Oil and Gas Reservoir Engineering

Reservoir Engineering

By : Khawar Nehal

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30 March 2016

Basic Reservoir Engineering

24 August 2012By : Khawar NehalUpdated 30 March 2016

Reservoir engineering

The working tools of the reservoir engineer are subsurface geology, applied mathematics, and the basic laws of physics and chemistry governing the behavior of liquid and vapor phases of crude oil, natural gas, and water in reservoir rock.

Environmental impacts

Enhanced oil recovery wells are regulated as Class II wells by the EPA. The regulations require well operators to reinject the brine used for recovery deep underground in Class II Disposal Wells.

Classes of wells

Class I wells are used to inject hazardous and non-hazardous wastes into deep, isolated rock formations. Class II wells are used exclusively to inject fluids associated with oil and natural gas production. Class III wells are used to inject fluids to dissolve and extract minerals.

Classes of wells

Class IV wells are shallow wells used to inject hazardous or radioactive wastes into or above a geologic formation that contains a Underground Source of Drinking Water (USDW). Class V wells are used to inject non-hazardous fluids underground. Most Class V wells are used to dispose of wastes into or above underground sources of drinking water. Class VI wells are wells used for injection of carbon dioxide (CO2) into underground subsurface rock formations for long-term storage.


Reservoir engineering is a branch of petroleum engineering that applies scientific principles to the drainage problems arising during the development and production of oil and gas reservoirs so as to obtain a high economic recovery.


Of particular interest to reservoir engineers is generating accurate reserves estimates for use in financial reporting to the Securities and Exchange Commission (SEC) and other regulatory bodies.


Other job responsibilities include numerical reservoir modeling, production forecasting, well testing, well drilling and workover planning, economic modeling, and PVT analysis of reservoir fluids.

PVT Analysis

PVT Analysis


Reservoir engineers also play a central role in field development planning, recommending appropriate and cost effective reservoir depletion schemes such as waterflooding or gas injection to maximize hydrocarbon recovery.


Due to legislative changes in many hydrocarbon producing countries, they are also involved in the design and implementation of carbon sequestration projects in order to minimize the emission of greenhouse gases.

Carbon Sequestration

Carbon sequestration is the process involved in carbon capture and the long-term storage of atmospheric carbon dioxide (CO2).Carbon sequestration describes long-term storage of carbon dioxide or other forms of carbon to either mitigate or defer global warming and avoid dangerous climate change. It has been proposed as a way to slow the atmospheric and marine accumulation of greenhouse gases, which are released by burning fossil fuels.

Sample Diagram

Screenshot of a structure map generated by Contour map software for an 8500ft deep gas & Oil reservoir in the Erath field, Vermilion Parish, Erath, Louisiana. The left-to-right gap, near the top of the contour map indicates a Fault line.

Sample Diagram

This fault line is between the blue/green contour lines and the purple/red/yellow contour lines. The thin red circular contour line in the middle of the map indicates the top of the oil reservoir. Because gas floats above oil, the thin red contour line marks the gas/oil contact zone. Reservoir engineers could use the map as a part of their well drill planning.

Sample Diagram

Reservoir engineers often specialize in two areas:

Surveillance

Simulation modeling

Types of Reservoirs

Surveillance (or production) engineering, i.e. monitoring of existing fields and optimization of production and injection rates. Surveillance engineers typically use analytical and empirical techniques to perform their work, including decline curve analysis, material balance modeling, and inflow/outflow analysis.

Surveillance

Simulation modeling, i.e. the conduct of reservoir simulation studies to determine optimal development plans for oil and gas reservoirs. Also, reservoir engineers perform and integrate well tests into their data for reservoirs in geothermal drilling.

Simulation modeling

Society of Petroleum Engineers

A resource related to Reservoir Engineering.

http://www.spe.org/

More resources

Craft, B.C. & Hawkins, M. Revised by Terry, R.E. 1990 "Applied Petroleum Reservoir Engineering" Second Edition (Prentice Hall).

Dake, L.P., 1978, "Fundamentals of Reservoir Engineering" (Elsevier)

Frick, Thomas C. 1962 "Petroleum Production Handbook, Vol II" (Society of Petroleum Engineers).

More resources

Slider, H.C. 1976 "Practical Petroleum Reservoir Engineering Methods" (The Petroleum Publishing Company).

Charles R. Smith, G. W. Tracy, R. Lance Farrar. 1999 "Applied Reservoir Engineering" (Oil & Gas Consultants International)

Enhanced oil recovery

Enhanced Oil Recovery (abbreviated EOR) is a generic term for techniques for increasing the amount of crude oil that can be extracted from an oil field. Using EOR, 30-60%, or more, of the reservoir's original oil can be extracted compared with 20-40% using primary and secondary recovery.

Enhanced oil recovery

Enhanced oil recovery is also called improved oil recovery or tertiary recovery (as opposed to primary and secondary recovery). Sometimes the term quaternary recovery is used to refer to more advanced, speculative, EOR techniques.

Quaternary

quaternary [kwtnr]adj1. consisting of fours or by fours2. fourth in a series3. (Chemistry) Chem containing or being an atom bound to four other atoms or groups a quaternary ammonium compound4. (Mathematics) Maths having four variablesn pl -nariesthe number four or a set of four

Injection well used for enhanced oil recovery

Volumetric Sweep Efficiency

The volumetric sweep efficiency at any time is the fraction of the total reservoir volume contacted by the injected fluid during the recovery. When using water, consideration of the mobility of the fluids, is an important factor when determining the area and vertical sweep efficiencies.


