US2914304A - Method of driving holes into ground comprising porous or sedimentary strata - Google Patents

Description

Nov. 24, 1959 F. LJuNGsTRM 2,914,304

y METHOD 0F DRIVING HOLES INTO GROUND COMPRISING POROUS OR SEDIMENTARY STRATA Filed Jan. 13, 1956 LAAT..

. INVENToR ATTORNEY United States Patent O METHOD F DRIVING HOLES INTO GROUND SOMPIISING POROUS 0R SEDIMENTARY IRAT Fredrik Ljungstrm, Fiskebackskil, Sweden, assignor to Svenska Skilferolje Aktebolaget, Orebro, Sweden, a corporation of Sweden This invention relates to the driving of substantially vertical holes into the ground.

More particularly this invention relates to a method of driving substantially vertical holes into ground comprising porous or sedimentary strata.

In the methods hitherto employed in mining for driving holes into the ground or rock the drilling mud was discharged out of the hole by injection of air or water supplied under pressure through a longitudinal bore provided in the borer so as in the borehole to cause a return flow of said air or water entraining the drilling mud to the open mouth of the hole.

When applying said method to the driving of holes penetrating porous or sedimentary strata, the iluid injected through the borer due to the porosity of the ground adjacent the Wall of the hole is partly forced into the zone of ground surrounding said hole. Especially in sedimentary formations said fluid escapes from the hole along the small horizontal spaces existent between various superimposed strata. This is in particular true when the hole penetrates shale formations within which strata hard as stone are separated from one another by intermediate more plastic strata chiey consisting of clay. Especially when the fluid injected is water, said layer of clay gives way for or is washed away by said water, which results in the formation of considerable spaces adapted to draw oif and distribute the washing water in substantially horizontally extending zones located radially around the borehole on the level of the injection place.

It is readily understood that the washing effect of the iluid introduced through the borer is considerably reduced by such escape. In order nevertheless to attain suicient rinsing effect the pressure under which the fluid is to be introduced must be increased still more. Such increase of pressure will again result in an increased escape of fluid from the borehole under drilling into the porous or sedimentary strata and thus in a continuous increase of the inconveniences encountered.

One main object of the invention is to procure a method adapted to eliminate or at least considerably to reduce said inconveniences by improving the effect of the measures applied for the discharge of the drilling mud from Ithe borehole. l

A further object of the invention is to increase the efficiency of the hole-driving operation. The speed of said driving operation depends, inter alia, on the eiciency of discharge of the drilling mud. An increase of the driving speed permitted by an improved discharge of said mud will again necessitate discharge of an increased quantity of drilling mud per unit time. As is readily understood the problem of discharging the drilling mud from the borehole under formation is the nucleus for any improvement of the driving operation.

In connection with the following description of the invention, the drawing shows a diagrammatic vertical section through strata with apparatus for carrying out the invention.

Patented Nov. 24, 1959 According to one feature of the invention there is produced within the zone of strata or rock radially adjacent the borehole a pressure surpassing the static pressure exerted in the ground or rock on the porous or stratiled structure thereof. Said static pressure is determined by the ground-water level or water table in the ground or rock in consideration. The water present in the various cavities of the ground or rock such as pores or horizontally extending spaces and vertical jointing planes constitute a system of communicating vessels which from the ground-water level and downwardly determine the liqlid pressure to be encountered within the ground or roc Kinds of rock of the nature in consideration have a specific weight substantially surpassing that of water and usually amounting to more than 2 compared to the value 1 of pure water. When according to the invention a pressure fluid such as air or water, for example, is introduced into the zone surrounding the borehole through a suitable supply channel, the excess pressure which can be distributed from the place of injection to the adjacent zone of ground or rock is not determined by the pressure of the water column above the water plane, but by the pressure exerted by the column of rock above the place of injection. If desired a higher pressure may be produced locally by suitably determined injection of water or air. The surface to be exposed to said excess pressure is loaded by an upwardly extending conical body of the mass or rock thus pressing on its small base with a power corresponding to the increased Weight of the conical body in consideration and besides depending on the cohering strength of the rock structure.

According to the invention an excess pressure is applied to the zone adjacent a borehole under formation, said pressure being calculated for the depth which said borehole has reached and the load of the conical body of rock above said depth. By creating said excess pressure the escape of Washing fluid into the zone of porous or sedimentary strata penetrated by the hole is avoided more or less completely, and the washing fluid supplied through the borer is available for its desired purpose and thus exercises its full effect. Said effect may be still further increased by supply of washing duid from outside through the zone surrounding said hole. Said external application of excess pressure will considerably increase the eciency of the boring apparatus in particular when the ground consists of or contains sedimentary strata permitting the supply of washing uid through the horizontally extending spaces instead of losing large quantities of said iluid escaping from the hole through said spaces.

