Publication Date:
2005-10-01
Description:
The stratigraphic architecture of a terminal Proterozoic carbonate ramp system (ca. 550 Ma, Nama Group, Namibia) was mapped quantitatively with digital surveying technologies. The carbonate ramp consists of a shoaling-upward ramp sequence in which thrombolite-stromatolite reefs developed at several stratigraphic levels. The reefs are associated with grainstone and heterolithic facies and exhibit diverse geometries and dimensions related to the position in the sequence-stratigraphic framework. Laterally extensive reefs with a tabular geometry developed when accommodation was relatively low, whereas discontinuous oblate dome-shaped reefs developed during times when accommodation space was relatively high. Collecting sedimentological and stratigraphic data digitally in an extensive canyon system allowed a comprehensive documentation of the three-dimensional (3-D) architecture and dimensions of the reefal buildups. Both deterministic and stochastic methods were used to extend outcrop observations to construct 3-D models that honor the observed stratigraphy. In particular, the accuracy with which dimensions of reefal buildups can be measured is critically important in the statistical modeling of the dome-shaped buildups. Calculations and corrections can be applied directly to the digital data set and serve as input during model building. The final 3-D model faithfully reproduces the outcrop distribution of facies and geological objects and has a high spatial resolution, compared with petroleum industry reservoir models. The organization of the reefal buildups in the stratigraphic framework has direct implications for reservoir continuity and connectivity in analogous settings. The digital characterization and 3-D outcrop models presented in this article can be subsequently used to condition dynamic reservoir-simulation modeling of geologically similar areas. Erwin Adams received his M.Sc. degree (1996) and his Ph.D. (2001) in geology from the Vrije Universiteit Amsterdam, Netherlands. He worked for three years at the Massachusetts Institute of Technology (MIT), deploying digital methods for mapping and modeling reservoir-scale carbonate outcrops in the terminal Proterozoic of the Nama Group, Namibia, and the Devonian of the Canning basin, Western Australia. Erwin joined the Carbonate Team at Shell in 2004.John Grotzinger is the Robert Shrock Professor of Geology at MIT. He received degrees in geology from Hobart College (B.Sc.), the University of Montana (M.Sc.), and Virginia Tech (Ph.D.). His research focuses on field-based outcrop studies of reservoir-scale heterogeneity, evaluation of biogeochemical events at the Precambrian–Cambrian boundary, and robotic investigations of the stratigraphic record of Mars. Wesley A. Watters is a graduate student in geophysics at MIT. He studies the effects of large impacts on planetary evolution and is a member of the Mars Exploration Rover Athena Science Team. He also works on problems relating to the morphometry and morphogenesis of stromatolites and early skeletogenous metazoa. Stefan Schröder received geology degrees from the Universities of Würzburg, Germany (M.Sc.), and Bern, Switzerland (Ph.D.). Since then, he has worked at MIT on Neoproterozoic reservoir rocks in Namibia and Oman. He is currently taking a postdoctoral study at the University of Johannesburg and studies Paleoproterozoic carbonates together with Nicolas Beukes. His research focuses on sedimentary processes and environmental factors governing sedimentation in the Precambrian. David McCormick is a senior research scientist and program manager at Schlumberger-Doll Research. He received geology degrees in sedimentology from Dartmouth College (B.A.), Columbia University (M.A.), and MIT (Ph.D.). Before Schlumberger, he worked at Chevron Petroleum Technology Company. His main interests lie in digital mapping and quantification of geology and outcrop analogs for reservoir characterization and modeling. Hisham A. Al-Siyabi holds an M.Sc. (1994) degree and a Ph.D. (1998) from the Colorado School of Mines. Hisham joined Petroleum Development Oman in 1999, and since 2001 has worked as a geologist and seismic interpreter on the South Oman Exploration Team, working exclusively on the terminal Proterozoic intrasalt Ara stringers. In 2005, Hisham joined Shell Exploration and Production Company as an exploration geologist.
Print ISSN:
0149-1423
Electronic ISSN:
1943-2674
Topics:
Geosciences
Permalink