Transcript Remediation is Enhanced Oil Recovery: Know Your Source

Remediation is Enhanced Oil
Recovery: Know Your Source
G.D. Beckett, R.G., C.HG.
AQUI-VER, INC. & SDSU
[email protected]
[email protected]
Which Scenario Works Best?
Steam Flood
Oil
Oil
Steam Flood
It’s Sort Of Obvious..
• E&P expends effort knowing oil distribution
– Aim for the oil
– Missing the oil misses revenues
• Environmental restoration has a more spotty record
– Sampling difficulty below water tables
– Some misnomers & misconceptions about NAPL
• Thickness exaggeration
• Sorption vs. residual
– Dissolved-phase thinking
– Hydrologic time bias in most environmental data sets
Talk Outline
• A few source principles & observations
– Chemistry will not be discussed
– Focus is source location relative to cleanup mechanisms
• Site examples where the source zone was missed
• Site example where source zone was pegged
• Conclusions
NAPL is the Source of Risk
Gasoline
LNAPL Mass
Equivalent
Volumes
Water, Vapor
& Sorbed Mass
Schematic of LNAPL Source Distribution
I
II
III
I
II
III
IV
V
IV
V
3
2
1
Predicted Saturations
Measured Saturations
0
0.00 0.05 0.10 0.15 0.20 0.25 0.30
Hydrocarbon Saturation
LNAPL
Z above oil/water interface (ft)
Equilibrium LNAPL Saturation
(uniform dune sand)
250
200
150
50
LNAPL
100
Measured
Predicted
0
-50
0.0
H2O
Z Above Oil/Water Interface (cm)
LNAPL Saturation in Heterogeneous Soil
(interbedded silty sands and sand)
0.1
0.2
0.3
0.4
0.5
0.6
Hydrocarbon Saturation
after Huntley et al., 1997
PHOTOGRAPH OF NAPL GANGLIA
Courtesy of Daugherty & Peuron;
Orange County Health Care Agency
A Peak Into the Pore Domain
(brine to oil mobility spectrum)
Courtesy of Terra Tek, Salt Lake City, UT
The Sites
Two Misses & One Hit
• Site 1: Service station adjacent to tidal stream
– Tidal influence affects product distribution & cleanup
– Several years of cleanup have not changed gw impacts
• Site 2: Service station with deep vadose zone
– Rise in gw table strands product
– 5 years of cleanup with no meaningful gw benefit
• Site 3: Former fuel terminal with effective targeting
– Dewatering with enhanced airflow delivery
– Source zone characterization was key to success
SITE 1
Gasoline LNAPL Adjacent to Tidal Stream
Site Plan & Plume Map
gw flow
LNAPL Source & Geologic Distribution
(after the fact)
CB-1
CB-3
CB-4
20
40
CB-7
CB-6
CB-10
-5.0
-10.0
-15.0
-20.0
0
LIF Intensity Contour
60
80
Section Distance (ft)
100
120
Sand Sand
Clays Silty Silty Sand
CPT Geologic Value
Remediation Actions
• Horizontal IAS, 18 fbg, uncontrolled flow responses
– Airflow in creek
– No direct capture by SVE
• SVE from available wells, pulling upper zone
• Groundwater pumping & skimming
• Combined SVE & groundwater recovery
Remediation Results after 7 years
• Free product thickness decrease in wells
– Product still present at low water stands
• No statistical reduction in gw concentrations
• Product discharges to adjacent creek
– Despite hydraulic containment in water phase
• System upsizing to pump more water
– Increase drawdown into deeper impact zone
– Force airflow into dewatered zone
SITE 2
Stranded LNAPL from Groundwater Rise
No gw benefit from SVE & Pumping
Site Plan & Initial Plume Distribution
Schematic Cross-Section
SVE &
Pumping Well
Dispensers
UST
F.P. Zone
Sandstone
Shale
Site Groundwater Elevation Hydrograph
160.00
GROUNDWATER ELEVATION (ft msl)
