Abstract: Based on the definition of production decline rate, the multifactor analytical model for composite decline rate is developed, which discusses affecting factors such as the startup well number, water cut, producing fluid thickness, pressure, relative production index, well spacing density, skin factor, etc.Integrated with the correlation between natural and composite decline rates as well as the characteristic of production testing data, the model for natural decline rate is established.The model can be used to analyze accurately the effect of individual interrelated factor on production decline rate, support regulative countermeasures and modify the natural decline rate in an oilfield.The case study indicates that this model is effective in practice and good for popularization.

Key words: waterflood, decline rate, model, application