Lateral Variations in the Reservoir Properties of the Middle Miocene Jeribe Formation in the Allas Dome of the Hamrin Oil Field, Northern Iraq

The reservoir properties of the Jeribe Formation have been investigated from three wells in the southern dome of the Hamrin Oilfield (Allas Dome) based on conventional log data and cutting rock samples. The studied wells are arranged along the axis of the structure, which is in a southeast-northwest direction, with well Hr-50 being at the southeast part, followed by Hr-51 and Hr-49 towards the northwest. The Jeribe Formation's microfacies and wireline log analysis in the three wells located at the Allas Dome of the Hamrin Oilfield led to the conclusion that both lithology variations and fluid content within the formation's pore spaces are responsible for the variations in the recorded data of the wireline logs in well Hr-50 toward the northwest locations of wells Hr-51 and Hr-49. The Jeribe Formation's lithology at well HR-50 is mainly dolostone, with more prevalent grainstone microfacies. As it moves toward the other two wells, it becomes predominantly limestone, with increasing contents of wackestone and packstone microfacies. The formation in well HR-50 has an average shale content of roughly 18.2% and an average porosity of about 18.8%. In well HR-51, the average shale content and porosity are nearly 16.21% and 12.37%, respectively, while in well HR-49, the average shale content is about 18% and porosity about 12.73%. In well Hr-50, the distribution of the formation's shale is dispersed, laminated, and structural, whereas in the other two wells, dispersed shale distribution is nearly the only type that exists in the Jeribe Formation. The secondary porosity in the formation appears to be represented by separated voids, molds, and vugs, with well HR-50 exhibiting the largest percentage of secondary porosity (average 3.1%). The Jeribe Formation in wells Hr-51 and Hr-49 have predominantly gas reservoired hydrocarbons, while in well Hr-50 the formation is more likely to have oil reservoired hydrocarbons with a sizable immovable fraction. The three study wells' computed RQI and FZI values for the Jeribe Formation show that the formation has a tight reservoir rock type.