CC BY
6UDC 622.245.54
IRSTI 52.47.27
DOI 10.56525/CBZE7367
EFFICIENCY ESTIMATION OF
HYDRAULIC FRACTURING AT
OIL DEPOSIT
*BISSEMBAYEVA K.
Caspian university of technology and
engineering named after Sh. Yessenov
Kazakhstan, Aktau
E-mail: karlygash.bissembayeva@yu.edu.kz
DZHALALOV G.
Institute of Oil and Gas under the
Ministry of Education of Azerbaijan, Baku
E-mail: dzhalalovgarib@rambler.ru
SABYRBAYEVA G.
Caspian university of technology and
engineering named after Sh. Yessenov
Kazakhstan, Aktau
E-mail: gulzhan.sabyrbayeva@yu.edu.kz
*Сorresponding author: karlygash.bissembayeva@yu.edu.kz
Abstract. As the practice of developing hydrocarbon deposits has shown, during the extraction of oil from multi-layer deposits, as a result of numerous hydrodynamic and geological-geophysical studies, separate sections of formations with more homogeneous structures are identified. In most cases, such formations, as shown by the results of the analysis of the state of development of deposits, turn out to have sufficiently low filtration and capacitance properties (porosity and permeability), while increasing the amount of hard-to-recover oil reserves. This circumstance of deposits worsens the state of the degree of efficiency of the production of hydrocarbon reserves from multi-layer deposits. In this regard, in order to increase the efficiency of the oil field development process, in practice, various measures aimed at intensifying the extraction process from low-productive intervals-formations are very often used. One of the active methods that allow the most complete displacement of oil from the productive reservoir is hydraulic fracturing.
In the article we considered one of the most common methods to increase the productivity of wells, opening up low-permeable reservoirs – hydraulic fracturing (HF). Authors obtained new improved formulas to determine the radial and tangential strains, and the radius of load with the plasticity of the porous medium, and flow rates in the formation of horizontal and vertical cracks.
The results of calculations, conducted on the example of Karakuduk field, showed that fracturing occurs at the average pressure of fracturing fluid injection. The results of the HF showed different effects in different wells
The relationship is constructed to establish the nature of flow rates growth change from the fracture length.
Keywords: Well; bed; productivity; hydraulic fracturing, fracture; pressure; oil saturation; technological effect, permeability; flow rates; influence; development; formation.
Introduction. Recently, most oil fields enter in the last stages of development, characterized by low flow rates of wells and high water cutting. The state analysis of oil fields development shown that the last stage of oil-saturated formations have low permeability and they are drained poorly. This problem is aggravated by the fact that new oil deposits have beds with the beds, which are characterized by low-productive parameters and complex geological structures [1,2]. In this connection, different methods are used to improve the oil displacement process from complex structured formations with low-productive characteristics. One of these methods is the hydraulic fracturing (HF) [3].
According to the technology, fluid is pumped into the gap under high-pressure during hydraulic. The pressure created at the bottom, with which fluid is injected – is injection pressure. After bed fracturing liquid with sand are injected for fixing cracks.
The mechanism of cracks creation is the main part of the formation hydraulic fracturing. It is conducted as follows. Rocks have natural micro - fractures that are compressed under the influence of the weight of the overlying rocks or rock pressure. The permeability of such fractures is small. All solids have some strength. Therefore, it is necessary to remove stress generated by the rock pressure in the slides for new fracturing and expansion of existing fractures. Also it is needed to overcome the strength of solids on the gap.
Fracturing pressure is inconstant even within one formation and it may be varied widely. Practice confirmed that in most cases the bottom-hole fracturing pressure Pf is lower than mountain and is equal (15 ... 25) * H, kPa (1.5 ... 2.5 kgf/cm2) (where H - well depth, m ) [2]. For low-permeable rocks, this pressure may be achieved during injection of low-viscous fluids of fracturing with limited rates of injection. If the rocks are high-permeable, the high rate of injection is required and it necessary to use liquid of high viscosity at limited rate of injection. Finally, great rates of high-viscous liquids injection should be used to achieve fracturing pressure in the case of very high permeability of the reservoir .
As previously mentioned, recently HF is made in formations with different permeability in the case of decrease of the flow rate or injectivity of injection wells.
