THE CASE FOR IN SITU

Keith Britton

Consultant

5718 McKinley Street

Bethesda, MD 20817-3639

ABSTRACT

It is aryued that in situ processing deserves

consideration for a wider variety of reasons than are

usually put forward, and particularly as a building

block for larger schemes rather than as an end in

itself. Factors important to in situ processes are

noted. It is found that use for primary recovery is

usually contra-indicated, that it may be useful for

secondary rccov>ry, but that integrated surface and

ir situ approaches offer the greatest return. It is

.shown that numerous circumstances exist which may

justify ir, situ processing for particular sites.

Examples are given. Imagination and creativity are

called for to identify such opportunities.

INTRODUCTION

Historically, the case for in situ processing

nas been put forward by proponents of a handful of

technologies, often only in the context of a

particular site or lithology. Inevitably, the

subject has been widely identified with the merits

and problems of the prominent projects, and probably

few perceived need for oroader treatment. Within the

USA, for example, there was need and opportunity for

a national policy regarding both technologies and

disposition of research funds, but the game was

dominated by the concepts of the major players rather

than wider strategic thinking. Some years of

depressed oil prices provide us with an enforced

opportunity for reflection -

and we need to take it.

An end to present conditions is inevitable; a period

of shortages and enormous stress upon the world

economic and political fabric will follow as

adjustments are made. We can expect that most

sources of liquid hydrocarbons will then be tapped,

possibly under conditions of great pressure on

available capital and industrial resources.

Nations and large corporations need a strategic

view of oil shale opportunities; smaller entities too

might gain from reviewing a broad option base prior

to technology commitment. This paper is intended to

offer such perspective. But it has also two further

purposes. One is to promote the view that in situ

processing should be considered less an end in

itself, but more a potential building block of larger

schemes. The other is to illuminate potential which

has gone unrecognised through lack of imagination and

creativity in this area.

As noted, there is an unfortunate tendency for

oil shale processing to be seen primarily in terms

of, or in comparison to, the major ventures of the

'70s and early '80s. But it is hardly wise to commit

at the outset to any particular technology, surface

or otherwise. Nor, for that matter, is it desirable

to make an early choice between surface and in situ

processing. Either or both may eventually be short

listed. Instead, a planner should bear in mind the

factors which are significant to in situ processing

(those touching lithology, fragmentation,

environmental questions and candidate technologies)

but should start by noting the general goals and

specific assets and constraints for the particular

case. Only then is there likely to be the breadth of

view needed to identify all opportunities and to

formulate a strategy to approach an optimum solution.

Space does not permit exhaustive treatment, so

discussion of important factors is limited to that

which will give a sense of the questions involved,

while helping to explain the examples which follow.

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SIGNIFICANT FACTORS FOR IN SITU PROCESSING

Lithology

Site lithology may exert constraints on options

or offer opportunities. Thin oil shale precludes

vertical retorting; thick overburden may similarly

resolve the question of obtaining space by surface

raising rather than by mining it out for Modified In

Situ. The dip of the strata may control drainage of

produced oil and hence direction of retorting.

Jointing may mandate retort or mine orientation and

affect detail of blast design. Overlying strata may

be strong or weak, rock or clay, with implications

for mine roof stability, retort leakage and surface

raising mechanics. But adjacent strata may offer

opportunities too. A coal bed or stringer might be

co-retorted or even combusted to retort the shale

with inert gas. An aquifer may be a disaster, an

irritation, or a welcome source of process water.

The properties of the oil shale matter too.

There may be preexisting permeability. Or response

to blasting may be good, rendering bed preparation

easy, or it may be so bad as to grossly affect

processing or prevent it entirely. High carbonate

content may impose an important energy cost on

retorting, or it may be an asset for pollution

control or cement manufacture. Bound water may

similarly act as a debit to the energy balance, and

may imply severe problems from subsidence or improved

permeability as retorting progresses. Sulfur too may

be pollutant or product.

Commonly, grade varies vertically or oil shale

is interbedded with barren rock. There then may be

several alternative strategies for even a single

site. If the interbedded material is lean shale, as

in the A groove rock of the Green River Formation, it

may be best to retort it along with the high grade

Alpha and Mahogany shales. But it may serve

temporarily as a useful structuralelement during

mining and blasting. Conversely, blast designs may

need to be modified to preserve the integrity of a

barren limestone interbed, so as to avoid the energy

penaltyfrom decomposing

carbonates. Permeability of

lean interbeds to oil or retorting gases may be an

embarrassment,perhaps forcing retorting to be

performed with careful phasing of burns to prevent

product drainingto combustion zones. Or lean shale

permeabilitymight provide

the primary retort gas

transportmechanism

and/orstructural support

resisting subsidence where the high grade shale

swells, flows or is intumescent during retorting.

Lithology thus imposes a general strategy

committment, plusinnumerable nuances which reappear

in the detail of project design. Many reappear in

aspects of blasting, which most in situ processes

require to produce a retort bed. This fragmentation

step is similar in that the necessities for effective

blasting impose both detail and general requirements

upon a project.

