New Techniques for the Generation of Subsurface Models
Authors: Bayer E. , Dooley K. 
Published: October 2008

Abstract
This paper will investigate new techniques of using interactive three dimensional graphics design software to generate subsurface models. This application uses object-oriented software technology that was originally developed for solids modeling design, The graphic representation of all the objects is based on NURBS (Non-Uniform Rational B-splines) math which allows each graphic element to be represented by the same basic mathematical expression. Solid and surface models created using these software techniques provide the geoscientist the capability to use Boolean logic to find intersection and volumes of complex geologic structures.

Introduction
In today's exploration environment, It is essential for the geoscientist to utilize all available data to generate the most accurate model possible of the subsurface geology. The more accurate the model, the more informed the decision maker Is In choosing between costly alternatives. Advances In computer technology have allowed the user to create three-dimensional displays for visualization of the model. Visualization alone, albeit a very powerful tool, does not allow the model to be modified, manipulated and analyzed to its fullest. A new technique, which has proven successful in the automotive and aerospace Industries, can now also be applied to subsurface data to create a dynamic three-dimensional model.
Traditional methods for gridding and contouring subsurface data to create a model are acceptable for many geologic structures which do not have a high degree of geometric complexity. However, when geologic and therefore geometric complexity Increase in areas such as salt domes or sand channels, the situation arises where there may be multiple z-values for a given x,y coordinate. In such cases it Is difficult for traditional methodology to describe an accurate model. When this occurs the geological structure has to be separated Into three parts or until each z value has Its own x,y. In addition, the Introduction of faults and/or boreholes (wells) increases the geometric complexity of the model. An approach which will allow the manipulation of the subsurface structure, as well as handle its geometric complexities, will allow the geoprofessIonal to more accurately define thesubsurface model. This paper proposes such an approach with examples which confirm Its validity for the cases studied.
The techniques used by professionals In many other industries to accurately define and manipulate three dimensional models is based upon advances In solids modeling. Recently, three key advances in softwaretechnology allow these techniques to be applied. The first is the ability to work in a three-dimensional graphics domain. The second Is the approach used tomathematically define the geometry of the model. This approach takes advantage of math libraries based upon NURBS (Non-Uniform Rational B-Spllnes), and their ability to represent multiple geometric shapes. The third advance is in the area of object-oriented software, a programming technique used to describe real-world objects and their relationships with each other. Thecombination of three dimensional graphics, NURBS, andobject-oriented programming techniques provides a powerful tool to describe the geometry of virtually any solid body.