Unconventional_reservoir_seminar

1. SEMINAR PRESENTATION
(GPH411)
UNCONVENTIONAL RESERVOIR
BY
OGUNDELE RICHARD ADEMOLA
15/56FJ041
SUPERVISED BY: DR W.O RAJI
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2. Introduction
The Reservoir rock
Unconventional and Conventional Reservoir
Hydrocarbon Evaluation of the Reservoir
Petroleum System Properties of Unconventional
Reservoir
Extraction of Unconventional hydrocarbon reservoir
Types of Unconventional reservoirs
Case Study
Recent Development and Conclusion
OUTLINE
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3. Introduction
Unconventional reservoir is becoming a large
resource potential gradually and making
explorationists shift their attention to this area.
Unconventional reservoir have been attached great
importance by countries and companies all over the
world. It will become the inevitable trend of industry
development that the extension from the conventional
oil and gas exploration to unconventional oil and gas
in oil and gas exploration and development field.
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4. Reservoir Rock are the rocks that have ability to store fluids
inside its pores, so that the fluids (water, oil and gas) can be
accumulated. In petroleum geology, reservoir is one of the elements
of petroleum system that can accumulate hydrocarbons (oil or gas).
Reservoir rock should have a good porosity and permeability to
accumulate and drain oil in economical quantities.
Oil and gas usually accumulate on the top of water and they are
always here relatively to their difference of densities.
In the cases the reservoir has yet been identified, key characteristic
crucial to hydrocarbon explorationists are bulk rock volume and net-
to-gross ratio.
The Reservoir rock
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5. Unconventional and Conventional Reservoir
Unconventional Reservoir: are reservoirs that requires special recovery
operations outside the conventional operating practices, the rocks have high
porosity and low permeability which keeps the hydrocarbons trapped in place,
therefore not requiring a cap rock.
Conventional Reservoir: is that which has a good permeability and can flow
with ease towards the well bore. the naturally occurring hydrocarbons, such as
crude oil or natural gas, are trapped by overlying rock formations with lower
permeability.
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6. Kerogen type
Predominant
hydrocarbon potential
Amount of
hydrogen
Typical depositional
environment
I Oil prone Abundant Lacustrine
II Oil and gas prone Moderate Marine
III Gas prone Small Terrestrial
IV
Neither (primarily
composed of vitrinite) or
inert material
None Terrestrial
Hydrocarbon Evaluation of an Unconventional Reservoir
Unconventional reservoirs are evaluated based on their potential to be a successful
hydrocarbon system. The following evaluations are completed to quantitatively determine
this:
•Maturity- Have the kerogens spent enough time in the oil window to turn into
hydrocarbons?
•Bulk Volume - Is the bulk volume of hydrocarbons within the source rock enough to
make it economical (40-60% max expulsion)?
•Clay Content- Clay content has to be low which makes fracking easy
•Kerogen Content- The type of kerogen found in the source rock is used to determine
what type of [hydrocarbon] your reservoir can contain.
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7. Generation
Unconventional reservoir is also generated as the same as conventional reservoir. The oil
shale in the reservoir gets matured thermally till petroleum is been formed. It is generated in
a Deep marine environment with no or low energy with Mixed organic matter and fine-
grained sediment. Oil and gas tapped is tapped in it (shale) Reservoir is the shale itself.
Maturity
Under the influence of high temperature, pressure and time, the kerogen in source rocks is
transformed, broken down into smaller molecules and finally into oil and gas.
Migration
Migration does not occur in the unconventional reservoir because the source rock is the
reservoir rock
Recovery
Unconventional is a method that allows to drill down, drill horizontally, and fracking
occurs. This allows oil and gas to be flowing from tight sands that we normally could not
retrieve with conventional methods of drilling. It can be recovered by using water and gas
injection which pushes the oil to the surface tank.
Petroleum System Properties of Unconventional Reservoir
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8. Hydraulic Fracturing
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9. Unconventional reservoir cannot be extracted or recovered freely. There has to a
presence of an external force. The well bore are drilling vertically and horizontally and
fracking occurs also called Hydraulic fracturing which produces fractures in the rock
formation that stimulate the flow of natural gas or oil, increasing the volumes that can
be recovered. Wells may be drilled vertically hundreds to thousands of feet below the
land surface and may include horizontal or directional sections extending thousands of
feet.
