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Abstract

In the northern part of Oman, gas and condensate have been discovered in the Amin formation at depths between 4,000 m and 5,000 m at pressures as low as 450 and more than 600 bar and reservoir temperatures of above 150 degC. The Amin formation is dominated by very heterogeneous Aeolian deposit reservoirs. Due to its age of more than 500 million years and its hard cementation, it poses challenges for the drilling equipment and the development concept. The reservoir reaches a thickness of 200 m and is very stratified with low-quality units: porosity < 5% and permeability < 0.1 mD, and high permeability streaks: porosity > 10% and permeability > 100 mD. Given the complexity and the challenges of this formation, the development started in a promising area with two fields, with good to moderate reservoir quality. At early stage of development, vertical wells were drilled and put into production and only small flow could be achieved without stimulation, leaving considerable hydrocarbon volumes not producible. Then hydraulic frac stimulations have been conducted in them to increase productivity. At 2007 Oman's first horizontal well in this tough rock was drilled. At a vertical depth of 4,033 meter subsea (4,578 meter along hole) the Amin tight sand reservoir was penetrated over a length of almost 400 m within the reservoir. The Image logs confirmed the presence of natural fractures almost perpendicular to the well orientation, which could enhance productivity. Conventional wireline and logging while drilling image logs were acquired to improve the geological understanding of the reservoir complexity. These logs showed important reservoir rock types and geological features such as natural fractures and other features were interpreted; such as type of bedforms that exist in eolian deposits that could correlate to different reservoir rock types and enabled to build geological description along the well, and in- situ stress induced features that indicated the stress concentrations around the wellbore. Production experience from Amin is limited, and there are still big challenges related to the understanding of the reservoir settings and characteristics. The first horizontal well in the deep Amin reservoir is now a major step forward to further developing the challenging Amin formation across the country. It allows exposing more reservoir sections along the horizontal well path to contribute to flow. The results are giving important insights into the lateral heterogeneity of the Amin formation and the existence of natural fracture systems, which could enhance well deliverability. The achieved successes so far from fracturing treatment demonstrate the value of further developing Amin formation.

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