Abstract: The invention in one aspect provides a method of testing drilling mud in use which comprises periodically sampling the circulating mud and analyzing its aqueous filtrate at the rig site by ion chromatography for selected positive and negative ions; one or more other parameters of the sampled mud and/or mud filtrate (e.g. pH, temperature) may also be measured; preferably the composition of the mud filtrate thus monitored is interpreted to indicate downhole interactions, with the composition of the mud supplied to the hole being adjusted to or towards the optimum as drilling proceeds. The invention also provides a method in which the solids of the periodically sampled mud are analyzed at the rig site, e.g. for sorbed ions and/or for cation exchange capacity; the values so obtained are preferably combined with those for the mud filtrate analysis and used in the diagnosis of downhole conditions for adjustment of the composition of freshly supplied mud.

Abstract: Samples of mud are taken periodically at the surface at one or several locations where the mud does not contain cuttings anymore. The mud samples are analyzed on the rig site to determine the successive values, as a function of time or depth, of a parameter representative of the weight of the fine solids present in the mud. In one aspect of the invention the weight of the fine solids present in the mud is determined by measuring the weight of the liquid phase of the mud and the weight of the electrolyte dissolved in a known weight of mud. Preferably the weight of the liquid phase is determined by drying to constant weight a given weight of mud and the weight of electrolyte is determined by chemical analysis of the mud filtrate using an ion chromatography system on the rig site.