Offshore implementation of LPS (Linked Polymer Solution)

Transcription

1 Wednesday 14:40 15:10 Offshore implementation of LPS (Linked Polymer Solution) Tormod Skauge, Kristine Spildo and Arne Skauge IEA OFFSHORE EOR SYMPOSIUM, Aberdeen 20 Oct. 2010

2 Motivation Water flooding can be more efficient in some reservoirs when nanosized particles are added to the injected water Field applications in China, South America and the USA show 1-18 % increase in recovery when injecting polymer particles (CDG) (e.g. SPE 89460, 27780, ) Laboratory core floods using nano-sized polymer particles (LPS) show a reduction of Sor of % (e.g. SPE ) Optimize the chemical system for offshore application Avoid large aggregates LPS (Linked Polymer Solution) = CDG (Colloidal dispersion Gels)

3 Distribution Functions Normalised Data vs Pore Throat Size 1,0 Core PQRS Core XX'YY' 0,8 Core TUVW Core ZZ'11' 0,6 0,4 Significant amount of micro pores in high perm cores 0,2 0,0 0,001 0,01 0, LPS or CDG CIPR design Pore Throat Radius (Microns) CDG macro particles with bullhead treatment

4 Outline Linked Polymer Solution (LPS) introduction Laboratory preparations for offshore implementation Offshore logistics and operational issues Laboratory optimisation according to operational restrictions Injectivity Transport properties Summary

5 Oil Recovery (HCPV) Core flood results Sandstone reservoir core (fresh core), K=900 md waterflooding Qi=0.1 cc/min (3.7 PV) Qi=1.0 cc/min (4.0 PV) CDG Qi=1.0cc/min (13.4 PV) Recovery: WF 45% OOIP LPS 33% OOIP 0.3 Waterflooding Qi = 1.0 cc/min (6.0 PV) waterflood LPS Volum e injected (PV) Reduction in Sor varies from 15 to 60% (average 30%) (e.g. SPE )

6 LPS mechanisms SEM photograph of LPS particles Microscopic diversion Scale 2 μm Linked Polymer solutions Spherical particles Typical size nm Pre-generated particles; 1. Less likely to be adsorbed 2. Expect less chromatographic separation SEM image, ref. M. Li, Univ. Of Petroleum Beijing

7 Linked Polymer Solution (LPS) Simplified: A solution of colloid size polymer particles dispersed in water Partially hydrolyzed polyacrylamide (HPAM) at low concentration crosslinked with Al (III) Crosslinker: Aluminum Citrate (AlCit) The ratio of HPAM/AlCit: 10:1 40:1

8 Viscosity (mpas) Viscosity of CDG compared to polymer P P+X P: 600 ppm Al: 15 ppm Salinity 1wt% NaCl Shear rate (s -1 ) The coiled polymer after crosslinking show nearly Newtonian behavior

9 Chemistry of the CDG Prefer intramolecular interactions (internal binding) One polymer molecule coiled due to Al Nano size particles can be formed Slow exchange of Al ligand from citrate to polymer Subtle change of physical properties but very important Prepared the crosslinked system by heating to 40C and mature the solution for 1 week???? Can this process be transferred to offshore conditions???? Coiled Polymer CDG or LPS-CIPR macro aggregates GEL Polymer concentration Al concentration Polymer / Al ratio Brine salinity

10 Chemistry of the CDG Prefer intramolecular interactions (internal binding) One polymer molecule coiled due to Al Nano size particles can be formed Slow exchange of Al ligand from citrate to polymer Subtle change of physical properties but very important Prepared the crosslinked system by heating to 40C and mature the solution for 1 week???? Can this process be transferred to offshore conditions???? Coiled Polymer CDG or LPS-CIPR macro aggregates GEL Polymer concentration Al concentration Polymer / Al ratio Brine salinity

11 Microscopic diversion Our working hypothesis is that enhanced oil mobilization by nano-sized particles is due to microscopic diversion Potential for macroscopic diversion, but is difficult to show at lab scale Microscopic diversion occurs when some pores are blocked and flow is diverted to neighbouring pores Saturation Water Oil Recoverable Oil (water injection) Residual oil Unswept area Pore volume 1. Viscosity 3. Straining 2. Adsorption 4. Log-jamming

12 Field Cases worldwide Onshore fields China (e.g. Chang et. al 2006, SPE 89460) North America (e.g. Mack and Smith 1994, SPE 27780) South America (e.g. Diaz et. al 2008, SPE ) Offshore fields None so far Injection pilot offshore North Sea performed recently

13 Offshore logistics and handling Transportation Onshore generation Pre-generated particles Well controlled environment Good QA/QC Large transport volumes, frequent loading Offshore mixing-on-the-fly Reduced volumes Requires controlled reaction time generate particles before reaching reservoir Operation Storage volumes Oxygen and iron free storage avoid chemical polymer degradation Low shear mixing avoid mechanical shear degradation Polymer crosslinker mixing point preferably downstream choke values and high shear points

14

15 Laboratory preparations Effect of injection water Composition divalent ions can act as crosslinkers Salinity high salinity coils polymer Crosslinking reaction time Topside, well and reservoir temperature Pre-generation or mixing-on-the-fly Macroscopic sweep efficiency Viscosity Injectivity Polymer size and concentration wrt permeability and heterogeneity Transport properties Injection water adsorption, chromatographic separation

16 Can we reduce time for preparation of the LPS?

17 Injectivity Particle generation in well stream Reaction kinetics to determine minimum residence time topside/well stream Reaction kinetics speeded up by increasing temperature when moving down the well string Mixing heated water, e.g. produced water or routing LPS through heat exchangers (ref. Oseberg surfactant pilot)

18 Experimental detection of intramolecular bound LPS Reduced solution viscosity compared to free (relaxed) polymers in solution - At low polymer concentration, or high salinity, change from intra- to intermolecular bindings may not be detectable from solution viscosity measurements Filter tests can differentiate intramolecular from intermolecular binding.

19 Transport through porous medium

20 Do the LPS particles propagate through porous medium? Measurement of particle size distribution Før Forsøk1, Z-average=18nm Before injection Etter Effluent flømming, production Kjerne C/D, Z-average= from 20nm the core

21 Chromatographic separation

22 Norm. conc Polymer retention (3630) Polymer conc 600 ppm, 2.14 PV Ads polymer: 52.5µg/g 1 0,9 0,8 0,7 Effluentprofil FP3630S i 1 % NaCl Polymer Tracer 0,6 0,5 0,4 0,3 0,2 0,1 0 0,00 1,00 2,00 3,00 4,00 5,00 Injected (PV)

23 Norm conc Adsorption values Polymer = 32.3 µg/g Al = 4.1 µg/g No detectable chromatographic separation Equilibrium ratio P/AL = 540ppm / 12ppm Production data LPS i 1 wt% NaCl Polymer conc Aluminiums conc PV injected

24 Normalised concentration Adsorption values Polymer = 39.8 µg/g Al = 3.97 µg/g No detectable chromatographic separation Equilibrium ratio P/AL = 540ppm / 12ppm Effluent production LPS (30 cm core) Polymer Aluminium PV injected

25 Summary LPS have low viscosities (good injectivity) Preparation time offshore has been reduced significantly Can be handled offshore Filter tests show good injectivity No chromatographic separation is observed