--> Abstract: Shargi Shale Challenge from Geology to Drilling, by Elias Al-Kharusi; #90105 (2010)

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AAPG GEO 2010 Middle East
Geoscience Conference & Exhibition
Innovative Geoscience Solutions – Meeting Hydrocarbon Demand in Changing Times
March 7-10, 2010 – Manama, Bahrain

Shargi Shale Challenge from Geology to Drilling

Elias Al-Kharusi1

(1) Exploration, PDO, Muscat, Oman.

The Fiqa Formation is an argillaceous to carbonate sequence which is present over most of North Oman. It is Late Cretaceous in age and the lower member is a shale unit known as the Shargi Shale (Santonian to early Campanian).

Drilling this sequence has been a challenge for PDO through out the years. The shale frequently reacts with the drilling mud fluids, although reactions can behave differently in some cases. The amount of time the shales are exposed to the drilling fluids is, however, important since the more exposure; the more the shales swell, often resulting in caving. The consequences of these drilling issues are over-sized hole, pack-off tendency, induced losses, stuck pipe and frequently result in severe problems in running and cementing casing..

Recent technology developments have been introduced and deployed and future technological improvements are to be implemented. Changing drilling parameters have resulted in mitigating the effect of caving and changes in well design have allowed the sections to be drilled faster meaning less exposure, reducing drilling problems. Significant improvements have been seen in drilling performance in terms of time and cost.

The paper plans to present case studies based on the experiences gained so far. The case studies are taken from Gas Exploration drilling in North Oman. They will show how various thickness of Shargi Shale in the area were encountered and how each was dealt with. Learning gained from drilling these wells has enabled PDO to reduce shale exposure times and prevent the shales swelling and reduce caving into the hole.