Evaluating Energy and Water Saving Opportunities in SAGD Oil Sands Plants via Process Integration

http://www.summitenergy.com/blog/2011/11/a-sticky-note-on-tar-sands/

http://www.energy.alberta.ca/OilSands/791.asp http://www.upstreamonline.com/live/article1261489.ece

The oil sands resource in Northern Alberta, Canada are produced as a mix of hydrocarbons (bitumen), clay, sand and water. The resource is recovered, and processed into products such as transportation fuels. In 2011, production was 1.74 million barrels per day [1] and has been forecasted to triple by 2030 [2].

http://www.ags.gov.ab.ca/graphics/CBM/oil_sands/bitumen_extraction.jpg

http://www.iosa.ca/our_process/in_situ/

Two techniques are currently used to extract bitumen. Mining can be used for ~ 20% of resource whereas in-situ techniques can used to recover ~80% of resource that is too deep to mine. Two in situ technologies are currently used: 1) Cyclic Steam Stimulation (CSS), 2) Steam Assisted Gravity Drainage (SAGD).

The development of the oil sands bring large economic benefits to Canada but also presents some major environmental challenges. For example, in 2010 37 % of Alberta’s GHG emissions were a result of this activity, of which, 13% is due to in-situ processing [3]. In addition, roughly 2 to 4 barrels of steam generation is required per barrel of bitumen produced which presents water/energy tradeoffs in the design and operation of these facilities.

Simultaneous Heat and Water Integration: Assessing the trade-offs in energy and water reductions

Oil sands developers are under pressure to simultaneously reduce energy and water consumption. Typically the potential for reductions has been evaluated separately for energy and water. This can lead to situations where the savings are limited or where a reduction on a performance metric (e.g., energy consumption) comes at the expense of the other (e.g., water). Only recently have new tools been developed to assess these options simultaneously in order to understand the tradeoffs associated with water and energy savings [4].

[1] http://www.energy.alberta.ca/org/pdfs/Alberta_Energy_Overview.pdf [2]http://www.policyalternatives.ca/sites/default/files/uploads/publications/National%20Office/2013/02/Bitumen%20Cliff.pd [3] http://www.energy.alberta.ca/oilsands/791.asp [4] Savulescu L, Kim J K and Smith R (2005b), “Studies on simultaneous energy and water minimization. Part II: Systems with maximum reuse of water”, Chemical Engineering Science 60, 3291-3308.

To date, simultaneous heat and water integration assessment has not been applied to oil sands in situ facilities. We apply this integrated approach to seek opportunities for improvements in energy and water consumption in the oil sands.

Motivation

Figure 2. Modification to the base case for water treatment in a SAGD typical central process facility

The base case analyzed corresponds to a Typical CPF for SAGD. HLS is used for the water treatment and the feed to the OTSG is a single stream.

Energy Analysis Case Base Modified

Heating (MW) 128.3 126.0 Cooling (MW) 2.08 1.46

Water requirements Case 1 2

Makeup fresh water (m3/yr)

57,000 22,000

Conclusions

Not including the medium pressure steam separator saves less than 2% of heating and saves about 30% for cooling, however because of the temperature at which the cooling is required and compared with the amount of heating required, cooling is not considered as a determinant factor. Water savings are significant. Work will be continued in order to identify the tradeoff between energy and water saving for bitumen extraction using SAGD.

Table 1. Utility requirements. Table 2. Water requirements.

Figure 3. Composite curves. Case 1 Figure 4. Composite curves. Case 2

Future work o Incorporate simultaneous energy and water assessment in SAGD bitumen

extraction. o Explore other factors that have an impact on energy savings such as: • Pressure of the steam injected into the wells • Steam pressure drop • Economic pipeline diameter

Carlos E. Carreón a, Zainab Dadashi a, Alberto Alva-Argaez b, Maryam Mahmoudkhani c, Joule Bergerson a*

a Institute for Sustainable Energy, Environment and Economy, University of Calgary, *jbergers@ucalgary.ca b Process Ecology Inc, c Department of Energy and Environment, Chalmers University of Technology

Figure 1. Base case for water treatment in a SAGD central processing facility

Analyzing a Central Process Facility for Bitumen Extraction (SAGD)

A typical Water Treatment Process in a Central Process Facility, CPF, for bitumen extraction by SAGD, Figure 1; is analyzed as a base case, in order to determine its energetic demands. Further modifications to the same process are analyzed and illustrated in Figure 2.

Analyzing the impact on energy and water consumption of design modifications in a typical CPF Case.

Base Case (Case 1)

Streams fed to the OTSG are considered independently, different Supply Temperature and the medium pressure steam separator is removed. Steam for the HLS is supplied from HP steam, which affects the water balance in the process.

Modified Case. (Case 2)

Composite Curves (Figure 3-4) and Grand Composite Curves (Figure 5-6) for both cases where obtained using Aspen Energy Analyzer®. Composite Curves differ mainly in that in Case 1, MP steam leaving the separator condenses before being sent to the OTSG, while in Case 2 the blowdown from the HP separator transfers its sensible heat to reach the temperature for the Evaporator Package. Grand Composite curves show that for case 1, the steam leaving the separator allows Process to Process heat transfer.

Figure 5. Grand Composite Curve. Case 1 Figure 6. Grand Composite Curve. Case 2

Table 1 shows utility requirements for both cases. Case 2 requires 2 MW less of hot utility than Case 1. Due to the removal of the MP steam separator, Case 2 requires 40% of the fresh water make-up required for Case 1.

Considerations for cases analyzed: Makeup fresh water is not included in the energy analysis. Latent heat in the OTSG is not included in the energy analysis. Same amount of water feed into the OTSG. Same amount of HP steam produced.

CANADA SCHOOL OF ENERGY AND ENVIRONMENT IS ACKNOWLEDGED FOR PROVIDING THE RESEARCH GRANT.