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21Chemical Journal of Kazakhstan
ISSN 1813-1107, elSSN 2710-1185 https://doi.org/10.51580/2021-1/2710-1185.28
Volume 2, Number 74 (2021), 60 - 71
UDC622.276.72
PREVENTION OF INORGANIC SCALE FORMATION IN THE UZEN AND ZHETYBAI FIELDS BY USING OF SALT DEPOSITION INHIBITIORS
A.O. Tarbanov 1, A.T. Khabiev 1, Ye.O. Ayapbergenov 2'
1Satbayev University, Almaty, Kazakhstan 2Branch of KMG Engineering LLP "KazNIPImunaygas", Aktau, Kazakhstan * E-mail: ayapbergenov_e@kaznipi.kz
Abstract: Development of the oil industry in Kazakhstan at the current stage is characterized by a decrease in the quality of the raw material base. In the total balance of fields under development, the fields that have entered the late stage of development prevail and, consequently, there is a significant deterioration in their structure, an increase in the share of hard-to-recover oil reserves, watering of beds and well production.One of the main challenges during the development of the field is the deposition of inorganic salts in the oilfield equipment.
This article describes the main reasons for the formation of solid inorganic deposits in oil fields, methods of scale inhibitors, as well as the classification of scale inhibitors. Presents the physical and chemical characteristics of the objects under study: the properties of oils and watersof Uzen and Zhetybai oil fields and the chemical reagents -inhibitors of scale formations.
Based on the results of laboratory studies, scale inhibitors were selected, which showed high efficiency (90 - 100 %) to prevent the precipitation of CaCO3, CaSO4 and BaSO4 under the conditions of Uzen and Zhetybai oil fields.
The study was conducted in the center of scientific and laboratory research branch of KMG Engineering LLP "KazNIPImunaygas".
Keywords: scale inhibitor, inhibiting efficiency, compatibility, deposit. 1. Introduction
The Mangistau region is one of the largest oil regions in Kazakhstan. The oil fields Zhetybai and Uzen are located in the Mangistau region, 80 - 150 km southeast of Aktau [1, 2].
Citation: A.O. Tarbanov 1, A.T.Khabiev 1, Ye.O.Ayapbergenov. Prevention of inorganic scale formation in the Uzen and Zhetybai fields by using of salt deposition inhibitors. Chem. J. Kaz., 2021, 2(74), 60-71. DOI: https://doi.org/10.51580/2021-1/2710-1185.28
Oils of Uzen and Zhetybai fields are characterized by low values of density 0.85 - 0.87 g/cm3, high content of paraffin hydrocarbons, which vary depending on horizon in the range of 17 - 26 % wt. and asphaltene-resinous substances up to 20 % wt. It has caused a number of specific characteristics of oils of the given fields: high solidification temperature (26 - 35 °C), increased viscosity, etc.
As it is known, oil production is accompanied by formation of solid inorganic deposits (SSI), the main reason of formation of which is formation water, extracted together with oil. Along the whole period, development of Uzen and Zhetybai fields was carried out with reservoir pressure maintenance by injecting water of different types: artesian, sea, fresh and wastewater into the formations. As well output became more watered, the volume of injected produced water increased.
Scaling usually occurs when the chemical equilibrium in a solution is disturbed, where the concentration of a particular substance or ion increases. Solid inorganic deposits thus accumulate in the bottomhole formation zone (BFZ), on the walls of production casing, in the pumping equipment and surface communications of oil gathering and treatment systems. As a consequence of salt deposition, the yield of the well decreases, the service life of the equipment is reduces, which also leads to a number of other complications in the fields [3].
The mechanism of sediment formation is quite complicated and is represented by a set of different processes. Analysis of literature sources showed [3 - 8] that the main causes for formation of deposits include:
- mixing of waters of different compositions incompatible with each other. Often, produced water contains Ca2+, Ba2+, Sr2+ cations and mixing them with injected water containing SO42- ions produces insoluble sulfate minerals such as barite, celestine, gypsum and anhydrite:
Ba2+(Sr2+, Ca2+) + SO%- ^ BaS04 I (SrS04, CaS04)
- change in thermobaric conditions, leading to the release into the gas phase of dissolved carbon dioxide, the decrease in concentration of which with increasing pH leads to a decrease in the content of carbonic acid, and as a consequence, significantly reduces the solubility of calcium carbonate CaCO3:
Ca2+ + 2(HCO-) ^ CaC03 I +C02 1 +H20
- evaporation of water by contact with heated equipment, which leads to oversaturation of fluids with poorly soluble salts and their desalinization.
