Practical Semianalytical Models for Pressure-Transient Analysis of Carbonate Reservoirs with Complex Fracture and Cave Distributions

Fracture-caved oil carbonate reservoirs are the focus of the exploration and development of carbonate reservoirs in China. However, the connections and distributions of well, fracture, and cave create a significant heterogeneity in the fracture-caved carbonate oil reservoirs, and the fluid flow behavior in the complex fracture-caved porous media is extremely hard to characterize. In this work, a series of simple, efficient, and practically applicable pressure-transient models exhibiting complex distributions are established with linear flow in the fracture zones and storage flow in the caves. The solutions for fracture-caved models are obtained by the Laplace transformation, Duhamel principle, and Stehfest numerical inversion. Flow behavior analysis shows that the pressure-transient analysis model for fracture-caved reservoirs may develop four flow regimes: wellbore storage flow, fracture-zone linear flow, cave storage flow, and transition flow. The results indicate that the start and duration of the linear flow are affected by the conductivity and length of the fracture zone, respectively. A larger cave volume causes a deeper and wider V-shaped segment on the pressure derivative curve. The semianalytical pressure-transient models are applied to field cases in the Shunbei block. The key physical parameters (i.e., fracture length, fracture conductivity, and cave volume) can be estimated by matching with the actual pressure and production data.