Production Performance Of Commingled Gas Reservoirs In Sebei Gasfield

It’s much more complex in exploring commingled gas reservoirs than the single one, and because of vertical heterogeneity,actual output and its decline rate may vary greatly from proration. Vertical heterogeneity is mainly on reservoirs’permeability, reserve volume and boundary properties. Therefore, we need a multi-layered gas reservoir model considering each layer’s permeability, thickness, porosity, discharge radius, boundary property and intial pressure. Two kinds of inner boundary conditions, constant bottom hole pressure and constant well head rate are also optional in our model.In order to solve the model, we use Laplace transformation, and then we get the solution in Laplace space using Duhamel superposition principle and Bessel function. We also need Stefest numerical method to change the solution to real space. There’s still one problem, if the inner boundary condition is constant well head rate, the well can’t maintain the rate when buttom hole pressure is a low value. In this case, we change the inner boundary condition to constant buttom hole pressure, and the production characteristics of peseud stable state can help us to get the solution.By the method mentioned above, we’ll get single layer’s production, average pressure and multi-layer’s average pressure, then material balance curve can be obtained. Observing the tend of single layer’s production curve while the inner boundary condition is constant well head rate, we’ll find out that late-production approach to a constant value, and this value related to single layer’s reserve shows the characteristics of pseud stable state. This characteristics can be certificated by the variation of the pseudopressure. While the inner boundary condition is constant bottom hole pressure, single layer’s production shows not-interfering situation, and total production’s decreasing index is great in early time and tends to a constant value in late time. Commingled reservoirs’material balance curve also shows difference to the single one’s because of the vertical heterogeneity. After the previous straight line, the curve begins to sag. The reason of sagging is the production’decreasing index is variable; When single layer’s production is close to zero, the curve become smooth, that’s because total production is single layer’s and the pressure is average. Through the research to material balance curve, there’s new idea to forecast dynamic reserve and analyze the state of mining condition.