Environmental Impact Assessment of Drilling Fluid in Niger Delta

Oloro & al./ Appl. J. Envir. Eng. Sci. 6 N°2(2020) 125-134

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Environmental Impact Assessment of Drilling Fluid in Niger Delta

J.O. Oloro(a)

, D.E Akpotu(b)

(a) Chemical and Petroleum Engineering, Faculty of Engineering, Delta State University, Nigeria.

(b) Drilling Laboratory of Chemical and Petroleum Engineering, Faculty of Engineering, Delta State

University, Nigeria.

Corresponding author. E-mail : [email protected]

Received 24 Apr 2020, Revised 29 May 2020, Accepted 14 Jun 2020

Abstract

Objectives of this study are to carry out an environmental impact assessment of drilling fluid with

emphasis on a case study of Oben Oil field, RIG 201.This field is located in Niger Delta of Nigeria. In

carrying out this study,soil samples and water from Oben oil field were analysed to determine

concentrations of heavy metals Physio-chemical characteristics were also examined and the results

were compared with the Department of Petroleum Resources (D.P.R) guidelines and World Health

Organization (W.H.O) standard. The results of the test showed that the values of the wastewater were

greater than the values of the treated water because it has undergone treatment and can be discharged

into the environment. Therefore, the waste water was above the acceptable recommended limit. Also,

the values of the soil sample around the drill site had a very high concentration of heavy metals

compared to that of the control sample. The study showed that the existence of high concentration of

contaminants in the spent drilling fluid from the reserve pit and as a result of the analysis carried out it

is then recommended that the waste resulting from drilling operations should be properly treated

before disposal into the environment.Objectives of this study are to carry out an environmental impact

assessment of drilling fluid with emphasis on a case study of Oben Oil field, RIG 201.This field is

located in Niger Delta of Nigeria .

Keywords: Disposal; Metals; Pit; Waste Soil; Drilling Mud.

1. Introduction

Drilling fluids are used generally in the upstream oil and gas industry and are complex mixtures

including of solids and liquids, as well as base oils and brines [1]. Drilling fluid, therefore, is generally

a combination of water, clay, weighing materials and a variety of chemicals to adjust the properties of

the fluids to meet the requirement of each well. The fluid has several roles throughout the drilling

mailto:[email protected]


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process including removing cuttings, cooling and lubricating the drill bit and carrying various

chemicals down the borehole [2]. Therefore, the key to making the rotary drilling system work is to

circulate drilling fluid (or drilling mud) consciously down the hole through drilling pipe and out

through the annulus back to the surface. The fluid is washed by passing over a shale shaker, where

unwanted solids are removed and the resultant cleaning fluid is then re-injected into the well [3].

Drilling operations are basically classified into offshore drilling and onshore drilling. Some

environmental difficulties have been connected with drilling fluid. A variety of wastes are generated in

drilling oil and gas wells including drill cuttings and used drilling fluids. The skill of mud mixing and

treatment is generally recognized as a major source of pollution from various pollutants such as

barium, mercury, and cadmium, diesel (from lubricants, spotting fluids and oil-based mud cuttings),

arsenic and formaldehyde (from biocides). However, the board environmental problems confronted by

the oil and gas exploration and production industry are revealed at both local and international levels.

The disruption of the ecological balance through drilling operation occurs through surface discharge of

pollutants from various activities affecting the environment. Environmental management of drill sites

is a serious problem to combat drilling pollution both at onshore and offshore [4]. Therefore, discharge

of untreated drilling effluents into seas, rivers or land constitutes a serious health hazard and is

detrimental to agriculture and fishes, also water can get contaminated. However, the most important

concern relates to the degradation of land, air, and water around the drill sites. Therefore, there is need

to conduct a comprehensive risk assessment when deciding the type of drilling fluid method to use

considering its effect on the environment. Drilling waste can have a different potential impact

depending on where it is discharged [5-6].

