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A Diagnostic of the Treatmentof Oil Well Drilling Waste in Algerian Fields

KHODJA Mohamed a, CANSELIER Jean Paul b, DALI Chafia c, HAFID Slimane a,

OUAHAB Redouane d,a SONATRACH/Division CRD, Avenue du 1er Novembre, Boumerdès 35000, Algeria

b Laboratoire de Génie Chimique, ENSIACET-INP, 5 Rue Paulin Talabot, 31106 Toulouse, Francec SONATRACH/HSE Centrale, Djenane El Malik, Hydra, Algiers, Algeria,

d MI-SWACO, Route d'El Borma, Hassi Messaoud, Algeria

AbstractIncreasing awareness of environmental risks led to undertake various programs aiming at reducing air,water and soil pollution. Downstream from oil drilling activity, the main research fields includedevelopment and checking of waste processing techniques. In this framework, numerous remediationtechniques, such as solidification-stabilization, thermal or biological treatments, have already beendeveloped. Processing techniques for liquid and solid phases of the waste pit will be described. In spite oftheir efficiency, these techniques still present a lot of drawbacks, possibly leading to air, water and/or soilpollution. While identifying the risks of the waste pit system, we try to analyze the various contaminants(hydrocarbons, heavy metals) and to examine the remedies considered so far. Upstream, drilling fluidformulation is being improved continuously, new biodegradable systems being developed to offer a betteralternative. Costly thermal treatments allow a nearly complete elimination (more than 99%) of thehydrocarbons; heavy metal pollution in solids and in air should still be removed.Our results show that :- according to leaching tests, solidification appears satisfactory as far as the reduction of the pollution byhydrocarbons and heavy metals is concerned. Pollutants are concentrated and kept in confinement but notdestroyed; besides, it is well known that storage time and conditions can affect the quality of the matrices,- "land farming" type pilot-plant scale experiments, based on preliminary tests in bioreactor, eliminate88% of hydrocarbons in five months: this alternative should be considered and promoted according to thenature of the ecosystem and the cost reduction generated, compared with other techniques (solidificationor thermal processes). Heavy metal pollution can be concentrated in vegetables (phytoremediation).Therefore, the present issue is a search for a compromise between economic aspects and environmentprotection. Managers should then be able to choose an appropriate waste treatment for each specific zonefrom South to North Algeria.

Keywords: drilling fluid, waste pit, stabilization, solidification, thermal treatment, biological treatment.

1. Introduction

1.1 General backgroundOil production is the driving force of the economic development of some countries. However, oilextraction, treatment and processing represent a major cause of environment degradation, often forsakenin favour of profitability. Now, Rosenfeld et al. (1997) estimate that, within the next decade, more than80% of the world’s new petroleum development will occur in humid tropical zones, housing most of theworld’s biological diversity. Thus, demonstrating that hydrocarbons can be exploited safely in suchecologically sensitive and biologically diverse areas is of paramount concern to world’s operators.Like water and air, polluted soil can affect people health and environment through its action on surfacewaters (rain-out), underground waters and vegetation (phytotoxicity, bioaccumulation).

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The contamination of soil and underground waters by hydrocarbons may arise either through accidentaldischarge or uncontrolled industrial wastes. It definitely constitutes one of the main environmentalproblems linked to the activities of oil and gas companies.During these last years, the number of polluted industrial sites to be rehabilitated due to oil explorationand exploitation operations, namely drilling, has constituted a major concern for the Sonatrach Company,then highlighting the necessity to work out an intervention strategy aiming at restoring thesecontaminated grounds progressively. The program undertaken by Sonatrach for the reduction and disposalof this kind of pollution lies on systematic mud pit containment and surface ceiling.Processing of drilling-fluid waste is a rapidly growing industry. Commercially available technologiesinclude dewatering, distillation, solvent extraction, cuttings reinjection, fixation, landfarming and otherbioremediation techniques. All of these affect the economics and the environmental acceptability ofdrilling operations.

