MODELING STRANDED OIL IN THE RESIDUAL OIL ZONE

Transcription

1 MODELING STRANDED OIL IN THE RESIDUAL OIL ZONE (Oil-Water Flushing Hydrodyamics) Prepared by: George J. Koperna Jr. Advanced Resources International, Inc. Prepared for: SPE International Conference on CO2 Capture, Storage, and Utilization Geological Aspects of CO 2 Injection in Subsurface Reservoirs Affecting CO 2 EOR and CO 2 Storage November 2, 2009 San Diego, California

2 Origin and Occurrence of Residual Oil Zones Examining the Effects of Hydrodynamics and Reservoir Properties on Creating a Tilted OWC. To explore whether hydrodynamic flow is truly able to reshape the oil column in a reservoir, resulting in a substantial ROZ: 1. We constructed a hypothetical 2-D 2 D cross section of a typical Permian Basin oil reservoir and its underlying aquifer, and 2. Subjected this reservoir to varying horizontal aquifer flow rates and permeability values to examine the effect of these variables on the OWC tilt and the creation of a ROZ. 2

3 Model Inputs Typical Wasson Denver 3 Porosity Permeability, Hz Permeability, V Oil Gravity Residual Oil Saturation Aquifer Reservoir Input Data TOTAL THICKNESS HORIZONAL LENGTH 12% 5 md 0.5 md 33 API 35% 2-D D Simulation System Main Pay Zone (MPZ) Transition Zone (TZ) 350 ft 50 ft 200 ft 600 ft 5,000 ft

4 Origin and Occurrence of Residual Oil Zones - Initial Oil Reservoir/Aquifer Conditions 4 5,000 5,100 5,200 5,300 5,400 5,500 5,600 5,700 5,800 5,900 6, ROZ: HYDRODYNAMIC FORCES RUN 1 Oil Saturation J layer: 1 0 1,000 2,000 3,000 4,000 5,000 INJ PROD Main Pay Zone Transition Zone Aquifer Water Contact (OWC) Base of Oil 5,000 ft feet 0 1,000 2,000 3,000 4,000 5,000 4,900 5,000 5,100 5,200 5,300 5,400 5,500 5,600 5,700 5,800 5,900 6, meters File: ROZ_02.irf User: gkoperna Date: Scale: 1:9412 Z/X: 4.00:1 Axis Units: ft

5 Origin and Occurrence of Residual Oil Zones - Effects of Low Hydrodynamic Flow on OWC Tilt The figure below depicts the changes in the oil-water contact (OWC), transition zone (TZ), and residual oil zone (ROZ) after 2,000 years of water r movement in this 2-D 2 system. A steady-state state aquifer flow system, with a low constant flows velocity of 0.1 feet per year was first introduced. Only modest OWC tilting and ROZ development d occurs following the initiation of this low rate of water flow. 5 5,000 5,100 5,200 5,300 5,400 5,500 5,600 5,700 5,800 5,900 6, ,000 2,000 3,000 4,000 5,000 INJ Main Pay Zone (Base of Oil) Aquifer ROZ: HYDRODYNAMIC FORCES RUN 1 Oil Saturation J layer: 1 ROZ Flow Direction Producing Oil Water Contact (OWC) 0 1,000 2,000 3,000 4,000 5,000 PROD Transition Zone feet 4,900 5,000 5,100 5,200 5,300 5,400 5,500 5,600 5,700 5,800 5,900 6, meters File: ROZ_02.irf User: gkoperna Date: Scale: 1:9412 Z/X: 4.00:1 Axis Units: ft Oil Saturation

6 Origin and Occurrence of Residual Oil Zones - Effects of Higher Hydrodynamic Flow on OWC Tilt Much more pronounced changes in the OWC, TZ and ROZ of the reservoir can be seen following the initiation of a higher, more representative aquifer flow rate of 1 foot per year. The result being a larger ROZ and a diminishing main pay zone. ROZ: HYDRODYNAMIC FORCES RUN 1 Oil Saturation J layer: 1 6 6,000 5,900 5,800 5,700 5,600 5,500 5,400 5,300 5,200 5,100 5, ,000 2,000 3,000 4,000 5,000 INJ PROD (Base of Oil) Producing Oil Water Contact (OWC) Transition Zone Main Pay Zone ROZ Aquifer Flow Direction feet 0 1,000 2,000 3,000 4,000 5,000 4,900 5,000 5,100 5,200 5,300 5,400 5,500 5,600 5,700 5,800 5,900 6, meters File: ROZ_03.irf User: gkoperna Date: Scale: 1:9412 Z/X: 4.00:1 Axis Units: ft Oil Saturation

