Heavy oil production

Last updated

Heavy oil production is a developing technology for extracting heavy oil in industrial quantities. Estimated reserves of heavy oil are over 6 trillion barrels, three times that of conventional oil and gas.

Contents

Factors that affect the difficulty of putting reserves into production include permeability, porosity, depth and pressure. The density and viscosity of the oil is the determining factor. [1] Density and viscosity determine the method of extraction. [2]

Oil viscosity varies with temperature and determines the ease of extraction; temperature can be controlled so that oil can be moved without employing additional techniques. [3] Density is more important for refiners since it represents the yield after distillation. However, no relationship links the two. [2]

Oil reservoirs exist at varying depths and temperatures. Although viscosity varies significantly with temperature, density is the standard in oilfield classification. Crude oil density is commonly expressed in degrees of American Petroleum Institute (API) gravity which are associated with specific gravity. The lower the API gravity, the denser the oil. The API gravity of liquid crude oil ranges from 4º for tar rich in bitumen to condensates that have an API gravity of 70º. Heavy oils are classified between ultra-heavy oils and light oils. They have API gravities ranging between 10º and 20º. [4]

Crude oil generated by petroleum source rocks has an API gravity of between 30º and 40º. Crude oil becomes heavy after considerable degradation, after entrapment and during devolatilization. Degradation occurs through chemical and biological processes when oil reservoirs become contaminated by bacteria through subsurface water. [5] The bacteria then break down some crude oil components into heavy components, making it more viscous. Water carries away low molecular weight hydrocarbons in solution form since they are more soluble. When crude oil is enclosed by a poor quality seal, lighter molecules separate and escape, leaving behind the heavier components through devolatilization. [6]

Heavy oils are commonly found in geologically young formations since they are shallow and have less efficient seals, providing the conditions for heavy oil formation.

Terminology

Injection pattern

The injection pattern refers to the arrangement of the production and injector wells to the position, size, and orientation of flow of a reservoir. [7] Injection patterns can vary over the well lifetime by moving the injection well to areas where maximum volume of contact can be achieved.

Geographical heterogeneity

Geological heterogeneity is the spatial distribution of porosity and permeability in a reservoir rock.

Permeability

Permeability depends on the size of the sediment grains that formed the rock and the manner in which they were packed. Permeability is the number of pores, and their interconnectedness in a rock and the existence of different layers in a rock with different permeability is a manifestation of geological heterogeneity. When steam injection takes place, water flows through the more permeable layers, bypassing the oil-rich less permeable layers. This causes low sweep efficiency and early water production with the volume of oil in contact with the water. [8]

Sweep efficiency

Sweep efficiency is the measure of the effectiveness of an EOR method that depends on the total volume of the reservoir that the injected fluid contacts. Sweep efficiency is affected by multiple factors: mobility ratio, directional permeability, cumulative water injected, flood pattern, geological heterogeneity and distribution of pressure between injectors and producers.

Displacement efficiency

Displacement efficiency is the fraction of oil that is recovered from a zone that has been swept by a steam injection or any other displacement method. It is the percentage volume of oil that has been recovered through displacement by an injected fluid or displacing element injected into the reservoir. It is the difference between the volume of the reservoir before the displacement begins and the volume after the displacement has ended. [9]

Amplitude versus offset

Amplitude Versus Offset (AVO) is a technique used in seismic inversion to forecast the existence of reservoirs and the rock types surrounding it. Literature reviews and studies incorporate the analysis of AVO and seismic inversion in oil exploration and rock physics studies. [10]

Seismic waves projected into oil reservoirs undergoing steam injection give data that show the existence of high values of wave attenuation. This attenuation is usually based on velocity dispersion. Studies show seismic wave reflection between an elastic overburden and an equivalent medium have coefficients of reflection that vary with frequency. This variation, depends on the behavior of AVO at the interface. The calculation of synthetic seismographs for the ideal model is carried out using the reflectivity technique for those materials whose velocities and attenuations are frequency dependent. This is usually used since the effects of velocity and attenuation variations are detectable on stacked data. [11]

