Reservoir engineering
Reservoir engineering is the technology concerned with the prediction of the optimum economic recovery of oil or gas from hydrocarbon-bearing reservoirs. It is an eclectic technology requiring coordinated application of many disciplines: physics, chemistry, mathematics, geology, and chemical engineering. Originally, the role of reservoir engineering was exclusively that of counting oil and natural gas reserves. The reserves – the amount of oil or gas that can be economically recovered from the reservoir – are a measure of the wealth available to the owner and operator. It is also necessary to know the reserves in order to make proper decisions concerning the viability of downstream pipeline, refining, and marketing facilities that will rely on the production as feedstocks.
The scope of reservoir engineering has broadened to include the analysis of optimum ways for recovering oil and natural gas, and the study and implementation of enhanced recovery techniques for increasing the recovery above that which can be expected from the use of conventional technology.
Oil recovery
The overall recovery of crude oil from a reservoir is a function of the production mechanism, the reservoir and fluid parameters, and the implementation of supplementary recovery techniques. In general, recovery efficiency is not dependent upon the rate of production except for those reservoirs where gravity segregation is sufficient to permit segregation of the gas, oil, and water. Where gravity drainage is the producing mechanism, which occurs when the oil column in the reservoir is quite thick and the vertical permeability is high and a gas cap is initially present or is developed on producing, the reservoir will also show a significant effect of rate on the production efficiency.
Initially, the reservoir pressure is considerably higher than the bottomhole pressure inside the wellbore. This high natural differential pressure drives hydrocarbons toward the well and up to surface. However, as the reservoir pressure declines because of production, so does the differential pressure. To reduce the bottomhole pressure or increase the differential pressure to increase hydrocarbon production, it is necessary to implement an artificial lift system, such as a rod pump, an electrical submersible pump or a gas-lift installation. Production using artificial lift is considered primary recovery.
The primary recovery stage reaches its limit either when the reservoir pressure is so low that the production rates are not economical, or when the proportions of gas or water in the production stream are too high. During primary recovery, only a small percentage of the initial hydrocarbons in place are produced, typically around 10% for oil reservoirs.
Reservoir engineering expertise, together with geological and petrophysical engineering expertise, is being used to make very detailed studies of the production performance of crude oil reservoirs in an effort to delineate the distribution of residual oil and gas in the reservoir, and to develop the necessary technology to enhance the recovery.
Petroleum enhanced recovery is the technology to increase oil recovery from a porous formation beyond that obtained by conventional means. Conventional oil recovery technologies produce an average of about one-third of the original oil in place in a formation. Conventional technologies are primary or secondary. Primary technologies rely on native energy, in the form of fluid and rock compressibility and natural aquifers, to produce oil from the formation to wells. Secondary technologies supplement the native energy to drive oil to producing wells by injecting water or low-pressure gas at injection wells. The target of enhanced recovery technologies is that large portion of oil that is not recovered by primary and secondary means.
Many of the challenges encountered by secondary technologies are identical to those encountered by enhanced recovery technologies. Those challenges include reducing residual oil saturation, improving sweep efficiency, fitting the technology to the reservoir heterogeneities, and minimizing up-front and operating costs.
Waterflooding is utilized primarily as a secondary recovery technique, where the primary drive mechanism used to produce the oil (dissolved gas) is depleted. Waterflooding is a process used to inject water into an oil-bearing reservoir for pressure maintenance as well as for displacing and producing incremental oil after (or sometimes before) the economic production limit has been reached. This is done through the displacement of oil and free gas by water. In waterflooding, water is injected into one or more injection wells while the oil is produced from surrounding producing wells spaced according to the desired patterns. There are many different waterflood patterns used in the industry.
Residual oil remains trapped in a porous rock after the rock has been swept with water, gas, or any other recovery fluid. The residual oil saturation is the percentage of the pore space occupied by the residual oil. The residual oil saturation depends on the pore size distribution and connectivity, the interfacial tension between a recovery agent and the oil, the relative wettability of the rock surfaces with respect to the recovery agent and the oil, the viscosity of the fluids, and the rate at which the fluids are moving through the rock.