7 Origin and Occurrence of Residual Oil Zones - Effects of Higher Hydrodynamic Flow on OWC Tilt An increase in hydrodynamic flow results in an increase in the OWC O tilt (and ROZ thickness). By plotting the results of these simulations, a relationship between velocity and POWC tilt was developed y = 240x POWC Tilt, ft/mile Aquifer Velocity, ft/year

8 Origin and Occurrence of Residual Oil Zones - Effects of Aquifer Permeability on OWC Tilt Using aquifer flow of 1 foot per year and a ten times higher horizontal permeability (50 md), leads to the creation of a more modest ROZ compared to the previous case. This indicates that high horizontal permeability will decrease the hydrodynamic interaction between the aquifer and the e oil column, suppressing the size of the ROZ. ROZ: HYDRODYNAMIC FORCES RUN 1 Oil Saturation J layer: 1 8 6,000 5,900 5,800 5,700 5,600 5,500 5,400 5,300 5,200 5,100 5, ,000 2,000 3,000 4,000 5,000 INJ PROD Producing Oil Water Contact (OWC) Main Pay Zone Transition Zone ROZ (Base of Oil) Aquifer Flow Direction feet 0 1,000 2,000 3,000 4,000 5,000 4,900 5,000 5,100 5,200 5,300 5,400 5,500 5,600 5,700 5,800 5,900 6, meters File: ROZ_06.irf User: gkoperna Date: Scale: 1:9412 Z/X: 4.00:1 Axis Units: ft Oil Saturation

9 Origin and Occurrence of Residual Oil Zones - Effects of High Kv/Kh on OWC Tilt Increasing the vertical to horizontal permeability ratio (kv/kh( kv/kh) ) from 0.1 to 1 does not appreciably change the final oil and water contact tilts. ROZ: HYDRODYNAMIC FORCES RUN 1 Oil Saturation J layer: 1 9 6,000 5,900 5,800 5,700 5,600 5,500 5,400 5,300 5,200 5,100 5, ,000 2,000 3,000 4,000 5,000 INJ PROD Producing Oil Water Contact (OWC) Base of Oil ROZ Flow Direction Main Pay Zone Transition Zone Aquifer feet 0 1,000 2,000 3,000 4,000 5,000 4,900 5,000 5,100 5,200 5,300 5,400 5,500 5,600 5,700 5,800 5,900 6, meters File: ROZ_04.irf User: gkoperna Date: Scale: 1:9412 Z/X: 4.00:1 Axis Units: ft Oil Saturation

10 Origin and Occurrence of Residual Oil Zones - Effects of Low Kv/Kh on OWC Tilt Decreasing the vertical to horizontal permeability ratio to 0.01 creates an S-shaped S OWC, with a very pronounced ROZ near the flow source and a subtle ROZ along the middle of the cross-section. section. ROZ: HYDRODYNAMIC FORCES RUN 1 Oil Saturation J layer: ,000 5,900 5,800 5,700 5,600 5,500 5,400 5,300 5,200 5,100 5, ,000 2,000 3,000 4,000 5,000 INJ Producing Oil Water Contact (OWC) Base of Oil ROZ Flow Direction Transition Zone Main Pay Zone Aquifer 0 1,000 2,000 3,000 4,000 5,000 PROD feet 4,900 5,000 5,100 5,200 5,300 5,400 5,500 5,600 5,700 5,800 5,900 6, meters File: ROZ_05.irf User: gkoperna Date: Scale: 1:9412 Z/X: 4.00:1 Axis Units: ft Oil Saturation