Improved spectral decomposition techniques have shown the frequency dependent parameters more clearly. Saturated rocks, for example, have seismic low frequency effects concerning hydrocarbon-saturated rocks. Furthermore, hydrocarbon-saturated zones have extremely high values of attenuation from the direct quality factor (Q) measurements. [10] Systemic variations of frequencies with offset, where the standard amplitude against the offset is the AVO, disregards attenuation resulting in the use of the purely reflective model. The primary objective is balancing the frequency content of near and far stacks, while correcting for the effect of the attenuation over the overburden. [12]

AVO is used to detect the existence of oil reservoirs because of the anomaly evident in oil reservoirs where AVO rising is prominent in oil-rich sediments. It is not as useful in defining the rock formations and permeability properties to improve sweep efficiency. Furthermore, not all oil reservoirs manifest the same anomalies associated with hydrocarbon oil reservoirs since they are sometimes caused by residual hydrocarbons from breached columns of gas.

Seismic analysis

Seismic surveys are the standard method used to map the Earth's crust. Data from these surveys are used to project detailed information about the types and properties of rocks. Bouncing sound waves off rock formations underneath the surface allows the reflected waves to be analyzed. The time lapses between the incident and reflected waves, as well as the properties of the received wave, provide information about the types of rocks and the possible reserves of petroleum and gas deposits

If the geological heterogeneity of a reservoir is known, the injection patterns can be designed to direct the injections to the less permeable layers of the rock that have oil. The challenge is that the reservoir's permeability distribution is hard to determine because heterogeneity changes from one area to another. Therefore, to maximize oil recovery (sweep efficiency), it is necessary to monitor and map the orientation of the permeability layers via seismic surveys. [13] Seismic waves are sent through the rock formations and the time lapse and distortions in the seismic waves are analyzed to map the permeability orientation to enhance the efficient installation of injection patterns. [14]

Oil production techniques

Oil recovery involves three stages of extraction: primary, secondary and tertiary. Since mobility is a ratio of effective permeability and phase viscosity, the productivity of a well is directly proportional to the product of layer thickness of the reservoir rock and mobility. [15] [16]

Primary recovery

Primary recovery uses the pressure build-up of gasses in the reservoir, gravity drainage or a combination of the two. These methods constitute cold production and are commonly referred to as using “natural lift". For conventional oil, cold production has a recovery factor of more than 30 percent while for heavy oil it raises 5 to 10 percent. [2]

One variation of the cold production method is called Cold Heavy Oil Production with Sand (CHOPS). CHOPS creates a wormhole or void where oil gets pulled from the surrounding rocks towards the wellbore. These methods are termed cold production, since they are used at reservoir ambient temperature. When natural lift pressure does not generate sufficient underground pressure or when the pressure declines and is no longer sufficient to move oil through the wellbore, primary production has reached its extraction limit, to be succeeded by secondary recovery.

Secondary recovery

Secondary recovery methods also use cold production, but employ external sources of pressure to generate the required internal pressure, still at reservoir temperature. [17] Secondary recovery methods involve the creation of artificial pressure through the injection of elements to create artificial pressure. Water, natural gas or carbon dioxide are the primary injectates. The pressure forces oil up the production well. [18] Over time the artificial pressure loses efficacy because the remaining (heavy) oil is too viscous to flow and is held by sandstone in the reservoirs. The two cold production recovery methods have a combination recovery factor of between 10 and 20 percent depending on the oil properties and types of rocks. [17]

Tertiary recovery

Tertiary recovery is commonly known as Enhanced Oil Recovery (EOR). It is the method of producing oil after the primary and secondary stages have extracted most of the oil in a reserve. Specifically, enhanced oil recovery is used to recover oil trapped in porous rocks and the heavy oil that is too viscous to flow. The three methods for tertiary recovery are: chemical enhanced recovery, thermal enhanced recovery, and miscible enhanced recovery. [12]

It involves both thermal and non-thermal methods. [17] Non-thermal methods include the use of chemicals and microbes to loosen trapped heavy oil and carbon dioxide under pressure. However, thermal methods - mainly steam injection - are the most efficient way of reducing viscosity and mobilizing heavy oil.

