halophytes for oilfield remediation

Use of Halophytes for the Cost Effective Assessment and Remediation of Oilfield Brine

Impacts in Arid Terrestrial Ecosystems

Phillip M. Rury, Ph.D.Arthur D. Little, Inc.

Cambridge, Massachusetts

David J. TurtonArthur D. Little, Inc.

Houston, Texas

David OwensDow, Cogburn and Friedman

Houston, Texas

6-Jan-11LFr (hou) Emp\Turton\Setac\Halophyte-4pg.ppt 2

AbstractElectrical conductivity of non-saline soils, lower than 2 deciSiemens per meter (dS/m), is tolerated by salt-sensitive crops. Halophytes are plant species that tolerate soil salinity greater than 8 dS/m and crops that yield satisfactorily above this level. Soil salinity impacts, floristic changes, and terrestrial ecological damages from produced water releases are a function of precipitation, hydrology, soil quality, and salt tolerance of plant communities at oilfield sites. Natural recolonization of brine-impacted soils by halophytes (e.g., family Chenopodiaceae) is most critical in arid habitats where precipitation cannot leach soil salts to below the rooting zone. Halophyte recognition helps focus parsimonious soil sampling to yield desired salinity impact data without the high costs of grid-based sampling programs otherwise needed when visible evidence of produced water releases (e.g., salt or petroleum stains) is lacking. Litigation-related mapping of brine-impacted soils and rangeland vegetation at a West Texas oilfield confirmed that halophytes are reliable indicators of saline soils. Soils were collected and floristic data recorded from potential brine impact areas which either lacked vegetation or supported combinations of halophytes and/or non-halophytes, including range grasses cultivated for grazing cattle. Soils with average salinity of 38 dS/m (maximum of 82 dS/m) were recolonized only by halophytes (e.g. Suaeda), whereas non-halophytes (e.g., Eragrostis Lehmanniana) recolonized soils with average salinity of 3.4 dS/m (maximum of 11.3 dS/m). Future colonization by halophytes is expected on bare soils with maximum salinity of 76 dS/m. These results confirm the reliability of halophytes for focusing soil sampling efforts to assess oilfield brine impacts and their ecological restoration value for use in saline soil phytoremediation.

A Case Study: Ecological and Historical Overview of a West Texas Oilfield• Located near Interface of Prarie and Chihuahuan Desert

Lowland Ecoregions

• Mesquite/Grama-Buffalo Grass and Tarbush-Creosote Bush Flora Dominates

• Mesquite/Grama-Buffalo Grass and Tarbush-Creosote Bush Flora Dominates

• Saline Soils and Halophytic Vegetation Occur Naturally in the Region

• Ranch owner introduced Lehmann's Lovegrass to Increase Cattle Yield

• Lehmann's Lovegrass Dominates Landscape and Colonizes Impact Areas

• Ranch owner confirmed cattle graze on native saltbush (Atriplex canescens)

• First well sites established in semi-arid range of cattle ranch in the 1930s

The Challenge: Cost Effective Assessment and Remediation of Oilfield Brine Impacts

• Releases of highly saline, produced waters occur even in well managed oilfields

• Salt concentrations in brine may exceed 100,000 parts per million

• Most native plants and field/forage crops cannot tolerate soil salinity above 4 dS/m

• Elevated soil salinity and sodium levels induce physiological drought in plants, dispersion of soil particles, exacerbate soil erosion, and damage habitat

• Absent visible soil stains, mapping of brine impacts is costly and problematic

• Grid-based sampling is too expensive, especially for ill-defined impact areas

• Allegations of damage may be overstated and/or ecologically premature

• Future land use may not warrant costly remediation to background conditions

• Evaluate potential for unassisted vegetative recovery to occur via natural processes

• Assess feasibility of using of native halophytes for low cost phytoremediation

General Crop Response to Soil Salinity

Salinity Class Salinity Plant Response

Nonsaline 0-2 Salinity effects negligible

Slightly Saline 2-4 Decreased yields in very sensitive crops

Moderately Saline 4-8 Decreased yields in many crops

Strongly Saline 8-16 Only tolerant crops yield satisfactorily

Very Strongly Saline >16 Very few crops yield satisfactorily (halophytes)

*Salinity classifications in dS/m as defined in Table 4-2 of API (1997).