1.2. Drilling fluidsDrilling techniques and fluids went through major technological evolution, from the first operations, inthe US, using a simple mixture of water and clays, to complex mixtures of numerous specific organic andinorganic products used nowadays. These products enhance fluid rheological properties and filtrationcapability to penetrate heterogeneous geological formations in the best conditions.The drilling fluids are intended to clean the well, hold the cuttings in suspension, prevent caving, ensurethe tightness of the well wall, flood gas, oil or water and form an impermeable cake near the wellborearea. They also have to cool and lubricate the tool, transfer the hydraulic power and carry informationabout the type of the crossed formation by raising the cuttings from the bottom to the surface.The complexity of the problems met in petroleum drilling has led to emerging techniques for theformulation of appropriate fluids. In most drilling fluids, fresh-, salt-, or seawater is the continuous phaseused (water-based muds, or WBM), but 5-10% are oil-based (usually gas oil) muds (OBM). OBM havebeen developed for situations where WBM were found inadequate (Chilingarian and Vorabutr, 1981).Petroleum contamination associated with drilling and production is derived primarily from the loss ofcrude oil from producing wells, oil-based drilling fluids and refined petroleum products used inmachinery operation and equipment. Light aromatics (from benzene to naphthalene) are considered to bethe most immediately toxic components more toxic than crude oil because of their rather high aqueoussolubility (McDonald et al., 1984).Out of the 55 different materials utilized as fluid additives, only 10-15 are commonly used in drillingtypical wells (Gettleson, 1980). Four products account for about 90% of all drilling fluid additives: barite(BaSO4) is added to increase density, bentonite clays to increase viscosity, and lignite and lignosulfonatesact as thinning agents (Kanz and Cravey, 1987). Other additives control pH and corrosion, while biocidescontrol bacterial growth. The exact composition of a drilling fluid depends on the specific geologicalformations and drilling conditions encountered during the drilling process.At the beginning of the 1990’s, three synthetic materials were introduced: esters, ethers andpolyalphaolefins (Friedheim and Conn, 1996). The development of this new generation of synthetic fluidstypically represents a compromise between environmental, economic, and performance considerations.This new approach, aimed at optimizing the design, delivery and management of wellsite fluids andwastes, exploits the natural grouping of all fluid-related products and services (Prutt and Hudson, 1998;Hudson and Nicholson, 1999; Hudson, 1999). Huge investments have been made through professionalservices companies, toward three main areas: treatment of drilled OBM cuttings, reinjection of drilledcuttings into the formation, research of novel, environmentally-safe fluid systems.The pollution impact on the environment showed a need for rapid solution and very restrictive regulationson the use of OBM and even WBM, containing numerous contaminants. In fact, the use of OBM,submitted to authorization, is always prohibited during the first stages of drilling; the oil content in wastemust be reduced from 100g to 10g/kg and the listing of additives used in drilling fluids and the evaluationof their toxicity must be provided.Waste is made of cuttings encapsulated with mud, waste mud during phase transfer, engine oil fromoperation maintenance of drilling equipment, washings, … Each waste contains contaminants with low

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toxicity (clays, carbonates, barite,…), medium toxicity (NaCl, CaCl2 or KCl brines, lignite derivatives,surfactants,…) and higher toxicity (heavy metals, amine derivatives, surfactants, …).The toxic heavy metals found in drilling muds persist in the environment and tend to accumulate in thefood chain. Most of those heavy metals are associated with barite and bentonite. In soil, redistribution ofheavy metals is characterized by initial fast retention and subsequent slow reactions, depending on themetal species, soil properties, level of input and time (Brummer et al., 1988; Han and Banin, 1997, 1999;Han et al., 2001). Adverse changes in microorganism reproductive potential and survival are consideredto be the most important biological responses of an organism to pollution stress. The following order ofincreasing chronic toxicity of the drilling wastes studied was observed: WBM < bentonite < barite <OBM (Capuzzo, 1988).

