Method for production of heavy oil from tar sands

An enhanced recovery process in which liquid sulfur is burned in an oyxgen-containing gas underground to form SO.sub.2. The SO.sub.2 may itself act as a drive fluid for the recovery of oil or it may react with limestone in the formation to form CO.sub.2, an alternate drive fluid.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention is concerned with the production of heavy oil from 
underground deposits of tar sands. 
2. Description of the Prior Art 
In applicant's copending application Ser. No. 189,997, filed Sept. 23, 
1980, there is disclosed a process for extracting organic matter from tar 
sands with liquid sulfur dioxide. The process is particularly applicable 
to tar sands that have been mined and transported to a plant for the 
extraction operation. There are, however, vast deposits of tar sands and 
other heavy oil reservoirs that are underground and are not susceptible to 
mining. For example, the Athabasca tar sands in Alberta Province, Canada, 
have been estimated to contain 860 billion bbls. with only 26 billion 
bbls. recoverable by current technology. Since the heavy oil in tar sands 
is highly viscous to ambient formation temperatures, it is not recoverable 
in its natural state through a well by ordinary production methods. Resort 
must be had to techniques to make the heavy oil more readily flowable, 
such as a suitable solvent or heat, or a combination thereof. 
It has been proposed to use various water-flooding processes, including the 
use of aqueous solutions of sulfur dioxide, in the recovery of flowable 
oil from subterranean reservoirs. Insofar as is now known, however, the 
process of this invention for recovering heavy oil has not been proposed. 
SUMMARY OF THE INVENTION 
This invention provides in the production of heavy oil from a subterranean 
reservoir penetrated by spaced injection and recovery systems, the method 
comprising: 
(a) introducing into said injection system adjacent to said reservoir 
liquid sulfur and oxygen-containing gas, thereby obtaining a mixture of 
sulfur and oxygen-containing gas, 
(b) igniting said mixture to produce sulfur dioxide, 
(c) maintaining the pressure of said oxygen-containing gas sufficient to 
keep said sulfur dioxide in the liquid state, at the temperature of the 
reservoir. 
(d) flowing liquid sulfur dioxide into said reservoir, whereby there is 
formed a solution of heavy oil in the reservoir in said liquid sulfur 
dioxide, 
(e) flowing said solution toward said production system, and 
(f) recovering said solution from said production system. 
DESCRIPTION OF SPECIFIC EMBODIMENTS 
The method of this invention is applicable to any subterranean reservoir 
that contains heavy oil, i.e., an oil or bitumen having an API gravity 
less than 16.degree.. It is particularly applicable to the production of 
heavy oil from subterranean tar sand beds. The following description is 
specifically directed to tar sand beds, but it will be recognized that the 
method is applicable to any reservoir or formation containing heavy oil. 
The present invention is carried out in a subterranean tar sand bed that is 
penetrated by spaced injection and recovery systems extending from the 
surface of the earth into the tar sand bed. The injection system consists 
of one or more wells into which are introduced liquid sulfur and an 
oxygen-containing gas. The recovery system comprises one or more wells 
from which product is recovered. The wells in the injection and recovery 
systems are spaced apart and can be arranged in any desired pattern, such 
as patterns well known in waterflood operations. For example, the pattern 
can comprise a central injection well and a plurality of recovery wells 
spaced radially about the injection well. 
In carrying out the invention, liquid sulfur and an oxygen-containing gas 
are introduced into the injection well in an area adjacent to the tar sand 
bed. Sulfur is readily available, as substantial sulfur surpluses are 
accumulating on-site with current processing sequences. 
The oxygen-containing gas can be air, although other oxygen-containing 
gases can be used, such as oxygen-enriched air or even pure oxygen. 
Although the oxygen (0.sub.2): sulfur mole ratio may range from about 0.1 
to 2, in the combustion of the sulfur to sulfur dioxide, a substantially 
stoichiometric amount of oxygen will normally be used. 
The sulfur and oxygen-containing gas introduced into the injection well 
admix in the area adjacent to the tar sand bed and the mixture is ignited 
to form sulfur dioxide. Any means can be used to ignite the mixture. For 
example, an electric heater can be placed in the injection well and 
activated to heat the mixture to combustion temperatures. 
Liquid, not gaseous, sulfur dioxide has been found to be a solvent for the 
organic matter in tar sand. Thus, the sulfur dioxide must be under 
pressure sufficient to obtain a liquid phase of reservoir temperatures. 
This can be accomplished by introducing the sulfur and the 
oxygen-containing gas under pressure. 
The liquid sulfur dioxide flows into the tar sand bed toward the recovery 
system. En route the liquid sulfur dioxide dissolves the organic matter in 
the tar sand and transports it to the recovery system. In reservoirs that 
contain limestone, the liquid sulfur dioxide in the presence of water 
contained in the tar sand bed reacts with the limestone to release carbon 
dioxide. The carbon dioxide so formed serves as an additional drive fluid 
to force the dissolved organic matter toward the recovery system. The 
dissolved organic matter is recovered from the recovery system by 
conventional production procedures. 
Other drive means may be employed to force the dissolved organic matter 
toward the recovery system, such as waterflooding, polymer flood, and 
chemical waterflood. It is optionally contemplated to separate the sulfur 
dioxide from the dissolved organic matter above ground, as by flashing, 
and recycling it to the injection system. 
The efficacy of liquid sulfur dioxide to extract organic matter from tar 
sand and to react with limestone to produce carbon dioxide was 
demonstrated in a small-scale pressurized flow apparatus, comprising a 
vertical stainless steel tube having 50 cc. Jerguson (sight) gauges at the 
top and the bottom. The sample was placed in the tube and heated to the 
desired operating temperature under helium, the Jerguson gauges being at 
room temperature. The liquid sulfur dioxide (and water in the case of 
limestone) was trickled through the sample and collected in the Jerguson 
gauge at the bottom.

EXAMPLE 1 
A 25 g. sample of oil sand from Oil Creek, Oklahoma, was placed in the flow 
apparatus and 24 cc. liquid SO.sub.2 was passed down flow at 90.degree. C. 
under 800 psig. The original sample contained 4.8% carbon and 6.1% 
volatiles (after drying at 150.degree. C.). The SO.sub.2 treatment 
extracted 83% of the oil in the sample. 
EXAMPLE 2 
A 60 cc, mixture of 60% SO.sub.2 and 40% water was flowed through a Todeto 
limestone sample in 20 minutes under 800 psig. at 90% c. About 25% of the 
calcium carbonate was converted to the sulfite (or sulfate) with evolution 
of CO.sub.2. 
Although the present invention has been described with preferred 
embodiments, it is to be understood that modifications and variations may 
be resorted to, without departing from the spirit and scope of this 
invention, as those skilled in the art will readily understand. Such 
variations and modifications are considered to be within the purview and 
scope of the appended claims.