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The AAPG/Datapages Combined Publications Database

AAPG Bulletin

Abstract


Volume: 66 (1982)

Issue: 5. (May)

First Page: 612

Last Page: 612

Title: Aracas Field--Reservoir Heterogeneities and Secondary Recovery Performance: ABSTRACT

Author(s): O. S. Nascimento, E. Bornemann, L. D. C. Jobim, M. D. Carvalho, A. M. Pimentel, E. J. Bonet, E. B. Rodrigues, J. R. L. Sandoval, V. Lassandro, T. C. Rodrigues, C. R. Hocott

Article Type: Meeting abstract

Abstract:

In the Aracas field (Reconcavo basin, Brazil), the Sergi Formation held about 30% of the 60 × 106m3 of the field's original oil in place. Its contribution for the field cumulative production is, however, less than 11%.

The Sergi Formation (Upper Jurassic) is a braided-stream sequence of conglomeratic and coarse to very fine-grained sandstones and minor siltstone and shale layers (< 5%) with an average thickness of 215 m. The pool has an area of 7.5 km2 and the reservoir average depth is 2,750 m.

Primary recovery started in 1967 and 37 wells were drilled for exploitation of the pool (29 for production and 8 for peripheral water injection). The water injection was initiated in 1973 and neither improved the production nor repressured the reservoir to the expected levels. Today an average production of 23 m3/day/well is obtained from 12 wells, far below the initial rates of 100 m3/day/well. To date, only 8% of the estimated original oil in place has been recovered from this pool.

The Sergi Formation was cored in two new wells and the measured petrophysical parameters (such as porosity, permeability and water saturation) served to establish a model for the log analysis of the remaining wells. A good correlation of log-derived permeabilities and core permeabilities was obtained by the method known as multidimensional histogram. Standard computerized log analysis in conjunction with estimation of permeability made possible a description of each of the 12 reservoir zones in the form of contour maps depicting mean porosity, water saturation, and permeability and development of a suite of structural and isopach maps.

Pressure data from new wells and geologic analysis derived from log and core interpretation strongly suggest that the present peripheral injection-well pattern is insufficient and that an infill drilling program could contribute to a more effective pressure maintenance.

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