DEVELOPMENT OF LUBRICATING GREASES FOR OIL AND GAS PRODUCTION EQUIPMENT I. A. Lyubinin and A. S. Gubarev

UDC 621.892+622.24.05

Prospects for growth in the oil and gas industry are contingent on expansion of drilling activity and increases in the depth of exploratory and developmental drilling in difficult, accessible regions and also in the shelf zone of seas and oceans. Becuase of the extremal conditions under which oil and gas production equipment must operate in zones with abnormally high formation pressures and high concentrations of hydrogen sulfide and carbon dioxide, the equipment must meet higher standards of strength and service life. The quality of the lubricating greases that are used is a major factor in meeting these requirements. In this article we will examine the three basic groups of greases and components that are used in drilling and in oil and gas production: for bearings in roller bits, for threaded joints between oil pipe lengths, and as seal greases for oil and gas fittings. Greases for the bearings of roller bits are being manufactured by the Berdyansk Experimental Petroleum Oil Plant under the designation "Dolotol." These greases were developed by the MASMA Scientific-Research Institute of the Petroleum Industry in cooperation with the Institute of Problems in Mateial Science (Ukrainian Academy of Sciences), the Special Design Bureau for Bits (a part of the Kuibyshevburmash Production Association), and the All-Union Scientific-Research Institute of Drilling Equipment. These greases are intended for use in low-speed roller bits manufactured under license from Dresser (U.S.) [1-3]. The greases contain additive packages that provide a high level of tribotechnical and service properties (Table i). As an antifriction filler, synthetic molybdenum diselenide has been used for the first time [4, 5]. For high-speed roller bits, a grease designed "Plastol" has been developed at the MASMA Scientific-Research Institute of Petroleum Production; this grease is distinguished by a high level of tribotechnical and adhesive properties (see Table i). This grease is also being manufactured at the Berdyansk Experimental Petroleum Oil Plant. In Table 1 we have listed for comparison the tribotechnical characteristics of greases that were previously used in the bearings of roller bits -- LpI-27, graphite grease, and Uniol-i and also greases of the XG series that are used by Dresser in the bearings of low-speed drill bits. As can be seen, the XG and Dolotol greases, as well as the Plastol grease, have excellent antiscoring properties and good antifriction and antiwear properties, so that the bit bearing life can be extended under conditions where they are subject to damage. The mechanism of action of greases for drill bit bearings was investigated in a fourball friction tester with balls made of the drill-bit steel 55SMSFA, under extremely severe conditions (load I000 N, l-h test), which reproduce in part the conditions under which the bits operate. The frictional surfaces were investigated* by means of Auger spectroscopy in a JAMP 10S spectrometer. A vacuum of 2"10 -7 Pa was maintained in the chamber of the instrument. Scanning electron microscopy was performed with an accelerating voltage of I0 kV, electron beam current 5"10 -7 A, and modulation voltage 5 kV. The surface layers were sputtered by means of Ar ions with an accelerating voltage of 3 kV and an ion current of 10 -7 A absorbed by the copper specimen. When using the graphite grease, analysis of the surface layer showed increased contents of sulfur, oxygen, and carbon in a carbide phase (Fig. la). The observation that a carbide phase (predominantly Fe2C and Fe3C) is formed on the friction surface now requires *These studies were performed by O. I. Nosovskii (MASMA Scientific-Research the Petroleum Industry).

Institute of

MASMA Scientific-Research Institute of the Petroleum Industry (Ukraine). Translated from Khimiya i Tekhnologiya Topliv i Masel, No. ii, pp. 23-26, November, 1992.

0009-3092/92/1112-0627512.50

9 1993 Plenum Publishing Corporation

627

TABLE 1

Grease for bearings of roller bits

LPI-27 Graphite Uniol-i XG-107 XG-249 XG-304 D o l o t o l NU Dolotol N

Dolotol AU Plasto 1

Tribotechnical characteristics ! in in UkrGiproin SRV vibroin four-ball tester (GOST 9490--75) SMTs-2 : N I I n e f t ' test tribometer:$~ appa- stand: mean steady-state wear, seizure weld wear s c a r diameter:'," ratus: time of wear,1% operation coefficient load load (ram) on steel mm-lO-2before of friction ~m Ps, N Pw, kN seizure, h ShKhl5 I 55SM5FA 140

3,15

670-- 1 0 0 0 2--2,15 800--1120 2,24--3,2 790 5,01 940 10,00 1000 7,08 1330 6,31 1260 10,00 1i20 7,90 1330 10,00

