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DESIGNING A WATERFLOODDesigning a water flood involves both technical and economic consideration. Economic analysis are based on estimates of water flood performance. These estimates may be arrgh or sophisticated depending on the requirements of a particular project and the philosophy of the operator. Factures to consider when designing a water flood are: Evaluation of the reservoir including primary production performance Selection of potential flooding plans.Estimation of injection and productive Rates,Projection of oil recovery over the anticipated life of the project for each flooding plan,Identification of variables that may cause uncertainly in technical analysis.Technical analysis of a water flood produces estimates of the volumes of fluids and rates. These estimates are used for sizing equipment and fluid – hardling systems. It is necessary to identify a source of water for injection that is compatible Rock. Design also includes arrangement for prepare disposal of produced water.
RESERVIOR DESCRIPTION • The purposes of a reservoir descriptive in water flood design are to: • Determine the areal and vertical extend of the reservoir, • Describe quantitatively the variation in rivk porosity, - such as permeability and porosity, witens the reservoir • Determine the primary production mechanical including estimates of the oil remaining to be produced under primary operation, • estimate the distribution of the oil reservoir in the reservoir • Evaluate fluid prepareties required fore predicting water flood performance, the data and interpretations that are obtained in developing a reservoir description make up many of the input data fore the…
The following information is usually available from a reservoir description: • Reservoir characteristics • areal and vertical extent of the producing formation, • Isopaech maps of gross and net sard. • Cover elation of layers and other zones. • Reservoir Rock properties • Areal variation of average permeability, including directional trends derived from geological interpretations, • Areal variation of porosity • Reservoir Hetenogeneity – particularly the variation of permeability with thickness and zone • Reservoir Fluid Properties • - Grarity, FVF and viscosity as a furction of reservoir pressure • Primary Production Mechanism • Identification of producing mechanisms such as fluid expansion, solution – gas fraive, or water drive. • Existence of gas caps or aquirters, • Estimation of oil remaining to be produced under primary operations • Pressure distribution in the reservoir
Continue • Distribution of oil Resources in reservoir at beginning of water flood • Trapped – gas saturation from solution gas drive, • Vertical variation of saturation as a result of gravity segregation • Presence of mobile connate water • Areas already water flood by national water drive. • Rock and Flood Properties • Relative permeability data for the reservoir rock.
CHOOSING POTENTIAL FLOOD PIANS • Choosing a water flooding plan is determined by factors that are after unique to such reservoir. In some reservoir, the water flood may be done with edge wells to from a peripheral flood. This is called pressure maintenance when water injection supplements deching reservoir energy from solution- gas drive or an a quiver of limited extend. Pressure maintenance often begins while the reservoir is still under primary operation to maintain masimn production rates. • Pattern flooding, an alteration to pressure maintenance, may be selected because reservoir preparations will not peruit water flooding through edge wells at desired injection rates. Injection and withdrawal pates are determined by well spicing as well as reservoir properties. Pattern size because a variation that is considered in economic analysis. • The chooses of water flooding patterns depends on existing wells that generally must be used because of economics. Pattern selection is constrained by the water of production wells. See fig. 6.1. any of these patterns can be used to water flood a reservoir, but final selection of spacing and patterns type , when these are several possibilities, is determined by compression of the economics of alterative flooding scheme. • Surface are sub-surface topology and/ or to the use of slant hole drilling techniques may result in production or injection we3lls that are non uniformly located.
INJECTION RATES • Oil revelry correlates with the completion volume of water injected. Injection rate is a key economic varable in the evaluation of a water flood. Injection rates are correlated in terms of injectivities as • barrels per day per area foot • Barrels per day per net foot per pounds per square which. • Specific values are dependent on reservoir rock properties, fluid / rock interactions. Spacing and available pressure drop. Comparable values would be expected under similar reservoir and operating conditions. • When rates are not known, injection rates can be estimated from relatively simple equations, under these conditions.
If water – gas saturation develops, the system may be treated as if it area liquid – filled. • For a depleted reservoir where a mobile – gas saturation develops during primary production by solution – gas drive. • FIRST –Pass Estimates of WF Performance estimates of water flood recovery, production rates, and productive time curves can be made in a relatively slimt time with simple models of the displacement process. • First – Pass or approximate methods serve as an order of – magnitude check on oil recovery, injection and production rates the methods is inadequate hmenere, for reservoir where reservoir heterogeneity, aquifers and gas caps introduce large uncertainties in water flooding performance and consequently the economic evaluation.
Estimation by material Balance:- Water flood recovery may be estimated from a material balance with core data and estimates of the sweep efficiency. The reservoir is considered to be subdivided into two parts – the volume swept by the water flood and the un swep volume. The volume of oil displaced is not equal to the volume of oil recovered.
