Perforated completions have become a standard process of well completions, where the wellbore is connected to the reservoir by perforating the casing/cement wall and the formation to provide flow paths through which formation fluids can enter the wellbore. This flow path (defined by the perforation tunnel) is usually encompassed by drilling damage, crushed and the native formation zones, which influence the ability of the tunnel to flow hydrocarbons into the wellbore. Most numerical models assume the tunnel to be uniformly cylindrical in shape due to limited information available from downhole conditions as well as complexity involved in modeling detailed geometries. Such an assumption leads to discrepancies between computed and true flow efficiency and productivity of the tunnel.
In this paper, our objective is to develop a novel production flow model combining the capabilities of a perforation flow laboratory, computerized tomography (CT scan) and Computational Fluid Dynamics (CFD). As a first step, the complex geometry of the perforation tunnel (from a typical API RP-19B Section IV experiment) is obtained using a CT-scan. Next, the CT scan images are transformed using image processing software to generate a CAD model. The CAD model is then translated to a CFD model, where the conservation equations of mass, momentum and energy are solved to conduct a full-scale three-dimensional flow simulation around the tunnel. The fluid flow simulations provide details on the fluid velocities, pressures, skin factors and most importantly, the productivity ratio. Additionally, we have developed an analytical model that is aimed towards complementing the CFD model by computing the static/dynamic underbalance effects in conjunction with the tunnel's inflow characteristics.
The computational approach presented in this study is a first step towards leveraging digital rock physics to characterize the efficiency of a perforated completion. The study provides understanding into the steady/transient flow dynamics around realistic perforation tunnel geometries along with providing the framework for a completion engineer to better understand the design and optimization of a perforating job. Subsequently, it provides insight into devising the overall completion strategy for enhanced reservoir productivity.