The Approach: Evaluation of Halophytic Floristic Signatures and Soil Salinity• Profiled range flora and analyzed soils from

upgradient background locations

• Mapped well sites with alleged brine impacts to soils and vegetation

• Mapped bare soils and halophyte occurrence to guide soil sampling

• Flora Types of Soils Sampled: None, Halophytes, Mixed, Non-halophytes

• Native halophytes: Atriplex, Kochia, Salsola and Suaeda (Chenopodiaceae)

• Documented salinity levels re-colonized by halophytes versus non-halophytes

• Evaluated potential for native flora to re-colonize bare soils unassisted

• Assessed future potential to cultivate Lehmann's Lovegrass or other beneficial crops

Soil Salinity Effects Thresholds for Selected Halophytes

Seedling or Transplant

Scientific Name Common Name Survival Success* Germination Yield**

Agropyron elongatum Wheatgrass - - 18

Atriplex (7 species) Saltbushes - 11 to 19 31 to >67

Atriplex canescens Four-winged Saltbush 26% @ 114 - -

Atriplex nummularia Oldman Saltbush 88% @ 23 to 93 - -

Batis maritima Maritime Saltwort - - 67

Buchloe dactyloides Buffalo Grass 10

Chloris (2 species) Rhodegrass - 9 to 16 11

Cynodon dactylon Bermuda grass - - 17

Dactyloctenium (2 species) Crowfootgrass - 6 to 20 -

Distichlis palmeri Salt Grass - - 57

Eragrostis Lehmanniana Lehmann Lovegrass Sdlgs. w/o Irrig. to 11 - -

Hordeum vulgare Barley 75% Cover @ 15 to 74 - 11

Kochia (3 species) Summer Cypress 90% Cover @ 15 to 74 - 27

Kochia prostrata Prostrate Kochia 48% Trans.Sdlg. @ 23 to 93 - -

Panicum coloratum Kleingrass Irrigated Sdlgs. to 93 - -

Salicornia bigelovii Saltwort (coastal) - - 50 to >67

Salsola baryosma Tumbleweed - 9 -

Sporobolus airoides Alkali Sacaton 19 to 24

Sporobolus virginicus Dropseed - - 50Suaeda (4 species) Seepweed - 19 57 to >67

*Salinity effects thresholds in dS/m from various authors, mostly from Texas A&M University

** Salinity effects thresholds in dS/m from Tables 4-6 and 4-7 in API (1997).

50% Reduction In:


Floristic and Soil Results: Apparent Correlation of Halophyte Occurrence and Soil Salinity

• Native halophytes colonizing pit, pad, pipeline, and off-pad impact areas

• Within impacted areas, the salinity of bare and halophyte-dominated soils exceeds background (see tables)

• Soil conductivity results are consistent among pad, off-pad, pipeline, and pit samples (see tables)

• Some bare uncolonized soils were capable of supporting halophytes (see tables)

• Background soil salinity: EC mean of 2 and range of 0.4 to 5.2 dS/m (see tables)

Top: Well Site – Dirt Road Dominated by Lehmann's Lovegrass

Bottom: Cattle at "Home on the Range"

Top left:Well pit recolonized by dense halophytes

Top right:Well pad Recolonization by Atriplex, Salsola, Suaeda

Middle:Suaeda recolonizing a pit

Bottom left:Saltbush and Lehmann's Lovegrass

Bottom right:Suaeda and Atriplex at edge of pad

Summary of Background Soil Salinity and Nutrient Analyses

Sample Number

Conductivity

(dS/m) SAR Salinity

Qual_Salinity

(Texas A&M) Sodium SSP

SS-002-698 2.93 2.08 481 None 126 21

SS-006-639 3.13 1.81 1261 Moderate 109 17

SS-010-658 1.04 0.96 204 None 59 19

SS-016-748W 2.54 1.19 1261 Moderate 55 12

SS-020-SAT4 0.59 0.90 136 None 12 21

SS-027-760 0.51 1.11 158 None 17 27

SS-029-780 1.91 1.39 585 None 27 17

SS-031-781 0.39 0.57 144 None 7 16

SS-038-307 0.93 0.70 169 None 20 13

SS-039-307 0.81 0.37 174 None 9 7

SS-044-312 1.80 0.54 223 None 18 10

SS-047-567 5.18 2.20 689 Slight 87 26

SS-054-682 4.60 7.03 1066 Slight 425 51

Summary (n=14): Cond. SAR Salinity Sodium SSP

Minimum 0.39 0.37 136 7 7

Maximum 5.18 7.03 1261 425 51

Average 2.03 1.60 503.9 74.69 19.7692

Standard Deviation 1.57 1.73 435.7 112.53 11.0465


Soil Conductivity and Vegetative Cover versus Land Uses

Halophytes in Pit at SS-024 with Soil EC=27.3 dS/m; Suaeda and Stressed Mesquite in powdery white soils of brine runoff swale at SS-025 with EC=3.44 dS/m; and Mixed Vegetation in reddish soils at SS-026 with EC=0.95 dS/m