11 Modeling Stranded Oil in the Residual Oil Zone 2. The Permian Basin

12 Evidence for ROZs in the Permian Basin Adapted from Brown, A., (2001), Effects of Hydrodynamics on Cenozoic Oil Migration, Wasson Field Area, Northwestern Shelf of the Permian Basin, West Texas Geological Society Fall Symposium, Pub (Viveiros, J.J. & Ingram, S.M. eds), Oct 2001, pp

13 Calibrating the Oil Recovery Models and Estimating Technically Recoverable ROZ Resources MPZ and TZ/ROZ Oil in Place 56 fields in five major Permian Basin oil plays that have potential for significant TZ/ROZ resources were identified. The TZ/ROZ OOIP in these 56 fields is estimated at 30.7 billion barrels. Field/Unit MPZ OOIP (BB) TZ/ROZ OOIP (BB) No. of Fields No. of MPZ Fields with CO2- EOR Projects No. of Fields with TZ/ROZ CO 2 - EOR Projects 1. Northern Shelf Permian Basin (San Andres) North Central Basin Platform (San Andres/Grayburg Grayburg) South Central Basin Platform (San Andres/Grayburg Grayburg) Horseshoe Atoll (Canyon) East New Mexico (San Andres) Total

14 Calibrating the Oil Recovery Models and Estimating Technically Recoverable ROZ Resources - Background on CO 2 -PROPHET The CO 2 -PROPHET model was developed by the Texaco Exploration and Production Technology Department (EPTD) as part of the DOE Class C I cost-share share program. In its simplest form, this model generates streamlines for fluid flow between injection and production wells, and then uses finite difference ference methods to determine oil displacement and recovery calculations along the established streamlines. Data input requirements are less demanding and computational times are much shorter than when using full-scale reservoir simulation. Input requirements for CO 2 -PROPHET can generally be obtained or calculated using engineering formulations. Key input parameters impacting oil recovery include: Residual oil saturation, 2. Dykstra-Parsons coefficient, 3. Oil and water viscosity, 4. Reservoir pressure and temperature, and 5. Minimum miscibility pressure.

15 Calibrating the Oil Recovery Models and Estimating Technically Recoverable ROZ Resources - Comparison and Calibration of CO 2 - PROPHET with a Full-Scale Reservoir Simulator Analysis of Simultaneous MPZ and TZ/ROZ Oil Recovery Simulation Results, Wasson Denver Unit 1,800 1,600 Reservoir Simulation Prophet - Mobile So Prophet - Immobile So 1,400 1,200 Cumulative Oil, MSTB 1, ,000 4,000 6,000 8,000 10,000 12,000 Time, days

16 Calibrating the Oil Recovery Models and Estimating Technically Recoverable ROZ Resources - Technically Recoverable Resources from the MPZ and ROZ Based on reservoir modeling of applying CO 2 -EOR to the TZ/ROZ resources, we estimate that 11.9 billion barrels is technically recoverable from the 30.7 billion barrels of TZ/ROZ oil in-place in these five Permian Basin oil plays Field/Unit Total CO 2 -EOR (BB) MPZ CO 2 -EOR (BB) TZ/ROZ CO 2 - EOR (BB) 1. Northern Shelf Permian Basin (San Andres) North Central Basin Platform (San Andres/Grayburg Grayburg) South Central Basin Platform (San Andres/Grayburg Grayburg) Horseshoe Atoll (Canyon) East New Mexico (San Andres) Total

17 Economically Recoverable Oil Resources in Transition and Residual Oil Zones - Basic Economic Model How much of the TZ/ROZ resource is economically recoverable from five Permian oil fields? To reflect the specific cost and economic requirements of recovering oil from the TZ/ROZ of Permian Basin oil fields, four changes overall l were made to the basic Advanced Resources CO 2 EOR economic model. 1. Well Deepening. 2. CO 2 Injection. The costs of injecting CO 2 were estimated using the following pricing formula for Permian Basin oil fields: Cost of Purchased CO 2 (per Mcf): 4 percent of oil price ($/Bbl) Cost of Recycled CO 2 (per Mcf): 1 percent of oil price ($/Bbl) 3. Oil Price. The oil price was assumed to be $35 per barrel (flat), with no basis differential. The oil gravity adjustment was based on a marker 40 API crude, using $0.25 per API, above or below 40 API. A 4. Economic Hurdle. The minimum economic threshold rate of return (ROR), before taxes, was set at 25% 17