This would help to determine the mobility ratio. If M is less than 1 then oil is capable of traveling at a rate equivalent to the water. An increase in the viscosity of the oil would mean that M would increase and this would lead to the injected fluid moving around the oil. This would also make it harder for the oil to penetrate the pore.


To improve this ratio then the viscosity of the water has to be increased. When M is greater than 1 the displacing fluid has greater mobility than the displaced fluid. Also the position of the water injection and the flooding patterns would go a long way to determining the recovery patterns.


Also to consider in oil recovery is the position and orientation of the injection wells around the production well. As the mobility ratio increases the sweep efficiency decreases. Once a channel of water exists between the injector and the producer then little additional oil would be recovered.


If permeability varies vertically then an irregular vertical fluid front can develop and this is as a result of the differing permeabilities and the mobility ratio.

Displacement Efficiency

This refers to the fraction of oil that is swept from unit volume of reservoir upon injection. This depends on the mobility ratio, the wettability of the rock and the pore geometry. The wettability is determined by whether or not the grains preferentially absorb oil of water.

How does it work?

Enhanced oil recovery is achieved by gas injection, chemical injection, microbial injection, or thermal recovery (which includes cyclic or continuous steam, steam flooding, and fire flooding).

Gas injection

Gas injection is presently the most-commonly used approach in enhanced oil recovery. In addition to the beneficial effect of the pressure, this method sometimes aids recovery by reducing the viscosity of the crude oil as the gas mixes with it.

Gases used include CO2, natural gas or nitrogen.

Gas injection

Oil displacement by carbon dioxide injection relies on the phase behavior of the mixtures of that gas and the crude, which are strongly dependent on reservoir temperature, pressure and crude oil composition.

Gas injection

In high pressure applications with lighter oils, CO2 is miscible with the oil, with resultant swelling of the oil, and reduction in viscosity, and possibly also with a reduction in the surface tension with the reservoir rock.

Miscible

Miscibility /msblti/ is the property of substances to mix in all proportions, forming a homogeneous solution. The term is most often applied to liquids, but applies also to solids and gases. Water and ethanol, for example, are miscible because they mix in all proportions.

Gas injection

In the case of low pressure reservoirs or heavy oils, CO2 will form an immiscible fluid, or will only partially mix with the oil. Some oil swelling may occur, and oil viscosity can still be significantly reduced.

Gas injection

In these applications, between one-half and two-thirds of the injected CO2 returns with the produced oil and is usually re-injected into the reservoir to minimize operating costs. The remainder is trapped in the oil reservoir by various means.

Chemical injection

The injection of various chemicals, usually as dilute solutions, have been used to improve oil recovery. Injection of alkaline or caustic solutions into reservoirs with oil that has organic acids naturally occurring in the oil will result in the production of soap that may lower the interfacial tension enough to increase production.

Interfacial tension

Interfacial tension is somewhat similar to surface tension in that cohesive forces are also involved. However the main forces involved in interfacial tension are adhesive forces (tension) between the liquid phase of one substance and either a solid, liquid or gas phase of another substance. The interaction occurs at the surfaces of the substances involved, that is at their interfaces.

Chemical injection

Injection of a dilute solution of a water soluble polymer to increase the viscosity of the injected water can increase the amount of oil recovered in some formations. Dilute solutions of surfactants such as petroleum sulfonates or biosurfactants such as rhamnolipids may be injected to lower the interfacial tension or capillary pressure that impedes oil droplets from moving through a reservoir.

Rhamnolipids

Rhamnolipids are a class of glycolipid produced by Pseudomonas aeruginosa, amongst other organisms, frequently cited as the best characterised of the bacterial surfactants.They have a glycosyl head group, in this case a rhamnose moiety, and a 3-(hydroxyalkanoyloxy)alkanoic acid (HAA) fatty acid tail. (Way too much biology here)

Rhamnolipids

Chemical injection

Special formulations of oil, water and surfactant, microemulsions, can be particularly effective in this. Application of these methods is usually limited by the cost of the chemicals and their adsorption and loss onto the rock of the oil containing formation.In all of these methods the chemicals are injected into several wells and the production occurs in other nearby wells.

This is the addition of chemical agents to the injected water to aid mobility and the reduction in surface tension.

Chemical EOR

Polymer flooding is a means of injecting long chain polymer molecules in an effort to increase the injected water viscosity. The addition of these chemicals means that the fluid would behave like a non-Newtonian fluid; at low velocities it is resistant to flow.

Chemical EOR

This method not only improves the mobility ratio (by lowering it) but also the vertical and areal sweep efficiency. The polymer causes a reduction in the permeability and allows the preferential filling of the high permeable zones in the reservoir. This lowers flow velocity and increases the sweep area.

Chemical EOR

Surfactant Polymer flooding these are surface additives that help to break down the surface tension between the oil and water. This allows for the oil and water to separate.The effect of the surfactant depends on the concentration. In low concentrations the rate is gradual but in higher concentrations the rate is increased until such time that the surfactant is diluted by the formation fluids. It also improves the mobility of the fluids and reverses the rock wettablity.

Wettability

The degree or extent to which something absorbs or can be made to absorb moisture.

Chemical EOR

Surfactants usually have additives to improve their performance. Their behavior is complex and difficult to predict.

Caustic flooding is the addition of sodium hydroxide to injection water to aid recovery. It does this by lowering the surface tension, reversing the rock wettability, emulsification of the oil, mobilization of the oil and helps in drawing the oil out of the rock.

