SAM™
Quick Dyno Makes
setup fast and operation easy
The SAM Quick
dynamometer system is a self-contained dynamometer that can record
surface and pump cards on a well within minutes. It automatically
calculates inferred production based on the pump card. It also
allows the operator to record valve checks, counterbalance, and
perform pump leakage calculations without an on-site computer. All
data can then be transferred to a desktop computer for a more
detailed analysis if desired.
Easy to use, SAM
Quick dynamometer delivers faster data collection than any other
dynamometer available. It allows an operator to obtain a quick
surface dynamometer card in a matter of minutes. Or a rod design can
be pre-entered to calculate an accurate downhole card within seconds
after the surface card is collected. Also included is a calculation
of the total fluid production, giving the operator a quick overview
of the well and its production.
Cost-effective,
reliable, oil-field proven, and easy to use, the SAM Quick
dynamometer helps operators optimize their wells, improve production
and minimize equipment failures.
Key
benefits
Accurate on-site analysis
- A
self-contained microprocessor provides accurate readings of
polished rod load and position throughout the stroke
- Valve
check and counterbalance program lets the user determine
standing and traveling valve loads, determine effective
counterbalance, and quantify pump leakage in barrels per day -
all on-site.
- Connect
a standard horseshoe load cell for accurate dynamometer data, or
use a clamp-on load cell for a quick card -
the fastest way to see if the well is operating normally.
Easy-to-use
- Generate
accurate information in just minutes
- Simple
software makes it easy to retrieve data from the dynamometer
instrument and transfer to a PC via serial or USB port.
Fully portable
- Battery
pack provides several days worth of data gathering capacity
between charges
- Automatic
turn-off helps conserve power
Equipment and Features
The dynamometer
system, shown above, includes a self-contained microprocessor with
advanced data acquisition circuitry which provide accurate readings
of polished rod load and position throughout the stroke. A built-in
large LCD and keypad eliminate the need for a dedicated laptop
computer while gathering dynamometer data at the site.
The user has the
option of connecting a standard horseshoe load cell for accurate
dynamometer data, or a clamp-on load cell can be used for a quicker
analysis. The clamp-on, as is well known, does not require the
operator to stand-off the well, but will sacrifice some accuracy in
the measured load, and suffers from not knowing the zero offset
which changes each time the device is clamped on a polished rod.
Position is
measured with a standard string potentiometer transducer. This has
been found to be the most accurate method of measuring position for
this application and has been used for many years. If a simple
calibration procedure is followed, it is not necessary to measure
the stroke length of the pumping unit and enter it manually.
Another feature
is the valve check and counterbalance program. The user can record
load and position while the well is stopped on the upstroke and
downstroke, and counterbalance measured. This data can be analyzed
on-site to determine the standing and traveling valve loads,
determine effective counterbalance, and quantify pump leakage in
barrels per day.
A serial and USB
interface provide flexibility for transferring stored data to a
personal computer, if desired. The utility software installed on a
laptop or desktop computer provides a means to archive the data
gathered, generate simple reports for printing or e-mailing, and
export the data for further analysis, for example using Lufkin
Automation’s DIAG software suite.
Since the system
is intended to be portable, a battery pack is included to provide
several days worth of data gathering capacity between charges
(assuming the unit is turned off between well sites). The battery is
of the sealed pure lead-tin type which have been manufactured for
about 30 years. This technology provides a much longer cycle life,
high stability voltage source, wider temperature range, and a longer
shelf life compared to conventional lead acid batteries.
In addition,
power saving features have been incorporated so that the dynamometer
will automatically turn off after a period of non-use. The user also
has direct control of the backlight (it can be turned off or on at
will, or come on with keypad activity and automatically turn back
off after a programmed period of inactivity).
Quick Cards
The fastest way
to see if the well is operating normally (e.g. full pump, little or
no gas interference) is to use the Quick Card option. Surface cards
are obtained by installing the end-devices on the well (most likely
a clamp-on load cell and string transducer), turning the dynamometer
and pumping unit on, and then selecting Quick Card from the menu.
