Abstract:
A method for driving a drive pipe into a subsea formation, the method being comprised of the following steps: suspending the drive pipe from a drill string; moving at least one mass in a direction having an upward component and within the drive pipe; accelerating at least one mass relative to the drive pipe, wherein the at least one mass is accelerated within the drive pipe; transferring energy from the accelerated at least one mass to the drive pipe; isolating the drill string from energy from the accelerated at least one mass; and removing a core of formation from within the drive pipe after the transferring. A system for driving a drive pipe into a subsea formation, the system having: a drill string suspendable from a marine vessel; a running tool attachable to the drill string, wherein a top of the drive pipe is connected to the running tool; at least one mass adapted to fit within the drive pipe; an accelerator of the at least one mass, wherein the accelerator is in mechanical communication with the running tool and the at least one mass; and a transferror of energy from the at least one mass to the drive pipe, wherein the transferror transfers energy after the at least one mass is accelerated by the accelerator.

Description:
CONTINUATION STATEMENT 
     This application claims the benefit of U.S. Provisional Application No. 60/133,828, filed May 12, 1999, and U.S. Provisional Application No. 60/125,768, filed Mar. 23,1999. 
    
    
     TECHNICAL FIELD OF THE INVENTION 
     The present invention relates generally to deep water offshore drilling operations which utilize floating rigs, and more particularly, to a method for installing a drilling assembly, including a drive pipe, into a sea-bottom formation. 
     BACKGROUND OF THE INVENTION 
     In deep water drilling operations, shallow water flow (SWFT) hazards have become increasingly troublesome. SWF derives its name from the phenomena of a flow, emanating from a subsurface and overpressurized zone, back to the seafloor. An overpressurized subsurface zone is formned naturally when an impermeable seal is formed over sandy settlements by rapid deposition of silty material. As the silty material is deposited over the sealed, sandy aquifer, the trapped water in the sandy settlement is unable to escape. Over time, the pressure increases in the sandy aquifer until the pressure developed is equal to or greater than the hydrostatic pressure at the depth of water at the location of the sandy aquifer. A shallow water flow occurs when the impermeable seal of silty material is penetrated to release the overpressure within the sandy aquifer. In some cases, the pressures are high enough to cause powerful flows of water and sand into the well bore. Waterflows destabilize the wellbore through erosion to collapse and in some cases damage the well bore and others adjacent thereto. Shallow waterflow hazards have been encountered in many areas of the world and continue to be a problem in deepwater drilling operations. 
     One solution for avoiding shallow waterflow hazards is to use a drive pipe. The drive pipe is driven into the formation past the high pressure sandy aquifer. The purpose of the drive pipe is to prevent the formation from collapsing into the borehole during this initial drilling. Since the drive pipe is driven into the formation, the soil is compressed and compacted in the immediate vicinity of the drive pipe. Compacted soil seals the drive pipe in the formation to prevent shallow water flow around the drive pipe. The drive pipe becomes the casing for the well bore through which subsequent drilling operations may be conducted. 
     In a typical offshore drilling installation, a length of drive pipe is hung from the floating rig by a string of drill collars and drill pipe lowered to the sea bottom. In such a deepwater installation, the water depth may be up to 10,000 feet or greater. In the drilling assembly, the string of drill collars are connected to the top of the drive pipe by way of a running tool having a J-latch, or other releasing mechanism. The drilling assembly may also be connected to the drive pipe by way of a conventional J-latch assembly engaged with lugs or other means attached to the inside or outside of the drive pipe. The drill string continues below the running tool and extends down the entire length of the interior of the drive pipe. The lower end of the drill string assembly terminates with a jet sub or downhole motor connected to a stabilized drill bit. 
     In a conventional assembly, the drill bit is located at the mouth or lower opening of the drive pipe, and is driven by the motor to function as a jetting assembly to drill a hole approximately the size of the inner diameter of the drive pipe. The drill string is initially connected to the drive pipe through a first position of the running tool to enable both elements to move downwardly together. Therefore, as the drill bit penetrates the sea bottom formation, the drill string lowers, and the drive pipe falls snugly into the bore hole made from the rotating and jetting action of the bit. This drilling continues until substantially the entire section of drive pipe penetrates the formation or until such time as the gravitational forces acting on the drive pipe will no longer overcome the effect of skin friction. Once this is accomplished, the drill string is disconnected from the drive pipe at the running tool connection to enable the drill string to move independently with respect to the drive pipe, and continue its drilling operation. In this mode, the drill bit continues to drill beyond the drive pipe, into the formation, while the drive pipe remains stationary. 
     During the initial drilling, when the drive pipe is penetrating into the formation due to gravitational force, regular seawater is utilized as the drilling fluid. Thus the sea water, traveling down through the interior of the drill string, functions to clean the bore hole bottom, and carry the cuttings up the annulus formed by the exterior of the drill string and the interior of the drive pipe. This fluid then exits the annulus at the top of the drive pipe to be released into the sea. 
     For subsequent drilling, the drill string is pulled out of the hole and the drill collars are stood back on the derrick of the floating platform. A conductor pipe is lowered from the rig to extend and attach to the top of the drive pipe to communicate with the annulus inside the drive pipe. Regular drilling mud is then utilized in the drilling operation by having it pumped down the drill string and up through the annuluses of the drive pipe and the conductor pipe. This conductor pipe also serves as a means to bring cuttings from the drill bit to the surface. 
