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© 2012 ARCADISMay 2, 20231
Optimized Geochemical Modeling of Produced Fluids Provides Important Insight into NORM-Related Issues
Imagine the result
Donald Carpenter, PGARCADIS
© 2013 ARCADISMay 2, 20232
NORM From Oil and Gas-Related Produced Fluids has been Known for Decades
1904 - NORM is found in oilfield hydrocarbons 1951 – NORM-bearing scale and sludges
in pipes and production equipment
American Petroleum Institute suggests that 1/3 of all producing U.S. oil and gas
wells have elevated radiation
NORM dominantly present as Radium-enriched Barite (Barium Sulfate [BaSO4])
© 2013 ARCADISMay 2, 20233
A Significant Mass of NORM may be Generated within a Typical Oil and Gas Field
~100 tons of scale per oil well is generated annually (thousands of tons per year per producing field)
The average radium activity from 480 pCi/g to 400,000 pCi/g.
Activity is often “diluted” by precipitation of other non-radiological-bearing scale and dispersal at the site – tens to hundreds of picoCuries per gram activity
© 2013 ARCADISMay 2, 20234
Estimation and Quantitation of Activity is Important Due to the Mode of Regulation of NORM
NORM is One of Five Radioactive Wastes Regulated in the US
1) High Level Radioactive Wastes
2) Uranium Milling Residues
3) “Transuranic Wastes” having an atomic number greater than 92 (Uranium)
4) Naturally Occurring Radioactive Material (NORM) or radioactive materials produced in an accelerator – Only Waste Regulated at State Level
5) Low Level Radioactive Waste
© 2013 ARCADISMay 2, 20235
Classification of NORM is Quite Variable by State Based on Total Radium Activity
State definitions cover a range of activities
Federal standards, if applied, are very much lower
27 pCi/g 100 pCi/g
5 pCi/g
Consideration is underway to lower standards
© 2013 ARCADISMay 2, 20236
The Following Systematic Process Will Be Followed For This Presentation
Uranium and Thorium Radioactive Decay Chains
Uranium Geochemistry and its separation from Radium
Barite Geochemistry
Approach to the Geochemical Modeling of the NORM Generation Process
7 May 2, 2023 © 2012 ARCADIS
Decay of Naturally Occurring Uranium and Thorium Generates Radioactive Progeny and NORM
Radium isotopes are produced within each decay chain
Comparatively short half-life of Radium-228 results in rapid natural attenuation
8 May 2, 2023 © 2012 ARCADIS
The Geochemical Behavior of Uranium can Help Explain The Potential Separation From Radium
UO2+2 oxidation state is stable under high Eh conditions – soluble
U+4 Oxidation state (Uraninite [UO2]) is stable under low Eh conditions
Same stability field of sulfides [H2S and HS-]
Very low uranium solubility
Area of enhanced barium and radium solubility
Thorium is very insoluble under all conditions
2 4 6 8 10 12 14
–.5
0
.5
1
pH
Eh
(vol
ts)
UO2++
UO2(CO3)2--
UO2(CO3)3----
UO2CO3
Uraninite
25°C
JGillow Fri Jun 15 2007
Dia
gram
UO
2++,
T
= 2
5 °C
, P
=
1.0
13 b
ars
, a
[m
ain
] =
10
–5.0
66,
a [
H2O
] =
1
, a
[H
CO
3- ] =
10
–3;
Sup
pres
sed:
U3O
8(c
,alp
h),
U4O
9(c)
UO2 and H2S or HS-
Ba+2 and Ra+2
9 May 2, 2023 © 2012 ARCADIS
Acid Insoluble
Physically Resistant Scale
Chemically Persistent
Dominantly Physical versus Chemical Dispersal
Precipitation of Alkaline Earth Sulfates May Co-Precipitate Radium Sulfate
Ba+2 + SO4-2 → BaSO4
Ba+2 + (Ra+2) + SO4-2 →
Ba(Ra)SO4
Sr+2 + (Ra+2) + SO4-2 →
Sr(Ra)SO4
10 May 2, 2023 © 2012 ARCADIS
Geochemical Modeling of NORM Formation Assesses the Implications of Critical Factors
Activity of Radium within Produced Fluids
Geochemical composition of brines
Concentration of dissolved Barium at depth
Barite precipitation mechanism at surface
Radium co-precipitation
11 May 2, 2023 © 2012 ARCADIS
Radiogenic Modeling Provides Insight into Radium Activity and NORM Formation Potential
Fixed rate of radium generation (and decay) from oil field host rock