1.3 Waste treatment technologies: an overviewOff-line and on-line treatment processes, such as stabilization/solidification, are currently applied onsome mud pits and seem to be very effective. However, the use of such remediation technologies is veryexpensive and more often consists of a pollution transfer and/or containment without removing or evenreducing the concentration of the initial soil pollution.Thermal treatments join high separation efficiency, recovered oil quality, cost effectiveness and lowemissions. However, several works showed the possibility of heavy metal diffusion in air andaccumulation after combustion. In fact, heavy metals are present in drilled formation solids (U.S. EPA,1980; Leuterman et al., 1988; Candler et al., 1992), in naturally occurring materials used as mud additives(e.g. barite) and also in miscellaneous refuse lying in waste pits.Thus, for oil companies, the great problem is efficient environmental protection avoiding overcosts thatmight affect competitiveness. Therefore, the search for effective solutions at lower cost has a promisingfuture: biological treatments offer a suitable combination between economic issues and environmentprotection. This should help operators to reduce drilling costs, while simultaneously increasingproduction and enhancing environment-oriented efforts.The need for emerging downstream treatment technologies is necessary. Treatment of waste from pitsincludes:- Physical and chemical processes: removal of free phase, thermal desorption, excavation and disposal inlandfill, deep injection in the wells, dehydration, incineration, neutralization, solidification andstabilization,- Biological processes: landfarming, biopiles, composting, phytoremediation and bioreactor.

2. Waste treatment at Hassi Messaoud and Hassi R'Mel fields

The Hassi Messaoud field (HMD), a historical field in the South of Algeria, is one of the most importantpetroleum reservoirs with more than 1100 oil wells drilled. On the HMD field, drilling operations, mainlyin the aquifer, salted and clay zones, were not conducted in a continuous manner because ofenvironmental issues. Further extension of oil exploitation recommends high precaution for drilling andselecting the adequate waste treatment. Discovered in 1956, the Hassi R'Mel (HR) field is the biggestAfrican natural gas reservoir: it still provides about 25% of the total Algerian natural gas production andsome oil. Since 2001, the site is equipped with a deoiling-filtration facility allowing rejectingcontaminated fluids and refuse into waste pits (abandoned wells).

2.1 Stabilization/SolidificationOn-line and off-line methods are used on Algerian fields. Solidification and stabilization are distincttechniques with similar goals. Solidification involves the production of a solid mass having sufficientlyhigh structural integrity to be transported and/or disposed of without secondary containment, i.e. mixingof sludge with shredded paper, sawdust, etc. This technique converts hydrologic-sensitive liquid andsemi-liquid wastes into a physical form that can be stored safely and conveniently. Stabilization, however,involves the immobilization of constituents in waste by chemical alteration to form insoluble compounds,or by entrapment within the solidified product. Stabilization/solidification provides an effective method

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for processing oil-based waste, producing an environmentally safe, dry material acceptable for onsiteburial, landfarming or disposal at an approved waste facility (Khodja et al., 2005).The stabilization/solidification technique used in this study reduces the physical and chemical mobility ofcontaminants (hydrocarbons and heavy metals) in their own environment. Several physical and chemicalmethods are able to remove foreign substances (inorganic and organic compounds, either dissolved, insuspension or under colloidal form) from water. For the on-line process, the following steps can be listed:oil removal, decantation, centrifugation, coagulation and flocculation.

2.1.1 Equipment, sample treatmentThis off-line or on-line stabilization/ Solidification method allows the treatment of drilling, work over andproduction cuttings collected from pits, according to European standards (AFNOR, 1998) (Fig. 1).

