Method for creating a zone of increased permeability in hydrocarbon-containing subterranean formation penetrated by a plurality of wellbores

A method for creating a zone of increased permeability in a subterranean hydrocarbon-containing formation penetrated by a plurality of wellbores by penetrating the formation with a first wellbore; positioning a plurality of other wellbores about the first wellbore with each of the other wellbores having at least one substantially horizontal borehole extending therefrom into the vicinity of the first wellbore; extending a plurality of substantially horizontal boreholes from the first wellbore into the vicinity of the other wellbores; positioning explosive charges in at least a portion of the boreholes and detonating the explosive charges to produce a rubblized zone between the first wellbore and the other wellbores.

This invention relates to a method for creating a zone of increased 
permeability in a subterranean hydrocarbon-containing formation. 
This invention further relates to an improvement in enhanced recovery 
methods for the recovery of hydrocarbons from hydrocarbon-containing 
formations which have poor drainage of hydrocarbons into wells penetrating 
such subterranean formations. 
In recent years, there has been an increased interest in the recovery of 
hydrocarbons from formations which have previously been considered 
unsuitable for the production of hydrocarbon materials. Some such 
formations are tar sands, heavy oil-containing formations, oil shales and 
tight gas reservoirs. Such formations are known to contain substantial 
quantities of valuable hydrocarbon materials. However, these materials are 
recoverable from such formations only with considerable difficulty. In 
many instances, the hydrocarbon materials are highly viscous and do not 
flow readily from the formations. Various enhanced recovery methods have 
been used to reduce the viscosity of such materials by heating the 
hydrocarbons, mixing viscosity-reducing materials with the hydrocarbons, 
diluting the hydrocarbons with solvents and the like. Such methods are 
designed to reduce the viscosity of hydrocarbon materials so that they 
will flow from the hydrocarbon-containing formation into wellbores, 
cavities in the formation or the like for recovery by pumping to the 
surface of the like. Many such methods are known to those skilled in the 
art. 
All such methods require that sufficient permeability be present in the 
formation so that the enhanced recovery methods can be practiced. In other 
words, contacting the heavy hydrocarbon materials by solvents, steam, hot 
water or the like requires that sufficient permeability be present in the 
formation so that these materials can be brought into contact with the 
hydrocarbon materials in the formation and so that the hydrocarbons can 
drain from the formation. Other methods such as electric heating and the 
like also require that the formation have sufficient permeability so that 
the hydrocarbon materials can flow to a zone where they can be collected 
and recovered. 
Many of the formations which contain such heavy hydrocarbon materials have 
relatively low to almost no permeability in their natural state. As a 
result, it is very difficult to recover hydrocarbons from such formations 
using enhanced recovery methods. Various alternatives to the use of 
conventional enhanced recovery methods in such formations have been 
proposed such as oil mining, tunneling, explosive fracturing with nuclear 
devices, and the like. Many of these approaches are directed to attempts 
to create zones of permeability in which enhanced recovery processes can 
be practiced. A prime requisite of any such method for creating a zone of 
increased permeability in such formations is that it must be economical 
and reliable. 
According to the present invention, zones of increased permeability are 
created between wellbores penetrating a hydrocarbon-containing 
subterranean formation by: 
(a) penetrating the formation with a first wellbore; 
(b) positioning a plurality of other wellbores about the first wellbore, 
each of the other wellbores having at least one substantially horizontal 
borehole extending therefrom into the vicinity of the first wellbore; 
(c) extending a plurality of substantially horizontal boreholes from the 
first wellbore into the vicinity of the other wellbores 
(d) positioning explosive charges in at least a portion of the boreholes; 
and, 
(e) detonating the explosive charges to produce a rubblized zone between 
the first wellbore and the other wellbores 
A variety of well patterns can be used in the practice of the method of the 
present invention.

