Title:3-D Seismic Enhances our 4-D World
Author: Donna S. Anderson
Publication: The Outcrop, February 2004, p. 3
February 27 marks the 10th anniversary of the 3-D seismic symposium for the RMAG. Co-hosted with the DGS (Denver Geophysical Society), the symposium brings together excellent case studies and other technical talks to a multidisciplinary audience. Mulling over the special significance of the upcoming symposium causes me to ask, “ why is 3-D seismic such a huge advance in our industry?” Certainly it brings increased risk reduction via increasingly accurate interpretations of the subsurface. 3-D seismic also creates a platform for visualization, imaging, and modeling that increasingly represents our “real” world.
3-D imaging, visualization, and modeling are hot topics in science and engineering. The medical profession has been heavily involved in 3-D imaging of the human body for nearly 20 years. Medical imaging brings better diagnoses and fosters more intricate solutions. Mechanical and other types of engineering use 3-D models to build and simulate engineering systems in order to affect better design and reliability. Architects and land-use planners use 3-D graphics to portray how buildings will fit into the landscape. Computing science is heavily involved in creating software for these and other applications.
In the petroleum industry, we say that we work in three dimensions in the subsurface (x-y-z dimensions). In reality our work is four-dimensional: x-y-z and time. The time dimension is multi-scalar: human versus geologic time. At the human time scale we worry about production rates and the economic life of a field. However, the subsurface always involves some function of geologic time: migration of hydrocarbons, deposition of reservoir rocks, building up of rock layers, diagenesis, and structural deformation. Hence, geologic time is implicit in everything we do, including the interpretation of 3-D seismic volumes.
To “see below the ground” we use a variety of tools: geophysical tools, such as seismic and well logs, which remotely image rocks and fluids via physical properties; geologic tools that include outcrops showing rock geometries; and petroleum engineering tools, such as fluid/pressure behavior through time at wellheads. What gives ultimate meaning to these tools is integration of the geology and rock-fluid physics and chemistry behind them. 3-D seismic has become a basic part of the foundation for this integration. It was the first tool that gave us a “picture” of the subsurface beyond 2-D x-y and x-z slices, or conventional maps and cross-sections, respectively. 3-D seismic forced us to truly work in three dimensions. It also gave new insights to our 4-D world by imaging over time to detect fluid/pressure changes and by providing higher resolution images of the subsurface. Finally, with the revolution in personal computing power, our enhanced 4-D world became accessible to our fingertips.