Fractures are created by pumping large quantities of fluids at high pressure down a
wellbore and into the target rock formation. Hydraulic fracturing fluid commonly
consists of water, proppant and chemical additives that open and enlarge fractures
within the rock formation. These fractures can extend several hundred feet away from
the wellbore.
Once the injection process is completed, the internal pressure of the rock formation
causes fluid to return to the surface through the wellbore. This fluid is known as both
"flowback" and "produced water" and may contain the injected chemicals with
naturally occurring materials such as brines, metals, radionuclides, and hydrocarbons.
The flowback and produced water is typically stored on site in tanks or pits before
treatment, disposal or recycling.
Extraction of Unconventional hydrocarbon reservoir
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10. Shale Oil
These are fine-grained sedimentary rocks, which are rich in immature organic
material called kerogen. Oil shale is a mother rock, which was not buried at a depth
great enough for thermal maturity, which is necessary to transform Kerogen into oil
and/or gas. Its heating value, when crushed and burned directly, ranges between (500-
4000 Kcal/kg). Shale oil exists in many countries including the U.S.A, Germany,
China, Brazil etc.
Shale oil is produced by surface or underground mining. The mined rock (oil shale)
is shipped for a chemical process called PYROLYSIS, during which the crushed rock
is heated to 400-500 oC (free of oxygen), so that the kerogen is converted to shale oil
and shale gas.
When shale extraction operation ceases, groundwater filtrates into the operation
area, which has become permeable, due to production and it may filtrate residual
hydrocarbons or chemicals, so it can be used to improve recovery. However, due to its
heavy environmental impact (e.g. groundwater contamination), environmentalists
oppose the production and usage of shale oil.
Types Of Unconventional Hydrocarbon
Reservoirs
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12. Tight Gas Sands
A tight gas reservoir is one having permeability less than 0.1 mD. The
sand is called tight since it has low permeability due to cementation, compaction,
fine rock grains.
Tight gas is difficult to produce because of its low permeability and because
production mechanisms are poorly understood, which results in high production
costs. The production mechanism involves expansion, compaction, and
turbulence around the wellbore due to micro-darcy range of permeability.
Permeability might also decrease around the wellbore due to the pressure load,
consequently tight well-spacing and/or fracturing or horizontal well completion
is required.
For an efficient and economical production from tight gas reservoirs, well
stimulation is required in both vertical and horizontal wells. The formation is
fractured in order to have a good conductive path between the reservoir rock and
the well.
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13. Coal-Bed Methane (CBM) Gas
Coal bed methane (CBM) is natural gas that is stored in deeply buried coal seams. It
has been employed with ventilation and/or drilled production wells to depressurize coal
seams in order to prevent the formation of an air-methane blasting mixture during coal
mining. Coal originates from buried organic matter in an environment free from oxygen.
Biogenic methane is produced during the transformation process.
Fluid movement in coal is controlled by diffusion in coal matrix and by Darcy flow
in a fracture system. The cleat system is filled with water at its initial condition in most
CBM reservoirs.
Gas injection significantly enhances CBM recovery. The injection takes place to
displace methane adsorbed on the coal (Kerogen) surface without decreasing reservoir
pressure. CO2 frontally displaces methane, while N2 decreases the partial pressure of
CH4, which results in it’s desorption. CO2 adsorbs on the coal surface until N2 breaks
through practically without adsorption. Adsorption of CO2 results in coal-swelling and
permeability reduction (e.g. 100 times lower). In the case of nitrogen injection, N2
breaks through very early, but the permeability of the cleats may multiply 10 times
compared to its original extent.
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14. Case Study
COALBED METHANE IN THE SAN JUAN BASIN OF COLORADO
Introduction
The San Juan is a mature, well-developed CBM that has been the leading
source of CBM in the nation. In the San Juan region in Colorado, much of the
tension has centered on conflicts between developing energy resources and
preserving lands for residential use, recreation, road-less areas, and other goals,
and possible impacts of development on drinking water quality.
Illustration of a
hypothetical
coalbedmethan
e well, showing
detail of coal
seam, how
water removal
causes gas
release, gas
transport pipes,
and above
groundwell site
equipment.
