Alaskan Viscous Oil: EOR Opportunity, or Waterflood Sand Control First?

Abstract

Abstract A regional depletion planning and comprehensive EOR screening was completed for Alaskan viscous oil (VO) resources, which have in-place volumes exceeding 10 billion barrels (Figure 1). Developed areas are shown in dark blue. With initial production dating from 1985 and a moderate development pace, viscous oil has experienced technology waves in drilling, completion, and EOR capability. Lower viscosity portions of the reservoir have typically been developed first. To date, ~ 150 million barrels of viscous oil have been produced. Ugnu heavy oil (HO) resource footprint is shown by the red outline; areas of overlap may yield development cost savings opportunities. This multi-year screening effort was undertaken and funded by BP to deepen understanding of extraction techniques, development options, and operability issues that need clarity prior to moving discrete development projects forward. Key viscous oil challenges are high well and facility costs, low well deliverability, and low waterflood oil recovery (less than 20%). This screening included technical evaluations and laboratory studies that led to separately funded geomechanics studies and field trials. This work addressed these main questions: Can we improve the oil recovery factor? How far up the viscosity continuum can we progress? Can development cost be reduced to acceptable levels? Alaska viscous oil resides in soft, friable, pressure/stress sensitive sands. A key performance issue in early- to mid-life for many waterflood patterns is catastrophic rock failure with water short-circuiting between producer and injector or producer and aquifer, called a matrix bypass event (MBE). Potential MBE mechanisms were evaluated using a coupled reservoir flow, rock mechanics, and sand transport model to predict sand failure processes and evaluate remediation and prevention options. Installing producer sand control, maintaining reservoir pressure, and moderating the interwell pressure gradient reduces sanding and MBE risks, extends waterflood pattern life, and increases oil recovery.