Page 134 - Shale Shakers Drilling Fluid Systems
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SHAKER USER'S GUIDE 117
Do not spray electrical equipment or mo- the reason for analysis, the goal is to determine
tors with oil or water. how the shaker and screen combination perform
in a particular application. The data can be used
to optimize performance of a given machine and
GENERAL GUIDELINES assist in determining the number of shale shak-
ers needed. By far the most frequent reason for
1. Shale shakers should run continuously while analyzing performance is to compare one brand of
circulating. Cuttings cannot be separated from shale shaker with another. This requires that test
drilling fluid if the shaker is not in motion. conditions remain constant and representative of
2. Drilling fluid should cover most of the screen. field performance.
If the drilling fluid only covers one-fourth to
one-third of the screen, the screen mesh is
too coarse. Comparison Methods
3. Torn screens should be repaired or replaced
at once. Holes in panel screens can become Four different comparison techniques are avail-
plugged preventing cutting removal. Install able as shown below. Each technique has advan-
screens according to manufacturer's recom- tages and disadvantages.
mended installation procedures.
4. Shaker screen replacements should be made Laboratory Field
as quickly as possible. This will decrease the
amount of cuttings remaining in the drilling Offset • •
fluid because the shale shaker is not opera- Side-by-Side • •
tional. Locate and arrange tools and screens
prior to actual replacement. If possible, re- Offset comparison combines information from
place the screens during a connection. In more than one test to determine relative perfor-
critical situations, pumps may be shut down mance. While this data may provide some usable
(or slowed) and drilling stopped while screens information, erroneous conclusions can result be-
are being replaced. cause conditions between tests are difficult, if not
5. Water should be added downstream and not impossible, to replicate between tests either in the
in the possum belly (or back tank) or onto laboratory or in the field.
the shale shaker screen. Field tests increase the likelihood of varifiable
6. Except in cases of lost circulation, the shale data. Accurate sampling and analysis are essen-
shaker should not be by-passed, even for a tial for these evaluations. Field tests, however, are
short time.
7. The possum belly (or back tank) should not subject to the uncontrollable nature of drilling
conditions. Solids arriving at the surface, even
be emptied into the sand trap or mud tank when drilling rates and formations are relatively
system before making a trip. This will elimi- constant, exhibit a significant variation in quan-
nate cuttings moving down the tank system tity during any particular time interval. Data rep-
and plugging desilters as the next drill bit lication must be demonstrated by sequentially test-
starts drilling.
ing the same machine three or four times, at the
same flow rate, under the same conditions. If two
machines are to be compared, data should alter-
COMPARISON AND ANALYSIS nately be collected from each machine three or
OF SHALE SHAKER four times. Experience shows significant variations
PERFORMANCE exist in the rate of discarded solids between tests
even though all other conditions appear constant.
Evaluation and comparison of two or more shale
shakers, although seemingly a straightforward pro- Laboratory testing. Laboratory conditions may
cess, is difficult to accomplish and may yield false increase the reproducibility of shale shaker perfor-
results. The process requires a methodical proce- mance since the variables are more easily con-
dure, accurate sampling, and control of all vari- trolled than in the field. Shale cuttings are virtu-
ables involved in the analysis. ally impossible to use in the laboratory because
Many reasons exist for analyzing shale shaker they deteriorate with repeated use. This deterio-
performance, ranging from legal analysis to objec- ration of particles (shale) is an important variable
tive comparison of different shakers. Regardless of in shale shaker performance. As an alternative,
