The Production Decline Laws of Water Drive Reservoirs Considering Variable Liquid Production

Previous studies have shown that a relationship between water drive curve method and the Arps decline method exists in constant liquid production. However, liquid production will gradually increase with the increase of water cut, and it is difficult to accommodate the condition of constant liquid production during oilfield development. The study on the production decline laws under variable liquid production was carried out. Based on the general formula of production decline rate under variable liquid production, the researchers derived a formula of production decline rate under variable liquid production for four kinds of commonly used water drive curves. Then a production calculation formula for the type B and type C water drive curves considering variable liquid production was established by aligning and analyzing the practical results of oilfield production. In the analysis, it was found that the production calculation formula of constant liquid production is a special case of that of variable liquid production. If production complies with the characteristics of type B water drive curve, the productivity of oilfield will remain stable when the oil production change rate is equal to the production decline rate as primarily forecasted. The research results showed that to maintain oil production of an oilfield by increasing liquid production will lead to an exponential increase in liquid production. Therefore, a reasonable working system should be formulated in combination with the actual situation in the process of oilfield development. Obtaining stable oil production from very high liquid production is not recommended.