To make hydraulic fracturing and correctly simulate the further process, flow test is done in the well. Wherein absorptivity and injection pressure are defined. Thus, during injection pressure increase , flow rate is measured until creation of maximum pressure.Then inectivity influences plots on injection pressure are made.
Amount and pressure, required for fracturing, are determined according tofluid absorbency of the well before and after the fracturing. For fracturing pressure they conventionally take the pressure at which the injectivity coefficient is increased by 3-4 times in compare with initial. [4]
It is necessary to clean critical area of formation (skin factor is negative) to reduce the injection pressure and fracture pressure.
Hydraulic fracturing (HF) is one of the most effective methods to improve the productivity of wells, opening up low-permeable, weak drainable collectors. HF is also used in the early stages of the field development.
Rock permeability is enhanced by artificial increase of the channels number and increase of rocks. Hydraulic fracturing is made in the wells of following categories: new wells with weak flow of oil during testing; wells with high reservoir pressure, but with low-permeability of beds; well with contaminated near well zone; wells having low flow rate; wells with high gas factor, but without gas breakthrough from the gas cap or gas reservoir; injection wells.
It was found that the best results of hydraulic fractures are obtained on beds with high pressure, with a less degree of drainability and having higher oil saturation, depletion of recoverable stocks which, as a rule, should not exceed 30% [3].
It is known that HF is primarily made in the wells, the productivity of which is lower than the surrounding wells. If the capacity of low rate wells due to the lack of formation energy, the fracturing is performed primarily in injection wells.
The maximum technological effect of hydraulic fracturing is provided by: a) the maximum width of cracks created in the formation; b) crack spread through the bed at maximum distance from the bottom of the well; c) the creation of cracks in the most productive area of the reservoir [5]. Hydraulic fracturing may create fractures of varying spatial orientation: horizontal, vertical or inclined.
Practice has shown that the fracture at hydraulic fracturing will be directed along the normal to the lowest stress. Because of this, cracks are vertical in almost all cases encountered in the development of oil fields [6]. This fact can be proved by the following example: pipe are usually broken along not across under high internal pressure. According to this idea cracks should be vertical. Vertical fractures naturally coincide with the flat of the crack.
Creation of horizontal cracks at depths greater than 600 m is the process more time-consuming and it involves the creation of large fracturing pressure. If there are horizontal cracks in the multi-layered oil reservoir, separated by impermeable layers, there is a serious problem of losing significant part of oil reserves in other neighboring oil-layers, unaffected by hydraulic fracturing [6]. Although cracking, their efficiency depends on their size. Here the parameters have different effects on the increase of flow rates. In this regard, we consider below the influence of the size of vertical and horizontal fractures in the process of oil production.
It is known that the reservoir is subjected to the deformation process during its operation due to the weight of the overlying rock at particular output of fluid from the reservoir. On the basis of studies carried out in work [3], it is found that the deformation processes lead to the emergence of the plasticity of the rock skeleton.
Materials and methods of research. The research was carried out on the example of the Karakuduk deposit (Kazakhstan). The tasks were solved comprehensively on the basis of modern ideas about the structure of complex deposits and mathematical modeling of the development process. Methods of statistics, probability theory, and experimental studies in field conditions were used.
According to research conducted by professor A.U.Aitkulov [3], we obtained new improved formulas to determine the radial ( ) and tangential ( ) strains, and the radius of load ( )with the plasticity of the porous medium, and flow rates in the formation of horizontal and vertical cracks, which have the following form:
(1)
(2)
(3)
Where и –respectively pressure on the counter of formation and at well bottom, MPa; – the difference between the vertical rock and hydrostatic pressure, MPa.
(4)
Where ; (5)
q –well flow rate,with horizontal crack m3/sec, К1and К2 - respectively permeability of porous medium and crack, m2, С - the coefficient showing the hydrodynamic well imperfection on degree and nature of the opening up; –.coefficient indicating change character of the formation hydraulic conductivity; - fluid viscosity, mPa*seс.
(6)
The results. The results of calculations, conducted on the example of Karakuduk field, are given at the table 1. They showed that fracturing occurs at the average pressure of fracturing fluid injection, which are ranged from 20 to 30 MPa.
