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A Drilling Reserve Mud Pit Assessment in Iran: Environmental Impacts and Awareness

S. R. Shadizadeha; M. Zoveidavianpoorb a Petroleum University of Technology, Ahwaz, Iran b Petroleum University of Technology, Abadan, Iran Online publication date: 03 August 2010

To cite this Article Shadizadeh, S. R. and Zoveidavianpoor, M.(2010) 'A Drilling Reserve Mud Pit Assessment in Iran:

Environmental Impacts and Awareness', Petroleum Science and Technology, 28: 14, 1513 — 1526 To link to this Article: DOI: 10.1080/10916460903117545 URL: http://dx.doi.org/10.1080/10916460903117545

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Petroleum Science and Technology, 28:1513–1526, 2010 Copyright © Taylor & Francis Group, LLC ISSN: 1091-6466 print/1532-2459 online DOI: 10.1080/10916460903117545

A Drilling Reserve Mud Pit Assessment in Iran: Environmental Impacts and Awareness S. R. SHADIZADEH1 AND M. ZOVEIDAVIANPOOR2 1

Downloaded By: [Islamic Azad Consortium] At: 06:33 10 August 2010

2

Petroleum University of Technology, Ahwaz, Iran Petroleum University of Technology, Abadan, Iran

Abstract The major objective of this work is to investigate the mud pit pollution caused by drilling operations at one of the Iranian onshore drilling well sites. In this study, sampling and monitoring of heavy metal concentrations (cadmium, chromium, nickel, and aluminum) in mud pit liquids was performed rigorously in two phases: during and after drilling operations on the selected drilling well site. Measured concentrations of heavy metals in the reserve mud pit of the well site are higher than the standard criteria. Environmental impacts of drilling mud in the investigated site and the causes of contaminations are discussed. Also, the pollution effects of the mud pit on natural resources of the selected drilling well site are presented. Keywords drilling waste, environment, heavy metals, human health, mud pit

1. Introduction Drilling muds may be water based, oil based, or synthetic based depending upon the drilling conditions encountered. Oil-based muds (OBMs) are the most toxic, followed by synthetic-based muds (SBMs) and then water-based muds (WBMs). Water-based drilling fluids are used in about 85% of the wells drilled worldwide. Oil-based fluids are used for almost all of the remaining wells (Reis, 1996). Three mechanisms of toxicity in drilling waste are chemistry of mud mixing and treatment, storage/disposed practices, and tilled rock. Drilling muds typically contain heavy metals like barium, chromium, mercury, and lead (Bleier et al., 1993). These metals can enter the system from materials added to the mud or from naturally occurring minerals in the formation being drilled through. A typical elemental composition of common constituents of drilling muds is given in Table 1. The technology of mud mixing and treatment has been recognized as a source of pollutants such as barium (from barite), mercury and cadmium (from barite impurities), lead (from pipe dope), chromium (from viscosity reducers and corrosion inhibitors), and diesel (from lubricants, spotting fluids, and OBM cuttings; Wojtanowicz, 1991). Drilling additives often contain potentially toxic substances. Barite weighting agents may contain concentrations of heavy metals such as cadmium or mercury. Few studies have addressed the measurement of heavy metals in drilling reserve mud pits. Address correspondence to Seyed Reza Shadizadeh, Petroleum University of Technology, Ahwaz Department of Petroleum Engineering, Abadan Highway, Ayat Allah Behbahani Road, Koot Abdollah, Ahwaz, 63431 Iran. E-mail: [email protected]

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S. R. Shadizadeh and M. Zoveidavianpoor Table 1 Elemental composition of drilling fluid constituents (ppm)a


Element

Water

Cutting

Barite

Clay

Lignite

Caustic

Aluminum 0.3 40,400 40,400 88,600 6,700 0.013 Arsenic 0.0005 3.9 34 3.9 10.1 0.039 Barium 0.1 158 590,000 640 640 0.26 Calcium 15 240,000 7,900 4,700 16,100 5,400 Cadmium 0.0001 0.08 6 0.5 0.2 0.0013 Chromium 0.001 183 183 8.02 65.3 0.00066 Cobalt 0.0002 2.9 3.8 2.9 5 0.00053 Copper 0.003 22 49 8.18 22.9 0.039 Iron 0.5 21,900 21,950 37,500 7,220 0.04 Lead 0.003 37 685 27.1 5.4 0.004 Magnesium 4 23,300 3,900 69,800 5,040 17,800 Mercury 0.0001 0.12 4.1 0.12 0.2 4 Nickel 0.0005 15 3 15 11.6 0.09 Potassium 2.2 13,500 660 2,400 460 51,400 Silicon 7 206,000 70,200 271,000 2,390 339 Sodium 6 3,040 3,040 11,000 2,400 500,000 Strontium 0.07 312 540 60.5 1,030 105 a Data

from Bleier et al. (1993).

