METHOD FOR DELIVERING OR FOR PREPARING THE DELIVERY OF FLUID MEDIA

Abstract

The present invention relates to a method for recovering or preparing to recover fluid media from underground reservoirs, which enables hitherto non-profitable reservoirs (mini-cavities) containing fluid media to be joined up underground to form a commercially viable reservoir. This object is established according to the invention by a method, is set forth in claim 1. for recovering or preparing to recover fluid media from underground reservoirs and comprising the following steps: sinking at least two substantially vertical boreholes or shafts into the earth's surface introducing at least one pipe consisting of at least one section into each of the vertical boreholes or shafts, the at least one section of pipe having at least one opening in the lower portion of its wall, the openings in the sections of the at least two pipes each being aligned with a selected point between two pipes and this point being located between the at least two substantially vertical boreholes. lowering an explosive charge to a desired depth in the pipe and detonating the explosive.

Description

The present invention relates to a method for recovering or preparing to recover fluid media from underground reservoirs.

Modern geological prospecting methods assist geologists in the search for underground rock formations that possibly contain fluid media, such as crude oil and/or natural gas. These occurrences of fluid media enclosed in rock formations are referred to as reservoirs.

By far the most important method of searching for fluid media is that of reflection seismology. Use is made of the fact that the speed at which seismic waves propagate varies according to the make-up of the subsurface, and, just like sound or light waves, are refracted or reflected at the interfaces between different layers of rock. The deflected and reflected seismic waves are registered by highly sensitive measuring instruments. The data thereby obtained is processed by high-performance computers and provide an informative, three-dimensional image of the geological subsurface.

An exploratory well will show whether a rock formation detected in this way indeed contains a fluid medium. If test drilling is successful, the dimensions, quality and productiveness of the newly discovered reservoir must be analysed.

Until now, production wells were not sunk until such time as it was clear from seismological testing and the first exploratory well that exploitation of the reserve would pay off commercially.

Three standard methods exist for recovering fluid media present in an underground layer of rock and contained within reservoirs, as they are termed, which are surrounded by impermeable layers: primary recovery, secondary recovery and tertiary recovery.

Primary recovery is the recovery phase during which the pressure in the reservoir is high enough, without artificial means, to recover oil or gas from it, irrespective of whether the oil or gas is forced out by means of natural drive (reservoir pressure) or by pumps.

If the reservoir pressure sinks during the course of oil production, it may be increased by injecting water or natural gas via injection wells formed by drilling. This recovery phase is termed secondary recovery. Thirty-to-forty percent of the entire oil reserve can be recovered by injecting water. The remaining oil, which becomes increasingly thicker and less viscous, makes continued steady recovery difficult.

The permeability of the reservoir rock may also be increased by injecting acids to dissolve components of the reservoir rock, for example carbonates.

Steam injection and the addition of chemicals is a means used to reduce the surface tension of the crude oil, making it easier to scrub the rock clean of oil and thereby increasing the yield. This method of recovery is termed tertiary recovery. Various different measures are employed (injection of hot water or steam, N₂ (nitrogen), CO₂ (carbon dioxide), light gasoline or liquefied gas and . . . ). Tertiary methods are also sometimes combined.

In the past, the known methods of recovering fluid media have only been used for high-yield, commercially viable underground reservoirs.

As the numbers of known profitable reservoirs decrease, new reservoirs will need to be discovered in order to secure the continued production of fluid media such as crude oil, natural gas, bitumen or the like. One argument in favour of new methods designed to increase the recovery of fluid media is the rising price of these fluids, which offers the possibility of exploring areas not previously subject to intensive prospecting and of exploiting unconventional reservoirs hitherto considered as commercially non-viable. These include tar sands, especially the large reservoirs in Alberta, Canada, oil shale, deep sea drilling, exploration in Siberia or Alaska, bitumen and other reservoirs.

Crude-oil and natural-gas reserves are known where, in specific areas thereof, the extent of the crude-oil or natural-gas reserve makes it seemingly worthwhile tapping. However, the crude oil or natural gas reserves in these areas are not contained in interconnected cavities making up a single volume of crude oil or natural gas but in a plurality of smallish cavities that are not interconnected. With the hitherto known production options, this would mean developing each of these cavities separately with the known recovery methods. The problem then is that production in these areas becomes altogether too expensive if yields from each of the smallish cavities are low, making separate development of each cavity unprofitable.