The dynamometer automatically observes the position and load range
from the end-devices and begins drawing real-time surface cards as
soon as these ranges are determined (usually within two strokes).
Multiple cards can be stored for later review and transfer to a
computer.
Figure 4 shows a
screen shot of a stored quick card obtained at a well in the Permian
Basin (7700 ft pump depth) using a clamp-on load cell and the string
position transducer. As shown, the card is automatically scaled
non-dimensionally (0 to 100%), both for position and load. Scaled
this way, the card will look the same whether a horseshoe load cell
or a clamp-on load cell are used. This type of card can provide
immediate visual feedback to the field analyst if there are problems
with the well that need to be further investigated. Types of
problems that may be found with this method include excessive
stuffing box friction, fluid pound, gas interference, pump tag, and
excessive pump leakage.
This particular
card shows a slightly higher than normal stuffing box friction, as
indicated by the flattened ends of the card. If it is desired to
further quantify the amount of friction and associated electrical
consumption, it would be necessary to go to the Dynamometer Card
option to obtain quantitative data.
Rod parts or
fouled or inoperative pumps may be difficult to catch with this
technique, since this condition would normally look like a flattened
horizontal oval on a quantitative dynagraph screen, but here the
card would be stretched to fill the screen and would look like a
large rounded oval, and could be mistaken as a full pump by an
inexperienced operator.
Dynamometer Cards
For quantitative
work, the Dyno Card option would be selected. Figure 5 shows a
quantitative card captured on the same well, using the horseshoe
load cell. As a comparison to the Lufkin Portable Analyst II (PAII)
Dynamometer, see Table 1. As presented in the table, peak and
minimum loads recorded by the two systems were very similar, within
1.5% of each other.
This dynamometer
has the capability built-in for calculating the pump card, if the
rod taper and related configuration data are entered. The algorithm
is similar to that implemented in the DIAG software, and uses the
Fast Fourier Transform method to solve the wave equation. A straight
hole is assumed in this model, which is adequate for most wells. If
a deviated well is encountered, it may be necessary to export the
surface cards to a diagnostic program that can account for rod drag
friction more accurately.
With the pump
card at hand, the analyst can immediately see if the pump is
properly filling (as seen in the figure), or if there are
operational problems with the well. It is well known that surface
card shapes are as unique as fingerprints, but pump card shapes are
very limited and definitive in nature. Thus it is easy
to discern what problems may exist with the well, and recommend
corrective action.
Other information
is provided by this simple analysis. Peak and minimum surface and
pump loads are shown, as well as the pumping unit period and strokes
per minute. The instantaneous inferred production is calculated, and
can be correlated to recent test data and percent run times to see
if there is a discrepancy due to a worn pump, tubing leakage,
leaking casing check valve etc. Gross and net pump stroke are
calculated, as well as pump fillage. Again, multiple dynamometer
cards can be stored for later review.
All this data can
be used in an initial diagnosis of a well. However, it must be kept
in mind that this analysis is simplified, and does not determine
equipment loading (e.g. motor, gearbox, structure, rod loading). It
also does not perform in-depth analyses of the entire system taking
into account such things as motor current, inertia effects (e.g. for
wells with significant speed variation), effects of rod drag in
deviated wells, or tubing movement. These features are best handled
by the more sophisticated computer-based dynamometer systems, and
the personnel trained to use them.
Clamp-on-Load / Offset Adjustment
Clamp-on load
cells have always been questionable as to their accuracy. There are
many reasons for this. A clamp-on load cell generally measures a
strain in the polished rod, and correlates this to rod stress, and
finally to rod load. Rod
load is related to the measured longitudinal strain in the clamp-on
load cell, and is proportional to the applied strain, the area of
the rod, and the Young’s Modulus. Part of the problem is that the polished rod
was not designed to be the spring element of a precision load
transducer. Thus there are uncertainties as to the Modulus, cross
section area and so forth. Also, the surface of the polished rod is
typically very rough, abused by polished rod clamps, liners,
weathering etc. A very simplified uncertainty analysis can be
performed. If each of the above terms in the formula have a 4%
uncertainty, then the measured load would have a root-mean-square
uncertainty of 7% (but the actual error could be higher). These
effects cannot be corrected for in a clamp-on design due to the
uncertainty of the material being measured.
