Abstract

It frequently happens that a gas well does not flow after being shut in; for example, after conducting a test. As a result, the well must be swabbed to put it back on production. Some wells suddenly stop flowing soon after production begins without there having been any indication of a decline in production rate. This so-called shortfall phenomenon of a gas well has rarely been studied and presented in the literature. However, it has been learned from field experience that condensation of water contained in the gas may be responsible for such a problem. In addition, it is unfortunate that this kind of occurrence is difficult to study through reservoir simulation since there is no facility available today to account for water condensation.

This paper presents some findings about the water condensation phenomenon around the wellbore of a dry-gas well. A single well model has been developed to predict the amount of water that may condense near the wellbore as the pressure changes i.e., as the gas flows into the well. The assumptions of the model include a circular and finite reservoir with constant temperature. The amount of water that is contained in the gas as function of pressure was then calculated. A sensitivity analysis has been conducted including effects of formation thickness, permeability, and tubing diameter.

It has been found from this study that a significant amount of condensed water may develop around the well and reduce the flow of gas. For a given pressure range, the distance of the gas front behind this condensed water has a linear correlation with the production rate-transmissibility ratio. Based on the drawdown limit testing theory, it has also been found that the water can be drained successfully only at a certain wellbore flowing pressure and production rate.