The object of the present invention is thus to propose a method for recovering or preparing to recover fluid media from underground reservoirs, with which fluid media contained in reservoirs (mini-cavities) that would not be profitable using prior-art recovery methods can be produced efficiently.

This object is established according to the invention by a method, as set forth in claim 1, for recovering or preparing to recover fluid media from underground reservoirs and comprising the following steps:

• • sinking at least two substantially vertical boreholes or shafts into the earth's surface,
  • introducing at least one pipe consisting of at least one section into each of the vertical boreholes or shafts, the at least one section of pipe having at least one opening in the lower portion of its wall, the openings in the sections of the at least two pipes each being aligned, with a selected area between two pipes and this area being located between the at least two substantially vertical boreholes,
  • lowering an explosive charge to a desired depth in the pipe,
  • detonating the explosive.

Detonation of the explosive charge at the desired depth in the pipe in the respective borehole sends a directional horizontal pressure wave through the at least one opening in the wall of the pipe section into the layer of earth. The desired depth referred to is the depth of the opening in the at least one section of pipe introduced into the vertical borehole or shaft.

By virtue of the opening in the wall of the pipe section, the horizontal pressure wave propagates in alignment with at least one given area. Provision of at least two substantially vertical boreholes or shafts in the earth's surface and detonation of the explosive charge in each of them enables a plurality of these horizontal pressure waves to collide in at least one desired area.

The invention provides for the horizontal pressure waves to set the ground between the boreholes in motion as the waves approach each other. On account of the different compressibilities of fluid media in the mini-cavities and the surrounding layers of rock, geological formations deep down in the ground undergo changes in those areas in which the pressure waves spread out. It has been found that this causes pluralities of mini-cavities to become interconnected and form one large cavity. Even if these mini-cavities are not necessarily joined to form one completely uniform volume, previously separated mini-cavities can now be developed jointly if there is at least a connection between them that allows fluid medium to be recovered from one mini-cavity by developing the other mini-cavity.

One explanation, by way of example, of the change in geological formations is that the hitherto non-profitable reservoirs referred to here as mini-cavities, which were previously surrounded by impermeable layers, experience a tremor, and that cracks form in the impermeable layers surrounding the mini-cavities.

Another is that the mini-cavities in the pressure-wave area are vertically compressed on account of the ground in general being set in motion and causing the earth to subside. The fluid media in the mini-cavities yield to this pressure by expanding approximately horizontally relative to the surface of the earth (perpendicular to the borehole). This then causes the mini-cavities to interconnect. A horizontal reservoir is formed as a result of the pressure of the pressure-wave from below and the sinking of ground from above. Fluid media can now be recovered from this profitable new reservoir by means of the standard methods described earlier on.

Naturally, it is also within the scope of the invention for at least two sections of the pipe to have at least one opening in a portion of the wall. The invention also provides for these openings in at least two sections per pipe to be aligned with at least one selected area between the two pipes, said at least one area being located between the two substantially vertical boreholes. It is thus also within the scope of the invention for a plurality of explosive charges to be lowered to different desired depths, which correspond to the openings in the pipe sections, in the respective pipe and to be detonated.

The ground surrounding the mini-cavities can be exposed more selectively to a stronger tremor by carrying out at least two detonations per pipe, the openings therein, being aligned with each other or with one or more selected points. The desired depth to which the explosive is lowered in each case may be below that of the mini-cavities, on a level with the mini-cavities (horizontal relative to the majority of the mini-cavities detected) or above the mini-cavities. It may also be advantageous to detonate explosives in the pipes at different depths.

Alternatively, the object is established according to the invention by a method, as set forth in claim 2, for recovering or preparing to recover fluid media from underground reservoirs and comprising the following steps:

• • sinking at least two substantially vertical boreholes or shafts into the earth's surface
  • introducing a wall liner into each of the vertical boreholes or shafts,
  • lowering a first explosive charge to a desired depth in the boreholes or shafts and
  • detonating the explosive at the desired depth,
  • lowering a second explosive charge to the desired depth in the boreholes or shafts and
  • detonating the explosive at the desired depth.

Detonation of the first explosive charge at the desired depth in the respective borehole or shaft sends a directional pressure wave towards the wail liner of the vertical borehole or shaft in question. The purpose of detonating the first explosive charge is to create holes in the wall liner in preparation for detonation of the second explosive charge. The wall liner may consist, for example, of cement, concrete or any other stabilising compound that hardens. The term “desired depth” corresponds in this context to the depth at which holes are to be created in the wall liner and the depth at which, after it has been lowered, the second explosive charge is detonated.