The actions involved in crude oil exploration and production normally have one impact or the other on

the environment. However, the highest effect arises from discharge of wastes into the environment in

concentrations that were not naturally found such environment. The wastes produced during petroleum

production can be generally classified into liquid (i.e. produced water and oil) and solid (i.e. drilling

mud and cuttings) [7-9].

Many of the additives used as the drilling mud are supposed to be toxic and be regulated. Drill mud

and cuttings may be oil-based or water-based in nature and are associated with changing

concentrations of hydrocarbons and heavy metals [10].

Drill cuttings have been observed to contain a wide range of organic and inorganic traces especially

when oil-based mud is used [11-13], Used up drilling fluids and cuttings account for about 2% of the

entire waste volume while other associated wastes like produced formation water contribute over 90%

of the total waste volume.

One of the immediate physical environments that suffer the direct impact of drilling wastes disposal is

onshore and offshore. The onshore environment includes the swampy, freshwater and the dry land

environments all of which have their peculiar features and ecological characteristics. Although,

drilling mud used for drilling onshore oil wells are disposed of in reserve pits. However, due to a large

number of drill wastes, most of the mud and cuttings can get into the adjacent soil and water bodies


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during precipitation and run-off. The heavy metal and hydrocarbon contents of the onshore drilling

wastes are capable of polluting the environment with subsequent effects on human health. Though,

this depends on the type, nature, and concentrations of heavy metals and hydrocarbons [14-15].

Drilling fluids become contaminated and must be replaced because of down-hole condition; therefore,

the fluids are displaced periodically. The most common practice is either dewatering of reserve pit

contents and subsequent backfilling with pits or land farming the reserve pit contents into the soil

around the drilling location. Therefore, it is important to examine whether it is possible to prevent

and/or avoid degradation of the environment where such despoliation had occurred.

Objectives of this study are to carry out an environmental impact assessment of drilling fluid with

emphasis on a case study of Oben Oil field, RIG 201.The aim is to determine effective measures to be

taken to avert the impact of drilling fluid on the environment. This work will reveal the impact of

indiscriminate discharge of drilling fluid by oil companies operating upstream and further discourage

them from such practices. The work is restricted or designed for the study of the effect of drilling fluid

in the environment (Onshore field) and to make certain recommendation that will reduce or stop the

undiscriminating discharge of untreated drilling waste.

2. Materials and Methods

2.1 Sample and Sampling Method

The samples used in this study is from a drilling rig site at Oben, Sapele, Delta State about 78

kilometers along Benin Road with coordinates of latitude 50 31

’ 0

’N and 5

0 45

’ 0

’E.

Two soil samples were collected. One of the soil samples was collected few meters from the reserve

pit (waste pit) at a depth of 3ft (drill site sample) and the other sample (control sample) was collected

at another location. The samples were kept in a container and were labeled sample A and sample B

respectively. Also, water from the reserve pit (waste pit) was collected and treated water from the

treatment plant which can be discharged into the environment was labeled wastewater and treated

water respectively. Both soil and water samples were collected at the rig site during the actual drilling

operation for analysis in order to evaluate their toxicity and possible environmental impacts.The

parameters analyzed were pH, salinity, electrical conductivity, Total Dissolved Solids (TDS) and

heavy metals such as iron, copper, lead, chromium, zinc, etc.

The equipment listed in Table 1 was used for the study.


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Table 1 : Equipment and Function

Equipment Function

Volumetric flask (pyrex) For measurement

Weighing balance Weighing of samples for analysis

Atomic Absorption Spectrophotometer Determination of heavy metals

Multi-parameter Determination of TDS, electrical conductivity

Heating Mantle (Hot Plate) Digestion of sample for analysis

pH meter (winlab model 290A) Determination of Ph

Polypropylene bottle Storage of sample

Mesh sieve (2mm) To sieve soil samples

The method adopted for this study is based on experimental analysis. The following sample groups

were investigated in this study.

