The Use of Galena As Weighting Material in Drilling Mud

Journal of Scientific Research & Reports 7(6): 455-465, 2015; Article no.JSRR.2015.227 ISSN: 2320-0227

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The Use of Galena as Weighting Material in Drilling Mud

U. Akpabio Julius1*, I. Akpanika Offiong1 and O. Etim Idorenyin1

1Department of Chemical and Petroleum Engineering, University of Uyo, Nigeria.

Authors’ contributions

This work was carried out in collaboration between all authors. Authors UJA and IAO designed the study, wrote the protocol, and wrote the first draft of the manuscript. Author OEI managed the literature searches, analyses of the study and managed the experimental process. All authors read and approved the final manuscript.

Article Information

DOI: 10.9734/JSRR/2015/15095 Editor(s): (1) Shahid Naseem, Department of Geology, University of Karachi, Pakistan. Reviewers: (1) Anonymous, Universiti Sains Malaysia, Malaysia. (2) Anonymous, Southwest Petroleum University, China. Complete Peer review History: http://www.sciencedomain.org/review-history.php?iid=1130&id=22&aid=9516

Received 5th November 2014 Original Research Article Accepted 16th February 2015 Published 30th May 2015

ABSTRACT

A successful oil well drilling depends largely on a good mud Program. During drilling, mud provides sufficient hydrostatic pressure, removes drill cuttings and cools drill bits. Mud additives are always required to provide sufficient hydrostatic pressure to ensure borehole stability. Barium Sulphate (BaSO4) also known as barite is the prevalent weighting material but there is need to develop local materials to augment the use of Barite. This study was aimed at assessing the suitability of galena, a lead sulfide (PbS), as an alternative weighting material in drilling fluids. Two mud samples A and B were prepared which comprised fresh water, caustic soda, bentonite and weighting material. The weighting materials were added to the mud separately to form the required mud weight ranges between 9.0 ppg and 15.0 ppg. Sample A was water-based mud with commercial barite while Sample B was water-based mud with local galena. These samples were analyzed and the density, rheological properties and solid contents were investigated. At 9.0 ppg, the yield point of galena was 20.0 lb/100ft2 and barite 22.0 lb/100ft2 while the 10 second gel strength of galena was 5.0 lb/100ft2 and 8.0 lb/100ft2 for barite. Similarly, little difference was observed in plastic and apparent viscosities. At 9.0 ppg, the plastic and apparent viscosities of galena was 13.0 cp and 23.0 cp while barite was 10.0 cp and 20.0 cp.

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*Corresponding author: Email: [email protected];

Julius et al.; JSRR, 7(6): 455-465, 2015; Article no.JSRR.2015.227

The result show that galena mud sample gave a little higher yield point and gel strength than barite mud sample. Therefore, galena has the potential to be used as weighting material in drilling mud in place of Barite thereby enhancing the local content initiative of the government. When Galena is sourced locally and used it will reduce overall mud and drilling costs.

Keywords: Barite; Galena; drilling mud; weighting material; hydrostatic pressure.

SYMBOLS / NOMENCLATURE

API - American Petroleum Institute AV - Apparent Viscosity BaSO4 - Barium Sulphate cc - Cubic Centimeter cp - Centipoises FeCO3 - Siderite Fe2O3 - Hematite Ib - Pounds Ib/gal - Pound Per Gallon Ib/100ft2 - Pound Per hundred Square Foot PbS - Lead sulphate PCF - Pound Cubic Foot pH - Hydrogen Concentration ion ppg - Pounds Per Gallon PV - Plastic Viscosity ROP - Rate of Penetration rpm - Revolution per Minute µm - Micrometer μP - Plastic Viscosity V-G - Viscosity – Gel Yb - Yield Point Ɵ600 - Torque reading dial at 600 rpm Ɵ300 - Torque reading dial at 300 rpm YP - Yield Point

