Assessing rheological properties of fluid mud samples through tuning fork data

Abstract

At the nautical bottom approach, part of the fluid mud layers can be included in the available depth if they present favorable rheology. As it is difficult to perform in situ rheological profiles, the most adopted procedure is to correlate these properties with other easier measurable ones, typically density. One technique for assessing in situ density profiles is the use of a tuning fork density probe. Density is calculated through frequency and amplitude signals, based in a specific algorithm from the employed device. This method requires a calibration, using local sediment at several densities, as it is conditioned by the rheology of the mud. In order to link the rheological properties of the fluid mud to the response of the tuning fork, first, an algorithm for density calculation was proposed and compared to the standard equipment software. Then, mud samples from different regions in Brazil were employed and a single curve associating the densitometer amplitude signal and the yield stress of the samples was obtained. The proposed approach enables a quick rheological assessment without laboratory rheological tests. It simplifies the steps of the protocol for establishing the critical limit once applying the nautical bottom concept, and it can be replied to other ports and navigation channels.