3-D Modeling of the Santa Terezinha Coalfield, Brazil: Implications for Estimation of the Coalbed Methane Potential
Heinz H. Burger1, Wolfgang Kalkreuth2, Michael Holz2, and René Prissang1
1 Freie Univ. Berlin, Berlin, Germany
2 Instituto de Geociencias, UFRGS, Porto Alegre, Brazil
The geometrical modeling of a coal
basin in Brazil was made possible due to conventional analysis of borehole data and a detailed study of the sequence stratigraphy. The most important controls for the coalbed methane (CBM) potential in the Santa Terezinha
coal
field in Rio Grande do Sul state, Brazil are a) basin geology, i.e. reservoir size, depth and thickness of
coal
seams; b)
coal
characteristics, i.e.
coal
rank,
coal
type and
coal
grade; c) in-situ methane content, measured by means of gas desorption tests and isotherm adsorption tests.
The geometrical 3D-model of the Terezinha coal
field is focused on a set of
coal
seams hosted in a succession of sandstones, mudstones, and shales of Early Permian age. The combination of logs from a rather small number of boreholes and information from paleogeography and sequence stratigraphy provide a powerful tool for the construction of a consistent 3D-model of the
coal
basin.
Assessment of coal
rank is based on vitrinite reflectance measurements of 120
coal
samples obtained from 27 borehole locations. Methane adsorption tests carried out in a number of
coal
seams indicate a general capacity of 2 - 6 m3/ton of
coal
. This result corresponds to those methane values calculated on the basis of empirical considerations including
coal
rank, ash yields and depth.
The combination of geometrical 3D-modeling and coal
property modeling is the basis for estimating the CBM potential of the Terezinha
coal
field and for selecting an optimal location for a first coalbed methane test well.