Presentation on theme: "Petroleum & Natural Gas Eng. Dept."— Presentation transcript:
1 Petroleum & Natural Gas Eng. Dept. 2008 SPE Saudi Arabia Section Technical SymposiumInvestigation of Polymer Adsorption on Rock Surface of High Saline ReservoirsMohammed M. AmroPetroleum & Natural Gas Eng. Dept.King Saud University
2 Outline Introduction Oil Recovery Methods Experimental Work Summary EOR MechanismsEOR ProcessesExperimental WorkExperimental ProceduresMaterial UsedResults and DiscussionSummary
3 Causes for Poor Recovery Physical Reasons:Existence of the interfacial tension between oil and water, and wettability (capillary forces)High mobility ratio between water and oil (viscous forces)Geological Reason:The heterogeneities in the reservoir rock
4 EOR Mechanisms The mechanisms of EOR: Eliminate or reduce capillary and Interfacial tension to improve the displacement efficiencyImprove sweep efficiency by reducing the mobility ratio between injected and displaced fluids (Polymer, Thermal)Act on both phenomena at same time (Nc)
5 Ratio of viscous forces to capillary forces Capillary number= Displacing fluid velocity [m/day]= Displacing fluid viscosity [mPa.s]s = Interfacial tension [mN/m]Assumptions for waterfloodingVelocity = 1 m/dayViscosity= 1 mPa.sInterfacial tension o/w = 20 mN/mNc = 0.57*10^-6In a reservoir, it is not practical to increase the pressure differential between producer and injector wells during water flooding. Infill drilling can reduce the distance between the wells by no more than a factor of two to four. This is usual process to increase the productivity of a reservoir. However, the reduction of is based on the economical aspects. Therefore, the only practical method of increasing the capillary number is to reduce the interfacial tension.If the Nc can be increased of four orders of magnitude or more, residual oil saturation will be reduced significantly.For waterflooding, Nc is 10-6 to 10-7 (under certain assumptions)If the Nc can be increased to 10-4 to 10-2,the residual oil saturation will be reduced significantly.
6 EOR Processes Tertiary Recovery Thermal Chemical Miscible/ Immiscible OtherSteam driveSteam stimulationHot waterIn-situ combustionPolymerSurfactantCausticCombinationCO2Inert gasMiscible SolventFlue gasMicrobialVibrationElectricalMiscible solvent such as LPG, lean gas, alcohol16-Apr-17
7 Chemical FloodingOffers good opportunity to maximizing the reserves in many depleted and waterflooded reservoirsOpportunities exist under economic conditions and current oil prizeChemical Properties Desirable:Good solubility (low concentration)High injectivityLong-term stability against:Electrolytes, - Bacteria, - TemperatureOxidation, - pH-Value changesLow adsorption on the rock, special focus on carbonate reservoirs (Polymer flooding)Simple handling and Low cost
8 Polymer Flooding Decreasing the mobility ratio (M) Influence on volumetric sweep efficiency EVEV =EA EITherefore, ED→Sorw will be reached more fasterEA = Areal efficiency andEI = vertical sweep efficiency
9 Mathematical Description of Polymer Rheology Effective water viscosityEffective polymer viscosityAssumption: Vw = Vp (No ‘‘Inaccessible Pore Volume‘‘ for polymer)The resistance factor describes the ratio of the mobility of water to the mobility of polymer solutionCase 1: Only viscosity increase : Kw = Kp16-Apr-17
10 Mathematical Description of Polymer Rheology Case 2: Viscosity increase and permeability decrease:RRF describes the ratio of the mobility of water measured before the injection of polymer solution to the mobility of water after polymer injection.Residual resistance factor (RRF)
11 Resistance factor (RF) and Residual resistance factor (RRF) RF & RRF are important factors to determine the concentration of polymer needed to perform polymer flooding (e.g. RF = & RRF = 1.5) or water shut off (Rf = 6 & RRF = 4).
12 Experimental Procedure Polymer solutions were prepared and evaluated at different salinities, shear rates, temperatures and concentrations.Core samples were flooded with polymer solutions (const. flow rate = 2.5 ft/day) until full adsorption (const. Pressure drop and const. effluent viscosity); RF was calculatedThe core samples were flooded with brine (Pressure drop and effluent viscosity were monitored); RRF was calculated.
13 Experimental Work Polymers (Xanthan, PAA), Biocide (Formaldehyde) Brine (83% NaCl and 17% CaCl2)Core samples (Berea SS with different Kranged from 200 – 1300 mD)Flooding apparatus.
14 Results and Discussion Effect of Shear Rate and Salt Concentration on Polymer Solution Viscosity
15 Viscosity of polymer solution of different xanthan concentrations in 10% brine. Increasing the shear rate reduces the polymer solution viscosity. At shear rate higher than 40 s-1, the effect of polymer concentration will be vanished. This means that increasing the shear rate drastically reduces the effect of polymer concentration
16 Effect of Salt concentration on Xanthan viscosity (14.7 s-1)
17 Effect of Salt concentration on PAA viscosity (14.7 s-1)
25 ConclusionsThe viscosity decreases with increasing the shear rate up to a certain value beyond which it becomes almost constant.Xanthan viscosity is more affected by the shear rate rather than salt concentration, while PAA viscosity depends strongly on both factors.A reduction of permeability using polymer solution depends on the porous medium, the particular polymer, concentration of polymer, salinity, and injection rate.Polyacrylamide (PAA) can reduce the heterogeneity in reservoir at low salinity. High PAA concentration will be needed to tolerate the high salinity.
26 Cont. ConclusionsPartially reversible adsorption (physical) from the rock surface occurred by brine flooding (RRF).The flooding velocity and the permeability have great effect on the adsorption.The temperature increase leads to delay the full adsorption on the rock surface. Therefore, more PV of solution is necessary .Thus, xanthan can be recommended, as a good polymer candidate to be used in high salinity reservoirs.