Risk assessment and remediation suggestion of impacted soilby produced water associated with oil production

Hashim R. Abdol Hamid & Walid M. S. Kassim &

Abdulah El Hishir & Salem A. S. El-Jawashi

Received: 13 April 2007 /Accepted: 25 October 2007 /Published online: 20 December 2007# Springer Science + Business Media B.V. 2007

Abstract Produced water is water trapped in under-ground formations that is brought to the surface alongwith oil or gas production. Oilfield impacted soil isthe most common environmental problem associatedwith oil production. The produced water associatedwith oil-production contaminates the soil and causesthe outright death of plants, and the subsequenterosion of topsoil. Also, impacted soil serves tocontaminate surface waters and shallow aquifers. Thispaper is intended to provide an approach for fullcharacterization of contaminated soil by producedwater, by means of analysis of both the producedwater and the impacted soil using several recommen-ded analytical techniques and then identify and assaythe main constituents that cause contamination of thesoil. Gialo-59 oilfield (29N, 21E), Libya, has beenchosen as the case study of this work. The field has along history of petroleum production since 1959,where about 300,000 bbl of produced water be

discharged into open pit. Test samples of contaminat-ed soil were collected from one of the disposal pits.Samples of produced water were collected fromdifferent points throughout the oil production process,and the analyses were carried out at the labs of LibyanPetroleum Institute, Tripoli, Libya. The results arecompared with the local environmental limitingconstituents in order to prepare for a plan of soilremediation. The results showed that the mainconstituents (pollutants) that impact the soil are saltsand hydrocarbon compounds. Accordingly; an actionof soil remediation has been proposed to remove thesalts and degradation of hydrocarbons.

Keywords Soil remediation . Produced water .

Impacted soil

Introduction

Produced water is water trapped in undergroundformation that is brought to the surface along withoil or gas. It is by far the largest volume byproduct orwaste stream associated with oil and gas production.Management of produced water and its environmentaleffects, present challenges to the oil industry andenvironmental experts.

Produced water can have different potentialimpacts on environment depending on where it isdischarged. For example, discharges to small streamsare likely to have a larger environmental impact than

Environ Monit Assess (2008) 145:95–102DOI 10.1007/s10661-007-0018-3

H. R. Abdol HamidInternational Technological University,London, UK

W. M. S. KassimAl Fateh University,Tripoli, Libya

H. R. Abdol Hamid (*) :A. El Hishir :S. A. S. El-JawashiLibyan Petroleum Institute,Tripoli, Libyae-mail: hashimrahh@hotmail.com

discharges made to the open ocean by virtue of thedilution that takes place following discharges. Regu-latory agencies have recognized the potential impactthat produced water discharges can have on theenvironment and have prohibited discharges in mostonshore or near-shore locations.

Produced water characteristics and physical prop-erties vary considerably depending on the geographiclocation of the field, the geological formation withwhich the produced water has been in contact forthousands of years and the type of hydrocarbonproduct being produced. Produced water propertiesand volume can even be varying throughout the lifetime of the reservoir.

Many constituents found in produced water, whenpresent either individually or collectively in highconcentrations, can present a threat to aquatic life,soil, crops, and ecosystem.

Oil and grease are the constituents of producedwater that receive the most attention in both onshoreand offshore operations, while salt content (expressedas salinity, conductivity, or total dissolved solids –TDS-) is also a primary constituent of concern inonshore operations. In addition, produced water con-tains many organic and inorganic compounds that canlead to toxicity. Some of these are naturally occurringin the produced water while other are related tochemicals that have been added for well-controlpurposes. These vary greatly from location to locationand even over time in the same well (Veil et al. 2004).

This paper is intended to provide an approach forfull characterization of contaminated soil by producedwater of Gialo-59 oilfield, where a bank of disposingpit has been chosen as a case study area, and analysisof both the produced water and the impacted soil

samples have been carried out by mean of severalrecommended analysis and then identify and assay themain constituents that cause pollution of the soil.Then analyses results have been based to recommenda plan of soil remediation.