From the table it is shown, that even in the well, in which the crack length is minimal from all fractures, flow rate increased by 6 times. In this case, the water cut is increased by 2 times, the effect lasted for 199 days, after which the flow rate began to decline. This fact can be explained by beginning clamping cracks formed due to the weight of the overlying rock. Assessing the conducted operations, we can say that water cut was increased slightly, wherein the effect is continued in six wells in which hydraulic fracturing is made. The efficiency duration was 265 days and flow rate was increased by 28,8 t/day in average.
Hydraulic fracturing was made in six producing well №№5, 107, 114, 155, 194, 200 (horizons Ю -I and II to further intensify production of crude oil from the beds of Karakuduk deposit (tables 1 and 2). All operations were conducted with application of gel solution made on water bases. Proppant Borovichi 16/30 was used as propping Gelling agent - J424, clay stabilizer - L55, bactericide - M275, surface active agent (SAA) - F103 and other additives were used in the preparation of the gel. The average speed of injection fluids was 1.3-3 m3/min.
The results of the HF showed different effects in different wells. For example, in well 5 flow rate increased by 25 times at maximum pressure from all of fracturing (table 2). After the effect of the method was stopped the well was transferred to injection wells.
The maximum duration of effect was noted in wells №№155, 107, 200 . Wells №№ 194, 107 were transferred to electric centrifugal pump (ECP) after HF. The average duration of effect was 332 days. Only in well number 114 flow rate was increased slightly, by 1 t / day. In the rest wells daily production was increased at least by 2 times. The best result was obtained after treatment of well № 155, 107 and 5. Oil flow rate was increased in average by 16 times It should be noted that prior to fracturing the wells №№ 5, 107 were operated by sucker rod way, then they were transferred to the electric centrifugal pump. On the analyzed period, the effect was continued on these wells, with the exception of well №5. In T wells № 194 and № 200 the growth oil production rate was 11.2 and 5.0 t / d, respectively, after fracturing. Duration of the effect in well 194 was 199 days, in well 200 - 407 days.
The relationship is constructed to establish the nature of flow rates growth change from the fracture length (see figure 1). The graph shows that the technological effect depends on the fracture length. When fracture length is increased, oil flow rate growth is increased too.
Table 1 - Technological parameters of hydraulic fracturing
№ Well number horizon Interval
of perforation Thickness of
treated interval Volume of injected agents р pressure of
fracturing, МPа
The total length of the fixed crack, m
The amount of proppant, t Specific discharge of proppant
t/m Gel volume,
m3
Volume of driving m3
1 107 Ю-I 2596.0-2608.0 12.0 75.0 6.3 215.7 12.3 30.0 124.26
2 114 Ю-I+II 2593.5-2605.0 2634.0-2636.0 13.5 72.0 5.3 211.8 12.2 30.0 109.61
3 194 Ю-I 2598.0-2611.0 13.2 61.5 4.7 225.6 12.3 25.0 61.44
4 200 Ю-I 2608.0-2619.0 11.0 66.6 6.0 196.2 12.2 25.0 85.23
5 155 Ю-I+II 2589.0-2600.0 2645.0-2649.0 11.0 70.7 6.4 227.0 12.4 33.0 138.56
6 5 Ю-I 2609.0-2620.0 11.0 23.2 2.1 162.6 12.2 34.0
Table 2- The results of HF in producing wells
№ п/п Number of well The parameters wells work Duration of effect, days Note
Before HF After HF
Method of exploitation, horizon Fluid flow rate, t/day Oil flow rate, t/day % of water Method of exploitation, horizon Fluid flow rate, t/day Oil flow rate, t/day % of water
1 107 Sucker rod
Ю-I 5.4 5.2 3.6 Sucker rod
Ю-I
60.9 58.0 4.7 632 Effect is continued
2 114 Flow ЮI+II 12.9 12.2 6.0 Sucker rod
Ю-I+II 14.4 13.2 8.3 145 Effect is finished
3 194 Sucker rod
Ю-I 2.6 2.5 4.8 Sucker rod
Ю-I
15.1 13.7 9.3 199 Effect is finished
4 200 Sucker rod
Ю-I 4.7 4.6 2.8 Sucker rod
Ю-I 10.4 9.6 7.3 407 Effect is finished
5 155 Flow ЮI+II 6.7 6.6 1.0 ECP Ю-I 64.8 61.2 5.6 354 Effect is continued
6 5 Sucker rod
Ю-I 1.8 1.8 1.1 ECP Ю-I 54.0 49.9 8.6 256 Effect is continued. Well is transferred for reservoir pressure keeping
We analyzed the effect duration from fracture length (see figure 2). The graph shows that the relationship is directly proportional. In well 155 the effect lasted for 354 days, at maximum length fracture 138 m. Assessing the increase of flow rate at slight growth of water cut, we can say that HF is the main method of oil production intensification on Karakuduk field.