     Drive pipes are usually 30 to 36 inches in diameter, having a wall one inch thick, although in some instances, the drive pipe can be 42 inches, or larger, in diameter, with a two inch wall thickness. Drive pipes are typically 350 to 450 feet in length for shallow water drilling operations if driven from the surface. In conventional drilling operations, it has been found that a drive pipe can not penetrate beyond a certain amount, usually around the 450 feet length, because at that length, the resistance caused by skin friction becomes greater than the force of gravity and the force applied from the surface by conventional hammer means. The drive pipe will reach a point of refusal and any further force applied to the uppermost section of the drive pipe will cause yielding of the pipe material and any further driving efforts must be discontinued. 
     In deep water drilling operations, drive pipes having lengths of 1000 feet or more are sometimes required to mitigate shallow water flow hazards. Therefore, auxiliary means for driving drive pipes are necessary to augment the gravitational forces acting on the drive pipes to increase the depth of penetration of the drive pipes. 
     One option has been to use a hammer applied to the top of the drill string to help drive the drive pipe at the end of the drill string downward. However, because of the great drill string lengths involved, the energy transferred to the drive pipe through the drill string is not sufficient. 
     A further option has been to apply conventional hammers directly to the top of the drive pipe at the connection between the drive pipe and the drill sting. Hydraulic pile and pipe drivers of various configurations are known. An example of a hydraulic pipe driver attached to the top of the pipe is disclosed in U.S. Pat. No. 4,964,473, incorporated herein by reference. The device has a submerged power converter wherein hydraulic pressure energy is generated in the power converter to drive the driver and wherein the power converter is driven by pressurized surrounding water after the energy transfer is exhausted into the surrounding water. Further examples of pipe drivers used to drive pipes and piles into a sea bed for securing platforms and other structures are disclosed in U.S. Pat. No. 4,601,349; 5,662,175; 5,090,485; 4,817,734; 4,818,149; 4,856,938; 5,088,567; 4,872,514; and 5,228,806, all incorporated herein by reference. 
     In any drive system using a conventional hydraulic hammer applied to the top of the drive pipe, there are significant drawbacks: (1) an umbilical conduit must be run from the floating vessel to the hammer; (2) conventional hydraulic hammers apply relatively low impacts; and (3) the drive pipe is not driven vertically. First, typical drive pipe hammers have umbilical cables which supply electrical or hydraulic forces to the hammers. At water depths where drive pipes are required (5,000-7,000 feet), the umbilical cord required is an impractical length. Second, conventional hydraulic hammers do not deliver large enough impacts to drive the drive pipe. Since the impact is delivered to the top of the drive pipe, the relative small impact energy is absorbed by the lengthy drive pipe. Impacts applied directly to the drive pipe may damage the pipe. Third, the drive pipe is not always driven straight down, as desired. Instead, the drive pipe more than likely deviates from vertical as it is driven. An installed drive pipe, which is not vertical, is generally unacceptable for subsequent drilling operations. 
     Conventional hammers are made even less effective by the need to use a “cone” shaped driving shoe to penetrate the formation. Since the conventional hammers must be attached to the top of the drive pipe, there is no ability to run a mud motor/drill device into the drive pipe from the drill string. Therefore, a driving shoe must be placed at the leading end of the drive pipe to compress and deviated the soil from locations immediately beneath the drive pipe to locations around the drive pipe. This increases the skin friction on the outside of the drive pipe which further impedes the drive pipe&#39;s progress into the formation. Similarly, if a conventional hydraulic hammer on an umbilical conduit is positioned within the drive pipe to impact the drive pipe at a point towards its bottom, a driving shoe must be employed. If the hydraulic hammer is within the drive pipe, it is impossible to dispose of the formation “core” as the pipe is being driven. Thus, it is impossible to place a conventional hammer within the drive pipe. 
     Therefore, there is a need for a drive pipe driving system which does not require an umbilical conduit, applies a sufficient impact to drive the drive pipe, and drives the drive pipe vertically. The drive system must also be versatile to allow for a drive pipe having a driving shoe or a drill located in the mouth of the drive pipe. 
     SUMMARY OF THE INVENTION 
     The present invention obviates the above-mentioned problems by providing impact forces from within the drive pipe at a location toward the bottom or leading end of the drive pipe. In this manner, the energy transfer is much more efficient, and the pipe will be driven vertically. 
     The drilling assembly includes an impact tool hung, under tension, to the drill string directly below the running tool connection. An isolator is installed into the drill string directly above the running tool connection to prevent shock loads from being transferred to the drill string above. 
     The impact tool comprises inner and outer tubular body members, relatively movable with respect to each other, in an axial direction. The inner body member is connected to the upper drill string extending to the rig. The outer body member is connected to the lower drill string section that extends within the drive pipe to the drill bit. In this embodiment, the inner body member remains stationary, while the outer body member is movable in the up and down direction. 