The most common types of deposits in oil production and the main causes of their formation are presented in Table 1 [9].
To prevent scale formation, various techniques such as removal of formed deposits and prevention of their formation are used. The choice of the method of sediment removal is determined by the nature of salt deposits, location and composition of the deposits. Technological methods for preventing scale formation, which are used in oil production, are presented in Figure 1.
Table 1- The most common salts, and the physical conditions of their formation
Name Chemical formula Reason of formation
Calcite CaCO3 Temperature, pressure, partial pressure of CO2, total mineralization, pH
Siderite FeCO3
Anhydrite CaSO4 Temperature, pressure, totalmineralization
Gypsum CaSO4 • 2H2O
Barite BaSO4
Celestine SrSO4
Figure 1 - Techniques to prevent scale formation [10].
The most effective way to prevent salt deposits nowadays are chemical methods, in particular - the use of scale inhibitors. Figure 2 shows the classification of scale inhibitors.
Hence, for effective oil production it is extremely important to choose optimal chemical reagents to prevent salt deposits formation, taking into account the specifics of Uzen and Zhetybai fields. By-product and injected waters of Uzen and Zhetybai fields are diverse in their ionic composition and mineralization. Their physico-chemical properties and composition are presented in Table 2.
Figure 2 - Classification of scale inhibitors [11].
Table 2 - Physico-chemical properties and composition of waters of Uzen (U) and Zhetybai (Zh) fields
Oil field Water type ffi a c> B o d Concentration, g/L TDSg/L Typeaccording ToSulin
+ O + + Na o O S Ci O o ffi -a "5 <U F + S + m
U F 5.5 1.059 5.41 1.34 24.97 51.05 - 0.24 0.053 0.26 0.011 83.01 Cl-Ca
U D 6.8 1.038 2.81 0.91 16.46 32.61 - 0.42 0.005 0.17 0.014 53.21 Cl-Ca
U A 7.8 1.008 0.25 0.13 3.26 4.21 2.01 0.24 - - - 10.08 SO4-Na
Zh F 7.3 1.028 2.00 0.61 11.77 22.33 1.26 0.34 - 0.11 - 38.32 Cl-Ca
Zh A 7.6 1.008 0.40 0.12 3.60 4.83 2.26 0.20 0.001 0.021 - 11.42 SO4-Na
- S 8.1 1.009 0.40 0.73 3.40 5.67 2.77 0.32 0.006 0.006 - 13.30 Cl-Mg
Note: F - formation water: D - drainage water; A - albsenomanian water; S - seawater.
Current properties of Uzen field waters by the level of salinity, according to the classification of underground mineral waters by V.A. Sulin belong to the chloride-calcium and sulfate-sodium types. Salinity of water reaches 83 g/L at a
density of 1.059 g/cm3. The main components of water are chlorides and sodium with potassium. The content of sulfates is 2.01 g/L, carbonates are absent.
Waters of Zhetybai field according to the classification of V.A. Sulin are represented by chloride-calcium and sulfate-sodium types with a total salinity of 38 g/L and 11 g/L, respectively. They contain a significant amount of sulfate ions (up to 2.3 g/L) that can combine with calcium, magnesium and barium ions. As a result of this interaction, precipitation of insoluble salts from the formed supersaturated solutions is possible.
Selection of the most effective inhibitor for protection of equipment against salt formation was carried out within the framework of laboratory researches:
- only powdered substances and non-separated liquids are allowed as inhibitors in terms of aggregate state. The content of suspended and settled impurities in liquids is not allowed;
- The inhibitor must be fully compatible with mineralized water of Uzen and Zhetybai fields without separation and sedimentation;
- The inhibitor must be compatible with the base demulsifier. The content of salts and water must not increase when treating the oil of the field with the composition of inhibitor and demulsifier;
- the efficiency of scale inhibition must be at least 90 % of mineral salts reduction under the given conditions.
It should be noted that the research was carried out at the Scientific Laboratory Research Center of "KMG Engineering" LLP branch "KazNIPImunaigas" on the basis of the Program of work on selection of chemical reagents in the fields of JSC "Ozenmunaigas" and JSC "Mangistaumunaigas".
In the course of testing of the scale inhibitor attention was also paid to the control of its physicochemical and technological properties. In addition to high protective properties, the reagent must be adaptable and applicable to the conditions of Uzen and Zhetybai oil fields. Physico-chemical properties of the tested inhibitors were obtained according to ST RK 2498-2014 and the results are presented in Tables 3-4.
