Abstract:
A method and apparatus for driving conductor pipe in an offshore drilling platform including the steps of mounting a block and tackle on the platform and then lifting a crane onto the platform with it before the drill rig is placed thereon, and driving the conductor pipe through use of a pile driver brought onto the platform with the crane, thus avoiding utilization of either a derrick barge or a drill rig for the conductor pipe driving functions.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to drilling operations associated with the setting of piling on offshore well drilling platforms and for driving conductor pipe through templates in the jacket thereof. More particularly, this invention, in an important aspect, relates to a method for installing a pile driving atop an offshore platform for driving conductor pipe, independently of a derrick barge or drilling rig. 
     Heretofore offshore operations preparatory to drilling have commonly been performed by utilizing a derrick barge to transport all necessary men and equipment to the offshore drilling site at which the barge is used as a base platform for driving the pile used to stabilize the legs of the jacket and for performing many other preliminary operations such as welding the platform and driving conductor pipe. Commonly, a pile driving rig is mounted on the derrick barge to perform the pile driving function. Also, the use of drilling rigs for driving pile on the platform is not uncommon. Use of drill rigs constitutes, however, an extremely expensive method for driving pile. Similarly, although derrick barges constitute an excellent platform for a base of operations, in calm weather conditions their use for pile or conductor pipe driving is a particularly uneconomical method for the construction of an offshore drilling platform since the day-to-day cost exceeds that of the drill rig even. 
     Commonly, the derrick barge is used to transport the drill rig to the well site. There the drill rig may be used to pick up the deck sections and to place them on the top of the legs of the offshore platform. The barge is not uncommonly used as a base of operation for the welding process which takes place when the jacket and the platform is utilized. Also, the derrick barge may remain on site to drive conductor pipe. After the platform is secure the derrick barge generally begins the operation of placing the drilling rig onto the platform. 
     Since the scarcity of petroleum products began and the costs thereof have increased, the cost of exploring for and retrieving oil and gas have taken on additional importance and the industry has begun to seek ways to reduce the costs involved. One substantial potential cost reduction would take place if a method were conceived in which there were less utilization of the derrick barge and/or drill rig, at least until the time that these pieces of equipment were absolutely necessary for their basic functions. Thus, it becomes advisable, for example, to not use the derrick barge as a base for the driving of conductor pipe but to instead use a less expensive piece of equipment. An even more economical method would be to provide for emplacement of the piling and the conductor pipe without the derrick barge or the drill rig. Heretofore, no satisfactory method for accomplishing this has been known. 
     BRIEF SUMMARY OF THE INVENTION 
     In accordance with the invention, there is provided a method and apparatus whereby the derrick barge and drill rig are not used for driving pile and/or conductor pipe. Instead, a conventional barge or work vessel may transport the requisite equipment to the legs of the offshore platform. Included in the equipment and supplies normally transported to the site, there additionally is, in accordance with the invention, transported a pile driving rig, a module crane and a portable winch which, through the method hereof, is mounted on the platform. After establishing the winch on the platform, in any of several ways, it is used to raise the modular crane from the barge to the deck of the platform. The modular crane is then erected and is used to bring the pile driving rig to the platform deck. The pile driving rig is erected on the platform deck and skidded or moved from slot to slot for the purpose of driving pile and/or conductor pipe into the receptacles of the platform. Numerous advantages accrue from the aforementioned method. 
     First of all, once the platform sections are set on the jacket, the derrick barge may depart the area since the pile and conductor pipe may be driven by the present method. The ability to complete the platform in the absence of the derrick barge results in substantial savings. 
     Furthermore, once the pile driving machine is established on the platform the piles may be driven and the conductor pipe placed without the use of a derrick drill rig, this further resulting in substantial savings. 
     Still further, it will be recognized that the personnel may proceed to drive the pilings, weld the platform, set the conductor pipe and do all other necessary construction in anticipation of drilling, independently of ocean conditions such as rough seas which frequently hamper if not preclude continuous day-to-day performance of the functions when they are carried out from the deck of the derrick barge itself. Although other patents have directed themselves to accomplishment of this particular feature, (see U.S. Pat. No. 3,825,076), none have been able to do so without the continued presence of the derrick barge itself. 
     These and numerous features and advantages of the invention will become more readily apparent upon a reading of the following detailed description, claims and drawings. 
    
    
     DETAILED DESCRIPTION 
     With reference now to the drawings and particularly to FIGS. 1-5 there is shown a sequence of illustrations setting forth in exemplary form the steps for accomplishing the invention. 
     FIGS. 6 to 8 illustrate steps relating to another aspect of the invention. 
    
    
     In FIG. 1 there is shown a conventional barge or boat 1 which has approached and is held adjacent to the jacket legs 3 of an offshore platform. Carried on the deck of the barge is a crane module 5. The crane module includes a base means or skid 5a, a crane tower and associatad structure 5b and a block and pulley means 5c. The module is further characterized by the parallel rails 7 which serves as sides on the module base for protecting the crane tower during shipment and lifting onto the platform, see FIG. 3. Also carried on the deck of the barge 1 is a conventional power generator 9 or diesel engine. 
