An Improved Blind Borehole Back-reaming Method

Abstract

An improvement in the method for gasifying subterranean carbonaceous deposits by injecting oxygen-containing gas into such deposits through an injection pipe positioned in a wellbore penatrating the deposits, gasifying the carbonaceous material and recovering gasification products through the wellbore. The improvement comprising positioning a high temperature injection nozzle in the lower portion of the injection pipe so that the injection of the oxygen-containing gas can be controlled. A nozzle for controlling the injection of the oxygen-containing gas also comprises a part of the present invention.

Description

FIELD OF THE INVENTION

This invention relates to the gasification of subterranean carbonaceous deposits. This invention further relates to the gasification of subterranean carbonaceous deposits by the use of a blind borehole backreaming technique. This invention further relates to an improved blind borehole backreaming technique wherein a high temperature nozzle is positioned in the lower portion of an air inlet line positioned in a wellbore penetrating the subterranean carbonaceous deposit.

PRIOR ART

In the gasification of subterranean carbonaceous deposits by injecting oxygen-containing gases into such coal deposits, a primary consideration is the economy with which such gasification operations can be conducted. In many instances, it has been found that a blind borehole backreaming technique is advantageous and economical. Such a technique comprises penetrating the subterranean deposit with a wellbore, positioning an air inlet line inside the wellbore, and thereafter injecting an oxygen-containing gas through the air injection line into the subterranean carbonaceous deposit, igniting the deposit and producing gasification products through the same wellbore. Typically, the wellbore is drilled to approximately the bottom of the carbonaceous deposit, and the air injection line is positioned so that the air is injected at substantially the bottom of the deposit. As combustion proceeds, high temperatures are generated at the combustion surfaces where the injected oxygen-containing gas contacts the carbonaceous material and is combusted to gasification products. As a result, the bottom portion of the air injection line is typically burned off as gasification of the deposit proceeds, thereby gradually raising the top level of the combustion zone as the lower portion of the air injection line is melted off. While economy of operation and desirable gasification results are achieved by the blind borehole backreaming method, it has been observed that in many instances it is difficult to control the rate at which the combustion surface moves upward since high temperatures are generated and the rate at which the air injection line is melted is relatively uncontrollable. A further disadvantage is that occasionally high temperatures are generated such that the air injection line burns off too quickly and air is allowed to bypass the combustion zone and pass directly from the air injection line into the wellbore with the gasification products, thus resulting in inefficient combustion, explosion hazards and the like.

As a result, much time and effort have been devoted to the development of a method whereby the movement of the combustion surfaces upward could be controlled and a method whereby the positioning of the lower end of the air inlet could be controlled.

OBJECTS OF THE INVENTION

It is an object of the present invention to provide a method whereby the advance of the combustion front in a blind borehole backreaming method can be controlled. It is a further object of the present invention to provide a method whereby the configuration of the combustion cavity can be controlled in a blind borehole backreaming method. It is a further objective of the present invention to provide a method whereby the configuration of the combustion cavity and the positioning of the air inlet can be carefully controlled by the use of a high temperature injection nozzle positioned in the lower end of the air inlet.

SUMMARY OF THE INVENTION

It has now been found that the objectives of the present invention are achieved in an improvement in the method for gasifying carbonaceous materials by injecting oxygen-containing gas into a subterranean carbonaceous deposit through an injection pipe positioned in a wellbore penetrating said deposit, gasifying said deposit, and recovering gasification products through said wellbore wherein the improvement comprises positioning a high temperature injection nozzle in the lower portion of said injection pipe so that the injection of said oxygen-containing gas can be controlled.

DESCRIPTION OF THE FIGURE

The FIGURE represents an embodiment of the method and nozzle of the present invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

In the FIGURE, a coal deposit, 1, is shown positioned beneath an overburden, 2, and penetrated by a wellbore, 4, from the surface, 3. The wellbore penetrates the coal deposit and ends at a combustion cavity, 7. An oxygen-containing gas is introduced through injection pipe, 6, in a manner shown by the arrows, 9. As shown, the oxygen-containing gas flows to the combustion surfaces, 8, where combustion occurs and gasification products are recovered through the wellbore and product gas recovery line, 11. The gasification product flow is shown by arrows, 10. The end of the air injection pipe, 12, is typically used to control the advance of the combustion surface upward. The advance of the combustion front is typically controlled by the rate at which the injection pipe end melts. By the improvement of the present invention a high temperature injection nozzle, 14, is positioned in the lower end of the injection pipe as shown. Sealing means, 15, are provided so that air is caused to flow from the injection pipe through the high temperature injection nozzle into the combustion cavity. Flow outward into the combustion zone from the high temperature injection nozzle is through vent, 6, as shown. A positioning means, 17, is conveniently used with the high temperature injection nozzle to achieve a desired placement of the injection nozzle. In the embodiment shown, a cable is used as a positioning means to vertically move the high temperature injection nozzle, thus allowing careful control of the upward advance of the combustion surface. As will be obvious, the configuration of the combustion cavity can also be controlled by adjustment of the positioning of the high temperature injection nozzle. The high temperature injection nozzle is also shown in conjunction with thermocouples, 18, which allow the operation of the nozzle by sensing the temperature and thereby determining the position of the nozzle. In the practice of the method of the present invention, the fire front would typically advance in a direction as shown by the arrows, 16, and as the fire front advances upward, various noncombustible components of the coal deposit will disintegrate and collapse forming a rubble zone, 20, as shown.

