Page 25 - Introduction to Petroleum Engineering

RESERVOIR MANAGEMENT 9

Example 1.3 Gas Recovery
The original gas in place (OGIP) of a gas reservoir is 5 trillion ft (TCF). How
3
much gas can be recovered (in TCF) if recovery from analogous fields is
between 70 and 90% of OGIP?

Answer
Two estimates are possible: a lower estimate and an upper estimate.
The lower estimate of gas recovery is 0 70 5 TCF 3 5 TCF.
.
.
The upper estimate of gas recovery is 0 90 5 TCF 4 5 TCF.
.
.
1.3 RESERVOIR MANAGEMENT

One definition of reservoir management says that the primary objective of reservoir
management is to determine the optimum operating conditions needed to maximize the
economic recovery of a subsurface resource. This is achieved by using available resources
to accomplish two competing objectives: optimizing recovery from a reservoir while
simultaneously minimizing capital investments and operating expenses. As an example,
consider the development of an oil reservoir. It is possible to maximize recovery from the
reservoir by drilling a large number of wells, but the cost would be excessive. On the
other hand, drilling a single well would provide some of the oil but would make it very
difficult to recover a significant fraction of the oil in a reasonable time frame. Reservoir
management is a process for balancing competing objectives to achieve the key objective.
An alternate definition (Saleri, 2002) says that reservoir management is a continuous
process designed to optimize the interaction between data and decision making. Both def-
initions describe a dynamic process that is intended to integrate information from multiple
disciplines to optimize reservoir performance. The process should recognize uncertainty
resulting from our inability to completely characterize the reservoir and fluid flow
processes. The reservoir management definitions given earlier can be interpreted to cover
the management of hydrocarbon reservoirs as well as other reservoir systems. For example,
a geothermal reservoir is essentially operated by producing fluid from a geological
formation. The management of the geothermal reservoir is a reservoir management task.
It may be necessary to modify a reservoir management plan based on new
information obtained during the life of the reservoir. A plan should be flexible enough
to accommodate changes in economic, technological, and environmental factors.
Furthermore, the plan is expected to address all relevant operating issues, including
governmental regulations. Reservoir management plans are developed using input
from many disciplines, as we see in later chapters.

1.3.1 Recovery Efficiency

An important objective of reservoir management is to optimize recovery from a
resource. The amount of resource recovered relative to the amount of resource
originally in place is defined by comparing initial and final in situ fluid volumes.