"About Geophysics, Geology, and Regional Hydrocarbon Systems A Discussion that Contrasts the Gulf of Mexico with Northeastern Venezuela"
Abstract:
Comparing and contrasting the Gulf of Mexico with northeastern Venezuela illustrates the importance of regional geology, based on the integration of old-fashioned surface geology with modern subsurface geology and interpretation of regional seismic reflection profiles.
The Gulf of Mexico and northern Venezuela both formed as Mesozoic passive margins connected with the North Atlantic and were initiated by a Late Triassic–Jurassic rifting phase followed by the deposition of widespread evaporites limited to the Gulf of Mexico. By Mid–Cretaceous times, the whole area formed part of the Tethys carbonate passive margin. Important hydrocarbon source bed intervals were formed during the Jurassic and Cretaceous in the Gulf of Mexico. In Venezuela, however, the main source bed is the Upper Cretaceous La Luna formation, which is less prominent in the Gulf of Mexico.
Beginning with the Senonian, the Gulf of Mexico and Venezuela followed widely different plate tectonic evolution, leading to a great variety of hydrocarbon systems and traps. Thus, the northern Gulf of Mexico developed into one of the world's largest petroliferous siliciclastic depocenters, characterized by complex growth faulting and some of the most spectacular salt tectonics ever observed. However, the western Gulf of Mexico was incorporated into the Paleogene and Neogene folded belt of the Sierra Madre in the north, the Neogene folded belt of the Sierra de Chiapas–Campeche in the south, and the uplift of the Mexican plateau. Both fold belts are conjugate to the east-dipping subduction zone that was active on Mexico's west coast.
Northern Venezuela developed in an overall transpressional setting related to relative eastward indentation of the Caribbean plate. This process led to the basement-involved compressional Neogene uplift of the Western Andes and the décollement folded belts of the Cordillera de la Costa and the Serrania del Interior. An eastward migrating Upper Cretaceous–Paleogene–Neogene foredeep was associated with the relative eastward displacement of the Caribbean plate. Toward the Orinoco delta, the foredeep merged with the preserved Atlantic margin. The northern Venezuela offshore is characterized by extensive transtensional faulting related to complex strain partitioning associated with the Bocono-El Pilar strike-slip fault system, and the boundary zone of the Caribbean and South American plates.
A comparison of the Gulf of Mexico with northern Venezuela illustrates that model earth systems of the future will have to link phenomena that occur at widely differing scales; this can be achieved with the help of integrated regional geological studies. In this context, the role of regional 2D and 3D reflection seismic surveys are the cornerstones for an in-depth understanding of hydrocarbon systems.
This brings us to the important role of 3D regional seismic surveys. I believe that the future of regional tectonics be completely recast when regional seismic 3D surveys become available for study to a larger community. Exposure to industry 3D data sets in several areas of the world leads me to conclude that discordantly superposed tectonic levels are ubiquitous. Typically, higher, relatively brittle levels are separated from discordant lower brittle levels by overall more ductile levels. Of course, in some cases, unconformities separate different tectonic domains, but more frequently, the discordant configuration of different levels appears to be due to vertical strain partitioning and/or the influence of paleostructures. In the long run, we are going to have to parlay seismic attributes into relative ductilities that respond to suites of different coeval stress orientations for each layer.
Furthermore, there is also a great need for (1) regional and supraregional time slices (i.e., composited mosaics of adjacent 3D surveys) and (2) regional seismic stratigraphic correlation sections connecting the structurally least-disturbed portions of the sedimentary basins (and if possible, tied to deep wells). All these are necessary to ensure common standards and a common language among, and often between interacting, competitors.?
The availability of a practically unlimited number of time slices to great depths, often in excess of four or five kilometers, amounts to the equivalent of an unlimited number of geological maps, which need to be interpreted as maps. Thus, the ability to read geological maps is of critical importance. Unfortunately, I find the map-reading ability of graduate students often deficient, and wish our schools would do a better job in this area. Thus, in the training of students, the understanding of scientific principles must be complemented with renewed training and versatility in geologic map reading if we are ever going to fully exploit 3D seismic data sets.
