The Use of Galena as Weighting Material in Drilling Mud

Transcription

1 Journal of Scientific Research & Reports 7(6): , 215; Article no.jsrr ISSN: SCIENCEDOMAIN international The Use of as Weighting Material in Drilling Mud U. Akpabio Julius 1*, I. Akpanika Offiong 1 and O. Etim Idorenyin 1 1 Department 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:.9734/JSRR/215/1595 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: Original Research Article Received 5 th November 214 Accepted 16 th February 215 Published 3 th May 215 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 (BaSO 4 ) also known as barite is the prevalent weighting material but there is need to develop local materials to augment the use of. 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. ppg and 15. 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. ppg, the yield point of galena was 2. lb/ft 2 and barite 22. lb/ft 2 while the second gel strength of galena was 5. lb/ft 2 and 8. lb/ft 2 for barite. Similarly, little difference was observed in plastic and apparent viscosities. At 9. ppg, the plastic and apparent viscosities of galena was 13. cp and 23. cp while barite was. cp and 2. cp. *Corresponding author: juliakpabio@yahoo.com;

2 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 thereby enhancing the local content initiative of the government. When is sourced locally and used it will reduce overall mud and drilling costs. Keywords: ; ; drilling mud; weighting material; hydrostatic pressure. SYMBOLS / NOMENCLATURE API - American Petroleum Institute AV - Apparent Viscosity BaSO 4 - Barium Sulphate cc - Cubic Centimeter cp - Centipoises FeCO 3 - Siderite Fe 2 O 3 - Hematite Ib - Pounds Ib/gal - Pound Per Gallon Ib/ft 2 - 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 μ P - Plastic Viscosity V-G - Viscosity Gel Y b - Yield Point Ɵ 6 - Torque reading dial at 6 rpm Ɵ 3 - Torque reading dial at 3 rpm YP - Yield Point 1. INTRODUCTION Expected increase in drilling activities, has necessitated the search for alternative sources of drilling mud additives so as to minimize or stop the importation of weighting materials such as barite. There are many local materials which could be investigated to know their suitability for use as weighting material [1]. This research was carried out on one of such weighting materials galena which is available in the lower Benue trough in Ebonyi state. Drilling mud formulation comprises of water, bentonite and weighting materials. The drilling mud is usually formulated to have adequate hydrostatic pressure, normally in the range of 25 psi to 45 psi higher than the formation pressure [2]. Imbalance between the hydrostatic pressure and the formation pressure may cause influx of formation fluid which may result in a kick and eventually a blowout. s are environmentally friendly if the drilling fluid is to be disposed [3]. Weighting materials increase mud density as well as penetration rate during drilling [4]. When there is reduction in rig time due to fast penetration rate the overall drilling cost is reduced because the target is reached earlier. A locally obtained weighting material that can be used in place of barite would be a new innovation in the industry. The main objective of the research is to examine the properties of a locally sourced material to substitute barite in drilling fluids. is a lead ore (lead sulfide (PbS)) which is found in Ameri and Ameka in the lower Benue-Abakaliki trough in Ebonyi state in Nigeria (Fig. 1) [5]; the rheological properties are being examined and compared with that of barite. Just as oyster sea shell, (which is locally available) can be used as lost circulation material, the mineral is being investigated to know its potential to be used as a weighting material in drilling mud [6]. 456