Fragmentation

The bed preparation step is critical for in situ

processing. There is no fix for a bad bed; a bad bed

burns with ruinous inefficiency or won't burn at all.

There are (untested) possibilities for burn control,

but the strategies used to date are palliative at

best, so the original blasting must produce favorable

fragmentation and permeability. Included in

permeability is not only the obvious need for a low

gross pressure drop across the bed to limit pumping

costs, but also control of local and gross bypassing.

Local bypassing is associated with small scale burn

front irregularity and hard or tight spots. It can

contribute massively to coking, cracking and product

combustion losses. Gross bypassing is synonymous

with sweep efficiency. It is generally associated

with edge effects or systematic factors like those

causing burn override in horizontal burns.

The possibilities for good blast design very

strongly reflect the available access to the

formation. Limited access limits the number of

charges which may be used, their geometry, their

possible range of locations and interactions, and

also their breakage geometries. Blast designs are

often compared on the basis of specific charge

(weight of explosive per unit volume) , but it is not

too harsh to describe many such comparisons as

witless. A single large charge does not, for

instance, produce the same results as ten smaller

ones, though the specific charge is the same. One

has to consider the specific distribution of charge

too (for cylindrical charges, conveniently expressed

as length per unit volume). Further, even neglecting

simultaneous firings and the profound effects of

varying the delays between detonations, there are N!

possible firing sequences for N charges-

each with

unique results.

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In practice, the blast designer does not proceed

by an exhaustive search through every possibility.

Typically, the bulk of the material can be broken by

numerous approaches and several are usually

practicable. But that is often untrue for critical

details. Permeability control at the edges of a

retort zone, for instance, may be a crucial element

for technical success. But if access to the

formation is poor, too few of the blast designer's

tools may be available to achieve it. But it isn't

only the extent of the formation access which

matters, its geometry tends to impose particular

geometries upon the charges and their breakage.

Breakage geometry is normally a function of the

general relative positions of the charge and the free

face, but the ability to break rock is also greatly

affected by the local geometry of the charge and

borehole. Cylindrical charges break rock relatively

easily in the radial direction, but only with

difficulty in the axial. (A factor of 10 has been

demonstrated for squat charges in cylindrical

blastholes. [1]) Poor access may limit drilling to

directions requiring axial breakage and hence impose

intrinsic inefficiency."Cratering"

designs result,

as in Occidental's Retorts 7 and 8. Similarly,

access limitations affect ability to use or avoid

rock anisotropy effects.

The nature and extent of the available free face

also profoundly affects blasting efficiency and

control, for two reasons. First, the quality of the

free face determines the effectiveness of the

reflection of the initial compressive shock as a

tension wave. Second, the degree of relief at the

free face appears to partly control the severity of

dilatancy effects during initial burden motion and

fragmentation. The first directly affects breakage,

the second may generate powerful clamping forces

which act to inhibit essential muck motions. [2]

The absolute volume of void space made available

by either mining or surface raising is usually used

to describe or categorize the ultimate retort bed (in

terms of % void). This is often grossly misleading.

Like specific charge, it may carry invalid and often

illusory connotations. It is assumed that, during

the fragmentation process, the original void is

uniformly redistriouted. In practice, fragments

jer.erf.ted clcse to the void have space to rotate and

prop, while more remote material is limited in

relative motion and forced to remain ordered. It

follows that material adjacent the free face consumes

most of the void space, resulting in often gross

systematic variation within a bed. This effect is

strongly dependent upon the original geometry and the

orientation of the blastholes, less so on the oil

shale materials properties, anisotropy, fragment

aspect ratio and size distributions.

Environmental Problems

In situ retorting suffers from several proven or

potential environmental problems. Retort gases

contain toxic, carcinogenic and teratogenic

hydrocarbons, as do retort waters. Leachates from

spent beds may carry mobilized metal ions and be

alkaline or acid. Sulfur is mobilized, potentially

in extraordinary quantities. There are some field

data regarding these problems, and they are generally

encouraging, but they are essentially all from the

comparatively benign Green River Shale. Until more,

and more definitive, data are available, most

questions remain open. There is, however, one new

area where discussion is appropriate, that of

contributions to the "greenhouse effect".

Ideally, we should immediately abandon both coal

and oil, moving to a nuclear and hydrogen economy.

That being impractical, the next best thing is to

minimize emissions of carbon dioxide relative to the

amount of fossil energy which we cannot avoid

consuming. Clearly high hydrogen liquid fuels are

preferable to coal, and parafins to aromatics. Shale

and conventional oil, therefore, seem preferred. But

there is also the question of the carbon dioxide

released during fuel production. Here there is a

clear difference between surface and in situ

retorting. The latter is less efficient, implying

intrinsically greater carbon dioxide contribution per

recovered energy unit. Worse, carbonates may be

dissociated, simultaneously decreasing efficiency and

releasing more carbon dioxide. Finally, much of the

retort energy may come from oxidising char or other

fixed carbon.

