Anomalies in the Measurement of Wetting Liquid Pressure Gradients
- Walter Rose (Gulf Research and Development Co.) | Bernard Greifer (Gulf Research and Development Co.)
- Document ID
- Society of Petroleum Engineers
- Journal of Petroleum Technology
- Publication Date
- June 1950
- Document Type
- Journal Paper
- 10 - 11
- 1950. Original copyright American Institute of Mining, Metallurgical, and Petroleum Engineers, Inc. Copyright has expired.
- 1.6.9 Coring, Fishing
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The purpose of this note is to call attention to a source of difficultywhich can be responsible for inaccurate estimates of wetting liquid pressuregradients in mixture flow experiments of the Hassler type. It has been ourexperience occasionally to observe what were indicated to be negative pressuregradients, and these were regarded as anomalous in the sense that physicallythey seemed to contradict the requirement that the flux be in the direction ofthe potential field.
At first it was thought that our scheme of assembling barriers and coresample led to such asymmetry in the distribution of isobars that the manometricleads at each end of the core were responding to internal pressures (within thecore sample) which could be either positive or negative with respect to eachother, and which in fact might tend to reflect on different effective corelengths in an unpredictable fashion as the wetting liquid saturation waschanged. However, no compelling evidence of this possibility has beenestablished. In addition, we were cognizant of the requirements to be satisfiedin selecting manometric instrumentation to minimize the delay in response ofthe manometer to the differential pressures being measured, and were thusassured that our observations of anomalous pressure gradients could not beexplained by faulty instrumentation.
What we suggest is that if a leak sink occurs in the fluid lines connecting thecore to either side of the differential manometer, errors exceeding 100 percent may result in the estimation of wetting liquid pressure gradient, eventhough the leak is of such small magnitude that its existence would tend to beobscured by evaporation effects. This is because in a system with leaks at thespecified places, the manometer records at steady state the pressure dropacross the manometer barrier elements in addition to the pressure drop acrossthe core sample.
This possibility will be illustrated below analytically and by numericalexample for the special case where the leak occurs on the high pressure side ofthe core, since we are especially desirous to explain the significance of ourobservations of the so-called negative pressure gradients. It will beindicated, however, that leak sinks on the low pressure side of the core canaccount for observations of anomalously high values of pressure gradient, andthat multiple leaks on both sides of the core can provide for some compensationso that the errors in pressure estimation are reduced. However, the major pointto be emphasized is the fact that the impracticality of detecting the smallleak sinks which give rise to the difficulties makes it a complicated task forthe experimenter in a particular case to know with certainty that hisestimation of pressure gradient lies within the limits of error which can betolerated.
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