1. INTRODUCTION are environmentally friendly if the drilling fluid is to be disposed [3]. Weighting materials increase Expected increase in drilling activities, has mud density as well as penetration rate during necessitated the search for alternative sources of drilling [4]. When there is reduction in rig time drilling mud additives so as to minimize or stop due to fast penetration rate the overall drilling the importation of weighting materials such as cost is reduced because the target is reached barite. There are many local materials which earlier. A locally obtained weighting material that could be investigated to know their suitability for can be used in place of barite would be a new use as weighting material [1]. This research was innovation in the industry. carried out on one of such weighting materials galena which is available in the lower Benue The main objective of the research is to examine trough in Ebonyi state. Drilling mud formulation the properties of a locally sourced material to comprises of water, bentonite and weighting substitute barite in drilling fluids. Galena is a lead materials. ore (lead sulfide (PbS)) which is found in Ameri and Ameka in the lower Benue-Abakaliki trough The drilling mud is usually formulated to have in Ebonyi state in Nigeria (Fig. 1) [5]; the adequate hydrostatic pressure, normally in the rheological properties are being examined and range of 250 psi to 450 psi higher than the compared with that of barite. Just as oyster sea formation pressure [2]. Imbalance between the shell, (which is locally available) can be used as hydrostatic pressure and the formation pressure lost circulation material, the mineral Galena is may cause influx of formation fluid which may being investigated to know its potential to be result in a kick and eventually a blowout. Barites used as a weighting material in drilling mud [6].

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1.1 Basic Properties of Galena and Barite advantages of the compound over barite was their high specific gravities. In his conclusion, Galena also called lead II sulfide is lead grey and iron-based materials were recommended for use silver in colour; it is cubic and octahedral in as a substitute for barite. shape and opaque. The hardness is 2.5 and the specific gravity is 6.7 (see Table 2). It is one of According to Saasen et al. [13] ilmenite has been the most abundant and widely distributed sulfide applied earlier as a weighting material. A higher mineral. It is found in igneous and metamorphic drilling penetration rate was reported from the rocks in medium to low-temperature use of ilmenite, because lesser colloidal solid hydrothermal. In sedimentary rocks it occurs as fractions were produced during drilling. The veins, breccia cements, isolated grains and as ilmenite used in the first two wells drilled in 1979 replacements of limestone and dolomite. The and 1980 in the North Sea, were finely ground lead element is toxic but while bound in the materials compared to the presently used crystal structure, it is safe to handle. However, ilmenite [14]. The second trial was conducted in prolonged exposure to the pulverized dust in the 1994 using a more finely ground ilmenite [15]. form of inhalation or ingestion, it is hazardous to Recently, Manganese Tetra oxide (Mn3O4) has human health. It often has common impurities been used as a weighting material for water like Ag (Silver), Cu (Copper), Fe (Iron) and Bi based drilling fluids [16]. Mn3O4 and CaCO3 were (Bismuth) [8]. The molecular mass is 239.3 prepared in the laboratory and used to conduct g/mol. experiments. Polymer starch degraded at 250ºF and cellulose were contained in the drilling fluid Barite is an inorganic compound that is white formulation to control fluid loss and rheological crystalline in appearance, insoluble in water and properties of the drilling mud. colourless. It can be heated with coke to give barium sulfide (BaS) which is soluble in water According to Symposium [17], important unlike BaSO4. It has a molar mass of 233.4 properties of drilling mud include: Density (which g/mol, and is odourless. It has a melting point of enhances borehole stability and prevents 1345ºC, boiling point of 1600ºC and refractive blowout); low viscosity and gel strength (which index of 1.64 [9]. The hardness is 3.0 and produce faster drilling and more efficient removal specific gravity is 4.5. Although, barite has a of drill cuttings). High filtrate will minimizes chip slightly higher molecular weight than galena hold-down and facilitates faster drilling [18]. (243.4 to 239.3) the molecular composition of lead in galena is higher (86.60%) [10] than According to Moore and Gatlin [19] and Eckel barium in barite (60.54%) in pure samples. [20], some of the more recognizable variables which affect penetration rate include: mud 1.2 Other Alternative Weighting Materials density, weight on bit, rotating speed and bit type [4,20]. Other factors which affect rate of A weighting material that can be sourced locally penetration are formation properties such as to substitute barite would be a good innovation in permeability, porosity and hardness, rig the drilling industry. In recent years ilmenite and efficiency and personnel efficiency. haematite have been investigated. Both minerals meet the requirements for chemical inertness The main role of the weighting materials in the and availability, but they differ from barite in drilling fluid is to increase density and ultimately specific gravity and hardness. Scharf and Watts to ensure borehole stability [21]. It also creates [11] assessed the benefits of haematite as a sufficient hydrostatic pressure in the hole and weighting material in heavy oil base systems. minimizes fluid loss by formation of thick filter This was achieved by conducting a laboratory cake on the walls of the well [22]. Increase in investigation to obtain a comparative basis density also results in increased penetration rate; between barite and haematite. Rheological however, when the density is excessive, it can properties as well as abrasiveness were studied cause differential sticking of the drill string [23]. and field results were predicted. Results from 2. MATERIALS AND METHODS experimental work show lower fluid rheology, density and slightly more abrasive nature of haematite. Two mud samples were prepared which comprised of fresh water, caustic soda, bentonite Walker [12] presented experiences with mined and the weighting material. The weighting iron oxide used as an alternative weighting materials are added to achieve the required material to barite. One of the observed density.

