Summary
The reuse of existing well bores is a cost-saving technique used by oil and
gas producers in mature fields. This process usually requires the removal of
tubing and packers to allow the well to be deepened or sidetracked. The tubing
removal process is often made difficult when the tubing is stuck inside the
casing because of mechanical binding or binding caused by dehydrated mud or
sand in the annulus between the tubing and casing. Conventional direct and
indirect methods of finding the stuck point(s) along an interval of tubing,
such as free-point indicator tools or acoustic attenuation measurements, have
proved themselves useful in finding the point(s) where the tubing is stuck.
However, when the sticking is caused by uncompacted sand that has entered the
annular space between the tubing and casing, these conventional stuck-pipe
indication methods are often inconclusive or misleading.
Technological advancements in the design and development of slim, 1
11;'16-in. outside diameter (OD), radial cement bond tools allow the
application of a new measurement to find sand-stuck tubing intervals. These
tools provide up to six independent, closely spaced acoustic attenuation
measurements distributed radially around the tool body. When the recording
operation is performed inside the tubing, the increased sensitivity of these
tools to sound attenuation, as compared with conventional omnidirectional
amplitude signals, allows sand intervals along the outside of the tubing to be
distinguished from intervals where little or no sand is present. This
information is used to select the best depth to sever or back-off the free
tubing in order to reduce the interval length and expense associated with the
washover process required to remove the remaining tubing from the
wellbore.
An overview of conventional stuck-pipe recovery techniques is provided here,
along with a brief explanation of applicable acoustic technology. A case study
of a South Louisiana well is presented to demonstrate the application and
illustrate the cost savings which can be gained by use of this very new
technology.
Introduction
Oil and gas producers operating in maturing fields such as the U.S. Gulf of
Mexico basin continually strive to reduce the expense of drilling new wells.
The presence of oyster leases and dredging restrictions in inland bay fields
severely limits, and in some cases prohibits, the drilling of new wells. One
method of overcoming these obstacles includes reentering existing wells to take
advantage of the casing string already cemented in place. This process usually
requires the removal of old tubing and packer assemblies that were once used to
produce hydrocarbons from now-depleted zones. Their removal clears the way for
recompleting to shallower zones, deepening the well, or sidetracking to reach
new reservoirs.
The recovery of stuck tubing has plagued the oil and gas industry since its
inception and is commonly necessary in remedial well operations (Bernat 2001).
Conditions that can cause tubing to get stuck are often mechanical in nature,
including collapsed or parted casing, dehydrated drilling mud, and formation
sand filling the annular space between the tubing and casing.
The most common methods of recovering stuck tubing include impact tools
(jars), washover operations, low-frequency vibrators, and milling tools (Stoesz
and DeGeare 2000). These recovery techniques have been used in the industry for
many years with varying degrees of success, depending upon the amount of time
spent on the process. Because jarring, washover, and milling techniques require
a drilling or workover rig to be moved to the wellsite, the amount of time
spent on the pipe recovery process is kept to a minimum so as to avoid a
negative impact on project economics.
Risk factors such as the type of sticking, hole angle, well depth, and
material to be removed should be evaluated to determine the best method of pipe
recovery (Stoesz and DeGeare 2000). The usual process for removing mud-stuck or
sand-stuck tubing is to reciprocate the tubing with the rig to free up a length
of tubing, and then to perform an electric line backoff to allow recovery of
the free section. Wash pipe is used to circulate and remove dehydrated mud or
sand by washing over the remaining tubing string, and then the free-point,
backoff, and recovery process is repeated (Walker 1984). When the tubing cannot
be freed by jarring and reciprocating, the challenge is to determine the proper
depth interval for washing over the tubing in order to minimize rig time and
other associated costs.
© 2007. Society of Petroleum Engineers
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