Steam injection

Among the three main types of steam injection, steam flooding, for example, injects pressurized steam into the injector well where it heats up and forces the more mobile oil out. EOR techniques are expensive due to the required energy and materials. [3] Therefore, the amount of heavy oil to be recovered from a reservoir depends on the economics. Because of this, ERO begins with analysis of the reservoir, rock formations, permeability, pore geometry and viscosity. Including the heterogeneity of a reservoir, these factors influence the success of any recovery method.

Overall efficiency is the product of the sweep efficiency and displacement efficiency.

Cyclic steam stimulation

Cyclic Steam Stimulation (CSS) injects steam through a single well for a period, leaving it to heat up and reduce viscosity, then extracting oil through the same well in alternating cycles of injection and extraction.

Steam-assisted gravity drainage

Steam-Assisted Gravity Drainage (SAGD) involves the use of stacked horizontal wells. The top horizontal well is used to inject steam which heats up the surrounding heavy oil which then flows into the bottom horizontal production well. [19]

Steam injection consists of two core methods: cyclic steam injection and steam flooding.

Cyclic steam injection

During cyclic steam circulation (CSC), steam is injected into the oil reservoir where the resulting high pressure ruptures the reservoir rocks and heats up the oil, reducing its viscosity. The oil is removed in three stages: injection, soaking and production. High-temperature, high-pressure steam is left in the reservoir from days to weeks so that the heat can be absorbed by the oil. Production then begins. Initially, production is high, but subsides as heat is lost; the process is repeated until it becomes uneconomical to do so. Cyclic steam injection recovers about 10 to 20 percent of the entire oil volume. When this method becomes uneconomical, steam injection is employed. [20]

Steam injection is usually used in horizontal and vertical oil wells for reservoirs with viscosity as high as -100,000cP. In cyclic steam injection wells, oil can be both viscous and solid. The principal mechanism is to dissolve the “solid”. [20] No consensus establishes the ideal soaking time, which may vary from days to weeks. However, shorter soaking times are favored for operational and mechanical considerations. After the first treatment, oil production takes place through natural lifting because of the initial reservoir energy. However, for subsequent cycles, production may have to be aided with pumping. Cyclic injection becomes less and less efficient in oil production as the number of cycles increases. [19] As many as nine cycles can be used depending on the reservoir characteristics.

Continuous steam injection (steam flooding)

This method recovers more oil than cyclic steam injection. It has lower thermal efficiency than CSC and requires a larger surface area. [21] It uses at least two wells, one for steam injection and the other for oil production. Steam flooding recovers about 50 percent of the total oil. Steam is injected at high temperature and pressure through an injector. Steam injection techniques have become more feasible and efficient. Several variations have been developed. [12] However, the high costs involved mandate careful evaluations, in-depth study of the oil reservoir and proper design. [22]

Rock physics

Traditionally, the properties of rocks and minerals beneath the earth's surface were defined through seismic exploration and seismology from earthquakes. Travel time, variations in phase and amplitude of seismic waves produced during seismic exploration show rock and fluid properties at the subsurface level. Previously, exploration seismology explored seismic data only for rock formations that could hold hydrocarbons. However, due technological advances, seismic data became useful to determine pore fluids, saturation, porosity and lithology. [23]

Reservoir properties and seismic data have been linkedby a recent development called rock physics. Rock physics has been employed in the development of essential techniques such as reservoir seismic monitoring, direct hydrocarbon detection and seismic lithology discrimination using angle dependent reflectivity. Rock physics applications are based on understanding the different properties that affect seismic waves. These properties influence how waves behave as they propagate and how a change in one of those properties can produce different seismic data. Factors such as temperature, fluid type, pressure, pore type, porosity, saturation and others are interrelated in such a way that when one element changes others change as well. [24]