A major oil supply disruption could cause the

collapse of the western civilizations. In extremis,

we may be justified in ignoring the greenhose effect

entirely. But under less drastic circumstances, if

we are responsible, we should ask whether extraction

of shale oil causes more or less contribution to the

greenhouse effect than do the alternatives. No

universal answer is likely, as conditions vary from

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country tocountry and site to site. But we should

be prepared to find that at least some in situ

resources are better left where they are.

Concern in this area does lead to some general

conclusions. It will usually be better to avoid in

situprocessing of high carbonate oil shales by

internal combustion retorting. Comparisons between

processes should not be limited to economics or the

ratio of oil produced to that in place, but should

also consider the implications of all contributions

to energy and chemical balances. Surface retorts

burn char too, and they also burn fuel for shale

haulage, for their manufacture etc. Perhaps there is

a premium on processes which leave a black shale, and

we might do better to bury it rather than recover

energy from it. There must also be a tenable

argument for using nuclear energy to produce

superheated steam for retorting and hydrogenation,

for surface or in situ processes.

Technologies

It must be realized that in situ technology is

far from mature. This has both good and bad points.

On the plus side, it is proven that commercial scale

retorts are practicable and tolerably efficient for

both the horizontal and vertical modes, and with void

supplied by mining or overburden raising. It is also

clear that the costs and recoveries experienced to

date can be improved upon, probably significantly.

On the other hand, there is not the experience to

give confidence that a new design will perform

effectively, or even work at all, a serious matter

for planning purposes. Nor is it proven that in situ

operations will be practicable in any lithology but

that of the Green River Formation. There are obvious

reasons for the failures, but the fact that all in

situ projects in other lithologies failed can hardly

be ignored, if only as a caveat that risk become

higher as one moves further from terra cognita.

Regarding the two processes tested to commercial

scale,Geokinetics has yet to demonstrate successful

raising of much more than 20m of overburden, or

retorting of shalethicker than some 10m. Occidental

Oil Shalesuffered poor sweep efficiency due to edge

effects in its large retorts.

Control of edge effectsis an important matter

for most in situ retort designs, and is a measure of

technologymaturity.

Accordingly, it is important to

note that theDepartment of

Energy's assertion, that

no methods of blasting exist for the purpose, is

quite incorrect. [3] Such were disclosed in the

patent literature and professional papers more than a

decade ago, and some were tested and proven effective

inGeokinetics'

commercial scale retorts. 14,5)

It follows that there is good reason to assume

that the Occidental problems are soluble. Still, the

company has not yet demonstrated that the edge

effects causing their difficulties can be controlled

merely by modifications to its basic blast design.

Until that is done, the possibility must be

considered that more radical redesign is needed.

They have two problems: their current design does not

provide good access for charge emplacement in the

critical area; their charge geometry and orientation

limits their options. Their difficulties in this

respect well illustrate the significance of mine

geometry to in situ blasting.

Mechanization and Automation

By far the most expensive and time consuming

mining activity is the driving of headings. Their

blasting is intrinsically inefficient, expensive and

cyclic. Men and equipment must be withdrawn during

blasting, then fumes must be cleared and the rubble

mucked out before redrilling can commence. This is

where mechanization and automation can make their

greatest contributions.

Unlike blasting, it makes little difference to

mechanical mining whether it is applied to the face

of a heading or elsewhere. Production is continuous

and advance should be rapid through the soft material

of high grade oil shale, even for a full face heading

20 feet square or larger. Full automation is a

formidable target for a complex geometry like a room

and pillar mine. But for in situ recovery we can

simplify a mine layout to maximize straight passage

sections. Doing so should permit not only a high

degree of automation even at the present state of the

art, but also simplified design and improved

performance from the miner.

This is of profound significance to in situ

recovery. Economical drift driving would allow

marked improvement in fragmentation control because

of better void distribution and formation access.

And advances in mechanical mining will not only

reduce costs for large mines, but will also make

practicable the working of small deposits which have

been previously discounted. There are few large oil

164

shale deposits, but small ones are scattered across

every continent. Large nations may benefit from the

ability to use local fuel sources and many smaller

ones which lack conventional oil will have indigenous

fuels.

Development of standardized mechanical miners

for oil shale could lead to a small new industry.

Standardization of mine dimensions and a market of

some scale could also lead to standardization and

automation of drilling, mucking and haulage equipment

too. Modular processing and gas cleanup equipment

are indicated as logical developments, and also

opportunities in consulting or contracting regarding

technical project management.

PRIMARY IN SITU PROCESSING

Primary in situ processing for oil recovery is

generally undesirable. The resource is finite and,

because of the fundamentally better opportunities for

precise process control, more cf it may be recovered

by surface retorting. Further, inefficient recovery

implies relatively increased carbon dioxide emission,

which is irresponsible, in view of the greenhouse

effect, if there is better technology. And it would

be equally irresponsible to ignore intrinsic

pollution control problems. But its use may be

justifiable where oil shale is of low grade and/or

under excessive overburden.

