SPE Drilling & Completion
Volume 25, Number 3, September 2010, pp. 290-299

Summary

Bitumen encounters in the deepwater Gulf of Mexico (GOM) are not unusual. In many cases, bitumen presence delayed or prevented reaching programmed total depth and adversely affected rig schedule and development planning. The cost from these events could be as high as USD 100 million. On the basis of a series of laboratory tests that investigate the effect of temperature, pressure, and drilling fluids on bitumen mechanical behaviors, this paper attempts to address four questions: (1) What is bitumen and what are its properties, especially at in-situ conditions (18,000-psi stress and 185°F temperature); (2) where is it found, in pore space or fracture; (3) what are the shapes of the in-situ accumulation; and (4) what drives it into the borehole? It has been found that the bitumen encountered at various depths may be significantly different. The bitumen adjacent to salt formation is likely to be stable and could accumulate in a large horizontal spread. The bitumen at the greater depth has to be close to vertical to survive in-situ stresses. For the horizontal bitumen spread, there is a potential to successfully drill through with a liner, and manipulating mud weight may also help. However, for the vertical-column bitumen, increasing mud weight may not be efficient, and sidetracking to avoid further encounter may be more practical. These findings are consistent with the drilling experience in the field and may help to develop a strategy to manage future bitumen encounters in the deepwater GOM.

© 2010. Society of Petroleum Engineers

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History

• Original manuscript received: 1 August 2009
• Revised manuscript received: 1 April 2010
• Manuscript approved: 6 April 2010
• Published online: 14 July 2010
• Version of record: 13 September 2010