The sweep efficiency specifies that portion of a reservoir that is contacted by a recovery fluid. Sweep efficiency increases with volume of injected fluid. It also depends on the pattern of injection and production wells in a formation, on the mobility of the oil and the recovery fluid, and on heterogeneities in the formation.
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Injection well Production well Pattern boundary |
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A wide variety of processes have been considered for enhancing oil recovery: thermal processes, high-pressure gas processes, and chemical processes. Specifically, low residual oil saturation can be obtained by selecting a recovery fluid that provides a very low interfacial tension between the oil and the fluid. With very low interfacial tension, the capillary number is large. And high sweep efficiency can be obtained by selecting a recovery agent with low mobility or by increasing the mobility of the oil.
Well testing
Well testing broadly refers to the diagnostic tests run on wells in petroleum reservoirs to determine well and reservoir properties. The most important well tests are called pressure transient tests and are conducted by changing the rate of a well in a prescribed way and recording the resulting change in pressure with time.
The information obtained from pressure transient tests includes estimates of (1) unaltered formation permeability to the fluid(s) produced in the well; (2) altered (usually reduced) permeability near the well caused by drilling and completion practices; (3) altered (increased) permeability near the well created by deliberately stimulating the well by injecting either an acid that dissolves some of the formation or a high-pressure fluid that creates fractures in the formation; (4) distances to flow barriers located in the area drained by the well; and (5) average pressure in the area drained by the well. In addition, some testing programs may confirm hypothesized models of the reservoir, including important variations of formation properties with distance or location of gas/oil, oil/water, or other fluid/fluid contacts.
Reservoir behavior can be simulated using models that have been constructed to have properties similar either to an ideal geometric shape of constant properties or to the shape and varying properties of a real (nonideal) oil or gas reservoir.
For application to petroleum reservoirs, it is necessary to predict the simultaneous flow behavior of more than one fluid phase having different properties (water, gas, and crude oil). The permeability, the relative permeability, and the density and viscosity of each phase constitute its transport properties for calculating its flow. The relative permeability is a factor for each phase (oil, water, gas) which, when multiplied by the permeability for a single phase such as water, will give the permeability for the given phase. It varies with the volume fraction of the pore space occupied by the phase, called the saturation of the given phase. Generally, the relative permeability of the water phase depends only on its own saturation, and likewise for the gas phase. The relative permeability of the oil phase is a function of the saturations of both gas and water phases. Calculation of relative permeability allows comparison of the different abilities of fluids to flow in the presence of each other, since the presence of more than one fluid generally inhibits flow.
Ex. 7. Answer the questions based on the text.
What disciplines are involved in the sphere of reservoir engineering?
What was the original function of a reservoir engineer? How has it changed?
What does the overall recovery of oil depend on?
What is primary recovery? What technologies are used in primary recovery?
Why is enhanced recovery technology needed?
What is residual oil?
What is waterflooding?
What are the types of patterns in waterflooding scheme?
What does sweep efficiency depend on?
What are the types of pressure transient tests? What is their main purpose?
What is reservoir simulation needed for?
Why is the notion of relative permeability important for reservoir engineers?
Ex. 8. Choose the correct variant.
Originally, the role of reservoir engineering was to count / to search for oil and natural gas reserves.
In general, recovery efficiency does not depend on the fluid parameters / the rate of production.
Production using artificial lift is considered secondary / primary recovery.
During primary recovery, a small / big percentage of the initial hydrocarbons in place are produced.
Waterflooding is a process used to inject water into an oil-bearing reservoir / aquifer for pressure maintenance.
Sweep efficiency increases / decreases with volume of injected fluid.
Sweep efficiency also depends on heterogeneities in the formation / fluids.
Pressure transient tests are conducted by changing the rate of a well in a prescribed way and recording the resulting change in pressure / fluid temperature with time.
Drilling and completion practices usually increase / reduce permeability near the well.
Injecting a high-pressure fluid increases / reduces permeability near the well.
Simulation models can be constructed to have properties similar to an ideal / real geometric shape of constant properties.
Calculation of relative / effective permeability allows comparison of the different abilities of fluids to flow in the presence of each other, since the presence of more than one fluid generally inhibits / stimulates flow.