Where materials handling and waste disposal for

surface retorting is impractical, for technical or

economic reasons, primary in situ processing is more

tenable as an option, or perhaps may be the only

option. Extreme depth of burial may also justify in

situ processing; process inefficiencies may compare

favorably to pillar losses, costs may be less and so

may hazards to personnel. In both cases, the primary

criterion is a fairly substantial thickness of even

but low grade oil shale. Where low and high grades

are interbedded, usually it seems better to design to

extract the high grade and treat the remainder in a

secondary recovery. And where overburden is

considerable, a substantial mineral matrix is needed

to prevent softening or flow with resulting loss of

permeability during retorting.

Applicability as a prinary recovery method is

Piuch wider if economic or other conditions (scale,

water availability etc.) preclude advanced, capital

intensive technologies, or if the main product is not

oil. At its crudest, in situ recovery can be

conducted with a compressor and rock drill, plus a

blower and a pump. Even adding gas cleanup for

hydrogen sulphide merely requires purchase of a

prefabricated package that is not high technology

equipment to operate.

Modified in situ requires a mining crew too, but

even employment of a mechanical miner would require

only a small cadre of specialist operators and

mechanics. This typifies personnel requirements. In

situ processing does require knowhow and some

extraordinary sophistication, particularly in

blasting technology, but the necessary leaven of top

experts is quite small. The rest of the workforce

needs only readily available skills. Primary in situ

processing is thus well suited for developing

countries, or for countries like China, which are

technologically advanced but under pressure regarding

investment priorities, or, generally, for deposits

too remote or too small to justify heavy capital

investment.

If the principal product needed is not oil, then

primary in situ processing may be the method of

choice simply on process merits. If the local need

is sulfur, then it may be recovered from hydrogen

sulfide in the gas stream. If the need is a

combustible gas, a true syngas, or hydrogen, probably

in situ processing is as efficient a method as any to

obtain it. If the need is electricity, then not only

the off gas but, as in in situ coal combustion,

sensible heat may be utilized, improving potential

energy recovery. [6] And for each case, water demand

is low or absent, capital cost is low and oil may be

produced as a bonus.

SECONDARY RECOVERY

Analysis of the secondary recovery case shows

that a final in situ phase is attractive for almost

all cases where primary extraction is by underground

mining. Usually, substantial additional recovery is

possible (comparable to or exceeding that from the

primary phase) for little extra operating or capital

expense. The major expense for modified in situ

processes, mining out the void, is already a sunk

cost from the extractive phase, but in addition,

there is common use of capital investments in surface

facilities and infrastructure. Against this, mine

use for waste disposal and high grade pillar robbing

must be foregone, environmental factors change and

'greenhouseeffect'

contributions rise.

165

Conventional mining may, however, render

optimization of a later in situ phase difficult or

impractical. Room and pillar mining, for example,

offers only limited access for drilling into the

surrounding rock, leading to unfavorable geometries

for breakage. Further, both bulk rubble motion and

initial free face are compromised by the presence of

pillars, so their removal is essential. This

involves the classic "pillar problem"

of blasting.

A charge located in the center of a pillar will

breakunpredictably to the point of least resistance,

leaving part standing. Biasing the burden by

offsetting the charge defines the breakage but leaves

a pillar remnant which must be similarly attacked,

leaving a smaller remnant etc. As demonstrated by

Occidental, there are methods by which pillar removal

can be performed, and as an initial step in a larger

fragmentation shot, but if the initial mining phase

was optimized for extraction, by definition, pillars

must be sized to approach critical dimensions for

overburden support. Minor sloughing and slacking is

then to be expected with time, making them nasty and

dangerous to drill and load with explosive.

Much nastier is the potential for losing the

entire mine to a fire. By definition, a highly

optimized room and pillar mine is structurally

marginal. It's not well suited to resisting powerful

seismic stresses from the huge concentrations of

explosives used in inefficient in situ rubblization.

Nor, since it is mostly space, is it easy to control

ventilation. Worse, oil shale mines have sufficient

height and scale to develop large convection cells

and so spread fire rapidly along the combustible

roof. Slacking of the back then constantly

contributes new fuel.

This danger is not easily exaggerated. The

secondaryexplosions in blasting gases which wracked

Occidental's Logan Wash mine would have been far more

serious in a room and pillar situation, as would

their fire from sill pillar collapse. And there is

also the potential for slow advance of combustion

from a retortthrough fractured rock at barriers.

Obvious optionsinclude leaving solid wall pillars as

barriers, withloss in extraction ratio, or building

barriers by backfillingwith spent shale, but the

potentialremains for an incident to become swiftly

catastrophic.

That secondaryin situ recovery may be worth

someeffort may be obvious from even a cursory glance

at the lithology. For a mine extracting 60 feet of

the Mahogany Zone of the Piceance Creek Basin, and

assuming that the void left by 80% extraction is

distributed to give 25% void in the retort bed, then

there is the potential to recover the oil in the

pillars- and in a swath 192 feet thick adjacent the

mined zone. The surrounding oil shale is, of course,

much leaner, but for representative figures, the oil

in place in the retort is still around 175% of that

in the extracted shale.

Assuming surface retorting is 100% efficient and

that, because of difficulty in optimizing the

fragmentation, in situ recovery is 50% from an 80%

sweep, then overall recovery will increase by some

70%. The expense for this is little more than the

drill and blast cost, plus that for operating

blowers, and spent shale disposal may cost more, as

the mine is no longer available.

