23 July 1994 For help in preparation of this article, thanks to John Boellstorf, Craig Jarchow, Susan Nissen and Gary Marny, Amoco Production Company Research, Tulsa, Okla- homa, USA; Bobbie Ireland, Frank Marrone, Jorgen Ras- mussen and Julie Rennie, GeoQuest, Houston, Texas, USA; Joe Kelly and Rich Lozier, Geco-Prakla, Stavanger, Norway; Paul Ware, Unocal, Houston, Texas; Robert Withers, ARCO, Plano, Texas. Charisma, CPS-3, DepthMap, GeoCube, GeoViz, IES (Integrated Exploration System), IESX, RM (Reservoir Modeling) and SurfaceSlice are marks of Schlumberger. 1. For a data processing review see: Boreham D, Kingston J, Shaw P and van Zeelst J: “3D Marine Seis- mic Data Processing,” Oilfield Review 3 no. 1 (Jan- uary 1991): 41-55. 2. SEG-Y is a digital tape format for data exchange speci- fied by the Society of Exploration Geophysicists. 3. The IES and IESX interpretation systems store 32-, 16- or 8-bit format. The Charisma system stores 16- or 8-bit format. Geophysical Interpretation: From Bits and Bytes to the Big Picture Workstations transport the seismic interpreter into a three-dimensional world, providing new ways to track and visualize reservoir geophysical data. This article describes methods and tools that help interpreters make the most of their time and data to create a likeness of the reservoir that can guide drilling and production decisions. Huw James Mark Tellez Houston, Texas, USA Gabi Schaetzlein Mexico City, Mexico Tracy Stark Exxon Production Research Houston, Texas, USA Well logs measure reservoir properties at intervals of a few inches, providing a high density of information mostly in the vertical direction. But the volume of reservoir sam- pled by logs represents only one part in bil- lions. Seismic data, on the other hand, cover the overwhelming majority of reser- voir volume but at lower vertical resolution. A processed three-dimensional (3D) seismic survey may contain a billion data points sampling a couple of trillion m 3 , and some surveys are 10 times bigger. 1 The geophysi- cal interpreter must handle this massive amount of information quickly and produce a clear 3D picture of the reservoir that can guide reservoir management decisions. In the overall seismic scheme, interpreta- tion builds upon the preceding work of acquisition and processing. Fast new ways to simultaneously visualize and interpret in three dimensions are changing how inter- preters interact with geophysical data. Seis- mic interpretation packages band together a collection of tools designed to simplify seis- mic interpretation and smooth the road from input to output. GeoQuest’s seismic inter- pretation tools—Charisma, IES Integrated Exploration System and IESX systems—offer a variety of levels of user-friendliness and sophistication. These packages complete the process in roughly four steps—data loading, interpretation, time-to-depth conversion, and map output. This article takes a look at how they help the geophysical interpreter harness a seismic workstation filled with a billion data points—and make it fun. Getting Data in the Right Place By the time 3D data arrive at the interpreta- tion workstation, they have already under- gone numerous quality control checks, and are ready to be loaded. The objective in data loading is to ensure that as much of the available data as possible is loaded onto the computer, and that these data points are correctly positioned. Data loading continues to be simplified by software advances. Fitting all the data onto the computer has been difficult because disk space has been expensive. To work around the problem, most data loading routines convert seismic traces from SEG-Y format to a compressed workstation format. 2 This compression can be perilous, because it reduces dynamic range of the trace data. SEG-Y data are usu- ally represented in 32-bit floating point for- mat, which allows a range of +/ _ 10 37 . Data in 16-bit format have a range of +/ _ 32,768, while 8-bit format has a range of +/ _ 128. 3 Converting data from 32-bit to 8-bit reduces computer storage requirements by a factor of four, but also reduces dynamic range. Reducing dynamic range may negate much of the care and money that went into acqui- sition and processing of the seismic data. Although the dynamic range of compressed data is usually more than the human eye can perceive, computer-driven interpretation can