Petrophysical Characteristic of the Lower Jurassic Formations in the Miran Oil Field, Kurdistan region/ NE Iraq
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Abstract
This study focuses on evaluating the Lower Jurassic Formations within the Miran Oil Field, located in Northeastern Iraq. A detailed analysis was conducted using well log data from the Alan, Mus, and Adaiyah formations encountered in the Miran-2 (MW-2) Well, with supplementary stratigraphic and lithological information from wells ME-1 and MW-3. The investigation employed both quantitative and qualitative well-log data, including Gamma Ray, Sonic, Density, Neutron, and Photoelectric Factor logs, rate of penetration (ROP), and gas chromatographic profiles. Additional datasets, such as Logging While Drilling (LWD), Measurement While Drilling (MWD), well reports, and master logs, were also used.
The results indicate that the upper part of the Lower Jurassic interval, comprising the Alan and Mus formations, is predominantly composed of carbonate rocks interbedded with shale, with intermittent evaporite bands. The presence and thickness of evaporite rocks increase downward, eventually dominating the lower part of the section, represented by the Adaiyah formation.
Due to the prevalence of shale in the upper units and evaporites in the lower units, the studied section lacks favorable reservoir characteristics. Porosity is generally classified as poor to negligible, and permeability is similarly low. Based on threshold values of 35% shale content, 0.1 millidarcy permeability, and 0.07 porosity, it was determined that of the 148-meter total thickness of the Alan, Mus, and Adaiyah formations, 26 meters are shale-dominated and 67.5 meters are evaporite-rich. Of the remaining 54.5 meters of carbonate lithology, only a total of 2.5 meters exhibit porosity and permeability values that exceed the minimum thresholds required for effective reservoir rocks.
Consequently, the study concludes that the Lower Jurassic successions in the Miran Oil Field do not constitute a viable hydrocarbon reservoir. However, due to its lithological composition, particularly the extensive evaporite and shale layers, it may serve as an effective seal rock for underlying reservoirs, such as the Butmah and Kurra Chine formations.
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