Comparison And Analysis Of Shale Shaker Performance
Evaluation and comparison of two or more shale shakers, although seemingly a straightforward process, is difficult to accomplish and may yield false results. The process requires a methodical procedure, accurate sampling, and control of all variables involved in the analysis.
Many reasons exist for analyzing shale shaker performance, ranging from legal analysis to objective comparison of different shakers. Regardless of
Offset comparison combines information from more than one test to determine relative performance. While this data may provide some usable information, erroneous conclusions can result because conditions between tests are difficult, if not impossible, to replicate between tests either in the laboratory or in the field.
Field tests increase the likelihood of varifiable data. Accurate sampling and analysis are essential for these evaluations. Field tests, however, are subject to the uncontrollable nature of drilling conditions. Solids arriving at the surface, even when drilling rates and formations are relatively constant, exhibit a significant variation in quantity during any particular time interval. Data replication must be demonstrated by sequentially testing 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 alternately be collected from each machine three or four times. Experience shows significant variations exist in the rate of discarded solids between tests even though all other conditions appear constant.
Laboratory testing. Laboratory conditions may increase the reproducibility of shale shaker performance since the variables are more easily controlled than in the field. Shale cuttings are virtually impossible to use in the laboratory because they deteriorate with repeated use. This deterioration of particles (shale) is an important variable in shale shaker performance. As an alternative, sand can be used, however, sand does not have similar particle sizes as shale. Additionally, the aspect ratio of sand is different than shale, therefore, their movement across the shaker will differ. Another concern with using laboratory testing is the problem with reproducing the rheological properties of drilling fluids. These properties can substantially vary from field drilling fluids even if the plastic viscosity and yield point are the same. Field drilling fluids generally have a higher percent volume of drilled solids. For this reason, field drilling fluid particle-size distributions will be skewed toward the smaller sizes when compared to laboratory-prepared drilling fluids, which will affect fluid movement across the shaker screen. Consequently, laboratory measurements of shale shaker performance can be reproduced but may have no significant relationship to field performance.
Field testing. Field testing requires careful planning and awareness of some variations in solids behavior. When comparing the performance of two shakers, an attempt to split the flow from the well in two equal streams for a side-by-side comparison is difficult to obtain even under the best conditions. Even a slight degree of unequal flow will cause uneven solids loading on the shakers. As an alternative, the entire circulation can be directed from one shaker to the other shaker but this procedure has its share of problems.
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