Factors affecting the development of deformation bands in the Nubian Sandstone, Central Eastern Desert, Egypt

Abstract

Reservoir quality prediction is a key element in petroleum exploration and investigation of reservoir potential. The Nubian Sandstone reservoir in Egypt has excellent potential for hydrocarbon production. However, many deformation bands of different scales were rerecorded regionally and have a substantial influence on the porosity and permeability of the Nubian Sandstone Unit. Therefore, the effects of these deformation bands need to be quantified. Samples from the Cretaceous succession along the Qift-El-Qusier road were petrographically and petrophysically studied. Three sets of deformation bands trending in a NE-SW direction were identified during mapping. The host sandstone unit is quartz arenite where is composed mainly of quartz. A significant petrographic difference in grain size was noticed, where deformation bands have smaller grain sizes. Two lithological facies were recognized based on the mineralogy, grain size, sorting, and porosity. Facies 1 is coarse-grained, well sorted and with high porosity characteristics, where deformation bands dominated. On the other hand, Facies 2 with fine grains, well sorting and low porosity possesses deformation bands with a lower degree of cataclasis. The deformation bands have negatively impacted the porosity and permeability of the sandstone. The porosity in the Nubian Sandstone ranges from 24.3 to 29.7%, which is reduced from 9.6 to 17.1% in plugs containing the deformation bands. A similar trend for permeability was also found, where permeability is tremendously reduced from 1200 to 8400 mD in the host sandstone to 0.08-0.3 mD in deformation bands.