WO1998037301A1

WO1998037301A1 - Subsurface probe system for chemical and mineral exploration

Info

Publication number: WO1998037301A1
Application number: PCT/US1997/007613
Authority: WO
Inventors: Ronald E. Rosensweig; Stephen M. Hinton
Original assignee: Exxon Research and Engineering Co
Current assignee: ExxonMobil Technology and Engineering Co
Priority date: 1996-05-07
Filing date: 1997-05-05
Publication date: 1998-08-27
Anticipated expiration: 1998-11-07
Also published as: EP0973992A1; NO985190L; CA2253227A1; BR9709061A; AU718865B2; AU2828497A; NO985190D0; EP0973992A4

Abstract

The present invention is a subsurface probe system (1-3) for providing information about the material below a surface. The probe includes a housing (2) and a means (1) for heating the surrounding material. The heat melts the surrounding material to allow the probe to descend. The probe provides information to the surface by a wire or other means (3, 21, 22, 30) for carrying information. The wire (3, 21, 22, 30) is stored on the probe and deploys as the probe descends.

Description

SUBSURFACE PROBE SYSTEM FOR CHEMICAL AND MINERAL EXPLORATION

BACKGROUND OF THE INVENTION

This invention relates to an inexpensive and minimally intrusive means for placing a probe below a surface. In particular, this invention relates to placing a probe at depths (up to 1000's of feet) into the Earth while concomitantly receiving high quality data giving compositional information at depth.

Exploratory drilling is expensive using present commercial practice in which typically 20 cm. boreholes are drilled. The present system is an alternative to conventional exploratory drilling.

SUMMARY OF THE PRESENT INVENTION

The present invention is a probe system and a method for providing information about the material below a surface. The information may be logging, seismic, chemical, and information about the structural and physical properties of the material below the surface. In particular, the information may provide the direct detection of hydrocarbon fossil fuel. The system includes a probe which includes a housing and a heating element. The heating element heats the material in the vicinity of the housing so that the probe may penetrate the material. If the surrounding material is rock then the temperature of the heating element must be sufficient to melt rock. The probe system also includes a means for connecting (e.g., cable) the probe to the surface. The connecting means is stored on the probe for deployment (spinning out) as the probe descends to depth. The probe also includes a means for fransmitting information from the probe back to the surface. This means for transmitting information may be wire or fiber optic filaments or may be an on board transmitter. The energy source may be included in a field module at the surface or at the point of departure of the probe if that is a different site. Alternately, the energy source may be located on the probe (see U.S. 3,693,731). If the energy source is not on the probe, then the probe system must include a means for transmitting energy from the energy source to the probe. The means for connecting the probe, means for transmitting information and the means for transmitting energy may be combined in various combinations or may all be the same means.

The probe system may also include a means for transmitting control signals to the probe, for example, for guidance, turning sensors on and off, measuring length of the spun-out wire for depth, etc. The means for connecting the probe, transmitting information, transmitting energy and ttansmitting control signals may be combined in various combinations. However, in a preferred embodiment, one means including two wires or filaments is used for all communication with the probe. The probe may also include logging, tracking, or other system apparatus.

The probe descends below the surface by heating the surrounding material. If the surface is the solid earth, then the probe descends by melting the surrounding rock. If the surface is water, the probe first is lowered into the water until it encounters the floor of the water body. Thereafter, it continues its descent by heating the surrounding material.

Brief Description of the Drawings

Figure 1 shows the basic elements of the present invention.

Figure 2 shows another embodiment of the present invention that includes a thermoelectric heat pump.

Figure 3 shows another embodiment of the present invention that includes uninsulated conductors.

Figure 4 shows a schematic of the use of the present invention in drilling operation.

Figure 5 shows another embodiment of the present invention that includes a swept back geometry.

Figure 6 shows another embodiment of the present invention that includes a swept back geometry and coaxial conductor. DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention is a subsurface probe system that includes a probe to provide information about the material below the surface. The probe will be described with respect to obtaining logging information below the Earth's surface. However, other types of information may be obtained. For the embodiments described below, the probe is a boring tool that melts the rock below it as it descends within the Earth yet results in no residual borehole.

