This paper uses hyperhybrid grid refinement to study iocal well effects and interwell inteiference in cyclic steam stimulation. The local well effects include a non-Newtonian oil component and visbreaking effects. A bottom water problem is also included. Interwell interference is illustrated with a grid type comparison and a comparison to an analytical pressure interference solution.
It is recommended that (contiguous) hyperhybrid grid refinement be used for analyzing problems where the local well region behaviour is important in the context of a field simulation.
There are only a few published papers that discuss the use of hybrid grids. Hybrid grids consist of combining a radial/cylindrical grid to represent the well with a rectangular grid to represent the remainder of the reservoir. This was proposed first by Akbar el al1 and Mrosovsky and Ridings2. Another treatment of the subject has been made by Pedrosa and Aziz3. Recently, Demetre4 extended the concept to contiguous hyperhybrid grids in steam stimulation simulation. Hybrid grid techniques may be thought of as extensions of the local grid refinement concept. Hybrid grids are used because of the shortcoming of inadequate description of the reservoir conditions by local grid refinement around a wellbore; that is, local grid refinement cannot take advantage of the radial (or nearly radial) flow nature around a wellbore.
This paper uses hyperhybrid grid refinement to study local well effects and interwell interference in cyclic steam stimulation. This is the first model to use hyperhybrid grids in thermal simulation. A hybrid grid is defined as a cylindrical grid system embedded into a single fundamental rectilinear grid block and a hyperhybrid grid is defined as a cylindrical grid system embedded into several contiguous fundamental rectilinear grid blocks. Examples of Canesian, hybrid, and hyperhybrid grids can be found in Figure I, in addition Figure 2 and Figure 3 illustrate contiguous hyperhybrid grids.
The local well effects study examined and compared rectilinear, hybrid and hyperhybrid grids. Non-Newtonian oil viscosity, visbreaking and bottom water cyclic steaming runs were made. The general conclusion was that a hyperhybrid grid design is more appropriate for studying local well effects in the broader context of a field simulation.
The interwell interference study is an extension of the above. The contiguous hyperhybrid grid design can be used to establish a communication path between wells that is direct unlike the zigzag path typical of rectilinear systems. Hyperbybrid grids and rectilinear grids were compared to analytical pressure interference solutions. The hyperhybrid design was found to be more appropriate.
To illustrate the effects of grid design, several runs were made using rectilinear, hybrid and hyperhybrid grids to model a single well. In addition to a base case set of runs, a set of runs where the heavy oil component viscosity behaviour was non-Newtonian and a hyperhybrid grid run with visbreaking were made. Figure 1 illustrates the grids used for all runs in this section.