Grabbing 3,88 1,94 1,44 1,36 0,90 1,38 0,98 0,90 0,95

3,50 2,00 1,27 0,96 0,97 0,96 IJ,~,, 0,95 1,00

1l 9 12 10 10 6 5 , 8 6 4 6

1,30 0,82 3,06 1,20 2,25 8,90 3,00 4,29 18,37 6,80

Grabbing 0,12--0,2 0,12 0,06--0,10 0,! 1 0,11 0;13--0,16 0,1 l 0,t0 0,10

. 2,2 0,95 1,15 1,90 0,35 0,45 0,50 0,35 0,55

in Falex i test stand: load-carrying capacity, kN

3,8 6,0 8,0 6,5 9,3 9,5 11,0 13,0 11,0 12,5

*With a load of 1500 N. %With 1800 m per mm of linear contact, slip coefficient 20%, and time 300 sec. SWith frequency 50 Hz, amplitude 600 pm, and load 200 N. a change in the existing concept of the lubricating mechanism of graphite in friction, according to which, because of the anisotropic structure of graphite, layers are readily sheared in accordance with the "sandwich" theory. Obviously, along with this mechanism, there is a deeper interaction of the graphite with the substrate material. The distribution of the elements through surface layers with a thickness of 450-600 nm indicates a decrease in the content of carbon in the carbide phase, and of sulfur, to a depth of 300400 nm (Fig. la). When using the grease Dolotol N, increased contents of sulfur, carbon, and oxygen were found in the surface layer (Fig. ib). After sputtering, the spectrum of this layer exhibited only the lines corresponding to the substrate material. The thickness of the surface layer was 600-800 nm. For the Dolotol N, we also noted the highest content of sulfur in the subsurface layer, evidently because of chemical interaction of the molybdenum disulfide with the substrate. The surface layer consisted mainly of carbon-, oxygen-, and iron-containing compounds. After the test of the XG-249 grease, the surface layer was found to contain increased amounts of sulfur, chlorine, carbon, and oxygen. After sputtering the layer, lines corresponding to small amounts of sulfur and carbon were observed (Fig. ic). Analysis of the carbon line indicated the presence of carbides in a surfce layer with a thickness (judging from the distribution of sulfur and oxygen) of 400-600 nm. From the results that were obtained, it can be seen that oxygen and carbon were the main elements present on the surface; in the surface layers, the main element was sulfur, with a maximum concentration at a depth of 10-40 nm. The thickness of the film with an increased content of oxygen was no more than 30 nm. On the whole, the XG-249 grease is very similar to the Dolotol N in the mechanism of chemical modification of the friction surface. In the surface layer of specimens from tests with the Plastol grease, we found phosphorus, sulfur, boron, carbon, calcium, oxygen, and zinc, i.e., those elements that are present in the additives and fillers of the grease. After sputtering the layer, the peaks in the spectrum corresponding to the substrate material were accompanied by other peaks indicating a small content of oxygen (Fig. Id). An analysis of the distribution of elements through the thickness of the surface layer indicated the presence of the active elements of the grease down to a depth of 300-350 nm. This means that under potentially damaging conditions, the active elements of the grease participate in the formation of secondary structures of the friction surface (according to B. I. Kostetskii) and that only the presence of grease in the bearing will prolong the service life of the roller bit. An analysis of failures of oil-field tubular goods has shown that up to 60% of the failures of drill strings made of steel or lightweight alloys involve failures of threaded pipe joints, and up to 80% of intercolumn flows in gas condensate fields involve leaks in threaded joints of the casing string [6-8]. These data demonstrate the need for improving threaded joints of oil field tubular goods, and also the lubricants (compounds) used for 628

m$

Fig.

1.

