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Abstract NEAG extension has been affected by two diverged consequent forces. The NE-SW extensional forces comes first resulting in NW-SE normal faults, followed by NE compressional forces of the Syrian arc system causing the inverted structures and responsible for variations in both vertical throw and thicknesses on the two sides of the former pure normal faults. These forces ended by late Cretaceous in Khoman time. The Khoman is onlapping on the condensed section of Abu Roach Formation in the west part of study area. Neag-1 located at the NEAG extension within the Abu Gharadig basin margin at -1000 m_below sea level; Neag-1 represents the shallowest structure in the study area and in all over the Abu Gharadig basin closer to the highly inverted Kattania high but Neag-1 still preserves the trap integrity for Hydrocarbon accumulation. The Neag-2 and Neag-3 are likely affected with the same tectonic events with moderate magnitude closer to Natrun basin in north direction. The stratigraphy of the Bahariya in study area represents a sophisticated setting affected primarily with the tectonic history of the area. Neag-2 and Neag-3 most likely were far from the marine influence at lower Bahariya and were not preserving the Upper Bahariya sediments. Meanwhile Neag-1 is preserving the marine character and holding the thickest clastic of near-shore sediments in the Upper Bahariya. The Bahariya-Kharita Para-conformity is well defined at both Neag-2 and Neag-3 associated with fluviatile distributary channels of second and third order. The provided laboratory measurements to this study were used by author to outline petrophysical properties of the Bahariya reservoir in order to determine and evaluate porosity, permeability, pore throat radius, formation factor, cementation factor, saturation exponent, cation exchange capacity and capillary pressure. The petrographic investigations are used for outlining mineralogy, porosity types and mode of occurrence of formation fines. The initial composition of the Bahariya rocks was dominated by monocrystalline quartz, glaucony pellets, lithic fragments and feldspars appeared as pore-filling and grain-coating shape. The lithological variations and clay laminations have major influence on petrophysical properties. Dissolution and cementation are considered as the main pore framework controls in the Bahariya reservoir rocks. Illite, kaolinite, calcite, dolomite and siderite are the common authigenic pore filling minerals in the Bahariya samples. In general clay content of the upper Bahariya is relatively higher than clay content of the lower Bahariya and it is regularly associated with increasing of residual oil against the pores of higher clay content. The petrographical investigations showed the influence of the pore filling minerals on petrophysical parameters as porosity and permeability. Generally, the increase of pore filling minerals has a negative effect on both porosity and permeability but without any unique signature for a single mineral. 1. Petrophysical Studies The reservoir properties has been investigated for the different Bahariya facies (tidal channel, tidal bar, sand flat,…etc.) and rock types (subfeldspathic Arenite, Feldspathic wakes, ….) that shows poor correlation and less significance petrophysical characteristics as most of the high quality rocks was affected by cement alteration and secondary porosity. The Bahariya facies are influenced by different and mixed sedimentary agents among the shallow marine and fluvial, although they were present at the same time. The identified rock types showed up to 50 % subfeldspathic arenites, with clear effect of diagenesis that reform and reshape the cement content inside the rock. This phenomenon is accounting for these changes in the Bahariya as a result of tectonics setting and uplifting. The mineralogy aggregates in-between the pores are from mixed lithology in variable amounts between kaolinite, illite, calcite, dolomite and siderite. Quantielan model is created from open hole logs to highlight this mixed mineralogy of Bahariya lithology. The results account for the reservoir lithology and pore filling minerals. The petrophysical correlations between porosity and pore filling minerals showed linear relation as at 50 % pore filling there is no porosity expected in the rocks. Permeability versus total pore filling minerals showed four classes in power relation. These classes are investigated with pore throat size measured by (MICP) to assess types of flow. Types of fluid flow are micro-pores, micro-meso pores, meso pores and macro pores, these types representing and shaping the hydraulic conductivity of the Bahariya reservoir rocks. The intercorrelation among porosity, permeability and pore throat radius (r35) is formulating the hydraulic flow units of the Bahariya reservoir. 1.1. Porosity Porosity of the Bahariya samples were investigated in both cores and borehole logs calibrated with core porosity. Porosity is statistically varies from 2.5 to 32 % with mean value of 19 %. The pore spaces is filled with clay minerals and calcareous cement decreasing the porosity while the higher porosity samples are mainly of secondary origin which affected by partial to near complete dissolution of carbonate cements and k-feldspars. 1.2. Permeability Permeability of the Bahariya samples varies from 0.005 mD to 874 mD with mean value of 54.75 mD. The permeability samples characterized by gradual increase of pore aperture to 2 μm (micro –meso pores); macro porosity type > 2 μm which showed the higher permeability. Samples No. 3R and No. 4R are showing total cement dissolution in thin sections and significant capillary curves are observed. 1.3. Pore throat radius; The calculated pore throat radius of the studied Bahariya samples are varies from 0.3 μm to 3.55 μm with mean value of 2.1μm. The mathematical approach to calculate pore throat radius from porosity and permeability equations is ranging from 0.13 μm to 3.89 μm with mean value of 1.12 μm. The higher pore throat radius is represented in many samples as they affected by partial to near complete dissolution of carbonate cement and k-feldspars. 