Sonic drilling method and apparatus

A drill string is advanced into the ground by inducing vibrations in the drill string at a resonant frequency. The drill string has an opening at a downhole end leading to a hollow interior. As drilling progresses, a core enters the hollow interior. A casing is driven around the drill string to seal the borehole. Sonic advancing of the drill string minimizes waste materials and can be operated without a circulating fluid.

BACKGROUND OF THE INVENTION 
The present invention is directed to a method of removing material from a 
subsurface and is particularly useful for drilling, well construction, and 
recovering soil, soil gas, and groundwater samples. 
A casing is often used when removing material from a subsurface. The casing 
seals the borehole, prevents cross-contamination of aquifers and the 
borehole environment, and prevents the borehole from caving in as drilling 
progresses. The casing also provides a conduit for well casing, sand, 
bentonite and cement. 
A known technique for casing a borehole is commonly referred to as air 
rotary casing hammer. A hollow rotary drill pipe having a drill bit at the 
downhole end is used to cut through the formation. The casing, which 
surrounds the drill pipe, is driven into the formation using a hammer 
which pounds the casing into the formation with a number of successive 
blows. The bottom of the casing has a drive shoe to facilitate penetration 
of the formation. 
Rotary drilling produces cuttings which must be removed for continued 
drilling. Air or mud is introduced through the interior of the drill pipe 
as a circulating medium to remove the cuttings. The air or mud flows down 
the hollow interior of the drill pipe to the bottom of the borehole and 
circulates back up the borehole in the annular area between the drill pipe 
and casing. The air or mud and cuttings are then discharged into a hopper 
for subsequent analysis, treatment and/or disposal. 
A problem with air rotary casing hammer is the production of waste products 
due to the use of a circulating medium and the fact that rotary drilling 
produces cuttings which must be removed for continued drilling. When 
operating below the water table, air rotary drilling also brings a 
substantial amount of water out of the formation which must be disposed 
of. The fluid and cuttings must be stored, tested, treated, and disposed 
of in accordance with strict Federal and State regulations when working in 
a potentially contaminated formation. Transportation, testing, treatment 
and disposal of the fluid and cuttings significantly increases the cost 
involved with the drilling, sampling and/or well construction. 
Another problem with air rotary casing hammer is that the circulating air 
can carry contaminated dust and water vapor outside the borehole and into 
the environment. 
SUMMARY OF THE INVENTION 
The present invention solves the problems associated with air and mud 
rotary casing hammer by providing a sonic drilling assembly which 
minimizes the amount of cuttings produced. Sonic drilling methods and 
apparatus are disclosed in U.S. Pat. Nos. 4,836,299, 4,548,281 and 
5,417,290 , which are herein incorporated by reference. 
Sonic drilling is accomplished by vibrating a drill string to produce 
compressive and expansive waves in the drill string. The vibrations are 
induced in a longitudinal direction of the drill string and the drill 
string is preferably vibrated at a resonant frequency. The resonant 
frequency is dependent upon a number of factors including the length of 
the drill string. 
The vibrational forces on the drill string causes the drill string to 
contract and expand in the longitudinal direction. The vibrational forces 
at the bottom of the drill string shear, displace and/or otherwise 
fracture apart the soil particles thereby cutting through the formation. 
The drill string preferably includes a number of drill rods which are 
connected together end-to-end. A sample barrel may be attached to one of 
the drill rods at a downhole end of the drill string. The sample barrel 
has an open end leading to a hollow interior which receives a continuous 
core of the formation. Although the term "sample barrel" is used herein, 
the sample barrel may also be used for drilling rather than sampling. 
Sonic drilling provides clear advantages over the gross sampling method of 
rotary drilling since near in-situ quality core samples are produced. When 
it is desired to collect a soil sample, the drill string is recovered from 
the subsurface and the material is saved for subsequent testing. 