The given results demonstrate that the tested inhibitors are homogeneous liquids with acceptable values of density, viscosity and mass fraction of active substances, resistant to negative temperatures (minus 42 °C).Thus, chemical reagents meet the requirements of ST RK 2498-2014 for physical, chemical and technological properties for liquid scale inhibitors.
Laboratory tests of new reagents were carried out by a sequential determination of inhibitory properties (ST RK 2604-2015) in relation to calcium carbonate, then in relation to calcium and barium sulfate. Inhibiting efficiency of a reagent to prevent sedimentation of salts (CaCO3, CaSO4 or BaSO4) is estimated by comparing sedimentation processes in inhibited and not inhibited media (control test). The effectiveness of inhibitors is estimated by the increase in the retention (dissolving) ability of salts in water in the presence of a certain amount of inhibitor. Laboratory tests of scale inhibitors for preventing sedimentation of calcium sulfate and calcium carbonate, barium sulfate are held in artificial water,
Table 3 - Physico-chemical parameters of scale inhibitors tested in the conditions of the Uzen field
№ Reagent Appearance P (20°C), kg/m3 Mass fraction of active substance, % v (20°C), mm2/c pHof the medium
The norm according to ST RK 2498-2014 750-1400 2-60 - -
1 Uz-1 Homogeneous liquid, dark brown in color 983.5 43.1 10.7 7.7
2 Uz-2 Homogeneous, transparent, colorlessliquid 1081.5 26.9 4.1 0.9
3 Uz-3 Homogeneous, transparent, colorlessliquid 1067.6 35.9 9.1 8.1
4 Uz-4 Homogeneous, transparent, colorlessliquid 983.4 30.2 5.8 9.2
5 Uz-5 Homogeneous liquid of light yellow color 1089.1 25.4 5.3 4.5
6 Uz-6 Homogeneous liquid of pale yellow color 1086.7 29.4 8.9 7.6
7 Uz-7 Homogeneous, transparent, colorlessliquid 1011.2 14.1 3.0 9.4
Table 4 - Physico-chemical parameters of scale inhibitors tested in the conditions of the Zhetybai field
№ Reagent Appearance P (20°C), kg/m3 Mass fraction of active substance, % v (20°C), mm2/c pH of the medium
The norm according to ST RK 2498-2014 750-1400 2-60 - -
1 Zh-2 Homogeneous, transparent, colorlessliquid 1042.2 33.8 8.2 5.8
2 Zh-3 Homogeneous, transparent, colorlessliquid 986.4 27.1 8.9 9.1
3 Zh-4 Homogeneous, clearyellowliquid 1044.9 25.0 5.3 7.4
4 Zh-5 Homogeneous, transparent, colorlessliquid 1079.6 26.5 5.3 0.6
5 Zh-6 Homogeneous, transparent, colorlessliquid 1069.4 32.4 11.2 7.7
Table 5 - Evaluation of the effectiveness of scale inhibitors in the conditions of the Uzen field
№ Name Dosage, Inhibition efficiency, %
of the reagent mg/L calcite gypsum barite
10 0 0 0
15 40 23.53 19.5
1 Uz-1 20 48 35.29 23.5
25 48 35.29 31
30 48 37.65 32
50 49.6 40 32.5
10 80 81 75
15 88 90 85
2 Uz-2 20 94.4 96 91.5
25 100 100 100
30 100 100 100
50 100 100 100
10 72 71.43 60.49
15 84.8 85.71 82.93
3 Uz-3 20 89.6 88.57 89.27
25 97.6 100 97.56
30 100 100 100
50 100 100 100
10 53.33 53.12 43.51
15 66.67 62.5 52.63
4 Uz-4 20 75.56 70.31 59.65
25 77.78 71.88 70.18
30 88.89 84.37 73.68
50 94.44 92.19 80.7
10 66.67 62.5 51.67
15 72.22 71.25 70.83
5 Uz-5 20 88.89 87.5 83.33
25 94.44 92.5 91.67
30 100 100 100
50 100 100 100
10 50 48.89 45
15 50 49.11 47.5
6 Uz-6 20 75 71.11 67.5
25 77.5 75.56 72.5
30 75 73.56 67
50 47.5 46.67 46
10 50 50 50.61
15 62.5 60 69.39
7 Uz-7 20 76.25 70 74.69
25 87.5 80 81.63
30 90 90 89.8
50 92.5 92 90.2
simulating sulfate, carbonate and barium waters of Uzen and Zhetybai oil fields at 60-80 °C for 5 hours at the dosage of 5-30 mg/L. The saline solution is prepared by mixing the equivalent amounts of salt-forming ions. The research results of effectiveness of scaling inhibitors are showed in Tables 5-6.
