Extensive experience in many different parts of the world has confirmed the prediction that while conventional oil production still delivers over 90% of the world’s demand, primary and secondary recovery techniques leave at least 50% of oil reserves in the reservoir as unrecoverable.
A detailed analysis prepared by Ivan Sandrea (StatoilHydro) and Rafael Sandrea (IPC) published in 2007 by Oil & Gas Journal concludes that the global average recovery rate is no better than 22%.
Since the application of secondary recovery techniques like natural gas and water injection became the norm in the late 1960s the focus was normally on larger fields. This implies that the majority of medium and smaller fields, from which 50% of the world’s cumulative production was extracted, were abandoned after the primary phase of recovery - for whatever reason - without any pressure maintenance, therefore leaving most of the oil reserves in the ground.
It is therefore quite obvious that there are abundant opportunities to employ EOR and that economics driven mainly by the market price for crude oil will determine the rate of adoption in future. The general industry consensus accepts that the global total of Original-Oil-In-Place (OOIP) is close to 12 trillion barrels.
A simple calculation suggests that based on the performance of this emerging and relatively novel technology to date, the potential exists to recover some 1500 billion barrels of additional oil from existing, partially exploited fields.
Carbon dioxide EOR – The most promising
The beneficial properties of carbon dioxide (CO2) injection over nitrogen, because of its miscibility with light oil, has been demonstrated extensively but the market demand for carbon dioxide for EOR remains price sensitive.
The majority of CO2-EOR projects to date have been located in or near the Permian basin in the US, where naturally occurring CO2 has been the source of supply. The prevailing higher price of oil in recent years has greatly improved the economics of using CO2 not only in this region, but worldwide.
The engineering costs to conduct a CO2-EOR project are considerable because it entails drilling and reworking the wells, installation of a recovery and recycle plant and the construction of CO2 pipelines. Despite this, and the recent escalation of engineering costs, the most significant single cost item remains the purchase of CO2.
For this reason operators have tried to economise on the consumption by minimising the volume of gas injected. It is very possible that the results achieved to date were compromised by this approach.
The greatest irony that exists concerning the accumulation of carbon emissions in the atmosphere, is that the supply of CO2 has often been inadequate to satisfy the demand for industrial applications such as food and beverage packaging and pH stabilisation of bulk water supplies.
The ‘IPCC Special Report on Carbon Dioxide Capture and Storage’ hints at a possible solution to the problem, “. . . it is important to note that CO2 EOR, as practiced today, is not engineered to maximise CO2 storage. In fact, it is optimised to maximise revenues from oil production, which in many cases requires minimising the amount of CO2 retained in the reservoir. In the future, if storing CO2 has an economic value, co-optimising CO2 storage and EOR may increase capacity estimates.”
The cost burden of implementing systems to attach a price to carbon emissions may well raise the price of electricity where fossil fuels contribute significantly to primary energy, but the benefit to the oil industry might be to expand the supply of suitable CO2 supply and therefore lower the cost of CO2-EOR.
A paper prepared by Advanced Resources International for the US Department of Energy in 2006 stated: “While high oil recoveries are theoretically and scientifically possible, the actual performance of CO2-EOR in the field, as presented above, has been much less.
Geologically complex reservoir settings, combined with lack of reliable performance information or process control capability during the CO2 flood, place serious barriers and constraints to achieving optimum oil recovery using CO2-EOR.”
Based on their analysis of the causes for below-optimal results achieved by CO2-EOR projects to date, four opportunities were identified.
1. Increasing the volume of injected CO2 to 1.5 hydrocarbon pore volume (HCPV), considerably beyond what has been traditionally used.
2. Examining innovative flood design and well placement options for contacting and producing the higher oil-saturated portions of the reservoir, often containing the bulk of the ‘stranded’ oil.
This would include adding new horizontal and vertical wells targeting selected reservoir strata and using gravity-stable CO2-EOR process designs to increase overall reservoir contact and oil displacement by the injected CO2.
3. Improving the viscosity of the injected water to reduce the mobility ratio between the injected CO2/water and the reservoir’s oil to reduce viscous fingering of the CO2 through the mobilised oil bank.
4. Adding ‘miscibility enhancers’ to extend miscible CO2-EOR to additional oil reservoirs that would otherwise be produced by the less efficient immiscible CO2-EOR process.
Unfulfilled needs and expectations
The developed world needs affordable energy to revive damaged economies and stimulate economic growth, while the emerging economies need it to drive industrialisation, urbanisation and poverty reduction.
Renewable energy is making rapid strides, but will not be ready in time to avert the socio-economic stress that threatens stability in many places.
The oil price is high mainly because of perceived scarcity and speculation and in order to stabilise the market at a more rational level, it will be necessary to ‘bust the myth’ of peak-oil. To achieve this, the oil industry needs lower cost, high performance CO2-EOR.
The industrial gas business can play a role here by contributing to the development of technology to capture waste CO2 and find cheaper ways of delivering it. The oil services industry is best placed to drive down the cost and optimise the performance of CO2-EOR.