Figure 1 - The influence of fracture length on flow increase after fracturing
Figure 2 - Influence of duration on fracture length
Conclusion. To increase the productivity of the well, it is necessary to create cracks in the horizontal plane in the bottom-hole zone of the formation. In this case, the value of the compressibility coefficient of the crack should be at the level of the elasticity of the porous medium.
It can be seen from the results obtained that the crack parameters mainly depend on the pressure difference at the bottom of the well and on the viscosity of the rupture fluid. Therefore, when conducting hydraulic fracturing, the closest attention should be paid to such hydrodynamic parameters as repression on the formation and the viscosity of the rupture fluid.
It should be noted that in comparison with non-porous rocks, cracks are formed more intensively in permeable reservoirs during hydraulic fracturing.
The mathematical formulas proposed in the paper can be used in calculations to assess the technological effectiveness of impact methods, as well as in processing the results of well studies at the Uzen, Zhetybai, Kalamkas fields (Western Kazakhstan). The results obtained can be applied in the relevant departments and departments of industry research and design institutes as methodological recommendations in the analysis and design of oil field development.
REFERENCES
[1]. N.T. Azhikhanov, Bissembaeva K. T., B.M. Temirov, N. M.Zhunissov. Mathematical Model of Fluid Filtration to Horizontal Well in Tight Heterogeneous Formation. Global Journal of Pure and Applied Mathematics. ISSN 0973-1768 Volume 12, Number 1 (2016), © Research India Publications.
[2]. Koilybayev B.N., Strekov A.S., Bissembayeva K.T., ...Akhmetov D.A., Kirisenko O.G. Decision-making on restriction of water inflows into oil wells in dependence on the type of initial information. XL International correspondence scientific and practical conference “European research: innovative in science, education and technology”. Poland, August 2018.
[3]. Aitkulov A.U. Improvement of regulating process efficiency of oil fields development / - M: VNIIOENG, 2000. – 272p.
[4]. Ahmedjanov T.K., Aitkulov A.U. and others. Ways of increasing the efficiency of producing wells exploitation of Zhetybai deposit / Geology and protection of mineral resources. - 2003. - № 11. - P. 68-73.
[5]. Ahmedjanov T.K., Aitkulov A.U. and others. The calculation of flow rates of horizontal bore-hole in the presence of fractures in the formation / Industry of Kazakhstan. - 2003. - № 5 (20). P. 71-75. Almaty. 2002.
[6]. Aitkulov J.A.Improving the efficiency of hydraulic fracturing of formation at oil field: Author. dis ... candidate of technical science. Aktau. 2004.
Бисембаева Қарлығаш Танабаева
Техника ғылымдарының кандидаты, қауымдастырылған профессор,
Ш. Есенов атындағы Каспий технологиялар және инжиниринг университеті, Ақтау, Қазақстан
Джалалов Гариб Исаакович
Техника ғылымдарының докторы, профессор, Әзірбайжан Ұлттық Ғылым академиясы, Әзірбайжан, Баку
Сабырбаев Гүлжан
Қауымдастырылған профессор, Ш. Есенов атындағы Каспий технологиялар және инжиниринг университеті, Ақтау, Қазақстан
МҰНАЙ КЕН ОРНЫНДАҒЫ ГИДРАВЛИКАЛЫҚ ЖАРУ ТИІМДІЛІГІН БАҒАЛАУ
Аңдатпа. Көмірсутектер кен орындарын игеру тәжірибесі көрсеткендей, көп қабатты кен орындарынан мұнай өндіру кезінде көптеген гидродинамикалық және геологиялық-геофизикалық зерттеулер нәтижесінде құрылымы біртекті қаттардың жекелеген учаскелері анықталады. Көп жағдайда мұндай қабаттар, кен орындарын игеру жағдайын талдау нәтижелері көрсеткендей, сүзгілеу және сыйымдылық қасиеттеріне (кеуектілік пен өткізгіштігі) ие, ал қиын өндірілетін мұнай қорларының саны артады. Кен орындарының бұл жағдайы көп қабатты кен орындарынан көмірсутек қорларын өндірудің тиімділік деңгейінің жағдайын нашарлатады. Осыған байланысты, мұнай кен орындарын игеру процесінің тиімділігін арттыру үшін іс жүзінде аз өнімді аралық қабаттардан өндіру процесін күшейтуге бағытталған түрлі шаралар жиі қолданылады. Мұнайды өнімді резервуардан толығымен ығыстыруға мүмкіндік беретін белсенді әдістердің бірі-бұл гидравликалық сыну.