Site visit and samples collection

A bank of produced-water disposal pit has beenchosen as polluted land, (Figs. 1 and 2) which isperiodically covered by produced water and dried.The land was divided into 16 equal sampling units ofarea 16 m×10 m each as shown in Fig. 3. Using ahand shovel, random duplicate soil samples werescooped out at depth of 20 cm within each unit. Atotal of 32 soil samples were collected from thepolluted land strip. One sample of uncontaminatedsoil was taken to be used as a reference. Ten samplesof produced water have been collected. S1–S4 fromtwo separators (multi lines), S5–S7 from settlingtanks, and S8–S10 from pumping station were alsocollected as well.

Experimental analysis

Many parameters have been determined for both soiland produced water samples in order to characterizethe polluted site and to develop guidelines for soilrestoration and remediation (Abdul Hamid 2004).

Fig. 1 Produced water disposal pit at Gialo-59 oilfield, Libya

Fig. 2 Delineated land at the bank of the produced-waterdisposal pit, Gialo-59 oilfield, Libya

96 Environ Monit Assess (2008) 145:95–102

1. Soil samples tests: soil samples were air dried andpassed through a 10-mesh sieve. pH and electricalconductivity (EC) were determined in 1:1 soil:water extraction by ION450 Ion Analyser, thenanions and cations, were determined as theASTM procedures D3561-96, D511-93 (Re ap-proved 1998), and D4327-97. Sodium adsorptionratio (SAR) was calculated. Total PetroleumHydrocarbon (TPH) was determined by CVHmodel Infracal TOG/TPH Analyzer according toEPA-Approval protocol (413.2 and 418.1/600/4-79-020).

2. Produced Water samples tests: direct pH and ECwere determined as well as cations & anions.TPH was determined by an EPA-Approval proto-col (413.2 and 418.1/600/4-79-020).

Results and discussion

Figure 4 shows pH values for soil, which are rangedfrom 6.73 and 7.52. The normal pH range for soil is6–9. Therefore it could be considered that pH of soilare within the normal rang (Deuel and Holliday 1997).Figure 5 shows EC values for soil are varied between18,590 and 189,922 µmhos/cm where the normalEC for soil should be less than 4,000 μmhos/cm, andthat is indicates to exist of high concentration of saltsin the soil. Accordingly the anions and cations resultswere very high as it showed in Tables 1 and 2. Wherethe Anions vary between; (chloride: 5,786 and76,510 ppm), (Sulphate: 767 and 2,178 ppm), (Bicar-bonate: 41 and 61 ppm) and cations vary between(Sodium: 3,350 and 45,500 ppm), (Potassium: 110 and

6.750

6.800

6.850

6.900

6.950

7.000

7.050

7.100

7.150

7.200

7.250

7.300

7.350

7.400

7.450

B A

Fig. 4 pH Values for con-taminated soil, Gialo59 oil-field, Libya

Fig. 3 Schematic showingpit delineated by unit, siteswithin units and replicatecore locations

Environ Monit Assess (2008) 145:95–102 97

680 ppm), (Calcium: 720 and 3,000 ppm), Magne-sium: 126 and 1,118 ppm). While for reference soilsample the Anions are (chloride: 272 ppm), (Sulphate:421 ppm), (Bicarbonate: 43 ppm) and Cations are(Sodium: 265 ppm), (Potassium: 35 ppm), (Calcium:60 ppm), Magnesium: 24 ppm) which are consideredlow and within the normal limits.

SAR values for the soil were calculated accordingto the following equation (SAR ¼ Na½ �

.pCa½ �2þ

Mg½ �2), (Deuel and Holliday 1997), as it shown inTable 3, where vary between 21.42 and 137.86, whichis considered high in comparing with normal value(equal or less than 12), where for reference sample is5.17, which is accepted.

