English Edition (6 MB pdf) - Saudi Aramco

favorable economics of drilling smaller holes, as smaller holes
require less drilling fluids and chemicals, cheaper casings and
completion materials, and ultimately results in cheaper wells
that are environmentally more efficient.
The favorable economics of slim hole wells has subsequently
become a value driver for the development of slim hole wireline
and logging while drilling (LWD) technology by the service
companies. At present, one of the service companies
(Weatherford) has been able to deploy successfully for Saudi
Aramco it’s suite of slim wireline tools in the diameter range of
2” to 2½”, capable of logging a typical traditional wireline
quad-combo made-up of density, neutron, resistivity, sonic and
gamma ray. In addition, several “specialized” measurements,
such as cross dipole sonic, formation pressure testing, and
resistivity imaging can also be acquired.
Further developments in the use of battery and memory
technologies has allowed some of these tools to be deployed
using a broader range of conveyance techniques, thereby
reducing the risks associated with slim hole well entry 2 .
THE HISTORY OF SMALL DIAMETER LOGGING TOOLS
The use of devices to measure the petrophysical and
geophysical properties of the subsurface began in 1927 when
the first electrical well logging operation was performed. Since
that time, the use of wireline conveyed logging tools has
become a key element for several industries with a need to
better understand the subsurface. For example, applications
for this type of data are well documented in ground water,
mining, petroleum, and geotechnical endeavors.
The technologies for acquiring this data range from simple
measurements of resistivity for ground water applications, to
sophisticated measurements that provide an understanding of
formation properties for the petroleum industry. Although the
actual logging tools that perform these measurements have all
evolved from the first instruments used in the 1920s. Their
development has taken different paths depending on their
industry of use. In the oil and gas industry where boreholes
tend to be large in diameter (up to 36”) and deep (over
30,000 ft), logging technology has tended to have a diameter
in the range of 3” to 5”. This size allows the tools to have
ample room to house the various components and electronics
necessary for them to make measurements in open hole
environments where temperatures can exceed 160 °C, and
pressures of over 20,000 psi. In cased hole applications,
however, smaller diameter tools have been developed for entry
into the well through production tubing, and for production
logging applications where flow measurements in the well
must be made with minimal disturbance when passing the
logging tool through the fluids being produced.
In the mining industry, the development of logging tools
has evolved in a somewhat different fashion because of the
tendency for slimmer wellbores, and shallower wells primarily
drilled to gather information about the subsurface, and not as
a production conduit. The resulting logging technology had a
small diameter, had open hole applications, and was designed
to be easily transported to remote locations where the drilling
footprint is much smaller than that of an oil field drilling
operation.
OPPORTUNITIES LEADING TO SMALL DIAMETER OIL
FIELD APPLICATIONS
For many years, the use of small diameter open hole logging
technology was confined to the mining industry. Aside from a
few specialized applications, the widespread use of this
technology in oil field applications was limited due to the
following factors:
• Borehole characterization. Smaller diameter tools
needed improved characterization to make accurate
measurement in larger holes.
• Pressure and temperature limitations. Typically, holes
drilled for evaluating mineral deposits are relatively
shallow, therefore the logging instrumentation did not
need to be constructed to the higher temperature and
pressure specifications required for oil field use.
• Range of measurement options. The applications for
evaluating mineral deposits from petrophysical data are
limited compared to those for oil and gas deposits.
Therefore, the number of measurement options was far
fewer, leaving many gaps in the types of information that
could be obtained from small diameter logging tools.
In the 1980s, oil field drilling technologies began to be
developed that allowed for the drilling of wells with increased
deviation, horizontal wells and slimmer wells. The acceptance
of this drilling technology and the subsequent rapid wide -
spread use began to produce challenges in evaluating these
wells. These challenges thereby created opportunities to
employ new logging techniques, including the use of small
diameter logging technologies.
To take advantage of the opportunities posed by the new
drilling technologies, initiatives into new research for small
diameter logging tools began in the late 1980s. The goal of
this research was to develop technologies that could meet the
following requirements:
• Produce accurate measurements in larger diameter
boreholes (at least 12¼”).
• Be able to operate at elevated borehole temperatures
and pressures.
• Produce the range of measurement options commonly
found in oil field logging operations.
• Be slim enough to access difficult boreholes through the
drillpipe.
• Constructed with a rigid length as short as possible to
help negotiate severe doglegs and to minimize rat hole
drilling.
SAUDI ARAMCO JOURNAL OF TECHNOLOGY SUMMER 2010 59