For example, the heavy metals contents in both the water and mud phases of 125 reserves pit scattered around the United States were measured in one study and the concentrations were determined (Leuterman et al., 1988). A survey conducted by the U.S. Environmental Protection Agency and the American Petroleum Institute found that liquids in some drilling reserve pits contained chromium, lead, and pentachlorophenol at hazardous levels, and that oil-based fluid may contain benzene (U.S. Congress, 1992). The Alberta Research Council (ARC, 1992) conducted a study of the trace metal content of samples of 651 drilling muds. On average, OBM had higher total barium content than WBMs. A potential source of heavy metals in drilling fluid is from crude itself. Crude oil naturally contains widely varying concentrations of various heavy metals. There are so many cases reported associated with mud pit contaminations. In Connery loop drilling mud pit, Alaska, 1.5 million gallons of drilling muds and associated hazardous waste were released in wetland, below the water table (Alaska Department of Environmental Conservation [ADEC], 2004). Between 1996 and 2002, the U.S. Environmental Protection Agency (EPA) in Wyoming, Utah, Colorado, Montana, South Dakota, and North Dakota conducted 475 field inspections at sites having one or more production pits or commercial facilities using disposal pits. Problems were found at 290 (more than 60%) of the sites (U.S. Environmental Protection Agency Region 8, 2003). The risk that oil pits pose to wildlife has been documented by several studies (Flickinger, 1981; Esmoil, 1995). In this article, the results of laboratory tests conducted on mud pit samples for heavy metals (Cd, Cr, Ni, and Al) concentrations during and after drilling operation on the selected drilling well site are presented.


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Figure 1. Surroundings of the drilling oil well site.

2. Material and Methods 2.1.

Site Selection

One of the Iranian southern oilfields was selected for this work. Figures 1 and 2 show photos of the selected drilling well site and its surroundings prior to the rig movement. As shown in Figure 2, the reserve mud pit in the selected drilling well site is shallow, unlined, and uncovered. It should be mentioned here that the mud pit is constructed by making wall barriers by scraping the earth around it.

Figure 2. The drilling oil well site and its mud pit.

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S. R. Shadizadeh and M. Zoveidavianpoor Drilling Fluids Used in the Selected Well

Table 2 shows the drilling fluid program of the selected well. In Iran, OBM is only used for drilling the reservoir interval. As can seen from Table 2, the weight of OBM is less than WBM because of a lower pore pressure gradient in the reservoir interval than the above formations. OBM fluid is discharged to the mud pit during drilling and after completion of reservoir depth.


2.3.

Sampling Technique

The sampling method in this work was utilized from the sampling procedure performed on API site 4 (Deuel and Holliday, 1990). Selected reserve mud pit was subdivided into six sections with dimension 15 m 20 m. Pit liquid samples were taken at three locations within each section. Each location was sampled at 0–0.3 m, mid-depth, and 0.3 m above solids using a weighted bailer. Location samples were combined to form a section composite. Three-liter subsamples from each section composite were combined for a representative pit composite. Sampling was conducted in two phases: during and after drilling operations including four times during drilling and seven times after reserve mud pit abandonment. Table 2 Drilling fluid used in the selected well Properties Mud properties Mud system pH Average salt concentration, mg/L Average calcium concentration, mg/L YP PV Initial gel 10 Min. gel Mud lost @ unit, bbl Density, pcf Barite, t Mud material Salt, t Starch, sx Bentonite, t Lime, sx CMS H.V, sx IRSATROL, sx Diesel, bbl

2400 hole 171/2 00 hole @ 60 m @ 1,510 m WBM 10–10.5 2,000 464

WBM 10.5–9.8 185,600 2,404

11 35 22 30 0 62–70 0

4–7 5–10 3–6 4–8 2,588 68–79 27

2 0 160 123 0 0 0

166 30 750 69 0 0 0

121/4 00 hole @ 2,158 m

81/2 00 hole @ 2,330 m

WBM 8–10 297,600 3,320

OBM 9–9.5 380,100 231

6–78 8–58 1–13 2–6 1,252 79–146 674.4 168 727 0 222 0 0 0

19–27 8–12 2 3 802 69.5 0 15 0 0 130 17 140 615

Note: YP D yield point; PV D plastic viscosity; bbl D barrel; pcf D pound per cubic feet; t D ton; sx D sacks.

