The Study and Application on a New Evaluation Index of Gas Well Productivity in Tight Gas Reservoir

The Shenmu gas field is a typical tight gas reservoir, developed with “downhole throttling” technology to cut costs. There is no natural stable production period for gas wells, and the production and wellhead pressure decrease at the same time when they are put into production. Traditional productivity evaluation indexes are not applicable for gas wells in Shenmu due to the lack of flowing pressure data. Therefore, in order to make full use of daily production data such as q and pc, this paper proposes a new gas well productivity evaluation index—the cumulative gas production of the unit casing pressure drop. From the theories of seepage mechanics, the calculation formula of the new productivity index is derived, and the change characteristics of the index over time and its influencing factors are theoretically analyzed. In addition, the index application is explored in the gas fields. The research shows that: (1) the new productivity index curve increases at first, then decreases with the time. The peak of the curve indicates that the pressure wave propagates to the supply boundary. Using this value, the well dynamic reserve can be estimated; (2) the new productivity index curve shape is affected by reservoir parameters, control radius, and production system. Compared with the IC indexes of different gas wells at the same stage, the rationality of gas well production can be analyzed, and the gas well production can be adjusted to the optimization. The new index can not only characterize the productivity of gas well, but also guide the production and allocation of gas wells, and estimate the control reserves of gas wells, which has high practical value for tight gas reservoir.