Мақалада кеңінен тараған әдістердің өнімділігін арттыру, ұңғымаларды вскрывающих низкопроницаемые қабаттарына – қыртысты сумен жару (ГРП). Радиалды және тангенциалды деформацияларды, сондай-ақ көлденең және тік жарықтар пайда болған кезде кеуекті ортаның икемділігі мен ағынның жылдамдығын ескере отырып, жүктеме радиусын анықтау үшін жаңа жетілдірілген формулалар алынды.
Қарақұдық кен орнының мысалында жүргізілген есептеулердің нәтижелері резервуардың гидравликалық сынуы сұйықтықтың гидравликалық сынуының орташа қысымымен жүретінін көрсетті. ГРП нәтижелері әртүрлі ұңғымаларда әртүрлі әсерлерді көрсетті. Жарықтың ұзындығына байланысты ағынның жылдамдығының өзгеру сипатын анықтауға тәуелділік анықталды.
Түйінді сөздер: ұңғыма, кеніш; өнімділігі, қабатты суарынды жару, қысымы, мұнайға қанығуы, технологиялық әсері, өткізгіштігі, дебиттері, әсері, игеру, қабат.
Бисембаева Карлыгаш Танбаевна
Кандидат технических наук, ассоциированный профессор,
Каспийский университет технологий и инжиниринга имени Ш. Есенова, Актау, Казахстан
Джалалов Гариб Исаакович
Доктор технических наук, профессор, Национальная академия наук Азербайджана, Азербайджан, Баку
Сабырбаев Гульжан
Ассоциированный профессор, Каспийский университет технологий и инжиниринга имени Ш. Есенова, Актау, Казахстан
ОЦЕНКА ЭФФЕКТИВНОСТИ ГИДРОРАЗРЫВА ПЛАСТА НА НЕФТЯНОМ МЕСТОРОЖДЕНИИ
Аннотация. Как показала практика разработки месторождений углеводородов, при добыче нефти из многослойных залежей в результате многочисленных гидродинамических и геолого-геофизических исследований выявляются отдельные участки пластов с более однородным строением. В большинстве случаев такие пласты, как показывают результаты анализа состояния разработки месторождений, обладают достаточно низкими фильтрационными и емкостными свойствами (пористостью и проницаемостью), при этом увеличивается количество трудноизвлекаемых запасов нефти. Это обстоятельство месторождений ухудшает состояние степени эффективности добычи запасов углеводородов из многослойных залежей. В связи с этим в целях повышения эффективности процесса разработки нефтяных месторождений на практике очень часто используются различные мероприятия, направленные на интенсификацию процесса добычи из малопродуктивных интервалов-пластов. Одним из активных методов, позволяющих наиболее полно вытеснить нефть из продуктивного пласта, является гидроразрыв пласта.
В статье рассматривается один из наиболее распространенных методов повышения продуктивности скважин, вскрывающих низкопроницаемые пласты – гидроразрыв пласта (ГРП). Получены новые улучшенные формулы для определения радиальных и тангенциальных деформаций, а также радиуса нагрузки с учетом пластичности пористой среды и скоростей потока при образовании горизонтальных и вертикальных трещин.
Результаты расчетов, проведенных на примере месторождения Каракудук, показали, что гидроразрыв пласта происходит при среднем давлении закачки жидкости гидроразрыва пласта. Результаты ГРП показали различные эффекты в разных скважинах
Выявлена зависимость для установления характера изменения скорости потока в зависимости от длины трещины.
Ключевые слова: скважина; залежь; продуктивность; гидроразрыв пласта; давление; нефтенасыщенность; технологический эффект; проницаемость; дебиты; влияние; разработка; пласт.
