Previous Talks

Wednesday, March 11th, 2009

Bitumen Encounters in a Deepwater Gulf of Mexico field: Expensive and Challenging

Gang Han, Mike Weatherl, Jerry Osmond, Hess Corporation

Abstract

Bitumen encounters in the deepwater Gulf of Mexico are not unusual. Significant challenges have been brought to operators such as Hess (Pony), BP (Mad Dog), Chevron (Big Foot), BHP (Shenzi), etc. In many cases, bitumen presence delayed or even prevented reaching programmed TD, adversely affected rig schedule and development planning.

This paper summarizes the bitumen encounters at a deepwater Gulf of Mexico filed. Drilling experience from two exploration wells is reviewed and followed by the efforts to address the fundamental questions such as what bitumen behaves at in-situ conditions (i.e. high stress and high temperature), what shape is bitumen formation, what mechanisms drive bitumen into wellbore. A series of lab tests have been done to investigate the effect of temperature, pressure, and drilling fluids on bitumen mechanical behaviors. Numerical models are developed to analyze the stress and deformation inside and around the bitumen formations with different lateral extensions and thickness, and evaluate the stability of various bitumen shapes at in-situ conditions and around a borehole.

There are two types of bitumen have been encountered at different depths: the shallower bitumen adjacent to salt formation and the deeper one. The shallower bitumen is likely stable and could accumulate in a large horizontal spread. The deeper one has to be close to vertical to survive in-situ stresses, which result in an unstable condition and the overburden effect that amounts to several thousand psi to drive the bitumen into wellbore. For horizontal bitumen spread, the potential to successfully drill through with a liner is high and manipulating mud weight may help. However for vertical column bitumen, increasing mud weight may not be efficient and sidetrack to avoid further encounter may be more practical. Those findings are consistent with the drilling experience in the field, and may help to develop a strategy to manage bitumen drilling in deepwater Gulf of Mexico.

Speaker Biography

Gang Han is a rock mechanics advisor at HESS Corporation.  He addresses geomechanical related issues for Hess global operations, covering oil and gas fields from Gulf of Mexico, North Sea, West and North Africa, Southeast Asia, South America, and Australia.  He has published more than 30 journal and conference papers in tar/bitumen drilling, salt modeling, sand production prediction, wellbore stability, reservoir geomechanics, hydraulic fracturing, and novel drilling technologies.  He holds a PhD in Chemical Engineering from the University of Waterloo, Canada.