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15. Geologic Setting Of San Juan Basin
The San Juan Basin is a major gas and oil
producing province located in the southeastern corner
of the Colorado Plateau. The basin has an elliptical
shape, and at its longest is about 100 miles (north-
south)by 90 mile (east-west), covering an area of
about 7,100 square miles (4.54 million acres). The San
Juan Basin is a large bowl in the bedrock that was
filled up over the past 500 million years with more
than 14,00010 feet of sedimentary rocks such as
sandstone, limestone, shale, and coal.
The vast majority of the coal bed methane resource
currently being developed in the San Juan Basin is
contained within the Cretaceous Fruitland Formation.
The organic plant material that formed the coal was
deposited in swamps that flourished for millions of
years. In the time since the plant material was
deposited, the western interior of North America has
undergone a series of mountain building and other
tectonic events during which the basin itself was
formed, the Hogback Monocline, which delineates the
northern and western edges of the Basin, was formed,
and the Colorado Plateau, containing the San Juan
Basin, was uplifted as a coherent block.
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16. Coalbed Methane In The San Juan Basin
The Coal-bed gas is present in all coal beds and is formed by biochemical and
physical processes during the conversion of accumulated plant material into coal. First,
the coal is both the source rock and reservoir rock of the methane, and water within the
coal seam is the trap. Second, the coal that generates the methane formed in the
swampy areas, so the source of the organic matter is plant material rather than animal
material. Third, when the plant material is subjected to increased heat and pressure
(diagenesis), the organic material undergoes chemical and physical changes and turns
into coal without moving from the original point of deposition, except for compaction.
The methane within the coal is generated by either microbial(biogenic) or thermal
(thermogenic) processes shortly after burial and throughout the diagenesis that results
from further burial. Fourth, the methane is not just occupying pore spaces within the
coal, but is in fact adsorbed or accumulated on the surface of the coal. Water contained
in fractures (cleats) in the coal exerts enough pressure on the coal to keep the methane
in place. This means that when the coal seam is tapped with a well, gas will generally
not flow until after the water has been removed from the coal seam. Removal of the
water releases pressure on the coal, and if the coal is sufficiently fractured, release of
the water pressure allows the methane to escape. As more water is removed, more
methane desorbs (releases) from the coal.
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17. No2/Co2 Enhanced Recovery
The injection of carbon dioxide and/or nitrogen into coal bed
methane reservoirs can greatly enhance gas recovery, from 30% to 400%
above expected returns. This technology can increase methane
production rates up to six-fold, and increase “producible gas reserves” up
to two-fold. The injected gas displaces the methane in the coal, and some
consider this to be the “ultimate methodology for extraction of this
valuable resource.”
“coal bed methane reservoirs that might otherwise not be economical to
develop under conventional production operations could become fully
developed.”Recovery of additional gas from the same well prolongs
useful well life, reducing the need to drill additional wells in order to
deplete the resource. Enhanced recovery via injection of gases has been
tested in the San Juan Basin and found to be economically and
technically feasible. Using carbon dioxide for enhanced recovery has the
additional advantage of disposing of a greenhouse gas with “virtually
permanent storage capacity.”
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18. Research revealed that miscible gas injection (produced gases,CO2, etc)
is the most promising method among the EOR techniques(miscible gas,
water flooding, surfactant, chemical and polymer). Experimental studies
shows that CO2 injection had the highest potential of improved recovery in
unconventionals followed by produced gas injection and that diffusion was
the most predominant mechanism.
The unconventional hydrocarbons, tight gas, coal-bed methane, heavy oil
and tar sands have become major domains in the exploration development of
unconventional hydrocarbons worldwide; and shale gas has become a
promising domain for the recovery of unconventional gas in the world In
China, the exploration and development of tight gas, shale gas, tight oil and
coal-bed methane have significant breakthroughs and the studies of oil
shales, gas hydrates and tar sands have been progressed greatly
Correspondingly the world’s emerging economies will require sustained use
of oil and gas for the foreseeable future. Because oil and gas from
conventional reservoirs is declining( the “easy oil” is gone), Unconventional
resources will become the focus for every petroleum explorationists.
Recent Development and Conclusion
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