GB1312719A - Method for determining the position of an interface separating two liquids - Google Patents

Abstract

1312719 Determining liquid level GA Z DE FRANCE 28 May 1970 [30 May 1969 20 May 1970] 25727/70 Heading G1A To determine the level of an interface 20 between two liquids, e.g. a column of petroleum oil 16 supported on brine 18 which is filling an underground cavity, a radio-active tracer is introduced at the interface and a detector monitors the radioactivity produced by the tracer. This method of interface detection can be used when an underground cavity is being excavated in salt-bearing rock by pumping water down an inner tube 13, pumping brine away up a second tube 12, and introducing the oil into an outer tube 11 to prevent erosion of the cavity roof. The tracer is either introduced directly into the oil or is introduced into a volume of water which sinks down the oil column until it reaches the interface. The y-ray detector is lowered down the inner tube 13 and its output, which is displayed in graphical form as a function of depth, decreases as the interface is passed. Spurious peaks and depressions on the record may be produced by radio-active material in the surrounding strata. To eliminate their effect, after a first suspected interface indication, more oil is introduced to depress the interface a known amount. If the detector produces a second interlace indication this known depth below the first, then the interface has been detected. The area of the cavity at a known depth below the surface may also be measured. This is done by introducing a known volume of water containing a tracer into the oil. When the water layer (60), Fig. 11 (not shown) reaches the brine/ oil interface it spreads out to form a layer whose thickness depends on the cavity area. The detector signal level also depends on the layer thickness, and hence provides a measurement of area.