© 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