     The impact tool further comprises a jar section for providing a downward jarring force on the inner body member which, in turn, transfers the jarring force to the top of the drive pipe through the running tool assembly. The tool also comprises one or more pull sections for providing a closing force between the two members to lift the outer member, the lower drill string, and the drill bit off the bore hole bottom. The jarring force is caused by releasing the last mentioned three components and allowing them to drop a predetermined distance, at which time impact occurs within the body of the jar. The impact tool further comprises a compression chamber or a mechanical device such as a spring, to function as an energy intensifier to augment the jarring force acting on the drive pipe. 
     The isolator includes two members axially movable with respect to each other, and interconnected to adjacent upper and lower drill collar sections. The isolator includes a compression chamber formed between the two members. The isolator functions to enable the drill string located above the running tool to elongate in order to compensate for the sudden travel of the drive pipe as it is being jarred downwardly. This enables the drill collars above the running tool assembly to remain in tension during operation to prevent unwanted vertical deviation of the drive pipe during installation. 
     Finally, a compensating tool is located on the drill string adjacent the motor and the bit. This tool also includes two members axially movable with respect to each other for connection to adjacent upper and lower drill collar sections. The compensating tool also includes a compression chamber formed between the two members. The tool functions to enable the drill string located adjacent the drill bit to become shorter to compensate for the sudden travel of the drive pipe downwardly and prevent the bit from impacting heavily on the formation. The compensating tool allows some slack in the string to allow the bit to rise and therefore prevent the bit from plugging while the drive pipe is being jarred into the formation. The drill bit and downhole motor drill out the formation “core”, if so desired. 
     Other advantages of the inventive system are the ability to infinitely vary the impact loads, alter the location of the impact within the length of the drive pipe and the equal distribution of a large uniform mass, all of which contribute to the desirability and performance of the tool. Overall, the assemblies and methods of the present invention perform better than conventional hydraulic hammers. 
     A system for floating rig installations is provided for efficiently driving an extraordinarily long length of drive pipe into the sea bottom formation, while still preserving the integrity of the rig and the bottom hole assembly. 
     With the system of the present invention, the drive pipe is driven into the subsea formation with the drill string above the drive pipe in constant tension. A reciprocation occurs within the drive pipe so that the drive pipe may be driven from a floating vessel. The entire weight of the drive pipe and impacting system is suspended on a compressed gas within a cylinder of an isolation sub. The isolation sub prevents shock loads from being transferred up the drill string to the floating vessel. 
     In one embodiment of the invention, pump pressure lifts the bottom hole assembly and closure jar. Thus, pump pressure is ultimately transformed into an impact force on the drive pipe when the lifted mass is allowed to free fall onto the drive pipe. Lift pistons within the impact tool are designed to move out of the way when a pressure differential across them changes. This insures that the lift pistons do not impede the falling velocity of the mass prior to impact. Depending on the particular system, welded or preformed lugs are positioned inside the drive pipe to transfer impact loads from the impact tool to the drive pipe. Some systems of the present invention have an isolator, an impact device and a cushion sub used in combination. 
     While some embodiments of the invention simply allow the mass (drill collars) to freefall, in other embodiments a device is used to enhance or amplify the downward acceleration of the mass. For example, released potential energy stored in a spring, compressed gas chamber, combustion chamber, etc. is used to accelerate the falling mass in addition to gravity. 
     Many systems of the invention use a vertically reciprocating weight suspended within the drive pipe, but attached to the top and bottom of the drive pipe. Thus, the impact tool is used in conjunction with the relatively stationary running tool. The running tool may be latched or unlatched from the drill string. Thus, if the drilling motor stalls, the running tool may be unlatched from the drill string so that the drilling motor may be lifted up relative to the formation core to free the drill bit. In alternative embodiments, gas or pump pressure is used to cushion the drill bit from impact forces on the drive pipe. If the drill-out system is used, the ability of the motor and drill bit to float on top of the formation and not impact the bottom is a key feature. 
     In alternative embodiments, the inner members of the impact device are held stationary relative to the drive pipe during impact. Of course, since the drive pipe is driven into a subsea formation, the impact tool is used underwater in most systems of the present invention. 
     One aspect of the present invention is to use a detent to suspend the mass (drill collars) momentarily to provide the lift cylinders enough time to decompress. In one embodiment, the detent is a cylinder with a detent ring. Belleville springs cushion the detent cylinder when the drill collars are at the end of the raising stroke. Depending on the time delay necessary for suspending the mass, the detent ring will be either a short cocking detent or a long cocking detent. An example of a “short cocked” detent is disclosed in U.S. Pat. No. 5,174,393, incorporated herein by reference. 
     While the present invention is described for use in driving a drive pipe into a subsea formation, the system could also be used to set subsea anchors or any other device which must be driven into a subsea formation. 
     Within the impact device, there are hydraulic tattle-tales to determine open and closed positions of the tool. While any type of tattle-tale known to persons of skill may be used, one particular type comprises a rubber sleeve containing grease or oil. A pressure sensor detects the pressure of the grease or oil within the rubber sleeve. This information is returned to the operator at the surface. 
     According to one aspect of the invention, there is provided a method for driving a drive pipe into a subsea formation, the method having the steps of: accelerating at least one mass relative to the drive pipe, wherein the at least one mass is accelerated within the drive pipe; and transferring energy from the accelerated at least one mass to the drive pipe. 
