Method of breaking shale oil-water emulsion

A technique is described for breaking the very strong emulsion of shale oil and water produced by an in situ oil shale retorting process so that separate shale oil and water phases can be recovered. The emulsion is broken by heating it to a temperature of at least about 120.degree. F. and holding at a temperature in the range of from about 120.degree. to 180.degree. F. for about one day. Preferably the shale oil and water are held in the range of from about 130.degree. to 150.degree. F. for about one day and the phases separated by gravity. Heat for the process can be obtained by injecting water into a spent in situ oil shale retort for generating steam and transferring heat from the steam to the emulsion.

There are vast deposits of oil shale in the world containing massive 
reserves of oil that can supplement or replace petroleum supplies. The oil 
shale contains kerogen which is a solid carbonaceous material from which 
shale oil can be retorted. Oil shale is retorted by heating the oil shale 
to a sufficient temperature to decompose kerogen and produce a liquid 
product known as shale oil which is recovered. Small amounts of 
hydrocarbon gas are also produced. The spent shale, after kerogen has been 
decomposed, contains substantial amounts of residual carbon which can be 
burned to supply heat for retorting. 
In a particularly desirable process for retorting oil shale a subterranean 
cavity or room known as an in situ oil shale retort contains a fragmented 
permeable mass of oil shale particles and retorting is conducted in situ. 
The fragmented permeable mass of particles in the underground retort is 
formed explosively by any of a variety of known techniques. This retort 
can be filled to or near the top with a fragmented permeable mass of oil 
shale particles sometimes known as a rubble pile. The top of this 
fragmented mass of oil shale particles is ignited and air or other oxygen 
bearing gas is forced downwardly therethrough for combustion of 
carbonaceous material in the shale. Initially some of the shale oil may be 
burned but as retorting progresses some of the combustion is of residual 
carbon remaining in the spent shale. This reduces the oxygen content of 
the air and the resultant gas passing downwardly through the retort on the 
advancing side of the combustion zone is essentially inert. This inert gas 
transfers heat downwardly and results in retorting of the shale in a 
retorting zone on the advancing side of the combustion zone without 
appreciable combustion of the resulting oil. 
The products recovered from the bottom of the retort include a low heating 
value off gas, liquid shale oil and water. Some separate shale oil and 
water phases can be recovered at the bottom of the retort but much of the 
product is in the form of a viscous emulsion of water and shale oil. This 
emulsion forms in the retort under conditions that are not fully 
understood and may very well involve condensation of water vapor on 
surfaces having dispersed oil. It is known that the emulsion from the 
bottom of the in situ oil shale retort is particularly difficult to break 
by known techniques. A variety of chemical treatments of emulsion have 
been attempted to cause a separation of the oil and water into separable 
phases and no appropriate economical technique has been discovered. 
Petroleum-water emulsions are sometimes encountered in producing oil from 
wells. Emulsion breaking chemicals can be used for separating such an 
emulsion. A heater-treater can be used either alone or in combination with 
chemicals. A heater-treater is essentially a large vessel wherein an 
emulsion is heated by immersed heater tubes and travels over trays or 
through a filtering medium to separate oil and water. Average residence 
time of oil in a heater-treater is in the order of two to ten hours, 
although four to five hours seems to be most typical. 
A heater-treater is shown in the Petroleum Production Handbook, edited by 
Thomas C. Frick and published by Society of Petroleum Engineers of 
A.I.M.E., Dallas, Tex. (1962), along with related information at pages 
6-27 to 6-35. Although this discussion concerns preparation of power oil 
for use in downhole hydraulic pumps for pumping oil wells, the description 
of the heater-treater is not unique to this application of the equipment. 
Efforts have been made to separate the shale oil-water emulsion from in 
situ oil shale retorting using a conventional petroleum heater-treater. 
Heating has been in the range of from about 150.degree. to 170.degree. F 
with various chemical additives and electrostatic fields employed for 
enhancing separation. Although some success has been obtained, the 
technique is not completely satisfactory and the equipment costs are high 
for a selected production rate. 
The large amount of water present in the oil significantly affects its 
properties, including its viscosity. The emulsion is sluggish and 
difficult to handle and can involve a substantial storage and shipment 
problem since there may be up to 75% water in the emulsion. It is also 
desirable to separate water from the oil for use at the site of retorting. 