3 1.1 Basic Properties of and also called lead II sulfide is lead grey and silver in colour; it is cubic and octahedral in shape and opaque. The hardness is 2.5 and the specific gravity is 6.7 (see Table 2). It is one of the most abundant and widely distributed sulfide mineral. It is found in igneous and metamorphic rocks in medium to low-temperature hydrothermal. In sedimentary rocks it occurs as veins, breccia cements, isolated grains and as replacements of limestone and dolomite. The lead element is toxic but while bound in the crystal structure, it is safe to handle. However, prolonged exposure to the pulverized dust in the form of inhalation or ingestion, it is hazardous to human health. It often has common impurities like Ag (Silver), Cu (Copper), Fe (Iron) and Bi (Bismuth) [8]. The molecular mass is g/mol. is an inorganic compound that is white crystalline in appearance, insoluble in water and colourless. It can be heated with coke to give barium sulfide (BaS) which is soluble in water unlike BaSO 4. It has a molar mass of g/mol, and is odourless. It has a melting point of 1345ºC, boiling point of 16ºC and refractive index of 1.64 [9]. The hardness is 3. and specific gravity is 4.5. Although, barite has a slightly higher molecular weight than galena (243.4 to 239.3) the molecular composition of lead in galena is higher (86.6%) [] than barium in barite (6.54%) in pure samples. 1.2 Other Alternative Weighting Materials A weighting material that can be sourced locally to substitute barite would be a good innovation in the drilling industry. In recent years ilmenite and haematite have been investigated. Both minerals meet the requirements for chemical inertness and availability, but they differ from barite in specific gravity and hardness. Scharf and Watts [11] assessed the benefits of haematite as a weighting material in heavy oil base systems. This was achieved by conducting a laboratory investigation to obtain a comparative basis between barite and haematite. Rheological properties as well as abrasiveness were studied and field results were predicted. Results from experimental work show lower fluid rheology, density and slightly more abrasive nature of haematite. Walker [12] presented experiences with mined iron oxide used as an alternative weighting material to barite. One of the observed advantages of the compound over barite was their high specific gravities. In his conclusion, iron-based materials were recommended for use as a substitute for barite. According to Saasen et al. [13] ilmenite has been applied earlier as a weighting material. A higher drilling penetration rate was reported from the use of ilmenite, because lesser colloidal solid fractions were produced during drilling. The ilmenite used in the first two wells drilled in 1979 and 198 in the North Sea, were finely ground materials compared to the presently used ilmenite [14]. The second trial was conducted in 1994 using a more finely ground ilmenite [15]. Recently, Manganese Tetra oxide (Mn 3 O 4 ) has been used as a weighting material for water based drilling fluids [16]. Mn 3 O 4 and CaCO 3 were prepared in the laboratory and used to conduct experiments. Polymer starch degraded at 25ºF and cellulose were contained in the drilling fluid formulation to control fluid loss and rheological properties of the drilling mud. According to Symposium [17], important properties of drilling mud include: Density (which enhances borehole stability and prevents blowout); low viscosity and gel strength (which produce faster drilling and more efficient removal of drill cuttings). High filtrate will minimizes chip hold-down and facilitates faster drilling [18]. According to Moore and Gatlin [19] and Eckel [2], some of the more recognizable variables which affect penetration rate include: mud density, weight on bit, rotating speed and bit type [4,2]. Other factors which affect rate of penetration are formation properties such as permeability, porosity and hardness, rig efficiency and personnel efficiency. The main role of the weighting materials in the drilling fluid is to increase density and ultimately to ensure borehole stability [21]. It also creates sufficient hydrostatic pressure in the hole and minimizes fluid loss by formation of thick filter cake on the walls of the well [22]. Increase in density also results in increased penetration rate; however, when the density is excessive, it can cause differential sticking of the drill string [23]. 2. MATERIALS AND METHODS Two mud samples were prepared which comprised of fresh water, caustic soda, bentonite and the weighting material. The weighting materials are added to achieve the required density. 457

4 Sample A: Water-based mud with commercial barite of density between 9. ppg and 15. ppg. Sample B: Water-based mud with galena of density between 9. ppg and 15. ppg. 2.1 Determination of Mud Density The weight of the mud samples was determined using the Baroid mud balance. The cup was filled completely with mud after calibration. The expelled mud was washed and the balanced arm was replaced on the base with the knife edge resting on the fulcrum. The rider was moved until the graduated arm was horizontal and the reading was taken. 2.2 Determination of Mud Viscosity The mud viscosity of the samples was determined using Fann V-G meter. The Fann V- G meter was filled to the 35 cc mark and placed on the movable work table. The table was adjusted until the mud surface was at the scribed line on the rotor sleeve. The motor was started with a high speed position (6 rpm) and the reading was taken from a steady indicator dial value. The reading was also obtained at the low speed of 3 rpm. This was repeated for both samples and at different mud weights. The following parameters are calculated: Plastic Vis cos 3 ity 6 ( cp) Apparent Vis cos ity 1/ 2 6 ( cp) Bingham ( Y Or b) ) Y b 2 Yield 3 Po int ( lb / ft 2 ( lb / ft ) af p 2.3 Determination of Gel Strength p 2 ) (1) (2) (3) The Fann V-G meter was also used to determine the gel strength of the mud samples. The mud samples were stirred thoroughly at 6 rpm. The lift gear was shifted slowly to the first position, and the motor was shut off. The motor switch was turned to low after seconds. The dial was read at maximum deflection units in Ib/ft 2 that is second gel. The steps were repeated for minutes. The Gel strength was obtained for the different mud weights. 2.4 Determination of Solid Content The sand content of the mud samples was determined using sand screen set (sand content kits). The glass tube was filled with mud sample to a mark labeled Mud to here and water was added to the next mark labeled Water to here. 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 added to the tube, shaken and poured onto the screen. Funnel was fitted down over the top of the screen, inverted slowly and washed sand back into the tube. Then it was allowed to settle. The quantity of the sand settled in the graduated tube as the sand content of the mud in percent by volume was recorded. This was repeated at different mud densities. 2.5 Determination of ph The ph meter which consists of a glass electrode system, an electronic amplifier and a meter calibrated in ph units was used to test the ph of galena mud. The electrical connection with the mud was established through saturated KCL solution contained in a tube surrounding the calomel cell. The electrical potential generated in the glass - electrode system by the hydrogen ions in the drilling mud was amplified and operated the calibrated meter which indicated the ph. The ph of the mud was noted. 3. RESULTS AND DISCUSSION The mud formulation is shown in Table 1. The properties were tested after ageing for 48 hours at 6ºC (14ºF). The experimental investigations of mud density, rheological properties and solid content analysis are shown in Table 3 and Figs Results of the comparisons of the two mud samples were investigated. used was found to be able to generate similar mud weight as barite. 3.1 Relationship between Plastic Viscosity and Mud Density The relationship between mud density and plastic viscosity, which is produced from the friction between the solid particles in the mud and the viscosity of the dispersed phase, is shown in Fig. 2. At 9. ppg, the plastic viscosity of galena was 13. cp while that of barite was. cp. It was observed that both minerals had the same viscosity at 13. ppg and then barite 458

