation under original formation pressure.In fact,many parameters as the deviation factor and viscosity of natural gas and the permeability and effective thickness of reservoir,which are closely related to the factors of productivity equation,are changed along with pressure decrease;only the variations in the permeability and effective thickness are very small,being able to be neglected by comparison.However,the variations in the deviation factor and viscosity of natural gas can't be ignored,because the product of both of them is unceasingly reduced so as to cause the Factor A and Factor B in the binomial of gas well to be uninterruptedly decreased.The relations expressing the corresponding changes of the Factor A and Factor B in the binomial with the deviation factor and viscosity of natural gas are derived in the paper.While the stable productivity equation of gas well at a certain time is known,according to the deviation factor and viscosity of natural gas under any formation pressure the stable productivity equation of gas well at the time corresponding to the formation pressure may be acquired.Thus the open-flow capacity of gas well at the time corresponding to the formation pressure can be determined more accurately and the stable productivity equation may be applied scientifically and reasonably in the process of production in gas well,the repeated well-test works being avoided,the manpower and material resources being economized and the economic benefit being raised.