18 Economically Recoverable Oil Resources in Transition and Residual Oil Zones - Economically Recoverable Resources This study suggests that nearly 2.5 billion barrels of residual ( stranded ) oil can be recovered from these five San Andres Reservoirs ervoirs through joint CO 2 -EOR flooding of the main and residual oil zones. CO 2 -EOR Project Recovery Totals for the Five Study Fields Of the 1.1 billion barrels estimated as recoverable due to CO 2 -EOR in the MPZ in these five study fields, 0.6 billion barrels has already been produced or proven 18

19 Economically Recoverable Oil Resources in Transition and Residual Oil Zones - Marginal Economic Analysis Does adding the TZ/ROZ and conducting a simultaneous CO 2 -EOR flood in both zones help or hurt overall economics? Based on a Marginal cost analysis, there is considerable economic benefit to adding TZ/ROZ target to a MPZ CO 2 Flood. Marginal Economic Analysis MPZ Only and Simultaneous MPZ and TZ/ROZ Floods 19

20 Modeling Stranded Oil in the Residual Oil Zone 3. The Williston Basin

21 Evidence for ROZs in the Williston Basin In the Billings Nose area oil accumulations in the Mission Canyon Formation, originally in stratigraphic traps, are tilted to the northeast at gradients of about 25 ft/mi (approximately the same as regional structural dip) by hydrodynamic flow. Additionally, some oil accumulations in the area owe their location entirely to hydrodynamic flow. Structure on Top of the Mission Canyon Formation (contour interval 1,000ft) and Important Oil Fields in the greater Billings Nose Area, A Williston Basin Prevalence of the Mission Canyon Formation throughout the Williston Basin and the presence of similar stratigraphic and hydrodynamic conditions suggest a potential for tilted OWC in other fields in other areas of the basin. 21 Adapted from Berg, R.R., DeMis, W.D. and Mitsdarffer, A.R., (1994), Hydrodynamic Effects on Mission Canyon (Mississippian) Oil Accumulations, Billings Nose Area, North Dakota, AAPG Bulletin, V. 78, No. 4, pp

22 Identifying and Evaluating Oil Fields with ROZ Resources - Williston Basin (Madison Group) Billings Nose Area Berg et al. (1994) summarized the evidence for the tilted OWC in the area and identified meteoric recharge from the Bighorn Mountains,, where the Williston Basin terminates 200 miles to the southwest, as the e source of the hydrodynamic flow and the Elevation of the Oil/Water Elevation of the Oil/Water Contact Field. in the Big Stick Oil Contact in the Elkhorn Ranch Oil Field. salinity decrease on the western portions of the Nose area, possibly when the mountains and the basin reached their present elevations two million years ago. The Big Stick and Elkhorn Ranch fields have well defined OWC dips of 25 ft/mile to the east, while the Knutson field has an OWC tilt of 15 ft/mile, with the potential for residual oil zones (ROZ) regions below their main pay zones. 22 Adapted from Berg, R. R., DeMis,, W. D., and Mitsdarffer A. R., (1994); Hydrodynamic Effects on Mission Canyon (Mississippian) Oil Accumulations, Billings Nose Area, North Dakota, AAPG Bulletin, V. 78, No. 4, pp

23 Identifying and Evaluating Oil Fields with ROZ Resources - Williston Basin (Madison Group) Billings Nose Area In some instances, oil deposits have been found to be displaced downdip to the northeast, in a parallel manner to the porosity pinchouts. Sequence of Oil Migration and Accumulation in the Billings Nose Fields, Williston Basin 23

24 Identifying and Evaluating Oil Fields with ROZ Resources Williston Basin (Madison Group) Evidence of tilted OWC s in the Billings Nose area suggests that the phenomenon may be basin-wide and may extend to other Madison/Mission Canyon oil accumulations such as a major anticlinal structure to the northeast, the Nesson Anticline. The Nesson contains six large fields with Madison reservoirs that were identified as candidates for miscible CO2- EOR in their ROZ s.. In addition, four large fields with Madison reservoirs were identified in northern North Dakota and Montana, referred to here as the Northern Tier play that are miscible CO 2 -EOR candidates. 24 Location Map of Major Madison Group: Williston Basin