Secondary recovery does not, however,

necessarily imply that the primary mining was for oil

shale. Oil shale is found adjacent both coal and

trona, for instance. For the former, there is mutual

benefit in co-retorting. The pillar material

contributes to the energy balance of the retort or it

may even supply the bulk of the energy for a

gasification. The shale provides oil and further

fuel, control of permeability and also control of

subsidence, a significant point for future use of the

surface. Trona is not as beneficial, but a secondary

oil recovery still may turn a mine abandonment into a

source of revenue.

INTEGRATED APPROACHES

Integrated approaches are defined as those where

there is significant interaction between jointly

applied surface retorting and in situ technologies.

Such offer numerous advantages. Some are obvious,

such as scale economies and common use of capitalized

infrastructure like process control laboratories and

roads. Others, like improved potential for

standardization and automation in mining, are not.

Further, the possible variety of site conditions and

other factors render each case unique. Two cases

from opposite extremes illustrate the extent of this

diversity: one is a conventional mine and surface

process project in Green River shale, with minor

modifications introduced to optimize an in situ

secondary recovery stage; the other is an ab initio

integrated approach for processing eastern shale.

166

The first example deals with the western

situation considered above, but with an integrated

approach adopted from the outset. The main change to

the extractive mine is to use a room and wall rather

than a room and pillar layout. Simply eliminating

the crosscuts would reduce the extraction ratio too

much, from 80% to 55%, but the maximum roof span is

the diagonal between pillars, or about 77 feet for a

layout on ICO foot centers, so it should be possible

to compensate by increasing the width of the rooms.

Compensation is likely to be only partial, however.

The limiting structural factor may be roof failure,

reflecting the square of the span, or resistance to

buckling, a function of pillar aspect ratio.

Increasing room width to 70 feet seems

reasonable, giving a 30 foot thick wall and a 70%

extraction ratio. Material extracted during the

driving of headings above the pillars then brings the

total shale for surface retorting to closely match

that for the original case.

The headings above the pillars are used to drill

the oil shale above the main mine level, and to drill

vertical blastholes through the walls. The shale

below the main level is drilled downwardly from it.

The drill and blast activities for the secondary

recovery are thus performed under good and safe

conditions, and pillar removal is simplified. The

"pillarproblem"

is avoided, as the walls are simply

and cheaply demolished by sequentially firing

staggered large diameter column charges.

Good free faces and favorable geometries sharply

reduce both the specific charge and distrioution

requirements, reducing drill and blast costs and,

coupled with reduced dilatancy effects from the

better geometry, seismic radiation to the adjacent

mine. Potential for damage is much reduced, and

potential for a catastrophic fire event is low, as

the mine rooms form a series of isolatable cells

rather than anastomoses.

Mining coulc proceed conventionally, but there

is obvious opportunity to standardize upon an opening

size and drive all headings with identical mechanized

miners. Since headings are linear, a comparatively

simple, cheap machine would suffice, and full

automation appears practicable, even at the present

state of the art. Headings are located in the

highest grade shale, so tool wear woulc be minimal

and advance rapid. Further opportunities exist for

inechanization and automation in the extractive

blasting, as standardized, reliable and highly

optimized rounds are endlessly repeated. There is

less potential for automated mucking, but high

production large scale equipment can be used.

Ventilation control can be local and excellent, as

vents required for eventual retorting may perform

double duty.

The in situ drill and blast costs are notably

lower, but mining of the extra headings is only

partially offset by the elimination of crosscutting.

However, all mining is now more efficient, so costs

should approximate those for the case above. Any

difference should certainly be minor relative to the

improved in situ recovery. For a good retort bed, it

seems reasonable to hope for 60% recovery from a 100%

sweep, giving a net 20% improvement in overall oil

recovery to boost the bottom line. And perhaps

equally important, the scheme seems safe for both

miners and mine.

Either concern for mining safety or greater

depth may, however, require a lower extraction ratio.

For a more conservative 60% extraction, there is

proportionately much more high grade oil shale in the

pillars. Further, the surface retorts may operate

with less than 100% efficiency. Assuming only 80%

efficiency and optimization from integrated design,

the net recovery increases by a factor of about four

compared to surface processing alone. Clearly, if

the intent is to maximize overall recovery from a

particular resource, an in situ phase is essential.

The difficulty of redistributing the mined void

may require the overall in situ bed void to more

approach 25%, reducing in situ recovery, and other

lithologies would be less favorable. But the

benefits from integration seem at least worthwhile in

this western shale example, though not necessarily

striking. However, the preceding was primarily

driven by its surface retorting aspects. The second

example, in 12 gpt New Albany Shale, is the reverse,

and the benefit from synergism more evident.

At first sight, where shale is lean and the

overburden too thick for an open pit approach, only

in situ processing seems practicable; there is simply

too much cost involved in materials handling and

spent shale disposal for the lean shale involved.

