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The Subandean basin of Colombia and Ecuador covers an area of approximately 50,000 sq mi, and is part of a foreland which extends from the Guyana shield to the Andes Mountains. The present structural basin is asymmetric and plunges toward the south. More than 30,000 ft of Paleozoic to Tertiary sedimentary rocks are present. During the Early Cretaceous, a marine transgression buried a basal sandstone member (Caballos in Colombia, Hollin in Ecuador). Later fluctuations in sea level resulted in deposition of marginal marine-fluvial sandstones of the Upper Cretaceous. Major petroleum reserves are trapped in large anticlines and faulted structures in these Cretaceous sandstones.
Texaco began exploration for petroleum reserves in the trackless jungles of the Upper Amazon region of South America in 1941. During the early 1940s, the Orito anticline was discovered and mapped in detail by geologic field parties. In 1963, the decision to drill Orito was made, and Texaco acquired an aggressive partner, Gulf Oil, which earned one-half interest in the Texaco holdings by drilling the Orito No. 1 discovery well.
Following the Orito field discovery, exploration was accelerated and geophysical exploration began in 1965 with air magnetics and analogic seismic work. The helicopter gave support to portable geophysical crews, and later the helirig opened the entire area for exploratory drilling. The helicopter also figured prominently in the subsequent construction of two pipelines across the Andes Mountains.
Production began in Ecuador in August 1972, climaxing the long, arduous exploration and development of the Texaco-Gulf holdings in the Oriente.
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