Energy & Fuels 2007, 21, 1741-1759
1741
Characterization of Sodium Emulsion Soaps Formed from Production Fluids of Kutei Basin, Indonesia Darrell L. Gallup* and Joseph A. Curiale CheVron Corporation, 14141 Southwest Freeway, Sugar Land, Texas 77478
P. Colin Smith Oil Plus Ltd, Hambridge Road, Newbury, Berkshire, RG14 5SS, United Kingdom ReceiVed May 2, 2006. ReVised Manuscript ReceiVed NoVember 20, 2006
Crude oils, produced waters, and emulsions retrieved from the Kutei Basin of Indonesia have been examined by a variety of analytical techniques to understand soap-formation mechanisms and origins of reactants. Crude oils contain long-chain, n-alkanoic or slightly branched monocarboxylic acids, which primarily have a landplant origin. Although the crude oils may contain up >1000 ppmw of carboxylic acids, the total acid number (TAN) is anomalously low (∼0.5 mg KOH/g, on average). Traces of mononaphthenic, bicyclonaphthenic, alkyl benzoic, diprotic, and tetraprotic acids are detected in some Kutei Basin oils. The oils and acids therein are significantly different from oils that have a marine algal origin, which, in certain areas of the world, contain high TAN values and concentrations of naphthenic acids synthesized by microbial biodegradation. The naphthenic acids combine with calcium in produced waters to form calcium naphthenates. Produced waters are enriched in sodium bicarbonate (NaHCO3), as a result of the decarboxylation of volatile fatty acids. When the pH of produced water exceeds a value of ∼6.2, NaHCO3 reacts with the carboxylic acids in a saponificationlike reaction to form interfacial sodium carboxylate soap emulsions. These emulsions may be stabilized by formation flour (reservoir formation of fine particulates of rock, such as quartz sand, silts, and aluminum silicate clays (for example, allophanes)), scale/corrosion debris, and high-molecular-weight acids. The Kutei Basin soap emulsions are resolved by heating and treatment with relatively high dosages of acid demulsifiers.
1. Introduction and Background Among the most challenging and potentially devastating forms of flow assurance problems faced by many oilfield operators today are a class of deposit-forming materials known as soaps. Two main types of soaps can form in production fluids:1 calcium naphthenate scales, which can manifest as in situ sticky or hardened deposits, and sodium emulsion soaps, which can create severe oil dehydration problems and lead to excessive slop oil/sludge volumes at crude-oil terminals. This paper concentrates on the latter type of soap, the sodium emulsion soap, which is common to fluids produced from the Kutei Basin of East Kalimantan, Indonesia (see Figure 1) and forms the main focus of this paper. Similar sodium carboxylate soaps are also common to other basins around Borneo (e.g., Sarawak, Brunei, and Sabah)2 and in other parts of southeast Asia (e.g., the South China Sea, Malaysia, offshore Vietnam, Bohai Bay in China, and elsewhere in Indonesia). While focusing on the emulsion soaps and the types of fluids that tend to create them, some comparisons will be made to the other main soap type, namely calcium naphthenate, and the fluids that tend to generate them. Since 2001, many papers have been published that detail the different types of production processing problems caused by * Author to whom correspondence should be addressed. E-mail:
[email protected]. (1) Turner, M.; Smith, C. P. Controls on soap scale formation, including naphthenate soapssdrivers and mitigation. Presented at the Seventh International Symposium on Oilfield Scale, Aberdeen, U.K., May 11-12, 2005, Paper No. SPE 94339. (2) Curiale, J.; Lin, R.; Decker, J. Org. Geochem. 2005, 36, 405-424.