     According to a further aspect of the invention, there is provided a method for driving a drive pipe into a subsea formation, the method being comprised of the following steps: suspending the drive pipe from a drill string; moving at least one mass in a direction having an upward component and within the drive pipe; accelerating at least one mass relative to the drive pipe, wherein the at least one mass is accelerated within the drive pipe; transferring energy from the accelerated at least one mass to the drive pipe; isolating the drill string from energy from the accelerated at least one mass; and removing a core of formation from within the drive pipe after the transferring. 
     According to still another aspect of the invention, there is provided a method for driving a drive pipe into a subsea formation, the method having the following steps: suspending the drive pipe from a drill string; removably attaching the drill string to the top of the drive pipe; moving at least one mass in a direction having an upward component and within the drive pipe; accelerating at least one mass relative to the drive pipe, wherein the at least one mass is accelerated within the drive pipe; transferring energy from the accelerated at least one mass to the drive pipe near a bottom of the drive pipe; and isolating the drill string from energy from the accelerated at least one mass. 
     Relative to another aspect of the invention, there is an impact tool for driving a drive pipe into a subsea formation, the impact tool having: at least one mass adapted to fit within the drive pipe; an accelerator of the at least one mass; and a transferror of energy from the at least one mass to the drive pipe, wherein the transferror transfers energy after the at least one mass is accelerated by the accelerator. 
     In a further aspect of the invention, there is provided a system for driving a drive pipe into a subsea formation, the system having: a drill string suspendable from a marine vessel; a running tool attachable to the drill string, wherein a top of the drive pipe is connected to the running tool; at least one mass adapted to fit within the drive pipe; an accelerator of the at least one mass, wherein the accelerator is in mechanical communication with the running tool and the at least one mass; and a transferror of energy from the at least one mass to the drive pipe, wherein the transferror transfers energy after the at least one mass is accelerated by the accelerator. 
     In an alternative aspect of the invention, there is a system for driving a drive pipe into a subsea formation, the system having: a drill string suspendable from a marine vessel; a running tool attachable to the drill string, wherein a top of the drive pipe is connected to the running tool; an isolator sub between and in mechanical communication with the drill string and the running tool; at least one mass adapted to fit within the drive pipe; an accelerator of the at least one mass having: a first body member mechanically communicable with the at least one mass, a second body member mechanically communicable with the running tool, an actuator of the first and second body members relative to each other, wherein the actuator works against gravity, and a detent of the first and second body members relative to each other; the system further having an impulse section that accelerates the at least one mass; and a transferror of energy from the at least one mass to the drive pipe, wherein the transferror transfers energy after the at least one mass is accelerated by the accelerator. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention is better understood by reading the following description of nonlimitative embodiments with reference to the attached drawings wherein like parts in each of the several figures are identified by the same reference characters, and which are briefly described as follows. 
     FIG. 1 is a schematic view of a floating rig incorporating the system for driving a drive pipe into the sea bottom formation according to the present invention. 
     FIGS. 2A-2C are side cross-sectional views of an isolator sub of the present invention, shown in a collapsed position. 
     FIGS. 3A-3C are side cross-sectional views of the isolator sub shown in FIGS. 2A-2C, except in these figures, the isolator sub is shown in a fully elongated position. 
     FIG. 4 is an end cross-sectional view of a section of an impact tool of the present invention. The view is a cross-section at line  4 — 4  shown in FIG. 5A, described below. 
     FIGS. 5A-5G are side cross-sectional views of the impact tool of FIG. 4, wherein the impact tool is shown in a fully closed position. 
     FIGS. 6A-6G are side cross-sectional views of the impact tool of FIGS.  4  and  5 A- 5 G, wherein the impact tool is shown in a fully opened position. 
     FIGS. 7A-7C are side cross-sectional views of a cushion sub of the present invention, shown in a fully closed position. 
     FIGS. 8A-8C are side cross-sectional views of the cushion sub of FIGS. 7A-7C, wherein the cushion sub is shown in a fully opened position. 
     FIGS. 9A-9C are side cross-sectional views of a second embodiment of a cushion sub, shown in a closed position. 
     FIGS. 10A-10C are side cross-sectional views of the cushion sub of FIGS. 9A-9C, wherein the cushion sub is shown in an opened position. 
     FIG. 11A is a cross-sectional side view of a system for driving a drive pipe into the sea bottom formation according to the present invention. The system has an impact surface with the drive pipe near the driving shoe of the drive pipe. The system is shown in a before-impact configuration. 
     FIG. 11B is a cross-sectional side view of the system shown in FIG. 11A, except that in this figure, the system is shown in an after-impact configuration. 
     FIG. 11C is a cross-sectional view of a release mechanism of the driving shoe of the system shown in FIGS. 11A and 11B. 
     FIG. 12A is a cross-sectional side view of a system for driving a drive pipe into the sea bottom formation according to the present invention. The system has an impact surface with the drive pipe at a midpoint location on the drive pipe, and a drilling motor suspended below the impact tool. The system is shown in a before-impact configuration. 
     FIG. 12B is a cross-sectional side view of the system shown in FIG. 12A, except that in this figure, the system is shown in an after-impact configuration. 
    
    
     It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, as the invention may admit to other equally effective embodiments. 