Another
uncertainty with the clamp-on is the zero offset. The transducer is
usually placed on the polished rod which already has an unknown load
on it, and the act of clamping the device may place additional
strain on the gaged element. These effects produce a measured
‘load’ which needs to be adjusted to a ‘known’ load. A
generally accepted practice in the industry is to stop the well on
the downstroke and correlate the indicated load with that of the
buoyant weight of the rod string.
A handy feature
of this dynamometer allows the zero offset of the clamp-on to be
automatically adjusted using the pump card and the calculated
buoyancy load at the end of the rod string. This adjustment is
feasible for wells with relatively low rod friction. In this manner,
the clamp-on can be made ‘almost’ quantitative, and is probably
adequate for a brief analysis. Figure 6 presents dynamometer cards
using a clamp-on load cell and the zero-offset adjustment on a
gas-engine driven well that would have been difficult to stand-off
for a true quantitative analysis.
This adjustment
technique was used with a clamp-on load cell on the well shown in
Figure 5 for comparison purposes. As presented in Figure 7, the
shape of the dynamometer cards compare very well with those in
Figure 5, but the adjusted clamp-on loads are about ~1300 lbs high.
Table 1 shows that the maximum polished-rod load error is 7%, while
the minimum polished-rod load error is about 12.5%.
In spite of this,
the indicated range of the clamp-on is within 2% of the horseshoe
load cell, a better than expected result, considering the prior
discussion on uncertainty. It should also be noted that this type of
range accuracy can only be expected with a clamp-on load cell that
is trim calibrated at the factory to have a consistent mV/V output.
There is no doubt that these results cannot be expected in the
general case, and there will be variability due to the care with
which the operator places the clamp-on load cell on the rod, and the
quality of the rod being clamped.
Well Configuration
Being a
simplified dynamometer, only limited information is needed to obtain
surface and pump cards. If only surface cards are desired, the user
simply enters the well name and stroke length. If pump cards and
inferred production are desired, the user enters the rod string data
(type, lengths, diameters) and pump diameter. An example screen is
shown in Figure 8. If a standard rod diameter is entered, the
dynamometer populates the rod weights and modulus so these entries
don’t have to be entered manually. The damping factor, stuffing
box friction, tubing head pressure, and tubing gradient have
defaults that can be edited if desired for more accurate results
(they have a secondary affect on the shape of many pump cards).
Valve Checks, Counterbalance, and
Pump Leakage
The quick
dynamometer system allows the operator to record valve checks and
counterbalance measurements, and then analyze this information.
Figure 9 shows an example of a well where the valve checks are being
analyzed to mark the standing valve load. The standing and traveling
valve loads, residual friction (if performed), counterbalance, and
pump leakage can all be analyzed in the dynamometer.
Laptop Utility Software
The utility
software provides a simple interface to retrieve all data from the
dynamometer instrument. Example screen shots are shown in Figure 10.
Well configurations can be transferred to and from the dynamometer,
as well as quick cards, dynamometer cards, and valve checks.
Features are provided to manage groups of wells, and synchronize the
dynamometer stored data to the computer’s database.
Figure 4. Stored Quick Card using a clamp-on load cell. Card shows
some stuffing box friction.
Figure 5. Stored quantitative dynamometer card, using horseshoe load
cell.
Figure 6. Dynamometer cards from a gas-engine driven well, using a
clamp-on load cell, with the automatic zero-adjustment.
Figure 7. Clamp-on load cell with automatic zero-adjustment; compare
to Fig. 5 and Table 1.
Figure 8. Example data entry screen needed to calculate pump cards.
Figure 9. Example valve check analysis.