Table 6 - Evaluation of the effectiveness of scale inhibitors in the conditions of the
Zhetybai field
Name Dosage, Inhibition efficiency, %
of the reagent mg/L calcite gypsum barite
5 75.75 74.5 70
10 88.5 86.25 86.85
1 Zh-2 15 100 100 99.26
20 100 100 99.63
30 76.6 74.1 74.07
5 66.67 65 63.4
10 83.33 82.2 80
2 Zh-3 15 86.67 85.6 83.4
20 83.33 81.7 80
30 83.33 81.6 79.62
5 43.48 42.4 38.18
10 52.17 50 46.91
3 Zh-4 15 43.48 42.2 39.64
20 43.48 42.22 39.45
30 43.48 42.24 39.49
5 86.67 84.2 81.82
10 100 98.4 97.82
4 Zh-5 15 100 100 100
20 93.33 92.6 87.27
30 80 79.6 72.73
5 79.33 78 72.73
10 89.67 89.2 86.91
5 Zh-6 15 99.67 98 97.45
20 100 100 100
30 100 100 100
Studies showed that the examined inhibitors are water-soluble, when mixed with saline waters of Uzen and Zhetybai fields at dosages of 10-90 g/L solutions are not turbid, do not form a viscous gel-like mass or solid precipitate, do not cause separation of the liquid. Based on the research results, we summarize that the inhibitors are compatible with saline waters of the studied oil fields.
The results of studies show that among the samples submitted for testing, the most effective inhibitors of scale deposition to prevent CaCO3, CaSO4 and BaSO4 are samples Uz-2, Uz-3, Uz-5 and Uz-7 with an efficiency > 90 % at the concentration of 20-30 mg/L. It was found that a highly effective inhibitor among the tested reagents is the sample Uz-2, the efficiency of which is > 90% at a specific flow rate of 20 mg/L, 100% reduction of mineral salt deposition at 25 mg/L. When compared samples Uz-3 and Uz-5 at a dosage of 25 mg/L it is revealed that the sample Uz-3 is more effective than Uz-5. The efficiency of Uz-7 at a specific flow rate of 30 mg/L is ~ 90%, which is lower than the basic reagent.
Among the samples submitted for testing, the most effective samples are Zh-2, Zh-5 and Zh-6 with an efficiency of > 90% and a dosage of 10-15 mg/L. The high efficiency is noted with the sample Zh-5, which provides 100% reduction of mineral salt deposition at 10 mg/L. The protective effect of samples Zh-2 and Zh-6 at a dosage of 10 mg/L shows < 90%, while at 15 mg/L it is ~100%. The efficiency of Zh-3 and Zh-4 at a dosage of 20 mg/L is < 90%.
To summarize, taking into account that the studied inhibitors of salt deposits are effective to prevent deposits of barium and calcium sulfate, as well as calcium carbonate, it is possible to use them:
- at the Uzen field samples Uz-2, Uz-3 and Uz-5 at dosages of 20-25 mg/L;
- at the Zhetybai field Zh-2, Zh-5 and Zh-6 at dosages of 10-15 mg/L.
In order to prevent risks of breakdown of technological processes of gathering, transportation of produced oil and oil treatment when using different types of chemical reagents introduced into "well - oil treatment" system, the demulsifying ability of demulsifiershas been defined in the presence of other chemical reagents and without them. Chemical reagents used in the field for different purposes must not worsen the demulsifying efficiency of the basic demulsifier used in the field.
To identify the possibility of combined application of reagents used in oil treatment for different purposes, studies were conducted on the mutual solubility and compatibility of basic demulsifiers of Uzen and Zhetybai fields and selected inhibitors of salt deposition. One of the ways to improve the process of collection, transportation and preparation of oil, to improve the quality of commercial oil is the use of special, selected for each field chemical reagents-demulsifiers.
According to the results obtained, the selected inhibitors and basic demulsifiers of Uzen and Zhetybai fields in different ratios are mutually soluble and with the lapse of time changes are not observed, and also at combined injection into the initial water-oil emulsion no negative impact on the process of oil dehydration is observed.