Microbial injection

Microbial injection is part of microbial enhanced oil recovery and is presently rarely used, both because of its higher cost and because the developments in this field are more recent than other techniques.

Microbial injection

Strains of microbes have been both discovered and developed (using gene mutation) which function either by partially digesting long hydrocarbon molecules, by generating biosurfactants, or by emitting carbon dioxide (which then functions as described in Gas injection above).

Microbial injection

Three approaches have been used to achieve microbial injection. In the first approach, bacterial cultures mixed with a food source (a carbohydrate such as molasses is commonly used) are injected into the oil field.

Microbial injection

In the second approach, used since 1985, nutrients are injected into the ground to nurture existing microbial bodies; these nutrients cause the bacteria to increase production of the natural surfactants they normally use to metabolize crude oil underground.

Microbial injection

After the injected nutrients are consumed, the microbes go into near-shutdown mode, their exteriors become hydrophilic, and they migrate to the oil-water interface area, where they cause oil droplets to form from the larger oil mass, making the droplets more likely to migrate to the wellhead. This approach has been used in oilfields near the Four Corners and in the Beverly Hills Oil Field in Beverly Hills, California.

Microbial injection

The third approach is used to address the problem of paraffin components of the crude oil, which tend to separate from the crude as it flows to the surface. Since the Earth's surface is considerably cooler than the petroleum deposits (a temperature drop of 13-14 degree F per thousand feet of depth is usual), the paraffin's higher melting point causes it to solidify as it is cooled during the upward flow.

Microbial injection

Bacteria capable of breaking these paraffin chains into smaller chains (which would then flow more easily) are injected into the wellhead, either near the point of first congealment or in the rock stratum itself.

Thermal methods

In this approach, various methods are used to heat the crude oil in the formation to reduce its viscosity and/or vaporize part of the oil. Methods include cyclic steam injection, steam drive and in situ combustion. These methods improve the sweep efficiency and the displacement efficiency.

Thermal methods

Steam injection has been used commercially since the 1960s in California fields. In 2011 solar thermal enhanced oil recovery projects were started in California and Oman, this method is similar to thermal EOR but uses a solar array to produce the steam.

Thermal EOR

This is the addition of heat to the reservoir so as to lower the viscosity of the oil and thus decrease the mobility ratio. The increased heat reduces the surface tension and increases the permeability of the oil. The heated oil may also vaporize and then condense forming improved oil.

Thermal EOR

Steam flooding is one means of introducing heat to the reservoir by pumping steam into the well with a pattern similar to that of water injection. Eventually the steam condenses to hot water, in the steam zone the oil evaporates and in the hot water zone the oil expands. As a result the oil expands the viscosity drops and the permeability increases. To ensure success the process has to be cyclical. This is the principal enhanced oil recovery program in use today.

Thermal EOR

In situ combustion is another means of recovering the oil from the well, which involves the generation of heat within the reservoir itself. There are 3 methods of combustion and they are; Dry forward, reverse and wet combustion. Dry forward uses an igniter to set fire to the oil and as the fire progresses the oil is pushed away from the fire toward the producing well.

Thermal EOR

In reverse the air injection and the ignition occur from opposite directions. Water is injected just behind the front and turned into steam by the hot rock this quenches the fire and spreads the heat more evenly. It is good for where the oil saturation and porosity are high.

Miscible EOR

This refers to removing the interface between the two interacting fluids. This allows for total displacement efficiency.

Miscible EOR

Hydrocarbon displacement is where a slug of hydrocarbon gas is pushed into the reservoir in order to form a miscible phase at high pressure. This however suffers from poor mobility ratio, and the solvents ability to dissolve the oil is reduced as it goes through. As with all methods, this is only attempted when it is deemed economical.

Miscible EOR

Carbon dioxide flooding is as its name suggests. Carbon dioxide is soluble in oil. Injection of the gas also has solution gas drive effects on the reservoir.

Economic costs and benefits

Adding oil recovery methods adds to the cost of oil in the case of CO2 typically between 0.5-8.0 US$ per tonne of CO2. The increased extraction of oil on the other hand, is an economic benefit with the revenue depending on prevailing oil prices. Onshore EOR has paid in the range of a net 10-16 US$ per tonne of CO2 injected for oil prices of 15-20 US$/barrel.

Economic costs and benefits

Prevailing prices depend on many factors but can determine the economic suitability of any procedure, with more procedures and more expensive procedures being economically viable at higher prices. Example: With oil prices at around 90 US$/barrel, the economic benefit is about 70 US$ per tonne CO2.

Examples of current EOR projects

In Canada, a CO2-EOR project has been established by Cenovus Energy at the Weyburn Oil Field in southern Saskatchewan. The project is expected to inject a net 18 million ton CO2 and recover an additional 130 million barrels (21,000,000 m3) of oil, extending the life of the oil field by 25 years.


There is a projected 26+ million tonnes (net of production) of CO2 to be stored in Weyburn, plus another 8.5 million tonnes (net of production) stored at the Weyburn-Midale Carbon Dioxide Project, resulting in a net reduction in atmospheric CO2).


That's the equivalent of taking nearly 7 million cars off the road for a year. Since CO2 injection began in late 2000, the EOR project has performed largely as predicted. Currently, some 1600 m3 (10,063 barrels) per day of incremental oil is being produced from the field.