25 Results: MPZ and TZ/ROZ Oil In Place 20 fields in the three Williston Basin oil plays that have potential tial for significant TZ/ROZ resources, were identified. The TZ/ROZ OIP in these 20 fields is estimated at 6.8 billion barrels, which is over three times the OOIP of the MPZ. Play MPZ OOIP (BBbls) TZ/ROZ OIP (BBbls) No. of Fields 1. Greater Billings Nose Area Nesson Anticline Northern Tier Total

26 Results: Technically Recoverable Resources from the MPZ and ROZ Based on reservoir modeling of applying CO 2 -EOR to the TZ/ROZ resources, we estimate that 3.3 billion barrels is technically recoverable r from the 6.8 billion barrels of TZ/ROZ oil in-place in these three Williston Basin oil plays. Play Total CO2-EOR (BBbls) MPZ CO2-EOR (BBbls) TZ/ROZ CO2-EOR (BBbls) 1. Greater Billings Nose Area Nesson Anticline Northern Tier Total To date, no CO 2 -EOR projects of the TZ/ROZ have been undertaken in these study fields. As such, no information regarding the potential tial performance of such a flooding scheme is available to validate the t results of this work. Nevertheless, the estimates of TZ/ROZ OIP for these 20 fields may make an attractive recovery target and data collected during the planned Beaver Lodge (Madison) CO2-EOR pilot flood may add further insight into the potential flood performance of these TZ/ROZ targets. 26 potential flood performance of these TZ/ROZ targets.

27 Modeling Stranded Oil in the Residual Oil Zone 4. The Big Horn Basin

28 Evidence for ROZs in the Big Horn Basin Based on previous studies, Bredehoeft,, et. al., concluded that along the eastern margin of the Big Horn Basin oil accumulations in the Tensleep Formation, originally in stratigraphic traps, mirror the structural dip in their location as a result of hydrodynamic flow. Prevalence of the Tensleep Formation throughout the Big Horn Basin and the enclosure of the basin by mountains suggest that tilted OWC s are most likely to be found in fields located around the edges of the basin. Based on the available geologic information and documented OWC tilts, a number of major oil reservoirs with ROZs were established in the Big Horn Basin oil plays. Location of Oil Fields, Structure and Direction of Hydrodynamic Flow, Big Horn Basin, Wyoming 2 Big Polecat 5 Byron 12 Elk Basin 13 Elk Basin, South 19 Frannie 20 Garland 21 Gebo 24 Grass Creek 26 Hamilton Dome 31 Little Buffalo Basin 37 Murphy Dome 41 Oregon Basin Reference: Bredehoeft, J.D., Belitz, K. and Sharp-Hansen, S., (1992), 28 The Hydrodynamics of the Big Horn Basin: A Study of the Role of Faults, AAPG Bulletin, v. 76, no. 4, pp Adapted from Stone, D.S., (1967), Theory of Paleozoic Oil and Gas Accumulation in Bighorn Basin, Wyoming, AAPG Bulletin, V. 51, pp

29 Identifying and Evaluating Oil Fields with ROZ Resources - Big Horn Basin (Tensleep( Reservoir) At first glance, the Frannie field (Tensleep reservoir), discovered in 1928, has a typical anticline trap reservoir geometry. However, during development of the field, producers found that wells could be successfully completed further down dip to the west of the crest than on the east. The Frannie Field, Big Horn Basin, Wyoming It was determined that the OWC in the field was dipping towards the southwest at 600 feet per mile, suggesting that a strong hydrodynamic flow through the Tensleep formation from the northeast was flushing the oil downdip.. This Hydrodynamic flow is thought to originate from the Tensleep formation outcrop in the Big Horn mountain range, 10 miles to the east. 29 Adapted from Hubbert, M.K., (1953) Entrapment of Petroleum Under Hydrodynamic Conditions, Bull. Of AAPG, v. 37, n. 8, p

