RIASSUNTO
SPE Member
Abstract
An integrated study of the geology, petrophysics, geophysics, and engineering aspects was made on the Libertador field in Ecuador. The study began after the field had produced approximately 6% of the oil originally in place.
Data from geophysics, petrophysics, geology, transient pressure analyses, laboratory core analyses, and laboratory PVT analyses were integrated in a classical black oil simulation model to allow the evaluation of alternate development methods. A history match was performed on a model which incorporated all four of the principal producing sands. This study produced an evaluation principal producing sands. This study produced an evaluation which demonstrated that the highest recovery would be achieved using a combination of infill drilling water injection, and artificial lift.
Introduction
Petro Production operates the Libertador Field in the Oriente Petro Production operates the Libertador Field in the Oriente portion of the country of Ecuador. This field and many others in portion of the country of Ecuador. This field and many others in the Amazon Basin portion of Ecuador produce from the Napo Sands. In the Libertador Field these sands are divided into four principal bodies designated the U Superior, U Inferior, T Superior, principal bodies designated the U Superior, U Inferior, T Superior, and T Inferior, respectively progressing from the shallowest to the deepest sands. Thirty-eight wells were available for analysis. The study was designed to produce information which would act as a guide to subsequent investment decisions.
GEOLOGY
Libertador is an oil field operated by Petro Production in the Oriente Basin of Ecuador. It lies some 250 kilometers east of Quito. (Figure 1).
The lower Napo formation consists of seven units, which are in ascending order: 1) limestone, 2) ""T"" inferior (TI), 3) ""T"" superior (TS), 4) limestone B, 5) ""U"" inferior (UI), 6) ""U"" superior (US), and 7) limestone A. The ""T"" and ""U"" intervals are hydrocarbon reservoirs and were the subjects of the reservoir study. Limestones in the wells of the fields are bay and lagoonal deposits which occasionally interfinger with the deltaic reservoir sands.
In order to establish a sedimentary model for the reservoir sands of the fields, 25 cores were examined from 12 wells. From the interpretation of sedimentary features within the core, the sedimentary model was considered to be deltaic. The main sub-environment is the occurrence of stream-mouth-bar sands. Minor occurrences of channel fill and crevasse splays were found. Abundant fossils and worm burrows were found in predominant quartz sands. Some fish scales, and sharks teeth were also noted. Glauconite and gilsonite were found in abundance and are believed to have an effect as barriers to fluid migration within the reservoirs.
Glauconite was found in both the ""T"" and ""U"" reservoir sands. The ""U"" sands only had a few feet of glauconitic sand in the top of each stream-mouth-bar. The ""T"" sand have a considerable amount of glauconite distributed throughout the entire sand.
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