Gassmann equation

Pore fluid properties and fluid substitution in rock physics are calculated using Gassmann's equation. It calculates how seismic properties are affected by the fluid change using frame features. The equation uses the known bulk moduli of the pore fluid, the solid matrix and the frame module to calculate the bulk modulus of a medium saturated with liquid. The rock-forming minerals are the solid matrix, the frame is the skeleton rock sample, while the pore fluid is gas, water, oil, or some combination. For the equation to be used, the underlying assumptions are that 1) the matrix and the frame are both macroscopically homogeneous; 2) the pores in the rock are all interconnected; 3) the fluid in the pores is frictionless; 4) the fluid system in the rock is a closed system that is it is undrained; and 5) that the fluid in the rock does not in any way interact with the solid to make the frame softer or harder. [20]

The first assumption assures that the wavelength of the wave is longer than the pores and grain sizes of the rock. The assumption meets the general range of wave wavelengths and frequencies of the laboratory to seismic range. Assumption 2) suggests that the permeability of the rock pores is uniform and no isolated pores are present in the rock such that a passing wave induces full equilibrium of fluid flow of the pores over a half period cycle of the wave. Since pore permeability is relative to the wavelength and frequency, most rocks meet the assumption. [19] However, for seismic waves, only unconsolidated sands satisfy this assumption, because of their high permeability and porosity. On the other hand, for the high frequencies such as logging and laboratory frequencies, most rocks can meet this assumption. As a result, the velocities calculated using Gassmann's equation are lower than those measured using logging or laboratory frequencies. Assumption 3) suggests that the fluids have no viscosity, but since in reality all fluids have the viscosity, this assumption is violated by Gassmann equations. Assumption 4) suggests that the rock-fluid flow is sealed at the boundaries for a laboratory rock sample meaning that the changes in stresses caused by a passing wave do not cause a significant flow of fluid from the rock sample. Assumption 5) prevents any disrupting interaction between the chemical or physical properties of the rock matrix and the pore fluid. This assumption is not always met because interaction is inevitable and the surface energy is usually changed because of it. For example, when sand interacts with heavy oil, the result is a high shear and bulk modulus mixture. [13]

Sources

Related Research Articles

<span class="mw-page-title-main">Petroleum engineering</span> Extracting crude oil and natural gas

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.

Petroleum geology is the study of the origins, 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.

<span class="mw-page-title-main">Oil well</span> Well drilled to extract crude oil and/or gas

An oil well is a drillhole boring in Earth that is designed to bring petroleum oil hydrocarbons to the surface. Usually some natural gas is released as associated petroleum gas along with the oil. A well that is designed to produce only gas may be termed a gas well. Wells are created by drilling down into an oil or gas reserve and if necessary equipped with extraction devices such as pumpjacks. Creating the wells can be an expensive process, costing at least hundreds of thousands of dollars, and costing much more when in difficult-to-access locations, e.g., offshore. The process of modern drilling for wells first started in the 19th century but was made more efficient with advances to oil drilling rigs and technology during the 20th century.

<span class="mw-page-title-main">Hydrocarbon exploration</span> Attempts to locate oil and gas

Hydrocarbon exploration is the search by petroleum geologists and geophysicists for deposits of hydrocarbons, particularly petroleum and natural gas, in the Earth's crust using petroleum geology.

<span class="mw-page-title-main">Petroleum reservoir</span> Subsurface pool of hydrocarbons

A petroleum reservoir or oil and gas reservoir is a subsurface accumulation of hydrocarbons contained in porous or fractured rock formations. Such reservoirs form when kerogen is created in surrounding rock by the presence of high heat and pressure in the Earth's crust.

Enhanced oil recovery, also called tertiary recovery, is the extraction of crude oil from an oil field that cannot be extracted otherwise. Although the primary and secondary recovery techniques rely on the pressure differential between the surface and the underground well, enhanced oil recovery functions by altering the chemical composition of the oil itself in order to make it easier to extract. EOR can extract 30% to 60% or more of a reservoir's oil, compared to 20% to 40% using primary and secondary recovery. According to the US Department of Energy, carbon dioxide and water are injected along with one of three EOR techniques: thermal injection, gas injection, and chemical injection. More advanced, speculative EOR techniques are sometimes called quaternary recovery.