V a r i a t i o n of chemical composition through

thickness of surface layer of 55SMSFA steel (I is the relative intensity; 9 is the surface layer sputtering time), when using the following greases: a) graphite grease; b) Dolotol N; c) XG-249; d) Plastol. these joints. However, the product mix of thread compounds (series R) has remained unchanged for many years [9], even though the demand for these greases is satisfied to the extent of only 10-15%. Any increase in production of thread compounds is being held back by the shortage of nonferrous metal powders and lead, which are used at concentrations of 50-70% by weight; other factors are the toxicity of these materials and their high cost. In place of the lead-containing greases R-2, R-402, R-416, and R-II3, the S. Shaumyan St. Petersburg Experimental-Commercial Petroleum Oil Plant, in cooperation with the All-Union ScientificResearch Institute of Drilling Equipment and the All-Union Scientific-Research and DesignTechnology Institute of the Pipe Manufacturing Industry, has developed thread compounds known as Rez'bol, grades 0 and B, with a zinc filler (Specification TU ]8.30108--88). However, any expansion of the production of these greases is also being held back by the shortage and high cost of the zinc powder. At the Ivano-Frankovsk Institute of Oil and Gas, Series GS thread compounds have been developed. These greases are based on an alkylresorcinol epoxy-phenolic resin, which is a negative factor in the volatility and stability of the greases, creating problems when they are used in joints that must be later disassembled. Also, the Series GS lubricants have a low level of tribotechnical properties [i0]. At the MASMA Scientific-Research Institute of the Petroleum Industry, two thread compounds have been developed: the hightemperature grease Burenol 250 and the hydrogen sulfide-resistant grease ~nkatol S. The Burenol 250 is intended for use on drill pipe tool joints in ultradeep drilling; the Enkatol S is intended for use on tubing in drilling and production operations in wells containing hydrogen sulfide. The new greases have been tested and approved under oil field conditions. The development of thread compounds is carried out by empirical methods without any investigation of the lubricating mechanism, since no specialized methods are available for the evaluation of these properties. Outside the CIS, studies have been made of certain features of thread compounds with lead and zinc fillers [Ii]. These two fillers differ substantially in physical and mechanical properties (Table 2), and hence the compounds based on these fillers also exhibit differences. 629

TABLE 2 Index s~rue of crystal cture

I

Zinc

Close-packed hexagonal

I

Lead

Face-centered cubic

Ultimate tensile 20 000 strength, Pa'6890" Yield strength, 15000 Pa'6890~ Type of fracture Brittle surface Elongation, % 5--I0

1800 800 Viscous 50

*Recalculated from values in pounds. TABLE 3

Service characteristic

Required value

Thread compound based on indicated metal zinc I lead (50%) (60%)

Stress level in tool Notgreaterthan420,29 joint (70%)*, MPa 413,4 Angle of rotation in Less than 32 30 tightening (70%)*, deg Resistance to additional Greater than 2924 tightening within well 2720 (50%)*, N'm

358,28 25 3060

*Fraction of torque reltive to yield point in torsion. Lead is a soft, malleable metal with a low melting point (327~ when a threaded joint is being tightened, lead particles may become interconnected by cold-welding. As a result, a thin but extremely effective metallic seal consisting of lead particles is formed on the face of the thread. Lead is not cold-welded to steel, and this protects the thread surfaces against wear. The lead particles manifest a high degree of plasticity in their functioning on the thread face. Particles of a second phase are added to the compound so that the sealing interlayer that is obtained will not be too thin. In lead'base thread compounds, the second phase may consist of oxides of other elements. The particles of the second phase strengthen the lead seal and greatly increase its resistance to tightening of the joint within the well. Zinc, as a consequence of the features of its crystal structure, is deformed nonuniformly, as a brittle solid with abrupt slipping; this may lead to sealing that is not completely satisfactory, and also (as a consequence of the ability of the crystals to slip) to degrees of tightening that are greater than required. Moreover, the zinc particles are far harder and stronger than the lead particles, and hence far greater forces are required to crush the zinc particles. Under certain conditions of deformation, zinc is capable of cold-welding to steel, and thiS will give increased wear. In Table 3 (based on the data of [ii]) we have listed the service characteristics of thread compounds with 60% lead or 50% zinc. It will be seen that the lead-based compound, in comparison with the zinc-based compound, has a smaller degree of tightening for the same torque; also, it creates a lower level of stress in the threaded joint, and is more resistant to tightening within the well. In studying the mechanism of the lubricating action of these compounds, we tested threaded joints on oil-well tubing for wear and tightness of sealing. The tubing size was 73 x 5.5 mm, strength group D, triangular threads (GOST 633--80). After applying the compounds R-402 and Enkatol S, the joint was tightened with a torque of 1500 N'm. The joints were checked for wear after 7, 14, and 21 cycles of making and breaking the joints. After each cycle, the joints were tested for tightness under an internal liquid pressure of 46 MPa and an internal gas pressure of 42 MPa. All of the joints remained pressure-tight.