158.00
156.00
154.00
MW-10
MW-11
MW-12
MW-13
152.00
150.00
148.00
146.00
144.00
142.00
10/1/90
10/1/91
9/30/92
9/30/93
DATE
10/1/94
10/1/95
9/30/96
SVE/P&T System Summary; 1991-1996
• Low flow gw pumping planned (< 2 gpm)
– Never really ran much, head loss issues
– No effective dewatering
– Water level rise over period of cleanup
• SVE from multilevel screens
–
–
–
–
Packers not maintained by new contractor
SVE from full interval
> 10,000 ppmv TPH initial to 500 ppmv final
However, discrete well sampling = 9,600 ppmv final
Chemical Hydrograph, Sentry Well MW-8
Concentration (ug/l)
1.0E+06
1.0E+05
1.0E+04
TPH
Benzene
Toluene
1.0E+03
12/23/88
5/7/90
9/19/91
1/31/93
6/15/94
10/28/95
3/11/97
Site Plan & Post SVE/Pumping Plume
Site Plan & Initial Plume Distribution
Site 2 Wrap Up
• Water table rose
– No effective dewatering of smear zone
• SVE did not access full smear zone
– Ran to asymptotic
– Lower zone pneumatically inefficient
• Dissolved concentrations unchanged at key points
• Despite this, no risk & site obtained NFA status
Fuel Terminal & Operations Site
LNAPL Smear Found & Targeted
Highly Effective Remediation Response
General Site Conditions
•
•
•
•
•
AST & terminal operation sources
Heterogeneous, interbedded fine materials
Water table approx. 15 feet below grade (fbg)
Observed free product gasoline in 12 wells
Widespread dissolved phase impacts
– Initial TPHg max = 500,000 ug/L
– Initial Benzene max = 58,000 ug/L
– Initial MTBE max = 24,000 ug/L
Site Plan; Plume Width  600 ft
Original Lithology & Source Understanding
Updated Source & Lithologic Setting
75
Elevation (ft msl)
70
65
60
55
50
45
LNAPL zones
40
35
30
0
25
50
75
100
Section Distance (ft)
Clays/silts
Silty Sands
Sands
125
Changes in Thinking
• LNAPL stranded below, not at the water table
• Original design unable to access impacted zones
• Went to dewatering, enhanced airflow strategy
– Specific target = smear zone
• Large improvement in subsurface cleanup efficiency
• Large improvement in mass per unit time per cost
Estimated Cleanup Improvement Factor
(multiphase calculations)
Stratigraphic Elevation (m)
14
13
12
11
10
9
8
7
6
Area #1
Area #2
5
4
0.0
20
40
60
80
Mass Recovery Improvement Factor
100
MTBE Through Remediation
100,000
MW-7
MW-12
10,000
MW-13
MW-14
1,000
100
10
1
Pre-remdiation
April-99
July-99
Oct-99
Benzene Through Remediation
100,000
MW-7
10,000
MW-12
MW-13
1,000
MW-14
100
10
1
Pre-remediation
April-99
July-99
Oct-99
Recovery to Date
• Full hydraulic capture
• 400,000 lbs TPH recovered over 6 months
– 18,000 as free phase; 2,000 in water phase; 15,000 in
biodecay; 365,000 in vapor phase
• Free product no longer observed in cleanup area
– 80-day removal, multiphase estimate was 2-3 months
• Orders of magnitude reduction in MTBE & benzene
– On average and against pre-cleanup maximums
– Mole fraction changes consistent with principles
Conclusions
• Targeting depends first on knowing smear zone
– Common limitations to characterization efforts
– Like E&P, no oil, no production
• Efficient designs directly access smear zone
– Geologic efficiency is order of magnitude
• Tracking of success is fairly straightforward
– Chemical milestones, molar & otherwise
– Physical relationships between fluid zones
• No matter what, you cannot have it all
– Some soil zones won’t produce in any phase
– Always uncertainty in geologic distributions