EOR-effects in sandstone:

Transcription

1 Evaluation of Low Salinity EOR-effects in sandstone: Effects of temperature and ph gradient H. Aksulu, D. Håmsø, S. Strand, T. Puntervold and T. Austad University of Stavanger, Norway, RD IEA EOR SYMPOSIUM AUGUST 26 30,

2 Suggested Low Salinity mechanisms Migration of fines (Tang and Morrow 1999). Increase in ph lower IFT; type of alkaline flooding (Mcguri et al. 2005). Multicomponent Ion Exchange (MIE) (Lager et al. 2006). Extension of the ionic double layer (Shell 2009) 2

3 Some experimental facts Porous medium Clay must be present Crude oil Must contain polar components (acids and/or bases) Formation water Must contain active ions towards the clay (Especially divalent ions like Ca 2+ and Mg 2+ ) LS EOR effect is related to increased Water wetness Increased P c Improved microscopic Sweep efficency 3

4 Ion composition of LS brine NaCl CaCl 2.2H 2 O KCl MgCl 2.2H 2 O (mole/l) (mole /l) (mole /l) (mole /l) Connate Brine Low Salinity Brine Low Salinity Brine Low Salinity Brine Low Salinity Brine LS EOR effect observed for all LS Brines Increased ph observed in teriary LS mode 4

5 Acidic or Basic Crude Oil Basic Crude Oil: AN=0.1 and BN=1.8 mgkoh/g Acidic Crude Oil: AN=1.9 and BN=0.47 mgkoh/g LS EOR effects observed for both Acidic and Basic crude oils. 5

6 Initial ph Core No. S wi % T Aging C T Floodin g C Oil LS brine Formation Brine B TOTAL Oil Saturated With CO 2 at 6 Bars B TOTAL Oil NaCl: 1000 ppm NaCl:1000 ppm TOTAL FW ppm TOTAL FW ppm CO 2 + H 2 O H 2 CO 3 + OH - HCO 3- + H 2 0 Lower initial ph increases the LS EOR effect. Increased ph with LS brine 6

7 Experimental observations: Adsorption of basic material, Quinoline Burgos et al. Evir. Eng. Sci.,19, (2002) Kaolinite Nonsweeling(1:1 Clay) Montmorillonite Swelling (2:1 clay, similar in structure to illite/mica) 7

8 Experimental observations on Kaolinite clay: Adsorption reversibility by ph Adsorption of Quinoline onto Kaolonite Samples 1-6: LS Brine (1000 ppm ) Samples 7-12: HS brine (25000 ppm) Adsorption reversibility by ph 8

9 Adsorption of Organic Acidic components onto Kaolinite Adsorption of benzoic acid onto kaolinite at 32 C from a NaCl brine (Madsen and Lind, 1998) ph initial max mole/m Increased ph reduces the adsorption of Acidic components onto Clay surface 9

10 Active Organic species versus ph The pk a values of protonated base and carboxylic acid are quite similar, pk a BH + H + + B RCOOH H + + RCOO - The concentration of the active species (BH +, and RCOOH) will have a similar variation versus ph. 10

11 Adsorption of polar components onto Illite Adsorption of Quinoline onto Illite at ambient temperature LS (1000 ppm) and HS (25000 ppm) fluids. LS brine reduces the water wetness Increased ph increases the water-wetness 11

12 Adsorption of Crude Oil onto Clays Deposit of asphaltenic crude oil onto kaolonite surfaces (Fogden and Lebedeva, SCA ) Highest deposits with LS-brine Increased ph increases water-wetness 12

13 Clay minerals Clays are the main wetting material in Sandstone Clays are chemically unique Permanent localised negative charges Act as cation exchangers General order of affinity: Li + < Na + < K + < Mg 2+ < Ca 2+ < H + Negative charges balanced by: Cations Ca 2+ Mg 2+ Na + Proton H + Polar organic matter R 3 -NH +, R-COOH 13

14 Chemical LS mechanism - Basic material 1. SPE PP, Tulsa Austad, et al. 2. Energy & Fuels 2011, 25, RezaeiDoust et.al Desorption of Cations by low salinity water Clay- Ca 2+ + H 2 O = Clay-H + + Ca 2+ + OH - Wettability alteration,basic material Clay-R 3 NH + + OH - = Clay + R 3 N + H 2 O 14

15 Chemical LS mechanism Acidic material 1. SPE PP, Tulsa Austad, et al. 2. Energy & Fuels 2011, 25, RezaeiDoust et.al Desorption of Cations by low salinity water Clay- Ca 2+ + H 2 O = Clay-H + + Ca 2+ + OH - Wettability alteration, Acidic material Clay-RCOOH + OH - = Clay + RCOO - + H 2 O 15

16 Rate controlling step in LS Mechanism Controlled by the desorption of active Cations: Clay-Ca 2+ + H 2 O Clay-H + + Ca 2+ + OH - + HEAT an increase in ph as active Cations are desorbed Desorption of Active Cations is sensitive to Changes in concentrations Divalent Cations are strongly hydrated in water and the reactivity it usually increases as the temperature t increases due to dehydration a smaller ph gradient at high Temperature Dissoluble Ca 2+ -salts (Anhydrite) Negligible increase in ph due to buffers: CO 2 (g) + OH - HCO3- H S + OH HS + H 2 O Mg OH - Mg(OH) 2 (s) 16

17 Reservoir core (RC1) HS- LS- HS flooding at C Changes in effluent ph at 40, 90 and 130 C Temp, C ΔpH (2nd) 2.6 ph should decrease as the temperature increased Test at 40 was repeated Changes in effluent ph at 40, 90 and 130 C in line with expectations 17

18 Reservoir core (RC1) HS- LS- HS flooding at C Concentration of Ca 2+ and SO 4 2- in the effluent 4 anhydrite gives less desorption Ca 2+ and less ph 18

19 Reservoir core (RC2) HS- LS- HS flooding at C effluent ph at 40, 90 and 130 C ph gradients in the order of decreasing temperature significant change in the slope of the ph gradient desorption rate of the active Cations decreases with increasing temperature. 19

20 Reservoir core (RC2) HS- LS- HS flooding at C Concentration of Ca 2+ in the effluent Very low conc. of Ca 2+ and SO 2-4 during LS flooding 20

21 Conclusions Adsorption and desorption by organic material and cations have been studied focusing on salinity and ph changes:. ph is a key parameter in the low salinity EORmechanism. the adsorption of basic material is always higher in the LS compared to the HS water. The salinity itself is not the mechanism for the wettability alteration in a low salinity EOR process. Successive core floods with HS-LS-HS water at different temperatures, 40, 90, and 130 C, confirmed an increase in ph as the injected fluid was switched from HS to LS the ph change decreased as the temperature increased, confirming that desorption of Ca 2+ from the clay surface is an exothermic process. 21

22 Conclusions cont. the ph gradient (slope), that can be related to the desorption rate of Ca 2+ from the clay surface, appeared to decrease as the temperature increased. The presence of anhydrite and/or calcite in the rock material affected the magnitude of the ph gradient as well as the rate of desorption of Ca 2+, which h both can have an impact on the low salinity it EOR-potential. Flooding a sandstone reservoir core successively with relevant HS-LS-HS brines at T res and monitoring the ph and the composition of the produced water may be a valuable first approach to evaluate the low salinity EOR-potential. 22

23 Acknowledgements : The authors acknowledge Talisman Energy Norge and Total Norge A for financial support and for permission to publish the results of this study. 23

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