A laser-based novel measuring apparatus has been developed to determine mudcake thickness with high precision and accuracy. The device is portable, easy to operate and suitable for quick measurement of mudcake thickness at the rig site. 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 apparatus needs no direct contact with the mudcake to measure its thickness and thus eliminates inaccuracies associated with the conventional direct contact methods of measurement. Cake thickness is determined by illuminating a 1 mm spot of the cake surface with a laser beam produced by an aluminium die-cast semi-conductor laser sensor. The peak quantity of the reflected light is detected by a light-receiving element of the laser head. The signal is then transferred to a signal conditioner to produce a current signal proportional to the distance travelled.

The newly developed apparatus is a precise and accurate tool for measurement of different mudcake thickness irrespective of the mechanical characteristics of the mudcakes. The proposed apparatus and the non-contact method of measurement will provide reliable inputs for cake thickness dependant parameters such as cake and formation permeabilities, numerical modelling of sticking forces, casing running loads, appropriate correction to log responses, design and formulation of muds with superior mudcake quality etc.

A correlation chart and equation having a coefficient of correlation greater than 0.999 were developed using a Standard Mitutoyo Gauge Block Set, Series-516. Statistical analyses of the measured thickness values of a solid disk showed a standard deviation of 0.025 mm and a coefficient of variation of less than 1%.

The performance of the newly developed laser apparatus was assessed by analysing the results of cake thickness measurements of a range of muds and compared with the thickness values obtained using a soft-touch digital dial gauge. The degree of accuracy and the precision of the measurement of the laser apparatus are independent of cake consistency i.e. mechanical characteristics of the mudcakes.

You can access this article if you purchase or spend a download.