Page 232 - Introduction to Petroleum Engineering

WELL PATTERNS 219
number and type of wells, well rates, and well locations. The distribution of wells is
known as the well pattern. The selection of a development plan depends on a
comparison of the economics of alternative development concepts. Reservoir flow
models are especially useful tools for performing these studies.
In many reservoirs, an injection program is used to push oil from injection wells
to producing wells. In many reservoirs, the injected fluid is water, which is immis-
cible with the oil. Immiscible fluid displacement between one injection well and
one production well is the simplest pattern involving injection and production
wells. A variety of other patterns may be defined. Some examples are shown in
Figure 11.9. A representative pattern element for the five‐spot pattern is identified
using shaded wells.
The ratio of the number of producing wells to the number of injection wells is
shown in Table 11.1 for common well patterns. The patterns in Table 11.1 and
Figure 11.9 are symmetric patterns that are especially effective for reservoirs with
relatively small dip and large areal extent. The injectors and producers are gener-
ally interspersed. Other patterns in which injectors and producers are grouped
together may be needed for reservoirs with significant dip. For example,
a peripheral or flank injection pattern may be needed to effectively flood an
anticlinal reservoir.
In addition to reservoir geometry and the displacement process, the well pattern
depends on the distribution and orientation of existing production wells and the
desired spacing of wells. Wells may be oriented vertically, horizontally, or at some
deviation angle between horizontal and vertical. The orientation of a well depends on
such reservoir features as formation orientation and, if fractures are present, fracture
orientation. For example, if a reservoir contains many fractures that are oriented in a
particular direction, recovery is often optimized by drilling a horizontal well in a
direction that intersects as many fractures as possible. Recovery is optimized because
recovery from fractured reservoirs usually occurs by producing fluid that flows from
the matrix into the fractures and then to the wellbore.
Well spacing depends on the area being drained by a production well. A reduction
in well spacing requires an increase in the density of production wells. The density
of production wells is the number of production wells in a specified area. Well density
can be increased by drilling additional wells in the space between wells in a process
called infill drilling.

11.6.1 Intelligent Wells and Intelligent Fields
It is often necessary in the management of a modern reservoir to alter the completion
interval in a well. These adjustments are needed to modify producing well fluid ratios
such as water-oil ratio or gas-oil ratio. One way to minimize the cost associated with
completion interval adjustments is to design a well that can change the completion
interval automatically. This is an example of an “intelligent well.”
Intelligent wells are designed to give an operator remote control of subsurface
well characteristics such as completion interval. In addition, intelligent wells are
being designed to provide information to the operator using downhole measurements