A Non-Destructive Method of Cake Thickness Measurement

摘要

A novel non-destructive laboratory technique and apparatusrnhave been developed to eliminate inaccuracies associated withrnthe conventional direct contact methods of mudcake thicknessrnmeasurement. The system consists of a laser head containing arntransmitter and a position sensitive receiver, a signalrnconditioner, a digital read-out system and a DC power source.rnThe position of the laser beam spot incident on the measuringrnsurface is recorded by the receiver, transferred to the controlrnbox where it is amplified and then displayed as a standardrncurrent signal on a digital read-out system. As the method isrnnon-destructive, the mechanical characteristic of the cake suchrnas softness has no influence on the accuracy of thernmeasurement.rnThe conventional methods of cake thickness measurementrnprovide an estimate only due to damage to the cake duringrnmeasurement. The accuracy varies depending on the cakernconsistency. The variation is low for hard mudcakes but highrnfor soft cakes. The newly developed apparatus andrnmeasurement technique eliminate the direct contact-relatedrnerrors and thus can provide reliable input values for modellingrnmudcake thickness dependent parameters such as formationrnand cake permeabilities, sticking force, friction coefficient etc.rnStatistical analyses of the measured values show a standardrndeviation of less than 0.025 mm and a coefficient of variationrnof less than 1%.rnThe apparatus is portable, easy to operate and suitable forrnquick measurement of mudcake thickness at the rig site. Thernperformance of the system was reviewed by analysing thernresults of a range of muds and also by comparing with thernmeasured values obtained using other methods.