1,2,3,4 and 5: Mechanical purification; 6: Corral 7: Centrifuge; 8: Static mechanical pad; 9: Directional mechanicalpad; 10: Knock out Tank; 11: Pump; 12: Mud treatment unit; 13: Water treatment unit; 14: Collecting unit;

15: Drilling equipment; 16: Platform; 17: Pits for water (200 m3); 18: Pits for mud (400 m3)

Figure 1: Processing unit for waste treatment during drilling operations

A mud cleaner screen removed the biggest fragments. These were sent through a moving mechanical padto static mixers. Chemicals were added in this order: cement, silicate polymer and water. A homogeneousmud was obtained at the outlet of the processing unit (Velpen and Minguet, 2003). Mud samples werecollected upstream and downstream. After the removal of larger solids, the samples were dried at 45 °C,ground, and passed through a 4 mm sieve. They were then treated according to the French standardizedprocedure (AFNOR, 1998). After this liquid/solid extraction, hydrocarbons and various elements weredetermined in the filtrate.

2.1.2 AnalysesCuttings were collected in glass bottles for analysis. Organic matter was extracted with CCl4 for filtrate

preparation using NFX 31-210 method. FTIR spectrometry was used for the determination of totalhydrocarbons (AFNOR, 1979). Atomic Absorption Spectroscopy (AAS) was used for the determinationof heavy metals (total Cr, Mn, Fe, Co, Ni, Cu, Zn, Cd and Pb) and colorimetry. for the determinationCr(VI). Mercury was determined as its volatile hydride by Cold Vapor AAS (AFNOR, 1997). Chlorideswere determined according to Mohr's method. The Biological Oxygen Demand measured for 5 days(BOD5), was carried out by respirometry.

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2.1.3 Results10 cuttings samples, coming from the HMD and HR areas (#2-6), were analyzed downstream, that is aftertreatment (leachates obtained from drill cuttings) resulting in solidification, and compared with twosamples collected upstream (#1: references). The contaminants selected were hydrocarbons, heavy metalsand chlorides. The BOD5 (Biochemical Oxygen Demand after 5 days) and COD (Chemical OxygenDemand) values were also measured. The initial total hydrocarbon concentrations were 1.30 mg/L(HMD) and 0.15 mg/L (HR). After treatment, the concentrations fell down to 0.05-0.08 mg/L and 0.02mg/L, respectively (Khodja et al., 2005). Thus, solidification ensures confinement of heavy metals andhydrocarbons: leaching, a simulation of rain wash, does not allow pollutant desorption. Losses can be dueto a combination of factors including biodegradation, abiotic degradation, volatilization, and migration.Heavy metal concentrations show significant but unequal reductions; they are always lower than themaximal admitted values by the Algerian Government (J. O. République Algérienne, 1993)(Table 1).After solidification, it appears likely that leaching, a simulation of rain wash, does not allow pollutantdesorption. High chloride and hydrocarbon (COD) contents appear in Table 2. The presence of chloridecan be explained by the use of a salt-saturated mud during the drilling of the salted layers of the senonianand triassic layers. High salt content (e.g. KCl muds) and high pH lime muds are potential soilcontaminants. In studies on green beans and sweetcorn, Miller and Pesaran (1980) suggest that muds ofthis kind are growth inhibitors in various soil/mud mixtures. Environmental factors, such as increasedsalinity and water logging, slow down the recovery rates of oil-contaminated salt-containing ecosystemsconsiderably. Biodegradation rates decrease with salinity increase (Okpokwasili and Odokuma, 1990).The pH of most drilling muds is maintained between 9.5 and 10.5 for corrosion inhibition and control ofthe solubility of calcium and magnesium salts (Bourgoyne et al., 1986). Change in ambient pH caused bythe discharge of strongly alkaline mud has a powerful toxic effect on certain plants and animals.