Soil Conductivi ty Data for Pipel ine Corridors Soi l Conductivi ty Data for Off Pad Areas

Vegetation Type

No.

Samples Min. Mean Max. Vegetation Type

No.

Samples Min. Mean

Halophytes 2 33.3 56.00 78.7 Halophytes 1 82.2 82.20

Mixed 1 2.03 2.03 2.03 Mixed 6 0.948 2.26

None 1 11.5 11.50 11.5 None 3 2.21 14.09

Non-Halophytes 2 0.676 5.99 11.3 Non-Halophytes 3 1.12 1.66

Overall 6 0.676 22.92 78.7 Overall 13 0.948 11.00

Soil Conductivi ty Data for Well Pads Soil Conductivi ty Data for Pits

Vegetation Type

No.

Samples Min. Mean Max. Vegetation Type

No.

Samples Min. Mean

Halophytes Halophytes 6 5.42 25.18

Mixed 5 1.017 1.84 3.23 Mixed 5 2.3 5.28

None 1 8.52 8.52 8.52 None 5 16.3 50.10

Non-Halophytes Non-Halophytes

Overall 6 1.017 2.95 8.52 Overall 16 2.3 26.75

Soil Conductivi ty Data for Al l Areas

Vegetation Type

No.

Samples Min. Mean Max. Notes:

Halophytes 9 5.42 38.36 82.2 1. Conductivity in deci-Siemens per square meter (dS/m)

Mixed 17 0.948 3.01 15.2 2. Halophytes are mostly species and genera of Chenopodiaceae

None 10 2.21 31.28 75.9 3. Background Soils: Mean of 2 dS/m; Max. of 5.28 dS/m

Non-Halophytes 5 0.676 3.39 11.3

Overall 41 0.676 17.71 82.2

Pad Recolonization by Halophytes and Lehmann's Lovegrass. SS-032 in Pit with Halophytes EC=65.9 dS/m; SS-033 in pit with mixed flora has EC=2.78; Undisturbed Lovegrass Range sampled (SS-031) with EC=0.39

Pad Recolonization SS-034 with EC=1.02 dS/m


Impairment Analysis:Vegetation Tolerance of Background vs. Impacted Soil Salinity

• Ecological Impairment Criteria used to evaluate alleged brine impacts

• Active operational "footprints" (i.e., pads, pits, etc.) excluded from estimates

• Existing/potential re-colonization of "impact areas" by native flora considered

• Potential for affected soils to support field and forage crops considered

• Surface area of obviously impaired soils estimated from flora/soil data

Soil Salinity and Floristic Criteria for Assessing Ecological Impairment

Ecological Impairment Analysis of Alleged Brine Impact Sites in West Texas

The average salinity of the impacted soils analyzed (17.7 dS/m) can be tolerated by many field and forage crops

Conclusions: Many Brine Impact Areas Can Support Salt-tolerant Flora and Crops

Not Soil Salinity is Comparable to Background;

Impaired OR Soil Salinity Exceeds Background but Non-

Halophytic Vegetation is Present;

OR Native, Non-Halophytic Vegetation is Recolonizing an

Impact Area.

Partially

Impaired

Soil Salinity Significantly Exceeds Background but is

Below Salt Tolerance Limit of Native Halophytes;OR Lack of Non-Halophytes but Halophytic Cover

Exceeds 5% of Soil Surface.

Impaired Soil Salinity Exceeds Background by Order of Magnitude;

OR Vegetation is Absent and Halophytic Cover is 5% or

Less of Soil Surface.

