ESTUDO DAS PROPRIEDADES HIDRODINÂMICAS DA FORMAÇÃO SERGI NUMA ÁREA EXPERIMENTAL NA REGIÃO DE COCOROBÓ-BAHIA

Resumo

Studies have been conducted for determination of detailed lithological characteristics of a sequence of Sergi sandstones from data colected during the drilling of six wells, in the Cocorobó region, in the Northeast of Bahia. Hydraulic parameters have been determined by laboratory tests on sandstone cores and samples from the drilling, showing quite uniform values, which averaged 3,1 x 10^{- 3} cm/s for the permeability and 29% for the effective porosity, and presenting anisotropy about 40% greater for the horizontal permeability. The laboratory tests included granulometric and petrographic analysis and X-ray difratometry, and have shown that the Sergi Formation for the area studied is quite uniform little cemented, and has only a small amount of clays and fine silt (less than 5%). A well test of the saturated lower section of the sandstones permitted to estimate a value of the permeability somehow lower compared to the laboratory one, and equal to 0,7 x 10^{- 3} cm/s. This value is neverthless consistent with the laboratory results and the electrical well log, which evidenciate an increase in the clay content towards the basis of the sandstone sequence. A combination of these two results yielded the better values, given as K = 2,5 x 10^{- 3} cm/s and n_c = 29%. The values of these parameters constitute the basic knowledge for defining the operation conditions for the adduction pipeline and injection system, which will be necessary to be constructed for a saturation experiment with the Cocorobó reservoir, in order to evaluate the feasibility of storage of water artificially in underground in that semi-arid region.