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Sample A: Water-based mud with commercial 2.4 Determination of Solid Content barite of density between 9.0 ppg and 15.0 ppg. The sand content of the mud samples was Sample B: Water-based mud with galena of determined using sand screen set (sand content density between 9.0 ppg and 15.0 kits). The glass tube was filled with mud sample ppg. to a mark labeled “Mud to here” and water was added to the next mark labeled “Water to here”. 2.1 Determination of Mud Density The mouth of the tube was closed over with the thumb and shaken vigorously. The mixture was poured onto the screen and more water was The weight of the mud samples was determined added to the tube, shaken and poured onto the using the Baroid mud balance. The cup was filled screen. Funnel was fitted down over the top of completely with mud after calibration. The the screen, inverted slowly and washed sand expelled mud was washed and the balanced arm back into the tube. Then it was allowed to settle. was replaced on the base with the knife edge The quantity of the sand settled in the graduated resting on the fulcrum. The rider was moved until tube as the sand content of the mud in percent the graduated arm was horizontal and the by volume was recorded. This was repeated at reading was taken. different mud densities.

2.2 Determination of Mud Viscosity 2.5 Determination of pH

The mud viscosity of the samples was The pH meter which consists of a glass electrode determined using Fann V-G meter. The Fann V- system, an electronic amplifier and a meter G meter was filled to the 350 cc mark and placed calibrated in pH units was used to test the pH of on the movable work table. The table was galena mud. The electrical connection with the adjusted until the mud surface was at the scribed mud was established through saturated KCL line on the rotor sleeve. The motor was started solution contained in a tube surrounding the with a high speed position (600 rpm) and the calomel cell. The electrical potential generated in reading was taken from a steady indicator dial the glass - electrode system by the hydrogen value. The reading was also obtained at the low ions in the drilling mud was amplified and speed of 300 rpm. This was repeated for both operated the calibrated meter which indicated the samples and at different mud weights. The pH. The pH of the mud was noted. following parameters are calculated:

3. RESULTS AND DISCUSSION Plastic Vis cos ity     (cp) (1) 600 300 The mud formulation is shown in Table 1. The

Apparent Vis cos ity  1/ 2 600 (cp) (2) properties were tested after ageing for 48 hours at 60ºC (140ºF). The experimental investigations Bingham Yield Po int of mud density, rheological properties and solid content analysis are shown in Table 3 and Figs. 2 (Yb) )   300   p (lb /100 ft ) (3) 2-7. Results of the comparisons of the two mud 2 samples were investigated. Galena used was Or Yb  2 aF   p (lb /100 ft ) found to be able to generate similar mud weight as barite. 2.3 Determination of Gel Strength 3.1 Relationship between Plastic Viscosity and Mud Density The Fann V-G meter was also used to determine the gel strength of the mud samples. The mud samples were stirred thoroughly at 600 rpm. The The relationship between mud density and lift gear was shifted slowly to the first position, plastic viscosity, which is produced from the and the motor was shut off. The motor switch friction between the solid particles in the mud was turned to low after 10 seconds. The dial was and the viscosity of the dispersed phase, is read at maximum deflection units in Ib/100ft2 that shown in Fig. 2. At 9.0 ppg, the plastic viscosity is 10 second gel. The steps were repeated for 10 of galena was 13.0 cp while that of barite was minutes. The Gel strength was obtained for the 10.0 cp. It was observed that both minerals had different mud weights. the same viscosity at 13.0 ppg and then barite

