Horizontal simulation grids as alternative to structure-based grids for thin oil-zone problems: a comparison study on a Troll segment

Abstract

The layering in reservoir simulation grids is often based on the geology, e.g., structure tops. In this paper we investigate the alternative of using horizontal layers, where the link to the geology model is by the representation of the petrophysics alone. The obvious drawback is the failure to honor the structure in the grid geometry. On the other hand, a horizontal grid will honor the initial fluid contacts perfectly, and horizontal wells can also be accurately represented. Both these issues are vital in thin oil-zone problems, where horizontal grids may hence be a viable alternative. To investigate this question, a number of equivalent simulation models were built for a segment of the Troll Field, both geology-based and horizontal, and various combinations of these. In the paper, it is demonstrated that the horizontal grid was able to capture the essentials of fluid flow with the same degree of accuracy as the geology-based grid, and near-well flow was considerably more accurate. For grids of comparable resolution, more reliable results were obtained by a horizontal grid than a geo-grid. A geo-grid with local grid refinement and a horizontal grid produced almost identical results, but the ratio of computing times was almost 20 in favor of the horizontal grid. In the one-phase regions of the reservoir, relatively coarse cells can be used without significant loss of accuracy.

Closed-Loop Feedback Control for Production Optimization of Intelligent Wells Under Uncertainty

“…However, a number of reservoir imaging technologies have been proposed or implemented that may allow water and/or gas fronts to be monitored at some distance from the well; these include surface and downhole seismic monitoring (Blonk et al 2000); electrical methods, including measurements of resistivity and spontaneous potential (e.g. Bryant et al 2002;Saunders et al 2006;Jackson et al 2011;2012), and downhole measurements of the gravitational field (e.g. Hadj-Sassi and Donadille 2010).…”

“…The total oil column thickness is 15m. We adopted a 'hybrid' gridding approach, consistent with previous studies, to capture the vertical movement of the initial horizontal gas-oil and oil-water interfaces towards the horizontal production well, whilst still honoring the morphology of geologic features (Vinje et al 2011;Pettersen 2012). In the gas cap and aquifer, the vertical layering is stratigraphic, conforming to the surfaces which delimit parasequence and facies boundaries, with a single layer for each M-and C-sand (Figures 3.3).…”