But in situ processing may not be not very attractive

either. The eastern shales have much fixed carbon

and lack endothermic carbonate reactions as an energy

cost, but much in situ oil loss results from coking

167

andcracking reactions, and fragmentation problems

intrinsic to the shale properties strongly imply that

no well optimized bed is practicable. Probably no

more than 50% of Fischer Assay recovery could be

expected, netting only a miserable 6 gpt.

The immediate implication is a selling price

between two and three times that for oil from a

comparable western operation, but inorganic sulfur

could also be recovered as a product ($120/tonne) .

At $20/bbl for oil and 5% inorganic sulfur,

coproduction from one tonne of New Albany Shale then

amounts to some $3 in oil and $6 in sulfur. Clearly,

the sulfur is critical, being presently worth more

than the oil, but coproduction economics look roughly

equivalent to pure oil economics for the West.

Equivalency is hardly sufficient though, since

western projects are not presently viable. But the

preceding does not include the potential for

recovering energy or hydrocarbon values from the 6%

carbon and 3% volatiles remaining (the equivalent of

about 9% wt. coal). Theoretical studies estimate

that gasification conversion to methane can preserve

up to 94% of the original energy, and experience with

coal syngas suggests a practical energy efficiency of

75-80%. Obviously, much of this energy must be

applied as process heat, but some fraction of this

can probably be recovered too. The Bureau of Mines

has demonstrated recovery of sensible heat from

burning coal mines and analysis showed the process

appeared economically viable for present electricity

production.

But though the potential looks better, the

critical problem for the future nation is liquid

fuels. If in situ processing does not maximize fuel

liquids from oil shale, it probably should not be

used where superior technology is available, i.e.

where surface retorting is practicable. However,

certain retort technologies using hydrogen or syngas

can recover over 100% of Fisher Assay. Product

upgradingalso needs hydrogen and/or syngas.

Supplying this from an in situ gasification leads

naturallyto a closely

coupled integration of

technologies and marked further improvement.

If 20% of the resource is extracted and surface

processed with 100% efficiency in terms of Fischer

Assay, thensurface oil

production would be half of

that from a 50% efficient in situ portion. Net

production is admittedly only 60% of the nominaloil-

in-place, butit must be remembered that for 100%

production, some 15% would be lost in upgrading the

remainder. This is not only avoided, but coproduced

hydrogen and/or syngas would be in excess of

upgrading and retorting needs, so some of the balance

could be sold or used to generate electricity.

Capital costs for the upgrader and surface retort

would be carried by three times the oil production

and, with copious internal hydrogen availability,

upgrading could be to finished products for local

markets, minimizing transport costs.

Either a greater extraction ratio or use of a

retorting technology which recovered more than 100%

of the Fischer Assay would improve recovery. For

both 30% extraction and 150% recovery, net recovery

rises to 80% of the oil-in-place, with more than half

being produced by the surface retort. There would be

some reduction in coproduced values, but gasification

of the excess of carbon is more than sufficient to

supply all needed syngas and hydrogen. The main

disadvantage is the higher cost of the retorting

technology.

Since only a fraction of the shale is extracted,

mining and waste disposal cost, normally a major

factor in shale oil economics, would be much reduced.

Further reduction could be anticipated from

mechanization and automation. Mechanization is

difficult for extractive mining. The mining phase of

an MIS project, however, can be designed with the

voids of such size and geometry as to well suit not

only mechanization, but even use of automated

machines. Openings may be of narrow span, making

roof stability intrinsically good, and cross sections

may be standardized. It follows that automated

mining could actually reduce the per tonne cost of

the broken shale produced from such a mine below that

from conventional extractive mining. Especially this

would be true if use of automation/remote operation

permitted elimination of miners, and hence relaxation

of present mine ventilation and safety standards.

This eastern shale case study showed that, while

neither surface nor in situ processes were attractive

alone, an integrated approach was promising

economically and could much increase overall resource

recovery. Both examples illustrated the importance

of treating in situ processing as an aspect of a

broader project. Implied, but less well seen, is the

importance of imagination. Many opportunities exist

for the application of in situ technology, but they

168

aren't always obvious or easy to identify. A variety

of "specialcases"

serves to make the point.

SPECIAL CASES

As noted above, in situ processing may be

attractive for production of industrial sulfur, but

that is not the only mineral of potential interest.

Certain black oil shales of Nevada are rich in

vanadium. They are rather too lean for conventional

surface processing, and simple leaching is

impracticable, as the metallic compounds are

protected by the organic content of the deposit. In

situ retorting has been considered to prepare the

formation for leaching, and appears a viable

approach. Oil and energy are potential byproducts,

and at least some of the sulfur needed for the

leachant should be internally generated. But what if

more is needed? Perhaps a local oil shale would

provide it at comparable expense to commercial sulfur

burdened by transport costs. If so, then the

retorting and sulfur stripping equipment would be

used twice, once on the vanadium deposit, then later

at the sulfur source.

For a leachable copper deposit in a remote

location, a local in situ operation coulc offer

electical power as well as sulfur. But there is the

possibility of direct thermal processing too.