630

TABLE 4 Index

IArmatol 238 Lubritol

9Lubricating properties (GOST 9490--75, four-ball tester) seizure load, N 890 weld load, kN 5,3 scoring index 76 wear scar diameter (ram) in l-h test with indicated load, N 0,9

0,8

1,9

1,2

680 1350 3000

175 250 410 710

400 , I000

Apparent viscosity (Pa'sec) with mean rate of shear i0 sec-s at indicated temperature, ~ --10 --20 --30 --40

1600 5,6 78

Not pump-

able I La

a

Fe

Fe

10 /C b

b

C

~b

O a

c

Fe o

c

[ #

0

2

4

6

~, rain

0

2

#

6

Fig. 2. Variation of chemical composition through thickness of surface layer of threaded joints on oil-well tubing, with the following thread compounds: a) none; b) Enkatol S; c) R-402; I, II, III) lightly, moderately, and heavily loaded zones, respectively. An analysis of the surface layer after seven test cycles (Fig. 2) showed that the introduction of the compound into the loaded zone (second to third turn of the thread) resulted in the formation of a surface layer in which the content of oxygen dropped off smoothly with increasing distance from the surface. For the specimen without any compound (Fig. 2a), we typically found a sharp decrease in the oxygen content at a depth of about 300 nm. This indicates that a thin film of iron oxides is formed on the surface of the thread. As the change was made from no thread compound (in air) to ~nkatol S to R-402, the thickness of the oxygen-containing layer decreased from 300-400 to 150-200 nm. After the test with the Enkatol S (Fig. 2b), the spectrum of the surface layer showed splitting of the carbon peak that is characteristic for iron carbide of the Fe2C type, and a corresponding

631

depth of 150-200 nm. For the specimen tested with the compound 5-402 (Fig. 2c), we noted the formation of a discontinuous surface film containing zinc and lead, as well as a decrease of the thickness of the oxygen-containing layer in the zones of the film. Also noted in these zones was a minimal carbon content and a sharp decrease of the carbon content with increasing depth from the surface. Investigation of the thread surfaces in the moderately loaded zone showed a sharp decrease of thickness of the oxygen-containing layer (to 50-150 nm), the absence of carbide formation for the Enkatol S, and the absence of films of soft metals for the R-402 compound. The thickness of the surface oxygen-containing layer on the specimen with the Enkatol S compound was 2.5-3 times that on the specimen with the R-402 compound, and the thickness reached its greatest value (150 nm) on the specimen without any thread compound. In the most lightly loaded zone of the thread, the chemical composition and thickness of the surface layer were practically independent of the type of compound that was used. An increase in the number of make-break operations to 14 gave very little change in the basic trends of the influence of the medium on the formation of surface structures or on the morphology. In the hevily loaded zone of the thread with the Enkatol S compound, the thickness of the surface layer that was enriched in carbon and oxygen increased to 500 nm; in the zone of the moderately loaded turns of the thread, the thickness of the carbide layer increased, and a carbide interlayer appeared. The thickness of the surface layer also increased in the lightly loaded zone of the thread. In the heavily loaded zone with the R-402 compound, we noted the formation of islandlike films containing zinc and lead; the thickness of the oxygen- and carbon-containing layer on the sections that were free of the light metal films reched a level of 500 nm; at a depth of about 200 nm, an iron carbide was formed. In the zone of the soft metal films, the thickness of the oxygen-containing layer was no greater than 150 nm, and hardly any carbon was present. These relationships remain the same when the number of tests was increased to 21. The results from our investigation of the mechanism of lubrication by thread compounds are in good agreement with data reported in [12] from tests on threaded pipe joints for durability and life; on this basis, we can reevaluate the role of these compounds in pipe service. Greases for fittings used on oil and gas field equipment are produced by the St. Petersburg Experimental-Commercial Petroleum Oil Plant. The grease LZ-162 is used in oil and gas well fittings, including service in deep and superdeep wells, with bottom-hole pressures up to i00 MPa [13]. For service in oil and gas fields in which the well product has high contents of hydrogen sulfide and carbon dioxide, this same plant, in cooperation with the Azerbaidzhan Scientific-Research Institute of Petroleum Machinery Construction and the MASMA Scientific-Research Institute of the Petroleum Industry, has developed two seal lubricants: Armatol 238 for Christmas tree assemblies and Lubritol for lubricator equipment used in sealing wellheads. In Table 4 we have listed certain tribotechnical and low-temperature characteristics of these greases in their hydrogen sulfide-resistant versions. This group of seal lubricants does not cover all service conditions for all types of oil and gas field fittings. This statement applies equally to other groups of lubricants for oil and gas field equipment. Future developments will be aimed at searching for promising types of raw material, developing special methods of quality evaluation, preparing greases for various service conditions and types of oil and gas field equipment, and organizing the manufacture of these lubricants. LITERATURE CITED i.

2. 3. 4. 5.