Having thus described the FIGURE, it is noted that the foregoing illustration is merely one embodiment of the invention which is by no means limited thereto, since many variations and modifications of the method of the present invention are possible. In particular, water alone, water and catalyst and the like may be introduced in conjunction with the oxygen-containing gas. The oxygen-containing gas is desirably selected from the group consisting of air, oxygen-enriched air, air-steam mixtures, and oxygen enriched air-steam mixtures and the like. Particularly desirable results have been achieved wherein air was used. It is anticipated that in many embodiments of the present invention, it will be found desirable to use air or air-steam mixtures for reasons of economy and convenience. It is, of course, obvious to those skilled in the art that the steam can be injected as such or generated in situ by the injection of water. The water, of course, may be injected through the same line as the oxygen-containing gas or through a separate line. Numerous such variations and modifications of the blind borehole backreaming technique are known to those skilled in the art and need not be discussed further. While the invention has been shown with reference to a coal deposit, it is noted that the improvement of the present invention is useful in the gasification of subterranean carbonaceous deposits as disclosed herein generally. Some suitable deposits are coal, peat, shale oils, tar sands, petroliferous deposits, and the like. Of these, coal is preferred.

Applicant's claimed improvement comprises the positioning the high temperature injection nozzle in the lower portion of the oxygen-containing gas injection line. The high temperature nozzle in its simplest form could comprise merely a high temperature tube having sealing means thereon and positioned in the lower end of the injection line in conjunction with a method for positioning the nozzle. In such an embodiment, the nozzle could be moved at regular intervals, temperature sensing means could periodically be lowered into the wellbore, and the like, to determine the desired positioning of the nozzle. As is obvious to those skilled in the art, more precise control is achievable wherein thermocouples are mounted in the high temperature nozzle as shown so that the temperature can continuously be monitored, thereby allowing precise positioning of the high temperature injection nozzle.

As noted, such positioning of the nozzle allows control of the advance of the fire front upward. When the upward advance of the fire front is so controlled, the advance of the horizontal combustion surfaces can be extended since the oxygen-containing gas tends to be forced to the combustion surfaces as it is injected. In a further embodiment of applicant's improvement, the nozzle may be modified to direct the oxygen-containing gas in one direction or the other. In such instances, the nozzle requires more precise positioning. Such more precise positioning can readily be achieved by mounting the nozzle rotatably within the injection line so that the air flow may be directionally controlled from the surface. Such positioning may be achieved by numerous methods well known to those skilled in the art, and, accordingly, it is believed that no further discussion is necessary.

The high temperature injection nozzle is fabricated of any convenient high temperature alloy or ceramic. Ceramic materials generally are suitable for use in the fabrication of the high temperature injection nozzle. Some examples of suitable ceramic materials are alumina (Al.sub.2 O.sub.3), silica carbide (SiC), boron nitrite (BN), mullite (3Al.sub.2 O.sub.3.sup.. 2), and the like. A particularly preferred ceramic material is shock-resistant mullite. High temperature metal alloys, such as chrome-nickel austenitic stainless steels, high-strength nickel base corrosion resistant (Hastelloy) alloys, and the like, are also suitable. It is believed that most high temperature alloys or ceramics will be found suitable for the fabrication of the high temperature injection nozzle since the primary criteria is that the nozzle be resistant to temperature degradation. As noted hereinbefore, preferred materials are shock-resistant mullite, chrome-nickel austenitic stainless steels, and high-strength nickel base corrosion resistant (Hastelloy) alloys. The primary criteria in such high temperature materials for the fabrication of the high temperature injection nozzle is that the material have a melting point of at least about 1,800.degree.F and preferably at least about 2,300.degree.F.

The means of positioning the high temperature injection nozzle from the surface can be as varied as the applications of the improvement of the present invention. For instance, in some instances a simple cable whereby the injection nozzle may be raised and lowered will be considered adequate, whereas in more complex applications, the cable may comprise a control column whereby rotation of the nozzle, temperature sensing, and the like are achieved.

Having described the invention, it is pointed out that the foregoing embodiments are illustrative in nature and are not limiting since many variations and modifications are possible within the scope of the present invention. In fact, it is anticipated that many such variations and modifications may appear obvious and desirable to those skilled in the art upon a review of the foregoing description of preferred embodiments.

Claims

Having thus described the invention, I claim:

1. In the blind borehole backreaming method for gasifying subterranean carbonaceous deposits by injecting oxygen-containing gas into a subterranean carbonaceous deposit through an injection pipe positioned in a substantially vertical wellbore penetrating said deposits, gasifying said deposits by partially combusting said deposits at a fire front and recovering gasification products through said wellbore; the improvement comprising; positioning a high temperature injection nozzle in the lower portion of said injection pipe to control the upward advance of said fire front and to control the rate at which the lower end of said injection pipe melts.

2. The improvement of claim 1 wherein said gasification products are recovered through the space between the inner diameter of the wellbore and the outer diameter of the injection pipe.

3. The improvement of claim 1 wherein said high temperature injection nozzle is made from a high temperature material having a melting point of at least 1,800.degree.F.

4. The improvement of claim 3 wherein said high temperature injection nozzle is made from a high temperature material having a melting point of at least 2,300.degree.F.

5. The improvement of claim 3 wherein said high temperature material is selected from the group consisting of alumina, silica carbide, boron nitrite, and mullite.

6. The improvement of claim 5 wherein said high temperature material is selected from the group consisting of shock-resistant mullite, chrome-nickel austenitic stainless steels, and high-strength nickel base corrosion-resistant (Hastelloy) alloys.

7. The improvement of claim 5 wherein said oxygen-containing gas is selected from the group consisting of air, oxygen-enriched air, air-steam mixtures, and oxygen-enriched air-steam mixtures.

8. The improvement of claim 1 wherein a plurality of thermocouples are positioned in said injection nozzle to determine the position of said injection nozzle relative to said fire front.