Remediation%20is%20Enhanced%20Oil%20Recovery:%20Know%20Your%20Source

1
Remediation is Enhanced Oil Recovery Know Your
Source

• G.D. Beckett, R.G., C.HG.
• AQUI-VER, INC. SDSU
• g.d.beckett_at_aquiver.com
• gbeckett_at_geology.sdsu.edu

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Which Scenario Works Best?
Oil
Oil
3
Its Sort Of Obvious..

• EP 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

4
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

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NAPL is the Source of Risk
Gasoline LNAPL Mass
Equivalent Volumes
Water, Vapor Sorbed Mass
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Schematic of LNAPL Source Distribution
I
II
III
I
II
III
IV
V
IV
V
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Equilibrium LNAPL Saturation(uniform dune sand)
3
2
Z above oil/water interface (ft)
1
LNAPL
Predicted Saturations
Measured Saturations
0
0.00
0.05
0.10
0.15
0.20
0.25
0.30
Hydrocarbon Saturation
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LNAPL Saturation in Heterogeneous
Soil(interbedded silty sands and sand)

250
200
150
100

Z Above Oil/Water Interface (cm)
LNAPL
50
M
e
a
s
u
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e
d

P
r
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0
O
2
H
-50
0.0
0.1
0.2
0.3
0.4
0.5
0.6
Hydrocarbon Saturation
after Huntley et al., 1997
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PHOTOGRAPH OF NAPL GANGLIA
Courtesy of Daugherty Peuron Orange County
Health Care Agency
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A Peak Into the Pore Domain (brine to oil
mobility spectrum)
Courtesy of Terra Tek, Salt Lake City, UT
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The SitesTwo 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

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SITE 1

• Gasoline LNAPL Adjacent to Tidal Stream

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Site Plan Plume Map
gw flow
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LNAPL Source Geologic Distribution(after the
fact)
CB-1
CB-3
CB-4
CB-7
CB-6
CB-10
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5
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0
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0
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0
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f
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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

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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

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SITE 2

• Stranded LNAPL from Groundwater Rise
• No gw benefit from SVE Pumping

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Site Plan Initial Plume Distribution
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Schematic Cross-Section
SVE Pumping Well
Dispensers
UST
Sandstone
F.P. Zone
Shale
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Site Groundwater Elevation Hydrograph
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SVE/PT System Summary 1991-1996

• Low flow gw pumping planned (lt 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
• gt 10,000 ppmv TPH initial to 500 ppmv final
• However, discrete well sampling 9,600 ppmv
  final

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Chemical Hydrograph, Sentry Well MW-8
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Site Plan Post SVE/Pumping Plume
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Site Plan Initial Plume Distribution
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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

26
Fuel Terminal Operations Site

• LNAPL Smear Found Targeted
• Highly Effective Remediation Response

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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

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Site Plan Plume Width ? 600 ft
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Original Lithology Source Understanding
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Updated Source Lithologic Setting
75
70
65
60
55
Elevation (ft msl)
50
45
LNAPL zones
40
35
30
0
25
50
75
100
125
Section Distance (ft)
Sands
Clays/silts
Silty Sands
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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

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Estimated Cleanup Improvement Factor(multiphase
calculations)
14
13
12
11
10
Stratigraphic Elevation (m)
9
8
7
6
Area 1
Area 2
5
4
0.0
20
40
60
80
100
Mass Recovery Improvement Factor
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MTBE Through Remediation
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Benzene Through Remediation
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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

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Conclusions

• Targeting depends first on knowing smear zone
• Common limitations to characterization efforts
• Like EP, 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 wont produce in any phase
• Always uncertainty in geologic distributions