5 had a higher viscosity at 15. ppg. This change was due to the presence of large amount of suspended barite particles in the mud sample, which was more than galena. This effect continues with increase in mud weight. Generally, friction between particles becomes apparent with the increase in the number of particles in the mud sample which in turns increases the plastic viscosity. Therefore galena has the potential to be used as weighting material in heavy mud, as it could increase the rate of penetration and the well cleansing efficiency. Fig. 1. Map of the Benue trough of Nigeria [7] Table 1. Water-based mud formulation Constituent Weighting material Fresh water (bbi) Bentonite (Ib) Caustic soda (Ib) Weighting material (Ib/gal) Table 2. Characteristics of weighting materials [24] Weighting material Specific gravity Hardness(mohs)

6 Table 3. Water-based mud properties at different densities Mud property Weighting material Mud density (Ib/gal) Apparent viscosity (cp) Plastic viscosity (cp) Ɵ Ɵ Yield point (Ib /ft 2 ) second gel (Ib/ ft 2 ) mins. gel (Ib / ft 2 ) Solid content (%) Plastic Viscosity (cp) Fig. 2. Plastic viscosity vs. mud density 3.2 Relationship between Apparent Viscosity and Mud Density Fig. 3 shows the relationship between apparent viscosity and mud density. The plot shows that galena has higher apparent viscosity than barite. At 9. ppg, the viscosities of the galena and barite were 2 cp and 23 cp respectively and at 15.ppg, the apparent viscosities were 42 cp and 39 cp respectively. This is a marginal difference of 3cp between the mud samples; thus galena could be used as barite substitute. 3.3 Relationship between Yield Point and Mud Density Fig. 4 is the relationship between yield point and mud density. Yield point is the maximum stress that a solid can withstand without undergoing permanent deformation either by plastic flow or rupture. The result shows that galena has a higher yield point readings than the barite sample. At 9. ppg, the yield point of barite and galena was 2. and 22. Ib/ft 2 while at 15. ppg, it increased to 28. Ib/ft 2 and 38. Ib/ft 2 respectively. This large difference might be because galena s attrition is higher than that of barite. But mud with optimal yield point could carry cuttings to the surface in a more efficient and effective manner. 3.4 Relationship between Gel Strength and Mud Density Figs. 5 and 6 show the relationship between gel strength at seconds and minutes with mud density respectively. Gel strength of drilling fluid is the measure of the shearing stress necessary 46

