Abstract:

Accurate evaluation of performance decline is crucial for efficient development of gas fields and ensuring stable energy supply. Production decline rate and productivity decline rate are two commonly used parameters for presenting performance decline in gas fields from different perspectives, but their definitions are different. In order to understand the physical meanings of production decline rate and productivity decline rate and clarify their inherent relationship and influencing factors, the calculation method of gas field decline rate was analyzed, and the influencing factors were identified. The results indicate that, for exponential decline, the productivity decline rate are consistent with the production decline rate, while for hyperbolic decline, the productivity decline rate is always greater than the production decline rate, and the difference between the two decline rates increases with the increase of decline index and initial decline rate, and the two rates gradually tend to be consistent with each other with the extension of production time. The concept of gas field exploitation intensity was introduced to eliminate the fluctuations in production decline rate caused by downstream gas consumption changes. A new method of production/productivity prediction was proposed. Specifically, an exponential decline model is used at the early stage of decline, and a harmonic decline model is used at the mid to late stage of decline; then, the average of the two model results is taken as the lower limit, and the result obtained from the harmonic decline model as the upper limit. The research results are of great significance to accurately analyze the decline behaviors of gas fields and scientifically formulate development plans.

Key words: gas field, decline rate calculation, production decline rate, productivity decline rate, exploitation intensity, exponential decline model, harmonic decline model