30 Identifying and Evaluating Oil Fields with ROZ Resources - Big Horn Basin (Tensleep( Reservoir) In the case of the Big Horn Basin, hydrologic flow moves from the outer edges of the basin towards the center. Potentiometric Surface, Tensleep Formation, Big Horn Basin, Wyoming and Montana. 30 Adapted from Todd, T.W., (1963), Post-Depositional History of Tensleep Sandstone (Pennsylvanian), Big Horn Basin, Wyoming, AAPG Bulletin, V. 47, No. 4, pp

31 Identifying and Evaluating Oil Fields with ROZ Resources Big Horn Basin (Tensleep( Reservoir) Field OWC dips indeed show this trend, with OWC s dipping basin-ward in many fields, and steeper dips occurring generally where the potentiometric gradients are steeper such as the north and south basin flanks. 2 Big Polecat 5 Byron 12 Elk Basin 13 Elk Basin, South 19 Frannie 20 Garland 21 Gebo 24 Grass Creek 26 Hamilton Dome 31 Little Buffalo Basin 37 Murphy Dome 41 Oregon Basin Note: the map also shows examples (e.g. Grassy Creek field) where the dip direction does not follow the general hydrodynamic flow pattern, suggesting that secondary controls on flow are present. 31 Adapted from Stone, D.S., (1967), Theory of Paleozoic Oil and Gas Accumulation in Bighorn Basin, Wyoming, AAPG Bulletin, V. 51, pp

32 Results - MPZ and TZ/ROZ Oil in Place 13 fields in the two Big Horn Basin oil plays that have potential for significant TZ/ROZ resources, were identified. Five of these fields, are heavy oil fields which will require immiscible CO 2 -EOR methods. The TZ/ROZ OIP in these 13 fields is estimated at 4.4 billion barrels, which is nearly equivalent to the OOIP of the MPZ. Play MPZ OOIP (BBbls) TZ/ROZ OIP (BBbls) No. of Fields 1. CO2-miscible fields CO2-immiscible fields Total

33 Results: Technically Recoverable Resources from the MPZ and ROZ Based on reservoir modeling of applying CO 2 -EOR to the TZ/ROZ resources, we estimate that 1.1 billion barrels is technically recoverable r from the 4.4 billion barrels of TZ/ROZ oil in-place in these Two Big Horn Basin oil plays. Play Total CO2-EOR (BBbls) MPZ CO2-EOR (BBbls) TZ/ROZ CO2-EOR (BBbls) 1. CO2-miscible fields CO2-immiscible fields Total To date, no CO 2 -EOR projects of the TZ/ROZ have been undertaken in these study fields. As such, no information regarding the potential tial performance of such a flooding scheme is available to validate the t results of this work. Nevertheless, the estimates of TZ/ROZ OIP for these 13 fields may make an attractive recovery target and data collected in ongoing oing Powder River basin MPZ CO2-EOR floods such as Sussex, Salt Creek, and Hartzog Draw fields may add further insight into the potential flood performance of these TZ/ROZ targets. 33

34 Modeling Stranded Oil in the Residual Oil Zone 5. Conclusions

35 Conclusions: Effects of Higher Hydrodynamic Flow on OWC Tilt Using the relationship between aquifer velocity and OWC tilt shown in the simulation exercise, and data from actual oil fields with tilted OWC s,, we can estimate the aquifer velocities that resulted in those dips POWC Tilt, ft/mile 100 Permian Big Horn Williston Linear (Simulation) Aquifer Velocity, ft/year

36 Conclusions: 1. Simulation has shown that hydrodynamic flushing can be modeled and that the rate of aquifer flow will dictate the tilt of the POWC. P 2. Evidence for ROZs have been documented in the Permian, Big Horn and Williston Basins. ROZs may be more widespread as indications of ROZs have also been found in California s Coalinga Nose oilfield and oilfields in the Powder River Basin. 3. The resource in place is large in these 3 study areas, which has implications for oil security as well as sequestration potential. Field/Unit MPZ OOIP (BB) MPZ Tech. Recoverable (BB) TZ/ROZ OOIP (BB) ROZ Tech. Recoverable (BB) 1. Permian Basin The Williston Basin The Big Horn Basin Total