7 to initiate a finite rate of shear. sample has a marginally higher gel strength compared to barite sample. At 9. ppg, the second gel strength of galena and barite was 8. and 5. Ib/ft 2 while the mins gel strength was. and 7. Ib/ft 2 respectively. There was a marginal increase in the parameter as the mud density increases. The high gel strength may be due to the presence of ions in the galena. But if the ions are excessive, it may cause clay flocculation via the complex electrical attractive/ repulsive balance that dispersed in water. Eventually they will aggregate. Mud with moderate gel strength could suspend cuttings and mud particles when mud circulation is stopped. 3.5 Relationship Between Solid Content and Mud Density The quantity of galena used was smaller than barite, thus producing smaller solid content. Solid content analysis involves the measurement of weighting material and sand content of the mud in order to prevent abrasion of pumps and drill pipes, and it is expressed in percentages. Fig. 7 shows that the solid content increased proportionally with mud density. At 9. ppg, the solid content of barite and galena was 5 and 3% while at 15. ppg; it was 23 and 17% respectively. Mud sample with barite gave the highest solid content. This is because the galena has higher specific gravity as compared to barite, thus requiring less quantity. The main advantage of using lower solid content drilling mud is the increase in rate of penetration, due to the presence of fewer solids around the rotating bit. Lower solid content fluid may decrease drilling time thus minimizing well and drilling costs. The abrasiveness of a fluid is dependent on many factors such as shape, concentration and hardness of these particles. As a fluid is circulated, some attrition is expected. This attrition would tend to round the individual particle edges creating a less abrasive solid. In a system weighted with galena, a reduction of particle volume would also lead to less abrasiveness. with lower hardness would tend to be less abrasive than barite. In a field situation the drilled solids may overshadow the abrasive nature of the weighting material. However, in oil-based mud the abrasiveness could be less significant. The ph of mud containing galena was found to be at 5.5 compared to tap water of 7. ph. This may be attributed to oxidation of the surface of the mineral particles during the grinding to very fine particles. The ph was therefore raised to.5 by adding caustic soda Apparent Viscosity (cp) barite galena Fig. 3. Apparent viscosity vs. mud density 461

8 4 35 Yield Point (Ib/ sq. ft.) Fig. 4. Yield point vs. mud density Sec. Gel strength Fig. 5. seconds gel strength vs. mud density 3.6 Toxicity and Cost of Lead is a highly poisonous metal when inhaled or swallowed in the pulverized form. It affects every organ and the nervous system. Long term exposure to lead can result in decrease in the performance of the nervous system, damage to the brain and kidneys and eventually death. If 462

9 galena is used in drilling mud, it will be in the pulverized form and while the drilling operation is on, it would be inhaled by all personnel on the drilling rig and this is very hazardous [,25]. An immediate precaution would be the use of gas mask by all personnel on the drilling Rig during the drilling operation. 3 mins. Gel Strength Fig. 6. minutes gel strength vs. mud density 25 2 Solid Content (%) Fig. 7. Solid content vs. mud density 463

10 The demand in the world for barite is more than 2 million tonnes/yr. This corresponds to 59% of total production [26]. This is one reason for the search for alternatives. Other weighting materials apart from include: Hematite (Fe 2 O 3 ) , Siderite (FeCO 3 ) and (Pubs) [26]. In terms of the cost of galena compared to barite, it is more expensive; however, it is still not being exploited in this country at the moment. This is one of the solid minerals which are to be exploited to diversify the economy. If the mineral is mined locally, the cost would not be as much as when it is imported; it would still be more cost effective if used instead of importation of barite. 4. CONCLUSION Based on the experiments, the following conclusions can be made: i. Local has the potential to be used as weighting material in drilling fluid as smaller quantity of galena could produce same mud density as barite. ii. gives a higher yield point and gel strength than barite, which can be reduced by increasing the lignosulfonate concentration. iii. The main advantage of galena over barite is their abrasive characteristics which could be controlled by proper grinding of the mineral into very fine particles. iv. Compared with barite, galena gives a lower solid content due to its higher specific gravity. v. Comparing galena and barite, differences between the apparent viscosity and plastic viscosity are very small vi. The rheological properties of galena are similar to that of barite and therefore could be used in place of barite. 5. RECOMMENDATIONS Problems such as high yield point and gel strength in galena, can be reduced by adding lignosulfonates, or other additives such as thinners and dispersants; and the acidic nature of galena mud suspected to be due to the presence of ions could be corrected by addition of inhibitors such as amines and phosphates. The exploitation of this mineral should be improved in order to reduce the importation of barite and use galena instead thereby enhancing the local content initiative of the government and making huge economic savings for the company. ACKNOWLEDGMENTS The authors wish to express their gratitude to the staff and technologists of the department of Chemical and Petroleum Engineering, University of Uyo; Mr. Brian Uduk who made the galena samples available for the work. Lastly, the staff of Shell Professorial chair of Petroleum Engineering, University of Ibadan. COMPETING INTERESTS Authors have declared that no competing interests exist. REFERENCES 1. Etim IO, Developing drilling mud weighting material with local galena. BSc. Project of the Department of Chemical and Petroleum Engineering, University of Uyo, Akwa Ibom State Nigeria; Ismail I, Ismail AR, Juhari Y. Managing drilling mud weight using ilmenite. Faculty of Chemical and Natural Resources Engineering, University of Technology, Malaysia. 24; Bruton JR, Bacho J, Newcaster JA. The future drilling-grade barite weight material A case for a substitute specification. Paper SPE 3135 presented at the SPE Annual Technical Conference and Exhibition in San Antonio, Texas, USA; Blattel SR, Rupert JP. The effect of weight material type on the rate of penetration using dispersed and non-dispersed waterbased muds. Paper SPE 961 presented at the 57th Annual Technical Conference and Exhibition of SPE in New Orleans, Louisiana, September; Where is galena found in Nigeria? Available: om/ore-process/does-ibonyi-nigeria-havelead-ore.html (Assessed 2 October 214). 6. Akeju OA, Akintola SA, Akpabio JU. The use of Crassostrea virginica as lost circulation material in water-based drilling mud. International Journal of Engineering Technology. 214;4(2): Fatoye FB. Ibitomi MA. Omada JI. Lead- Zinc-Barytes mineralization in the Benue Trough, Nigeria: Their geology, occurrences and economic prospective. Pelagia Research Library: Advances in Applied Science Research. 214;5(2):

