Field development of a heterogeneous carbonate reservoir in Abu Dhabi-United Arab Emirates focused mainly on the geo- steering technique to penetrate the target level of the reservoir and drill and place long radius open horizontal hole for final completion as single producers or injectors. Tough drilling environment of natural islands, manmade islands, shallow and deep waters based on poor seismic data and depth uncertainties added to difficulties of predicting the setting depth of the 7" liner before geosteering operations of the open horizontal hole. Wells clustering to minimize drilling and surface facilities foot prints, top drive drilling using rotary steering system (RSS) techniques together with real time LWD helped to better control trajectory and placement of the horizontal holes as planned. Fluid identification in pilot holes as well as across the horizontal holes was successfully acquired to capture necessary reservoir fluid samples.

Geosteering operations and the experienced difficulties of placing the horizontal holes as planned were affected by rock heterogeneity, rate of penetration, mud system, and real time monitoring and follow up. The implemetation of geosteering and real time data acquisition was supervised by the team abd resulted in timly decisions for proper action and achievement of the target development plan. However, depth uncertainties resulted in improper placement of three wells but these well were worked over to correct the location. In addition, coiled tubing accessibility problems have been experienced following production and injection commissioning. This problem was attributed to the undulating horizontal hole and the well completion technique.

This paper presents a field case of drilling and geosteering of long radius open horizontal holes and wells completion. It points to possible reasons for experienced poor coiled tubing accessibility and the lessons learned for future development.

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