Example 1: Probe System

The basic elements of a simple probe are shown in Figure 1. The probe includes a refractoiy tip (1), filament storage compartment (2) and conductor or fiber optic filament (3). An energy source (not shown) is located at the point of departure of the probe as the probe descends.

A problem arises in conventional drilling in disposing of the removed material which can accumulate in the gap between the drill and the borehole, causing the drill to become immovable and hence inoperative. The present invention makes it unnecessary to transport drilled out material. The probe couples a refractoiy tip having a diameter considerably larger than that of the conductor or fiber optic filament onto the end of the filament. The transmitted energy heats the tip which in turn melts the rock, creating a molten zone suiTounding the tip. The heated tip melts rock in its path of descent with the molten rock flowing around the drill body as a thin layer that enters the wake. Upon cooling and resolidification the solid rock (9) embeds the wires. The invention avoids feeding the wires from ground level. The wires are stored as a coil inside the filament storage space (2) of the probe and spun out as the drill descends. Thus, deployed filament is stationaiy relative to the surrounding rock so no problem of friction arises as would be the case, for example, if filament were fed through a borehole from the surface.

The probe is provided with a bulk mass density greater than that of the magma. In operation, under the influence of gravity, the probe and a molten zone suiTounding the probe descend together through the Earth. OTHER EMBODIMENTS

Example 2: Probe with Heat Pump

Objectives of this embodiment of the probe are to minimize the energy that must be transmitted to the probe through the filaments and to permit faster descent to deeper depths.

An example of one system is shown in Figure 2. The probe consists of a heated hemispherical tip (10) with heat supplied from a heat pump (5) such as a thermoelectric device employing the Peltier effect. The heat pump is shown surrounded by filament storage space 16 in the figure. The heat pump draws its input heat from the molten rock in the wake (8) of the probe via thermal fins (7) in contact with the wake magma. Electric energy supplied from ground level through conductive wires (4) powers the heat pump.

The heat energy delivered by the heat pump to the probe tip can in principle greatly exceed the electrical energy input to the teπninals of the heat pump. As predicted by the second law of thermodynamics the ratio of heat to work can approach 2/ T2-T1 ) where T1 is temperature of the wake magma and T2 is temperature of the tip. For example, with Ti of 1990K and T2 of 2000 K the ratio is 200. In practice, non-idealities reduce the ratio. However, using this mode of operation the input power is reduced, filament diameter reduced, greater length of filament may be stored on board, and deeper depths can be probed faster.

Example 3: Probe with Uninsulated Conductors

In one embodiment of Example 1 the probe is heated electrically with energy transmitted through insulated, conductive filaments. Example 2 provided a heat pump means for increasing the velocity of probe descent by amplifying the heat delivered to the hot tip for a given input of electrical energy. The present embodiment provides an alternative system for minimizing the energy that must be supplied by the source. The system yields a probe that can descend deeper and faster than the probe of Example 1. The probe, illustrated schematically in Figure 3, employs bare filament with solidified rock furnishing the effective insulation. Rock insulation provides two benefits; the space taken up in the filament storage compaitment by clad insulation is replaced by conductor thus reducing the filament resistance and allowing increased power to be supplied to the heated probe. In addition, the onboard filament is stored in a manner such that the current is shunted to the heating element of the probe yielding negligible ohmic loss in the stored filament.

Referring to Figure 3, the shunting of stored conductor (13) and (15) is accomplished by tightly packing the coiled filaments and/or filling the storage compartments with conductive liquid, e.g., a molten metal (17) that wets and fills interstices between the coils of the conductive filament. The storage compartments are insulated from each other by an insulating wall (14). A guide plate (11) contains openings (7) that guide the spun out filaments into a spaced- apart configuration to prevent their contacting each other. This permits a relatively high voltage difference to be maintained across the filaments while preventing electrical breakdown. The wide spacing also minimizes parasitic conduction current through the molten rock (8) of the wake.