632

A. S. Gubarev, I. A. Lyubinin, V. V. Poletukha, et al., Neft. Prom. Neftegaz. Geol. Geofiz. Burenie, No. 1, 52-53 (1985). I. A. Lyubinin, A. S. Gubarev, V. A. Oparin, et al., Ekspress Inform. (TslNTlkhimneftemash, Moscow), Ser. KhM-3, No. 4 (1984). I. A. Lyubinin, A. S. Gubarev, and A. V. Kivva, Ekspress Inform. (TslNTlkhimneftemash, Moscow), Ser. KhM-3, No. 5 (1985). I. A. Lyubinin, A. S. Gubarev, and M. B. Nakonechnaya, Neftepererab. Neftekhim. (Kiev), No. 25, 64-66 (1983). I. A. Lyubinin, M. B. Nakonechnaya, A. S. Gubarev, et al., Neftepererab. Neftekhim. (Moscow), No. 8, 12-14 (1984).

6. 7. 8. 9. i0. ii. 12. 13.

G. M. Fain, V. F. Shtamburg, and S. M. Danelyants, Light Alloy Oilfield Pipe [in Russian], Nedra, Moscow (1990). L. A. Lachinyan, Drill Stem Operation [in Russian], Nedra, Moscow (1979). S. F. Bilyk, Tightness of Seal and Strength of Conical Threaded Joints of 0ilfield Tubing [in Russian], Nedra, Moscow (1981). I. G. Fuks and V. V. Vainshtok, Seal Lubricants [in Russian], TsNIIT~neftekhim, Moscow (1968). N. A. Severinchik and E. V. Ludchak, Obzor. Inform. VNIIOENG, Moscow (1990). R. D. Prengaman, "Making the right connection -- a comparison of zinc and lead thread compounds," Drilling (Preprint), p. I0 (1985). V. F. Shtamburg, G. M. Fain, S. Mo Danelyants, et al., Aluminum Alloy Drill Pipe [in Russian], Nedra, Moscow (1980). V. V. Sinitsyn, Lubricating Greases in the USSR [in Russian], Khimiya, Moscow (1984).

USED LUBRICANTS AND ECOLOGICAL PROBLEMS UDC 502.55:665.6

A. Yu. Evdokimov, A. A. Dzhamalov, and V. L. Lashkhi

Our planet is undergoing a severe ecological crisis. The consequent problems include not only how to prevent the destruction of contemporary civilization, but also how to preserve mankind as a biological species [i]. In the onset of this crisis, used lubricants (ULs) play a role that is by no means the least important. Every year, the worldwide discharge of petroleum products to the biosphere is approximately 6 million tonnes, of which more than 50% consists of ULs [2-5]. The ecologically dangerous components of both commercial lubricants and used lubricants are the polycyclic aromatic hydrocarbons (PAHs) that are originally present in crude oil; polyhalobiphenyls, mainly polychlorobiphenyls (PCBs) of anthropogenic origin; sulfur- and chlorine-containing additives; a number of biocides; organic compounds of metals (lead, barium, antimony, zinc); and nitrites. These substances are distributed in the atmosphere, water, and soil, entering the food chain and appearing in foodstuffs. Moreover, hydrocarbons of petroleum and synthetic oils with a low degree of biodegradability (10-30%) accumulate in the environment and may shift the ecological equilibrium (accelerated multiplication and mutation of microorganisms that assimilate petroleum products). Environmental pollution by ecologically hazardous UL components is taking on a global character. Little is known about the true dimensions of such pollution, mainly because of the isolation and demarcation of different fields of knowledge: chemistry, biology, ecology, medicine. Specialists in one field are sometimes very poorly informed on the factural material that has been accumulated in other fields. Also, insufficient attention is given to questions of ecology in the modern educational system. Lack of knowledge gives a misleading picture of the ecological equilibrium on the planet. The situation that we have described is characteristic not only for the developing countries, but also for highly developed countries. Atmospheric pollution results from UL evaporation and particularly combustion. Toxic components are carried with clouds throughout the entire planet, thus leading to global pollution. When used oils enter the soil, so-called oil lenses are formed. The character of spreading of UL components from these lenses is determined by the soil structure and the presence of ground water in which these components are dissolved and migrate. Polluted ground water is one of the basic sources of pollution of surface water. In addition, surface waters are severely contaminated by regular operations of river ships and seagoing vessels. About 85% of the total volume of pollutants comes from small "chronic" leaks and spills, and only some 15% from major catastrophes [6].

I. M. Gubkin State Academy of Oil and Gas (GANG). GNIIKh. Tekhnologiya Topliv i Masel, No. ii, pp. 26-30, November, 1992. 0009-3092/92/1112-0633512.50

Translated from Khimiya i

9 1993 Plenum Publishing Corporation

633