A significant portion of the world’s hydrocarbon reserves is found in heavy oil reservoirs. Heavy oils are often found in
shallow and highly unconsolidated reservoirs, or sometimes in deep, tight formations. Often the high asphaltic content of
these oils results in relatively higher oil density and viscosity; hence, their lower reservoir mobility poses significant
challenges to both sampling and PVT data measurements. Furthermore, modeling these fluids for reservoir evaluation
requires special techniques to capture their unique phase behavior.
The challenges of representative down-hole or surface fluid sample acquisition demand customized sampling methods to deal
In addition, the prerequisite for laboratory measurement is special sample preparation to remove emulsified water. These high
viscosity oils exhibit slower gas liberation below the bubble point and hence delayed gas-phase formation, thus making
“true” oil property measurements a challenge. Difficulties associated with fluid modeling include characterizing apparent
bubble point behavior, large viscosity changes with pressure and temperature, and asphaltene dropout.
In this paper, we present a comprehensive methodology for heavy oil sampling and characterization in unconsolidated sands
as well as in low permeability reservoirs. We present field examples to highlight the challenges and illustrate the
methodology for fluid sampling, down-hole fluid analysis, laboratory PVT data acquisition, and modeling. Sampling methods
for heavy and asphaltic oils were custom designed with special tools and sensors to obtain representative samples and precise
down-hole fluid analysis data. New laboratory techniques were developed to prepare the samples for analysis and to
distinguish between the “true” and “apparent” bubble point behavior exhibited by the heavy oil due to its non-equilibrium
behavior. Fluid models based on...