Potential for EOR in United States

The United States has been using EOR for several decades. For over 30 years, oil fields in the Permian Basin have implemented CO2 EOR using naturally sourced CO2 from New Mexico and Colorado. The Department of Energy (DOE) has estimated that full use of 'next generation' CO2-EOR in United States could generate an additional 240 billion barrels (38 km3) of recoverable oil resources.


Developing this potential would depend on the availability of commercial CO2 in large volumes, which could be made possible by widespread use of carbon capture and storage. For comparison, the total undeveloped US domestic oil resources still in the ground total more than 1 trillion barrels (160 km3), most of it remaining unrecoverable.


The DOE estimates that if the EOR potential were to be fully realised, state and local treasuries would gain $280 billion in revenues from future royalties, severance taxes, and state income taxes on oil production, aside from other economic benefits.


Enhanced oil recovery wells typically produce large quantities of brine at the surface. The brine may contain toxic metals and radioactive substances, as well as being very salty. This can be very damaging to drinking water sources and the environment generally if not properly controlled.


In the United States, injection well activity is regulated by the United States Environmental Protection Agency (EPA) and state governments under the Safe Drinking Water Act.EPA has issued Underground Injection Control (UIC) regulations in order to protect drinking water sources.

Fluid dynamics

In physics, fluid dynamics is a sub-discipline of fluid mechanics that deals with fluid flowthe natural science of fluids (liquids and gases) in motion. It has several subdisciplines itself, including aerodynamics (the study of air and other gases in motion) and hydrodynamics (the study of liquids in motion).

Fluid dynamics

Fluid dynamics has a wide range of applications, including calculating forces and moments on aircraft, determining the mass flow rate of petroleum through pipelines, predicting weather patterns, understanding nebulae in interstellar space and reportedly modeling fission weapon detonation. Some of its principles are even used in traffic engineering, where traffic is treated as a continuous fluid.

Fluid dynamics

Bernoullis Law Derivation Diagram

Fluid dynamics

Fluid dynamics offers a systematic structurewhich underlies these practical disciplinesthat embraces empirical and semi-empirical laws derived from flow measurement and used to solve practical problems.

Fluid dynamics

The solution to a fluid dynamics problem typically involves calculating various properties of the fluid, such as velocity, pressure, density, and temperature, as functions of space and time.

Fluid dynamics

Historically, hydrodynamics meant something different than it does today. Before the twentieth century, hydrodynamics was synonymous with fluid dynamics. This is still reflected in names of some fluid dynamics topics, like magnetohydrodynamics and hydrodynamic stabilityboth also applicable in, as well as being applied to, gases.

Teardrop Shape

Teardrop Shape

Typical aerodynamic teardrop shape, assuming a viscous medium passing from left to right, the diagram shows the pressure distribution as the thickness of the black line and shows the velocity in the boundary layer as the violet triangles.

Teardrop Shape

The green vortex generators prompt the transition to turbulent flow and prevent back-flow also called flow separation from the high pressure region in the back. The surface in front is as smooth as possible or even employs shark like skin, as any turbulence here will reduce the energy of the airflow.

Teardrop Shape

The truncation on the right, known as a Kammback, also prevents back flow from the high pressure region in the back across the spoilers to the convergent part.

Geothermal energy

Geothermal energy is thermal energy generated and stored in the Earth. Thermal energy is the energy that determines the temperature of matter. The Geothermal energy of the Earth's crust originates from the original formation of the planet (20%) and from radioactive decay of minerals (80%).

Geothermal energy

The geothermal gradient, which is the difference in temperature between the core of the planet and its surface, drives a continuous conduction of thermal energy in the form of heat from the core to the surface. The adjective geothermal originates from the Greek roots (ge), meaning earth, and (thermos), meaning hot.

Geothermal energy

At the core of the Earth, thermal energy is created by radioactive decay and temperatures may reach over 5000 degrees Celsius (9,000 degrees Fahrenheit).

Geothermal energy

Heat conducts from the core to surrounding cooler rock. The high temperature and pressure cause some rock to melt, creating magma convection upward since it is lighter than the solid rock. The magma heats rock and water in the crust, sometimes up to 370 degrees Celsius (700 degrees Fahrenheit).

Geothermal energy

From hot springs, geothermal energy has been used for bathing since Paleolithic times and for space heating since ancient Roman times, but it is now better known for electricity generation. Worldwide, about 10,715 megawatts (MW) of geothermal power is online in 24 countries.

Geothermal energy

An additional 28 gigawatts of direct geothermal heating capacity is installed for district heating, space heating, spas, industrial processes, desalination and agricultural applications.

Geothermal energy

Geothermal power is cost effective, reliable, sustainable, and environmentally friendly,[5] but has historically been limited to areas near tectonic plate boundaries. Recent technological advances have dramatically expanded the range and size of viable resources, especially for applications such as home heating, opening a potential for widespread exploitation.

Geothermal energy

Geothermal wells release greenhouse gases trapped deep within the earth, but these emissions are much lower per energy unit than those of fossil fuels. As a result, geothermal power has the potential to help mitigate global warming if widely deployed in place of fossil fuels.

Geothermal energy

The Earth's geothermal resources are theoretically more than adequate to supply humanity's energy needs, but only a very small fraction may be profitably exploited. Drilling and exploration for deep resources is very expensive.

Geothermal energy

Forecasts for the future of geothermal power depend on assumptions about technology, energy prices, subsidies, and interest rates. Polls show that customers would be willing to pay a little more for a renewable energy source like geothermal. But as a result of government assisted research and industry experience, the cost of generating geothermal power has decreased by 25% over the past two decades. In 2001, geothermal energy cost between two and ten cents per kwh.