Steam-assisted gravity drainage is an enhanced oil recovery technology for producing heavy crude oil and bitumen. It is an advanced form of steam stimulation in which a pair of horizontal wells are drilled into the oil reservoir, one a few metres above the other. High pressure steam is continuously injected into the upper wellbore to heat the oil and reduce its viscosity, causing the heated oil to drain into the lower wellbore, where it is pumped out. Dr. Roger Butler, engineer at Imperial Oil from 1955 to 1982, invented the steam assisted gravity drainage (SAGD) process in the 1970s. Butler "developed the concept of using horizontal pairs of wells and injected steam to develop certain deposits of bitumen considered too deep for mining". In 1983 Butler became director of technical programs for the Alberta Oil Sands Technology and Research Authority (AOSTRA), a crown corporation created by Alberta Premier Lougheed to promote new technologies for oil sands and heavy crude oil production. AOSTRA quickly supported SAGD as a promising innovation in oil sands extraction technology.

Petrophysics is the study of physical and chemical rock properties and their interactions with fluids.

Carbon dioxide (CO2) flooding is a process in which carbon dioxide is injected into an oil reservoir to increase the output when extracting oil. This is most often used in reservoirs where production rates have declined due to depletion.

<span class="mw-page-title-main">Extraction of petroleum</span> Removal of petroleum from the earth

Petroleum is a fossil fuel that can be drawn from beneath the Earth's surface. Reservoirs of petroleum are formed through the mixture of plants, algae, and sediments in shallow seas under high pressure. Petroleum is mostly recovered from oil drilling. Seismic surveys and other methods are used to locate oil reservoirs. Oil rigs and oil platforms are used to drill long holes into the earth to create an oil well and extract petroleum. After extraction, oil is refined to make gasoline and other products such as tires and refrigerators. Extraction of petroleum can be dangerous and have led to oil spills.

<span class="mw-page-title-main">Steam injection (oil industry)</span> Method of extracting heavy crude oil

Steam injection is an increasingly common method of extracting heavy crude oil. Used commercially since the 1960s, it is considered an enhanced oil recovery (EOR) method and is the main type of thermal stimulation of oil reservoirs. There are several different forms of the technology, with the two main ones being Cyclic Steam Stimulation and Steam Flooding. Both are most commonly applied to oil reservoirs, which are relatively shallow and which contain crude oils which are very viscous at the temperature of the native underground formation. Steam injection is widely used in the San Joaquin Valley of California (US), the Lake Maracaibo area of Venezuela, and the oil sands of northern Alberta, Canada.

Downhole oil–water separation (DOWS) technologies are apparatuses and methods that separate production fluids into a petroleum-rich stream and water-rich stream within an oil well. A DOWS system installed in a borehole will receive the fluids from an oil-producing zone in an oil reservoir and separate the mixture into a stream that is mostly water and a stream that is primarily crude oil and natural gas and direct the streams to different destinations. After the separation in the borehole, DOWS systems pump the petroleum-rich stream to the surface and inject the water-rich stream into a different zone or formation accessible to the same wellbore.

<span class="mw-page-title-main">Batı Raman oil field</span>

The Batı Raman oil field (batı meaning west in Turkish) is located in Batman Province, in the Southeastern Anatolia Region of Turkey. With estimated reserves of 1.85 billion barrels (252×106 tonnes) and a production rate of around 7,500 barrels per day (1,190 m3/d) from 300 wells (as of 2007), it is the largest and most productive oil field in Turkey.

Microbial Enhanced Oil Recovery (MEOR) is a biological-based technology involving the manipulation of functions or structures within microbial environments present in oil reservoirs. The primary objective of MEOR is to improve the extraction of oil confined within porous media, while boosting economic benefits. As a tertiary oil extraction technology, MEOR enables the partial recovery of the commonly residual 2/3 of oil, effectively prolonging the operational lifespan of mature oil reservoirs.

