The Stages of Oil Recovery

Transcription

1 Smart water flooding

2 The Stages of Oil Recovery Stage Waterflood Injecting high pressure water Implications Hold production steady, grow recovery Facilities in place Maintenance costs increasing with age Improved Oil Recovery (IOR) Optimizing waterfloods through sweep, pattern or voidage improvements Conducting lab work to screen for EOR potential Enhanced Oil Recovery (EOR) Reducing residual oil saturation and improving sweep efficiency Grow production & recovery Spending capital up front for future benefit Expand facilities Convert vertical producers to injection Drill horizontal producers Maintenance costs improved Grow production and recovery Spending capital up front for future benefit Increasing op costs Facilities for polymer injection Polymer

3 Smart water flooding Ø What is smart water flooding Ø Recovery mechanisms Ø Lab results Ø Pilot and field results Ø Limita?ons

4 What is Smart Water? Smart water can improve wetting properties of oil reservoirs and optimize fluid flow/oil recovery in porous medium during production. Smart water can be made by modifying the ion composition. No expensive chemicals are added. Environmental friendly. Wetting condition dictates: Capillary pressure curve; P c =f(s w ) Relative permeability; k ro and k rw = f(sw)

5 Smart water flooding and Conven?onal water flooding Smart water flood The scien?fically devised method in the which salinity and ionic composi?on of the water are op?mized to modify the wecability and rock/brine/crude. Rock- fluid interac?on results in the reduced capillary pressure and increase the capillary number. Conven/onal water flood In the conven?onal flood, water is injected into the reservoir to sweep and displace the oil physically. It s efficiency is low because it is not altering the reservoir proper?es to reduce Pc or increase the viscous force.

6 Smart water flood Also called as a. Low salinity water flood b. Advanced ion management c. Designer water flood

7 Smart water flooding - Conven?onal water flooding

8 Ekofisk Outline What is the chemical mechanism for Ekofisk field? enhanced Highly fractured oil recovery by Smart Water?? Why is injection i of seawater such a tremendous success in the High temperature, 130 o C. Carbonates Low matrix permeability, 1-2 md Sandstones Wettability: Tor-formation: Preferential water-wet Are there any similari?es?? Lower Ekofisk: Low water-wetness Upper Ekofisk: k Neutral to oil-wet Estimated recoveries 1976: 18% 2001: Goal: 46% NPD; 2002: 50% 2007: Goal 55 % OIL RATE, MSTBD (GROSS S)

9 Smart Water to obtain improved Carbonates we7ng condi/ons OPen neutral to preferen?al oil wet Water injec?on difficult without wecability modifica?on. Sandstones Op?mal water flood at weakly water- wet condi?on (Morrow) Mixed wet (oil- wetness linked to clays)

10 Chalk: SW as smart water 50 Oil Recovery, %OOIP C#4 at 110 C C#5 at 110 C SI FW SI SW VF FW VF SW Time, days Fig. 3. Oil recovery from the cores C#4 and C#5 at 110 C by successive spontaneous imbibition and forced displacement. The injection rate was in the range of PV/day, and the ΔP across the core varied from 6 psi at the start to 3 psi at the end. S wi ~0.1 and AN=1.9 mgkoh/g.

11 Sandstone: Low Salinity flooding 0.7 Oil Production (Total Pore Volume) High Salinity Low Salinity Water Throughput (Pore Volumes) 0.61 PV PV (15,000 ppm) (1,500 ppm) By: Webb et al

12 Low Salinity Water Flood Lager et al

13 We7ng proper/es for carbonates Carboxylylic acids, R- COOH AN (mgkoh/g) Bases (minor importance) BN (mgkoh/g) Charge on interfaces Oil- Water R- COO - Water- Rock Poten?al determining ions Ca 2+, Mg 2+, SO 4 2-, CO 3 2-, ph Ca2+ Ca2+ Ca SO 2-4 SO 2-4 SO

14 Condi/ons for LoW Salinity effects (Morrow et al. 2006) Porous medium Sandstones (not documented in carbonates) Clay must be present Oil Must contain polar components (acids and bases) Water FW must contain divalent ca?ons (i. e. Ca 2+, Mg 2+ Lager et al. 2007) Ini?al FW must be present Efficiencyn related to S wi Low Salinity fluid (Salinity: ppm) Appears to be sensi?ve to ion composi?on (Ca 2+ vs. Na + ) ph of effluent water usually increases a licle, but also decrease in ph has been observed. In both cases, Low Salinity effects were observed. Are small changes in ph important for Low Salinity effects??