Petroleum

Petroleum (L. petroleum, from Latin: 'petra' (rock) + Latin: oleum (oil)) or crude oil is a naturally occurring flammable liquid consisting of a complex mixture of hydrocarbons of various molecular weights and other liquid organic compounds, that are found in geologic formations beneath the Earth's surface.

Petroleum

A fossil fuel, it is formed when large quantities of dead organisms, usually zooplankton and algae, are buried underneath sedimentary rock and undergo intense heat and pressure.

Petroleum

Petroleum is recovered mostly through oil drilling. This comes after the studies of structural geology (at the reservoir scale), sedimentary basin analysis, reservoir characterization (mainly in terms of porosity and permeable structures).

Petroleum

It is refined and separated, most easily by boiling point, into a large number of consumer products, from petrol (or gasoline) and kerosene to asphalt and chemical reagents used to make plastics and pharmaceuticals. Petroleum is used in manufacturing a wide variety of materials[6], and it is estimated that the world consumes about 88 million barrels each day.

Petroleum

The use of fossil fuels such as petroleum can have a negative impact on Earth's biosphere, releasing pollutants and greenhouse gases into the air and damaging ecosystems through events such as oil spills.

Petroleum

Concern over the depletion of the earth's finite reserves of oil, and the effect this would have on a society dependent on it, is a field known as peak oil.

Oil - proved reserves 2009

Pumpjack pumping an oil well near Lubbock, Texas

An oil refinery in Mina-Al-Ahmadi, Kuwait

Etymology

The word "petroleum" comes from Greek: (petra) for rock and Greek: (elaion) for oil. The term was found (in the spelling "petraoleum") in 10th-century Old English sources. It was used in the treatise De Natura Fossilium, published in 1546 by the German mineralogist Georg Bauer, also known as Georgius Agricola.

Etymology

In the 19th century, the term "petroleum" was frequently used to refer to mineral oils produced by distillation from mined organic solids such as cannel coal (and later oil shale), and refined oils produced from them; in the United Kingdom, storage (and later transport) of these oils were regulated by a series of Petroleum Acts, from the Petroleum Act 1862 c. 66 onward.

Composition

In its strictest sense, petroleum includes only crude oil, but in common usage it includes all liquid, gaseous, and solid (e.g., paraffin) hydrocarbons. Under surface pressure and temperature conditions, lighter hydrocarbons methane, ethane, propane and butane occur as gases, while pentane and heavier ones are in the form of liquids or solids.

Composition

However, in an underground oil reservoir the proportions of gas, liquid, and solid depend on subsurface conditions and on the phase diagram of the petroleum mixture.

Composition

An oil well produces predominantly crude oil, with some natural gas dissolved in it. Because the pressure is lower at the surface than underground, some of the gas will come out of solution and be recovered (or burned) as associated gas or solution gas. A gas well produces predominantly natural gas.

Composition

However, because the underground temperature and pressure are higher than at the surface, the gas may contain heavier hydrocarbons such as pentane, hexane, and heptane in the gaseous state. At surface conditions these will condense out of the gas to form natural gas condensate, often shortened to condensate. Condensate resembles petrol in appearance and is similar in composition to some volatile light crude oils.

Composition

The proportion of light hydrocarbons in the petroleum mixture varies greatly among different oil fields, ranging from as much as 97 per cent by weight in the lighter oils to as little as 50 per cent in the heavier oils and bitumens.

Composition

The hydrocarbons in crude oil are mostly alkanes, cycloalkanes and various aromatic hydrocarbons while the other organic compounds contain nitrogen, oxygen and sulfur, and trace amounts of metals such as iron, nickel, copper and vanadium. The exact molecular composition varies widely from formation to formation but the proportion of chemical elements vary over fairly narrow limits as follows:

Composition

Composition by weightElement Percent rangeCarbon 83 to 87%Hydrogen 10 to 14%Nitrogen 0.1 to 2%Oxygen 0.05 to 1.5%Sulfur 0.05 to 6.0%Metals < 0.1%

Composition

Four different types of hydrocarbon molecules appear in crude oil. The relative percentage of each varies from oil to oil, determining the properties of each oil.

Composition by weight

Composition

Crude oil varies greatly in appearance depending on its composition. It is usually black or dark brown (although it may be yellowish, reddish, or even greenish). In the reservoir it is usually found in association with natural gas, which being lighter forms a gas cap over the petroleum, and saline water which, being heavier than most forms of crude oil, generally sinks beneath it.

Composition

Crude oil may also be found in semi-solid form mixed with sand and water, as in the Athabasca oil sands in Canada, where it is usually referred to as crude bitumen.

Composition

In Canada, bitumen is considered a sticky, black, tar-like form of crude oil which is so thick and heavy that it must be heated or diluted before it will flow.Venezuela also has large amounts of oil in the Orinoco oil sands, although the hydrocarbons trapped in them are more fluid than in Canada and are usually called extra heavy oil.

Composition

These oil sands resources are called unconventional oil to distinguish them from oil which can be extracted using traditional oil well methods. Between them, Canada and Venezuela contain an estimated 3.6 trillion barrels (570109 m3) of bitumen and extra-heavy oil, about twice the volume of the world's reserves of conventional oil.

Composition

Petroleum is used mostly, by volume, for producing fuel oil and petrol, both important "primary energy" sources.84 per cent by volume of the hydrocarbons present in petroleum is converted into energy-rich fuels (petroleum-based fuels), including petrol, diesel, jet, heating, and other fuel oils, and liquefied petroleum gas.

