ADVANCES IN THE HYDROCARBON GAS-LIQUID EQUILIBRIUM UNDERSTANDING IN WATER AND OIL-BASED DRILLING FLUIDS

DETERMINATION OF C1-C5 HYDROCARBONS IN DRILLING MUDS Davide Doninelli, Jenny Rizzola, and Paolo Gronchi Politecnico di Milano - Chemistry, Material and Chemical Engineering Dept. “G. Natta”; P.za Leonardo da Vinci, 32 20133 Milano, Italy. E-mail: paolo.gronchi@polimi.it. The aim of this work was to evaluate the amount of C1-C5 gases dissolved in the drilling muds through the definition of a analytical model of the partition coefficient between the hydrocarbon concentration in the gas phase and in the muddy. The conveniences of the work may be: • to verify the convenience of a possible gas recover; • to evaluate the environmental impact of the degassing treatment unit associated to the gas discharge in atmosphere; • to evaluate the desorption times in order to optimize the mud treatment process. The method is centered on the calculation of the partition coefficient starting from the analysis of gas phase at the equilibrium with a known amount of dissolved hydrocarbon. A laboratory apparatus was built, constituted by a heated jacketed reactor, with temperature control, to simulate the absorption of the hydrocarbon gas during the drilling and a second vessel for the gas desorption until equilibrium. The study is divided in two parts as the operations were performed at 303 K and at 323 K temperatures. The first part (at 303K) included the study of the absorption and desorption of C1-C4 gases in different muds: aqueous-based muds (PHPA and HPWBM) and oil-based (LTOBM). The choice of the sludge was made in reason to emulate in a laboratory, the properties of most drilling fluids. In the second part we examined pentane too. Pentane is a liquid hydrocarbon at ambient condition (boiling point 310 K) but could be used as gas at 323K . The right technology for the use pentane in gas phase must takes into account the vapor-liquid equilibrium when injected as liquid for the absorption into the muds. We observed that the partition coefficient decreases increasing molecular weight up to butane with all the mud, with pentane instead we have two different behaviors for water and the oil based muds: with the PHPA and HPWBM (water-based) the constant decreases instead in the LTOBM (oil-based) it remains constant. As regards the trend with the temperature we observed two different behaviors: with the aqueous mud the constant increases with temperature, and for the oil mud remains constant. Discussion about relation between mud composition and the gas concentrations are tentatively reported. Acknowledgements The authors would like to acknowledge financial support from GEOLOG S.p.A. (Italy