Changes

Producible oil from shales or closely associated organic-lean intraformational lithofacies such as carbonates is referred to as a shale-oil resource system. Organic-rich mudstones, calcareous mudstones, or argillaceous lime mudstones are typically both the source for the petroleum and either a primary or secondary reservoir target, but optimum production can be derived from organic-lean juxtaposed carbonates, silts, or sands. Where organic-rich and organic-lean intervals are juxtaposed, the term hybrid shale-oil resource system is applied.

Producible oil from shales or closely associated organic-lean intraformational lithofacies such as carbonates is referred to as a shale-oil resource system. Organic-rich mudstones, calcareous mudstones, or argillaceous lime mudstones are typically both the source for the petroleum and either a primary or secondary reservoir target, but optimum production can be derived from organic-lean juxtaposed carbonates, silts, or sands. Where organic-rich and organic-lean intervals are juxtaposed, the term hybrid shale-oil resource system is applied.

These systems are classified as (1) organic-rich mudstones without open fractures, (2) organic-rich mudstones with open fractures, and (3) hybrid systems that have juxtaposed, continuous organic-rich and organic-lean intervals ([[:File:M97Ch1.2FG1.jpg|Figure 1]]). For example, the Bakken Formation production is accounted for by both open-fractured shale (e.g., Bicentennial field) and hybrid shale (e.g., Elm Coulee, Sanish, and Parshall fields), where organic-rich shales are juxtaposed to organic-lean intervals, such as the Middle Member (dolomitic sand) and Three Forks (carbonate). However, Barnett Shale oil is almost always from a tight mudstone with some related matrix porosity.<ref name=EOGResources2010>EOG Resources, 2010, [http://wwgeochem.com/references/EOGMay2010Investorpresentation.pdf Investor presentation], 223 p.</ref> Monterey Shale-oil production is primarily from open-fractured shale in tectonically active areas of California. Various shale-oil resource systems are classified based on available data in Table 1. To suggest that these types are mutually exclusive is also incorrect because there can be a significant overlap in a single shale-oil resource system.

These systems are classified as (1) organic-rich mudstones without open fractures, (2) organic-rich mudstones with open fractures, and (3) hybrid systems that have juxtaposed, continuous organic-rich and organic-lean intervals ([[:File:M97Ch1.2FG1.jpg|Figure 1]]). For example, the Bakken Formation production is accounted for by both open-fractured shale (e.g., Bicentennial field) and hybrid shale (e.g., Elm Coulee, Sanish, and Parshall fields), where organic-rich shales are juxtaposed to organic-lean intervals, such as the Middle Member (dolomitic sand) and Three Forks (carbonate). However, [[Barnett shale play|Barnett Shale]] oil is almost always from a tight mudstone with some related matrix porosity.<ref name=EOGResources2010>EOG Resources, 2010, [http://wwgeochem.com/references/EOGMay2010Investorpresentation.pdf Investor presentation], 223 p.</ref> Monterey Shale-oil production is primarily from open-fractured shale in tectonically active areas of California. Various shale-oil resource systems are classified based on available data in Table 1. To suggest that these types are mutually exclusive is also incorrect because there can be a significant overlap in a single shale-oil resource system.

[[File:M97Ch1.2FG1.jpg|thumb|500px|{{figure number|1}}Shale-oil resource systems. A simple classification scheme includes continuous (1) organic-rich mudstones with no open fractures (tight shale), (2) organic-rich mudstones with open fractures (fractured shale), and (3) organic-rich mudstones with juxtaposed organic-lean facies (hybrid shale).]]

[[File:M97Ch1.2FG1.jpg|thumb|500px|{{figure number|1}}Shale-oil resource systems. A simple classification scheme includes continuous (1) organic-rich mudstones with no open fractures (tight shale), (2) organic-rich mudstones with open fractures (fractured shale), and (3) organic-rich mudstones with juxtaposed organic-lean facies (hybrid shale).]]

A special, but separate, shale resource system is oil shale. It is preferred to refer to oil shale as a kerogen resource system or as kerogen oil as it does not contain sufficient amounts of free oil to produce, but must be heated to generate oil from kerogen either in the subsurface or after mining and retorting. This 2d part of chapter 1 will only discuss shale-oil resource systems that have already generated petroleum because of geologic heating processes.

A special, but separate, shale resource system is oil shale. It is preferred to refer to oil shale as a kerogen resource system or as kerogen oil as it does not contain sufficient amounts of free oil to produce, but must be heated to generate oil from kerogen either in the subsurface or after mining and retorting. This 2d part of chapter 1 will only discuss shale-oil resource systems that have already generated petroleum because of geologic heating processes.

With the remarkable success in locating and producing shale-gas resource systems, an overabundance of gas has reduced its current economic value and there has been an exploration and development shift toward locating producible shale-oil resource systems. Recent announcements of the oil resource potential of several shale-oil resource systems have substantiated the volume of oil they contain, for example, 5.88253 times 107 m3 (370 million bbl of oil equivalent [BOE]) in the Barnett Shale, 1.430886 times 107 m3 (90 million BOE) in the Bakken Formation core area, and 1.430886 times 108 m3 (900 million BOE) in the Eagle Ford Shale.<ref name=EOGResources2010 /> However, the keys to unlocking these high volumes of oil are not fully understood or developed to date.