If desired, heat may be generated in a component of the probe that is spaced apart from the tip, transmitting the heat energy by radiation, heat pipe, or other means to the tip material which can then be chosen for its physical and chemical compatibility with magma. Alternatively, the rock melting energy may be deposited more directly in the rock, e.g. by ohmic or arc discharge in magma adjacent to the tip of the probe.

Logging data and other types of information can be generated by any convenient sensor, such as optical or infrared emission, electrical resistance, thermoelectric, etc. that may be stored in or constitute part of the probe. Transmission of the sensed signals from the probe to ground level may be accomplished using the same or additional electiical and/or optical filaments that supplied the heating power. Alternatively, signals may be transmitted by acoustic, electromagnetic wave, or other means. Although the present invention is described in reference to placing a probe beneath the surface of the Earth, it will be evident that the technique is also applicable to prospecting on planetary bodies and satellites in space exploration, probing of concrete and rock structures, probing beneath polar ice, etc.

Example 4: Subsurface probe with swept back geometry

In this embodiment, four different cases are presented in Figures 5 and 6. In all of them, the body of the probe is in the shape of a frustum 20 of a cone. This shape is chosen for the puipose of better heat management. Heat loss from the melt layer is reduced, preventing the layer from freezing and arresting the motion of the probe. In addition, if the body were cylindrical, the melted rock would form a relatively thin layer flowing over the cylinder surface, and the drag force on the probe would tend to be excessive for large aspect ratios. The drag force, in turn, would position the nose of the probe at a relatively large standoff distance from the approaching solid rock, resulting in increased required surface and interior temperatures to maintain a given advance rate. The swept back shape of the frustum creates a thicker layer around the frustum. Because viscous drag is inversely proportional to the layer thickness, the drag force and corresponding operating temperatures are substantially reduced.

Because of the wire spin out feature, heat management during descent is a dynamic issue. As wire is spun out, the probe mass and corresponding downward force decrease, tending to increase surface and interior temperatures for a given advance rate. To counteract this effect, rock melt is allowed to enter the rear of the probe. Perforations or slots in the probe body, not shown in the figures, can be provided, if desired, to facilitate melt flow into the probe.

Case I. Insulated conductor

Power is supplied by two insulated filaments 21, 22. These filaments, for example, may be alumina-coated or boron-nitride-coated tungsten. Both filaments are stored on board the probe and spun out as the probe descends. Figure 5 illustrates major design features. The filaments are wound on spools, 23, 24, with the assembly termed a "bobbin". Each bobbin is stored in a separate compartment, with the bobbin rotatable on a fixed rod, 25, 26. Filament unwound from a bobbin is led through a narrow conduit in the probe outer wall and exits through an opening in the guide plate 27 at the rear of the probe. The bobbin can be provided with a tensioning device so that a specified torque is required to rotate the bobbin (detail not shown). The effect of tensioning is to prevent excess filament from unwinding while maintaining spun out filament taut in the wake.

Electrical contact between a filament and spool rod is achieved through a rotary contact, with a current lead connected from a spool to the heating element 28. The heating element is in good thermal contact with the nose of the probe 29 in order to minimize temperature drop to the surface. Good thermal insulation 30 between the heating element and the wire storage compartment is required to minimize heat loss to the rear.

The nose of the probe is constructed of a refractory material, for example, molybdenum disilicide. The refractoiy metal molybdenum may be chosen for the body material because of its demonstrated high temperature performance and compatibility with other materials although other suitable materials may be used such as tantalum, molybdenum disilicide, coated surfaces, composites, etc.

The long length of probe is required to store the bulky insulated filaments. Power dissipated in stored filaments is thermally conducted out of the probe through the surrounding melt layer and contributes to maintenance of the melted state of the layer along the probe body.

Case II. Uninsulated conductor

The probe layout is the same as shown in Figure 5. However, in this case the probe body is fabricated from a refractoiy nonconductor such as zirconia to avoid leakage currents to the body of the probe. Probe size can be significantly smaller than Case I because filament insulator is not carried on board. Supply power is reduced because current can be shunted through the stored filaments, assumed to be in good electiical contact with each other.

