Estimate of Secondary Porosity from Surface Crossed Square Array Resistivity Measurements

Abstract

The secondary porosity of rocks and formations plays an important role in water exploration and exploitation in crystalline rocks. Furthermore, cracks and voids are paths for contaminated fluid propagation and, thus, their location can be very important in environmental studies. Usually, secondary porosity is estimated from well logging observations, but some previous works have pointed out that azimuthal resistivity measurements and the square array can be used to estimate this parameter. Herein, the use of the square array and of the crossed square array will be investigated to estimate the secondary porosity. Thus, the analogue model and field resistivity data obtained with those arrays are discussed and interpreted. The analogue model simulates contacts between the isotropic and anisotropic media and between two different anisotropic media. The field data are from an area where steeply dipping formations prevail and contacts between the isotropic and anisotropic media are present. The calculated secondary porosity values are compared with the lateral changes in the resistivity and anisotropy, and pseudo sections are shown to aid the interpretation. In addition, 2D resistivity models for the field survey are produced to provide a better image and interpretation of the data. The overall results and limitations are discussed, and data acquisition procedures are proposed to optimize the field work.

Keywords

• secondary porosity
• resistivity
• surface
• measurements
• crossed square
• array