Bureau of Economic Geology, The University of Texas at Austin (www.beg.utexas.edu).
Keynote Address, Rocky Mountain Association of Geologists, Denver, Colorado, February 28, 2003
Lasers Light the Way: 3-D Outcrops Will Revolutionize Subsurface Modeling
Scott W. Tinker,
Jerome A. Bellian, Charles Kerans, and David C. Jennette
Throughout the 1960's and 1970's modern depositional system studies combined with outcrop studies led to advanced understanding of depositional systems in the subsurface. However, 2-D studies of oil fields consisted mainly of linking well log cross sections and qualitative core descriptions between wells and constructing isopach and structure maps to identify sand trends, calculate volumetrics, and help design field management strategies. Two-dimensional seismic data resolution was too poor to support development geology, and stratigraphic understanding as we know it today was too poorly understood to help construct adequate reservoir architecture frameworks.
In the early 1980's, there was a growing need for secondary and tertiary recovery processes in many of the larger U.S. fields. Development geology became known as reservoir geology, and multidisciplinary approaches-integrated teams of engineers and geoscientists-were beginning to be recognized for the value they added to the corporate bottom line. Seismic stratigraphy was becoming mainstream for exploration-scale studies but for the most part was not yet being applied at the field scale, and reservoir work was still done using paper logs, seismic sections, and hand-drawn maps.
In the late 1980's and 1990's-with the explosion of computer technology, digital petrophysics, 3-D modeling software tools, and 3-D seismic data-rock, log, seismic, and production data began to be fully integrated into digital reservoir models, visualized in color and animated 3-D space. Advanced outcrop studies were being conducted to define the nuances of high-frequency sequence stratigraphy and to place reservoir parameters into a proper stratigraphic framework. Lessons from the outcrop were being applied at the reservoir scale to open new levels of reservoir architecture understanding, and complex 3-D models were being scaled up and used in fluid flow simulation.
The decades ahead promise a 4-D world of instrumented fields and real-time data streaming. Advanced recovery processes on producing fields will require an even greater knowledge of the reservoir, and new discoveries will be developed with fewer wells requiring an increased understanding from remote sensing data. Three-dimensional outcrop studies that incorporate land- and air-based laser, radar, electromagnetic, and other remote sensing technology will have a significant impact on subsurface exploration and production success.
Preliminary efforts to collect and incorporate remote sensing data, particularly land-based lidar, into high-frequency outcrop studies are yielding remarkable results. In a matter of days to weeks, high-frequency laser data can be collected and processed for most outcrop settings. The initial product is a 3-D digital elevation model with vertical resolution on the centimeter scale that can be used to (1) visualize topography and plan field work; (2) merge with photographs or other remote sensing data; (3) interpret stratigraphic horizons, joints, faults, macroscale diagenetic processes, and bed-scale sedimentology; (4) drape and interpolate measured section data; (5) calculate first derivative, second derivative, reflection strength, and other derived properties to help characterize such things as lineaments (faults and fractures), solution features, and lithology; and (6) provide the framework for input into 3-D modeling.
Our near-term goal is to use the high-frequency 3-D outcrop models to derive, perhaps for the first time, realistic 3-D synthetic seismic data that can then be used to examine seismic response as a function of frequency; to test a broad range of seismic attribute sensitivities to small changes in lithology, fluid and gas saturation, and porosity and pore type; and to create a portfolio of analogs for siliciclastic and carbonate outcrop settings worldwide. Let the rock revival begin!