11 8. CRC Handbook of Chemistry and Physics 85 th edition CRC press. 24;4-45. (Handbook) 9. Anthony JW, Bideaux RA, Bladh KW, Nichols MC ed., Handbook of Mineralogy (Elements, sulfides, sulfosalts) Chantilly VA. US; Mineralogy Society of America. 199;2.. Lead Wikipedia, the free encyclopedia.htm. Retrieved 12 January Scharf AD, Watts RD. Itabirite: An alternative weighting material for heavy oilbased mud. Paper SPE presented at the 59th Annual Technical Conference and Exhibition in Houston, Texas, September; Walker CO. Alternative weighting material. Journal of Petroleum Technology. Paper SPE PA presented at the SPE Annual Technical Conference and Exhibition New Orleans, September; Sassen A, Hoset H, Rostad EJ, Fjogstad A, Aunan O, Westgard E, Norkyn PI. Application of ilmenite as weight material in water based and oil based drilling fluids. Paper SPE 7141 presentation at SPE Annual Technical Conference and Exhibition in New Orleans, Louisiana, 3 September 3 October; Blomberg NE, Melberg B, Evaluation of ilmenite as weight material in drilling fluids. SPE 185-PA Journal of Petroleum Technology. 1984;36(6): Idris AK, Ismail I. The use of Malaysia ilmenite as weighting material in drilling mud. Presented at the international Conference in Recent Advances in Materials and Mineral Resources held in Penang, Malaysia 3-5 May; Al-Yami AS, Nasr-El-Din HA. An innovative manganese Tetroxide/KCl water-based drilling-in fluid for HT/HP wells. Paper SPE 1638 presented at the 27 SPE Annual Technical Conference and Exhibition, Anaheim, California USA November; Simpson JP, The drilling mud dilemmarecent examples. SPE PA Journal of Petroleum Technology. 1985;37(2): American Petroleum Institute. Specifications for oil well drilling fluid material. API Specification 13A, 16th Edition Washington DC; Moore PL, Gatlin C. Six variables that affect penetration rate. Oil and Gas Journal. 196;15(58): Eckel JR. Microbit studies of the effect of fluid properties and hydraulics on drilling rate. SPE 152-PA SPE Journal of Petroleum Technology. 1967;19(4): Akpabio JU, Inyang PN, Iheaka CI. Effect of drilling fluid density on rate of penetration. International Journal of Scientific Innovations. 212;4(1): Gatlin C. Petroleum engineering: Drilling and well completions. New Jersey, Prentice-Hall Inc. USA. 196; Darley HCH, Gray GR. Composition and properties of drilling and completion fluids. 5th Edition; Gulf Professional Publishing Houston, London; Available: specific_gravity_of_common_materials1.p df Specific gravity of barite and other common materials. (Assessed 2 October 214). 25. Kinder C. Lead contamination in our environment Lead Contamination in our environment.html. Assessed 12 January Klempa M. Bujok P. Struna L. Pinka J. Fundamentals of onshore drilling in Nguyen, JP(ed.) Drilling - Fundamentals of Exploration and Production, Editions Technip, Paris; Available: drilling/theory.html (Assessed 7 th March 215). 215 Julius et al.; This is an Open Access article distributed under the terms of the Creative Commons Attribution License ( which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Peer-review history: The peer review history for this paper can be accessed here: 465