Mobility reduction is one of the critical parameters in polymer flooding. The EOR polymers have shear thinning bulk rheology, while core flood experiments with hydrolysed polyacrylamide (HPAM) in this paper show four different viscosity regimes. Through a systematic work, in which the molecular weight and degree of hydrolysis as well as the permeability and brine salinity were varied, the apparent viscosity was well-matched with theoretical models. The following four viscosity regimes were identified: (i) At low shear rates, the apparent Newtonian viscosity is less than the bulk viscosity; this effect is because of the inaccessible pore volume (IPV) with the polymer not entering the entire pore space. (ii) Shear thinning behaviour which is controlled by the polymers relaxation time, λ 1 . (iii) At high shear rates, the apparent viscosity increases by increasing the shear rate caused by elongation whose onset is controlled by a critical shear rate which depends on the relaxation time. (iv) At very high shear rates, the apparent viscosity decreases by increasing the shear rate because of mechanical polymer degradation caused by polymer rupture.The controlling parameter is the bulk relaxation time for the polymer. The critical shear rates for elongation and shear degradation increase when the effective molecular weight decreases. Typical injection shear rates in offshore matrix reservoirs exceed the critical shear rate for elongation and shear degradation. Consequently, high molecular weight HPAM will either have poor injectivity or cause fracturing. For injection into fractured wells, the shear rate is substantially reduced and the shear degradation can be avoided. Acrylamido-Propyl-Sulfonate (AMPS) co-polymers have similar apparent viscosity versus shear rate as the HPAM. However, the AMPS co-polymers seem to tolerate higher shear rates before degradation sets in.For comparison, core flood experiments with Xanthan have been performed. This polymer was shear stable and the shear thinning apparent viscosity was similar to the bulk viscosity.The polymers reduced the permeability and the permeability reduction is understood by the polymer size, i.e., the permeability reduction increases by increasing the molecular weight. IntroductionPolymer flooding is an EOR method for improving the sweep efficiency. Polymers increase the water viscosity and reduce the water permeability. The most frequently used EOR polymers are HPAM which can be produced in large volumes and transported to the field as dry powder; biopolymers, such as Xanthan, have also been applied. The EOR polymers are pseudoplastic fluids, with their viscosity decreasing when the shear rate increases; this behaviour is very important in terms of injectivity.Polyacrylamide polymers are known to be sensitive to shear degradation and shear thickening at high shear rates. An overview was given by Heemskerk et al. (1984) and in a recent work by Seright et al. (2009). In this work we relate the shear degradation to the rheological properties of the polymer. When a po...

Mobility reduction is one of the critical parameters in polymer flooding. The EOR polymers have shear thinning bulk rheology, while core flood experiments with hydrolysed polyacrylamide (HPAM) in this paper show four different viscosity regimes. Through a systematic work, in which the molecular weight and degree of hydrolysis as well as the permeability and brine salinity were varied, the apparent viscosity was well-matched with theoretical models. The following four viscosity regimes were identified: (i) At low shear rates, the apparent Newtonian viscosity is less than the bulk viscosity; this effect is because of the inaccessible pore volume (IPV) with the polymer not entering the entire pore space. (ii) Shear thinning behaviour which is controlled by the polymers relaxation time, λ 1 . (iii) At high shear rates, the apparent viscosity increases by increasing the shear rate caused by elongation whose onset is controlled by a critical shear rate which depends on the relaxation time. (iv) At very high shear rates, the apparent viscosity decreases by increasing the shear rate because of mechanical polymer degradation caused by polymer rupture.The controlling parameter is the bulk relaxation time for the polymer. The critical shear rates for elongation and shear degradation increase when the effective molecular weight decreases. Typical injection shear rates in offshore matrix reservoirs exceed the critical shear rate for elongation and shear degradation. Consequently, high molecular weight HPAM will either have poor injectivity or cause fracturing. For injection into fractured wells, the shear rate is substantially reduced and the shear degradation can be avoided. Acrylamido-Propyl-Sulfonate (AMPS) co-polymers have similar apparent viscosity versus shear rate as the HPAM. However, the AMPS co-polymers seem to tolerate higher shear rates before degradation sets in.For comparison, core flood experiments with Xanthan have been performed. This polymer was shear stable and the shear thinning apparent viscosity was similar to the bulk viscosity.The polymers reduced the permeability and the permeability reduction is understood by the polymer size, i.e., the permeability reduction increases by increasing the molecular weight.