Conceptually, passages could be mined for an

horizontal modified in situ process in a planar oil

shale deposit and backfilled with ore prior to the

main blasting. Retorting would then roast it,

preparing it for leaching and electro-winning.

Capital requirements would be low and investment

would be in portable equipment rather than fixed

facilities, so a series of small deposits could be

sequentially worked.

Coprocessing of coal and oil shale has also been

suggested, utilizing convectively transported heat

from an ir. situ combusted coal bed to retort oil

shale in an inert atmosphere. The process would have

traded low grade (high ash) coal for almost complete

recovery of much more valuable liquid hydrocarbons

from tiie oil shale and, with care in temperature

control, coulc have avoided the problems of carbonate

decomposition. Transporting and incorporating the

coal into the retort bed might be practical too. The

rationale for this night be as above, or the purpose

n.ight be to use the spent shale as a sink to permit

use of high sulfur coal for power production without

acid rain pollution.

A spent bed has its points as a monstrous depth

filter to strip particulate emissions too, but use as

a chemical absorbent is not necessarily limited to

the hot gas phase. A flooded alkaline retort bed

seems remarkably well suited for neutralization and

ion immooilization of waters from acid mine waste,

and it offers a substrate for biological water

treatment. There are other uses:

Fractured rock has been considered for urban

thermal storage -

summer heat, winter cold, or both.

A retort bed has not only the needed mass and

permeability but, with some forethought, it could

also have the necessary plumbing. Water storage is

attractive too, as it does not involve risk of dam

collapse or loss of valuable land surface, and

extensive deposits could even be developed to form

large aquifers. Here particularly a sense of

perspective is needed. A few years of hydrocarbon

extraction would be followed by decades of pollutant

leaching to produce an environmental modification

which would be significant in terms of centuries or

rtiillenia.

Water may be an issue in another way. Much of

the world is arid. In situ processing requires little

water and may actually be a net producer. And it

isn't only the question of process water which may

argue against surface retorting, there is also the

water demand from both a larger work force and a more

complex infrastructure.

Even presence of conventional oil may suggest in

situ processing. The ultimate purpose is to maximize

liquid hydrocarbon production- from whatever source.

Water produced during retorting could be injected to

help displace conventional oil (solving a disposal

problem) as could carbon dioxide from the combustion

process. So too can steam from the electricity

production which runs oilfield pumps. Even recovered

sulfur might be burnt for power and the acid injected

to produce carbon dioxide by reaction.

Several minerals are found associated with or

adjacent oil shale beds. Perhaps the best known

example is Nahcolite, the extraction of which has

been studied in Colorado. For such deposits, their

scale alone is sufficient justification for interest,

and their existence is obvious. For smaller and more

obscure deposits, opportunities to exploit values

169

beyond the hydrocarbons may need patience, diligence

and imagination to find.

Underlying clay might, for instance, suggest a

novel method of working an oil shale deposit,

extracting the clay to provide the needed void

space.. Could clay extracted in the process form a

revenue producing byproduct? Perhaps a nearby dam

construction project would provide a market. Given a

national or regional development policy, it might be

possible to have a dam design changed from a concrete

to a clay seal to enable the oil shale project. The

British Kimmeridge shale was used as a self firing

clay in the Fletton Brick Process. Perhaps the clay

might be found to fire well for brick or tile

manufacture, suggesting local sale or use of retort

off gas for firing.

Sometimes potential uses may be found in

surprising situations. The large oil shale deposits

of the Queensland coast seem ideally suited to open

pit mining with surface retorting. By definition,

this should rule out in situ processing, but even

here there may be a niche. The oil shale is

basically a clay, implying formidable stability

problems for any open pit. If slides are to be

avoided, presumably the average pit slope must be

comparatively low. This has bad implications for the

quantity of waste which must then be stripped

adjacent the deposit, or alternatively for the

percentage of the in place deposit which must be

abandoned when the pit reaches its maximum depth.

One could certainly attempt to recover a little more

by using in situ methods as a last step, but it seems

likely that the recovery would compare quite

unfavorably to surface retorting. But perhaps there

is a better alternative.

Retorted shale from such deposits has properties

akin to those of a bad brick. But unlike the

original "clay", the internal angle of friction is

quite large. Accordingly, in situ retorting of the

peripheryshould produce a stabilizing member

permitting a significantlysteeper pit. Depending

upon the dimensions and grades, loss in oil through

less efficient recoveryat the periphery could then

be more than compensated for by increased depth and

hence extraction from the interior. But as in most

cases, for in situ processing to be most usefully

applied as a facet of a larger scheme, it must be

consideredfrom the outset of the project, not tacked

on as anafterthought.

Development of in situ technology could prove

important for projects of national importance -

even

if it is never used. The United States national oil

reserve is not a cheap facility, nor is it cheap to

fill. But it will serve a useful purpose even if no

emergency occurs to cause it to be drawn down; by its

existence, it tends to deter energy blackmail or

other political adventures, more than paying for

itself by adding to world stability. Oil shale could

perhaps perform the same role, and perhaps with more

credibility and at less cost.

