This paper presents well geosteering and advanced completion technologies utilized to successfully tap attic oil reserves in the most mature giant of the Saudi Arabian carbonate fields. After more than sixty years of continuous production, approximately 57% of the oil initially in place in the primary reservoir has been produced. The upper 10% of the main reservoir (-20 feet net) has a lower quality rock relative to the layer below; accordingly, it remains untapped across the whole field area. The attic oil was unattractive due to very low vertical well oil rates caused by excessive water production from the prolific, but now largely flooded reservoir section located immediately below. Most attempts to produce the attic oil selectively in vertical wells were short-lived due to low well productivity combined with water production. The first real development of these reserves started in the mid 1990's with short radius sidetracks. These early horizontal wells were plagued with poor directional control and high failure rate. The next step was medium radius sidetracks yielding much better oil production rates. In 2003, the drilling of the first mutli-Iateral Maximum Reservoir Contact well revolutionized this attic oil development. By mid 2007, 12 of these wells have been drilled, placed mainly downdip of the original first line producers. Each well produces up to four times the initial horizontal well production rates at low watercut. The wells are equipped with smart completions to reduce contribution from high watercut laterals. The main challenge for the development has been lateral placement, which requires the most sophisticated geosteering tools available in the industry. The attic oil development is now contributing more than 1/3 of the total oil production and have brought the overall field watercut down to approximately 30%..

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