US3434757A - Shale oil-producing process - Google Patents

Description

FE T5311 March 25, 1969 M. PRATS SHALE OIL-PRODUCING PROCESS Filed Feb. 2, 1967 FIG.

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INVENTOR MICHAEL PRATS 5Y3 ;,%6W

HIS AGENT 3,434,757 SHALE OIL-PRODUCING PROCESS Michael Prats, Houston, Tex, assignor to Shell Oil Company, New York, N.Y, a corporation of Delaware Filed Feb. 2, 1967, Ser. No. 613,600

Int. Cl. E211: 47/08, 41/02 ILStCl, 299-4 5 Claims ABSTRACT OF THE DISCLOSURE Background of the invention The present invention relates to a process for recovering shale oil. from a subterranean oil shale and, more particularly, to a method for utilizing highenergy explosives to cause the formation of a rubble zone of the oil shale affected by the detonations.

The fact that thermonuclear explosives may be come available for a fraction of a mill per kilowatt-hour equivalent has led to the realization that ultra-high energy explosives can be used in mining operations to break up formations and in the oil industry to increase or stimulate productivity by heating or raising the pressure of a reservoir,

The present invention is primarily directed to the pro-= duction of oil In accordance with the instant invention, oil is recovered from a subsurface bituminous formation by mining and retorting oil shale and then detonating a series of explosives adjacent to the tunnels and producing oil by an in situ treatment of the resulting permeable zones within the oil shale.

Previous attempts at utilizing high-energy explosives to recover shale oil involved the cost of drilling access holes that were useful only in the placement of the explosive devices. In the present process, the access holes are formed as by-products of an oil-pr0ducing mining operation. The tunnels formed by the mining operation are then utilized, after an explosion or explosions, as rubble filled permeable zones that materially increase the extent of a permeable zone that can result from the generation of a given amount of explosive energy within a subter ranean oil shale.

Summary of the invention Advantageously, in accordance with the present inven" tion, a series of long tunnels paralleling each other are drilled by mining oil shale in a predetermined pattern from a subterranean formation of oil shale. In other words, the tunnels are spaced in such a way that the arches between the tunnels can be removed by blasting in order to create a roof of large unsupported areal extent. It is the intent to allow this roof to collapse with the material falling into the tunnels. The process of this invention may be considerably enhanced by utilizing techniques well known in the practice of block caving. For example, after the initial roof fall following the removal of the supporting arches, it is preferred to have other explosive charges detonated at dififerent distances above the original tunnel roof.

Broadly, bituminous deposits containing oil shale can be produced in accordance with the method of the present invention, This process is especially suitable for rock nited States Patent 0 M 3,434,757 Patented Mare 25, 1969 formations known as oil shale which contain a 60111 bination of organic and inorganic sediments which have become hardened into impermeable rock.

Further objects and features of the invention and an exemplary manner in which it is to be performed will be more readily apparent from the accompanying descrip tion taken in connection with the drawing.

Brief description of the drawing FIGURE '1 .is a schematic view of a shale-bearing formation taken in cross-section and showing a series of tunnels together with the location of explosives in the adjacent formation;

FIGURE 2 is a view showing the tunnel areas of FIG- URE 1 after the arches have been removed;

FIGURE 3 is a view showing the tunnel areas of FIG URE 1 after the arches have been removed and the first roof fall has taken place; i

FIGURE 4 is a view showing rubble formed after the second roof fall takes place, i.e., the second series of explosives have been detonated;

FIGURE 5 is a view showing rubble formed after the last detonation has taken place; and

FIGURE 6 is a view showing a plurality of horizontal ly and vertically aligned tunnels.

Description of the preferred embodiment Referring to the drawing in detail, FIGURE 1 shows a plurality of horizontally aligned tunnels A formed by mining shale oil from subterranean oil shale B. These tunnels A are preferably formed by mining the richer zones within theoil shale B along inclined paths having lengths correlated with'the economics of transporting the oil shale to a surface location for retorting it to produce oil. Thus, shale oil can be recovered from the material obtained from these initially formed tunnel areas A As seen in FIGURE 1, tunnels A can comprise a series of drilled long tunnels paralleling each other, and spaced such that the arches between the tunnel areas can be removed or made permeable by blasting, for example, the arches can be removed in order to create a roof of large unsupported areal extent which then collapses and al lows the rubble formed to fall into the area occupied by the original tunnels. If the initial tunnel cross-sectional area is A (FIGURE 1), the cross-section of the final rubble volume is A (FIGURE 5) and the void fraction is p, then A'=A.