Composition

The lighter grades of crude oil produce the best yields of these products, but as the world's reserves of light and medium oil are depleted, oil refineries are increasingly having to process heavy oil and bitumen, and use more complex and expensive methods to produce the products required.

Composition

Because heavier crude oils have too much carbon and not enough hydrogen, these processes generally involve removing carbon from or adding hydrogen to the molecules, and using fluid catalytic cracking to convert the longer, more complex molecules in the oil to the shorter, simpler ones in the fuels.

Composition

Due to its high energy density, easy transportability and relative abundance, oil has become the world's most important source of energy since the mid-1950s. Petroleum is also the raw material for many chemical products, including pharmaceuticals, solvents, fertilizers, pesticides, and plastics; the 16 per cent not used for energy production is converted into these other materials.

Composition

Petroleum is found in porous rock formations in the upper strata of some areas of the Earth's crust. There is also petroleum in oil sands (tar sands). Known oil reserves are typically estimated at around 190 km3 (1.2 trillion (short scale) barrels) without oil sands[16], or 595 km3 (3.74 trillion barrels) with oil sands.

Composition

Consumption is currently around 84 million barrels (13.4106 m3) per day, or 4.9 km3 per year. Which in turn yields a remaining oil supply of only about 120 years, if current demand remain static.

Chemistry

Petroleum is a mixture of a very large number of different hydrocarbons; the most commonly found molecules are alkanes (linear or branched), cycloalkanes, aromatic hydrocarbons, or more complicated chemicals like asphaltenes. Each petroleum variety has a unique mix of molecules, which define its physical and chemical properties, like color and viscosity.

Octane, a hydrocarbon found in petroleum. Lines represent single bonds; black spheres represent carbon; white spheres represent hydrogen.

Chemistry

The alkanes, also known as paraffins, are saturated hydrocarbons with straight or branched chains which contain only carbon and hydrogen and have the general formula CnH2n+2.

They generally have from 5 to 40 carbon atoms per molecule, although trace amounts of shorter or longer molecules may be present in the mixture.

Chemistry

The alkanes from pentane (C5H12) to octane (C8H18) are refined into petrol, the ones from nonane (C9H20) to hexadecane (C16H34) into diesel fuel, kerosene and jet fuel. Alkanes with more than 16 carbon atoms can be refined into fuel oil and lubricating oil. At the heavier end of the range, paraffin wax is an alkane with approximately 25 carbon atoms, while asphalt has 35 and up, although these are usually cracked by modern refineries into more valuable products.

Chemistry

The shortest molecules, those with four or fewer carbon atoms, are in a gaseous state at room temperature. They are the petroleum gases. Depending on demand and the cost of recovery, these gases are either flared off, sold as liquified petroleum gas under pressure, or used to power the refinery's own burners. During the winter, butane (C4H10), is blended into the petrol pool at high rates, because its high vapor pressure assists with cold starts.

Chemistry

Liquified under pressure slightly above atmospheric, it is best known for powering cigarette lighters, but it is also a main fuel source for many developing countries.

Propane can be liquified under modest pressure, and is consumed for just about every application relying on petroleum for energy, from cooking to heating to transportation.

Chemistry

The cycloalkanes, also known as naphthenes, are saturated hydrocarbons which have one or more carbon rings to which hydrogen atoms are attached according to the formula CnH2n.

Cycloalkanes have similar properties to alkanes but have higher boiling points.

Chemistry

The aromatic hydrocarbons are unsaturated hydrocarbons which have one or more planar six-carbon rings called benzene rings, to which hydrogen atoms are attached with the formula CnHn. They tend to burn with a sooty flame, and many have a sweet aroma. Some are carcinogenic.

Chemistry

These different molecules are separated by fractional distillation at an oil refinery to produce petrol, jet fuel, kerosene, and other hydrocarbons. For example, 2,2,4-trimethylpentane (isooctane), widely used in petrol, has a chemical formula of C8H18 and it reacts with oxygen exothermically:

Chemistry

2 C8H18(l) + 25 O2(g) 16 CO2(g) + 18 H2O(g)

(H = 10.86 MJ/mol of octane)

Chemistry

The amount of various molecules in an oil sample can be determined in laboratory. The molecules are typically extracted in a solvent, then separated in a gas chromatograph, and finally determined with a suitable detector, such as a flame ionization detector or a mass spectrometer.

Chemistry

Due to the large number of co-eluted hydrocarbons within oil, many cannot be resolved by traditional gas chromatography and typically appear as a hump in the chromatogram. This unresolved complex mixture (UCM) of hydrocarbons is particularly apparent when analysing weathered oils and extracts from tissues of organisms exposed to oil.

Chemistry

Incomplete combustion of petroleum or petrol results in production of toxic byproducts. Too little oxygen results in carbon monoxide. Due to the high temperatures and high pressures involved, exhaust gases from petrol combustion in car engines usually include nitrogen oxides which are responsible for creation of photochemical smog.

Empirical equations for thermal properties

Heat of combustion

At a constant volume the heat of combustion of a petroleum product can be approximated as follows:

Where is measured in cal/gram and d is the specific gravity at 60 F (16 C).


Thermal conductivity

The thermal conductivity of petroleum based liquids can be modeled as follows:

where K is measured in BTU hr1ft2 , t is measured in F and d is the specific gravity at 60 F (16 C).