Assumption of “Secular Equilibrium” – radium activity in a steady state(safe assumption)
Uranium concentration – 3 milligrams per kilogramPorosity of Rock – 20%Brine Density – 1.35 grams per literRadium Transfer to Brine Phase – 1% to 5%
Radium activity is dependent on:
Empirical measurements document 1,500 pCi/L (1.3 ppt)
12 May 2, 2023 © 2012 ARCADIS
Modeling of Deep Subsurface Brines Must Factor in Geothermal Gradient-Induced Heating
Temperature of the Earth increases with depth
Increase is nominally about 22° C per Kilometer (or about 3,300 feet)
For a 3 kilometer (10,000 foot) deep well base temperatures will approach near-boiling conditions
15° + (3 * 22°) = 81° C
This temperature increase must be factored into the geochemical behavior of NORM forming constituents
13 May 2, 2023 © 2012 ARCADIS
Applicable Assumptions Allow an Estimate as to the Geochemical Composition of the Brine at Depth
Constituent Concentration (mg/kg)
Ba+2 42CO3
-2 23Ca+2 8Cl- 228,000Mg+2 6Na+ 148,000SO4
-2 29SiO2 87
6 Molar NaCl Brine
RaSO4 5 orders of magnitude undersaturated - it is in solution
Temperature of 81° CEquilibrium with respect to:
Barite [BaSO4]
Halite [NaCl]
Dolomite [CaMg(CO3)2]
Amorphous Silica [SiO2]
Near neutral pHUse of specialty adapted “ARCADIS Brine Model”
14 May 2, 2023 © 2012 ARCADIS
Modeling Results Also Document Relationship Between Barium and Total Dissolved Solids
Empirical relationship has been noted between NORM formation and Total Dissolved Solids (and depth)Barium solubility can be shown to be a function of chloride concentration (activity)
Barium (brine) Barium (chloride-free)0
10
20
30
40Barium Solubility (ppm) – 81° C
15 May 2, 2023 © 2012 ARCADIS
Modeling can Assess the Impact of Cooling on the Brine as it is Pumped to the Surface
Barite becomes supersaturated by a factor of 7 strictly due to cooling
Precipitate 40 milligrams of barite per kilogram of brine – conservative estimate – no oxidation of sulfides to sulfate
Above model would predict about 133 metric tons per well per year – matches EPA estimate of nominally 100 tons per well per year
Constituent
Equilibrium Concentration (mg/kg) – 81° C
Equilibrium Concentration (mg/kg) – 15° C
Precipitated mass (in mg/kg) of brine
Ba+2 42 19 23SO4
-2 29 13 16
16 May 2, 2023 © 2012 ARCADIS
An Estimate as to the Radium Activity within the Barite Scale can Also be Made
Consistent with “near maximum” radium activities that have been reported
Increased scale mass but at lower activity (6,000 pCi/g)
Radium-enriched scale is “diluted” though by an equal mass of silica scale formation
Equates to about 12,000 pCi/g of barite
4.9 * 10-7 milligrams of radium will be concentrated within 40 milligrams of barite
Although remaining undersaturated some radium (up to 38%) will be incorporated into the barite [Curti, et al, 2010]
17 May 2, 2023 © 2012 ARCADIS
Geochemical Modeling can Identify Locations and Conditions Leading to NORM Formation and Activity
Cooling Sulfide oxidation (formation of new sulfate
ion) Mixing of multiple solutions Reactions with surface soils and sediments Changing geochemical conditions
Assess effects of:
Direct benefit in proactively
understanding likely areas of NORM and
insight into its radioactivity
18 May 2, 2023 © 2012 ARCADIS
Optimized Geochemical Modeling of Produced Fluids Provides Important Insight into NORM-Related Issues
A Significant Mass of NORM may be Generated within a Typical Oil and Gas FieldEstimation and Quantitation of Activity is Important Due to the Mode of Regulation of NORMDecay of Naturally Occurring Uranium and Thorium Generates Radioactive Progeny and NORMPrecipitation of Alkaline Earth Sulfates May Co-Precipitate Radium Sulfate Forming a NORMGeochemical Modeling Provides Insight into Radium Activity and NORM Formation PotentialModeling can Assess the Impact of Cooling on the Brine as it is Pumped to the Surface
19 May 2, 2023
Imagine the result