EVALUATION OF DRILLING STRATEGIES IN HIGHLY DEVIATED WELLS THROUGH DEPLETED TOP NUKHUL RESERVOIR, GULF OF SUEZ, EGYPT

Abstract

Casing setting at the top of Nukhul reservoir in the Gulf of Suez area presents a critical decision as a result of the depleted pressure underlying a pressurized formation and the faulty nature of Gulf of Suez area. In this area, fault throws may reach 2000-3000 meters across few meters as horizontal distance at the surface. The presence of unconformity at the top of Nukhul depleted reservoir reasoned the absence of transition zone between highly pressurized shaly Rudies Formation and top Nukhul sand. In this work, ten highly deviated wells penetrating the depleted top Nukhul reservoir have been analyzed to determine the optimum drilling scenario that ensure both economic and safe drilling operations, and determine some drilling criteria to identify the top Nukhul. Data analysis pointed out four strategies applied in drilling through the depleted top Nukhul reservoir designated as cement plug – sidetrack 12 ¼” hole strategy, zero offset LWD - PBL sub strategy, geosteering technique strategy, and complete loss - cement plug - sidetrack 8 ½” hole strategy. The comparison of the various strategies pointed out that the optimum drilling strategy is the geo-steering technique with minimum Non Productive Time (NPT) with the least reported mud losses. In addition, the rate of penetration and background gas formulated two important parameters that should be carefully observed where drilling the proximity of the depleted top Nukhul. Using these drilling parameters, a simplified flow work is suggested to confirm the depleted top Nukhul, once a fast drill break is undertaken, that comply with the International Well Control Form (IWCF) principles. This involves immediate stop drilling and continuous circulation at reduced flow rate to achieve the cutting bottom-up, report background gas response, and sample the last drilled section. The present analysis showed some practical drawbacks that should be avoided and highlighted the importance of background gas and ROP in detecting the depleted top Nukhul reservoir.