By virtue of the holes created in the wall liner, the horizontal pressure wave generated by detonation of the second explosive charge that was lowered to the desired depth propagates into the ground.

The invention provides for the horizontal pressure waves, as they approach each other, to alter the geological formations in such a manner that a plurality of mini-cavities connect up to form one larger cavity. The effects of this have already been discussed above.

The invention also provides for several explosive charges to be lowered to different desired depths in the same waft-lined shaft, or borehole and to be detonated.

Detonation of at least two explosive charges per shaft or borehole enables a plurality of pressure waves to be generated, also at different depths depending on the circumstances. The desired depth to which the explosive is lowered in each case may be below that of the mini-cavities, on a level with the mini-cavities (horizontal relative to the majority of the mini-cavities detected) or above the mini-cavities.

According to the method of the invention as set forth in claim 1 or claim 2, the explosive may be a commercial explosive (powdered explosive, gelatinous explosive, emulsion explosive and slurry blasting agent) and/or at least one propellant from stripped-down weapon systems.

According to the method of the invention as set forth in claim 1 or claim 2, furthermore, a detonating cord is connected to the explosive charge before it is lowered, the other end of the detonating cord being connected to a transmission line, this end of the transmission line being lowered together with the explosive to the desired depth and the other end of the transmission line being connected to an ignition device shortly before the step of detonating the explosive.

Of course, the invention also provides for the step of detonating the explosive to be performed by way of remote control.

As set forth in claim 3, it is also within the scope of the invention that, for the method of the invention according to claim 1 or claim 2, the fluid media are liquid or gaseous organic hydrocarbon compounds.

These hydrocarbon compounds preferably exist in the reservoir or mini-cavity as crude oil, natural gas or a mixture of crude oil and natural gas.

In the case of an open explosion, for which the explosive is suspended in the respective vertical shaft or borehole, the explosive power of the explosive suspended in the vertical shaft distributes itself over the length of the vertical shaft or borehole. As a result, the explosive power is not concentrated and a lot of it is lost, meaning that the explosive power does not impact on the desired area of the opening in the borehole or in the wall liner of the shaft; in consequence, the blasting result is deficient or poor.

As set forth in claim 4, a useful embodiment of the invention therefore provides for the explosive to be lowered within a blasting device.

An open explosion of the explosive charge in the vertical borehole or shaft may also be performed with a blasting device. The fact that the explosive power of the explosive distributes itself over the open upper and lower sections of the vertical shaft or borehole may lead to losses in explosive power and, once again, hinder concentration thereof.

As set forth in claim 5, the invention therefore advantageously provides for the blasting device to be reinforced, at least at the top or bottom thereof, with a blast-resistant or explosion-proof material.

The blast-resistant or explosion-proof material at the top or bottom of the blasting device enables the explosive power of the explosive to be concentrated in a direction perpendicular to the direction of the vertical shaft or borehole. Another advantage of this arrangement is that, at the desired depth, the wall liner of the vertical shaft is prevented from collapsing, or the pipe in the borehole from being destroyed, by the effect of the blast.

Alternatively, as set forth in claim 6, provision is advantageously made for the blasting device to consist of a blast-resistant or explosion-proof material, or to be reinforced completely with a blast-resistant or explosion-proof material, and for the blasting device to be adapted, at least in part, to the internal geometry of the pipe or of the wall liner and to have at least one blast opening.

The blasting device may take the form of a cylinder, a prism, a sphere, a cuboid or the like. At least at one end, however, part of the blasting device is shaped to match the internal geometry of the wall liner or the pipe. The advantage of this configuration is that, on insertion, the blasting device is unable to vibrate back and forth within the pipe or the wall liner. A further advantage of this configuration is that, thanks to the blasting device being adapted to fit the geometry of the internal pipe, the recoil is advantageously supported by large-area surface contact with the internal pipe. It is of further advantage that, thanks to its matching shape, the blasting device is already in surface contact with the internal pipe at the time of detonation, and is not burled against the surface of the internal pipe by the recoil.

Provision is also made for the blasting device to have at least one blast opening. This blast opening enables a concentrated, horizontal and directional pressure wave to be routed into the ground.

