Abstract: Qingxi oilfield, a major area for rolling exploration and development, accounts for 56 percent of the total annual production of Yumen Oilfield Company. Long-5 block, a major oil producing region, is a relatively independent and deeply fractured conglomerate reservoir with bottom water.Up to now, there are 3 wells which yields over 100 t/d of oil have been watered-out seriously for bottom-water breakthrough, threatening the normal development of this field. This paper makes a preliminary investigation of the hydrody namicsystem, water-invaded mechanism and watered-out controlling factors, based on material balance equation integrated with field productiondata. It is pointed out that the bottom water invades into payzones mainly along high-angle and high-permeability fractures; the free-waterrecovery phase is primarily subjected to vertical permeability and depth of fractural extension, which provide realistic basis for stable oilproduction and water control in future.

Key words: Yumen, Qingxi oilfield, fractured reservoir, bottom-water, water