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The waterflood sweep efficiency can be increased considerably by in-depth placement of a blocking agent. Sodium silicate is one of the few PLONOR chemicals applicable for water control. This paper highlights key results obtained from a research program on qualifying sodium silicate for offshore applications. The main findings of this work can be summarized as follows: Sodium silicate is an alkaline liquid containing nano-size particles with water-like viscosity and good buffer capacity.Sodium silicate should be diluted in brines with a low divalent ion concentration addressing the need of a sufficiently large preflush.Upon reaction, triggered by an activator, sodium silicate forms silicate aggregates and gel which reduce rock permeability.The reaction rate is controlled by the formation temperature and sodium silicate concentrations.The flow behaviour of reacted silicate aggregates is understood by the classical theory on fine particle transport through porous medium, which includes a velocity-dependent deposition rate.Coreflood experiments at high flow rates demonstrated both a good injectivity of non-reacted sodium silicate and dynamic reaction rates similar to bulk reaction rates. At low injection rates, the plugging time decreased and was explained by fines particle transport which increased the deposistion rate of silicate.Interpretations of coreflood experiments unfold the effect of cation exchange. It is concluded that large volumes of sodium silicate can be injected into offshore oil reservoirs. Prior to the injection, a preflush is needed and the silicate is to be diluted in desalinated water. The permeability reduction can be obtained either during dynamic injection or shut-in period. The design parameters involve temperature, velocity and concentration gradients.

Ccpyr,ght 1996 SCCICVYof Pelro!+wm Engmers This pap6r was prepared for presenlalmo al the 1996 SPEMOE Tenth Sympcmum cm Improved CM Recrwe~he!d in Tulsa OK 21-24 A@ 1996. This paper was selacfad Ior W=anlatlon b the SPEProgram Ccmmdtea fcskwng rawaw of i ndorma!!on contained In on abstracl sutmltad y lhe author(s) Ccotants of tha Papr as presenmrj have not km raviewed by the Sooaly d Petroleum Engumars and ale subqad to corrackm by the authors(s) The mater! al, as presentad, doss not rmcassanhf reflect any paskm of the Sc.mry of Patrolaum Engina+rs or Its mamhr Papers presaiued at the SPE meatings are subpsct to publtca!on rewew by Edlorm CommMee of the Scc!e cd Petro!eum Engnwars Permlsacn 10 CWY IS restr~tad Y to an abstract of nol more than 3YJ wor s lllustalmas may not ha coped The abstract akwkj contain cmspcuous acknowkdgmmant d harm and by wfnnn Iha paper was Presrnlti Wr!te L#brian, SPE P O Box 8?.33636, Richardson, TX 75043 -3S3S U S A, lax 01-21 d-952-9435 AbstractAluminium citrate/polyacry lamide gels are found to be more sensitive and less robust than similar chromium systems. The main motivation for investigating aluminium based systems is the environmental constraints. This paper summarize the status on research of aluminium citrate gels. Several field experiments have been carried out, some of them claimed to be a success but yet (he gelation mechanisms has not been fully understood. This paper demonstrates one possible gelation mechanism, where oligornerisation of the aluminium citra[e complex is essential. The variation in gelation kinetic observed and to some exlend gelation mechanisms for the different sources of aluminium is mainly because of the difference in oligomerisation. The ratio between aluminium and citrate is critical. In seawater, precipitation of aluminium is observed at low amount of citrate (2:1) and precipitation of calcium citrale at ratios above 1:2. Within this window robust gels may be formed as long m pH is below 6 and hydrolyses polyacrylamide are used. In core flo~ds gel is formed if the sources to polymer degradation is removed. At aluminium tocitrate ratios of 1:1 no precipitation and face plugging, that is a severe problem at lower citrate concentrations, have been observed.