Table 1: Heavy metal concentrations

Sample Cr

(mg/L) Ni

(mg/L) Zn

(mg/L) Cd

(mg/L)Pb

(mg/L) Hg

(mg/L)HMD area

# 1# 2# 3# 4# 5# 6

HR area# 1# 2# 3# 4# 5# 6

0.050.010.020.010.010.02

0.170.010.020.010.020.02

0.04< 0.04< 0.04< 0.04< 0.04< 0.04

0.070.010.010.020.010.01

0.01< 0.01< 0.01< 0.01< 0.01< 0.01

0.02< 0.01< 0.01< 0.01< 0.01< 0.01

0.020.010.010.020.010.01

0.030.020.020.010.020.02

0.08< 0.05< 0.05< 0.05< 0.05< 0.05

0.50< 0.1< 0.1< 0.1< 0.1< 0.1

0.001< 0.001< 0.001< 0.001< 0.001< 0.001

0.001< 0.001< 0.001< 0.001< 0.001< 0.001

HMD: Hassi Messaoud; HR: Hassi R'Mel; # 1: Samples collected upstream (references);# 2-6: Samples collected downstream.

The BOD5 and COD results can be related to the rather high hydrocarbon content of these wastes (Table2). In fact, the variation of organic matter depends on the mineralogical and petrophysical properties ofthe geological layers drilled.Given the width of the HMD area, the region can be divided into five zones (1 to 5), starting from Northto South, according to their geographical and geological properties (Table 3). Therefore, many mudsystems must be employed and, in a selected zone, the type of fluid and the treatment methods can bepredicted. Detailed data, collected for each zone, include: well volume and profile, drilling fluid type,average drilling fluid cost per well and drilling waste management (current and proposed treatments andtheir average costs).

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Table 2: Chloride content, BOD5 and COD (mg/L)

Geological sample Number of samples Cl- BOD5 COD

Mio-plioceneEoceneCarbonateAnhydrite (CaSO4)CenomianAlbianAptianBarremianNeocomianMalmSalted TriasTrias (clay)Trias (clay, sandstone)

2233331222222

480820530500

6,0003,3004,7402,9502,2503,8003,5003,0803,260

5.55.06.28.59.68.88.18.38.28.09.19.610.2

65.264.662.275.396.895.696.896.796.797.2100.5104.6109.8

BOD5: Biological Oxygen Demand measured for 5 days; COD: Chemical Oxygen Demand (mass of oxygenconsumed per liter of solution, according to NFT 90-101 or ISO 6060 (1989).

Table 3: Treatment of different drilling zones

Zone 1 2 3 4 5Drilling fluid type WBM OBM OBM WBM and OBM WBMVolume (m3/well) 2900 515 1100 255 3,000

Drilling fluid cost/well ($) 420,000 468,500 670,000 162,500 450,000Current waste treatment Burial Solidification No treatment Waste pit left open

with all contaminantsfor later treatment

Burial

Proposed waste treatment Dewatering Solidification 1.VERTI-G Dryera

2. Solidification3. Thermal desorpt.

Dewatering (WBM)Solidification (OBM)

Dewatering

Treatment cost ($)/well 100,000 200,000 1. 240,000b

2. 210,0003. 950,000/pit

320,000 100,000

a: solid-liquid separation technique used during drilling for reducing solid content and hydrocarbon cuttingscontamination; b: Respective corresponding costs for the three waste treatment methods.

2.2. Thermal Phase Separation System (TPS)Thermal recovery involves distillation of oil-wet cuttings. Critical fluid extraction compresses gases intoliquid solvents that wash the oil cuttings. Solvent and oil are easily separated by pressure reduction. It isideal for remote drilling sites, ecologically sensitive areas, and cases where relatively small volumes ofmud and cuttings are anticipated. This technique:- treats a wide variety of mud, cuttings, sludge, soils and tank bottoms,- recovers more than 99% of synthetic oil, gas oil or low toxicity mineral oil for immediate reuse,- reclaims oil with no significant fractionation or degradation,- effectively treats solids containing up to 66% oil and water, as well as solids containing highpercentages of small particles (< 100 mm),- yields compact treated solids (less than 0.1% oil and less than10 ppm leachable transphilic compounds),- operates with negligible emissions.Thermal techniques contribute significantly to the presence of heavy metals in aerosols. It is thusimportant to ascertain the quantities and chemical forms of the heavy metals that are emitted. Thebehaviour of heavy metals strongly depends on the thermal and chemical environments.Trace metal compounds are emitted as fine particles in the gaseous phase when sludge is burnt (Roy etal., 1987; Dajnak et al., 2003; Ninomiya et al., 2004; Leckner et al., 2004; Åmand and Leckner, 2004).Health and environmental studies have identified their adverse effects. For instance, Utsonomiya et al.(2004) showed that airborne As, Cr, Pb and Se nanoparticles could pose a serious human health risk