For every barrel of oil in the shale removed to

build a 20% void retort, four barrels are prepared

for in situ processing. If, as seems likely, we can

work with only 15% void, then the ratio becomes

nearly 6:1. It follows that, if we constrain a

50,000 bpd surface retorting plant to obtain its

shale from development of a dual purpose mine, each

day's operation would add about 200,000 barrels of

oil to a strategic national reserve.

In Situ production could be commenced in days if

blastholes were already drilled, a few weeks if not,

and the number of retorts simultaneously burnt would

determine the production rate. Substantial

production could certainly be commenced in a fraction

of the time needed to build equivalent surface

retorting capacity, and with only a fraction of the

impact on the nation's capital and industial fabric.

Only a major emergency would justify the

pollution and inefficient recovery entailed, but

likely the existence and scale of the reserve would

prove a deterrent to interruption of the flow of

conventional oil. It might also act as a price

discipline, if testing to demonstrate the national

emergency capability clearly showed that, given a

price incentive, the nation could return to an

indigenous fuel economy. If so, investment in

development of in situ technology may be repaid many

fold even if the retorts were never used. Certainly

it would be best if the dual purposepassages'

ultimately service was as development drifts for

continued extractive mining and surface retorting.

But there is another possibility.

In situ retorting by internal combustion

dissociates carbonates because it is impractical to

limit the peak temperatures. Much loss occurs from

cracking for the same reason, and loss also occurs

because of product combustion when oil is evolved

into an oxidizing environment. Given a large retort

170

bed, a nuclear reactor could be used to heat an inert

sweep gas. Temperature control coulc then be quite

good and recovery would compare favorably with

surface processing. Compared to a nuclear power

station, safety and cost questions seem promising. A

mine room would provide a massive containment

structure and it could be readily backfilled with

spent shale cement as an encapsulant in the event of

a major accident. The reactor coulc be broken down

and moved through the large passages as a series of

modules, pemitting rapid relocation and reuse. The

passages and rooms would also provide secure storage

for process and emergency cooling water.

There are still other possible uses for such

passages. The Green River formation, for instance,

could become a tunnel complex extending over an area

of a thousand square miles. Such would offer the

military not only fuel, but storage for materiel and

protection for personnel, in short a force and

equipment capable of surviving a nuclear exchange.

Missiles too (Midgetman or MX) would have not only an

invulnerable base but, given portals part way up the

south facing cliffs of the Colorado deposits,

invulnerable launch sites too. The cliffs would

screen the portals from incoming polar missiles, and

rock dislodged by a groundburst would fall past them

into the valley.

Much of the preceding presupposes an efficient

mechanical miner to rapidly drive large cross section

passages. At least one suitable machine has been

designed, and current experiments with high pressure

water jet assisted cutters appear promising for the

development of others. [7] Given such equipment and

the shale oil produced to help defray costs, other

countries could perhaps find solutions to outstanding

problems. The oil shale of Great Britain might, for

instance, offer a means of building underground

transportation corridors and military installations

secure from both terrorists and protestors.

SUMMARY

While there are certainly cases where in situ

processing is justified for primary or simple

secondary recovery, integrated approaches appear to

hold the most promise. The broad scope of this

category extends from tightly coupled cases, where

surface and underground technologies are mutually

dependent or jointly optimized, to loosely coupled

ones where an assemblage of operations act in

synergism. In addition, numerous special local or

regional conditions may suggest use of in situ

technology.

To find and profit from these opportunities, we

need to start with an open mind and consider all

alternatives. And we must do so from the outset.

Once decisions are made, options are limited and the

possibility of meaningful optimization much

diminished. Further, many opportunities require not

only vision and creativity, but also a national or

multinational perspective and committment. Again,

this is easier to achieve if we plan early enough to

deal with long term strategies rather than the

tactics and immediacy of players in current crises.

Clearly, in situ technology is not the universal

answer to tomorrow's energy needs. But equally

clearly, it is a building block deserving of more

consideration than it has usually received.

REFERENCES

1. Johansson CH. and Persson P.A. (1970) "Detonics

of HighExplosives"

Academic Press, London and New

York, pp 273-274.

2. Britton K. & Walton O.R. (1987) "Brittle

Fracture Phenomena - AnHypothesis"

Proc. 2nd Int.

Symp. on Rock Fragmentation by Blasting (Soc. Exp.

Mech., Bethel, CT) pp. 16-29. or UCRL 96585 Lawrence

Livermore National Laboratory

3. October 1986 "Oil Shale Technology Status

Report", DOE/METC-878/0258 (DE88001018) page 40

4. Britton K. and Lekas M. 1979. U.S. Patent

4,175,4905.

5. Britton K.C. (1980) "Principles of Blast Design

Developed for In Situ Retorts of the Geokinetics

Surface UpliftType"

Proc. 13th Oil Shale Symposium

6. Chaiken R.F. (1983) "Economic Benefits from

Burnout of Abandoned Coal MineFires"

Proc. Ninth

Annual Underground Coal Gasification Symposium

p. 523-533.

7. Haspert J.C. (1982) "Haspert Oil Shale Mining

System"

Final Report, 2 Vol. DOE/CS/15006-T1

(DE81026351)

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