The major oil sands deposits of Alberta are estimated to contain 197 billion cubic meters (1.23 × 1012 bbls) of heavy oil. In situ, thermal recovery techniques must be used to recover the vast majority of this resource. These techniques are complicated by the fact that about 25% of the deposits have a high water saturation zone underlying the formation. The extent of this bottom water zone varies from a few meters to tens of meters under a payzone averaging between 10–25 meters depending on the particular reservoir. In designing a suitable thermal recovery method for these deposits, the presence of bottomwater is likely to have two important but competing effects. First, it may serve the purpose of providing initial injectivity in the highly viscous oil sand deposits. The second effect, however, is that this zone may act as a heat sink and significantly reduce the efficiency of heating oil sand above. The magnitude of these effects will depend on a variety of factors, notably oil viscosity, vertical permeability, injection rates, and oil saturation in the water sand, if any. Thus it is evident that for most reservoirs, the injection-production strategy must be "tailor-made" to optimize recovery. This paper presents the results of numerical simulation studies undertaken to evaluate the effectiveness of steam and steam-additive processes to recover heavy oil from deposits with bottom water zone. It is concluded that additives such as carbon dioxide and permeability blocking agents do not improve recovery in many cases. However, it is shown that suitable injection-production strategies can be developed to improve oil recovery by using steam-additive processes.
The MacCulloch oilfieldliesinBlock 15/24b inthe UK CentralNorthSea.The fieldisproduced usinga floatingproduction storage andofftake facility from two sub-sea centresandhasbeenonproduction since 1997.The originalgeophysicalmappingofthe fieldwasbased on 3Dseismic dataacquired in1993. InApril2002,a repeat3Dsurveywasacquired overthe fieldwiththe aimofbetterunderstandingthe depletion ofthe fieldusing time-lapseseismic analysis.The MacCulloch Fieldreservoirs areturbiditesofthe UpperBalmoralSandstoneUnitinthe ListaFormation of the UpperPaleocene, which areconnected to alarge aquiferinthe underlyingLowerBalmoralSandstoneUnit. Connection to such alarge aquifermeans thatpressuresupport overfieldlife hasbeenvery good( , 100 psidrop overfieldlife). Thisfact,coupled withthe lack ofagascap,means thatfor the time-lapseanalysisany change shouldprimarily be dueto asubstitution ofwaterfor oil.The MacCulloch Fieldreservoirismade up offivediscreteturbiditesandstone-dominated sandbodies,which canbe distinguished on the seismic data.Examination ofthe time-lapseresponseinthesebodiesshows thatthey haveacted asaprimary control on the depletion ofthe field.The individualbodieshavebeenanalysed using3D visualization andi nterpretation techniques,a ndi ncorporated into the geologicalm odelw ithd ifferingrock propertiesassigned to each.Withinthe reservoirsimulation model,the assignment ofdirectionalpermeabilitiesto theseunits andthe placingoftransmissibility barriers attheirboundariessubstantially improved the history match ofthe field, therebyenhancingour ability to predictfutureperformance andi dentifyp ossiblei nfill drilling locations.
This paper examines the use of agrochemicals in modern agriculture and horticulture. It begins by reflecting on the uncertainties of agricultural and horticultural production prior to the use of synthetic chemicals, then discusses the improved quantity and quality of output which is possible using agrochemicals. The social, environmental and agricultural hazards attendant upon chemical use are also considered. Provided that proper safeguards are observed, the use of agrochemicals is a sine qua non for the majority of farmers and growers in the UK.
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