It has been found that sonic drilling advantageously minimizes the amount 
of waste produced during drilling and, in some applications, no waste is 
produced other than the core sample itself. Formation material not taken 
as sample into the hollow interior of the sample barrel is displaced back 
into the formation. The fluidization of the cuttings around the drill 
string permits the cuttings to be reabsorbed by the formation. The 
minimization of cuttings and waste advantageously reduces the cost of 
storing, transporting, testing, treating and disposing of the cuttings. 
Furthermore, sonic drilling does not require a circulating medium since the 
cuttings are reabsorbed into the formation. Air and mud rotary drilling, 
on the other hand, requires a circulating medium to remove the cuttings 
from the borehole for continued drilling. When working in a potentially 
contaminated site, the present invention does not require a circulating 
medium and, therefore, there is no need to save, analyze, treat and 
dispose of the circulating medium and cuttings. 
Sonic drilling is particularly useful, and finds distinct advantages over 
air and mud rotary drilling, when drilling or sampling below the water 
table. When drilling below the water table, air rotary drilling can 
generate significant quantities of groundwater waste which must be saved, 
analyzed, treated and disposed of. Sonic drilling, on the other hand, does 
not require a circulating medium and, thus, groundwater is not brought out 
of the borehole during drilling. Another problem encountered when using 
mud rotary drilling is that the mud and fluid can easily become 
contaminated and cross-contaminate other aquifers. The mud also can 
impregnate the aquifer and reduce the yield or plug it off from further 
production. 
In a preferred embodiment, the sonic drill string and casing are driven 
into the formation simultaneously. Although it is preferred to drive the 
casing and sonically advance the drill string simultaneously, the casing 
may also be driven before or after the drill string. The drill string is 
also preferably rotated during sonic vibration to improve the cutting 
action. 
The casing preferably has an inner diameter compatible with the outer 
diameter of the sample barrel so that spoils and cuttings are minimized or 
even eliminated altogether. Specifically, the inner diameter of the casing 
has a diameter which is preferably equal to or less than 4 inches larger 
than the outer diameter of the sample barrel, more preferably equal to or 
less than 2 inches larger, and most preferably equal to or less than 1 
inch larger than the outer diameter of the sample barrel. When using mud 
or air rotary casing hammer, the casing must be sized sufficiently larger 
than the rotary bit and drill pipe so that an annular area is provided 
between the bit and casing for the circulating medium. 
Although an advantage of sonic drilling is the ability to drill without 
requiring a circulating fluid, a fluid may be introduced for the purpose 
of enhancing reabsorption of the cuttings into the formation. 
In another aspect of the invention, two sonic head assemblies are provided, 
one for driving the drill string and one for driving the casing. A cable 
tool assembly is also preferably provided with the drill rig. The cable 
tool assembly includes a cable and a cable manipulator for manipulating 
the cable. When using the cable tool assembly, the cable extends through 
the throughhole in the casing sonic head. The cable tool assembly works in 
a manner known to those having skill in the art. 
Other features and advantages of the invention will appear from the 
following description in which the preferred embodiments have been set 
forth in detail in conjunction with the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
A drill rig 2 constructed in accordance with the present invention is shown 
in FIG. 1. The drill rig 2 includes a carrier 4 having a mast 6 to which 
is mounted a sonic head 8, a casing hammer 10, and a cable tool assembly 
12. The drill rig 2 also has wheels 14 so that it may be moved to various 
sites. 
The sonic head 8 is configured to advance a drill string 16 into a 
subsurface by inducing vibrations in the drill string 16. The casing 
hammer 10 is configured to drive a casing 18 into the subsurface with a 
number of successive blows. The cable tool 12 assembly operates in a 
manner known to those having skill in the art and may be used for removing 
spoils from the borehole as described in greater detail below. The cable 
tool assembly 12 includes a cable 19 and a cable manipulator 21 for 
manipulating the cable 19. 
