Print this pageSedimentological Controls of Physical Properties in Caprock Seals: From Example from Campos and Santos Basins, Brazil Souza, M.K. ; Santos, V.S.S
Caprock seals play an important role in a petroleum system due to the capacity to hold back hydrocarbons. They are important in the production and exploration of hydrocarbons by preventing the loss to the surface as well as by controlling the production by compartmentalizing reservoirs. This work is aimed to understand how fine grained rocks (< 0,062mm) vary in their capacities to hold hydrocarbons or compartmentalize reservoirs in two cases in the Brazilian continental margin basins - Campos and Santos.
Starting with the data obtained from mercury capillary pressure and comparing that with results from grain size analysis and composition, it is possible to recognize some controls of petrophysical properties. Although it is well established that the grain size diameter and compaction are important due to their effect in reducing the pore throat sizes, in this paper it has been observed that additional controls related to the diagenesis, are even more determinant in modifying the porous media of fine grained rocks.
The Campos system was deposited in an upper/middle slope setting, and in an outer shelf setting in Santos Basin deposits. The results were based on the analysis of 31 samples from six fined grained units in Campos and ten samples from two units in Santos. The units studied comprise silt rich mudstones that, despite the grain size results, show an excellent compositional control in the petrophysical properties, such as carbonate content in Campos and chlorite in the Santos Basins. These compositional differences are related to the source areas that supplied these deposits.
Comparison between carbonate content and the respective capillary displacement pressure in the Campos Basin show better correlation between high carbonate content and high seal capacity, than with grain size diameter.
The Santos Basin samples showed the highest overall displacement pressures, due to the diagenetic chlorite content, even though they present a high degree of bioturbation which mixes different grain sizes and causes a reduction in seal capacity.
AAPG Search and Discover Article #90100©2009 AAPG International Conference and Exhibition 15-18 November 2009, Rio de Janeiro, Brazil