Alleged

Impact

Location

Type

Alleged

Impact

Not

Evident

Reported

Area Not

Impaired

Reported

Area

Partially

Impaired

Reported

Area

Impaired

Arthur D. Little Estimate of

Surface Area Impaired (Soil

Salinity in dS/m)

Unknown l EC=16.3; 2.78; 1.45

Off-Pad l EC=2.21; 3.26; 1.37; 8.52

Unknown

Unknown

Pit l

Unknown

Pit l 150' x 125'

Pipeline l

Unknown l

Unknown l

Pit l

Pit l

Pit l EC=37.3; 2.86; 1.45

Pipeline l

Off-Pad l

Pad l NA: Pad Proper-Reasonable Use

Pit l 150' x 75'

Pit l

Unknown l

Pit l

Off-Pad l (EC=1.12)

Off-Pad l (EC=2.42)

Off-Pad l (EC=82.2)

Pit l 250' x 150'

Pipeline l

Pit l 270' x 150' (EC=64.3)

Pad l NA: Pad Proper - Reasonable Use

Pipeline l EC=33.3; 11.5

Pit l

Alleged

Impact

Location

Type

Alleged

Impact

Not

Evident

Reported

Area Not

Impaired

Reported

Area

Partially

Impaired

Reported

Area

Impaired

Arthur D. Little Estimate of

Surface Area Impaired (Soil

Salinity in dS/m)

Pit l

Off-Pad l NA: "Impact" is an outcrop area

Pad l NA: Pad Proper - Reasonable Use

(EC=37.2;2.52)

Pit l 200' x 125' (EC=56.7)

Pit l 250'x145' (EC=31.9; 78.7)

Pit l 125' x 75'

Pipeline l EC=11.3

Pad l NA: Pad Proper – Reasonable Use

(EC=9.32; 2.14)

Pit l EC=5.42; 15.2

Pit l EC=27.3; 3.4; 0.948

Pit l EC=2.3; 11.23; 2.13

Pipeline l EC=2.03

Pipeline l EC=1.257

Pit l 120'x120' (EC=65.9)

Pit l

Pit l 250' x 110' EC=1.017

Pit l EC=65.9

Pit l EC=2.78

Unknown l EC=3.34; 75.9

Pit l EC=3.34; 75.9

Off-Pad l EC=3.34; 75.9

Pit l 200'x40'

Flare Pit l NA: Reasonable Use

Pipeline l

Pipeline l (EC=0.676)

Off-Pad l (EC=37.2; 2.52)

• Halophyte mapping rapidly guides parsimonious but effective soil sampling

• Native halophytes colonized soils with the maximum salinity levels found

• Salinity of all bare impacted soils sampled will not preclude halophyte colonization

• Salinity of some bare impacted soils also can be tolerated by many non-halophytes

• Lehmann's Lovegrass and related species, as well as non-halophytes inhabited soils to an EC of 11 dS/m

• Other field and forage crops cannot tolerate the maximum soil salinity levels found

• Many field and forage crops can tolerate the average salinity of all soil samples

• Remediation may not be needed to re-establish all field and forage crops

• Damage allegations ignore actual/potential vegetative re-colonization, thus significantly overstate the actual ecological impairment of rangeland

• While remediation may be warranted at some sites, assisted natural recovery or phytoremediation with halophytes is feasible for even the most saline soils

Scientific Name Common Name

50% Yield

Loss*

Maximum

Tolerance*

Field Crops:

Arachis hypogea Peanut 5 7

Beta vulgaris Sugar Beet 15 24

Carthamus tinctorius Safflower 10 15

Gossypium hirsutum Cotton 17 27

Hordeum vulgare Barley 18 28

Linum usitatissimum Flax 6 10

Lycopersicon esculentum Tomato 8 13

Triticum aestivale Wheat 13 20

Zea mays Corn (Field) 6 10

Forage Crops:

Agropyron elongatum Tall Wheatgrass 19 32

Agropyron sp. Wheatgrass 15 22

Cynodon dactylon Bermuda Grass 15 23

Dactylis glomerata Orchard Grass 10 18

Eragrostis Lehmanniana Lehmann's Lovegrass - 11

Festuca elatior Tall Fescue 13 23

Lolium perenne Perennial Rye 12 19

Lotus corniculatus Small Trefoil 10 15

Medicago sativa Alfalfa 9 16

Phalaris tuberosa Harding Grass 11 18

Sorghum bicolor Sorghum 11 18

Sorghum sudanense Sudan Grass 14 26

Trifolium spp. Clover 10 19

Zea mays Corn (Forage) 9 16

*Salinity thresholds in dS/m from API (1997).

halophytes for oilfield remediation

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