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Untested carbonate buildups in the Bermejo field, Ecuador: A potential new play type in the western Oriente Basin

¹ Department of Environmental Exploration Engineering, Pukyong National University, Busan 608-737, South Korea; gwanglee{at}pknu.ac.kr
² Department of Geosciences, University of Houston, Houston, Texas 77204; jpcastagna{at}uh.edu

Gwang H. Lee is a professor in the Department of Environmental Exploration Engineering at Pukyong National University, South Korea. He received his B.S. (1981) and M.S. (1983) degrees in oceanography from Seoul National University and his Ph.D. (1990) in geological and geophysical oceanography from Texas A&M University. He worked for Shell Offshore Inc. from 1991 to 1994. His main research interest is the application of seismic reflection to basin analysis and hydrocarbon exploration.

John P. Castagna holds the Sheriff Chair in Geophysics at the University of Houston. He earned his B.S. and M.S. degrees in geology in 1976 and 1981 from Brooklyn College, New York, and his Ph.D. in exploration geophysics at the University of Texas–Austin in 1983. His interests include quantitative analysis of seismic data for exploration and development applications.

ABSTRACT

We identified a previously unknown carbonate buildup in the Cretaceous M1 limestone in the Bermejo field, northwestern Oriente Basin of Ecuador. Thinner carbonate builduplike features are also seen in the deeper A limestone, which has produced small volumes of oil in the northern Bermejo field. The carbonate buildups can represent a significant new play type in the western Oriente Basin, where limestones have been known principally as a source rock. The M1 carbonate buildup, imaged as a lenslike event in three-dimensional seismic data, forms a circular feature in the isopach, amplitude, and dip maps. It is characterized by generally high but variable seismic amplitude, and its thicknesses (20 to >40 m; 66 to >131 ft) exhibit a complicated pattern, suggesting weathering and/or localized carbonate growth. The dark and rough top surface and irregular edges of the M1 carbonate buildup, revealed by the dip map, probably suggest the formation of fracture-cavity-karst–type reservoirs. The Late Cretaceous convergence along the western Oriente Basin may have further fractured the carbonates in the area. The M1 carbonate buildup, assuming a porosity of 10%, can contain more than 4.0 x 10⁷ bbl of liquid, which is particularly significant in the Bermejo field where production has been marginal.