Unlocking Deepwater Heavy Oil Reserves - A Flow Assurance Perspective
Authors: Mehta Ajay P. , Zabaras George J. , Schoppa Wade , Peters David J. 
Published: October 2008

As the industry's deepwater developments continue to mature, newer discoveries in the ultra deepwater demonstrate a trend towards more difficult and heavier hydrocarbons that are far removed from existing infrastructure. Since heavy oils represent a significant reserve-base, there is a strong economic incentive within the industry to develop technologies to profitably produce these hydrocarbon reserves. Heavy oils are often characterized by their high viscosity, low API gravity and low reservoir energy. Heavy oils are also prone to the formation of emulsions. The combination of these factors makes the production and transportation of heavy oils a major challenge from a flow assurance perspective. Development of a robust flow assurance strategy will play a central role in the system selection, detailed design, and operation of deepwater heavy oil fields. In this paper, we identify some of the most significant flow assurance challenges associated with heavy oil production and discuss technology developments needed to overcome them. In particular, we have focused our attention on viscosity management techniques and emulsion formation tendencies of heavy oils and also assessed the risk posed by solids such as hydrates, wax and asphaltenes. We also present a brief analysis of the operability aspects for producing deepwater heavy oils, describe major differences from conventional lighter oils, and evaluate its impact on the topsides infrastructure and subsea system selection and design.

Introduction

Heavy oils have been successfully produced for several decades from various locations around the world. A majority of this heavy oil production has come from either onshore or shallow water fields in Venezuela, Mexico, Canada, Oman and California. The profitability of production from heavy oils is directly correlated to the price of oil. In high price environments, producing these heavy oil fields can be relatively profitable, but in low price environments they can be marginal or non-economic. The high cost of producing heavy oils is attributed to its intrinsic qualities that are characterized by a low API gravity (usually less than 20), high viscosity, low pour point, high acid number, strong emulsion tendency and low reservoir energy. Each one of the above factors leads to a high cost of producing each barrel of heavy oil and it commands a relatively lower price compared to conventional light oil. The challenge of producing heavy oil reserves in deepwater is further exacerbated by the discovery of reserves in remote locations that are cut-off from production facilities and infrastructure. The recovery, lift, transportation, processing and eventual upgrading for sulfur, metal and acid removal, poses some unique challenges for economically producing deepwater heavy oil reservoirs as recently summarized1,2,3 by some of the major industry players active in developing these resources.

While the deepwater environment represents much more complex technical and economic challenges for producing heavy oils, some of the basic issues pertaining to heavy oil are essentially the same regardless of its origin. Consequently, as the industry begins to develop technical solutions for unlocking heavy oils, it would be prudent to first tap into the vast body of experience and knowledge that has already been gained in producing onshore and shallow water heavy oil fields.