oa Shargi Shale Challenge from Geology to Drilling

The Fiqa Formation is an argillaceous to carbonate sequence which is present over most of North<br>Oman. It is Late Cretaceous in age and the lower member is a shale unit known as the Shargi Shale<br>(Santonian to early Campanian).<br>Drilling this sequence has been a challenge for PDO through out the years. The shale frequently reacts<br>with the drilling mud fluids, although reactions can behave differently in some cases. The amount of<br>time the shales are exposed to the drilling fluids is, however, important since the more exposure; the<br>more the shales swell, often resulting in caving. The consequences of these drilling issues are oversized<br>hole, pack-off tendency, induced losses, stuck pipe and frequently result in severe problems in<br>running and cementing casing..<br>Recent technology developments have been introduced and deployed and future technological<br>improvements are to be implemented. Changing drilling parameters have resulted in mitigating the<br>effect of caving and changes in well design have allowed the sections to be drilled faster meaning less<br>exposure, reducing drilling problems. Significant improvements have been seen in drilling performance<br>in terms of time and cost.<br>The paper plans to present case studies based on the experiences gained so far. The case studies are<br>taken from Gas Exploration drilling in North Oman. They will show how various thickness of Shargi<br>Shale in the area were encountered and how each was dealt with. Learning gained from drilling these<br>wells has enabled PDO to reduce shale exposure times and prevent the shales swelling and reduce<br>caving into the hole.