Initial study on porosity and permeability of evaporitic rock samples from Abu Dhabi coastal area, united Arab emirates

This study provides initial information about porosity and permeability of the evaporitic rocks from the coastal area of Abu Dhabi Emirate of the United Arab Emirates (UAE). This rock material may constitute the bedrock for construction sites and foundation of structures. The rock quality may directly affect and may threaten such structures either on or in evaporitic rocks. Moreover, this surface rock facies have vital role as a similar sealing rock material for the subsurface hydrocarbon traps. Therefore, twelve rock block samples were collected from ten different locations and core samples were prepared to investigate the porosity and permeability of evaporitic rocks. Further, petrographic descriptions were obtained using polarized-light microscope, scanning electronic microscope (SEM) and X–ray diffraction (XRD) analyses for some representative samples. The study indicates that the porosity ranges between 1.69 and 7.78 % and the permeability 0.001and 15 mD, respectively. The porosity and permeability relationship showed an optimum exponential best-fitted trend. As the majority of the samples increase with the increase of effective porosity. Moreover, a permeability at one location was extremely higher than the average. This could be due to heavy fracturing on gypsum samples. The distribution of porosity and permeability were mapped and presented for the study area. As well as, microphotograph (crossed-polarized) of some of the rock samples displayed gypsum crystals with anhydrite inclusions. White megacrystalline gypsum with parallel fractures filled with clay sized carbonates and clay-sized carbonate patches (matrix inclusions). The SEM images of gypsum samples exhibited dissolution cavities in a gypsum crystal filled with small anhydrite and anhedral gypsum crystal decorated by small anhydrite grains. In addition, the XRD pattern of the initial gypsum was qualitatively identified, where the gypsum and anhydrite minerals were recognized by X–ray diffraction technique. The study designated low to moderate porosity and permeability ranges in the study area. In general, the porosity measurements showed that it was increased from south west to the north and north east of the study area. The findings confirm good to intermediate quality of evaporitic rock facies. This study should be considered as initial phase and will be completely achieved with more sampling and analysis to cover all the questionable locations to enhance the results and having a detailed map of the porosity and permeability distribution of the study area. In any case, this initial study will help and provide useful initial information to decision makers in resolving various foundation problems at the construction sites and sealing rock material for the subsurface hydrocarbon traps in Abu Dhabi region.