Thus, the final volume which can be rubbled is never larger than 1/ times the volume of the tunnel. Since the value of o has been discovered experimentally to be of the order of 0.1 to 0.4-, the final rubble volume may be about 2.5 to 10 times the initial tunnel volume. Accord" ingly, the initial tunnel areas and locations are prefer-= ably arranged so that the volume of rubble that is formed by exploding charges in the formation adjacent to each tunnel is about 2.5 to 10 times the original cross-sectional areas of the tunnels and each volume of rubble is con-= nected with an adjacent volume of rubble in a permeable zone within the oil shale formation.

The permeable zone formed by such a series ofinterconnected, rubble-filled tunnels within an oil shale is penetrated by interconnected cracks, fractures, and voids between rough, irregular pieces of oil shale, etc. The void space within such a permeable zone preferably amounts to from about 5 to 40 percent of the volume of the zone. For example, where the walls of four mutually equidistant, horizontal tunnels are caved to form four contiguous rubble-filled tunnels amounting to one large, generally square, rubble zone, and the rock properties are such that the void space within this zone is about 30 percent of the volume of the zone, it is advantageous to detonate additional explosives within the surrounding rock; The additional explosives expand the permeable zone by compressing the rubble within the central zone and. creating voids within the surrounding rock, This forms a larger permeablezone, which has a permeability lower than that of the central zone, In some instances, the initial tunnels can be spaced so that when their walls are caved, the tunnels are converted to separate, but adjacent, rubble zones which can be interconnected into a large permeable zone by forming fractures that extend between the rubble zones. Such fractures can be formed by injecting fluid into the rubble zones and pressurizing the fluid to form and extend fractures by means of fracturing techniques that are well known in the art of treating oil wellsv Where the areal extent and dimensions and slope of the oil shale formation permit, the layers of tunnels hav ing' cross-sectional. areas adapted to being interconnected by block. caving and fracturing the surrounding rocks can advantageously be disposed to form at least one intersection with a common substantially vertical line as seen in FIGURE 6. With such an arrangement, a series of rubble-filled tunnels can be interconnected by fluidpermeable openings by completing a Well that extends along a substantially vertical line as shown in FIGURE 6 and communicates with each of the rubble-filled tunnels.

Explosives suitable for use within a subsurface bitumi nous deposit are well known in the artv Due to the space limiation inherent in the process involving detonation of an explosive in a Wellbore, explosives having a high-energy yield for their size are preferred. However, inexpensive chemical explosives such as ammonium nitrate can also be employed. In one embodiment, the method of the present invention can be carried out utilizing a thermo nuclear device, such as a hydrogen or atomic bomb. Suitable thermonuclear devices are now available for under ground explosions.

In one embodiment of the instant invention, a rubblecontaining permeable zone is created by mining the shale encountered by a series of tunnels, caving the walls of the tunnels and interconnecting the rubble volumes, and then detonating an explosive emplaced at a distance such that the direction of propagation of the fractured volume from this explosion will be preferentially toward the location of the permeable zone. Where a nuclear explosive is used, this creates a more eflicient lateral distribution of heated and fractured formation, and makes the use of a nuclear device feasible in respect to a relatively thin oil-bearing interval. The use of high porosity intervals in an otherwise dense interval (such as tuff zones in the oil shale) or the use of propped artificial fractures to direct the force of such an explosion toward such a previously formed permeable zone is advantageous in such uses of nuclear blasts or other high explosives.

Preferably, the process of the present invention involves placing a series of explosives along substantially horizonta] planes extending substantially parallel to the longitudinal axes of the original tunnels as shown by the dots in the oil shale in FIGURE 1, The charges at the dots in and adjacent to the arches of the tunnels A (indicated by numerals 1) are initially detonated in order to remove the tunnel arches (FIGURE 2). This creates a roof of large unsupported areal extent that collapses and forms rubble which falls into the areas occupied by the original tunnels (FIGURE 3). The second and subsequent series of explosives are then sequentially detonated until the final rubble volume of FIGURE 5 is attained. The se qnential detonating of the second series of explosives (that: is, the explosive charges designated by numerals 2 through 5 in FIGURES 1 through 4) are staggered in time so that all of the explosives along the substantially horizontal plane nearest to the original tunnels are initially detonated (numerals 2 in FIGURES it through 3) until thefinal detonation of all of the explosives along the substantially horizontal plane spaced furthest from the original tunnels, Of course, the number of series of explosives can be more or less than five, depending on the size of the oil shale, the type and size of explosive charges, etc. Further, the placement of the explosives need not follow a strict order of progression upwardly from adjacent the original tunnels as can be seen in FIG- URE l, for example, wherein the explosives designated by the numerals 5 are slightly below the series of explo sivcs designated by numerals 4.