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 shows an offshore, floating drilling unit, generally indicated by arrow  10 . The drilling unit  10  comprises a drill ship or semi-submersible floating platform  11  having conventional tool handling equipment  12  mounted on it. The platform  11  also has conventional means for supporting a drill string, generally indicated by arrow  13 . The platform  11  is adapted to operate on the open sea  15 , which has a bottom formation  17 , generally in the range of, but not limited to, 5,000 to 7,000 feet below sea level. In some instances, there may also be underground streams  19  flowing beneath the sea bottom  17 . 
     The drill string  13  comprises a plurality of drill pipe and drill collars  21  extending from the drilling unit  10  and attached to the top of the predetermined length of drive pipe  27 , when the bottom of the drive pipe is approximately at the depth of the ocean floor. Both drill pipe and drill collar sections are approximately 30 feet in length and are supported in tension from the drilling unit  10  above. 
     An isolator  23  is mounted on the drill string  13 , directly below the upper section of drill collars  21 . The isolator  23  functions to isolate and prevent the jarring impact forces and accelerated movements occurring below from travelling up the string of drill pipe and drill collars  21  to the floating platform  11 . 
     Located directly below the isolator  23  is a running tool  25 , which is adapted to support a drive pipe  27 . The drive pipe  27  is usually around 750 feet in length, although other lengths may be utilized. The drive pipe  27  also is usually 30 to 48 inches in diameter, having a wall thickness of one to two inches, although other dimensions can be utilized. In operation, it is desired to lower the drive pipe  27  onto the sea bottom  17 , and have it penetrate the bottom formation to substantially the entire length of the drive pipe  27 . 
     The running tool  25  also includes a J-slot, or other means to allow the drill string to be released and pass therethrough. In one position, the length of drill string extending through the running tool  25  is fixed with the drive pipe  27  to travel downwardly together. In a second position, the drill string can move downwardly, to pass through the drive pipe  27 , while the drive pipe  27  remains stationary. 
     Located directly below the running tool  25 , and extending downwardly within the drive pipe  27 , is an impact tool  29 . The impact tool  29  functions to impart, through the running tool  25 , a downward jarring force to the top of the drive pipe  27  to assist in causing the drive pipe  27  to penetrate the bottom formation  17 . The lower end of the impact tool  29  is connected to an additional string of drill collars  31 , which extend downwardly, within the drive pipe  27  to substantially the bottom thereof. This length is approximately that of the aforementioned drive pipe. 
     A cushion sub  33  is mounted directly below the lower section of drill collars  31  and is adapted to function as a means to cushion the impact energy passing through to the bottom hole assembly described below. 
     This bottom hole assembly comprises a downhole motor  35  connected to a stabilizer  37  and a drill bit  39 . The motor is hydraulically driven to impart a rotary motion to an output shaft which, in turn, drives the stabilized drill bit  39 . The drill bit  39  extends near the mouth of the drive pipe  27  and operates to drill into the bottom formation  17  as the drive pipe is being driven, and with its jetting action, drill a borehole approximately the size of the inside diameter of the drive pipe  27 . During the initial operation of the drilling assembly, the drive pipe  27  penetrates the bottom formation by gravity, as the borehole is being drilled. However, after a while, the skin friction of the drive pipe and the formation outside the drive pipe increases to the point at which it can no longer be overcome by the forces of gravity and any further penetration of the drive pipe ceases. At this point, the impact tool  29  is used to impart a jarring force to the drive pipe  27  to assist in the penetration thereof. A more detailed description of the operation will be given with a further description of the components already described. 
     Referring now to FIGS. 2A-2C and  3 A- 3 C, the isolator  23  will be described going from left to right on the figures, with the far left being the upper end of the tool, and the far right being the lower end of the tool as it is positioned in the drill string. FIGS. 2A-2C are side cross-sectional views of the isolator sub  23  shown in a collapsed position and in FIGS. 3A-3C the isolator sub  23  is shown in a fully elongated position. The upper end of the isolator  23  begins with a kelly mandrel  24  which is adapted to be connected to the lower end of the drill string extending down from the platform. The mandrel is a tubular element which is adapted to extend within a kelly cylinder  26 . The upper end of the kelly cylinder  26  forms a drive cylinder  28 , which is internally shaped as a six sided polygon to register with the kelly mandrel  24 , which is externally shaped as a six sided polygon. Other drive means, such as pins may also be used. This structure enables the kelly mandrel to move longitudinally with respect to the drive cylinder and kelly cylinder, while being prevented from rotating with respect thereto. The lower end of the kelly cylinder  26  includes an end wall  32 , which enables a chamber  34  to be formed between the drive cylinder  28  and the end wall  32 . A hammer  30  is mounted on the kelly mandrel  24  and is adapted to reciprocate within the chamber  34 . The chamber  34  is vented to the exterior of the tool to allow drilling fluid to enter the chamber. 
     The cylinder and mandrel continue downwardly below the end wall  32  to form an enclosed chamber  38 . The lower end of the chamber terminates  38  at a lower end wall  40 . The chamber  38  is pressurized with gas. A valve  36  is mounted on the mandrel to reciprocate within the chamber  38 . The valve  36  comprises a ring  43  formed on the mandrel, and a cylindrical sleeve  44  slidably mounted on the mandrel. The sleeve  44  is retained on the mandrel by a ring  45 . 