Ex. 9. VOCABULARY. In the text above, find the equivalents to the following words and phrases. (The sequence corresponds to their occurrence in the text.)
разработка месторождения
извлечение, отдача
рентабельность
нисходящий трубопровод
очистка
исходное сырье
рамки, сфера
технологии повышения нефтеотдачи
механизм добычи
дополнительный, вспомогательный
дебит
гравитационное разделение фаз
дренаж
нефтяная часть залежи
вертикальная проницаемость
газовая шапка
эффективность нефтеотдачи
забойное давление
снижаться
механизированная добыча
штанговый глубинный насос
электропогружной насос
установка газлифтной эксплуатации
первичная добыча
геологические запасы углеводородов
профессиональный опыт, компетенция
отдача пласта
определять границы
остаточная нефть
повысить нефтеотдачу
пористый
коэффициент сжатия
водоносный горизонт
дополнять
нагнетать, закачивать
остаточная нефтенасыщенность
эффективность вытеснения
неоднородность
первоначальные затраты
эксплуатационные издержки
заводнение
механизм вытеснения
истощать
нефтеносный
поддержание пластового давления
вытеснять
дополнительная нефть
экономический предел добычи
сетка (размещения скважин)
гидродинамическая связь
межфазное натяжение
смачиваемость
в отношении
вязкость
подвижность
отношение вязкостных сил к капиллярным силам
эксплуатационные испытания, ГДИС (гидродинамические испытания скважин)
испытание скважины по методу КВД (кривых восстановления давления)
оценка
неизмененный
заканчивание (скважины)
намеренно
стимулировать скважину
кислота
растворять
моделировать
одновременный
поток
относительная проницаемость
умножить на
насыщенность
затруднять, препятствовать
Ex. 10. From the Vocabulary List above, find synonyms to the following items.
on purpose
professional knowledge
assessment
scheme
be an obstacle
add
unchanged
as regards
exhaust
sphere
decrease
Ex. 11. Match words from Column A to the words from Column B in order to form phrases. Translate the resulting phrases into Russian. Make up five sentences with these phrases.
Column A
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Column B |
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Ex. 12. The Vocabulary List contains a number of useful terms. Match the terms and their definitions.
rate of production |
capillary number |
relative permeability |
oil column |
well testing |
sweep efficiency |
enhanced recovery |
pressure transient test |
compressibility |
viscosity |
completion |
interfacial tension |
The ratio of effective permeability of a particular fluid at a particular saturation to absolute permeability of that fluid at total saturation.
The analysis of pressure changes over time, especially those associated with small variations in the volume of fluid.
The activities and methods necessary to prepare a well for the production of oil and gas.
The vertical height (thickness) of an oil accumulation above the oil-water contact.
A means of assessing reservoir performance by measuring flow rates and pressures under a range of flowing conditions and then applying the data to a mathematical model.
The relative change in fluid volume related to a unit change in pressure.
The volume of produced fluid per unit of time
Techniques used to increase or prolong production from crude oil and natural gas fields.
The property that indicates the fluid’s resistance to flow.
In fluid dynamics, the factor that represents the relative effect of viscous forces versus surface tension acting across an interface between a liquid and a gas, or between two immiscible liquids.
The surface free energy that exists between two immiscible liquid phases, such as oil and water.
A measure of the effectiveness of an enhanced oil recovery process that depends on the volume of the reservoir contacted by the injected fluid.
Ex. 13. Insert appropriate items from the box into the following sentences. Sometimes you will have to change the form of the word.
a) residual oil |
g) relative permeability |
m) pattern |
b) hydrocarbons in place |
h) viscosity |
n) viability |
c) heterogeneity |
i) estimate |
o) waterflooding |
d) aquifer |
j) flow |
p) mobility |
e) inject |
k) fluid saturation |
q) expertise |
f) artificial lift |
l) interfacial tension |
r) wettability |
__________ is a widely practiced secondary recovery method.
In multiphase flow in porous media, the __________ of a phase is a dimensionless measure of the effective permeability of that phase.
__________ is the total hydrocarbon content of an oil reservoir, referring to the amount of oil before the commencement of production.
When two immiscible liquids, such as oil and water, are in contact, __________ causes each liquid to maintain as small a surface as possible.
