ABSTRACT:

It is reported about the geotechnological investigations and the subsequent analysis as well as about the pre-design considerations of a planned underground refrigerated cavern system for gas in Brazil.

PRELIMINARIES

The Brazilian state oil company - PETROBRAS intends to construct the first underground storage facility in Brazil. It will be a fully refrigerated one and for imported LPG at 43 C. The planned plant is to be located between Rio de Janeiro and Sao Paulo at the southeast coast of Brazil in the S. Sebastiao maritime terminal. Storage space will result from 2 traditionally mined caverns of 115 000 m3 nominal capacity each.

According to the observations of Prof. Lindblom in his first Review Report to PETROBRAS: "The interaction between the stored (refrigerated) product and the rock masses poses an advanced engineering problem which requires careful planning and design. "That assertion implies the necessity of a cautious conduct concerning the design criteria and the layout conception.

This paper summarizes the results of the investigations and anas already made as well as the resulting pre-design layout and preferred solutions. These solutions partly translate the formal opinion and judgment of Prof. Lindblom. However, whatever faults and defects the conceptual scheme still has they are of author's full responsibility.

GEOLOGICAL BACKGROUND

The rock masses at the selected site belong to the Brazilian Pre-Cambrian Shield. It is locally constituted of a diversified gnaissic complex traversed by recent sub-vertical diabase diques. Most of the occurring gnaisses conform to typical migmatites. The general foliation plunge is N-36 /27. The depth of the weathered cover attains 30 to 40 m. Occasionally, deep altered zones, locally related to megafractures, faults and/or diques crossings, are found below the 100 m depth.

The major geological features examined for determining the caverns location, were the poor exposed megafractures, faults and diques. The statistical distribution of the slickensides planar features was also attentively contemplated. Figure 1 shows the photo-interpreted megafractures.

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