--> Implications of Cell Dimensions on Dipping Bed Continuity in Flat-Layered Geomodels
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Implications of Cell Dimensions on Dipping Previous HitBedNext Hit Continuity in Flat-Layered Geomodels

Abstract

There is a mathematical relationship between cell width/length/height, Previous HitbedNext Hit thickness, Previous HitbedNext Hit dip angle, and the degree of continuity that a horizontally-layered model framework can preserve. With very small cells, the continuity of beds at any dip angle can be approximately represented in a geologic model. However, as cell sizes get larger, Previous HitbedNext Hit continuity cannot be accurately represented by flat model layers. At certain critical dip angles and Previous HitbedNext Hit thickness, cells of a given size will fail to maintain continuity. Two types of Previous HitbedNext Hit continuity are important to preserve in geologic models destined to be used in flow simulation: flow barriers and flow conduits. For flow barriers, edge-to-edge continuity must be maintained to prevent flow-through in simulations. If the Previous HitbedNext Hit dip exceeds the threshold for a given cell size and Previous HitbedNext Hit thickness, gaps will form between the barrier cells, allowing flow-through. A simple trigonometric relationship exists between the Previous HitbedNext Hit thickness, dip angle, and the maximum allowed cell width to maintain edge-to-edge continuity of barrier beds: 1) MaxWidth = BedThickness / TAN(BedDip) For flow conduits, face-to-face continuity must be maintained to allow flow within the Previous HitbedNext Hit in simulation. However, the degree of face-to-face contact between adjacent cells is necessarily degraded as Previous HitbedNext Hit dips increase in a flat-layered framework. Beds with zero dip have 100% face to face contact, but as dip angles increase, the amount of elevation offset at cell edges causes fewer and fewer layers to communicate, until at a critical angle, only non-flowing corner-to-corner continuity exists. Beyond that critical angle, conduit beds do not touch and therefore do not flow in simulation. The algorithm for approximating the fraction of face-to-face contact of conduit beds is: 2) VertOffset = (CellWidth*TAN(RADIANS(BedDip))) 3) MinLayers = ROUNDDOWN( BedThickness / LayerThickness, 0) 4) Fraction = MAX(0, IF( OR( BedThickness / 2 < LayerThickness, (CellWidth * TAN(RADIANS(BedDip)) >= BedThickness)), 0, 1- ROUNDUP((VertOffset / LayerThickness), 0) / MinLayers)) These algorithms can be used to optimize cell sizes to a combination of Previous HitbedNext Hit thickness and Previous HitbedNext Hit dip. However, to avoid the continuity problem entirely, geologic models should be built with model layers inclined parallel to the beds. With Previous HitbedNext Hit-parallel layering, the occurrence of stair-step Previous HitbedTop boundaries will be kept to a minimum.