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Table 3 EPA standard methods for heavy metals measurement


2.4.

Test

Standard methods

Cadmium Chromium Nickel Aluminum

EPA-213.1 EPA-218.1 EPA-249.1 EPA-202.1

Determination of Heavy Metals

The procedures for determination of metals are derived from Federal Regulations Title 40 Protection of Environment Part 136 (40 CFR 136), according to U.S. EPA standard methods. The EPA reference methods for these approved test procedures are listed in Table 3.

3. Results The concentrations of cadmium, chromium, nickel, and aluminum in the mud pit are shown in Figures 3 through 6. As can be seen from these figures, the concentrations of the above metals are changed significantly with respect to time. Figure 2 shows the mud pit condition before drilling operation. The bottom surface of the mud pit is the original earth surface. Figures 7 and 8 show chronic conditions of mud pit during the drilling operation. Mixture of all types of wastes in the mud pit can be

Figure 3. Comparison of measured cadmium with TLV standard.


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S. R. Shadizadeh and M. Zoveidavianpoor

Figure 4. Comparison of measured chromium with TLV standard.

Figure 5. Comparison of measured nickel with TLV standard.


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Figure 6. Comparison of measured aluminum with TLV standard.

seen from these figures. The most important things observed during drilling operations are the discharge of oil base mud and producing crude oil with the water base mud, drilling cuttings, and other discharge wastes to the mud pit. Figures 9 through 11 show chronic mud pit conditions after drilling operations. Figure 9 shows the mud pit condition during flood time at the investigated well site. Figures 10 and 11 show the chronic vaporization

Figure 7. A view of the drilling rig and mud pit condition during drilling operation.


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Figure 8. Mud pit condition during drilling operation.

Figure 9. Mud pit condition after drilling operation and during flood time.


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Figure 10. Disposal of OBMs and WBMs in the mud pit during the drilling operation.

processes of liquids in the mud pit. Figure 11 shows unvaporized hydrocarbons that are absorbed by clay materials and minerals of drilling cuttings.

4. Discussion 4.1.

Comparison of Reserve Mud Pit Components with Environmental Standards

The toxicities of many metals found in the selected mud pits have been summarized by the American Conference of Governmental Industrial Hygienists (ACGIH-1993) and are

Figure 11. Mud pit condition after drilling operation and during flood time.

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S. R. Shadizadeh and M. Zoveidavianpoor Table 4 TLV (ppm) for heavy metals in reserve mud pit (ACGIH-1993 Standards) Metal


Cadmium Chromium Nickel Aluminum

TLV, ppm 0.5 0.5 0.1 0.2

10 10 10 10

4 3 3 2

listed in Table 4. The concentrations of heavy metals found in the reserve mud pit are shown in Figures 3–6. These figures show that the concentrations of heavy metals (Cd, Cr, Ni, and Al) are more higher than the ACGIH standards. 4.2.

Environmental Impacts of Drilling Muds (WBM and OBM) in the Investigated Site

In the selected well a combination of WBMs and OBMs has been used. The major components of WBMs in the investigated site were barite, salt, starch, bentonite, and lime (as shown in Table 3). The metals of greatest concern, because of their potential toxicity and/or abundance in drilling fluids, include chromium, cadmium, and nickel (Neff, 2002). Some of these metals are added intentionally to drilling muds as metal salts or organometallic compounds. Others are present as trace impurities in major mud ingredients, particularly barite and bentonite. One of the major drilling mud additives used in both WBM and OBM in the investigated well is barite. The amount of barite used in the investigated well as shown in Table 2 is 702 tonnes. Barite contains variable amounts of heavy metals and it is the main source of heavy metals in the investigated site. Metals concentrations in mud pit of selected well during and after drilling operation are presented in Figures 3–5. Chromium concentration was detected in the samples at 0–0.08 ppm. Other heavy metals were also at high levels and showed significantly higher values specially by using OBMs: cadmium 0–0.006 ppm, nickel 0–0.024 ppm, and aluminum 0–341 ppm. However, these heavy metal levels are generally above toxic levels. As shown in Figures 3–5, the concentrations of cadmium, chromium, and nickel increased progressively in the fourth sampling periods because of the contamination of the mud pit with OBMs that was initiated in the fourth sampling period. Concentration of aluminum increased from the first to the third sampling periods, whereas in the fourth period it shows decreased values from 0.05 ppm to 0.006 ppm. Aluminum was not observed in the fifth and sixth sampling periods but maintained an increased value from the seventh to the end of the sampling periods (as shown in Figure 6). In the entire study area, chromium levels ranged from 0 to 0.08 ppm but no concentration was observed after the seventh period of the sampling. This can be explained by the storm runoff water at the investigated well site that washes away all these wastes, especially in the mud pits to other locations (Figures 9 and 12) or seepage from the discharge pits into the surrounding soils. 4.3.