Referring to FIG. 2, the sonic head 8 includes an oscillator housing 20 
which is coupled to the mast 6. The oscillator housing 20 includes two 
bores 22 which serve as bearing races. The bores 22 provide orbital 
pathways for two steel rollers 24 of equal weight. The rollers 24 
preferably occupy about 2/3of the volume of the bores 22. 
The rollers 24 are mounted on shafts 26 which are off-center with respect 
to the bores 22. During operation, the rollers 24 rotate in opposite 
directions at the same rotational rate and are synchronized so that the 
rollers 24 are at the bottom and top of the bores 22 at the same time. By 
timing the rollers 24 in this manner, radial forces are eliminated and 
only longitudinal forces are imparted on the drill string 16. As will be 
described in greater detail below, the resulting longitudinal forces 
produce compressive and expansive pressure waves in the drill string 16 
along a longitudinal axis 27 of the drill string 16 for cutting through 
the formation. The drill string 16 essentially acts as a conduit for 
storing and transferring the energy from the sonic drill head 8. Although 
it is preferred to use the sonic head 8 described above, any type of 
mechanical or electro-mechanical vibrator may be used. 
An air spring 28 is attached to the oscillator housing 20 for cushioning 
the oscillator housing 20 as it cycles through the longitudinal 
displacements. A piston 30 is attached to the oscillator housing 20 and 
air chambers 32 are provided above and below the piston 30. The air spring 
28 isolates movement and vibration of the oscillator housing 20 from the 
rest of the drill rig 2 thereby preventing destructive metal to metal 
contact. The air spring 28 also supports the weight of the suspended drill 
string 16. 
A rotating drive motor 34 and associated gears 36 are provided for rotating 
the drill string 16. The drill string is connected to the sonic head 8 at 
an adapter flange 37. The rotating drive motor 34 is used for connecting 
and disconnecting sections to and from the drill string 16 and for 
rotating the drill string 16 to assist in drilling. Although it is 
preferred to rotate the drill string 16 during sonic drilling, the drill 
string 16 may also be kept rotationally still during drilling. 
The drill string 16 is preferably vibrated at a resonant frequency. At the 
resonant frequency, the vibrations induced in the drill string 16 coincide 
with the reflected stress waves travelling through the drill string 16. At 
the resonant frequency, the maximum displacements theoretically and 
preferably occur at the top and bottom of the drill string 16. The 
displacements at the bottom of the drill string 16 are attenuated due to 
the absorption of energy used to drill through the formation. A node of 
minimum displacement theoretically and preferably occurs at the middle of 
the drill string 16 since the superimposed pressure waves cancel one 
another at the midpoint. 
Although it is preferred to resonate the drill string 16 at the primary 
resonant frequency, the drill string 16 may also be resonated at higher 
order resonant frequencies. The fundamental, or primary, resonant 
frequency of a length of drill string 16 may be determined by the 
following formula: 
##EQU1## 
The formula provides a theoretical fundamental resonant frequency with the 
drill string 16 longitudinally unrestrained at the top and bottom. The 
bottom is, of course, restrained by contact with the formation and, thus, 
the value is only a theoretical calculation. The theoretical calculation 
will, however, aid the operator of the drill rig 2 to find the actual 
resonant frequency when the interaction between the drill string 16 and 
formation is taken into account. Typical frequencies for sonic drilling 
are between 50 to 200 cycles per second (cps) and more preferably between 
80 to 150 cps. 
The drill string 16 penetrates the formation by shearing, displacing and/or 
fracturing the soil under the bottom of the drill string 16. The 
fluidization of the soil, which typically occurs within a quarter inch of 
the drill string 16, also reduces frictional forces that constrain the 
drill string 16 so that the drill string 16 penetrates the subsurface 
easily. A distinct advantage of sonic drilling is the speed and ease with 
which the drill string 16 can pass through hard formations. 