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had a higher viscosity at 15.0 ppg. This change particles in the mud sample which in turns was due to the presence of large amount of increases the plastic viscosity. Therefore galena suspended barite particles in the mud sample, has the potential to be used as weighting which was more than galena. This effect material in heavy mud, as it could increase the continues with increase in mud weight. rate of penetration and the well cleansing Generally, friction between particles becomes efficiency. apparent with the increase in the number of

Fig. 1. Map of the Benue trough of Nigeria [7]

Table 1. Water-based mud formulation

Constituent Weighting material Barite Galena Fresh water (bbI) 3.14 3.14 Bentonite (Ib) 0.11 0.11 Caustic soda (Ib) 0.0022 0.0022 Weighting material (Ib/gal) 9.00-15.00 9.00 – 15.00

Table 2. Characteristics of weighting materials [24]

Weighting material Specific gravity Hardness(mohs) Barite 4.25-4.50 3.0-3.5 Galena 6.50-6.7 2.5-3.0

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Table 3. Water-based mud properties at different densities

Mud property Weighting material Barite Galena Mud density (Ib/gal) 9.0 11.0 13.0 15.0 9.0 11.0 13.0 15.0 Apparent viscosity (cp) 20 25 32 39 23 28 34 42 Plastic viscosity (cp) Ɵ600 40 50 64 78 46 56 68 84 Ɵ300 30 36 42 53 33 41 50 61 10 14 18 25 13 15 18 23 Yield point (Ib /100ft2) 20 22 24 28 20 26 32 38 10 second gel (Ib/100 ft2) 5 7 10 12 8 10 13 16 10 mins. gel (Ib /100 ft2) 7 10 14 18 10 13 18 24 Solid content (%) 5 11 18 23 3 7 12 17

25 ) p c (

y 20 t i s o

c 15 s i V

c i

t 10 s a l P 5

0 8 10 12 14 16 Mud Density (ppg)

Barite Galena

Fig. 2. Plastic viscosity vs. mud density

3.2 Relationship between Apparent permanent deformation either by plastic flow or Viscosity and Mud Density rupture. The result shows that galena has a higher yield point readings than the barite sample. At 9.0 ppg, the yield point of barite and Fig. 3 shows the relationship between apparent 2 viscosity and mud density. The plot shows that galena was 20.0 and 22.0 Ib/100ft while at 15.0 ppg, it increased to 28.0 Ib/100ft2 and 38.0 galena has higher apparent viscosity than barite. 2 At 9.0 ppg, the viscosities of the galena and Ib/100ft respectively. This large difference might barite were 20 cp and 23 cp respectively and at be because galena’s attrition is higher than that 15.0ppg, the apparent viscosities were 42 cp and of barite. But mud with optimal yield point could 39 cp respectively. This is a marginal difference carry cuttings to the surface in a more efficient of 3cp between the mud samples; thus galena and effective manner. could be used as barite substitute. 3.4 Relationship between Gel Strength 3.3 Relationship between Yield Point and and Mud Density Mud Density Figs. 5 and 6 show the relationship between gel Fig. 4 is the relationship between yield point and strength at 10 seconds and 10 minutes with mud mud density. Yield point is the maximum stress density respectively. Gel strength of drilling fluid that a solid can withstand without undergoing is the measure of the shearing stress necessary