With the remarkable success in locating and producing shale-gas resource systems, an overabundance of gas has reduced its current economic value and there has been an exploration and development shift toward locating producible shale-oil resource systems. Recent announcements of the oil resource potential of several shale-oil resource systems have substantiated the volume of oil they contain, for example, 5.88253 times 107 m3 (370 million bbl of oil equivalent [BOE]) in the [[Barnett shale play|Barnett Shale]], 1.430886 times 107 m3 (90 million BOE) in the Bakken Formation core area, and 1.430886 times 108 m3 (900 million BOE) in the Eagle Ford Shale.<ref name=EOGResources2010 /> However, the keys to unlocking these high volumes of oil are not fully understood or developed to date.

==Background==

==Background==

===Mississippian Barnett Shale-oil System, Fort Worth Basin===

===Mississippian Barnett Shale-oil System, Fort Worth Basin===

[[File:M97Ch1.2FG9.jpg|thumb|500px|{{figure number|9}}Geochemical log of Four Sevens 1-Scaling Ranch A, Clay County, Texas, Fort Worth Basin showing the oil crossover in the lower Barnett Shale with its lean carbonate content. TOC = total organic carbon; S1 = Rock-Eval measured oil contents; S2 = Rock-Eval measured kerogen yields.]]

[[File:M97Ch1.2FG9.jpg|thumb|500px|{{figure number|9}}Geochemical log of Four Sevens 1-Scaling Ranch A, Clay County, Texas, Fort Worth Basin showing the oil crossover in the lower [[Barnett shale play|Barnett Shale]] with its lean carbonate content. TOC = total organic carbon; S1 = Rock-Eval measured oil contents; S2 = Rock-Eval measured kerogen yields.]]

The Barnett Shale has produced limited amounts of oil since the 1980s. Certainly much conventional production in the Fort Worth Basin has been sourced by the Barnett Shale, as substantiated by Hill et al.<ref>Hill, R. J., D. M. Jarvie, R. M. Pollastro, M. Henry, and J. D. King, 2007, [http://archives.datapages.com/data/bulletns/2007/04apr/BLTN06014/BLTN06014.HTM Oil and gas geochemistry and petroleum systems of the Fort Worth Basin], AAPG Bulletin Special Issue: AAPG Bulletin, v. 91, no. 4, p. 445–473, doi:10.1306/11030606014.</ref>

The Barnett Shale has produced limited amounts of oil since the 1980s. Certainly much conventional production in the Fort Worth Basin has been sourced by the Barnett Shale, as substantiated by Hill et al.<ref>Hill, R. J., D. M. Jarvie, R. M. Pollastro, M. Henry, and J. D. King, 2007, [http://archives.datapages.com/data/bulletns/2007/04apr/BLTN06014/BLTN06014.HTM Oil and gas geochemistry and petroleum systems of the Fort Worth Basin], AAPG Bulletin Special Issue: AAPG Bulletin, v. 91, no. 4, p. 445–473, doi:10.1306/11030606014.</ref>

Some oil carryover into the remaining generation potential (Rock-Eval S2 peak) likely occurs but not sufficient to affect Tmax to any substantial amount. The Tmax values range from 440 to 450degC (824 to 842degF) (or sim0.75 to 0.95% Roe), placing the Eagle Ford Shale in this well in the peak oil-generation window.

Some oil carryover into the remaining generation potential (Rock-Eval S2 peak) likely occurs but not sufficient to affect Tmax to any substantial amount. The Tmax values range from 440 to 450degC (824 to 842degF) (or sim0.75 to 0.95% Roe), placing the Eagle Ford Shale in this well in the peak oil-generation window.

In the Barnett Shale, as TOC increases, carbonate carbon content generally decreases ([[:File:M97Ch1.2FG12.jpg|Figure 12]]). However, the Lower Cretaceous Eagle Ford Shale shows no particular trend, with high TOC Eagle Ford Shale samples having ample carbonate content in this data set ranging from about 30 to 70%, whereas organic-lean intervals show both high and very low carbonate contents.

In the [[Barnett shale play|Barnett Shale]], as TOC increases, carbonate carbon content generally decreases ([[:File:M97Ch1.2FG12.jpg|Figure 12]]). However, the Lower Cretaceous Eagle Ford Shale shows no particular trend, with high TOC Eagle Ford Shale samples having ample carbonate content in this data set ranging from about 30 to 70%, whereas organic-lean intervals show both high and very low carbonate contents.

The Eagle Ford Shale-oil resource system may be an ideal case to study the impact of CO2 and organic acid generation because of the intimate association of carbonates with organic matter.

The Eagle Ford Shale-oil resource system may be an ideal case to study the impact of CO2 and organic acid generation because of the intimate association of carbonates with organic matter.