ĐỊA CHẤT DẦU KHÍ ( PETROLEUM GEOLOGY ) - CHƯƠNG 7 docx

Cross Cross - - section diagrams in section diagrams in 3 3 Dimentions Dimentions Fence Diagrams Fence Diagrams In petroleum exploration, the development of a prospect is a In petroleum exploration, the development of a prospect is a three three - - dimensional problem. One of the drawbacks of cross dimensional problem. One of the drawbacks of cross sections is that they are limited to two dimensions. How can sections is that they are limited to two dimensions. How can we illustrate the three we illustrate the three - - dimensional geology of an area? dimensional geology of an area? The most common type of diagram showing geological The most common type of diagram showing geological relationships in three dimensions is a fence diagram ( relationships in three dimensions is a fence diagram ( Figure Figure ). Fence diagrams consist of a three ). Fence diagrams consist of a three - - dimensional dimensional network of geological cross sections drawn in two network of geological cross sections drawn in two dimensions. The diagram is built on a map base which is dimensions. The diagram is built on a map base which is seen in plan view. seen in plan view. Figure 01 Figure 01 Fence Diagrams Fence Diagrams In constructing a fence diagram, the plane of the map base In constructing a fence diagram, the plane of the map base corresponds to the chosen datum plane, and the well location corresponds to the chosen datum plane, and the well location on the map is taken to be the point where the well intersects on the map is taken to be the point where the well intersects the datum plane. The wells are hung on the datum and then the datum plane. The wells are hung on the datum and then individual cross section panels are filled in, beginning at the individual cross section panels are filled in, beginning at the front of the diagram. front of the diagram. In fence diagrams, one must consider the overall orientation of In fence diagrams, one must consider the overall orientation of the figure, bearing in mind that panels oriented parallel to the the figure, bearing in mind that panels oriented parallel to the viewing direction will appear only as straight lines. Such viewing direction will appear only as straight lines. Such panels are usually omitted from the diagram. If important panels are usually omitted from the diagram. If important panels are not displayed to the best advantage, the viewing panels are not displayed to the best advantage, the viewing direction can be changed so that the features of interest are direction can be changed so that the features of interest are presented in the most effective way. presented in the most effective way. Fence Diagrams Fence Diagrams Front panels sometimes obscure parts of rear panels Front panels sometimes obscure parts of rear panels in fence diagrams. Where two panels overlap, the in fence diagrams. Where two panels overlap, the correlations on the front panel are drawn in with correlations on the front panel are drawn in with solid lines and highlighted with colors, while the solid lines and highlighted with colors, while the correlations on the overlapped part of the rear panel correlations on the overlapped part of the rear panel are simply dashed in. are simply dashed in. When the vertical scale is too large or the spacing of When the vertical scale is too large or the spacing of sections is too close, very large parts of the rear sections is too close, very large parts of the rear panels may be obscured ( panels may be obscured ( Figure 2 Figure 2 ). ). Figure 02 Figure 02 Fence Diagrams Fence Diagrams Usually, this problem can be minimized if the vertical scale Usually, this problem can be minimized if the vertical scale and the panel spacing are carefully chosen. However, it is and the panel spacing are carefully chosen. However, it is not always possible to change the scale or spacing without not always possible to change the scale or spacing without losing important details illustrated by the diagram. In such a losing important details illustrated by the diagram. In such a case, one can construct an isometric projection of the fence case, one can construct an isometric projection of the fence diagram ( diagram ( Figure 4 Figure 4 , o , o nly lines parallel to the North nly lines parallel to the North - - South South and East and East - - West axes are undistorted West axes are undistorted ). ). The map base in an isometric projection is shown as if it The map base in an isometric projection is shown as if it was turned at an angle and tilted toward the viewer. The was turned at an angle and tilted toward the viewer. The conversion is actually a transformation from orthogonal to conversion is actually a transformation from orthogonal to nonorthogonal nonorthogonal axes. A rectangular map base will become a axes. A rectangular map base will become a parallelogram in an isometric projection ( parallelogram in an isometric projection ( Figure 3 Figure 3 and and Figure 4 Figure 4 ). ). • All lines that were parallel to the original horizontal and vertical axes remain parallel to the corresponding new axes, and the scale along these lines also remains unchanged. However, lines which were not parallel to the original axes will be distorted. Points along such lines must be transferred onto the projection by coordinates relative to the new axes. A grid system is helpful in this process. Figure 03 Figure 03 Figure 04 Figure 04 Block Diagrams Block Diagrams • Along with the fence diagram, another type of diagram illustrating three- dimensional geological relationships is a block diagram ( Figure 5). • This type of figure is a two-dimensional representation of a rectangular block. Two intersecting cross sections often form the sides of the block; the top of the block shows either a mapped surface or relief on the uppermost geological boundary shown in the cross sections. The block may be rotated to achieve the most effective viewing angle, and it may be drawn with or without the use of perspective. [...]... (Figure 6 , Figure 7 , and Figure 8) The top of this type of block diagram may be given any degree of tilt toward the viewer Figure 06 Figure 07 Figure 08 • A large amount of tilt emphasizes features on the top surface of the block; a smaller degree of tilt brings out details on the sides of the block Scales along the x, y, and z axes need not be equal • The scale along the sides of the figure (y)... need not be equal • The scale along the sides of the figure (y) is sometimes chosen to be smaller than the scale across the front and back edges (x), thus creating an illusion of perspective • Perspective can be used in constructing block diagrams (Figure 9) Figure 098 In perspective blocks, all parallel lines with a component in the y direction converge to a vanishing point on the horizon Sets of . dimensions is a fence diagram ( relationships in three dimensions is a fence diagram ( Figure Figure ). Fence diagrams consist of a three ). Fence diagrams consist of a three - - dimensional dimensional. projection of the fence diagram ( diagram ( Figure 4 Figure 4 , o , o nly lines parallel to the North nly lines parallel to the North - - South South and East and East - - West axes are undistorted West. to be larger (Figure 6 , Figure 7 , and Figure 8). The top of this type of block diagram may be given any degree of tilt toward the viewer. Figure 06 Figure 06 Figure 07 Figure 07 Figure 08 Figure