oilfield soaps, and discuss the various methods used for soap mitigation and control.1,3-10 An important area of interest is the source of these soaps, which is thought to be precursor organic acids in crude oils. An understanding of the source rocks that generate oils prone to forming soap emulsions would be beneficial, as would an understanding of how different oils yield different soap types. We have analyzed a set of oil, water, and soap samples from the Kutei Basin over the last 10 years. These analyses have resulted in geochemical data that provide clues (3) Rousseau, G.; Zhou, H.; Hurtevent, C. Calcium Carbonate and Naphthenate Mixed Scale in Deep Offshore Fields; Society of Petroleum Engineers, 2001, Paper No. SPE 68307. (4) Gallup, D. L.; Smith, P. C.; Chipponeri, J.; Abuyazid, A.; Mulyono, D. Formation and Mitigation of “Metallic Soap” Sludge, Serang, Indonesia Field, 2002; Society of Petroleum Engineers, 2002, Paper No. SPE 68307. (5) Turner, M.; Smith, P. C. Experiences in Handling Production Fluids that Form Metallic Soaps/Naphthenate Scales, Produced Water Society 12th Annual Produced Water Seminar, 2002, Houston, TX. (6) Vinstad, J. E.; Bye, A. S.; Grande, K. V.; Hustad, B. M.; Nergard, B. Fighting Naphthenate Deposition at the Heidrun Field; Society of Petroleum Engineers, 2003, Paper No. SPE 80375. (7) Roden, J. Calcium Naphthenate Control on the Blake Field. Flow Assurance Europe; International Quality and Productivity Center (IQPC), London, U.K., 2003. (8) Gallup, D. L.; Star, J. Soap Sludges: Aggravating Factors and Mitigation Measures; Society of Petroleum Engineers, 2004, Paper No. SPE 87471. (9) Ubbels, S. J. Preventing Naphthenate Stabilized Emulsions and Naphthenate Deposits During Crude Oil Processing. In Proceedings of the 5th International Conference on Petroleum Phase BehaViour and Fouling, Banff, Canada, 2004. (10) Gallup, D. L.; Smith, P.C.; Star, J.; Hamilton, S. West Seno Deepwater Development Case HistorysProduction Chemistry; Society of Petroleum Engineers, 2005, Paper No. SPE 92969.
10.1021/ef060198u CCC: $37.00 © 2007 American Chemical Society Published on Web 05/02/2007
1742 Energy & Fuels, Vol. 21, No. 3, 2007
Figure 1. Location map of the Kutei Basin in Indonesia. The coordinates of the center of the map are ∼0° N, ∼114° E. The inset shows the position of Indonesia within southeast Asia. (Modified after Curiale et al.2)
about the source of precursor compounds that can lead to the formation of soap emulsions. Several of our results and conclusions are presented in this paper. The Kutei Basin of East Kalimantan, Indonesia is a worldclass petroleum province that has produced hydrocarbons since the late 19th century. Recoverable reserves from the basin are estimated to be 70 TCF (TCF ) trillion cubic feet) of gas and 5.4 billion barrels of oil. These hydrocarbons are present predominantly in Miocene sands that are several kilometers thick. Hydrocarbons are sourced from coals and carbonaceous shales with kerogen assemblages derived from land plants of primarily Type III organic matter, which is a classification consistent with high ratios of pristane to phytane. In addition to the Kutei Basin, hydrocarbon liquids generated from land plant debris encased within clastic source rocks are also found in the northern Borneo Miocene sands of Malaysia2 and elsewhere in southeast Asia (see Figure 2). Gas, oil, and condensate of the Kutei Basin are characterized by their very low concentrations of non-hydrocarbon components, including sulfur, nitrogen, and metal-bearing compounds such as asphaltenes and porphyrins. API gravities of the liquids generally are in the range of 20°-50°. Wax concentrations vary significantly, from only trace levels up to ∼20%. The oils and condensates are enriched in long-chain fatty acids, which are derived from plant lipids and exhibit predominantly even-overodd (EOO) carbon number distributions.2,11 Table 1 provides identities and some concentrations of the fatty acids from samples whose locations are shown in Figure 2. (11) Lin, R.; Sailer, A.; Dunham, J.; Teas, P.; Kacewicz, M.; Curiale, J.; Decker, J. Source, Generation, Migration and Critical Controls on Oil vs. Gas in the Deepwater Kutai Petroleum System. In Proceedings of the Indonesian Petroleum Association, Thirtieth Annual ConVention & Exhibition, 2005.
Gallup et al.