The sequential detonating of the explosives forms a permeable zone within the oil shale with the zone hav ing interconnected fluid-permeable openings formed therein. Hot fluid can then be injected into or formed within the zone so that oil shale components are converted to oil-containing fluid which can be recovered from the permeable zone. Shale oil can then be recovered from the produced oil-containing fluid by any known means.

Suitable materials and techniques for use in treating the fragmented oil shale within the permeable zone are disclosed in my copending application Ser. No, 632,006, filed. Apr, 19, 1967, copending application Sert No. 656; 815, filed July 28, 1967, The extraction process to be fol-- lowed, however, is not necessarily important for the'pur pose of this invention except that it may be desirable to use inclined tunnels for better recovery efficiency, and thus the direction of flow, up or down the inclined tunnels and cavities formed from them, may be based on the process in mind, For example, in a dry combustion process, one might. choose a downdip flow as preferred, Whereas in a, solvent or hot liquid extraction process, the upward direction might be preferred. Access into the ends of the final rubbled volume may be had through outdrops (the tunnels need not be straight) or through shafts.

The present invention utilizes mining and surface-re torting operations to form a void into which rock is dis placed, in order to creat a permeable zone for an in-situ. treatment of the oil shale to produce oil, This combina tion provides an access opening, for the emplacement of explosives to creat a subterranean permeable zone, as a. by-product of a normally profitable mining operation. It also allows the permeable zones to be selectively created, within deposits of selected composition, by following veins or streaks by means of conventional mining practices. The subterranean oi]. shales may contain streaks or veins which are rich in valuable components other than their organic minerals such as dawsonite and anarlcite, and the like. The

occurrences of such minerals are often mutually exclusive.

In practicing the present invention, a vein of a selected one of such a mineral can be opened for production at the time the demand for that mineral is particularly high,

While in the foregoing a preferred embodiment. of the present invention has been shown and described, it is to he understood that minor changes in details of the process may be resorted to without departing from the spirit and scope of the invention as claimed,

I claim: 1., A process for producing shale oil from a, snbter reanean oil shale comprising:

forming at least two tunnels by mining oil shale from a subterranean oil shale formation; forming said tunnels so that the volume of rubble that: would be formed by caving in the walls of said tun-=- nels is considerably greater than the initial crosssectional areas of said tunnels; placing at least a first series of explosives within the oil. shale adjacent the tunnels so that, when said first series are exploded, they remove the arches between the tunnels, thereby creating a roof of large unsupported areal extent which collapses and the com position of said roof falls into the space occupied by the original tunnels; placing at least a second series of explosives at a plu= rality of different radial distances from the original tunnels; the placing of the second series of explosives comprising placing said plurality of second series of explosives along a plurality of planes extending radially upwardly and substantially parallel to the longitudinal axes of each of said original tunnels, at least some of said explosives extending subsLant-ially parallel to the iongitudinal axes of each of said original tunnels lying in substantially the same generally horizontal plane;

detonating said first series of explosives thereby remov ing the arches between said tunnels;

sequentially detonating said second series of explosives,

the sequential detonating of the second series of explosives including staggering in time the detonation of said second series of explosives, said staggering including the iilitial and simultaneous detonation of all of the explosives along the generally horizontal plane nearest'jtjo the original tunnels to the final simultaneous detonation of all of the explosives along the generally horizontal plane spaced furthest from said original tunnels, the sequential detonation of both series of said'j'explosives thereby forming a permeable zone within the oil shale, said permeable zone having interconnected fluid-permeable openings formed therein;

circulating hot fluid within the fluid-permeable openings formed in said zone and removing thereby shale oi1- containing fluid from said permeable zone; and

recovering shale oilfrom :both the mined oil shale and and the shale oil-containing fluid removed from said permeable zones 2. The process of claim! 1, wherein the placing of said explosives further comprises including at least one explosive of nuclear energy.

3. The process of claim 1, wherein said tunnels are formed so that the volume of the rubble that would be formed by exploding charges within the walls of each of said tunnels is about 2 /2 to 10 times the original crosssectional area of said tunnels.

4. The process of claim. 1, further comprising forming said tunnels by mining said oil shale along inclined paths.

5. The process of claim 1, wherein forming at least two tunnels comprises forming at least some of said tunnels along a substantially vertical plane and drilling a single wellbore penetrating said vertically aligned tunnels so that said wellbore can be used to facilitate entry to said tunnels.

References Cited UNITED STATES PATENTS 1,913,395 6/1933 K-arrickn rrrrrrrrrrr M 299-4, 1,919,636 7/1933 Karrick w, 299-2 3,316,020 4/1967 Bergstrom 299-2 ERNEST R. PURSER, Primary Examiner.

US. Cl. X.R.

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