Characterizing Sulfur in Foster Creek Bitumen Using Rock-Eval Sulfur, for Assessing H2S Production Risk in SAGD Operations

H2S emissions from thermal recovery operations of bitumen and heavy oil are becoming an increasing concern. Many Steam Assisted Gravity Drainage (SAGD) programs are finding H2S level rising as wells are aging. Steam injection causes aquathermolysis reactions between bitumen, reservoir rock and high temperature steam, converting some organosulfur compounds into H2S. To precise its origin, a pre-SAGD oil sand sample from Foster Creek-Athabasca was submitted to aquathermolysis laboratory tests at 250°C, 45 bar and various durations up to one year. After each run, H2S yield was quantified, the extracted SARA fractions and the mineral fraction were weighed. Their total and labile sulfur contents were measured using Rock-Eval Sulfur pyrolysis, enabling the calculation of total sulfur and labile sulfur distributions over the fractions. The results show that aquathermolysis reactions led to sulfur depletion of the asphaltene fraction and to sulfur enrichment of the resin and aromatic fractions, simultaneously to H2S generation. This suggests that labile sulfur containing asphaltenic compounds generate H2S, resins and aromatics upon aquathermolysis conditions. These data can be used to entirely calibrate an integrated aquathermolysis kinetic model in reservoir simulator, for simulating H2S production in a SAGD project at Foster Creek existing producing asset.