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Lubricity Evaluation Monitors are designed for the static or dynamic testing of
drilling fluids or muds and lubricants at atmospheric and reservoir conditions.
Excessive torque and drag can have many adverse effects during the drilling process.
To optimize the drilling process, various drilling mud and lubricant combinations
need to be evaluated. This series of instruments is designed to allow the end user
to measure the mud lubricity or friction coefficients between a simulated tool joint
and a well bore surface under simulated reservoir conditions. The instruments are
designed to test reservoir core samples as well as various drill pipes or casing
materials. From this information, the user can recommend proper mud systems, determine
optimum lubricant concentrations, develop new lubricant additives, predict drill
string loads, minimize torque and drag, and improve drill string design techniques.
From this information, the end user will be able to optimize the drilling process
to reduce the overall drilling costs.
The series of LEM instruments all operate in a similar fashion. A test sample of
sandstone, limestone, quartz glass, ceramic, field core, or casing is installed
into the sample holder within the mud test cell. A carbon steel bob, which simulates
the drill stem or tool joint, is inserted into the mud test cell. With the bob rotating
at the desired test speed, a constant load is applied to the test sample, forcing
the test sample up against the rotating bob. The torque on the rotating bob and
axial load are both measured and recorded. From this information, the torque as
a function of the friction or axial load can be determined. These measurements can
be performed as a function of pressure and temperature. Chemical additives can then
be blended into the drilling fluid to evaluate the change in the friction factors.
A fluid leak-off test can be performed with certain models and a filter cake can
be deposited on the test sample under static or dynamic conditions. The drilling
fluid can be either static or re-circulating, depending upon the instrument. Once
the filter cake has been deposited, the load can be applied and the friction values
can be determined in the presence of the filter cake buildup. A differential sticking
test can also be performed where after the filter cake has been deposited, the load
is applied and then the simulated drill bite is rotated. The torque required to
move the simulated drill bit is measured.
The load being applied to the test sample in the LEM-2000 is a direct measurement
by weights. The load being applied under pressure with the LEM-3000 and 4000 series
is measured with an electronic load cell. The movement of the test sample is measured
with a linear transducer so the rate of wear on the sample can be determined. Pressures
are measured with electronic pressure transducers and temperatures are measured
with thermocouples. The computer control software for the Model LEM- 4100, SmartLub™,
controls the instrument and collects all of the data.