The reservoir engineer uses __________along with porosity and permeability to determine the profitability of developing a particular reservoir.
An __________contains water-filled pore spaces, and, when the spaces are connected, the water is able to flow through the matrix of the rock.
__________of a rock depends on the nature of interaction of the rock and oil or water.
Even a moderate __________ of 800 billion barrels of recoverable oil from oil shale in the Green River Formation is three times greater than the proven oil reserves of Saudi Arabia.
Reservoir engineering is increasingly relying on professional __________ of mathematicians and IT-specialists.
Inverted nine-spot __________ showed best results for sweep efficiency in reservoir simulation.
__________is needed in wells when there is insufficient pressure in the reservoir to lift the produced fluids to the surface, but often used in naturally flowing wells (which do not technically need it) to increase the flow rate above what would flow naturally.
Extra heavy oil from the Orinoco region has a __________ of over 10,000 centipoise.
The recovery of the __________ parallels the recovery of the mobile water just as in the case of the stable displacement.
The lack of commercial __________of oil shale-derived oil has inhibited the development of better technologies that might reduce its cost.
Water is _________to support pressure of the reservoir and to sweep or displace oil from the reservoir, and push it towards a well.
Oil __________ in the transition zone has been determined by actually measuring residual oil saturation, relative permeabilities and capillary pressures at various initial oil saturations.
The __________ of fluid through fractures in the rock is an important process in many areas of geosciences, including oil engineering.
The study of reservoir __________ study helped to understand the shale and the sand distribution.
Ex. 14. Translate the following sentences into English, using vocabulary from the text and terms given at the beginning of the Unit. (The items are underlined.)
Разработка месторождений должна обеспечивать максимально возможную нефтеотдачу пластов и может осуществляться либо на естественных режимах, либо с методами повышения нефтеотдачи.
При режиме растворенного газа пластовое давление падает в процессе разработки ниже давления насыщения и выделяющийся из нефти газ расширяется, вытесняя нефть к скважинам.
Применение заводнения позволило резко сократить число скважин и получить большую эффективность вытеснения.
Ежегодно методами КВД исследуется в среднем 13 % от общего числа скважин на месторождении, а гидродинамические исследования скважин проводятся преимущественно на добывающих скважинах.
Поддержание пластового давления закачкой воды, кроме повышения нефтеотдачи, обеспечивает интенсификацию процесса разработки.
Вода, нагнетаемая в пласт, должна отвечать определенным требованиям в зависимости от цели закачки – для поддержания пластового давления или заводнения.
Лишь небольшой процент геологических запасов углеводородов может быть извлечен методами первичной добычи.
Начальное пластовое давление в коллекторах с газовой шапкой значительно ниже давления насыщения, поэтому только часть газа растворена в нефти, остальная же находится над нефтью.
При нагнетании пара повышается температура пласта, снижается вязкость и увеличивается подвижность нефти.
Этот коллектор характеризуется высокой неоднородностью, что затрудняет применение заводнения.
Регулирование разработки месторождения зависит от сетки расположения добывающих и нагнетательных скважин, расстояния между ними, объемов нагнетаемой воды.
Для более эффективной разработки коллектора необходимо уменьшить межфазное натяжение в зоне водонефтяного контакта.
Насосы ЭЦН обеспечивают экономичную добычу путем повышения нефтеотдачи на низкопродуктивных зрелых месторождениях.
При такой семиточечной сетке скважин водоносный горизонт обеспечивает эффективное вытеснение нефти.
Автор статьи предлагает новый метод разработки нефтяных месторождений с учетом гравитационного разделения флюидов.
Даже если мы будем внедрять методы повышения нефтеотдачи, экономический предел добычи нефти с этого месторождения наступит через несколько лет.
Относительная проницаемость газовой и жидкой фаз почти пропорционально зависит от их насыщенности.
Внедрение системы механизированной добычи может повысить отдачу до 30%.
Новый метод извлечения остаточной нефти основан на том, что при контакте нефти с большим количеством газоконденсата при определенных давлениях и температуре газ растворяет нефть и все углеводороды переходят в однофазное состояние.
Speaking and Communication Skills