It is therefore desirable to provide a technique for economically breaking 
the shale oil-water emulsion from an in situ oil shale retort. 
BRIEF SUMMARY OF THE INVENTION 
There is, therefore, provided in practice of this invention a simple 
process for breaking the emulsion of shale oil and water from an in situ 
oil shale retort by holding the shale oil and water at a temperature of at 
least about 120.degree. F for at least about one day and separating shale 
oil and water. Good separations are obtained by holding the shale oil and 
water at a temperature in the range of from about 130.degree. F to 
150.degree. F for about one day or until the shale oil and water are 
substantially separated.

DESCRIPTION 
The drawing is a semi-schematic vertical cross section drawn without regard 
to scale since relative dimensions are not of significance in practice of 
this invention. As illustrated in this presently preferred embodiment 
there is an active in situ oil shale retort 10 containing a fragmented 
permeable mass of particles bounded by unfragmented formation containing 
oil shale. 
The fragmented permeable mass of oil shale particles is formed by 
excavating at least one void within the boundaries of the retort being 
formed and explosively expanding a portion of the formation toward such a 
void. Several techniques have been described for forming an in situ oil 
shale retort. 
After the fragmented permeable mass is formed a combustion zone is 
established by igniting carbonaceous material in the oil shale. Air or 
other oxygen bearing gas is introduced through a conduit 11 to the 
fragmented permeable mass in the retort 10. The oxygen bearing gas 
introduced into the combustion zone causes the combustion zone to advance 
through the fragmented permeable mass. Heated gas from the combustion zone 
passing through the retort establishes a retorting zone on the advancing 
side of the combustion zone. Oil shale particles are heated within the 
retorting zone and kerogen in the oil shale is decomposed to form gaseous 
and liquid products including shale oil. Shale oil percolates through the 
fragmented permeable mass and flows from the in situ oil shale retort into 
a sump 12 in a laterally extending drift 13. Off gas from the in situ oil 
shale retort is also withdrawn through the access drift 13 through a gas 
tight bulkhead 14. 
Water vapor is present in the retorting zone in an active in situ oil shale 
retort. There are several potential sources for such water including 
connate water in the subterranean formation, water leaking into the in 
situ oil shale retort from underground aquifers, water introduced with the 
oxygen bearing gas for retorting, and/or combustion products from the 
combustion zone. 
Raw or unretorted oil shale on the advancing side of the retorting zone can 
be at a temperature below the dew point of the gas in the retorting zone. 
This leads to condensation of water. The unretorted oil shale can also 
include shale oil on its surfaces percolating downwardly from the 
retorting zone. Some components of the shale oil may be vaporized in the 
retorting zone and also be condensing on unretorted oil shale. The exact 
mechanisms occurring in the retort on the advancing side of the retorting 
zone are not known. It is known, however, that a shale oil-water emulsion 
is recovered from the sump 12 on the advancing side of the retorting zone. 
In some cases reasonably dry shale oil and/or reasonably clean water can 
be obtained. Substantial amounts of shale oil-water emulsion can also 
occur. 
The emulsion of shale oil and water from an in situ oil shale retort turns 
out to be particularly difficult to break as compared with ordinary 
emulsions of petroleum and water. It is believed that this can be a result 
of the mode of formation of the emulsion by condensation on oil shale on 
the advancing side of the retorting zone in an in situ oil shale retort. 
It is also possible that the products of retorting are sufficiently 
different in chemistry or structure to form more stable emulsions than are 
usually encountered in petroleum production. 
The tight, or difficult to break, emulsion of water and shale oil is 
withdrawn from the sump 12 to a heat exchanger 19. Steam from a spent in 
situ oil shale retort 16, as described in greater detail hereinafter, is 
also passed through heat exchanger 19 so that the shale oil and water are 
heated by heat extracted from the steam. The heat exchanger 19 can be of 
any conventional variety or can simply be an arrangement of pipes immersed 
in a temporary reservoir for the shale oil and water. A suitable reservoir 
is a tank or a subterranean chamber having a capacity of at least one day 
of production from the in situ oil shale retort. 
Sufficient heat is supplied to the emulsion to raise its temperature to at 
least about 120.degree. F and preferably into the range of from about 
130.degree. to 150.degree. F. Temperatures as high as 180.degree. F can be 
used although not considered necessary. It is found that when the shale 
oil-water emulsion is held in about this temperature range for at least 
about one day the shale oil and water are substantially separated. The 
mixture is separated into these two phases in a separator 21 which can 
simply be a reservoir with weirs and separate outlets so that the shale 
oil and water fractions can be separately removed by gravity separation. 
