الفهرس | Only 14 pages are availabe for public view |
Abstract The Paleozoic Nubia as four rock units; Araba, Naqus, Abu Durba, and Ahemir ormations. The present study deals with results of petrophysical analyses of 51 surface plug samples were collected from the outcrops at Gebel Abu Hasswa to represent the different lithofacies of the Nubia Sandstone units in the eastern side of Gulf of Suze. The study area is located between Latitude 28° 20’ -28° 40’ N and Longitude 33° 10’-33° 30’ E. The sedimentological studies that was carried out on Abu Hasswa section samples included the petrography description and XRD analysis, where the petrographyical study referred that all the study samples are of quartz arenite facies, but they are different in the diageneses processes or the compaction. The study samples were divided into four lithofacies depending on the type and degree of cementation; the divided lithofaices are calcareous quartz arenite, ferruginous sandstone, highly ferruginous quartz arenite, and siliceous quartz arenite. The XRD analysis showed that the main mineral that formed samples is silica mineral, while the minor minerals are calcite, hematite, and kaolinite. The correlation between thin sections and XRD results concluded that the samples had been suffered from dissolution process that caused the oversized porosity, in addition to, cementation process with multiple types of cements like silica overgrowth, ferruginous, and calcite minerals. The petrophysical evaluation of porosity and permeability of Nubia sandstone samples were carried out for storage and flow capacity Assessment, and to detect the degree of heterogeneity by several statistical techniques such as Lorenz, Dykstra – parson, and Coefficient of variation. The Nubia sandstone samples reflect good storage and flow capacity properties at some 110 | P a g e intervals, while in other some intervals show fair to bad storage and flow capacity properties. This is due to the heterogeneity degree of the study samples that can be controlled by the sedimentological and diagenetic processes. Heterogeneity quantification was derived using Lorenz and Dykstra parson methods where Lc = 0.23 and Vc = 0.48. These values reveal that the Nubia sandstone samples are slightly heterogeneous. Five hydraulic flow units (HFUs) in the study samples were derived and identified using FZI and R35 values. HFU5 is the highest quality unit with high porosity and permeability values, while HFU 1 is the lowest quality unit with low porosity and permeability values. R35 values indicated that the study samples varied from nano to mega porous units. The next step was to study the change in the electrical properties of Nubia sandstone rocks. In addition, linked this change to rock quality in order to quantify the ability of the rock to transfer fluids. The different electrical properties that were acquired are electrical resistivity, formation resistivity factor, and tortuosity; all of the previous electrical properties were acquired for a saturated sample of Abu Hasswa section with three solutions of different concentrations started from 6000 ppm, passed to 30000 ppm, finally 60000 ppm. The Nubian sandstone samples showed good relationships between the electrical properties and porosity; especially the formation resistivity factor with porosity that produced numerical values for a and m, where a = 2.86, 3.232, and 3.04 and m = -1.322, -1.333, and -1.318 respectively. Otherwise, the tortuosity showed a bad relationship with porosity that may be related to the quality of rock samples. Consequently, the concept of current zone indicator (CZI) was used to classify the different rock samples by its quality. 111 | P a g e The CZI concept divided the samples into three electrical flow units (EFU) by their electrical quality such as electrical radius index (ERI). The produced EFUs were redrawn for tortuosity and formation resistivity factor with porosity and permeability; where the produced values of m were been different for EFU to another, where EFU1 has m equal -1.37, EFU 2 has m equal -1.359, and EFU 3 has m equal -1.242. acoustic wave properties investigation for Nubia sandstone samples of Abu Hasswa section illustrates the relationships with different petrophysical properties such as rock density, porosity, and permeability; and their effects on the different elastic moduli such as bulk, rigidity, and Young’s modulus in addition to lame’s constant and Poisson’s ratio. The compressional and shear waves have a direct relationship with the bulk density of rocks, which is based on porosity and cementation (iron oxides) content. High correlation coefficients were found in the relationships between acoustic waves and porosity and bulk density. Several relationships were carried out as a combination between the different elastic moduli and porosity, bulk density and acoustic velocities. These relationships can prove the lithology of the samples as sandstone and the high correlation coefficients make them very useful for parameters prediction from the others. The compressional have mean values of samples of Malha Fm, Araba Fm, Abu Durba Fm, and Ahemir Fm are 2.76, 2.26, 3.63, and 2.28 m/sec, while shear wave velocities have mean values of samples of Malha Fm, Araba Fm, Abu Durba Fm, and Ahemir Fm are 1.7, 1.59, 2.37, and 1.59 m/sec/ in addition, they showed a well correlated indirect relationships with porosity percentage of the rock samples, moreover they were used to calculate the 112 | P a g e slowness, and vp/vs ratio and studied the relationships with different petrophysical parameters. The elastic parameters revealed that there is a significant relationship to the nature of rocks and the diagenesis processes of the study samples, especially the poisons ratio, where the regretted curve was started from 1.17 m/sec and -0.86 which indicate the high degree of diagenesis processes. The intercorrelation between the different petrophysical parameters such as porosity, permeability, grain density, resistivity, and also compressional, and shear wave velocities was carried out using the multiregression algorithm. The modeled petrophysical parameters showed a significant empirical equation with good to excellent correlation coefficients. Finally, I represent the change in the petrophysical parameters vertically and its relationship with the rock quality, where Araba Formation showed varied rock qualities as showed in the sedimentological part, while the other formations showed a slight homogeneity in reservoir rock quality. |