Also, in the same context, seismic contractors will need to explore more aggressively joint projects with researchers in academia. Many operators in industry, due to their evident inability to forecast oil price fluctuations, are periodically economically overstaffed while remaining technically understaffed. Consequently, they are unable to fully exploit the scientific message—and with it a great part of the new play potential—contained in these huge but under-interpreted 3D seismic data banks. The will to cooperate with academia certainly exists on the industry side, but, unfortunately, a reasonable understanding of the industry's perspective and constraints is often lacking in academic institutions.
There is much talk about teamwork today, as if teamwork did not exist before. There is also much talk about geological systems with dreams that go well beyond the exciting geographic information systems of today. Only teams can further develop these geological systems. Teams do not need dictators, but leaders akin to inspirational orchestra conductors. Above all this, teams need steadily evolving institutions and a modicum of staff stability and continuity. All of these are indispensable for both the development of geological exploration systems and creative teamwork.
Biographical Sketch
Albert W. Bally is Emeritus Professor of Rice University. In 1952, he obtained his Ph.D. degree from the University of Zurich in Switzerland. His thesis project was in the Central Apennines of Italy. After a year of postdoctoral work at the Lamont Geological Observatory of Columbia University, he joined Shell Canada in Calgary. In 1966, he was transferred to Houston to become manager of geological research at the Shell Development Company. He advanced to become chief geologist and senior exploration consultant for the Shell Oil Company. Between 1981 and 1996, Dr. Bally was the Harry Carothers Wiess Professor of Geology in the Department of Geology at Rice University.
Title of talk
Abstract:
Tectonic Significance of the Accumulation of the Voluminous Early Paleozoic Reservoir- Containing Quartz-Rich Sandstones of North Africa and Arabia
Abstract:
About ten million cubic kilometers of quartz-rich sandstones were deposited close to sea level in the area presently occupied by North Africa and the Arabian peninsula between Middle Cambrian (c. 520 Ma) and Late Ordovician (c. 440 Ma). The preserved sandstones represent parts of a sheet that extended from Mauritania to Oman and from Guinea to the Atlas mountains (Burke and Kraus, 1998). This constitutes an area somewhat larger than that of the United States of America. It seems possible that the sandstones may have formed one of the largest bodies of siliciclastic sedimentary rock of a single dominant lithology ever to have been deposited on continental crust. The sandstones, which have an average thickness of about one kilometer, have been well-studied both at outcrop and in the subsurface, particularly in Algeria (Petroleum Frontiers, 1993, 1994) and in Oman (Droste, 1997). In both these areas the sandstones contain major oil and gas producing reservoirs.
I relate the deposition of this remarkable body of sandstones to the collapse and the erosion of mountains that had been constructed during the continental collisions which assembled western Gondwana at the end of the latest Precambrian during the Pan-African and Brazilian mountain building episodes (c. 650-550 Ma).
Two processes were involved:
Cambro-Ordovician sandstones similar to those of North Africa and Arabia were also being deposited in other parts of Gondwana. Examples are now preserved in Pakistan, Iran, Turkey, Europe, the Cape fold belt, and South America. The area over which these comparable sandstones were deposited may serve to increase the estimate of the original extent of deposition.
Weathering of Panafrican rocks to produce the large volume of quartz-rich sandstones can be expected to have generated a comparable volume of fine-grained siliciclastic sediment. No such large volume of fine-grained sediment is preserved on the Gondwana continent, but giant accretionary wedges (such as that of the Lachlan fold belt of Australia, which were forming while the voluminous sandstones were being deposited) exemplify the kind of continental margin deposit into which material complementary to the North African and Arabian quartz-rich sandstones may have found its way.
A paucity of finer-grained intercalations among the sandstones of North Africa and Arabia may be attributable in part to the absence of vascular land plants during the Cambrian and Ordovician. In later times vascular plants and especially their roots have impeded stream flow and fostered more general intercalation of finer-grained siliciclastic sediments among coarse-grained sediments.
The deposition of the vast Cambro–Ordovician quartz-rich sandstones of North Africa and Arabia was a closing episode in the extraordinary continental collision and mountain-building events that led to the final assembly of the great southern continent of Gondwana.
References
Burke, Kevin and Jeffrey U. Kraus (1998) Are thick, quartz-rich, Cambro-Ordovician sandstone sequences in northern Africa and Arabia products of the collapse and erosion of huge, Pan-African, Tibetan-style plateaus? Jour. Afr. Earth Sciences, Vol. 27, no. 1A, p. 42.