     The valve  36  prevents any transfer of fluid therethrough and functions to prevent any flow of fluid between the inner and outer members of the tool as the exterior member of the tool is moved downwardly in respect to the inner mandrel. This forces the fluid above the valve to be compressed to cushion and restrain the movement between the inner and outer members of the tool. In the extreme position of downward movement of the exterior of the tool, the hammer  30  will abut against the shoulder of the drive cylinder  28 . As a result, the fluid in chamber  38  above the valve  36  is compressed during this movement to impede the movement of the mandrel. It should also be noted that other mediums such as gas or mechanical springs may be used in this tool. 
     In summary, the isolator  23  functions to absorb the shock of the jarring downward movement of the drive pipe and isolate such impact loads from the drill string located above the isolator  23 . The isolator  23  also allows the drill string to be freely lowered relative to the drive pipe  27 . p FIGS. 4,  5 A- 5 G and  6 A- 6 G illustrate an embodiment of the impact tool  29 . The upper end of the tool  29  comprises a kelly mandrel  50  which is adapted to be connected to the lower extending tubular member of the running tool  25 . The kelly mandrel  50  is adapted to extend within a kelly cylinder  52 . The upper end of the kelly cylinder  52  includes a drive cylinder  54 . As shown in FIG. 4, the interior of the drive cylinder  54  is configured as a six-sided polygon, while the kelly mandrel  50  has a mating exterior shaped as a six-sided polygon. As with the isolator tool, this structure on the impact tool enables the kelly mandrel  50  to reciprocate within the kelly cylinder  52  without any relative rotation. The kelly mandrel  50  and cylinder  52  also coact to for m a chamber  56  therebetween. A hammer  58  is mounted on the end of the kelly mandrel  50  and a detent mandrel  61 . An end wall  57  forms the lower end of the chamber  56 . The lower end of the drive cylinder  54  includes a shoulder  54 ′ which is adapted to strike the upper end of the hammer  58  when the exterior of the impact tool  29  is allowed to drop with respect to the interior of the tool. 
     The impact tool  29  further comprises a detent cylinder  59  cooperating with the detent mandrel  61  to form an annular chamber  60  therebetween. A detent ring  62  is adapted to be slidably mounted on the detent mandrel  61  and to abut against an annular projection  64 . A retainer  63  is adapted to be secured to the detent mandrel  61  to retain the detent ring  62  in position. An end wall  66  forms a barrier between the detent annular chamber  60  and the upper end of lift chamber  69 . The detent cylinder  59  also includes an inwardly extending cylindrical projection  65 . In alternative embodiments of the invention, detents similar to those disclosed in U.S. Pat. No. 5,174,393, incorporated herein by reference, are used. The operation of this mechanism will be described later with the overall operation of the tool. 
     The impact tool  29  further includes an upper lift section comprising a lift cylinder  67  and an interior lift mandrel  68 , with a lift chamber  69  formed therebetween. A lift piston  70  is mounted within the lift chamber  69  and is adapted to abut against a shoulder  71  on its upper end and against a shoulder  72  on its lower end. The chamber is adapted to be pressurized with hydraulic pump pressure through ports  72 ′. This fluid pressure functions to pressurize the chamber  69  to lift the external members of the tool with respect to the interior mandrels. 
     The impact tool  29  further includes a lower lift section comprising a lift cylinder  73 , a lift mandrel  74  having a chamber  75  formed therebetween. The lower lift section functions identically to the upper lift section and comprises a lower piston  76  abutting against shoulders  77  and  78 . 
     According to alternative embodiments of the invention, the impact tool comprises alternative devices to actuate or lift the mass for impacting the drive pipe. For example, the impact tool may lift or actuate by a worm gear mechanism, a rack and pinion gear mechanism, an electro-magnetic servo device, a lever device, a pulley and cable mechanism, a pneumatic system, or any other system known to persons of skill in the art. 
     The impact tool  29  further includes an auxiliary gas impulse section comprising an outer cylinder  80  and an inner mandrel  81  forming an enclosed pressure chamber  82  therebetween. The chamber  82  is bounded at its ends by end walls  83  and  84 . The chamber  82  is filled with a gas. A fluid valve  85  is mounted within the chamber  82  and comprises a sleeve  86  slidably mounted on the mandrel  81  and adapted to abut against a ring  87  formed on the mandrel  81 . A retainer  88  is provided to retain the sleeve  86  on the mandrel  81 . Finally, a bottom section  90  is located at the lower end of the tool and includes a pin section  91  which is adapted to be connected to the drill string supporting the bottom hole assembly. 
     FIGS. 7A-7C and  8 A- 8 C show, in detail, the cushion sub  33  which is mounted directly below the lower section of drill collars  31 . FIGS. 7A-7C are side cross-sectional views of the cushion sub, shown in a fully closed position, and FIGS. 8A-8C are similar views of the cushion sub shown in a fully opened position. The top of the cushion sub  33  comprises a kelly mandrel  100 , which is adapted to be connected to the lower end of the drill collars  31 . The kelly mandrel  100  extends downwardly to form an inner tubular member  101 , which extends within a drive cylinder  102  and a cylinder  103 . The portion of the inner tubular member  101  extending through the drive cylinder  102  is configured like the inner drive members of the isolator  23  and impact tool  29  to register with the interior of the drive cylinder  102 . The interior of the drive cylinder  102  is configured like the other drive cylinders to enable the inner member  101  to reciprocate with respect to the drive cylinder  102 , while being prevented from relatively rotating with respect thereto. 