1. a pH of soil and water samples

2. Metal content of soil and water samples

3. Salinity

4. Total Dissolved Solids

5. Electrical Conductivity

A. Determination of pH of soil

The hydrogen ion concentration of the soil was determined using a pH meter (Winlab model 290A).

other materials used including weighing balance, beaker and distilled water.

Procedure

Dried soil samples were passed through a 2mm mesh sieve

The pH meter was calibrated with pH 4.0 and pH 7.0 buffer before use

Soil to water solution in the ratio 1:2:5 was measured

10g of air-dried soil sample was weighed with a weighing balance into a 50ml beaker and

25ml distilled water was added

The suspension was stirred intermittently for 30mins with a glass rod

The electrode of the pH meter was dipped into the partly settled suspension and the pH valve

was read.


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B. Determination of pH of water

For the water samples, the electrodes were dipped into the samples directly and reading taken.

C. Determination of Heavy Metals in soil

Equipment and Materials used

Atomic Absorption Spectrophotometer, weighing balance, conical flask, filter paper.

Procedure

The soil sample which had been dried at room temperature was sieved with 2mm mesh sieve.

2.5g of the soil was weighed with a weighing balance into 300cm3 conical flask.

1ml of concentrated HCLO4, 3ml conc. HNO3 and 1ml conc. HF was added and heated under

a fume hood until dense white fumes appeared.

It was allowed to cool.

40ml distilled water was added and the solution was completely filtered with a filter paper into

a 100ml volumetric flask.

The soil extracts filtrate and standard solutions were aspirated into the air acetylene flame of

Varian 220 Atomic Absorption Spectrophotometer and results were recorded in mg/kg. It

operates at a different wavelength for each metal.

The metals and their wavelengths are showing in Figure 1.

Fig. 1 : Showing different metals and their wavelengths


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D. Determination of heavy metals in water

Equipment and materials used

Atomic Absorption Spectrophotometer, hot plate, beaker, polypropylene bottle.

Procedures

100ml of a well-mixed water sample was measured into 150ml beaker.

5.0ml of conc. HNO3 was added.

The solution was heated on a hot plate to near dryness using a low to medium heat.

The beaker was returned on the hot plate and the temperature of the hot plate increased from

medium to high.

Heating continued and HNO3 was added until light-colored residue was obtained.

1-2ml of conc. HNO3 was added to the residue.

The residue was filtered into 100ml volumetric flask to remove silicate and other insoluble

materials and made up with distilled water.

The solution was stored in 125ml polypropylene bottle and trace metals were tested using

Atomic Absorption Spectrophotometer.

E. Determination of Salinity as Chloride (cl)

100ml of the sample was measured into a 250ml conical flask.

1ml of K2CrO4 was added.

Titrate with 0.01N AgNO3.

The color changes from yellow to reddish-brown at end-point.

F. Determination of calcium

50ml of the sample was measured into 150ml conical flask.

1ml of KOH was added.

4 drops of calcon indicator were also added.

Titrate with 0.01N ehtylenediaminetetraacetic acid (EDTA).

The color changes from wine to blue at an endpoint.

G. Determination of total dissolved solids and electrical conductivity

The total dissolved solids and electrical conductivity were determined using a multi-parameter

3. Results and discussion

This section covers the result obtained in the experiment that was carried out. The results obtained in

the experiment were compared with both the Department of Petroleum Resources (DPR) 1991

guidelines and World Health Organization Standards (Burke C.J and J.A. Veil J.A, 1995) [13].

The results of water analysis are shown in Table 2


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Table 2 : Showing results for heavy metals in water

Parameters (mg/l) Treated Water Waste Water DPR/WHO Standard

Iron 0.03 0.6 0.3

Nickel BDL 0.11

Manganese BDL 0.07 0.05

Chromium BDL BDL 0.05

Zinc 0.08 0.36 3

Copper 0.02 1.9 1.0

Lead BDL 0.05 0.5

BDL means Below Detection Limit <0.001

From Table 3, the values obtained from the analysis of the wastewater are higher compared to that of

the treated water. It indicates that the treated water has undergone treatment and can, therefore, be

discharged into the environment because it is within the acceptable limit of DPR guidelines and WHO

standard. The wastewater on the other hand is not within an acceptable limit.