Figure 6 shows total petroleum hydrocarbon (TPH)for soil samples, where vary between 164 and24,000 ppm, and that is indicates impaction of soilby discharged hydrocarbon associated produced water.

The determined pH for produced water is shown inFig. 7, with a range between 6.41 and 7.16, which isclose to accepted criteria. Where E.C. values ofproduced water are varying between 20,773 and61,087 μmhos/cm, which is refer to high concentra-tion of ionic constituents (salinity) in produced water,(Fig. 8). Therefore the obtained results of anions andcations were high, as shown in Table 4. The anionsvary between (chloride: 6,235 and 27,529 ppm),(Sulphate: 1,276 and 1,864 ppm), (Bicarbonate: 220and 1,537 ppm) and the cations vary between(Sodium: 5,050 and 15,000 ppm), (Potassium: 150and 370 ppm), (Calcium: 60 and 1,840 ppm),(Magnesium: 85 and 807 ppm).

Figure 9 depicts the total petroleum hydrocarbon inproduced water with a range between 2 and 354 ppm.The variation in TPH values of produced water is dueto the difference in oil/water ratio through thedifferent location of sampling points throughout theprocess till the disposal pit.

Impact and remediation action

The impaction can be summarized as follows:

1. The soil is badly infected by brain water over longterm of disposing; so that high concentration ofanions and cations are exist in the soil, especiallysodium, magnesium, calcium, potassium, sulfateand chloride. All together caused poor physicalcondition and law hydraulic conductivity. Accord-ingly the soil is considered as saline and sodic.

2. The soil suffers from high concentration ofhydrocarbons constituents (crude oil base) whichare accumulated due to direct produced waterdisposing. Hydrocarbons effect and threaten wildlife, soil biomass and groundwater resources(Epstein and Selber 2002).

The remediation action should be taken for thissort of contamination could be described as follow:

1. Remediation technologies applicable to salts-contaminated soil show that only a rinse or leachprocess with fresh water that reduces salts in soilis appropriate. Poor physical condition and

20000

30000

40000

50000

60000

70000

80000

90000

100000

110000

120000

130000

140000

150000

160000

170000

[micromhos/cm]

B

A

Fig. 5 Electrical conductiv-ity for contaminated soil

98 Environ Monit Assess (2008) 145:95–102

inherently low hydraulic conductivity preventsfree exchange of salt without the aid of structur-ing amendments, wetting agents and/or mechan-ical processes.

Calcium amendments counteract sodicity and highsalinity. If the material is both saline and sodic, as isthe case in the present case study, therefore, calciumshould be introduced prior to the leach process.

Alternatively, the amendment of choice is elemen-tal sulfur, when time is not a consideration, andmechanical means are available to distribute theamendment. The sulfur gets oxidized to sulfuric acid.These react with calcium carbonate (CaCO3) to form

calcium sulfate (CaSO4). However, in situations,when time is a factor or mechanical means are notavailable for distribution, soluble calcium sources,such as calcium chloride (CaCl2) or calcium nitrate(CaNO3) are necessary. Agricultural grade gypsum isan effective calcium amendment when time is not afactor and mechanical means are available fordistribution. Gypsum is readily available at low cost.

2. Remediation technology applicable to hydrocarbon-contaminated soil containing TPH less than50,000 ppm, is bioremediation, which is more activeand suitable for soil restoration (PEC 1999).

Table 2 Cations in for soil, Gialo59, Libya

Sample Na+

(mg/l)K+

(mg/l)Ca+2

(mg/l)Mg+2

(mg/l)