In FIG. 1 a subterranean hydrocarbon-containing formation 10 is shown an 
overburden 16. Formation 10 is penetrated by a first wellbore 20, a second 
wellbore 22 and a third wellbore 24 from the surface 18. Wellbores 20, 22, 
and 24 as shown extend to near the bottom 13 of formation 10 and are cased 
with casings 20', 22', and 24', respectively, to the top 12 of formation 
10. Boreholes 28 extend substantially horizontally outwardly from wellbore 
20 into the vicinity of wellbores 22 and 24. Boreholes 26 extend 
substantially horizontally from wellbores 22 and 24 into the vicinity of 
wellbore 20. Explosives are conveniently positioned in either boreholes 26 
or 28 at points indicated by arrows 30. Explosives need not be positioned 
in both boreholes 26 and 28 unless required, but it is desirable that the 
material between boreholes 26 and 28 be rubblized upon detonation of the 
explosives, so that a rubblized zone of increased permeability is 
positioned between wellbore 22 and wellbore 20 and wellbore 20 and 
wellbore 24. 
FIG. 2 is a top view of a five well pattern including boreholes positioned 
for the practice of the present invention. Additional wellbores 32 and 34 
are positioned as shown. Explosives may be positioned in any or all of the 
boreholes as required for the efficient rubblization of the zone between 
the boreholes. Suitable locations for the explosives are shown by arrows 
30. 
The drilling of boreholes 26 and 28 is readily accomplished by means known 
to those skilled in the art by drainhole drilling techniques using 
vertical whipstock settings so that the boreholes are drilled at a common 
level from each well or at least from a rear common level in each well. 
Desirably, boreholes 26 and 28 are substantially horizontal or in the 
event of formations which are not horizontal, generally parallel to the 
plane of the formation. By the use of explosives in boreholes 26 and 28, a 
zone of increased permeability is created between the wellbores by 
rubblizing portions of formation 10 between boreholes 26 and 28. The void 
space required in a rubblized zone for increased permeability is available 
in the form of the space comprising boreholes 26 and 28. The space 
comprising the boreholes permits the formation of a rubble zone which is 
not compacted and which permits the flow of liquid or gaseous materials 
freely through the rubblized zone. 
The explosives used are desirably conventional explosives which may be 
positioned in boreholes 26 and 28 by a variety of techniques known to 
those skilled in the art. For instance, the explosives used could be 
conventional explosives packed into a flexible plastic pipe which is then 
inserted into a borehole to position the explosive at the desired 
location. 
The recovery of hydrocarbon materials from such formations may then be 
accomplished by a variety of enhanced recovery methods. These methods 
comprise techniques such as electric heating, steam injection, hot water 
injection, in-situ combustion, solvent extraction, and the like. 
In the use of electric heating, an electric current is used to heat at 
least a portion of the formation so that the hydrocarbons contained in the 
formation have a reduced viscosity and are more readily recovered from the 
formation. In the use of steam, steam or superheated steam may be injected 
alone or in combination with other materials to reduce the viscosity of 
hydrocarbons contained in a subterranean formation and in some instances 
as a driving fluid to cause the hydrocarbons to move toward a recovery 
well. Similarly, hot water has been used to enhance the recovery of 
hydrocarbons from subterranean formations. In-situ combustion has been 
used to enhance the recovery of hydrocarbons from such formations but 
unlike the use of in-situ combustion for the recovery of gasification 
products from coal and carbonaceous deposits, such in-situ combustion 
processes are generally designed to result in the use of combustion gases 
produced in-situ to reduce the viscosity of the remaining hydrocarbon 
materials in the formation to facilitate the recovery of such hydrocarbon 
materials from the formation. Gases from such in-situ combustion generally 
contain carbon oxides and may contain minor amounts of hydrogen and light 
hydrocarbon materials. Such gases are known to reduce the viscosity of 
heavy hydrocarbons and the thermal energy introduced into the formation by 
the in-situ combustion also tends to result in a reduction in the 
viscosity of such hydrocarbons, thus facilitating their recovery from the 
formation. Solvent extraction generally involves the injection of a 
solvent for the heavy hydrocarbons so that the heavy hydrocarbons are 
recovered as a solution of the solvent and heavy hydrocarbons. 