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to initiate a finite rate of shear. Galena sample respectively. Mud sample with barite gave the has a marginally higher gel strength compared to highest solid content. This is because the galena barite sample. At 9.0 ppg, the 10 second gel has higher specific gravity as compared to barite, strength of galena and barite was 8.0 and 5.0 thus requiring less quantity. The main advantage Ib/100ft2 while the 10 mins gel strength was 10.0 of using lower solid content drilling mud is the and 7.0 Ib/100ft2 respectively. There was a increase in rate of penetration, due to the marginal increase in the parameter as the mud presence of fewer solids around the rotating bit. density increases. The high gel strength may be Lower solid content fluid may decrease drilling due to the presence of ions in the galena. But if time thus minimizing well and drilling costs. the ions are excessive, it may cause clay flocculation via the complex electrical attractive/ The abrasiveness of a fluid is dependent on repulsive balance that dispersed in water. many factors such as shape, concentration and Eventually they will aggregate. Mud with hardness of these particles. As a fluid is moderate gel strength could suspend cuttings circulated, some attrition is expected. This and mud particles when mud circulation is attrition would tend to round the individual stopped. particle edges creating a less abrasive solid. In a system weighted with galena, a reduction of 3.5 Relationship Between Solid Content particle volume would also lead to less and Mud Density abrasiveness. Galena with lower hardness would tend to be less abrasive than barite. In a field The quantity of galena used was smaller than situation the drilled solids may overshadow the barite, thus producing smaller solid content. Solid abrasive nature of the weighting material. content analysis involves the measurement of However, in oil-based mud the abrasiveness weighting material and sand content of the mud could be less significant. The pH of mud in order to prevent abrasion of pumps and drill containing galena was found to be at 5.5 pipes, and it is expressed in percentages. Fig. 7 compared to tap water of 7.0 pH. This may be shows that the solid content increased attributed to oxidation of the surface of the proportionally with mud density. At 9.0 ppg, the mineral particles during the grinding to very fine solid content of barite and galena was 5 and 3% particles. The pH was therefore raised to 10.5 by while at 15.0 ppg; it was 23 and 17% adding caustic soda.

40 )

p 35 c (

t 30 i s o

c 25 s i V 20 t n e

r 15 a p

p 10 A 5

0 8 10 12 14 16 Mud Density (ppg)

barite galena

Fig. 3. Apparent viscosity vs. mud density

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35 ) . t f

. 30 q s

0 25 0 1 / b

I 20 (

t n i

o 15 P

d l 10 e i Y 5

0 8 10 12 14 16 Mud Density (ppg)

Barite Galena

Fig. 4. Yield point vs. mud density

18 16 14 h t

g 12 n e r t

s 10

l e G 8 . c e S 6 0 1 4 2 0 8 9 10 11 12 13 14 15 16 Mud Density (ppg)

Barite Galena

Fig. 5. 10 seconds gel strength vs. mud density

3.6 Toxicity and Cost of Galena organ and the nervous system. Long term exposure to lead can result in decrease in the Lead is a highly poisonous metal when inhaled or performance of the nervous system, damage to swallowed in the pulverized form. It affects every the brain and kidneys and eventually death. If

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galena is used in drilling mud, it will be in the immediate precaution would be the use of gas pulverized form and while the drilling operation is mask by all personnel on the drilling Rig during on, it would be inhaled by all personnel on the the drilling operation. drilling rig and this is very hazardous [10,25]. An

25 h t g n

e 20 r t S

e 15 G

. s n i 10 m

1 5

0 8 9 10 11 12 13 14 15 16 Mud Density (ppg) Barite Galena

Fig. 6. 10 minutes gel strength vs. mud density

20 ) % (

n 15 e t n o C 10 d i l o S 5

0 8 9 10 11 12 13 14 15 16 Mud Density (ppg)

Barite Galena

Fig. 7. Solid content vs. mud density

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The demand in the world for barite is more than 2 ACKNOWLEDGMENTS million tonnes/yr. This corresponds to 59% of total production [26]. This is one reason for the The authors wish to express their gratitude to the search for alternatives. Other weighting materials staff and technologists of the department of apart from Barite include: Hematite (Fe2O3) 4.9 - Chemical and Petroleum Engineering, University 5.3, Siderite (FeCO3) 3.7 - 3.9 and Galena of Uyo; Mr. Brian Uduk who made the galena (Pubs) 6.5 – 6.7 [26]. In terms of the cost of samples available for the work. Lastly, the staff of galena compared to barite, it is more expensive; Shell Professorial chair of Petroleum however, it is still not being exploited in this Engineering, University of Ibadan. country at the moment. This is one of the solid minerals which are to be exploited to diversify the COMPETING INTERESTS economy. If the mineral is mined locally, the cost would not be as much as when it is imported; it Authors have declared that no competing would still be more cost effective if used instead interests exist. of importation of barite. REFERENCES 4. CONCLUSION

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