الفهرس 
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Abstract
This study utilizes data obtained from the offshore Mediterranean Sapphire field, renowned for its significant gas production from Pliocene reservoirs. Sapphire sand reservoir petrophysical analysis was based on a series of mathematical equations that reflect the log response interpretation and identify the main lithology of the reservoir which is sandstone reservoir with shale intercalations. The most useful logs for this purpose are the density, neutron, sonic, gamma-ray and resistivity logs) fluid typing: hydrocarbon or water (. The main lithology was identified by the use of Schlumberger cross-plot as RHOB and NPHI.
The presence of shale in any formation is considered one of the serious problems for determining formation porosity. So, a reliable gamma-ray linear equation was used for shale content calculations. Reservoir porosity is very important in calculating fluid saturation, which can be calculated from density, neutron or sonic logs and even their combination. Both total porosity and effective porosity were calculated. The determination of water saturation is very important to complete the petrophysical parameters of the studied reservoir rocks. There are many equations for calculating the water saturation, such as Archie, Indonesia… etc. In our study; The Indonesia equation has been used for calculating the water saturation for the Pliocene sand reservoir, where this equation is more applied for the shaly sand.
Net Pay is defined as the thickness of rock that contributes to economically viable production. Net-pay is determined by applying appropriate cutoffs to the reservoir properties so that non-productive or non-economic layers are not counted. This can be done with both the log and core data, the applied cutoffs were: (10% <=PHIE), (0% <VSh<= 40%) and SW (0% <SW<= 60%).The petrophysical characteristics of Pliocene sand reservoir show that, the shale content ranges from 2 to 5 %. The effective porosity of this reservoir ranges between 25 and 28 %, and the water saturation range from 32% to 46%.
Permeability derived from magnetic resonance advanced logging tools was used to unlock the Pliocene sandstone reservoir heterogeneity. Permeability prediction from well logs is a significant target due to the unavailability of core data. The hydraulic flow units’ (HFU) approach is used to classify the reservoir rocks according to their porosity-permeability relationship. The predicted permeability is calculated using Sapphire-Dh magnetic resonance porosity and permeability relationship for each flow unit. Flow Zone Indicator (FZI) and the quality flow unit have a direct proportion relationship. For the model’s verification, the predicted permeability is plotted against the measured resonance permeability in Sapphire-Dh as a reference studied well, showing highly matching results. Accordingly, the applied approach is implemented in the other three wells, which have neither core samples nor advanced logs measurements.
Some of the Sapphire field wells encountered notable geomechanical issues during drilling. The study focuses on constructing a 1D Mechanical Earth Model (MEM) for analysis. A comprehensive assessment evaluates the sensitivity of mud weight to wellbore orientation concerning Sapphire formations. The goal is to establish correlations between required mud weights for shear failure (breakout) and tensile failure (drilling induced fracture initiation) with wellbore inclination and azimuth at specific depths. Results enable drilling engineers to identify stable inclination and azimuth options aligned with other design constraints.
By generating stereographic plots depicting breakout mud weight against inclination and azimuth, coloration represents the minimum mud weight for ensuring safe drilling operations and mitigating risks necessitating designing a mud weight window meeting specific criteria. Similar plots indicate the maximum allowable mud weight to prevent tensile-induced fractures. Findings reveal a narrowing mud weight window with increasing wellbore inclination.