February, 1999 HGS Meetings Calendar

February, 1999HGS Meetings

HGS Dinner Meeting w/HAPL
Loma Vieja Field: Structural Geology and Related Velocity Fault Shadow in the Upper Wilcox (Fandango) in S. Texas

Authors: James C. Meyerhoff and Rion Braddock, Samedan Oil CorporationDate: Monday Feb. 8, 1999 Place: Westchase Hilton, 9999 Westheimer Time: 5:30 Social 6:30 Dinner

Abstract: A new Upper Wilcox (Fandango) field discovery was made at Loma Vieja field in 1989 in Zapata County, Texas. Production from the field to date is 44.1 BCF from numerous Fandango sands that trend from Bob West field northward to E. Seven Sisters field.
The principal trapping mechanism for Loma Vieja field is a high side closure against a very large down-to-the-coast fault. The fault trends across Zapata County through Escobas field, which is immediately updip to Fandango field, northward to NE Thompsonville field in northwest Jim Hogg and southeast Webb counties.
The large down-to-the-coast fault that creates the trap for the field has a definitive velocity shadow resulting in a significant time sag on conventional migrated seismic data. Expansion of Weches, Queen City, and Reklaw shales on the downthrown side of the fault causes major changes in the average and interval velocities across the trapping fault at Loma Vieja field. Seismic data and time structure maps over the field have southeast dip toward the fault (Fig. 1) where actual dip as measured from well log correlations and dipmeter data is northwest away from the fault. Figure 2 is a depth structure map that is significantly different structurally from the time structure map.
Although the field was discovered with 2D seismic data, 3D seismic data confirmed the presence of a velocity gradient across the field and reduced structural risk during continued drilling in the field. However, structural complexities in the geologic section above the Fandango sands have a major impact in the velocity regime across the field. To reduce risk in drilling wells, it is crucial for the explorationist to understand the effects of velocity in a 3-dimensional domain by considering all structural features, as well as stratigraphic bodies, that may have any effect on the ray paths and velocity of seismic energy.
Biographical Sketch:
Jim Meyerhoff is a geophysicist for Samedan Oil Corporation working the Vicksburg, Yegua, Queen City, and Wilcox trends in South Texas. Prior to his 3-year tenure at Samedan, Jim worked 12 years for Diamond Shamrock — Maxus Exploration Company and four years at Amoco Production. He has worked various Gulf Coast trends in Texas, Louisiana, Mississippi, Alabama, and Florida throughout most of his career and has done international work in Argentina, Bolivia, and Peru. He received a B.S. in mathematics in 1978 and an M.S. in geology in 1983, both from Baylor University.

HGS Environmental / Engineering Section Dinner Meeting
"Location and Depth Determination of Buried Ferro-Magnetic bodies in Environmental Site Assessments Using Euler''s Homogeneity Equation"

Author: Mustafa Saribudak, Environmental Geophysics, Inc.Date: February 10, 1999 Place: Jalapeno''s - 2702 Kirby (at Westheimer) Time: 6:00 - 7:00 PM - Dinner; 7:00 - 8:30 PM Lecture, Career Opportunities, and NetworkingCost: $16.00 per person for a full dinner including tip. Dinner is optional.

Abstract:
Geoscientists apply magnetic and gravity data to determine the depth to the top of the geologic features that produce observed anomalies. For hydrocarbon exploration, this is usually equivalent to determining thickness of the sedimentary section. For minerals exploration, depth estimates help locate geologic structures that produce a magnetic or gravity anomaly.
Since the application of Euler''s homogeneity equation by Thomas (1982) and Red et al (1990), it became clear that the location and depth determination of buried ferro-metallic bodies could be achieved if the object''s delineation could be based on Euler''s relationship. The conventional technique required manual and/or computer-assisted interpretation procedures that were time consuming and, as such, expensive. The results were always dependent on the geophysicist''s capabilities.
Euler''s homogeneity relationship offers a quasi-automated way to derive plan location and depth estimates of buried objects from a gridded potential data set (magnetic or gravity). The equation relates the potential field and its gradient components to the location of the source, with the degree of homogeneity expressed as structural index, SI (Thompson, 1982). Structural index is a measure of the rate of change of the field versus distance from the source (fall off rate) and is directly related to the source of the observed magnetic anomalies. The technique, called Euler deconvolution, is advantageous over the conventional depth interpretation methods and can be directly applied to large grid data sets. It reduces interpretation time significantly.
The Euler deconvolution method has been applied to data collected over four sites (three magnetic and one gravity). Objects buried at the sites were drums, pipes, and underground storage tanks. Analyses of the data sets have provided characteristic Euler deconvolution signatures and structural indices associated with ferro-metallic features. The solutions obtained indicate the ability to quickly and accurately map the location and depth of buried ferro-metallic objects from gridded potential survey data.
Biographical Sketch
Mustafa Saribudak is a principal of Environmental Geophysics, 9406 Palm Shores Drive, Spring, TX 77379. He received a master''s degree in geology and a doctorate in geophysics from Istanbul Technical University, Turkey. He came to the University of Houston in 1989 to work on a project funded by the National Science Foundation. Between 1990 and 1993, he worked for Tierra Environmental and pioneered the application of geophysical methods to environmental problems. Mustafa founded Environmental Geophysics in 1994 to provide near-surface geophysical services for the engineering, environmental, oil and gas industries, and real estate developers. During the last five years he has conducted geophysical surveys at more than 100 sites in the U.S. and Central America. He has published broadly in geophysical and environmental journals.

International Dinner Meeting
Post-Rift Hydrocarbon Systems, Greater Amazon Mouth, Brazil: Transition from Shelf to Basin and Source Distribution Controls

By David M. Advocate, Steven W. Young, Arthur H. Ross, Thomas P. Buerkert, Exxon Exploration Company; Jack E. Neal, Keith I. Mahon, Exxon Production Research Company Authors: By David M. Advocate, Steven W. Young, Arthur H. Ross, Thomas P. Buerkert, Exxon Exploration Company; Jack E. Neal, Keith I. Mahon, Exxon Production Research Company Date: Monday Feb. 16, 1999 Place: Westchase Hilton, 9999 Westheimer Time: 5:30 Social 6:30 Dinner

Abstract:
Three post-rift marine petroleum systems in the Amazon mouth are characterized, with maturation, migration, and Neogene reservoir distribution controlled by rapid deposition related to Andean tectonics. Two of the potential hydrocarbon source intervals (Upper Cretaceous and Paleogene) are present on the shelf and upper rise, but their basinward extension is only inferred (Fig. 1). Extrapolation of potential sources from the shelf into the basin requires an understanding of the controls on distribution and preservation of organic matter. Amaz