Laboratory studies and pilot project tests have shown that appreciable amounts of H 2 S and CO 2 could be generated as a result of the aquathermolysis reaction between bitumen and steam or hot water during thermal recovery operations. A detailed experimental study was carried out to investigate the H 2 S generation mechanism that occurs during the recovery processes. A laboratory setup was designed and assembled that allowed for aquathermolysis tests to be carried out under controlled pressure conditions and at temperatures to 250 °C. Aquathermolysis tests on a defined ratio of bitumen and water sample were carried out at 225 and 245 °C over 3, 10, and 30 day reaction periods. Phase sampling and analysis procedures were developed to quantify the amount of H 2 S and CO 2 generated during the individual vapor and aqueous phases. Vapor-and liquid-phase composition and bitumen properties, including viscosity and density, were analyzed after each reaction. The results of the investigation showed that the amount of H 2 S and CO 2 generated increased with the reaction time and temperature and the CO 2 concentration tended to flatten out over the test period. Data generated during the study were used to develop a kinetic model on a laboratory scale for predicting the time and temperature effects on H 2 S and CO 2 production during the bitumen−steam/hot water aquathermolysis.

Thermal recovery processes are widely applied for heavy oil and bitumen production. Unique thermal properties of water and water steam allowed efficient reduction of extremely high viscosities by several orders of magnitude and made a vast heavy oil and bitumen reserves production technically and economically feasible. Steam effect on heavy oil and bitumen in traditional reservoir engineering for a long time has been considered as physical only, i.e. viscosity reduction, improved flow parameters, distillation effects, emulsification, etc. However multiple laboratory studies and field observations suggest that initial oil undergoes chemical alteration and gases such as H2S and CO2 could be produced in increased quantities. Estimation of H2S and CO2 production potential is important due to considerable corrosivity of these gases, associated environmental, economical and other issues. In this study a practical approach has been developed to simulate and forecast H2S and CO2 production during thermal recovery using common reservoir simulation tools. First, analytical data was matched and then chemical reaction had been implemented to the sector model. Steam Assisted Gravity Drainage (SAGD) was chosen to demonstrate the concept of suggested approach and analyze the results. Generated gases were considered to be soluble both in water and oil. The importance of accounting for gas solubility in water was demonstrated and discussed. Simulated volumes of H2S and CO2 are in good agreement with that observed in the field applications of steam assisted recovery methods.

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The Mariner field - license 9/11 in the UK – was discovered in 1981 and is situated on the East Shetland platform. Mariner consists of two tertiary reservoir intervals of unconsolidated sand at depths between 1200 and 1500 mMSL. The deeper Maureen reservoir consists of stacked non-channelized sheet-like sand lobes deposited in a shelf to slope setting. The Maureen oil water contact (OWC) is stepping considerably and is shallower to the west. The Heimdal reservoir consists of deep-marine slope-channel sands within the mudstone-rich Lista interval, ranging in thickness from a few meters up to 40 m. The reservoir is heavily remobilised. The Heimdal OWC is uncertain with variable ODT (Oil Down To) observations and anticipated perched water. The total Mariner oil reserves are estimated to app. 400 MMBO (Million Barrels). The Maureen reservoir has 67 cp oil (14°API) in a 0–40 m oil column and a large bottom aquifer. The Heimdal reservoir contains two thirds of the reserves and has 508 cp oil (12 API). Steady State SCAL studies indicate that Krw may be viscosity dependent. The Heimdal reservoir is planned to be developed using an inverted 9-spot well pattern due to uncertainty in mapping of the reservoir. The Maureen reservoir will be developed with horizontal wells. As the recovery factors are only 22%, Enhanced Oil Recovery using polymer is investigated as an upside to be matured towards production start. IOR through use of down-hole inflow control devises is progressed in a technical qualification program. OBC (Ocean Bottom Cable) data will be acquired to improve the mapping of the Heimdal reservoir.