Co-produced waters from the Kutei Basin are of the NaCl-HCO3-acetate type and exhibit a neutral to basic pH (see Table 2). These waters contain some of the highest bicarbonate and volatile fatty acid (VFA) concentrations encountered in the world. As a result of mixing with fatty acid-laden oils and condensates, the vast majority of the alkaline waters form emulsions stabilized by carboxylate soaps. The soaps are typically sodium salts of n-alkanoic or slightly branched fatty acids exhibiting the formula RCOONa, where R generally ranges from C16 to C34 and even-numbered hydrocarbons predominate.12 It is generally accepted that high total acid number (TAN) oils and condensates are prone to emulsification upon contact with produced waters.3 In the vast majority of published cases, calcium in produced waters reacts with naphthenic acids to form calcium naphthenates, which can have low to high interfacial activity and, therefore, can be weak to powerful emulsion stabilizers.13 The calcium naphthenate type of soap is usually quite viscous within separators. When subjected to a shutdown of surface equipment, cooling, and exposure to air, calcium naphthenates harden.1,3,6,7 Calcium naphthenate scales have been reported in produced oils of the North Sea, West Africa, the NW Shelf in Australia, Bohai Bay in China, and the Gulf of Mexico.1,14 A recent characterization of Norwegian calcium naphthenate deposits has led to development of the term, “ARN acids”.13 The calcium salts of ARN acids are suggested to form from tetraprotic, unsaturated cyclic acids that exhibit molecular weights as high as 1230 g/mol. As will be shown in the present study, the Kutei Basin soaps are clearly different from this material, in regard to the physicochemical characteristics, although, in some instances, traces of ARN-like soaps have been detected. However, the ARN-like soaps that have been detected in the Kutei Basin are very low in concentration and do not seem to have any significant effect on the nature of the emulsions formed. Thus, the class of soaps that form emulsions in east and north Borneo is quite different from that of the calcium naphthenates, as discussed below. 2. Samples and Analytical Methods Numerous produced or tested Miocene-reservoired hydrocarbon liquids from on-shore, shelf, and deep-water wells of the Kutei Basin were examined in the present study (see Tables 1 and 2). Analytical methods used to characterize the oils, soap emulsions, and produced waters included gas chromatography-mass spectroscopy (GCMS), gas chromatography-mass spectroscopy, using fatty acid methyl ester (GC-MS-FAME), inductively coupled plasma-atomic emission spectroscopy (ICP-AES), ion chromatography, pH, high-performance liquid chromatography (HPLC), electrospray mass spectroscopy (ESMS), ion-trap mass spectrometry (ITMS), MSSV-GC-MS, Fourier transform ion cyclotron resonancemass spectroscopy (FTICR-MS), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy coupled with energy-dispersive X-ray analysis (SEM/EDXA), X-ray diffracto(12) Gallup, D. L. Ca-Naphthenates and Metallic Soap Deposits: Formation and Mitigation. In Flow AssurancesA Holistic Approach, Kuala Lumpur, Malaysia, December 2004; International Quality and Productivity Center (IQPC). (13) Baugh, T. D.; Wolf, N. O.; Mediaas, H.; Vinstad, J. E.; Grande, K. Characterisation of a Calcium Naphthenate Depositsthe ARN Acid Discovery. Presented at the Seventh International Symposium on Oilfield Scale; Aberdeen, U.K., May 11-12, 2005, Paper No. SPE 95111. (14) Smith, P. C. Soaps (Naphthenates) Scales Management from Deepwater Flow Assurance Aspects to Oil Terminal Sludge Processing Workshop. In Flow AssurancesA Holistic Approach, Kuala Lumpur, Malaysia, December 2004; International Quality and Productivity Center (IQPC).
Characterization of Sodium Emulsion Soaps
Energy & Fuels, Vol. 21, No. 3, 2007 1743
Figure 2. Sampling locations in wells of the Kutei Basin; squares indicate wells on the continental shelf, and circles indicate wells on the continental slope. Identities of some of these locations are provided in Table 1. (Figure modified after Curiale et al.2)
metry (XRD), nuclear magnetic resonance (1H NMR and 13C NMR), and high-temperature gas chromatography (HTGC). The results of those methods that were not previously reported are provided in this paper.4 The calibrations for decanoic acid to pentatriacontanoic acid were derived from pure acids (Sigma Aldrich) chromatograms, as were the volatile fatty acids, (VFAs). One of the laboratories used to analyze the waters titrated the total alkalinity as HCO3and CO32- (CO2 alkalinity). We know that Kutei Basin waters are enriched in VFAs, which also contribute to alkalinity. A titration method has been developed to separate CO2 alkalinity from VFA alkalinity.15 However, the fatty acids are lumped together and (15) Tomson, M. B.; Kan, A. T.; Fu, G.; Wu, X.; Al-Thubaiti, M.; Kirk, J.; Martin, R.; Prukop, G.; Esra Inana, E.; Davis, S. T. Simultaneous Analysis of Total Alkalinity and Organic Acid in Oilfield Brine; Society of Petroleum Engineers, 2005, Paper No. SPE 93266.
calculated as acetic/acetate. Two other laboratories that have analyzed produced waters from Kutei Basin measured the VFAs directly by ion chromatography and speciated CO2. Instead of titrating CO2 and VFA alkalinity,15 one of the laboratories analyzed for total inorganic carbon and then converted it to CO2 alkalinity.
3. Kutei Basin Oil and Soap Characterization Results Some Kutei Basin soap characterization results have been previously reported.4,8,10,11 Generally, the results of these initial analyses showed that Kutei Basin soaps consist primarily of n-alkanoic or slightly branched sodium salts of carboxylic acids. The acids identified in the earlier studies were typically in the carbon range of C16-C36. The soaps were postulated to be formed by the acids in oil reacting with sodium bicarbonate-
1744 Energy & Fuels, Vol. 21, No. 3, 2007
Gallup et al.