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since, due to the small size of the particles, metal solubility and reactivity could be enhanced and favourabsorbtion into lung tissue (Hochella, 2002). Some countries have enacted strict regulations for thecontrol of these metals (Linak and Wendt, 1993; Moritomi, 2001).

2.3. Biological treatmentWith a high potential for destroying environmental pollutants, bioremediation of crude oil-polluted soils(by degradation and detoxification) is becoming an increasingly important remedial option (Song et al.,1990). The use of inexpensive equipment, the environmentally-friendly nature and simplicity of theprocess are some of its advantages over remedial alternatives such as physical and chemical treatments.Biostimulation and bioaugmentation, variations of bioremediation, either in-situ or ex-situ, involve theaddition of external (indigenous or exogenous) microbial populations or that of appropriate microbialnutrients to a waste stream, respectively (Lee et al., 1993). The objective is to stimulate the indigenousmicrobial flora. In a first phase, we focused on the development and experimentation of two rehabilitationprocesses in the laboratory: bioreactor and landfarming technologies. The goal was to optimize theconditions of the ground natural degradation while achieving biostimulation (Atlas, 1981a) andbioaugmentation (Atlas, 1981b) Landfarming removes contaminants from soils by a combination ofvolatilization, incorporation of the contaminant into the soil matrix and degradation. Inlandfarming/spreading, oil-contaminated cuttings are applied onto a soil surface and then ploughed toensure adequate mixing. In laboratory and field experiments, gas oil, gasoline, crude oil etc… can bedegraded. Biodegradable organic waste components are metabolized by the soil microorganismpopulations (Huddleston, 1984; Bartha and Atlas, 1977).In a second phase, a pilot test was implemented for the first time on the field for in situ biologicaldecontamination (landfarming) of drilling cuttings as part of an agricultural project. A feasibility studywas achieved to check its efficiency. Three tests were executed:a) autobiodegradation: degradation of hydrocarbons by the soil autochtonous microorganisms without anyexternal supply (reference test);b) biostimulation: degradation of hydrocarbons by the soil autochtonous microorganisms with addition offertilizers at various concentrations;c) bioaugmentation: degradation of hydrocarbons by the soil autochtonous microorganisms with additionof exogenous microbial inoculum (microorganisms specific to oil phase degradation, isolated andenriched in the laboratory, brought to reinforce bacteria existing in the soil).Such experimentation was aimed at:- evaluating the real capacity of the soil autochtonous microorganisms and examining the direct influenceof the addition of a fertilizer and a bacterial inoculum adapted to hydrocarbon degradation on a potentialincrease of the biodegradation rate,- following the degradation evolution in a controlled environment in order to establish bacterial kineticsand hydrocarbon degradation kinetics.

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4

2

1

3

2.3.1 BioreactorAs opposed to the landfarming process, thebioreactor system treats the soil in an aqueousenvironment. A flat-bottomed cylindrical 12.5Lreactor is equipped with four diffusers. A fourdeflected-blade agitator creates a verticalcirculation of the liquid (Fig. 2).

1: pump for aeration; 2: flowmeter; 3: gas diffuser; 4: reactor; 5: agitation system

Figure 2: Bioreactor scheme

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49% 59%

85% 81% 79%

91%53%

73%

0%

50%

100%

150%

250%

15 days 49 days 56 days

LAND FARMING+ Fertilizer

HC

Elim

inat

ion

%

During this experimentation we focused on:- The study of the influence of the agitation and air flowrate to be injected in order to optimize thecirculation of the reaction mixture;- The comparison of the power of the autochtonous bacteria for hydrocarbon degradation and that of anenriched, isolated bacterial inoculum from the ground.