     A knocker  104  is mounted on the lower end of the inner tubular member  101 . The lower end of the knocker  104  is connected to an inner tubular member  107  which, in turn, extends through an end wall  105 . Beneath the end wall  105 , the inner member  107  extends within a pressure cylinder  106 . The intermediate portion of the inner tubular member  107  includes an enlarged flange  109  formed thereon. The flange  109  is similar to the previously mentioned flanges. A valve sleeve  110  is slidably mounted over the inner member  107  and is retained thereon by a retaining ring  111 . This valve assembly is adapted to reciprocate within a pressure chamber  108  formed between the pressure cylinder  106  and the inner member  107 . The pressure chamber  108  is pressurized with a fluid. The lower end of the pressure chamber  108  is formed by an end wall  112 , through which the inner member  107  extends. 
     The lower end of the cushion sub  33  is formed by a bottom cylinder  113 , which terminates with a pin section  114 . The pin section  114  is adapted to be threadedly connected to the lower section of drill collars. 
     FIGS. 9A-9C and  10 A- 10 C show a second embodiment of the cushion sub, in which the only change in structure from the first embodiment is that the pressure chamber  108  is vented to the pump pressure found within the inner tubular member. In the first embodiment, the pressure chamber is enclosed with the pressurized fluid. This venting structure is accomplished by a plurality of ports  115  extending through the inner member  107 . These ports enable the pressure chamber  108  to communicate with the pump pressure inside the inner member  107 . Furthermore, a piston  116  and flange  117  are substituted for the valve  110 . 
     In operation, the impact tool  29  is shown in its fully retracted, or cocked (before-impact) position in FIGS. 5A-5G. In FIGS. 6A-6G, the impact tool is shown in an extended or after-impact position. To activate or cock the tool, the pump pressure from the floating platform  11  is increased. This increase in pressure travels down the interior of the drill string. Inside the tool, this increase in pump pressure passes through the ports  72 ′ and  78 ′ to increase the pressure within the lift chambers  69  and  75 , which, in turn acts on the lift pistons  70  and  76  to cause the pistons to abut against shoulders  72  and  78 . This causes the lift chambers  69  and  75  to expand to enable the outer lift cylinder  80 , along with the hanging assembly below it, to rise with respect to the interior of the tool. To accomplish this, the force exerted to expand the chambers  69  and  75  must overcome the weight of the hanging assembly beneath the tool. 
     While this upward movement of the outer assembly continues, the gas within the chamber  82  located below the fluid valve  85  is compressed, because the action of the valve is to close as it moves relatively closer to the lower end wall  84 , and the chamber becomes smaller. This movement continues until the drive cylinder  54  contacts the lower shoulder of the kelly mandrel  50 . This is the fully cocked position shown in FIGS. 5A-5G. 
     When in the fully cocked position, the pump pressure is reduced until the lifting force is less than the weight of the assembly beneath the tool. When this occurs, two things happen. First, the weight of the assembly below the tool, and the auxiliary force from the chamber  82 , causes the outer structure of the tool, and the hanging assembly, to move downwardly. Secondly, in the fully cocked position the detent ring assembly  62  is located below the restriction of the cylindrical projection  65 . As the restriction of the cylindrical projection  65  passes downwardly relative to the ring  62 , fluid flow is stopped from passing around the ring  62  and the fluid within the chamber above the ring is sufficient to support the hanging assembly. The ring  62  does permit a small amount of fluid to pass through the small ports inside the ring to allow the hanging assembly to move downwardly as the pressure chambers  69  and  75  are being evacuated. Finally, as the restriction  65  passed completely passes over the ring  62 , the fluid in the chamber  60  is allowed to freely pass over the ring  62  to provide no further resistance to the downward movement of the hanging assembly. In addition, the gas charge below the lift pistons  70  and  76  raises the lift pistons off the lower shoulders  72  and  78  to rest against the upper shoulders  71  and  77 . This enables the pistons to be removed from contact with shoulders  72  and  78  and not restrict the falling movement of the hanging assembly. The ring  62  functions as a delay mechanism to allow sufficient time for the various chambers to be evacuated, before the full force of the hanging weight and the auxiliary pressure act on the tool. As a result, this movement of the hanging assembly, accelerated by the fluid pressure, causes the outer structure to impact onto the hammer  58  and the inner structure of the tool to transfer this impact energy to the top of the drive pipe as shown in FIGS. 6A-6G. 