Table 1. Fatty Acid Analyses of Oils, Soaps, and Sludges (from the Oil and Sludge Carboxylic Acid Database) sample S-1 S-2 S-3 S-4 S-5 S-6 S-7 S-8 S-9 S-10 S-11 S-12 S-13 S-14 S-15 S-16 S-17 S-18 S-19 S-20 S-21 S-22 S-23 S-24 S-25 S-26 S-27 S-28 S-29 S-30 S-31 S-32 S-33 S-34 S-35 S-36 S-37 S-38 S-39 S-40 S-41 S-42 S-43 S-44 S-45 S-46 S-47 S-48 S-49 S-50 S-51 S-52 S-53 S-54 S-55 S-56 S-57 S-58 S-59 S-60 S-61 S-62 S-63 S-64 S-65 S-66
C8
C9
C10
C11
C12
C13
C14
C15
C16
C17
43
present present present
0.68
1.6
0.75
present
present
9.1
0.23
1.4 0.91
0.35
oleic
C19
C20
10
25
dominant present present present
present
present
8.5 7.5
6.1 3.5
1.8 1.2
4 1.9
5 41.7
4 26.5
0.51
4.6
0.24 0.5
2 4.8 11
present present
C18 38
average
18.3 21.4 14
present
0.35
3 20 25 17 19 38 24
present
present
present
present
present
present
present
present
6.1 1.8 present 8 4
present
present
present
present
present
present
present
present
present
12.7 15.6 13 10 3 14 18 18 16 12 23 17
C21 18
2.9 1.4
10 13 21 14 12 11 24 16
present
2.5 1 present
4.9 0.6 present
present
present 5 3
present
present
present
present
present
10 17 12 9 16 10
0.7 present 4 2 present present
?
rich produced waters. As an example, the soap-forming reaction may be envisioned as
CH3(CH2)xCOOH + NaHCO3 f CH3(CH2)xCOONa + (where x ≈ 16-36) H2O + CO2v We postulated that sodium soaps of C16-C36 fatty acids form as the water pH rises during depressurization and as fluids cool. The soap-forming reaction may be driven to the left by decreasing the pH of the water, heating, and/or maintaining
0.5
pressure. Because hydrocarbon production requires depressurization and cooling, known methods for inhibiting or dissolving the soaps include acidification and heating. Soaps are a class of surface-active materials derived from natural oils and fats. Soap molecules are amphiphilic and consist of a polar headgroup and a nonpolar tail, which causes their preference for assembly into sheetlike structures, with hydrophobic groups on one side and hydrophilic groups on the other side. The curvature of the interface at which an amphiphilic molecule absorbs preferentially is dependent on temperature,
Characterization of Sodium Emulsion Soaps
Energy & Fuels, Vol. 21, No. 3, 2007 1745
Table 1 (Continued) sample
C22
S-1 S-2 S-3 S-4 S-5 S-6 S-7 S-8 S-9 S-10 S-11 S-12 S-13 S-14 S-15 S-16 S-17 S-18 S-19 S-20 S-21 S-22 S-23 S-24 S-25 S-26 S-27 S-28 S-29 S-30 S-31 S-32 S-33 S-34 S-35 S-36 S-37 S-38 S-39 S-40 S-41 S-42 S-43 S-44 S-45 S-46 S-47 S-48 S-49 S-50 S-51 S-52 S-53 S-54 S-55 S-56 S-57 S-58 S-59 S-60 S-61 S-62 S-63 S-64 S-65 S-66
37
C23 25
C24
C27
C28
C29
C30
33
105
27 present
65 dominant
27 present
39 dominant
6.5 1.8 5.3 4.9
5 2.2 3.7 3.8
present 106 86 11.5 4.5 6.6 8.4
present 57 41 7.9 6 4.4 5.3
present 269 204 14.2 7.6 7.5 16.9
present 112 90 7.6 5.6 6.7 8.7
average 686 515 14.2 7.5 8.4 24.5
1.5 11 0.51 1.2 21 49
0.54
15
50
43
34 72 32 43
35 74 49
85
C25
C26
C31
C32
C33
C34
total 496
present
4.6 1.4
4.1 1.4
2.5 7 0.83 1.8 11 18
0.51
21 42 22 19 11 37 24
16 33 17 16 11 27 16
48 117 42 48 20 98 55 18
18 42 19 22 31 20
51 118 40 58 23 88 59
present 15 7 present present
present 12 5 present present
present 64 25 present present
present 22 10 average present
dominant 99 39 present dominant
0.29 0.48 14
30 moderate moderate
minor
91 major major major 1403 1587 1806
21
moderate 1110 1506 1201
present 170 165 7.8 5.9
present
present
present
6.5