Droste, Henke H.J. (1997) Stratigraphy of the Lower Paleozoic Haima Supergroup of Oman. GeoArabia, Vol. 2, no. 4, pp. 419–472.
Petroleum Frontiers (1993) Ghadames basin of north central Africa. Vol. 10, no. 3, 49 pgs.
Petroleum Frontiers (1994) Ghadames basin and adjoining areas. Vol. 10, no. 4, 77 pgs.
Sengor, A. M. C. (1995) Sedimentation and tectonics of fossil rifts, pp. 53–117 in Busby, Cathy J. and Raymond V. Ingersoll (editors) Tectonics of Sedimentary Basins. Oxford, England: Blackwell Science. 579 pgs.
Using Seismic Attributes to Predict Reservoir Properties & Potential Risks
Abstract:
The advance of software for generating seismic attributes and the growing emphasis on production geophysics has led to the widespread use of seismic attributes as predictors of reservoir properties. In many cases, we can show -- using seismic modeling or from rock physics -- that there is a physically justifiable relationship between a seismic attribute and the reservoir property of interest. When this is true, we are able to greatly reduce the uncertainty of interwell predictions of reservoir properties.
The first critically important step to the use of seismic attributes is accurately tying the well and seismic -- both vertically and areally. Successful application relies on then identifying a seismic attribute that is significantly correlated with the reservoir property being modeled. If found, the dense seismic data can be used to guide the interpolation between sparse well data using geostatistical, regression or neural network techniques. The purpose of this process is estimating in place hydrocarbon volumes or making reservoir management decisions -- such as location and number of wells, depletion strategy, or gas and water injection operations.
All of the prediction methods, regression, geostatistics, and neural networks, require making inference from a small number of wells to a larger population assumed to be represented by that sample. This inference should not be based solely on an empirical relationship between a seismic attribute and reservoir property derived from the small sample. This study quantifies the probability of observing spuriously high correlations between the well and seismic data; that is, the probability of observing a significant sample correlation when the seismic attributes are actually uncorrelated with the reservoir property. If the correlation is indeed spurious and the seismic attribute is used as a predictor, then not only will the estimated reservoir property be biased, but its error variance will be underestimated. This can lead to highly confident, but very inaccurate predictions and ultimately poor reservoir management decisions.
Speaker Biography:
Dr. Cynthia T. Kalkomey received a Ph.D. in Statistics from Southern Methodist University. She worked for 18 years for Mobil's E&P Technical Center in both exploration and producing, most recently as Manager of Reservoir Characterization. She left Mobil in 1998 to start her own consulting and training company; Kalkulations, Inc. Her technical interests are in probability and statistics, risk analysis, geostatistics, 3D reservoir modeling, and reservoir characterization.
The paper she will be presenting was voted to be among the top 5% of the presentations at the 1996 SEG Annual Meeting and was published in the March, 1997 issue of The Leading Edge. Dr. Kalkomey can be contacted at: Kalkulations, Inc., 4330 Southcrest Rd., Dallas, TX 75229, Phone: (214) 366-1140, Fax: (214) 358-0736, Email
"Restructuring the Petroleum Industry"
Abstract:
The Houston Association of Professional Petroleum Landmen is pleased to present Jim Hackett as our featured speaker. An energetic leader, Mr. Hackett currently serves as chairman, president, and CEO of Seagull Energy. He was featured in a national business publication several years ago as one of the country's top 100 rising executives. He has worked in planning, marketing, and operational as well as management roles at numerous companies. His current challenge as CEO of a large independent involved in a merger makes him uniquely qualified to give his views on our potent business environment. His sure-to-be dynamic presentation will focus on three important topics confronting the explorationist and today's oil and gas industry:
James T. (Jim) Hackett was named to his present position with Seagull Energy in September 1998, coming from Duke Energy, where he was president of energy services.
He was executive vice president of Pan Energy before that company and Duke Power Company merged in 1997 to form Duke Energy. Previously, he held a variety of positions in finance, marketing, and engineering in the exploration and production and midstream sectors of the industry for Amoco Oil Company, Burlington Resources, Inc., and NGC Corporation (now Dynegy Inc.).
Mr. Hackett holds a B.S. degree in finance from the University of Illinois and an M.B.A. from Harvard University.