Improved Waterfloods: From Laboratory to Field

Transcription

1 Improved Waterfloods: From Laboratory to Field Norman Morrow Chemical & Petroleum Engineering University of Wyoming Enhanced Oil Recovery Institute 3 rd Annual Wyoming IOR/EOR Conference Jackson, WY September 12-13, 2011

2 Oil Recovery : Waterflooding Single 5-Spot Well Pattern

3 Oil Recovery, %OOIP Laboratory Measurement of Oil Recovery by Waterflooding Target for Tertiary Recovery brine core Oil Recovery by Waterflood Brine Injected, PV

4 Part I: Part II: Injection Brine Optimization -Low Salinity Waterflooding Improved Recovery by Sequential Waterflooding- Proposed Single-Well Pilot Test

5 Low salinity waterflooding at S wi First observations

6 242 ppm 2,417 ppm 24,168 ppm Waterflood recovery vs. pore volume (PV) showing LSE for LSW at S wi. Connate and injected brine have identical ionic concentrations.

7 June 1995 The British Petroleum Research Center sent their representative, Cliff Black, for a three day think tank session.

8 Necessary Conditions for LSE Tang and Morrow (1999) a significant clay fraction, the presence of connate water, and exposure of the rock to crude oil to create mixed-wettability. These conditions are not sufficient; many outcrop sandstones meeting these conditions have not shown LSE recovery.

9 LSW at S wi for Berea sandstone Dagang crude oil, and a matrix of connate and injected waterflood ionic compositions (Tang and Morrow, 1997). Oil Recovery (%OOIP) Connate: HS MS LS Injected: HS MS LS 56 80

10 First applications of low salinity waterflooding have been for watered-out reservoirs at residual oil saturation.

11 Oil Recovery (%OOIP) Test of LSW on reservoir core at S or after HSW LSE HSW LSW Brine injected, PV Distinct advantage of demonstrating LSE in a single piece of core.

12 S oe (%) BP: All clastic reservoir systems studied to date have shown an average of 14% additional oil recovery So Hisal So Losal Soe 100% S S o initial o Hisal Lager et al., 2006

13 Sor BP: Single Well Tracer Tests 0.45 Residual Oil to Waterflood, % Pore Volume 0.40 HiSal 9 HiSal HiSal LoSal 11 LoSal LoSal / Sor_HiSal Sor_LoSal Lager et al., 2006

14 Improved oil recovery observed - McGuire, P. et al., SPE (BP 2005) - Seccombe, J. et al., SPE (BP 2008) - Seccombe, J. et al., SPE (BP 2010) No response Reported Field Pilots - Skrettingland, K. et al., SPE (Statoil 2010) Corefloods were consistent with reservoir response - encouraging with respect to use of laboratory screening

15 Low Salinity Effect - Mechanism Many laboratories and organizations have grappled with identifying, reproducing, and explaining LSE.

16 Interest in LSW has increased as indicated by the number of publications and presentations focused on LSE. From review of LSW by Morrow and Buckley: SPE Distinguished Author Series, JPT, May 2011.

17 Low salinity - mechanism Despite growing interest in low salinity waterflooding, a consistent mechanistic explanation has not yet emerged.

18 Wettability Alteration Exposure of rocks to crude oil is known to cause wettability alteration towards decreased water-wetness. Subsequent wettability alteration, usually towards increased water-wetness during the course of low salinity flooding, is the most frequently suggested cause of increased recovery.

19 Spontaneous Imbibition The most direct, but less frequently used, measure of the wettability of rocks. In addition to waterfloods, companion sets of spontaneous imbibition data were measured for duplicate cores.

20 comparable initial rates of imbibition are measured in all three cases the extent of imbibition increases significantly with decrease in salinity.

21 Explaining the increases in the microscopic (pore level) displacement efficiency observed for both spontaneous imbibition and waterflooding is key to understanding the low salinity effect.

