dc.description.abstract | Waterflooding is a commonly used operation in the oil industry. It is used to in-
crease oil recovery from the reservoir, and is considered as a secondary recovery
technique. In short, the reservoir is flooded with water to increase pressure, and to
displace oil from pore spaces. This thesis has explored three general methods for
optimizing this operation, with special attention paid to treatment of constraints.
As means of background theory, a brief introduction to petroleum engineering is
provided, the concept of dynamic optimization is stated, and reservoir simulation
is presented.
The three methods of interest are gradient-based control optimization, reactive
control, and techniques based on simulator-embedded constraints. The popularity
of gradient-based control optimization has grown during the last decade, and there
has been conducted a vast amount of research on the topic during this period. Such
optimization is usually referred to as adjont-based optimization, as efficient com-
putation of gradients serves as a prerequisite for the method to remain tractable for
reservoir optimization. Next, reactive control is widely used in the industry, and its
popularity is among others due to simplicity, robustness, and model-independence.
The last method considered is based on simulator-embedded constraints, which of
today is a relatively unexplored area. A new heuristic has however been developed
during this work, which combines output unconstrained control optimization and
simulator-embedded constraints.
The three general approaches are implemented using the Matlab Reservoir Simu-
lation Toolbox. A series of four case studies are employed to assess the merits of
the methods. In short, if geological uncertainty is put aside, gradient-based op-
timization appeared as the preferred method. Furthermore, the popularity of the
reactive control approach can be understood, as the method performed adequately
- keeping its simplicity in mind. The heuristic that was developed showed some
potential, but there are three issues at the current stage that must be addressed
and resolved. | |