2. Hydraulic Conductivity The hydraulic conductivity of the Bahariya samples showed high degree of heterogeneity in pore spaces especially in Neag-1 field. The hydraulic flow units approach was used to study this heterogeneity. Ten hydraulic flow units are obtained, while each one has unique pore throat radius (r35) controlling the pore geometry. The first HFU holds the lowest reservoir quality while HFU-10 is the best reservoir quality. The Bahariya reservoirs can be divided into three main types’ according to pore systems characteristics of their hydraulic conductivity, to micro-pores, meso pores and macro pores. The overlapped area between micro-meso pores is not sharply identified due to limitation in the number of MICP test but this overlap is happened as a result of the partial dissolution of k-feldspars and calcareous cement in pores. This boundary is well identified by graphical methods (storage and flow capacities). Coefficients of micro-meso pores and macro pores showed different correlations with porosity, permeability, residual oil saturation and pore throat radius (r35). It is used to build a saturation height function with Lambda method. The water saturation in the transition zone is addressed with characteristic equations function of capillary pressure comparing between the J-function and lambda methods. The lambda fitting gives more representative equations of capillary curves than the J-function. Seven reservoir curves were initiated for porosity starting from 5 to 35 % using the lambda method. The coefficients (a) and (λ) is ranging from 1.1 to 1.3 and 0.22 to 0.33 respectively. 3. The Electrical Conductivity The Bahariya reservoirs in the presented study can be divided into four main types’ of electro-facies as: 1) clean sand, 2) shaley sand (sand flat), 3) siltstone and 4) shale as structural and dispersed sand doesn’t exceed 3 %. The borehole logs showed low vertical resolution (10 cm) according to that any thin beds will be missed. The high resolution borehole images (0.5 cm) are helpful in borehole logs calibration. Three different equations can conclude and characterize the Bahariya reservoir electro-facies. The saturation exponent (n) increases with the increase of cementation factor (m); these coefficients showed poor correlation compared with hydraulic conductivity coefficients. Cation exchange capacity and mounce potential is showing poor correlation with most of the investigated petrophysical parameters. Kaolinite and saturation exponent of Archie are found to be functions of cation exchange capacity (CEC) and mounce potential (ϕ). Formation factor (F) showed relatively good correlation with the cation exchange capacity (CEC) and mounce potential (ϕ) in both clean and shaley sands. While in siltstone the CEC is above 0.63 sm-1 showed poor correlation with formation factor (F). 3.1. Formation Factor Formation factor of the Bahariya samples varies from 14.4 to 44.7 with mean value of 26.7. The Formation factor is characteristic for clean and shaley sand; shaley sand has higher formation factor value than the clean sand samples as the formation factor increase with the decrease of porosity and tortuosity. The Archie multiplier (a) is estimated in clean sand as 0.6 and for shaley sand is 0.55, the cementation factor in clean sand is ranging from 1.95 to 2.2 with mean value of 2.07 and shaley sand is ranging from 1.79 to 2.02 with mean value of 1.87. 3.2. Formation resistivity index Formation resistivity index is mainly used to calculate the saturation exponent (n) of the Bahariya samples dominated by salinity and brine saturation. Saturation exponent varies from 2.0 to 2.67 with mean value of 2.36. The higher cementation factor (m) the higher saturation exponent (n); while the coefficient of correlation is founded to be 0.90 between them. 3.3. Cation exchange capacity Cation exchange capacity (CEC) of the Bahariya samples varies from -1.09 to -0.07 sm-1 with mean value of -0.46 sm-1. The higher quantity of the clay minerals the higher cation exchange capacity (CEC) and mounce potential (ϕ); the coefficient of correlation between them is 0.83. Cation exchange capacity has higher values in shaley sand and fine siltstone. 4. Borehole logs Open hole logs are used to validate and calibrate the shaley facies of the Bahariya with high resolution borehole image and further Qaunti-elan model is produced from well logs responses calibrated with the petrography of the Bahariya reservoir. The lower Bahariya is rich in glauconite, kaolinite and illite; carbonate cement is common in the Bahariya reservoir which increases the matrix density to 2.69 gm/cc as porosity is calculated from logs. The porosity were investigated and calibrated by core porosity with calculated equations. The log Porosity of the Bahariya is statistically varies from 0.6 to 36 % with mean value of 14 %, the variance is 29, skewness is 0.19 and kurtosis is -0.16. The kurtosis remains positive for all zones but for the lower Bahariya zone it gives negative sign. The borehole logs are used to validate the rock properties; such as the bulk density and photo electric factors is influencing porosity and permeability. The photo electric factor is indicating the cement, lithology while, bulk density is high in low porosity and permeability rock samples. 4.1. Fluid Saturation Water and hydrocarbon saturation are calculated by different methods; from open hole logs , core measurements and integrated open hole logs and core using Archie, Indonesia, Simandoux, Waxman smith and low resistivity pay. Among all these methods Waxman Smith and LRP are found to meet the realistic saturation measured by laboratory method. The cation exchange capacity value for each electro-facies is solving the clay extra conductivity masking hydrocarbon zones in the borehole logs. 5. Petrophysical Models Several formulas have been developed and eight petrophysical models having high and reliable coefficient of correlation. The reservoir heterogeneity is solved by the hydraulic flow units while permeability can be predicted and obtained correctly from two parameters while the extra low permeability layers less than 0.4 mD is not consistent in hydraulic conductivity. The mercury injection capillary pressure proved high tortuosity in hydraulic flow units (HFU-1&-2) with limited storage capacity 2.5 % but starting from hydraulic flow unit (HFU-3) the storage and flow capacity are increased. The results showed good correlation between Waxman smith and low resistivity pay methods and the same for hydraulic pore volume derived from initiated capillary curve which indicated by matching with coefficient of correlation reaching 0.9 and low covariance 0.04. |