22 Low Salinity and Dissolution of Minerals Increased recovery has been demonstrated for sandstone and carbonate cores containing anhydrite

23 Studies on Wyoming Reservoirs using Coal Bed Methane Water (an abundant source of low salinity water)

24 Target Formations Minnelusa (Gibbs) and Tensleep (Teapot Dome) eolian sandstones One half of Wyoming s oil production Abundant dolomite & anhydrite cement Formation water salinity: 3,300 38,650 ppm Low salinity water: Coalbed Methane Water (1,316 ppm) Phosphoria (Cottonwood) dolomite formation Recovery factor as low as 10% Patchy anhydrite Formation water salinity: 30,755 ppm Low salinity water: Diluted formation water (1,537 ppm)

25 Phosphoria Rock from Cottonwood Creek Field 100 mm Vug Dolomite Dolomite Mineralogy: Crystalline dolomite and patchy anhydrite Porosity: % Permeability: md Pu et al., 2010

26 Oil recovery, %OOIP Pressure drop, psi P1 K g = 6.8 md, f = 9.5% S wi = 22.7% K we1 = 2.1 md K we2 = 1.1 md % PW 30,755ppm Brine injected, PV 5% PW dilute 1,537ppm 5 0 Low Salinity Waterflooding for Phosphoria Rock Pu et al., 2010

27 Summary of evidence for increased oil recovery through dissolution of anhydrite

28 Micro-X ray CT: Dissolution of anhydrite from Tensleep sandstone by low salinity waterflooding Dry: P=7.7%; Q=79.6%; D+A=12.6% Wet: P=7.6%; Q=79.6%; D+A=12.7% Lebedeva, E., Senden, T.J., Knackstedt, M., Morrow, N.R. (2009)

29 Summary - dissolution Tensleep and Minnelusa reservoir sandstones, and Phosphoria reservoir dolomite all contained anhydrite and all responded to low salinity waterflooding Tensleep sandstone from an aquifer and Silurian dolomite outcrop did not contain any noticeable anhydrite and did not respond to low salinity waterflooding

30 Low Salinity Waterflooding-Current Status Initial field studies concerned recovery of waterflood residual oil. Well-to-well field tests have given increased recovery. Low salinity flooding has now progressed to application in new reservoirs at the outset of water injection. ( can sometimes be planned in conjunction with treatment of brine by membrane separation to avoid reservoir souring)

31 Advances in Low Salinity Flooding and waterflooding in general Will result from development of broad understanding of the factors that determine waterflood recoveries for crude oil/brine/rock combinations for wide ranges of ionic strength and composition. Identification of the sufficient conditions for response to low salinity waterflooding and the circumstances under which there is little or no response remain as outstanding challenges.

32 Part II Improved Recovery by Sequential Waterflooding-Proposed Single-Well Pilot Test including application to natural residual oil zones

33 Sequential waterflooding Technology arose from further observations related to investigation of low salinity waterflooding involving re-use of individual reservoir cores

34 Cyclic flooding with cleaning, re-aging and change in salinity

35 T a = 75 o C 1,500 ppm seawater Combination of low salinity and seawater flooding without cleaning and re-aging between flood

36 Baselines for assessment of improved oil recovery No previous study of reproducibility of recovery of crude oil by waterflooding

37 Test of repeat flooding on a companion LK 2 reservoir core with only initial cleaning and no change in salinity This process will be referred to as sequential waterflooding

38 R wf (%OOIP) LK 2 T a = 75 o C T d = 60 o C k g = 886 md R1/C1 : S wi = 11% : S or = 32% R1/C2 : S wi = 11% : S or = 27% R1/C3 : S wi = 21% : S or = 15% R1/C4 : S wi = 23% : S or = 13% PV Brine Injected Sequential floods with seawater of friable reservoir sandstone without cleaning/re-aging between cycles (Loahardjo et. al., 2008) Loahardjo, et al., Energy & Fuels, 2010

39 Sequential waterfloods of outcrop sandstones and carbonates No initial cleaning needed (the notorious problems of cleaning reservoir cores are avoided) No change in salinity No cleaning or re-aging between floods Can a water flood be reproduced?

40 Outcrop Berea Sandstone T a = 75 o C t a = 14 days T d = 60 o C WP Crude Oil

41 Sequential flooding of sandstone

42 Outcrop Bentheim Sandstone (very low clay content) T a = 75 o C t a = 14 days T d = 60 o C WP Crude Oil

43 Sequential flooding of Bentheim sandstone (Bth 01) with seawater

44 Outcrop Limestone (EdGc) T a = 75 o C t a = 14 days T d = 60 o C WP Crude Oil

45 Sequential flooding of Limestone with crude oil at 60 o C

46 Summary of change in S or for sequential waterflooding (T d = 60 o C)

47 Limestone Berea Sandstone (BS) Reservoir Bentheim Sandstone Residual oil for sequential waterflooding for LK reservoir, limestone and sandstone cores at T d = 60 o C at 6 PV of seawater injection

48 Confirmation of Reduction in Residual Oil Saturation by Sequential Waterflooding Magnetic Resonance Imaging (ConocoPhillips Facility)

49 Limestone BS/MRI/3D Berea Sandstone (BS) BS/MRI/2D Reservoir Bentheim Sandstone Residual oil for sequential waterflooding for displacement of WP crude oil at 60 o C

50 Conclusion Sequential waterfloods for recovery of crude oil without core cleaning and restoration between floods and without change of salinity, usually exhibit large reductions in residual oil.