Specific heat

The specific heat of a petroleum oils can be modeled as follows:

where c is measured in BTU/lbm-F, t is the temperature in Fahrenheit and d is the specific gravity at 60 F (16 C).


In units of kcal/(kgC), the formula is:

where the temperature t is in Celsius and d is the specific gravity at 15 C.


Latent heat of vaporization

The latent heat of vaporization can be modeled under atmospheric conditions as follows:

where L is measured in BTU/lbm, t is measured in F and d is the specific gravity at 60 F (16 C).


In units of kcal/kg, the formula is:

where the temperature t is in Celsius and d is the specific gravity at 15 C.

Petroleum engineering

Petroleum engineering is a field of engineering concerned with the activities related to the production of hydrocarbons, which can be either crude oil or natural gas. Exploration and Production are deemed to fall within the upstream sector of the oil and gas industry.


Exploration, by earth scientists, and petroleum engineering are the oil and gas industry's two main subsurface disciplines, which focus on maximizing economic recovery of hydrocarbons from subsurface reservoirs.


Petroleum geology and geophysics focus on provision of a static description of the hydrocarbon reservoir rock, while petroleum engineering focuses on estimation of the recoverable volume of this resource using a detailed understanding of the physical behavior of oil, water and gas within porous rock at very high pressure.


The combined efforts of geologists and petroleum engineers throughout the life of a hydrocarbon accumulation determine the way in which a reservoir is developed and depleted, and usually they have the highest impact on field economics.


Petroleum engineering requires a good knowledge of many other related disciplines, such as geophysics, petroleum geology, formation evaluation (well logging), drilling, economics, reservoir simulation, reservoir engineering, well engineering, artificial lift systems, completions and oil and gas facilities engineering.

Overview

The profession got its start in 1914 within the American Institute of Mining, Metallurgical and Petroleum Engineers (AIME). The first Petroleum Engineering degree was conferred in 1915 by the University of Pittsburgh.

Overview

Since then, the profession has evolved to solve increasingly difficult situations as much of the "low hanging fruit" of the world's oil fields have been found and depleted. Improvements in computer modeling, materials and the application of statistics, probability analysis, and new technologies like horizontal drilling and enhanced oil recovery, have drastically improved the toolbox of the petroleum engineer in recent decades.

Overview

Deep-water, arctic and desert conditions are usually contended with. High Temperature and High Pressure (HTHP) environments have become increasingly commonplace in operations and require the petroleum engineer to be savvy in topics as wide ranging as thermo-hydraulics, geomechanics, and intelligent systems.

Overview

Petroleum engineering has historically been one of the highest paid engineering disciplines, although there is a tendency for mass layoffs when oil prices decline. In a June 4th, 2007 article, Forbes.com reported that petroleum engineering was the 24th best paying job in the United States.

Overview

The 2010 National Association of Colleges and Employers survey showed petroleum engineers as the highest paid 2010 graduates at an average $125,220 annual salary.For individuals with experience, salaries can go from $170,000 to $260,000 annually. They make an average of $112,000 a year and about $53.75 per hour.

Types

Petroleum engineers divide themselves into several types:

Reservoir engineers work to optimize production of oil and gas via proper well placement, production rates, and enhanced oil recovery techniques.Drilling engineers manage the technical aspects of drilling exploratory, production and injection wells.

Types

Production engineers, including subsurface engineers, manage the interface between the reservoir and the well, including perforations, sand control, downhole flow control, and downhole monitoring equipment; evaluate artificial lift methods; and also select surface equipment that separates the produced fluids (oil, natural gas, and water).

Petroleum geology

Petroleum geology is the study of origin, occurrence, movement, accumulation, and exploration of hydrocarbon fuels.

It refers to the specific set of geological disciplines that are applied to the search for hydrocarbons (oil exploration).

Sedimentary basin analysis

Petroleum geology is principally concerned with the evaluation of seven key elements in sedimentary basins:

Source Reservoir Seal Trap Timing Maturation Migration

A structural trap, where a fault has juxtaposed a porous and permeable reservoir against an impermeable seal. Oil (shown in red) accumulates against the seal, to the depth of the base of the seal. Any further oil migrating in from the source will escape to the surface and seep.


In general, all these elements must be assessed via a limited 'window' into the subsurface world, provided by one (or possibly more) exploration wells.


These wells present only a 1-dimensional segment through the Earth and the skill of inferring 3-dimensional characteristics from them is one of the most fundamental in petroleum geology. Recently, the availability of inexpensive, high quality 3D seismic data (from reflection seismology) and data from various electromagnetic geophysical techniques (such as Magnetotellurics) has greatly aided the accuracy of such interpretation.


Evaluation of the source uses the methods of geochemistry to quantify the nature of organic-rich rocks which contain the precursors to hydrocarbons, such that the type and quality of expelled hydrocarbon can be assessed.


The reservoir is a porous and permeable lithological unit or set of units that holds the hydrocarbon reserves. Analysis of reservoirs at the simplest level requires an assessment of their porosity (to calculate the volume of in situ hydrocarbons) and their permeability (to calculate how easily hydrocarbons will flow out of them).


Some of the key disciplines used in reservoir analysis are the fields of structural analysis, stratigraphy, sedimentology, and reservoir engineering.


The seal, or cap rock, is a unit with low permeability that impedes the escape of hydrocarbons from the reservoir rock.

Common seals include evaporites, chalks and shales. Analysis of seals involves assessment of their thickness and extent, such that their effectiveness can be quantified.


