Non-thermal Heavy Oil Recovery
Table 1: Current Enhanced Oil Recovery Methods Thermal
Non-thermal
Improved waterflooding Gas methods Hot waterflooding
Alcohol-miscible solvent ‘Inert’ gas injection flooding
Steam and hot water Micellar/polymer injection
Steam stimulation Steamflooding
In situ combustion Forward combustion Wet combustion
Nitrogen injection (surfactant flooding)
Low IFT waterflooding Flue-gas injection Alkaline flooding
ASP flooding Polymer flooding 300,000
Hydrocarbon-gas (and liquid) injection
High-pressure gasdrive Enriched-gasdrive
Gels for water shuttoff Miscible solvent (liquified petroleum gas or propane) flooding
O2-enriched Microbial injection combustion
Reverse combustion Surface mining and extraction ASP = alkaline sufactant polymer; IFT = interfacial tension.
displacement, on the other hand, could develop at the reservoir conditions below the minimum miscibility of the air-oil mixture. The
latter is then similar to N2-immiscible displacement process and it can be acceptable – perhaps even desired – from the reservoir pressure maintenance point of view, although the recovery may rely on limited sweep efficiency of the immiscible displacement. Some of these processes are suitable for improved recovery from deep and low-permeability reservoirs, and they are likely to impact the future recoveries.
Hydrocarbon Miscible Gas – a New Optimism for the Future of Heavy Oil Figure 3 depicts recent US trends in thermal and non-thermal heavy oil recovery. Here, those with oil gravity less than 26oAPI are classified as heavy oil projects. Two cases related to the reservoir depth are considered separately: the column on the left is related to those projects at depths larger than 2,000 ft and the column on the right is with the depth greater than 3,500 ft. Hence, it is easy to see in the figure that roughly half of the heavy oil projects are from the reservoirs at depths in between. Clearly, total heavy oil production is significantly less than the total non-thermal EOR production (typically
Nowadays, gas injection methods are consolidated as the most widely used non-thermal EOR techniques in the field over improved waterflooding methods.
with a 1:7 ratio) but the trends that we earlier observed persist with the heavy oils: production due to improved waterflooding is almost negligible; in addition, the contribution of thermal techniques are becoming significantly less at depths larger than 2,000 ft and almost negligible at depths larger than 3,500 ft. Heavy oil recovery has primarily been due to gas injection for the last four years.
Table 2 is a list of the heavy oil projects in the US in 2008. Hydrocarbon miscible gas injection is standing out as the dominant
EXPLORATION & PRODUCTION – VOLUME 9 ISSUE 2 200 150 100 50 0 1988 1992
1996 Thermal
Non-thermal 200
Figure 2: Status of Non-thermal EOR Methods 1988 # Proj,
Improved water flooding Gas injection
1988 project Gas
injection 42%
Improved water
flooding 58%
[B/d] # Proj, 1998 project Gas
injection 89%
Improved water
flooding 11%
1998 [B/d] 11 [139] # Proj, 2008 [B/d]
90 [130,997] 87 [313,544] 122 [350,36] 124 [22,501]
2 – 2008 project Gas
injection 98%
Improved water
flooding 2%
2004 2008 250 CO2 flooding 200,000 100,000 0 1988 1992
1996 Thermal
Non-thermal 200
2004 2008 Figure 1: Comparison of Thermal and Non-thermal EOR Methods 500,000 400,000
recovery technique with a 73 % of the total recovery. Figure 4 illustrates the miscible hydrocarbon injection success over the last two decades. The success in this case is mainly due to the recovery of oil with a gravity in the range 24-28oAPI from reservoirs at depths varying in from 6,000–8,800 ft.
Total hydrocarbon injection – both miscible and immiscible – represents about 78 % of the heavy oil production using non-thermal methods. The methods typically involve injection of light hydrocarbons – flaring gas – into the reservoir. The displacement can be miscible or immiscible primarily depending on whether the reservoir pressure is above or below the minimum miscibility pressure for the fluids. Two distinct fluid injection approaches are practiced in order to maintain miscibility: 2–5 % pore volume (PV) slug of propane or Liquefied Petroleum Gas (LPG); and 10–20 % PV slug of natural gas enriched by the intermediate components C2–C6. The injected hydrocarbon slug is often followed by natural gas or water-alternating-gas (WAG) as the
41
# US EOR projects
US EOR production [B/d]
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