Referring to FIGS. 8 and 9, the casing hammer 10 has a retractable hammer 
11 which is preferably pneumatically-driven, although any other driving 
mechanisms may be used. The top of the casing 18 is slidably attached to 
an anvil 38 which is pounded by the hammer to drive the casing 18 into the 
ground. FIG. 8 shows the hammer in a retracted position and FIG. 9 shows 
the hammer in a driving position in which the hammer impacts and drives 
the anvil 38. 
Referring again to FIG. 1, the bottom of the casing 18 includes a 
conventional drive shoe (not shown) to aid in penetrating the formation 
and to protect the bottom end of the casing 18. The casing hammer 10 has a 
throughhole 42 through which the drill string 16 extends. The sonic head 8 
is preferably movably mounted to the carrier 4 between a working position 
(FIG. 1), in which the drill string extends through the throughhole 42, 
and a standby position (FIG. 6), in which the drill string 16 is 
positioned outside the throughhole 42. When the sonic head is in the 
standby position, the sonic head is positioned away from the centerline of 
the hole being drilled. The sonic head 8 may be movably mounted to the 
carrier 4 in any manner and is preferably rotatably coupled to the carrier 
4 as shown in FIGS. 1 and 6. 
Referring to FIG. 3, the drill string 16 preferably includes a number of 
drill rods 35. A preferred drill rod is a 4 1/2" OD steel tube having a 10 
foot length. The drill rods 35 are threaded at both ends so that a number 
of drill rods 35 can be connected together to drill to the desired depth. 
The drill rods are connected together using the motor 34 and associated 
gears 36 of the sonic drill head 8. 
The drill string 16 has a sample barrel 44 connected to one of the drill 
rods 35 at the downhole end. The sample barrel 44 has a hollow interior 50 
into which material from the subsurface enters as the drill string 16 
advances through the subsurface. When taking soil samples of the 
formation, the material is saved for subsequent testing. The sample barrel 
44 is preferably formed with two sections along longitudinal split lines 
(not shown). The two halves of the sample barrel 44 are connected together 
at the downhole end with a drive shoe 46 and at the uphole end with a cap 
having a threaded pin which connects to one of the drill rods 35. The 
drive shoe has an angular cutting edge which facilitates penetration of 
the formation. 
A first, preferred method of removing material from a formation is now 
described in connection with FIG. 3. As shown in the left-hand part of 
FIG. 3 marked T1, the drill string 16 and casing 18 are preferably 
advanced in the formation at the same time. Thus, both the casing hammer 
10 and the sonic head 8 are activated to advance the casing 18 and sample 
barrel 44 simultaneously. The sample barrel 44 is then removed from the 
formation as indicated at the part of FIG. 3 marked T2. The simultaneous 
driving of the casing 18 and sample barrel 44 is then repeated as shown at 
time interval T3 and the sample barrel 44 is retrieved again as shown at 
interval T4. 
Although it is preferred to drive the casing 18 and drill string 16 
simultaneously, the drill string 16 and casing 18 may be driven in any 
order. For example, the sample barrel 44 may be driven ahead of the casing 
18 or the casing 18 may be driven before the drill string 16. 
The casing 18 preferably has an inner diameter compatible with the outer 
diameter of the sample barrel 44 so that spoils and cutting are minimized 
or even eliminated altogether. Specifically, the inner diameter of the 
casing 18 has a diameter which is preferably equal to or less than 4 
inches larger than the outer diameter of the sample barrel, more 
preferably equal to or less than 2 inches larger, and most preferably 
equal to or less than 1 inch larger than the outer diameter of the sample 
barrel 44. As discussed above, sizing the sample barrel 44 and casing 18 
in this manner reduces or even eliminates waste products altogether. Since 
no spoils are produced other than the core itself, no circulating medium 
is required to remove cuttings. 
A second, preferred method of removing material from a formation will now 
be described in connection with FIG. 4. Although it is preferred to 
provide the relative dimensions between the casing 18 and drill string 16 
as described above, the sample barrel 44 may also be sized smaller 
relative to the casing 18 than the preferred dimensions. The sample barrel 
44 in the second preferred method is preferably smaller than the sample 
barrel 44 of FIG. 3 so that spoils 52 from the subsurface remain in the 
casing 18 after removal of the sample barrel 44. 
