Numerical Rate Transient Analysis (RTA) and production forecast models for unconventional reservoirs usually rely on single well analysis, with relatively simple assumptions regarding the geometry of the hydraulic fractures (identical and uniformly distributed). In this paper, we describe a transient numerical model for deviated well trajectories intercepting a complex distribution of fractures. The model can incorporate multiple wells and account for various modes of interference, including fracture hits. This approach enables the initialization and calibration of new types of transient models, which are directly compatible with the results of advanced completion diagnostics.
In the proposed approach, the near-well region is discretized with a fully automated unstructured grid, rigorously constrained to the fractures. The algorithm accounts for independent fracture properties (ex: azimuth, half length, thickness, offset…). Hydraulic fractures originating from a given well can intercept one or several other wellbores or existing fractures. Complex transient interference modes between fractures, as well as fracture-driven communications between wells can then be analyzed. The geometrical grid resulting from complex fracture distributions may contain a very large number of cells. To overcome this issue, a new "aggregation" scheme is proposed, which reduces the size of the computational system and considerably accelerates the calculations.
The model is validated in single and multiwell configurations, with different fracture distributions and interference modes. The impact of wells interference on the RTA interpretation and the production forecast is accounted for. This model is also tested for multiphase simulation - including phase changes. The proposed aggregation scheme results in a reduction of the computational system size by up to 2 orders of magnitude, leading to much faster direct simulations. Comparisons of the log-log derivatives show that the different flow regimes are accurately captured with the new scheme, even at very early-time. Because the aggregation scheme proceeds on zones with similar pressure behavior, there is no need for pseudo-relative permeability derivations, and the results remain accurate for multiphase flow and pressure-dependent petrophysical properties.
This model provides a new solution for transient, nonlinear numerical simulation of fractured horizontal wells with complex geometries. The model can be applied to numerical Rate or Pressure Transient Analysis in unconventional reservoirs, without being limited to a geometrical element of symmetry.