Information about authors:
Tarbanov A.O. - PhD student; e-mail: ato441@mail.ru; ORCID ID: https://orcid.org/0000-0002-7955-5302
Khabiyev A.T. - Doctor Ph.D., Assoc. Professor; e-mail: a.khabiyev@satbayev.university; ORCID ID: https://orcid.org/0000-0001-9397-2367
Ayapbergenov Y.O. - Head of laboratory of oilfield chemistry; e-mail: ayapbergenov_e@kaznipi.kz; ORCID ID: https://orcid.org/0000-0003-3133-222X
References
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Тушндеме
вЗЕН ЖЭНЕ ЖЕТ1БАЙ КЕН ОРЫНДАРЫНДА Т¥З ЦАЛДЬЩТАРЫНА ЦАРСЫ ИНГИБИТОРЛАРДЫ ЦОЛДАНУ АРЦЫЛЫ БЕЙОРГАНИКАЛЬЩ ШвПНДШЕРДЩ ТУЗ1ЛУШЩ АЛДЫН АЛУ
А.О. Тарбанов1, д.Т. Хабиев1, Е.О. Аяпбергенов2
1Satbayev University, Almaty, Kazakhstan
2Branch of KMG Engineering LLP "KazMPImunaygas", Aktau, Kazakhstan *E-mail: ayapbergenov_e@kaznipi.kz
БYгiнгi танда Казакстандагы м^най-газ кен орындарында вндiрiлетiн шиш-заттын сапасы твмендеуде. Колданыстагы кен орындарынын квпшiлiгi шик1зат вндiрудiн сонгы сатысында, осыган байланысты геологиялык к^рьшымньщ нашар-лауы, киын вндiрiлетiн м^най корынын всуi, кабаттар мен ^нгымалардагы внiмнiн сулануы артуы байкалуда.
Макалада м^най кен орындарында тYзiлетiн бейорганикалык катты швпн-дiлердiн тYзiлу себептер^ олардын алдын алу эдiстерi мен т^з швгiндiлерiне карсы колданылатын ингибиторлардын тYрлерi карастырылган. Зертелетiн объектiлердiн физикалык-химиялык сипаттамалары, ягни взен жэне Жепбай кен орындарынын м^найы мен суынын жэне химиялык реагенттердiн сипаттамалары келпршген.
Зертханалык ж^мыстар нэтижесiне CYЙене отырып, т^з калдыктарынын тYзi-луiнiн алдын алуда колданылатын ингибиторлар тандалды. Олар взен жэне Жеть бай кен орындары жагдайында СаСО3, CaSO4 жэне BaSO4 т^здарынын тYзiлуiнiн алдын алуда 90-100% нэтижелшпн кврсеттi.
Зертханалык ж^мыстар ЖШС «КазМ^найГаз Инжиниринг» филиалы «КазГЗЖИм¥найгаз»-дын гылыми-зертханалык зерттеу орталыгында жYргiзiлдi.
Тушн свздер: т^з калдыктары тYзiлуiнiн алдын алуга арналган ингибиторлар, ингибиторлеу касиеп, YЙлесiмдiлiк, швгiндi.
Резюме
ПРЕДУПРЕЖДЕНИЕ ОБРАЗОВАНИЯ НЕОРГАНИЧЕСКИХ ОТЛОЖЕНИЙ НА МЕСТОРОЖДЕНИЯХ УЗЕНЬ И ЖЕТЫБАЙ С ИСПОЛЬЗОВАНИЕМ ИНГИБИТОРОВ СОЛЕОТЛОЖЕНИЙ
А.О. Тарбанов1, А.Т. Хабиев1, Е.О. Аяпбергенов2
1Satbayev University, Алматы, Казахстан
2Branch of KMG Engineering LLP "KazMPImunaygas", актау, Казахстан *E-mail: ayapbergenov_e@kaznipi.kz
Освоение нефтяного промысла Казахстана на текущей стадии сопровождается снижением качества сырья. Среди всех эксплуатируемых месторождений превалируют месторождения, перешедшие на поздний этап разработки, и, как следствие, отмечается значительное ухудшение их геологической структуры, увеличение доли трудноизвлекаемых запасов нефти, обводнение пластов и скважинной продукции.
В статье рассматриваются основные причины образования твёрдых неорганических отложений на нефтяных месторождениях, методы борьбы, а также класси-
фикация ингибиторов солеотложений. Приведены физико-химические характеристики исследуемых объектов: свойства нефти и воды месторождений Узень и Жетыбай, химических реагентов.
По результатам лабораторных исследований подобраны ингибиторы солеотложений, показавшие высокую эффективность (90 - 100 %) для предупреждения выпадения осадка СаСО3, СаБ04 и BaSO4 в условиях месторождений Узень и Жетыбай.
Работа была выполнена в центре научно-лабораторных исследовании Филиала ТОО «КМГ Инжиниринг» «КазНИПИмунайгаз».
Ключевые слова: ингибитор солеотложений, ингибирующая способность, совместимость, отложение
