In conducting performance analysis, prorating production, injection and working put development plan, decline rate is often used to analyze the change of oil production and forecast the future tendency of oil area, oilfield, unit, as well as well group and single well. Therefor the concept of decline rate is very important. There are rules made by CNPC as to the calculation method of decline rate, but actually different methods are applied to different oil fields. These decline rates calculated by different methods reflect the actual production decline of each oil field and are of different implications. If they are quoted and compared as a same index, there must be some problems. Based on decline theory, this paper further deepens the knowledge of the expressions of different decline rates is further deepened, the relationship and differences among different calculation methods at different decline rules and finally derives some relations among annual oil production decline rate, annual productivity decline rate and monthly decline rate are studied. With these relations and their decline regulation, decline rate could be forecasted rapidly and easily so as to confirm the arrangement of monthly production of each year and development program, guide the management of oil field development and production.