A1 40,960 656 2,456 1,064B1 45,500 650 2,320 1,118A2 8,700 570 1,920 535B2 10,903 587 2,088 584A3 15,750 625 2,460 693B3 20,597 662 2,831 801A4 22,800 680 3,000 851B4 17,757 532 2,408 663A5 8,392 257 1,311 313B5 3,350 110 720 126A6 8,000 270 960 292B6 6,125 200 840 228A7 4,250 130 720 165B7 9,125 194 1,096 288A8 14,000 270 1,472 408B8 13,837 291 1,443 398A9 13,406 309 1,367 374B9 12,798 325 1,259 340A10 12,100 337 1,136 301B10 11,402 347 1,012 261A11 10,794 354 905 227B11 10,263 358 828 203A12 10,200 360 800 194B12 14,475 331 1,270 326A13 18,750 290 1,740 474B13 18,717 262 1,737 502A14 18,486 236 1,718 525B14 17,860 211 1,668 543A15 16,642 189 1,569 557B15 14,632 169 1,406 567A16 11,634 152 1,163 573B16 7,450 140 825 575Ref. 265 35 60 24

Table 1 Anions in for soil, Gialo59, Libya

Sample Cl−

(mg/l)SO4

−2

(mg/l)HCO3

−

(mg/l)CO3

−2

(mg/l)

A1 69,683 2,154 52 0B1 76,510 2,157 51 0A2 17,290 2,178 44 0B2 21,209 2,100 45 0A3 29,832 1,922 48.9 0B3 38,454 1,725 53 0A4 42,373 1,592 56 0B4 32,887 1,518 58 0A5 15,272 1,459 60 0B5 5,786 1,436 61 0A6 13,614 2,034 59 0B6 10,211 2,122 60 0A7 6,807 2,152 61 0B7 15,929 1,459 60 0A8 25,050 767 59 0B8 24,705 775 57 0A9 23,795 801 56 0B9 22,508 845 55 0A10 21,034 906 53 0B10 19,559 984 51 0A11 18,272 1,081 50 0B11 17,362 1,194 48 0A12 17,017 1,326 46 0B12 24,505 1,786 43 0A13 31,993 2,176 41 0B13 31,974 2,174 41 0A14 31,839 2,161 41 0B14 31,474 2,127 42 0A15 30,763 2,060 43 0B15 29,590 1,949 45 0A16 27,841 1,784 48 0B16 25,400 1,555 53 0Ref. 272 421 43 0

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Native soils generally contain a sufficient numberand species diversity in microflora (bugs) to degradepetroleum hydrocarbon under controlled applications.Fertility adjustments in the form of fertilizer amend-ments, aeration and moisture are necessary forbioremediation program. Fertilizer amendment in-clude nitrogen (N), phosphorous (P) and potassium(K). Ammonium nitrate (NH4NO3), ammonium sul-fate ((NH4)2SO4) and urea are good nitrogen sources.They should be applied in multiple applications toincrease efficiency, because nitrogen is lost to the

atmosphere with time. Nitrogen should be disked-into distribute the application and aerate the system.Nitrogen is applied at rate yielding a carbon:nitrogen(C:N) ratio 150:1. Phosphorous and potassium areapplied at 1/4 the rate of nitrogen (660:1). Super-phosphorous and muriate of potash are suitablesources. Phosphorous and potassium are applied withthe first nitrogen treatment. Moisture contain need tobe maintained within 50–80% of field capacity toeffect optimum degradation rate, e. g., about 2.5 cmof water per week.

Conclusion

This study revealed the wide range effects of highconcentration of cations, anions, and petroleum

Table 3 Sodium adsorption ratio for soil, Gialo59, Libya

Contaminated soil

SAR Sample SAR Sample

58.64 A9 122.96 A158.45 B9 137.38 B158.34 A10 32.01 A258.49 B10 38.45 B258.94 A11 51.11 A358.64 B11 62.27 B359.38 A12 66.94 A466.33 B12 58.45 B472.743 A13 38.24 A572.00 B13 21.42 B570.84 A14 41.05 A668.71 B14 34.21 B665.01 A15 26.29 A758.92 B15 44.89 B749.37 A16 58.89 A834.47 B16 58.83 B8

5.17 Ref.

Fig. 6 Surface plot depict-ing total petroleum hydro-carbon of soil samples at thebank of produced-water pit

Fig. 7 pH of produced water, Gialo59, Libya

100 Environ Monit Assess (2008) 145:95–102

hydrocarbons components that caused by oil-fieldproduced water disposal on soil properties, where theaccumulation of pollutants constituents in the soilduring long term of disposal are lead to environmentaldamage at the effected area.