     During this operation, the isolator  23  functions in the following manner. The initial position of the isolator is shown in FIGS. 2A-2C. This position is dependent on the weight of the hanging assembly below the tool, and must be balanced with the gas pressure in the isolator  23 . In other words, the initial gas pressure in the isolator is predetermined by the known weight to be suspended. In addition, the stroke of the isolator, i.e., the amount of elongation of the tool between FIGS. 2A-2C and  3 A- 3 C, should accommodate the amount of movement of the impacted drive pipe  27 . If not, any residual forces will be transferred upwardly to the platform. In operation, nothing happens to the isolator  23  until impact, and the hanging position is shown in FIGS. 2A-2C. Upon impact, the outer tubular structure moves downwardly equal to the amount the drive pipe  27  is moved upon impact. When this occurs, the chamber above the valve  36  becomes smaller. In this direction of movement, the valve  36  is closed to compress the fluid within the chamber. This action absorbs the energy caused by the impact and prevents any impact energy from being transferred above the isolator  23 . The operator then lowers the drill string to restore the stroke, going from the position shown in FIGS. 3A-3C back to the position shown in FIGS. 2A-2C. 
     The cushion sub  33  operates from its initial position shown in FIGS. 10A-10C. In this position, the downward movement of the hanging assembly lowers the inner structure of the cushion sub  33 . This movement causes the valve to compress the fluid in the chamber beneath the valve to absorb the energy of the impact of the bit  39  as it impacts the formation  17 . The drilling of the bit  39  through the formation  17  causes the sub  33  to move from the position shown in FIGS. 9A-9C to that shown in FIGS. 10A-10C. 
     With reference to FIGS. 11A and 11B, an alternative embodiment of an assembly  212  of the present invention is shown wherein drive pipe  210  is impacted from its inside toward its bottom. The system shown in FIG. 11A is in a before-impact configuration, while the system depicted in FIG. 11B is in an after-impact configuration. With this embodiment, the impact loads, the location of the impact within the length of the drive pipe, and the equal distribution of a large uniform mass may be altered to fit the parameters of the particular application. Each of these factors contributes to the desirability and performance of the tool. 
     As shown in FIGS. 11A and 11B, the impact tool  224  imparts a jarring force to the bottom or leading end of the drive pipe  210 , wherein a driving spear  214  sits on a driving shoe  216 . The driving shoe  216  and driving spear  214  are rotationally and axially locked together with a shear device  218  (see FIG.  11 C). Under impact loads, the driving shoe  216  and driving spear  214  perform as a single, integral unit. Above the driving spear  214  is conventional bumper sub  220  or slack joint, having a stroke length somewhat greater than the available downward travel of the impact tool  224 . Consequently all impact forces from the impact tool  224  are imparted to the impact surface  226  of the bumper sub  220  rather than the top of the drive pipe  210  through the running tool  230 . This impact force is transferred through the bumper sub  220  to the driving spear  214  to the driving shoe  216  to internal shoulder  228  of drive pipe  210 . Although this method may also use a driving cone similar to that which is proposed for use with a hydraulic hammer, impact forces achieved by the present invention are sufficiently large to overcome the negative effect thereof. Similar to the previously described impact tools, the impact tool  224  has a gas accelerator  232  and two hydraulic lift pistons  234 . The impact tool  224  in this embodiment is disposed within drive pipe  210  below the running tool  230  which is removably connected to the top of the drive pipe  210 . 
     As shown in FIGS. 12A and 12B, a downhole motor  236  is used to drill out the formation “core”. The system shown in FIG. 12A is in a before-impact configuration, while the system depicted in FIG. 12B is in an after-impact configuration. The embodiment of FIGS. 12A and 12B is similar to that of FIGS. 11A and 11B in driving function and components. The difference in the embodiment shown in FIGS. 12A and 12B is that the impact point with drive pipe  210  is moved upward to an interior shoulder  240  of the drive pipe  210 . The driving shoe  216  is modified to be disposed on the shoulder  240  for impact therewith upon impact by the impact tool  224  on the surface  226  of the bumper sub  220 . Beneath the driving shoe  216  is a telescoping sub  242  with a top portion  244  connected to the driving shoe  216  and a bottom portion  246  slidably connected to the top portion  244 . A drilling motor  248  is connected to the bottom portion  246  and has a drilling bit  250  mounted at the bottom thereof. 
     In operation, upon impact, drive pipe  210  is driven down into a formation  211  by length L. The bottom portion  246  of the telescoping sub  242 , with the drilling motor  248  and the bit  250  attached to its distal end, initially stay fixed relative to the formation  211 . The top portion  244  of the telescoping sub along with the driving shoe  222  and drive pipe  210  move downward into the formation  211  by a length L. Once the impact is over, the drill bit  250  is rotated by the drilling motor  248  to remove the core  252  of the formation  211  within the drive pipe  210  until the bit  250  is once again proximate the bottom of drive pipe  210  as shown in FIG.  12 A. 
     In these embodiments, the area of impact to the drive pipe can be placed virtually anywhere within the length of the drive pipe, and if desired, may also be placed in close proximity to the bottom. By virtue of the “floating” downhole motor, it is also possible to remove the “core” as the drive pipe is being driven, which will remove all skin friction from inside the drive pipe as it is being driven, thus allowing the drive pipe to be driven deeper. 
     While the particular embodiments for assemblies and methods for jarring a drilling drive pipe into undersea formations as herein shown and disclosed in detail are fully capable of obtaining the objects and advantages hereinbefore stated, it is to be understood that they are merely illustrative of the preferred embodiments of the invention and that no limitations are intended by the details of construction or design herein shown other than as described in the appended claims.