Potential Effects on Natural Resources and Human Health

Heavy metals can harm ecosystems, plants, and animals and cause health problems


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Figure 12. Presence of Peregrine birds in the well site during storm water runoff season.

in humans. Many materials that are released into reserve mud pits also release heavy metals into the environment, which calls for public awareness as well. When released heavy metals are discharged into unlined pits the toxic substances in the pits can leach directly into the soil and may contaminate groundwater. In contrast to most organic pollutants, trace metals are not usually eliminated from aquatic ecosystems by natural processes due to their nonbiodegradability. Both toxic and nontoxic heavy metals tend to accumulate in bottom sediments, from which they may be released by various processes of remobilization. Frequently, these metals can move up the biological chain, eventually reaching humans, where they can cause chronic and acute ailments (Ankley et al., 1993). As presented in the Introduction, routine drilling wastes such as drilling muds and cuttings contain a variety of toxic chemicals that are known to be hazardous to wildlife, livestock, and human health. If pollutants from oil well drilling build up in the food chain, people who consume sheep, cows, birds, and even fish from the selected well oilfield area in this work could be at risk of health problems such as genetic defects and cancer. Figures 12– 14 show birds, sheep, and cows that are exposed to pollutants at the investigated well site. These figures show that if the mud pit is inadequately fenced and netted, wildlife and livestock can access the pit contents.

4.4.

Minimization of Environmental Impacts of the Mud Pit

For environmental protection the following engineering manners should be considered: (1) once the well has been drilled and the drilling rig removed from site, the well site should be restored to its natural state. (2) Due to the nature of the selected well oilfield area, the best method for reserve mud pit reclamation is evaporation. As shown in Figure 11, natural evaporation of the water held in the mud pit had occurred by sun during the hot season in the area. On elimination of the fluids in the reserve mud pit, the precipitated solids and contaminated construction soil of the mud pit should be excavated


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Figure 13. A flock of sheep in an adjacent area of the investigated well site’s reserve mud pit.

and hauled off to the approved disposal site. (3) Bioremediation techniques can be used for soil remediation of the entire location. After that, the topsoil should be spread over the reclaimed area, followed by seeding. Local seed mixture can be used to quicken reintroduction of native plants. (4) The best alternative solution in the investigated well site is to use a multipit system in order to separate the generated wastes of WBMs, OBMs, drilling cuttings, and storm and runoff waters.

Figure 14. View of cows chewing the refuse at the investigated mud pit.

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5. Conclusions 1. This investigation has been conducted for the first time in Iran. 2. All the generated wastes include drilling fluid, drilling cuttings, wash-down fluids, sanitary wastes, solid waste, oil sludge, and refuse were directly discharged into the reserve mud pit of the well site. 3. The concentration of heavy metals (cadmium, chromium, nickel, and aluminum) found in the reserve mud pit are much higher than the ACGIH standards. 4. This work shows that birds, sheep, and cows are exposed to pollutants at the investigated well site. If pollutants build up in the food chain, people who consume sheep, cows, birds, and even fish from the selected oilfield area could be at risk of health problems. 5. This work shows that the well site construction, especially the mud pit, could be sources of storm runoff water contamination in the area during storm season. Thus, in the design of well site construction a storm water pollution prevention plan should be considered. 6. For minimizing the damage to the environment of selected well site area, a multipit system should be used. 7. In order to minimize the negative effects of applying OBMs, synthetic-based muds (SBMs) are suggested for drilling wells in the selected oilfield.

Acknowledgment The authors thank the Research and Development Department of the National Iranian Oil Company and the National Iranian Drilling Company for financially supporting and helping make this work success. Special thanks to Dr. F. Ghadiry from Pars Oil and Gas Company for his helpful assistance.

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