As shown at time interval T1 of FIG. 4, the sample barrel 44 is first 
sonically driven into the formation to force the soil sample into the 
hollow interior 50 of the sample barrel 44. The casing 18 is then advanced 
around the sample barrel 44 as shown at time interval T2. At time interval 
T3 the sample barrel 44 is removed leaving the spoils 52 behind. A spoils 
barrel 54 is then attached to the drill string 16 and the spoils 52 are 
removed as shown at time intervals T4 and T5. The process is then repeated 
and the sample barrel 44 is lowered into the borehole to retrieve more 
material as shown at time interval T6. As discussed above in connection 
with the first preferred method, the order of advancement of the casing 18 
and drill string 16 may be in any other order. For example, the casing 18 
may be driven before or at the same time as the drive string 16. Although 
the second preferred method produces spoils 52, the second preferred 
method still does not require a circulating fluid and, thus, provides an 
advantage over conventional mud and air rotary casing hammer. 
A third preferred method of removing material from a formation will now be 
described in connection with FIGS. 5 and 6. The third preferred method is 
substantially the same as the second preferred method except that the 
spoils 52 are removed using a cable tool clean-out barrel 56 which is 
operated with the cable tool assembly 12. The cable tool clean-out barrel 
56 is a conventional tool and is known to those having skill in the art. 
As shown at time interval T1 of FIG. 5, the sample barrel 44 is first 
sonically driven into the formation. The casing 18 is then driven around 
the sample barrel 44 as shown at time interval T2 and the sample barrel 44 
is removed as shown at time interval T3. The spoils 52 are then removed 
with the cable tool clean-out barrel 56 as shown at time interval T4. The 
cable tool assembly 12 provides an efficient method of removing the spoils 
since it can be lowered to the bottom of the borehole quickly thereby 
saving time when drilling or sampling at large depths. 
The drill rig 2 is configured as shown in FIG. 6 for removing the spoils 52 
during time interval T4 of FIG. 5. The sonic head 8 and casing hammer 10 
are moved to the standby position and the cable 19 of the cable tool 
assembly 12 is moved over the centerline of the casing 18. The casing 
hammer 10 is also preferably movably mounted to the carrier 4 so that the 
throughhole 42 is no longer aligned with the centerline of the casing 18. 
When the casing hammer is moved to a standby position, the cable 19 does 
not extend through the throughhole 42 of the casing hammer 10 in a manner 
similar to the sonic head 8 which is swung out of the way. 
A second preferred drill rig 2A is shown in FIG. 7. The second preferred 
drill rig 2A includes a second sonic head 58 for driving the casing 18. 
The second sonic head 58 is preferably larger or at least the same size as 
the sonic head 8 described above in connection with FIG. 2. The casing 
sonic head 58, like the casing hammer 10 of the drill rig 2, includes a 
throughhole 60 through which the drill string 16 extends. The sonic head 8 
is movably mounted to the carrier 4 as described above in connection with 
the drill rig 2. 
The second preferred drill rig 2A may be operated in accordance with any of 
the three preferred methods with the only difference being that the casing 
18 is driven into the formation with the second sonic head 58 rather than 
the casing hammer 10 of FIG. 1. An advantage of providing the casing sonic 
head 58 is that the cuttings and spoils are further minimized since the 
cuttings produced from driving the casing 18 are reabsorbed by the 
formation as described above. 
Modification and variation can be made to the disclosed embodiments without 
departing from the subject of the invention as defined by the following 
claims. For example, the drill rods 35 may have any cross-sectional shape 
other than circular, the spoils may be removed with any other conventional 
tool, and the methods described herein may be used to provide boreholes 
for soil gas and groundwater sampling.