Electric fabric of Cretaceous clastic rocks in Abu Gharadig basin, Western Desert, Egypt

Measuring the petrophysical properties of sedimentary rocks in three-dimensions (3-D) has a high priority for interpretation of their physical behaviour. The present work attempts to study the 3-D electric behaviour of the Upper Cretaceous sandstones and clayey sandstones in the Abu Gharadig basin, Egypt. These rocks belong to the Betty, Bahariya, and Abu Roash Formations. The apparent electrical resistivity (R(o)) was measured in three perpendicular directions, one normal to the bedding plane along Z-axis, and the other two directions parallel to the bedding plane and normal to each other, along X-axis and Y-axis. The electrical resistivity (R(o)) was also studied at three NaCl-saline concentrations of R(w) = 0.53, 0.13, and 0.07 Omega m in ambient conditions, using A-C bridge at 1 kHz. It is proposed that, processing and matching the electric data in 3-D as ellipsoids instead of in 2-D, has led to the electric fabric concept. It is a combination of electric foliation (F) and electric lineation (L). Statistical analyses of measured electrical resistivity reveal that the electric fabric at the second brine concentration should be taken into consideration to avoid the effect of clay content. The electric lineation and foliation of the studied sandstones and clayey sandstones at the second concentration are mostly small (1.1-1.5) to moderate (1.5-2.5), with few sandstone samples having high (2.5-5.0) to very high foliation (5.0-7.5), whereas the electric anisotropy values for these samples are small to moderate (1.1-2.5). This fabric is contributed mainly from their electric foliation, indicating some load pressure compaction that led to small to moderate anisotropic grains and flow paths/network pore spaces. (C) 2008 Elsevier Ltd. All rights reserved.