Boring or penetrating the earth – Enlargement of existing pilot throughbore requiring...
Patent
1992-10-19
1994-12-27
Buiz, Michael Powell
Boring or penetrating the earth
Enlargement of existing pilot throughbore requiring...
175 19, F21B 700
Patent
active
053756681
DESCRIPTION:
BRIEF SUMMARY
The invention concerns a borehole for producing e.g. hydrocarbons preferably in a soft or relatively soft underground formation, such as chalk or sandstone.
Such boreholes are drilled in most cases by means of drill bits which are tightened against the drill zone with a relatively large pressure. Usually, it causes no major problem to provide this pressure since the own weight of the drill string is used for this purpose as well as equipment on the surface, but in case of relatively inclined or horizontally extending holes there are limits to how far the pressure force can be introduced into a borehole in the formation in this manner. Today, however, there is a constantly increasing need for the ability to reach deeper into the shallow hydrocarbon-bearing strata, which are present e.g. in the underground below the North Sea, via horizontal holes so that it will be possible to exploit these fields economically. With this end in view, various self-moving or self-propelling drive assemblies have been developed, which can drive the drill bit forwardly through a horizontal hole in a formation, the reaction force from the drilling process being transferred to the wall of the borehole. This takes place in some methods by means of sets of clamping shoes which are alternately clamped against the wall of the borehole and are reciprocated axially with respect to each other, and in other methods by means of caterpillar belts or wheels which, to obtain a sufficiently great propulsion power, are provided with teeth to penetrate the relatively soft formations, such as chalk or sandstone which frequently constitute the main component of the above mentioned shallow, hydrocarbon-bearing strata. It is common to these known structures that they are able to impart a greater pressure force to the bit than has been possible in the past solely with the own weight of the drill string and the surface equipment, but this has been at the expense of the borehole wall which is seriously damaged when clamping shoes are used, or are torn when wheels caterpillar belts with teeth are used. This per se involves a new problem which limits the usefulness of the these methods since it is frequently necessary to pull the drive assembly in and out of the borehole to change the worn drill bit, and this is difficult or impossible in long boreholes when the borehole wall has been damaged, and the hole has therefore collapsed to a greater or smaller degree.
Moreover, the patent publications SE-B-395,300, U.S. Pat. No. 4,193,461 and AU-B-547,821 disclose methods and devices for driving underground holes or galleries in plastically deformable soil, such as clay. To this end there is used a tapered, conical tool which is screwed into the soil by means of rollers, augers or a combination of these to displace the soil substantially radially outwardly in the surrounding soil, which is consolidated in a region of considerable thickness around the underground hole. The soil is now so much stiffer and stronger in this region that the hole does not collapse. The method is useful for forming underground holes in soil, such as clay, where no great requirements are made with respect to the ability of the hole wall to mechanically withstand e.g. a flow of drilling mud and the wheel pressure of a self-propelling drilling tool. A travelling path proper for such a driving tool is not involved at all; on the contrary, the rollers or augers of the known tapered, conical tools cut into the wall of the underground hole. In fact, the mentioned publications state that after withdrawal of the tool the hole may be filled with concrete to form a load supporting column. The publication AU-B-84028 moreover discloses a method whereby such a liner may be formed while driving the underground hole. It is common to the methods and devices known from the above-mentioned patent publications that they are vitiated by the drawback that they can only be used for plastically deformable soil, such as clay, but not for firmer underground formations, such as chalk or sandstone requiring the
REFERENCES:
patent: 4193461 (1980-03-01), Lamberton et al.
patent: 4496011 (1985-01-01), Mazo et al.
patent: 4570723 (1986-02-01), Kostylev et al.
patent: 5031707 (1991-07-01), Gerasimenko et al.
Buiz Michael Powell
H T C A/S
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