2.3.2 Experimentation on the fieldVarious criteria have been considered (technical, economical and environmental). According to thesecriteria and as part of this survey, the selected option was a well drilled in 1996 at 2329 m depth. Themain muds used were OBM (from 55 to 86% gas oil). The bioreactor principle has been applied to thissite. Environmental context of area (arid to semi-arid climate), particle size distribution, physicalchemical properties of soil, nature of contamination (light hydrocarbons), biological characteristics of soil(microbial soil composition) offer high potential for this biological application. In our industrial field, allexisting factors influence and favour soil hydrocarbon natural biodegradation. The biodegradation powerof soil could be increased by using water treated in domestic waste station units.

2.3.3 Results and interpretationThe bioreactor results obtained in the laboratory proved satisfactory. It clearly appears that this soiltreatment is more efficient than the decontamination technique through the landfarming process in termsof time/efficiency (Fig. 3). The bioaugmentation tests achieved for the two techniques (landfarming andbioreactor) resulted in an enhancement of hydrocarbon biodegradation potential although the soilautochtonous mixed colonies already showed a rather effective decontamination of the oil phase.On the other hand, due to the influence of an external supply in nutriments (nitrogen and phosphorus) onthe microbial degradation of hydrocarbons, the biostimulation tests resulted in further biodegradationimprovement. We may then conclude that satisfactory results at the laboratory level deserve to undertakepilot tests of decontamination in situ through the landfarming process.The chemical and microbiological follow-up reveals the presence of hydrocarbon biodegradation byautochtonous microorganisms (elimination percentage of about 60% in five months) when theenvironment conditions are controlled (dampness, aeration and pH) (Fig.4). However, we notice that anutriment supply allows a better elimination (88%). This means that hydrocarbon degradation dependsupon the nutriment source added to the soil.

Reference Biostimulation Bioaugmentation

Fig.3: Evolution of Hydrocarbon Elimination Fig.4: Degradation kinetics of hydrocarbons

2.3.4 Vegetable growth on treated soilAt the end of this pilot experimentation, the cleaned up field was exploited as a basis for an agriculturalfarming (beans). The aim was to verify if the treated soil could be reexploited for plant farming. 32 grainseeds were observed on a pilot test and on a biostimulated test. On a short period (15 days), out of 32seedbeds, 11 grains grew on the stimulated area, none on the pilot area (without fertilizer) and 32 on theuncontaminated area. Samples of bean plants from the stimulated, decontaminated soil and from the

BIOREACTOR

LANDFARMING+Fertilizer

0

5

10

15

20

25

30

1 2 3 4 5Time (Months)

[HC]: g/Kg

Reference

Biostimul.

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uncontaminated soil were analyzed for heavy metal content (Table 4). As regards kinetics, several worksshow an adaptation period is often required before biodegradation. The decrease in hydrocarbon could beindicative of the microbial adaptive response.

Table 4: Heavy metal content in bean vegetation

* After hydrocarbon elimination

In opposition to what was expected from this experimentation, the results on heavy metal content (Table4) show a bioaccumulation in the bean plants grown on a contaminated soil, after hydrocarbonelimination, compared with the bean plants sampled from the uncontaminated soil. Therefore,phytoremediation (use of plants in a downstream bioremediation to eliminate residual heavy metalpollution) occurs (Costes and Druelle, 1997). This bioaccumulation effect brings about a double profit: achange in the image of industrial sites with a new plant cover and soil decontamination and stabilizationof the pollutants.

