A Non-Destructive Method of Cake Thickness Measurement

Abstract

Abstract A novel non-destructive laboratory technique and apparatus have been developed to eliminate inaccuracies associated with the conventional direct contact methods of mudcake thickness measurement. The system consists of a laser head containing a transmitter and a position sensitive receiver, a signal conditioner, a digital read-out system and a DC power source. The position of the laser beam spot incident on the measuring surface is recorded by the receiver, transferred to the control box where it is amplified and then displayed as a standard current signal on a digital read-out system. As the method is non-destructive, the mechanical characteristic of the cake such as softness has no influence on the accuracy of the measurement. The conventional methods of cake thickness measurement provide an estimate only due to damage to the cake during measurement. The accuracy varies depending on the cake consistency. The variation is low for hard mudcakes but high for soft cakes. The newly developed apparatus and measurement technique eliminate the direct contact-related errors and thus can provide reliable input values for modelling mudcake thickness dependent parameters such as formation and cake permeabilities, sticking force, friction coefficient etc. Statistical analyses of the measured values show a standard deviation of less than 0.025 mm and a coefficient of variation of less than 1%. The apparatus is portable, easy to operate and suitable for quick measurement of mudcake thickness at the rig site. The performance of the system was reviewed by analysing the results of a range of muds and also by comparing with the measured values obtained using other methods.