15 Recovery mechanisms WeCability altera?on mechanism At low temperature, low salinity is major mechanism At high temperature, sulphate presence triggers the wecability IFT reduc?on might be a possibility Dual wecability effects also plays the role

16 Smart water flooding poten?al in Sandstone- Lab Zhang and Morrow (1995) compared the inves?ga?on of low salinity brine in secondary and ter?ary modes Reservoir sandstone showed becer response to low salinity injec?on than outcrop sandstone Injec?on of low salinity brine increases the recovery that is accompanied by marked rise and drop in the pressure drop. Effluent of ph also rises to about 9 and then drops. This suggest the effect of ions interac?ons on the recovery. Mostly the oil is recovered in secondary and ter?ary mode. Very rarely, the secondary mode fails to generate recovery

17 Smart water flooding poten?al in Sandstone- Field case Lager et al reported that the injec/on of low salinity brine into Alaskan reservoir was successful. Low salinity flood increases the oil rate and decreases the water cut

18 Smart water flooding poten?al in Sandstone Improved recovery due to the mobiliza?on of bound oil Magnesium ions in produced water is nil during peak produc?on due ionic interac?ons that results in the oil mobiliza?on

19 Smart water flood poten?al in carbonate Yousuf et al As the water gets more diluted, the recovery factor increases 2. It is due to the reduced contact angle at the reduced water salinity. 3. Low contact angle renders water- wetness to the carbonate forma?on 4. Altered wecability causes an addi?onal recovery. WeCability altera?ons is the main reason. What causes wepability altera/ons? What causes the wecability altera?ons?

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21 What causes wecability altera?ons? What causes wepability altera/ons? Surface charge altera/ons Due to the posi?ve charge on the carbonate surface in the presence of high saline forma?on water divalent ions such as calcium and magnesium ions and lots of sodium and chloride ions will be present in the double layer. The same is the case for sulphate ions. If the chloride ions concentra?on is decreased, the sulphate ions would have becer access for surface altera?on and thus recovery. Enhancement in the connec/vity between different pore systems through microscopic dissolu/ons

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23 Smart water flood- Recovery due to dual wepability effect Lots of oil remains as disconnected aper ini?al water flood As smart water invades, it alters the wecability. Two dis?nct regions Yousuf et al Because of altered wecability, oil becomes redistributed and forms globules. It hinders the water flow Oil film across the invaded zones depletes faster. Also, as more oil film coalesce behind the water front, they tend to form an addi?onal oil bank. This might be beneficial for dual porosity system.

24 Aramco case study- well A Three modes of injec?ons are conducted Mode A: Sea water of ppm was injected. Mode B: Sea water was injected to con?nuously to make sure residual oil is not being mobilized because of sea water Mode C: 10 Times diluted water was injected. Tracer was to compare the recovery poten/al of the slugs

25 Aramco case study- well A: Recovery poten?al of smart water flood No recovery by persistent sea water injec?on Resulted in residual oil reduc?on of 7 satura?on units by smart water flood

26 Aramco case study- well B Three modes of injec?ons are conducted Mode A: Sea water of ppm was injected. Mode B: Twice diluted sea water was injected Mode C: 10 Times diluted sea water was injected. Tracer was to compare the recovery poten/al of the slugs

27 Aramco case study- well B: Recovery poten?al of smart water flood Slight Recovery by injec?ng twice diluted sea water Reduc?on of 6 satura?on units by injec?ng 10?mes diluted sea water. Lower the salinity, higher the recovery

28 Smart water flood- Advantages and Disadvantages Advantages: 1. Significant oil recovery with less capital (unlike other EOR methods such as low tension flood) 2. Easy implementa?on and handling 3. Environmental friendly 4. Sea water can be used during offshore opera?ons 5. Low cost

29 Smart water flood- Advantages and Disadvantages Disadvantages: 1. Mechanism not clear especially for carbonates 2. Neutral wecability is favorable (Morrow, 1990 and Agbalaka et al. 2008) 3. Poten?al scaling problems 4. Prone to channeling in the fractured reservoirs which will result in poor sweep efficiency (lab studies will overlook them) 5. Research are not that large in numbers

30 Low Salinity Waterflooding Limestone Composite Core

31 Dissolu/on of anhydrite quartz anhydrite Tensleep sandstone before and after flow of low salinity water (Lebedeva et al, 2009)

32 Conclusion on Smart Water Carbonate The chemistry of fluid- rock interac?on is well characterized Wemng agent: Carboxylic materials, difficult to remove WeCability modifiers: Ca 2+, Mg 2+, SO 4 2-, Temp. Wemng modifica?on at SW- salinity, which is not regarded as a Low salinity fluid. Sandstone The chemistry of fluid rock interac?on is more complicated The organic material adsorbs differently onto clay minerals, but it is more easily removed compared to carbonates. So fare, no single proposed mechanism has been clearly accepted for the observed Low Salinity effect. A hypothesis involving Sal?ng In effects has been suggested, and actual experiments are proposed to verify the hypothesis.

33 Conclusion on Smart Water The chemical mechanism for using Smart Water for wecability altera?on to enhance oil recovery is different for Carbonates and Sandstones.