3. Discussion and Conclusion

Considering the large volume of OBM used as drilling fluids in HMD field, gas oil is the first importantsource of contamination by hydrocarbons. Now, aromatics content in the gas oil obtained from petroleumrefinery by catalytic cracking is of the order of 35 wt. % and sulfur content is 0.2 wt. %. Many actionswere proposed to modify gas oil composition: techniques for aromatics removal through refinery process(hydrotreatment) yielding an aromatic content of 5% and a low sulfur content to obtain low-toxicity oil(LTO). Another way is the use of inorganic or synthetic fluids as substitutes for gas oil.The oil pollution level can be reduced significantly from completely oil-based fluids (98% oil) to inverseemulsion systems (~ 50% oil). On a smaller scale the research and use of biodegradable additives such asbiopolymers and biosurfactants are in progress.Nevertheless, we must keep in mind the following recommendations for the purpose of pollution controlon HMD and HR fields:- OBM with an oil/water ratio of about 50/50, depending on technical specifications and drillingconditions,- Possible substitution of WBM (namely containing biopolymers) for OBM,- Reduction of the number of drilling phases and wellbore diameters, leading to smaller volumes of drillcuttings to be treated and cutting down of waste treatment cost.The effect of whole drilling mud on biological resources is difficult to generalize. Potential impacts aredetermined by numerous factors, including the composition, concentration and condition (e.g. new or“used”) of drilling mud, the duration of exposure, and the specific organisms (species, age and stage ofdevelopment) involved (Carls et al., 1995).On-line and off-line advantages and drawbacks of solidification treatment can be discussed consideringthat:1. Climate and ecosystem types contribute to pollution reduction; high temperature can favourvolatilization and hydrocarbon reduction;2. Autochtonous microorganisms reduce hydrocarbon content on the site before any treatment;3. Probable pollution infiltration may occur from the waste (bad oil-tightness) or on the drilling site (afterincidental spill).Strategical and economical considerations highlight two main recommendations:For the 1st and 2nd points, an initial pollution evaluation on the site, before treatment, for selecting asuitable method; for the 3rd point, the possibility to perform coring before waste treament and estimatethe depth of pollution invasion.

Metal (mg/L) Si Cr Mn Fe Co Ni Cu Zn Cd Pb

Uncontaminated sample 0 0.04 0.18 6.34 0.0 0.0 0.09 0.53 0.04 0.20

Contaminated sample* 0 0.05 0.40 17.2 0.0 0.03 0.11 0.60 0.03 0.46

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The selection of the treatment and the remediation technology of contaminated soils in the oil industry ishighly dependent on the environment regulations of the countries, geographic conditions, hydrogeology,drilling fluid composition and climate of the drill sites. The results obtained from the analyses of leachatesamples have shown that the treatment of the cuttings from pits collected from Algerian oilfield areas areefficient and successful for the neutralization of the contaminants (hydrocarbons and heavy metals).In summary, drilling fluid chemistry is quite complicated, and the effect of discharged mud into theenvironment is still not completely understood, despite a growing body of related research. Finally, forhydrocarbon decontamination, landfarming, a rapidly growing process, presents satisfactory economic,scientific and environmental issues. In fact, this biological technique, cheaper than the other ones, provesto be very efficient in different soil types and ecosystems and presents undeniable advantages: noadditional pollution, biodegradation either with autochtonous microorganisms or with added fertilizers ormicroorganism consortium. For heavy metals, a combination of bioremediation with phytoremediationcan afford better results. It would be of great interest to promote those biological techniques on industrialAlgerian sitesMost authorities maintain that, if reasonable precautions are taken and current applicable standards andregulations obeyed, the environmental impact of drilling fluids is negligible (Gettleson, 1980; Monaghanet al., 1980). For instance, the American Petroleum Institute (API) recommends to eliminate heavy metalspresent in barite. However, an average well uses 100-400 metric tons of drilling fluid (Neff, 1982) so thatthe release and accumulation of mud additives in the environment may be a matter of volume as well asconcentration. Finally, hydrocarbon pollution is, by far, the main concern.In conclusion, the performance evaluation of all remediation techniques used so far can significantly helpmanager decision in choosing an appropriate waste treatment for each specific zone from South to NorthAlgeria and possibly for offshore exploitation.

Acknowledgements:We thank the Sonatrach Company, for permission to publish this paper.

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