The trap is the stratigraphic or structural feature that ensures the juxtaposition of reservoir and seal such that hydrocarbons remain trapped in the subsurface, rather than escaping (due to their natural buoyancy) and being lost.


Analysis of maturation involves assessing the thermal history of the source rock in order to make predictions of the amount and timing of hydrocarbon generation and expulsion.


Finally, careful studies of migration reveal information on how hydrocarbons move from source to reservoir and help quantify the source (or kitchen) of hydrocarbons in a particular area.

Major subdisciplines in petroleum geology

Several major subdisciplines exist in petroleum geology specifically to study the seven key elements discussed above.

Analysis of source rocks

In terms of source rock analysis, several facts need to be established. Firstly, the question of whether there actually is any source rock in the area must be answered.Delineation and identification of potential source rocks depends on studies of the local stratigraphy, palaeogeography and sedimentology to determine the likelihood of organic-rich sediments having been deposited in the past.


If the likelihood of there being a source rock is thought to be high, the next matter to address is the state of thermal maturity of the source, and the timing of maturation. Maturation of source rocks (see diagenesis and fossil fuels) depends strongly on temperature, such that the majority of oil generation occurs in the 60 to 120C range.


Gas generation starts at similar temperatures, but may continue up beyond this range, perhaps as high as 200C. In order to determine the likelihood of oil/gas generation, therefore, the thermal history of the source rock must be calculated.


This is performed with a combination of geochemical analysis of the source rock (to determine the type of kerogens present and their maturation characteristics) and basin modelling methods, such as back-stripping, to model the thermal gradient in the sedimentary column.

Basin analysis

A full scale basin analysis is usually carried out prior to defining leads and prospects for future drilling. This study tackles the petroleum system and studies source rock (presence and quality); burial history; maturation (timing and volumes); migration and focus; and potential regional seals and major reservoir units (that define carrier beds).

Basin analysis

All these elements are used to investigate where potential hydrocarbons might migrate towards. Traps and potential leads and prospects are then defined in the area that is likely to have received hydrocarbons.

Exploration stage

Although a basin analysis is usually part of the first study a company conducts prior to moving into an area for future exploration, it is also sometimes conducted during the exploration phase. Exploration geology comprises all the activities and studies necessary for finding new hydrocarbon occurrence. Usually seismic (or 3D seismic) studies are shot, and old exploration data (seismic lines, well logs, reports) are used to expand upon the new studies.

Exploration stage

Sometimes gravity and magnetic studies are conducted, and oil seeps and spills are mapped to find potential areas for hydrocarbon occurrences. As soon as a significant hydrocarbon occurrence is found by an exploration- or wildcat-well the appraisal stage starts.

Appraisal stage

The Appraisal stage is used to delineate the extent of the discovery.

Hydrocarbon reservoir properties, connectivity, hydrocarbon type and gas-oil and oil-water contacts are determined to calculate potential recoverable volumes.

Appraisal stage

This is usually done by drilling more appraisal wells around the initial exploration well. Production tests may also give insight in reservoir pressures and connectivity. Geochemical and petrophysical analysis gives information on the type (viscosity, chemistry, API, carbon content, etc.) of the hydrocarbon and the nature of the reservoir (porosity, permeability, etc.).

Production stage

After a hydrocarbon occurrence has been discovered and appraisal has indicated it is a commercial find the production stage is initiated. This stage focuses on extracting the hydrocarbons in a controlled way (without damaging the formation, within commercial favorable volumes, etc.).

Production stage

Production wells are drilled and completed in strategic positions. 3D seismic is usually available by this stage to target wells precisely for optimal recovery.

Sometimes enhanced recovery (steam injection, pumps, etc.) is used to extract more hydrocarbons or to redevelop abandoned fields.

Analysis of reservoir

The existence of a reservoir rock (typically, sandstones and fractured limestones) is determined through a combination of regional studies (i.e. analysis of other wells in the area), stratigraphy and sedimentology (to quantify the pattern and extent of sedimentation) and seismic interpretation.


Once a possible hydrocarbon reservoir is identified, the key physical characteristics of a reservoir that are of interest to a hydrocarbon explorationist are its bulk rock volume, net-to-gross ratio, porosity and permeability.


Bulk rock volume, or the gross rock volume of rock above any hydrocarbon-water contact, is determined by mapping and correlating sedimentary packages.

The net-to-gross ratio, typically estimated from analogues and wireline logs, is used to calculate the proportion of the sedimentary packages that contains reservoir rocks.


The bulk rock volume multiplied by the net-to-gross ratio gives the net rock volume of the reservoir. The net rock volume multiplied by porosity gives the total hydrocarbon pore volume i.e. the volume within the sedimentary package that fluids (importantly, hydrocarbons and water) can occupy.


The summation of these volumes (see STOIIP and GIIP) for a given exploration prospect will allow explorers and commercial analysts to determine whether a prospect is financially viable.


Traditionally, porosity and permeability were determined through the study of hand specimens, contiguous parts of the reservoir that outcrop at the surface and by the technique of formation evaluation using wireline tools passed down the well itself.


Modern advances in seismic data acquisition and processing have meant that seismic attributes of subsurface rocks are readily available and can be used to infer physical/sedimentary properties of the rocks themselves.

Thanks for listening and reading

By : Khawar Nehal

Applied Technology Research Centerhttp://atrc.net.pk

The Training Companyhttp://atrc.net.pk/the-training-company

30 March 2016

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Oil and Gas Reservoir Engineering

Engineering

Transcript of Oil and Gas Reservoir Engineering