As set forth in claim 7, provision is also advantageously made for the step of detonating the explosive in the at least two substantially vertical boreholes or shafts to be mutually coordinated.

This is especially advantageous if the area at which blasting is directed cannot be selected centrally on account of underground rock formations or if earth formations are encountered that interfere with pressure-wave propagation.

As set forth in claim 8, it is to advantage for the method of the invention according to claim 2 that, after the step of introducing a wall liner, said wall liner is partially reinforced with a blast-resistant or explosion-proof material in the area of the desired depth.

This configuration prevents the pressure wave from propagating on the side where no mini-cavities are assumed to exist. It is also thanks to this configuration that the first detonation only makes holes on those sides of the shaft's wall liner where mini-cavities exist. Horizontal pressure-wave propagation is directed at a defined area through the opening in the wall liner. Provision of at least two substantially vertical shafts in the earth's surface and detonation of the explosive in each of them enables a plurality of these horizontal pressure waves to collide in a desired area. Geological formations are altered in consequence, as has already been described.

As set forth in claim 9, it is to advantage for the method of the invention according to claim 1 that the section of pipe having at least one opening in the lower wall portion thereof is at least partially reinforced with a blast-resistant or explosion-proof material.

This configuration prevents the pipe from caving in or collapsing at the desired depth when the explosive charge is detonated.

Alternatively, as set forth in claim 10, it is to advantage for the method of the invention according to claim 1 that the section of pipe having at least one opening in the lower wall portion thereof consists of a blast-resistant or explosion-proof material.

The invention is explained in detail below by reference to embodiments.

The drawing in

FIG. 1 shows the sinking of at least two substantially vertical boreholes or shafts into the earth's surface.

FIG. 2 shows the introduction of at least one pipe, consisting of three sections.

FIG. 3 shows the lowering of an explosive charge into a pipe.

FIG. 4 shows the detonation of an explosive charge.

FIG. 5 shows the formation of an economically viable underground reservoir.

FIG. 6 shows a possible arrangement of boreholes or shafts in the earth's surface, as seen from above.

FIG. 7 shows another possible arrangement of boreholes or shafts in the earth's surface, as seen from above.

FIG. 1 shows the earth's surface (5), into which at least two substantially vertical boreholes (3) or shafts (4) are being sunk. If possible, the at least two boreholes (3) or shafts (4) are sunk at locations surrounding the hitherto non-viable underground reservoirs (2). The earth's surface (5) may be flat, but also hilly or mountainous. Underground reservoirs (2) (mini-cavities) exist in the ground and, as shown in FIG. 1, are relatively small. Until now, their separate development for production purposes was therefore considered commercially non-viable.

FIG. 2 shows the introduction of at least one pipe (6) into each of the vertical boreholes or shafts. In FIG. 2, the pipe is made up of three sections (6a-6c), with the lowest section (6a) of the pipe (6) having at least one opening (8) in the lower portion of its wall (7). The pipe (6) may naturally consist of considerably more sections. This at least one opening (8) in the section (6a) of the respective pipe (6) is aligned in each case with a selected area (9) between the at least two pipes, this area (9) being located between the at least two substantially vertical boreholes.

This area (9) defines a volume into which the pressure waves enter. The pressure waves may by all means enter this area (9) at different geometrical depths.

FIG. 3 shows the lowering of an explosive charge (10a) to a desired depth (11) in each of the pipes (6). In FIG. 3, the pipe is made up of three sections (6a-6c), with the lowest section (6a) of the pipe (6) having at least one opening in the lower portion of its wall (7). The desired depth (11) corresponds here to the depth of the opening in the at least one section of pipe (6a) introduced into the vertical borehole or shaft.

FIG. 4 shows the detonation of the explosive charge (10a). Detonation of the explosive charge (10a) at the desired depth (11) in the pipe (6) within the respective borehole (3) or shaft (4) sends a horizontal and directional pressure wave through the at least one opening in the wall (7) of the pipe section (6a) into the layer of earth. By virtue of the opening in the wall (7) of the pipe section (6a), the horizontal pressure wave propagates in alignment with a given area (9). Provision of at least two substantially vertical boreholes (3) or shafts (4) in the earth's surface and detonation of the explosive charge (10a) in each of them enables a plurality of these horizontal pressure waves to collide in one desired area (9) or in several desired areas. The invention provides for the horizontal pressure waves to alter the geological formations in the ground as they approach each other.