     After the barge has established its position with respect to platform legs 3 there is manually carried onto the deck 11 of the platform a plurality of machinery components constituting a portable lifting means such as block and pulley system 13. The block and pulley system is appropriately affixed on the deck and a power line 15 is connected thereto from the generator 9. The cable from the block and pulley is thereafter lowered to the barge 1 in order to be connected to the aforementioned module 5, see FIG. 3. It will be recognized that the block and pulley 13 and associated cable can of course be brought to the deck of the platform in the most facile manner so that the aforementioned manual transportation of the block and pulley up the stairs (see FIG. 2) of the platform may be replaced by utilization of a crane or other means that may exist on the deck of the barge of vessel 1. 
     In FIG. 3 there is shown an enlarged view of module 5, thus more clearly illustrating the side rails 7 and the crane tower 5b disposed therebetween. The crane includes connection points 5d on each side of the skid means 5a, the connection points being so disposed along the length of the skid means as to substantially coincide with the center of gravity of the module. A harness 21 is affixed to connection points 5d and includes a spreader bar 23 for keeping the harness cables in parallel relation to the skid means 5a. The cables of harness 21 meet at common point 25 at which there is also attached the moment arm cable means 27. The cable 27 extends from common point 25 to the end of the skid means 5a and has a length which is greater than the linear distance from common point 25 to the point at which cable 27 is attached to the skid means. The purpose of the moment arm cable 27 will be more clearly described hereinafter. 
     After the clock and pulley system, that is lifting means 13 has been properly disposed and installed on deck 11, the cable wound on the pulley is deployed over the side of the deck where it is dropped to the barge 1 and attached to the skid means 5a via the aforementioned harness 21. By utilization of the power generator 9, the module 5 is carefully lifted from the barge upwardly toward the deck 11 of the platform, see FIG. 4. In so doing, the module is adapted to hang in a substantially vertical position due to attachment of the harness 21 at the center of gravity (5d) of the module. As the module approaches the level of the platform the cables of harness 21 begin to slacken and the moment arm cable 27 begins to tighten due to the fact that the horizontal distance parallel to the deck between pulley 13 and pulley 33 is shorter than the distance between pulley 13 and module connection point 31. As connection points 5d reach the level of pulley 33, the moment arm cable 27 becomes taut and takes over the load previously carried by the harness 21. In so doing, the moment arm cable 27 beings to turn the module about its contact point with the pulley 33 thus enabling movement of the module heavy end first thereabout and toward the deck 11 of the platform. Without utilization of the harness 21 and moment arm cable 27, lifting of the module onto the deck 11 would be significantly hindered or even prevented by the inability of the lifting means or lifting cable to withstand the tension force exerted thereon between the pulleys 13 and 33. As shown in FIG. 5 therefore, the module 5 is slid onto the deck 11 and set upon the transfer skids 41 which enable movement of the crane thereon in longitudinal and lateral directions on the deck. The crane tower 5b is deployed to its operating position adjacent the edge of the deck. The power line 15 may, if necessary, be connected to the crane in order to lift a power source 43 onto the deck, after which the power line 15 is disconnected and the crane connected directly to the source of power on the deck. 
     After the crane is positioned on the deck it is used to sequentially lift and position the transfer skids 41 which may be used to support and enable movement of the pile driving rig. The pile driving rig is then lifted in components from the barge to the deck of the platform and assembled thereon. The pile driving rig may be adapted for movement over the deck by means of the skids or other appropriate structure. In any event, the rig 45 is adapted to be moved from slot to slot on the deck 11 in order to set the conductor pile or drive piles for the jacket legs. Similarly, it may be used to lift other equipment and even supplies and living accommodations to the platform. 
     From the foregoing it will be recognized that after equipment and supplies are removed from the deck of the vessel the offshore platform becomes relatively self-sufficient so that construction work on the platform may continue independently of any barge or vessel. The derrick barge, if it has been used to set platform sections, is free to depart from the offshore location and thus not be occupied with the driving of conductor pipe or pile and the welding of the legs to the jacket and platform. The barge may however be used to erect the drill rig after the platform is constructed. Thus, it is not necessary to operate the drill rig prior to the initiation of drilling operations since all of the pile driving may be conducted from the deck of the platform by the pile driving rig in accordance with the mounting method disclosed herein. 
     The present method of utilizing a pile driving rig not only significantly reduces the costs of construction of the offshore platform by more efficient use of the derrick barge and drill rig, but enhances the possibility of continuous operation by removing the pile setting function from the deck of the derrick barge, thus isolating the pile setting from the wave action effect to which the barge is vulnerable. Construction of the platform may thus take place more independently of the weather and surrounding water conditions thus reducing the overall construction time and construction costs. 
     In addition, it becomes feasible for the pile driving rig to perform any other functions, such as washing out of the pile, in preparation for the actual drilling operation, all of which facilitates construction of the offshore platform and reduces the costs thereof. 
     Although the present invention has been described with reference to a preferred form and sequence of steps, it will be appreciated that additions, modifications, substitutions and deletions may be made without departing from the spirit and scope of the invention as defined in the appended claims.