51 Sequential waterflooding has potential application as a new improved recovery technique Two patents filed by UW: 1. Field wide application 2. Single well testing and diagnostics Covers both waterflood and natural residual oil zones

52 depth oil Oil distribution after waterflooding upper transition zone oil water transition zone Free water surface P c = 0 aquifer 0 100% Water saturation

53 depth Waterflood residual oil Conventional view of oil distribution in a reservoir oil Free water surface P c = 0 aquifer 0 100% Water saturation

54 depth Oil reservoir with residual oil retained in aquifer oil oil upper transition zone water transition zone P c = 0 natural residual oil (NROZ) 0 100% Water saturation

55 depth oil WROZ Distribution of residual oil above and below transition zone after waterflooding water NROZ 0 100% Water saturation

56 depth NROZ Only oil WROZ any oil once held in reservoir has spilled water NROZ VROZ 0 100% Water saturation

57 Single-Well Tests of Sequential Floods Calculations are based on a simple piston-like displacement model f =20.9%, 30 ft reservoir oil-zone thickness

58 Increased Oil Recovery by Oil Injection Followed by Water Injection S or reduction taken from laboratory data : Bth 01 3D MRI WF WF WF

59 Reservoir at residual oil saturation after waterflood (WF1) S OR (WF1)=36.2% target zone radius = 45 ft Day ft

60 Injection of oil into the target zone S OR (WF1)=36.2% target zone radius = 45 ft oil injected = 100 bbl S O =64.9% Day ft

61 Displacement Radial length of of injected oil reaches oil by minimum injection before of brine growing upon more (WF2) injection of brine S OR (WF1)=36.2% inner radial distance START WATER INJECTION oil bank radial length oil bank minimum radial length= 4.5 ft Day ft oil bank volume = 406 bbl

62 Continuation of oil bank displacement by injection of brine (WF2) S OR (WF1)=36.2% S O =64.9% S OR (WF2)=28.8% oil bank radial length= 5.9 ft oil bank volume = 1,149 bbl Day ft

63 The well is put on production and the oil bank grows in volume and radial length S OR (WF1)=36.2% Day ft

64 The well is put on production and the oil bank grows in volume and radial length S OR (WF1)=36.2% S OR (WF2)=28.8% S OR (WF3)=24.0% Day ft

65 Single Well Field Test 100 bbl oil 2,000 bbl brine 900 bbl oil in 14 days (as high as 3200 bbl optimistically) 100 bbl oil 10,000 bbl brine 4,000 bbl oil in 62 days (as high as 15,000 bbl optimistically)

66 Many possibilities exist for other approaches to improved recovery by injection of small volumes of oil Example 1 : Inject multiple oil banks Example 2 : Improve recovery of sequential floods by displacing injected oil with low salinity brine. Example 3 : Pre-injection of oil will convert a tertiary mode low salinity flood into a much more effective secondary mode low salinity waterflood. Example 4 : Pre-inject low salinity brine Example 5 :Develop connectivity of oil phase in a natural residual oil zone

67 Field test : advantages/diagnostics Low cost: Injected brine and oil are directly available: Required oil volume is small Single well test gives direct volumetric measure of oil production Tracers added to the injected oil and brine will allow monitoring of mixing of injected oil and brine with reservoir oil and brine Oil/brine production ratios will indicate heterogeneity and viscous fingering Flow reversal will tend to counteract rock heterogeneities and phase distribution effects

68 Conclusions Sequential waterflooding without change in salinity and without cleaning or re-aging between cycles showed reductions in residual oil saturation NMR imaging confirmed the effect of sequential waterflooding Single-well field testing of sequential waterflooding for recovery of oil from waterflood and natural residual oil zones is justified

69 Acknowledgements University of Wyoming Enhanced Oil Recovery Institute BP, Total, StatoilHydro, ARAMCO, ConocoPhillips, Chevron The Wold Chair