<span class="mw-page-title-main">Morris Muskat</span> American petroleum engineer

Morris Muskat was an American petroleum engineer. Muskat refined Darcy's equation for single phase flow, and this change made it suitable for the petroleum industry. Based on experimental results worked out by his colleagues, Muskat and Milan W. Meres also generalized Darcy's law to cover multiphase flow of water, oil and gas in the porous medium of a petroleum reservoir. The generalized flow equation provides the analytical foundation for reservoir engineering that exists to this day.

Morris Muskat et al. developed the governing equations for multiphase flow in porous media as a generalisation of Darcy's equation for water flow in porous media. The porous media are usually sedimentary rocks such as clastic rocks or carbonate rocks.

<span class="mw-page-title-main">Oil and gas reserves and resource quantification</span> Industry concept of crude oil and natural gas reserves and resources

Oil and gas reserves denote discovered quantities of crude oil and natural gas that can be profitably produced/recovered from an approved development. Oil and gas reserves tied to approved operational plans filed on the day of reserves reporting are also sensitive to fluctuating global market pricing. The remaining resource estimates are likely sub-commercial and may still be under appraisal with the potential to be technically recoverable once commercially established. Natural gas is frequently associated with oil directly and gas reserves are commonly quoted in barrels of oil equivalent (BOE). Consequently, both oil and gas reserves, as well as resource estimates, follow the same reporting guidelines, and are referred to collectively hereinafter as oil & gas.

In petroleum engineering, TEM, also called TEM-function is a criterion to characterize dynamic two-phase flow characteristics of rocks. TEM is a function of relative permeability, porosity, absolute permeability and fluid viscosity, and can be determined for each fluid phase separately. TEM-function has been derived from Darcy's law for multiphase flow.

<span class="mw-page-title-main">Fault zone hydrogeology</span>

Fault zone hydrogeology is the study of how brittlely deformed rocks alter fluid flows in different lithological settings, such as clastic, igneous and carbonate rocks. Fluid movements, that can be quantified as permeability, can be facilitated or impeded due to the existence of a fault zone. This is because different mechanisms that deform rocks can alter porosity and permeability within a fault zone. Fluids involved in a fault system generally are groundwater and hydrocarbons.

<span class="mw-page-title-main">Unconventional (oil and gas) reservoir</span> Type of hydrocarbon reservoir

Unconventional reservoirs, or unconventional resources are accumulations where oil and gas phases are tightly bound to the rock fabric by strong capillary forces, requiring specialised measures for evaluation and extraction.

References

  1. ↑ Toole & Grist 2003.
  2. 1 2 3 Ambastha 2008.
  3. 1 2 Alusta et al. 2011.
  4. ↑ Martinius et al. 2005.
  5. ↑ Drummond & Israelachvili 2004.
  6. ↑ Awan, Teigland & Kleppe 2008.
  7. ↑ Sydansk & Seright 2007.
  8. ↑ Frampton et al. 2009.
  9. ↑ Ohms et al. 2009.
  10. 1 2 Passalacqua & Strack 2016.
  11. ↑ Teng et al. 2017.
  12. 1 2 3 Muggeridge et al. 2014.
  13. 1 2 Wilson 2014.
  14. ↑ Lumley 2012.
  15. ↑ Alkouh, Ahmad; Irani, Mazda; Putra, Dike; Jia, Bao; Abdelfatah, Elsayed; Tran, Minh; Canbaz, Celal Hakan; Temizel, Cenk (2018-12-10). A Comprehensive Review Heavy Oil Reservoirs, Latest Techniques, Discoveries, Technologies and Applications in the Oil and Gas Industry. Society of Petroleum Engineers. doi:10.2118/193646-MS. ISBN   9781613996409.
  16. ↑ Jayasekera & Goodyear 2002.
  17. 1 2 3 Istchenko & Gates 2014.
  18. ↑ Moulds et al. 2005.
  19. 1 2 3 Ren et al. 2016.
  20. 1 2 3 Shabelansky, Malcolm & Fehler 2015.
  21. ↑ Al-Mutairi et al. 2017.
  22. ↑ Berron et al. 2015.
  23. ↑ Beiranvand et al. 2017.
  24. ↑ Al-Kindi et al. 2015.
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.