Illinois Basin Point Bars and Channel Fills: 3D Models from Legacy Mapping
This research investigates conversion of 2D legacy subsurface mapping of Illinois Basin oil fields to 3D geometric models. The term legacy mapping refers to existing mapping showing the results of previous drilling and interpretation that is available only in hard-copy format. This research addressed three questions: First, what workflows support rapid and accurate legacy map conversion? Second, what geometry is typical of subsurface point bars and channel fills? And third, how can point bars and channel fills be accurately modeled?
Three Illinois Basin oil fields with available legacy mapping served as study areas. To examine conversion workflows, each field was digitized using a defined coordinate system and specific digitizing protocols. The protocols identified mistakes in data input and model calibration and located errors in digitizing. Project output was a standard suite of map and data products. This provided a consistent format and avoided time needed for unique map design.
To examine point bar and channel fill geometry, the 3D surface models developed in the standard mapping suite were manipulated to show each field with different tilts, rotations, and projections. Point bars were relatively easy to identify from their subsurface geometry and by comparison to surface analogs. Channel fills were more complex, perhaps due to deformation and compaction.
Accurate 3D modeling of point bars and channel fills required careful model manipulation. A default 45 degree rotation and 30 degree tilt were initially used, but changes generally were needed to clearly show subsurface shape. Use of draped structural contours or isopachs quantified size and slope, and map colors were selected to match strata.
It was concluded that the conversion process employed facilitated rapid conversion and 3D visualization of legacy maps. Digitizing protocols ensured data quality, and standard map design decreased conversion time. Conversion efficiency depended heavily on understanding process workflows and on early identification of mistakes. Experience with the 3D models tilts, rotations, and projections provided the opportunity for personnel to develop a mental reference for the subsurface signature of point bars and channel fills. Finally, it was concluded that successful legacy map conversion requires not only sound graphics ability but an intimate understanding of geology, geophysics, and geomorphology if maximum benefit is to be taken from the effort.
AAPG Search and Discovery Article #90154©2012 AAPG Eastern Section Meeting, Cleveland, Ohio, 22-26 September 2012