Title:

Effects of Temperature and Stress on the Compressibilities, Thermal Expansivities, and Porosities of Cerro Prieto and Berea Sandstone to 9000 Psi and 280 Oc

Authors:

E. Contreras, E. Iglesias, F. Bermejo

Geo Location:

Cerro Prieto, Mexico

Conference:

Stanford Geothermal Workshop

Year:

1982

Session:

Geophysics and Well Logging

Language:

English

File Size:

688KB

View File:

Abstract:

We measured matrix and bulk conpressibilities and thermal expansion coefficients of Berea sandstone and of a sandstane from Cerro Prieto swell M-94. Futhermore, we developed and demonstrated a novel technique for computing porosities as functions of effective stress or temperature from uniaxial compression and thermal expansion measurements respectively. Unlike previous results, which are limited to tenperatures below 200oc, our measurements cover the range from ambient temperature to 280OC. Our data for Berea sandstone generally agree with previous results. 'Ihe matrix and bulk compressabilities of the Cerro Prieto sandstone are considerably greater than those of two Imperial Valley sandstones, reported in the literature, indicating significantly greater subsidence potential for Cerro Prieto. The porosities of the rocks studied decrease with increasing effective stress; our results indicate that porosity reductions due to pore pressure drawdown in sandstone dominated geothermal reservoirs are probably small. Posities decrease also with increasing temperatures because the grains expand at the expense of the pore volume. Porosity increases due to thermal drawdown are likely to be small in sandstone geothermal reservoirs but greater porosity relative changes are expected for tighter sandstones.


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