When in accordance with the invention air is used as the washing duid, the additional effect is obtained that not only the borehole but also the zone of rock or ground around said hole is drained.

When applying the invention to sedimentary strata of rock such as shale, for example, the injection of air is preferably performed on different levels between the surface and the maximum depth to be reached by the hole. Due to the geological structure of the shale strata a plurality of horizontally extending streams is formed between the various sedimentary strata, as is disclosed in my co-pending patent application Serial No. 288,946, led May 20, 1952, now Patent No. 2,780,450, which is referred to for a more detailed description of the particular features of interest in this respect. For the reasons set forth hereinbefore, the excess pressure under whichthe air is supplied is increased in response to increasing depth. According to the invention the pressure of the supplied air can always be adjusted so as suciently to surpass the pressure of the overburden at the same level in the borehole thereby ensuring the favorable effect described hereinbefore.

To provide the possibility of adjusting the air pressure to various excess pressures 'in response to various levels of injection andthus to higher values for (greater depths, a plurality of air pipes *is introduced into vertical boreholes and tightened at -a predetermined depth by application of known methods and Vmeans disclosed forexample in my co-pending patent application Serial No. 399,137, filed `December 18, "1953, now Patent No. 2,732,195, as divisional from my co-pending application Serial No. 756,624, filed `lune 24, 1947 and Serial No. 487,681, filed February 11, 1955 as continuation-impart of my application Serial No. 75 6,626, filed June 24, 1947 and now abandoned. In 'this `way every 'portion of the rock or ground can be subjected to an excess pressure varying in accordance .to the conditions which are the most suitable for performing "the hole driving operation.

When applying the invention to sedimentary strata such as shale, for example, the property of 'said geological formations of forming horizontally extending spaces when subjected to excess pressure vas disclosed in my co-pending application Serial No. 288,946, "filed May 20, 1952, now Patent No. 2,780,450, can Vbe made kuse of by employing a few holes only for distribution of the excess pressure over a field containing a many times larger number of holes. All Vthese holes may receive the required air from the few holes, a minor portion of said larger quantity at one time during the hole-driving operation receiving the injected air flow, the remainder of said holes and in particular already finished holes being sealed against the flow of injected air by a packing of granular material or other suitable sealing means well known inthe art, such as rubber sleeves, for example. In this way the injected air is concentrated to the few holes under driving.

Referring to the accompanying drawing which has for its purpose to illustrate a preferred means 'to realize the method according to the present invention without, however, limiting it to the details shown in the drawing or described in connection with the description "thereof, the drawing represents a diagrammatic vertical section through a plurality of superimposed geological strata including bituminous substances carrying sub-surface stratum to be exploited by means of vertically drilled holes or Wells.

Covered by a layer of earth is stratum 11 of limestone overlying a sedimentary stratum 12 represented to consist of oil shale. Down to this stratum v12 and deeply penetrating thereinto are drilled two wells '14 and 15.

These wells when they have `reached the desired depth, are provided with casing 16 of steel tubes projecting slightly above the upper surface of earth layer 10. The continuation of two further wells 18 and l19 to the same depth is barred by deposit 20 of a porous mineral such as quartz sand embedded in stratum 12. Mounted above the top end of well 19 is rotary drilling equipment 22 hollow drilling rod 24 of which at its llower open end carries drill crown 26. Rinsing 4liquid such as Water is supplied under pressure normally used in the art through hollow drilling rod 24 and debouched from said open end of drilling rod 24 and raises in return flow outside the rod but inside the casing of the well 19 together with the drilled mud and escapes through outlet 26 provided in sleeve 28 constituting the casing of the finished portion of well 19 `and sealing the top opening thereof. A large portion of the rinsing liquid instead of ascending in well 19 would, however, be Wasted by penetration into the porous deposit 20.

In order to counteract this very unpleasant and annoying result finished wells 14 and 15 and also well 18 sunk closely adjacent porous deposit 20 are sealed by means of rubber plugs 30 in known manner. Plug 30 located within well 15 is attached to bar 32 projecting out of the well and making it possible .to keep the Vplug ata desired predetermined level. This plug as well as rubber plugs 30 in Iwells 14 and V18 are Vkept at levels ensuring that communications from the porous deposit 20 to the ground surface through horizontally extending ssures or spaces 46 extending to wells 14, 15 and 18 are effectively sealed o.