The concentration of iron in the wastewater (0.6mg/l) is higher than the treated water (0.03mg/l) and

also higher than the recommended 0.3mg/l [16]. Nickel has no comparison in the DPR guideline.

Although, the concentration of the wastewater is also higher than the treated water. Manganese

concentration is higher in wastewater (0.07mg/l) than treated water (<0.001mg/l) and fall short in the

recommended DPR/WHO standard. Chromium is within the acceptable limits recommended by

DPR/WHO for both treated water and wastewater. The value of zinc and copper is also higher for

wastewater when compared to the treated water and they are both below acceptable limit. Lead within

acceptable limit [17]. The concentration of pH for the wastewater was found to be 5.48. The pH value

falls short in meeting the recommended 6.5-8.5 for the wastewater. Therefore it is acidic.

The entire dissolved solids in the wastewater (4700mg/l) is greater compared to the treated water

(441mg/l). 4700mg/l is not within the commended 500mg/l – 1500mg/l by WHO. The wastewater

(3518mg/l) has a higher salt content when compared with that of the treated water (654.5mg/l). The

calcium content in the wastewater (75.62mg/l) is slightly within acceptable limit (75mg/l) of DPR

guidelines and WHO [18-23].


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Figure 2 : Heavy metals in soil

Figure 3 : Other parameters in Soil

From Figure 2, the heavy metals values obtained from sample A (drill site sample) is of higher

concentration than sample B (control sample). The control sample was used to know the level of

contamination at the drill site.The concentration of iron sample A (245.26mg/kg) is higher compared

to that of sample B (148.43mg/kg).

Manganese concentration is sample A (10.56mg/kg) in also higher compared to sample B

(3.71mg/kg). Chromium, zinc, copper and lead are of higher concentration in Sample A (2.82mg/kg,

81.45mg/kg, 35.62mg/kg, 8.35mg/kg respectively) compared to that of sample B (control sample).

The concentration of trace metals in the drill site may be due to seepage around the reserve pit. Hence,


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a very high concentration on the area around the drill site. Although, the pH of both samples are below

the recommended 6.5-8.5 DPR and WHO [17]. Therefore, both samples are acidic as shown in Figure

3.

4. Conclusion

In the experiment carried out, the following conclusions were made. The study revealed the presence

of high concentration of contaminants in the spent drilling fluid from the reserve pit (waste pit). The

detailed trace metal investigation helps to establish the degree of toxicity before discharge into the

environment because when these metals are above stipulated regulatory limits, they must impact on

the environment.

It was observed that the concentration of waste pit sample was higher and has to be treated before

discharge into the environment. The high metal content of the soil samples around the reserve pit may

have resulted due to seepage from the reserve pit or move by rainfall and deposited on soil, also

contaminating the underground water. Although, some of the heavy metals were within acceptable

limits and some other parameters were still very high. Hence continuous discharge of spent drilling

fluid and dewatering of pits without adequate treatment will further damage the environment. As a

result of the analysis carried out at Oben oil field (Rig 201) it is therefore recommended that waste

(spent drilling fluid and cuttings) resulting from drilling operations should be properly treated before

disposal into the environment. Other recommendation includes;

1. Companies should practice an effective drilling fluid waste management plan.

2. The sludge left at the end of the drilling process should be backfilled with the excavated material

on-site and permanently buried.

3. Companies should adhere strictly to the guiding rules and regulations in order to prevent

environmental degradation from drilling operations.

Nomenclature

CMC – Carboxylic acid

HClO4 – Hydrogen Iodide

HNO3 – Nitric Acid

HF – Hydrogen Flouride

K2CrO4 – Potassium Chromate

AgNO2 – Silver Nitrate

KOH – Potassium Hydroxide

EDTA – Ethylenediaminetetraacetic acid


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Environmental Impact Assessment of Drilling Fluid in Niger Delta

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