Canada Oil Sands: Some operations are actually not net energy generating—i.e., the energy injected via steam exceeds the recovered chemical energy in the retrieved bitumen.

U. Calgary analysis of energy balances and emissions of SAGD oil sands production finds need for improved processes; some operations not thermally efficient or net generators of energy

A team at the University of Calgary has assessed the thermal efficiencies, energy balances, and emissions of Steam-Assisted Gravity Drainage (SAGD)—both theoretically and as deployed at scale, using field data from the ERCB—for the production of bitumen from Athabasca oil sands reservoirs. In a paper in the journal Fuel, they report that current SAGD projects in Alberta show a very wide range of field performance.

Although optimized SAGD can yield “reasonably high” recovery factors, they found, the economic and environmental costs can be large given the amount of steam required. The data suggests that at the extreme, some operations are actually not net energy generating—i.e., the energy injected via steam exceeds the recovered chemical energy in the retrieved bitumen. The results suggest that in situ bitumen recovery processes need to advance well beyond current capabilities “if practical and sustainable energy balance and emissions scenarios are to be achieved,” they said.

For a successful in situ oil sands bitumen recovery process, two requirements must be met: first, it is necessary to raise the oil mobility (often done by lowering its viscosity which results from raising its temperature) until it can be moved by natural forces such as gravity, and secondly, it is necessary to move the mobilized oil to a production wellbore so it can be produced to the surface.

Currently, commercial steam-based in situ processess used to recover bitumen from oil sands reservoirs are either one of Cyclic Steam Stimulation (CSS), or Steam-Assisted Gravity Drainage (SAGD).

   The geology of the reservoir is a key factor, the two researchers explain. Production reservoirs are “completely different” from the homogeneous sandstones with uniform fluids envisaged by the engineers that developed SAGD.

 After accounting for the energy required (and the bitumen lost) during the upgrading process to convert the bitumen to synthetic oil, and then refining into transportation fuels, they found that the overall breakeven point was equal to a cSOR of about 6.5 m³/m³.

Based on the cSOR field data...many operations exceed this value and thus are not net energy generation processes yet may be “economic”! With disconnected price markets for natural gas and bitumen, it is possible for bitumen recovery under these conditions to be economically viable today even though it makes no sense to pursue such an energy inefficient process when cSOR values are high.

—Gates and Larter

Source:Green Car Congress