If desired the heat exchanger and separator can be combined by providing a 
reservoir sufficiently large to hold the shale oil and water at the 
selected temperature for at least about one day with heating pipes 
immersed in the liquid in the reservoir. An underground reservoir with 
weirs can be used and heating can be by way of hot retorting off gas from 
the in situ oil shale retort. 
The shale oil-water emulsion from an in situ oil shale retort is found to 
be quite resistant to conventional techniques for breaking a 
petroleum-water emulsion. No conventional dewatering agents or 
de-emulsifying chemicals have been found which significantly enhance 
breaking of the emulsion at a reasonable cost. Residence times of a few 
hours in a conventional heater-treater at 150.degree. to 180.degree. F are 
no more effective in breaking the emulsion than the simple and economical 
technique provided in practice of this invention. 
It has been found that by holding the emulsion at a temperature of at least 
about 120.degree. F and preferably in the range of from about 130.degree. 
to 150.degree. F for at least about one day the emulsion breaks into 
easily separable fractions and only about 1% of water remains in the oil, 
which is considered a clean separation in light of the high proportion of 
water originally in the emulsion. 
Prior to breaking the emulsion it can be a thixotropic fluid that flows so 
long as pumping is continued. When pumping is stopped the fluid tends to 
set up much like a gel and it is difficult to get moving again. After the 
emulsion has been heated to break the emulsion, the shale oil has a pour 
point in the order of about 70.degree. F which can be handled without 
significant difficulty. 
After the combustion zone has passed through the fragmented permeable mass 
of oil shale particles in an in situ oil shale retort, there is 
considerable sensible heat remaining in the spent shale which was heated 
during retorting and burning. Some portions of the spent shale in the 
retort can be at temperatures of several hundred degrees Fahrenheit 
although portions near the top can be substantially cooled by passage of 
inlet air or oxygen bearing gas as lower portions are retorted. The 
drawing illustrates a spent retort 16 which contains substantial residual 
heat. Shale oil has been recovered from the spent retort 16 by advancing a 
retorting zone therethrough. A combustion zone has also advanced through a 
substantial portion of the fragmented permeable mass of oil shale 
particles in the spent retort to provide heat for retorting. The structure 
of the spent retort 16 is generally similar to that of the active retort 
10 hereinabove described, and remains closed at the bottom out of 
communication with the balance of the mining system employed in initially 
forming the retorts. The structure at the bottom of the spent retort 16 is 
of no further concern. 
A conduit 17 is provided into the spent retort 16 and through cool parts of 
the fragmented permeable mass so that water can be injected into a heated 
portion of the fragmented permeable mass of spent oil shale particles 
therein. When water contacts heated spent shale particles substantial 
amounts of steam are generated. Although this steam can be at nominal 
pressures and temperatures, large amounts of heat can be involved. A 
second conduit 18 extracts steam from a heated portion of the spent shale 
retort. The two conduits 17 and 18 can be separated from each other so 
that water is injected into one portion of the spent retort and steam is 
extracted from a different portion. Alternatively the same bore hole can 
be used for both a water pipe and a steam pipe even though somewhat wet 
steam is obtained when water is injected near the steam exit. Steam from 
the conduit 18 from the spent retort can be used in the heat exchanger 19 
for maintaining the emulsion at temperatures sufficient to separate the 
shale oil and water. 
Although but one embodiment of technique for breaking the emulsion of shale 
oil and water from an in situ oil shale retort has been described and 
illustrated herein many modifications and variations will be apparent to 
one skilled in the art. Thus, for example, instead of using steam from a 
spent in situ oil shale retort, off gas from an active retort can be 
burned to provide heat for this purpose. Hot retorting off gas, waste heat 
from generators or other economical sources of relatively low temperature 
heat can be used. It is desirable, however, to use the heat from a spent 
in situ oil shale retort since it would otherwise be wasted, and off gas 
from an active retort can be usable as a fuel for generating electric 
power or the like. Many other modifications and variations will be 
apparent to one skilled in the art and it is therefore to be understood 
that within the scope of the appended claims the invention may be 
practiced otherwise than as specifically described.