unconventional hydrocarbon production€¦ · k – rdöls kapitel 8 –unconventional hydrocarbon...

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Kapitel 8 – Unconventional Hydrocarbon Production

Unconventional hydrocarbon production – Fracking

The objective of modern fracking is to reopen and/or create

fractures over a wide range of scales in tight shales and

keep the pores open for oil extraction by application of a

proppant so that oil and gas can migrate to a production well

through the proppant filled fractures.

In a modern fracking treatment, approximately swimming

20,000 m3 is injected into the target formation. Simply using

large volumes of water in tight shale fracking is not sufficient.

The major development leading to the success of modern

fracking was the use of slickwater as the injection fluid. Its

main additive is polyacrylamide added at low concentration.

This high-molecular-weight chain polymer suppresses fluid

turbulence, thereby reducing the frictional resistance to fluid

flow during injection.

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Basins with major shale formations in the continental U.S. from which oil and/or gas are being extracted (current plays) and those with future potential (prospective plays).

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Average US natural gas wellhead price in $ per thousand

cubic feet for the period from 1970 to 2012. Mass production

of unconventionals led to a strong decrease in fuel costs.

frackin

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(a) Traditional fracking. A sandstone reservoir lies below a low-permeability shale sedimentary trap in an anticlinal fold. A vertical well is drilled into the formation, and a fracking injection of water with additives (including sand as a proppant) from a vertical production well creates a single hydraulic fracture through which oil and/or gas flow to the production well.

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(b) Modern (high-volume) fracking. Directional drilling produces a horizontal production well in the horizontal target stratum, allowing several high-volume fracking injections of large volumes of a fluid with low frictional resistance to create a wide distribution of hydraulic fractures. Oil and gas migrate through this network of fractures to the production well.

<1 km

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Use of Slickwater in Hydraulic Fracking

The frictional resistance of slickwater is approximately an order of magnitude less than the frictional resistance of water under the same conditions, and approximately two orders of magnitude less than the frictional resistance of traditional fracking fluids. This reduction in frictional resistance allows the injection of much larger volumes of fluid at the same driving pressure. A typical modern fracking injection stage uses 7.5 × 103 to 11.0 × 103 m3 of water, approximately 100 times as much water as in a typical traditional fracking injection.

The typical rate of injection for a single modern fracking event is 0.4 m3/s, and the injection time is approximately 6 h.

High-pressure injection of slickwater typically reopens sealed natural fractures and generates new fractures.

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Oriented Drilling – Hydrofracking

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Two dimensional scheme of fracking operations draining a larger area via oriented drilling when compared to conventional rotary drilling.

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Three dimensional scheme of fracting operations from 4 pads draing a large area via oriented drilling.

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Fracking creates microseismicity that may be an environmental stressor for local population or induce unintended slickwater disperal. Map of the epicenters of microseismic events from a four-stage modern fracking treatment of the Barnett Shale, Texas.

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Growth pattern of a typical slickwater invasion percolation. Note the stepwise progradation of the slickwater front, which in both direction and extent is highly unpredictable. Unintended results may occur and create environental hazards.

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Fracking cluster growth in invasion percolation occurs in separate bursts. When a growing cluster enters a region with low rock strength, a subcluster forms. A burst is defined as a sequence of rock ruptures. Three examples of burst structures are illustrated with the four largest fracking bursts differentiated by color. The burst structures tend to resemble the microseismicity pattern observed in modern fracking.

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Shale Gas Systems

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8

9

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0.01 0.1 1 10 100

% TOC

Gas Shales

CBM

Tight Gas Sands

All Free Gas

All

Adsorbed

GasMixed Free And Adsorbed Gas

Geomark, 2008

• What are they?

– Organic-rich shales (source rocks)

– Free and adsorbed gas

– System Permeability

• Very low matrix permeability

• Natural fractures

• Common traits of gas shale reservoirs

– Abundant gas (40 to 150 BCF/mi2)

– Large developments

– Require fracture stimulation

– Long well lifeRed = hydrocarbonBlue = water

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What is Shale Gas: Expulsion Losses?

EOM - movable

Original TOC

C - reactive C – non reactive

C – non reactive

C – non reactive

oil gas

expelled gas retained gas

expelled oil

Expelled Retained

EOM – non

movable

Shale Gas

cracking

thermal maturation

expulsion/migration

Conventional oil and gas

1

2

1. Compositional generation kinetics

2. Compositional expulsion/retention

3. Compositional cracking kinetics

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Jarvie – Barnett: 60% expulsion

Horsfield – Posidonia: 95% expulsion

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The Middle Devonian Marcellus Shale (394–380 Ma) occurs in the Appalachian Basin. Most gas production is from Pennsylvania, but the Marcellus Shale also extends into New York, West Virginia, and Ohio, with a total area of approxim. 250,000 km2. The average thickness is 15 to 60 m, and production is generally from depths of 1.2 to 2.5 km. The Marcellus Shale is relatively little deformed, mostly horizontal, and slightly older than the Bakken Shale. Production of gas between 2000 to 2013 increased sharply in 2010. Pennsylvania now produces more gas than any state except Texas, with estimated reserves of 1,500 Tcf.

Marcellus Shale Unconventional Gas source

Middle Devonian Marcellus Shale

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Lower Marcellus

‘Hot Shale’

On

on

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Fayetteville

Marcellus Haynesville

Barnett

Porosity is primarily distributed between intergranular (fIG) and intrakerogen (fk)

Marcellus or Barnett:

fIG:fk ≈ 20:80

Haynesville:

fIG:fk ≈ 50:50

Microporosity controls retainment of gas/oil in unconventional source rocks acting as reservoirs. In unconventional sources, porosity mainly residesin the kerogen itself and not in the intergranular pore space.

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The Late Devonian Bakken Shale (385–340 Ma) is located in the Williston orWestern Canada Sedimentary Basin. Most production has been in North Dakota, but the shale extends into Montana and Canada. The Bakken Shale is a little-deformed, mostly horizontal black shale in which modern fracking was first shown to be effective in extracting oil from a tight shale. There are more than 6,000 producing wells in the Bakken Shale, primarily horizontal. Within the period 2000 to 2014 the annual production of oil in North Dakota increased rapidly from 0.03 billion barrels (Bbbl) in 2004 to 0.40 Bbbl in 2014. This compares with a total US annual production of 3.16 Bbbl in 2013. North Dakota now produces more oil than any state but Texas.

Bakken Shale Unconventional Oil source

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unconventional hydrocarbon production€¦ · k – rdöls kapitel 8 –unconventional hydrocarbon...

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