Characterization of Doba-Chad heavy crude oil in relation with the feasibility of pipeline transportation

摘要

A heavy crude oil was characterized in view of the recent commercial exploitation of Doba oilfield in landlocked Chad from where the crude oil is extracted and expected to be routed to the Atlantic shore through pipeline transportation. The elemental composition of Doba feedstocks is 86.25 percent C, 12.10 percent H, 0.25 percent N, 0.14 percent S and 1.16 percent O. Atmospheric distillation indicated an initial boiling point at 85 deg C, a 10 vol percent fraction distilling before 250 deg C and an onset of crude thermal cracking at 300 deg C. Crude API gravity is 18.8 deg API, corresponding to a specific gravity of 0.94 at 15.6 deg C. The Doba crude oil was found to exhibit non-elastic purely viscous Newtonian behavior over the temperature range typical of crude transportation by pipeline. The crude was fractionated into 97.4 percent maltenes (n-pentane solubles), 1.8 percent asphaltenes (n-pentane insolubles), and 0.1 percent toluene insolubles. The maltenes were subsequently split into four sub-fractions: 45.0 + - 1.2 percent saturates (MF1), 11.0 + - 0.3 percent mono and diaromatics (MF2), 26.8 + - 1.2 percent polyaromatics (MF3), and 12.8 + - 0.8 percent polars (MF4). FT-IR characterization and proton nuclear magnetic resonance identification of the maltenic and asphaltenic fractions provided evidence of the chemical nature of the different fractions. The high values of the kinematic viscosity of crude oil (184.4cSt at 50 deg C) and deasphalted crude (152.4cSt at 50 deg C) suggest that partially upgrading the oil would be necessary to comply with the viscosity specifications recommended for crude transportation by pipeline.