The main conclusion could be drawn are:

1. Soil pH values are not optimum (average 7.12),but they are within the normal range (6–9) and arelow enough.

2. The most concerned soil-contaminants that car-ried by produced water are salts and hydrocarboncompounds (EC tall to 60,000 μmhos/cm, andTPH toll to 360 ppm). While other contaminantsare considered low and less effect.

3. High concentration of salts, (EC tall to189,922 μmhos/cm), in the soil has bad influenceson the soil properties, and those threats the environ-ment echo system, so that chemical amendment forsoil should be done to manipulate the high salinity.

4. High TPH values for soil, (tall to 24,000 ppm),indicate that the natural attenuation of petroleumhydrocarbons constituents in the soil can not be

satisfied for soil remediation, so that completeplan of remediation has to be made.

Recommendation

1. Further studies must be done for more inves-tigations on the same field, where soil samplesshould be collected at different depths (more than1meter) in order to demonstrate pollutants migra-tion profile.

2. Laboratory scale of bio-remediation of hydrocar-bon contaminated soil should be done in order toevaluate the optimum conditions of degradation,then applied at field.

3. Concentrated studies on active technologies fordeveloping of produced water discharge quality.

Table 4 Anions and cations of produced water

Property 1 2 3 4 5 6 7 8 9 10

Chloride (Cl−) [mg/l] Anions 8,588 10,221 16,354 16,013 6,235 27,529 22,895 17,444 18,330 22,061Sulphate (SO��

4 ) [mg/l] 1,560 1,276 1,716 1,671 1,502 1,864 1,831 1,745 1,694 1,606Bicarbonate HCO�

3 ) [mg/l] 756 771 273 464 1,537 268 229 390 522 220Carbonate CO��

3 ) [mg/l] 0 0 0 0 0 0 0 0 0 0Sodium (Na+) [mg/l] Cations 5,800 6,500 9,500 9,500 5,050 15,000 13,100 10,400 10,900 11,400Potassium (K+) [mg/l] 180 210 300 300 150 370 320 205 310 320Calcium (Ca++) [mg/l] 328 400 880 840 60 1,840 1,520 928 1,040 1,240Magnesium (Mg++) [mg/l] 182 224 437 389 85 807 408 360 330 413

Fig. 8 Electrical conductivity of produced water, Gialo59,Libya

Fig. 9 Total petroleum hydrocarbon of the produced water,Gialo59, Libya

Environ Monit Assess (2008) 145:95–102 101

Acknowledgment I greatly appreciate the wide supportand constructive cooperation from Petroleum ResearchCenter staff, Tripoli. My regardful thanks and respect aredue to Dr Maher Al Baghdadi for his assisting and fruitfuladvices.

References

Abdul Hamid, H. R. (2004). Investigation and remediation ofcontaminated soil by oil-field produced water. M.Scthesis, International Technological University (ITU),London, UK.

Deuel, L. E., & Holliday, G. H. (1997). Soil remediation for thepetroleum extraction industry (2nd ed.). Tusla, Oklahoma:PennWell.

Epstein, P. R., & Selber, J. (2002). ‘Oil’ a life cycle analysis of itshealth and environmental impacts. The Center for Healthand the Global Environment, Harvard Medical School.(Available at: http://www.med.harvard.edu/chge/oil.html).

PEC (1999). Survey of technology for remediation of oil-contaminated soil in Kuwait. by Staff of Petroleum Energycenter, Japan.

Veil, J. A., Puder, M. G., Elcock, D., & Redweik, R. J. (2004).A white paper describing produced water from productionof crude oil, natural gas and coal bed methane. Preparedfor U.S. Department of Energy and National EnergyTechnology Laboratory, January.

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