This may cause the earths surface (5) to subside, as indicated by the arrow in FIG. 5. FIG. 5 also shows a reservoir (2) that has formed, development of which for production purposes would be commercially viable.

FIG. 6 shows a possible arrangement of boreholes (3) or shafts (4) in the earths surface (5), as seen from above. Here, the pressure waves emanating from the detonated explosive charges (10a) are all directed at a single area (9).

FIG. 7 shows another possible arrangement of boreholes (3) or shafts (4) in the earth's surface (5), as seen from above. Here, the pressure waves emanating from the detonated explosive charges (10a) are directed at two areas (9a, 9b). However, the pressure waves emanating from the detonated explosive charges could conceivably be directed at several areas.

A matrix that will ensure controlled propagation of pressure waves into the area surrounding the mini-cavities can be formed by arranging a plurality of boreholes or shafts in suitable relation to one another. This is extremely advantageous with respect to controlling subsidence of the earth's surface.

The areas 9, 9a and 9b are always shown as a single point in the drawings, it being evident that this point merely represents the centre of the respective area. The pressure waves spread out in the form of a solid angle from the place they were generated. Since the pressure waves are not focused on a distant point but diverge, they cause a correspondingly large area to vibrate.

Claims

1: Method for recovering or preparing to recover fluid media (1) from underground reservoirs (2), at least two vertical boreholes (3) or shafts (4) being sunk into the earth's surface (5) and at least one pipe (6) comprising at least one section (6a-6c) being introduced into each of the vertical boreholes (3) or shafts (4), comprising the steps of:

lowering an explosive charge (10a) to a desired depth (11) in the pipe (6) of the respective borehole, the at least one section (6a) of the pipe (6) having an opening (8) in the lower portion of its wall (7), the openings (8) in the sections (6a) of the at least two pipes each being aligned with a selected area (9) between two pipes, this area (9) being located between the at least two vertical boreholes (3) and the desired depth (11) being the depth of the at least one opening (8) in the at least one section of the pipe (6a) inserted in each case into the vertical borehole or shaft, and

detonating the respective explosive charge (10a).

2: Method for recovering or preparing to recover fluid media (1) from underground reservoirs (2), at least two vertical boreholes (3) or shafts (4) being sunk into the earth's surface (5), comprising the steps of:

introducing a wall liner into each of the vertical boreholes (3) or shafts (4),

sinking of a first explosive charge (10b) to a desired depth (11) in each of the boreholes (3) or shafts (4), the desired depth being the depth at which it is intended to subsequently detonate the second explosive charge for horizontal propagation of the pressure wave,

detonating the first explosive charge (10b) at the desired depth (11) in such a manner that holes are created in the wall liner by the detonation of the first explosive charge,

lowering a second explosive charge (10a) to the desired depth (11) in each of the boreholes (3) or shafts (4), and

detonating the second explosive charge (10a) at the desired depth (11).

3: Method according to claim 1, wherein the fluid media (1) are liquid or gaseous organic hydrocarbon compounds (13).

4: Method according to claim 1, wherein the explosive charge (10a; 10b) is lowered in a blasting device (18).

5: Method according to claim 4, wherein the blasting device (18) is reinforced, at least at the top or bottom thereof, with a blast-resistant or explosion-proof material (14).

6: Method according to claim 4, wherein the blasting device (18) comprises a bleat-resistant or explosion-proof material (14) or is reinforced completely with a blast-resistant or explosion-proof material (14), and wherein the blasting device (18) is adapted, at least in part, to the internal geometry of the pipe (6) or of the wall liner (12) and has at least one blast opening (19).

7: Method according to claim 1, wherein the step of detonating the explosive (10a) in the at least two substantially vertical boreholes (3) or shafts (4) is mutually coordinated.

8: Method according to claim 2, wherein, after the step of introducing a Wall liner (12), said wall liner (12) is partially reinforced with a blast-resistant or explosion-proof material (14) in the area of the desired depth (11).

9: Method according to claim 1, wherein the section (6c) of the pipe (6), which has at least one opening (8) in the lower portion of its wall (7), is at least partially reinforced with a blast-resistant or explosion-proof material (14).

10: Method according to claim 1, wherein the section (6c) of the pipe (6), which has at least one opening (8) in the lower portion of its wall (7), comprises a blast-resistant or explosion-proof material (14).