Various such enhanced recovery methods are known to those skilled in the 
art and need not be discussed further. Most such methods require that the 
formation from which the hydrocarbons are to be recovered have sufficient 
permeability so that the enhanced recovery method materials may pass 
through or into the formation or sufficient permeability so that the 
hydrocarbon products may drain from the formation into a recovery well or 
the like. The practice of these methods is improved by the creation of a 
zone of increased permeability between wellbores penetrating such 
subterranean hydrocarbon containing formations. According to the method of 
the present invention, such a zone of improved permeability is readily 
created. Clearly a variety of well patterns could be used. Similarly, it 
may not be necessary in all instances that explosives be positioned in all 
boreholes. In other words, in some instances, if the formation is 
sufficiently friable and otherwise suitable, a zone of increased 
permeability may be created between the wellbore in a given pattern 
without the use of explosives in all boreholes. It may be desirable in 
some instances that additional boreholes be drilled to create additional 
volume to result in increased permeability in the rubblized zone, i.e. the 
zone of increased permeability. 
Various advantages are achieved by the practice of the method of the 
present invention as follows: 
(a) a rubble zone (zone of increased permeability) of limited vertical 
extent and wide areal extent can be created; 
(b) expansion room for the formation solids is provided by the boreholes 
and the porosity of the rubblized zone should be nearly equal to the 
volume of the boreholes; 
(c) substantial quantities of explosives can conveniently be positioned in 
the formation in the boreholes; 
(d) the expansion room provided by the boreholes will tend to reduce 
compaction of formation solids and loss of any natural permeability which 
might be present during the enhanced recovery processes; 
(e) the vertical height and areal extent of the rubblized zone can be 
controlled which is an important consideration in situations where the 
formation might be damaged by breaking into gas caps or water zones; 
(f) a rubblized zone of wide areal extent could provide sufficient drainage 
area for the successful production of right gas reservoirs and heavy oil 
reservoirs; 
(g) all work is done from the surface, i.e., no mining is required; 
(h) existing wells can be used; and 
(i) conventional explosives can be used. 
The practice of enhanced recovery methods is considered to be to known to 
those skilled in the art and it is not considered necessary to discuss the 
use of such methods in detail. In general, in such methods, a fluid which 
may or may not be heated is injected into a subterreanean formation to 
improve the recovery of hydrocarbon materials from the formation. Tubing 
36 has been shown in wellbores 20 and 24 to indicate that tubing can be 
used in the wellbores for the recovery of hydrocarbons from formation 10. 
The tubing in many instances will extend to near the bottom of the 
wellbore as will the casing in the wellbore, i.e., casings 20', 22', 24' 
as shown in wells 20, 22, 24, respectively. In many instances, the tubing 
and/or casing may be positioned to a desired depth after the formation of 
the rubblized zone and the like. The specific method by which the casing 
is positioned to a desired depth and by which the tubing is positioned to 
a desired depth are highly dependent upon the particular type of enchanced 
recovery chosen and will not be discussed in detail. Clearly, if 
necessary, wells 20, 22, and 24 could be re-drilled to a desired depth 
through a rubblized zone after formation of the rubblized zone. Such 
techniques are well known to those skilled in the art and need not be 
discussed in detail. 
Having thus described the present invention by reference to certain of its 
preferred embodiments, it is noted that the embodiments described are 
illustrative rather than limiting in nature and that many variations and 
modifications are possible within the scope of the present invention. Many 
such variations and modifications may be considered obvious and desirable 
by those skilled in the art upon a review of the foregoing description of 
preferred embodiments.