Page 201 - Introduction to Petroleum Engineering

188 WELL COMPLETIONS

Example 10.2 Productivity Index
.
Calculate J for the following values: well radius = 033 ft and r = 745 ft, formation
e
thickness h = 100 ft, permeability = 8 md, oil viscosity = 15 cp, formation volume
.
factor B = 105 RB/STB, and skin = 45.
.
.
o
Answer
Substitute the physical values into Equation 10.7:
(8md )(100ft )
J = = 031STB//psid
.
 
1
.
141. ( 21 5cp )(1 05RB/STB ln 745ft −+ 45.  
.
) 
.
 033ft 2 
10.2 PRODUCTION CASING AND LINERS
Usually, the first task of completion is to install production casing or other hardware
in the well adjacent to the target formation. Casing is a pipe, usually steel, that
extends from the producing formation to the surface. Figure 8.10 illustrates the
placement of casing in a well. If the operator chooses to install casing, it is generally
cemented in place with the cement covering any open formations and continuing
upward to previously installed surface or intermediate casing. When cemented in
place, casing mechanically supports the formation surrounding the hole. Furthermore,
it allows for selective connection to the surrounding formation with perforations.
After the cement has set, a cement‐bond log is run on wireline to assess the quality
and location of cement in the annulus. Along with the cement‐bond sensor, the log-
ging assembly has a gamma sensor and a casing‐collar locator. The gamma response
is needed to correlate the collar‐depth chart to the formation intervals that will be
perforated later. In addition to the cement‐bond log, a cased and cemented well will
be pressure tested to assess mechanical integrity. The nature of the pressure tests
vary, but generally the wellhead equipment is tested to its maximum rated operating
pressure, and the casing is tested to the maximum pressure that is expected during the
remainder of completion operations.
If the producing formation is sufficiently strong, an operator may choose to leave
the hole open, without casing. All fluid production is commingled in an open hole.
A liner is an alternative between cemented casing and open hole. It is a steel pipe
that is perforated with slots or holes, and it is anchored to the bottom of surface
casing or intermediate casing. The liner extends downward through the producing
formation. A liner does not provide as much mechanical support as the support
provided by cemented casing, but the liner can catch solids that slough from the
wellbore. Undesirable portions of a formation can be isolated by placing a hole‐free
liner with packers. These packers have expandable sleeves that seal the annular gap
between the liner and the formation. The elastomeric sleeve can be expanded by a
variety of means, including rotation of the liner to actuate mechanical compression
of a sleeve against the formation.