EOR in the High Oil Price Environment
With crude oil peaking at just over $50 per barrel in the second half of 2004, there is a clear shortage of supply compared to demand. It is obvious that oil producers will be looking to increase their output in the short term, and will be reviewing their medium and long term plans. Economic projects already in the pipeline will be accelerated and projects that, in the past, have been uneconomic may well now be economic. But will EOR appear on the radar screen? David Hughes (david.hughes@senergyltd.com), a Principal Reservoir Engineer with Senergy Ltd and editor of IOR Views ponders this question.
Typically Half the Oil-in-Place Remains Unproduced
In the North Sea, recovery factors are typically in the high 40s percent and ongoing efforts, particularly infill drilling guided by time-lapse seismic, are stretching recovery. However, whatever the recovery factor, it is a truism that if the oil price increases, then the value of the oil remaining in the ground also increases. Assuming that static modelling and the dynamic performance of the reservoir has confirmed your volumetrics calculations, you know the oil is there - there are no costs involved in finding this oil. Typically the base development plan will call for cessation of production when half the oil in place is still unproduced.
However, well into the normal operating life of the field there is a wealth of experience relating to the field. So the question is what can be done to stretch the life of the field? Already there is a significant amount of infill drilling going on. Existing wells are being worked over to increase their output and facilities are being reconfigured. Also, opportunities for third-party business are being exploited to provide an additional income stream for ageing facilities.
All this activity, fuelled by the high oil price, is extending the life of existing developments and thereby extending the window of opportunity for EOR.
EOR is Happening Already in UK Sector
In the UK sector of the North Sea, there were trials of microbial EOR in the early 1990s, but the emphasis has been on hydrocarbon gas injection. In addition there is the Brent depressurisation project where the strategy was to lower the pressure and produce the freed gas.
The major gas injection projects are in South Brae [1], Alwyn North and Magnus.
Figure 1: Magnus EOR Project (Gas is piped from Foinaven and Schiehallion to Sullum Voe where it is enriched in intermediates to ensure miscibility, and then exported to Magnus).
At both Brent and Magnus there was a substantial redevelopment of the field's facilities. So perhaps this is the key. We should not be thinking of EOR as a bolt on - rather a mature oil field with 50+ percent of the oil remaining in place should be looked on as nearer to a " greenfield " opportunity than the conventional thinking of a "brownfield" opportunity. Thus redevelopment plans need to be bold and inspired. The high current oil price, with the long term likelihood that, because of demand, the price will remain high, and the opportunity to delay the expense of abandonment should act as a spur for more imaginative thinking. The improved displacement of oil offered by EOR processes should be considered an integral part of these redevelopment plans, together with advanced technology and cost-reduction options.
Emphasis on CO2 but Other Processes in the Frame
The leading EOR processes involve injecting gas or chemicals. As I mentioned in the last issue of IOR Views, at the SPE/DOE IOR Symposium in Tulsa in April 2004 I noticed a renaissance in the use chemicals such as polymers and surfactants for onshore applications. However, for offshore application the leading candidate has always been gas injection in its various guises.
Hydrocarbon gas with sufficient intermediates added to achieve miscibility has been the EOR method of choice to date, but this is only possible where an economical supply of gas is available, which is usually gas produced with oil but where there is no export route for the gas. However, CO2 injection is an alternative that has been considered for the North Sea in the past, e.g. [2], and has come to the fore again because the debate surrounding global warming. CO2 injection (often combined with water in a WAG process) is known to be successful onshore and is second only to hydrocarbon gas injection as the most widely practiced EOR process in light oil fields. The prospects of a high long term oil price, and subsidies for disposing of CO2 which would otherwise pollute the atmosphere is raising interest in this process.
In 2002, BP looked in detail at converting Forties to CO2 injection and Statoil published a similar study on Gullfaks in 2004. Both of these studies involve substantial field redevelopments. For Gullfaks, Statoil showed that adding and reactivating sufficient wells to change the development from peripheral water injection to a pattern waterflood would increase recovery in its own right. The well pattern was then more suitable for CO2 injection which provided further incremental recovery.
One of the main objections to the application of EOR techniques offshore is the wide well spacing and the consequent length of time it takes for the mobile oil bank to be produced. If because of the high oil price it is economic to add infill wells and move towards the more conventional waterflood pattern developments seen onshore, this can only be beneficial for EOR.
It will be interesting to see if the much discussed air injection technique (e.g. http://ior.rml.co.uk/issue8/rnd/universities/bath/) finds any takers in the North Sea - BP reported work on this in an earlier article in IOR Views. Also, as noted above, chemical processes such as polymers, gels and surfactant are being successfully used onshore, although I am not aware of any current activity looking at applying these chemicals in flooding processes on the UKCS.
Your Views
I don't have a crystal ball so I don't know what the future holds. However, it seems to me that conditions are now right for EOR to have a higher profile in the North Sea than hitherto. I would like to know your views. Please let me know what you think by using the feedback box below.
References
- D.J. Jethwa, B.W. Rothkopf, C.I. Paulson, Successful Miscible Gas Injection in a Mature U.K. North Sea Field, SPE 62990, SPE Annual Technical Conference and Exhibition, Dallas, Texas, October 2000
- David S Hughes, John D Matthews, Robert E Mott, Theoretical Aspects of Calculating the Performance of CO2 as an EOR Process in North Sea Reservoirs, European EOR Symposium, Bournemouth, September 1981, Elsevier