On the Use of PEBI Grids in the Numerical Simulations of Two-Phase Flows in Fractured Horizontal Wells

摘要

The accuracy of numerical simulation of a two-phase (oil and water) flow in a fractured horizontal well depends greatly upon the types of grids used in the computation. Cartesian grids have been widely used in recent years, but they have some disadvantages in describing complex structural wells, such as fractured horizontal wells. For example, Cartesian grids are not efficient in describing the main wellbores and the fractures of fractured horizontal wells, and the results can frequently suffer from grid orientation effects, even though a grid-refinement is often introduced to enhance the adaptability of a Cartesian grid. The PEBI (Perpendicular Bisector) grid is defined as a region which is closer to its grid point than any other grid points of the space, and it is locally orthogonal, i.e. the block boundaries are normal to the lines joining the nodes on the two sides of the boundary. The PEBI grid is more flexible than a Cartesian grid and it can be constructed according to the orientation of the wellbores and the fractures, which feature is very important to simulate the multi-phase flow near the fractured horizontal wells. Moreover, the characteristic of PEBI grid allows for a fine-scale gridding near the wellbores and the fractures. A hybrid PEBI grid (a combination of Cartesian grid and a hexagonal grid) is presented in this paper. A Cartesian grid and hexagonal grid are used to simulate the region of the fractured horizontal wells, and the region of the reservoir, respectively. It is found that the more flexible aspects of the hybrid PEBI grid system allow for a better grid construction near the fractured horizontal wells. The fractures as well as the wellbores are better simulated in this grid system. An example of a five-spot well pattern of a fractured horizontal well is presented in this paper.