Aim of this work was to evaluate the concentration of hydrocarbon gases in drilling muds by a static headspace analysis and the hydrocarbon gas-liquid partition coefficient (PC). Aqueous-based muds (salt-saturated and polymer-based) and oil-based (Low-Toxicity OBM) were examined and relation of the gas adsorption and the fluid composition is tentatively proposed. The work wishes to contribute to the knowledge of the desorption kinetics from drilling muds times that is necessary for the mud treatment process. The method is centred on the calculation of the gases' PC starting from the analysis of gas phase at the equilibrium with a known amount of hydrocarbon dissolved in the drilling fluid. A laboratory apparatus was assembled and the analysis was performed at two temperatures: 303 K and at 323 K. The first part (at 303K) included the study of the absorption and desorption of C1-C4 gases. The second part of the experiment focused on pentane. The PC decreases with increasing molecular weight with all mud types, and the phenomenon is controlled more by physical than chemical mechanisms. Further discussion about relation between mud composition and the gas concentrations are also reported. With regards to the effect of temperature, we observed two different behaviours: with the aqueous mud the constant increases with temperature, with oil-base mud it remains constant.

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