关键词: Sulige gas field, tight gas reservoir, decline exponent, flow period, linear flow, boundary-dominated flow, decline prediction, combined model

Abstract: The Permian fluvial sandstone gas reservoirs in Sulige gas field are tight and contain most effective sand bodies that are mostly isolated or banded. After gas wells are put into production, reservoir fluid stays consistently in an unsteady flow state, and the boundary-dominated flow state occurs later. In this case, the traditional Arps production decline analysis method is not sufficient for field application. This paper analyzed the causes for the poor adaptability of the Arps production decline analysis method. On this basis, the variation law of the decline exponent of wells in tight gas reservoirs was identified by numerical simulation, and the relationship between the decline exponent and the flow period of fluid in gas wells was clarified. Finally, it was proposed to use the channel linear flow model to predict the production in the unsteady flow period and the Arps model to predict the production in the boundary-dominated flow period. For the gas wells in the unsteady flow period, the critical point time to attain boundary-dominated flow is determined by the theoretical formula; in the boundary-dominated flow period, the time of inflection point deviating from the linear flow is the critical point time. The field application shows that the proposed combined production decline model is accurate and effective in predicting the decline characteristics and indicators of gas wells.

Key words: Sulige gas field, tight gas reservoir, decline exponent, flow period, linear flow, boundary-dominated flow, decline prediction, combined model