New Method of Water Influx Identification and Ranking for a Super-Giant Aquifer Drive Gas Reservoir

Abstract

For gas reservoirs with strong bottom or edge aquifer support, the most important thing is to avoid water breakthrough in gas well. Because water breakthrough in gas wells can explicitly reduce well productivity and reservoir recovery. Therefore, how to identify aquifer influx of gas wells are urgent in order to guide the well production rate optimization and improve gas field performance.This paper provides a new method with 3 diagnostic curves to identify aquifer influx status for gas wells, which are mainly based on well production and pressure data. And the whole production period of gas wells can be classified into 3 periods based on the diagnostic curves: no aquifer influx period, early aquifer influx period, middle-late aquifer influx period. And a suite of index with both static and dynamic description understanding are established for aquifer influx identification and ranking. Also how to use the index to identify aquifer influx are illustrated.This new method has been used for evaluation of all gas wells in Kela 2 gas field. It is one of the biggest abnormal high pressure gas field in the world, which is of high gas column, high productivity of a single well and strong aquifer support. Until now 2 of 17 production wells have been water-breakthrough and risks of water breakthrough for other wells are increasing. Water breakthrough sequence of all wells in Kela 2 gas field are determined based on 12 aquifer influx index evaluation by analytical hierarchy process and fuzzy evaluation method. Then all wells are ranked into 4 types based on evaluation results: water breakthrough wells, wells in middle-late aquifer influx period, wells in early aquifer influx period, and no aquifer influx wells. Actual gas well performance validate this new method. Then evaluation results are applied to well production rate optimization. In order to keep the whole gas field production rate, production rate of wells in middle-late aquifer influx period are decreased, while production rate of no aquifer influx wells are increased. Finally gas field performance are explicitly improved. This paper offers a new method and a case study of aquifer influx identification and ranking for aquifer drive gas reservoir. It also provides a methodology and reference case for engineers to develop other similar gas fields.