Conduit 34 for compressed air has branch conduits 36 and 38, respectively, entering into wells 14 and 18, respectively, and penetrating through rubber plugs 30. Shortly behind the branching-off place each branch conduit has pressure reducing valve 40 and manometer 42. The branch conduits debouch adjacent the lower end of wells 14 and 18, respectively, where casing 16 is provided With small outlet holes 44. Compressed air from the source passes through conduit .34 and the pressure reducing valves 40 and is forced under appropriate pressure through conduits 36 and 38 and outlet holes 44 into the geological formation surrounding the outlet holeprovided portion of casing 16 of wells 114 and 18. As this formation is sedimentary shale, the compressed air produces fissures 46 extending substantially horizontally or causes spaces and fissures already existing naturally to become enlarged and brought into communication so as to -form passages for the compressed air to porous deposit 20. This forming or enlarging of horizontal passages entails application of pressure surpassing the static pressure ofthe geological formation over the zone where the compressed air leaves outlet holes 44 until it reaches porous deposit 20. If there are sufficient natural communications between outlet holes 44 anddeposit 20, the pressure to which the compressed air is subjected need only be high enough to force the air through the pores of the deposit and to create a pressure zone in the deposit around drill crown 26 and the portion of well 19 immediately above said crown. The pressure in said pressure zone must exceed the pressure of the `rinsing liquid in well 19 after its escape through the open lower end of drilling rod 24, but will not reach the magnitude of the static pressure of the overburdening formation at this spot. As the higher pressure prevails in the porus deposit the rinsing liquid is prevented from penetrating thereinto. Instead it ascends within well 19 together with part of the compressed air while carrying the mud produced by the drilling action of drill crown 26 along with it to outlet 29. The drilling operation can be continued undisturbed and any waste of rinsing liquid by penetration into the vsurrounding porous formation is effectively avoided.

The pressure under which the compressed air is introduced into well 14 and 18 is controlled by means of pressure reducing valves 40 to a value ensuring fissures 46 to be formed or enlarged and the air to vbe forced through the pores of deposit 20 to the zone surrounding drill crown 26 to arrive there under a pressure surpassing that of the rinsing liquid upon escape from drilling rod 24. This pressure differential can easily be surveyed by observation of the rinsing liquid leaving outlet 29. Said liquid should always contain a moderate quantity of air bubbles.

It is to be understood that the invention is not to be limited to the preceding description of various possibilities of application, but its scope is to be determined by the appended claims.

What I claim is:

1. In a method of driving substantially vertical holes into ground having porous deposits embedded in sedimentary strata and for preventing lost circulation in a `drilling operation in which a rinsing liquid is introduced into a hole being formed, debouched under pressure near the bottom of said hole and ascends through said holo together with drilled mud produced by said drilling operation, the step of producing excess pressure in a zone of porous deposit adjacent and around said hole under formation and preventing fluid loss therefrom by building up pressure by supplying through pores of said deposit and spaces in said strata to said zone during the drilling operation from a source outside said hole a pressure fluid at a pressure to produce the said excess pressure in said zone surpassing the pressure of the debouched rinsing liquid.

2. In the method as claimed in claim l the steps of utilizing at least one hole already driven into the ground outside said porous deposit as a channel for the feeding of the pressure fluid downwards from the surface and natural spaces existent in the strata as communications to at least one borehole under formation through said porous deposit.

3. In the method as claimed in claim 2 the step of sealing several boreholes against said spaces in the strata so as to concentrate the flow of pressure fluid under excess pressure to the holes under formation through the porous deposit.

4. In the method as claimed in claim l the step of utilizing compressed air as the fluid to be introduced into the strata at a predetermined level under a pressure surpassing the static pressure of the overburden at said level so as to lift the overburden and to produce spaces of communication between the place of introduction of said compressed air and the porous deposit adjacent the hole under formation.

5. In the method as claimed in claim 4 the step of introducing the compressed air into the strata simultaneously at different levels.

References Cited in the le of this patent UNITED STATES PATENTS 1,400,962 Leonard Dec. 20, 1921 1,753,440 Miller Apr. 8, 1930 2,230,001 McConnell et al Jan. 28, 1941 2,584,059 Ramsey 1 Apr. 10, 1951 OTHER REFERENCES Brantly: Rotary Drilling Handbook, 5th edition, Pal- 20 rner Publications, New York (1952), pages 240-241.

Images