Case III. Coaxial conductor

A design expected to achieve size/performance intermediate between Cases I and II is illustrated in Figure 6. A single filament is employed in the form of a coaxial conductor 30. It consists of a central conductor 34 surrounded by an annular conductive layer. The space between the conductors contains an insulator 35. The outer conductor or clad 36 is uninsulated on its outer surface, so that shorting of stored filament provides self shunting of the outer conductor. Furthermore, conductivity of rock surrounding the spun-out filament assists the outer conductor in conducting current, since the rock and outer conductor are electrically parallel. A junction 38 provides electrical contact of core conductor to the end of the heating element 28 that is in contact with the nose 29.

Another feature of the design in Figure 6 is the absence of rotating parts in the probe interior. The spool rod 31 extends nearly to the guide plate 32 but does not touch it. The conductor is stored 39 about the spool rod 31 in the body 20 of the probe. The end of the rod is fitted with a spring-loaded tensioner 33 which maintains the desired level of tension on the spun out filament. No bobbin is required as the filament is free to circle the end of the rod. The same feature can be used, if desired, in the embodiments of Cases I and II. Alternatively, a rotatable bobbin can be employed in the embodiment of Case III.

Case IV. Single conductor with ground return

This case is similar to Case III shown in Figure 6. However, electiical power is supplied through a single filament using ground return. In this case, the coaxial conductor, shown in Figure 6 is replaced by a single conductor. The conductor may be insulated. Alternatively, a bare filament is used with insulation furnished by resolidified rock. Using bare filament permits shunt storage. This arrangement permits more filament to be stored in a given size probe, hence enables probes that can descend to deeper depths in a given amount of time. Alternatively, the benefit can be taken as a lower power consumption.

Claims

CLAIMS:

1. A subsurface probe system for providing information about the material below a surface comprising:

a) a probe which includes a housing and a means for heating material in the vicinity of said housing so that said probe may penetrate said material,

b) means for connecting the probe to said surface wherein said connecting means is stored within the probe and deployed as the probe descends,

c) means for transmitting information from said probe to said surface.

2. The probe system of claim 1 wherein said means for connecting the probe and said means for ttansmitting information are the same means.

3. The probe system of claim 1 further comprising means for transmitting energy.

4. The probe system of claim 3 wherein said means for connecting the probe and said means for ttansmitting energy are the same means.

5. The probe system of claim 3 wherein the said means for transmitting information and said means for ttansmitting energy are the same means.

6. The probe system of claim 3 wherein the connecting means and all the transmitting means are the same means.

7. The probe system of claim 1 further comprising a means for transmitting control signals.

8. The probe system of claim 7 wherein said means for transmitting information and said means for transmitting conttol signals are the same means.

9. The probe system of claim 3 further comprising a means for transmitting control signals.

10. The probe system of claim 9 wherein said means for transmitting information and said means for transmitting energy and said means for transmitting conttol signals are the same means.

11. The probe system of claim 10 wherein the connecting means and all the transmitting means are the same means.

12. The probe system of claim 1 wherein the energy source for said heating means is located at said surface.

13. The probe system of claim 1 wherein the energy source for said heating means is located on said probe.

14. The probe system of claim 1 wherein said surface is a solid.

15. The probe system of claim 1 wherein said surface is liquid.

16. The probe system of claim 1 wherein said probe further comprises a heat pump.

17. The probe system of claim 1 wherein said means for transmitting information are electiical conductors.

18. The probe system of claim 8 wherein said electiical conductors are uninsulated.

19. The probe system of claim 1 wherein said means for transmitting information are fiber optic filaments.

20. The probe system of claim 1 wherein said housing includes swept back geometry.

21. The probe system of claim 1 wherein said means for transmitting information is a coaxial cable.

22. The probe system of claim 1 wherein said means for transmitting information is a single filament and ground.

23. A method for providing information about the material below a surface comprising

a) placing a probe below said surface wherein said probe heats said material in the vicinity of said probe so that said probe penetrates said material,

b) connecting the probe to said surface wherein said connecting means is stored within the probe and deployed as the probe descends,

(c) transmitting information from said probe to said surface.

24. The method of claim 23 further comprising the step of ttansmitting energy from said surface to said probe.

25. The method of claim 24 further comprising the step of ttansmitting control signals.