Abstract:
A method for monitoring a leg of an oilfield platform, the platform having a plurality of legs, each leg with a plurality of chords, each chord with a corresponding rack, the platform including a rack-and-pinion leg jacking system with a motor and gear system with pinions for jacking the legs up. The method, in certain aspects, including providing a load monitor with a strain sensing apparatus on a selected pinion of each rack-and-pinion system, providing a rack path differential monitoring system for monitoring rotation of the selected pinions to provide an indication of a linear displacement of the selected pinions for comparison to indicate rack path differential for racks of the legs of the platform. This abstract is provided to comply with the rules requiring an abstract which will allow a searcher or other reader to quickly ascertain the subject matter of the technical disclosure and is submitted with the understanding that it will not be used to interpret or limit the scope of the invention, 37 CFR 1.72(b).

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    The present invention and application claim priority under the Patent Laws from U.S. Application Ser. No. 60/997,784 filed on 5 Oct. 2007 which is co-owned with the present invention. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention is directed to systems and methods for monitoring offshore platform supports, and, in certain particular aspects, to systems and methods for monitoring rack path differential of jack-up platform legs and loading on the legs. 
         [0004]    2. Description of Related Art 
         [0005]    Offshore platforms and rigs for well operations, some of which are called “jack-up platforms,” are floating vessels with legs driven by jacking units extending down and contacting the sea floor. A “jackup” rig or platform is any self-elevating offshore platform or deck with one or more legs, each leg consisting of one or more chords, used for any of a variety of operations, including, but not limited to, drilling, production, workover, or other offshore operations or work, which has the ability of being supported on jackable leg(s) to the seafloor, optionally with the capability of relocating from one offshore location to another by lowering to an afloat position, being moved to a new offshore position, and raising itself again to an elevated position. Such “off-shore” rigs and platforms are well-known and typically include a drilling rig or “hull” generally mounted on multiple legs, e.g. three or more legs, each provided with a base forming a supporting foot (“spud can” of the leg). In certain systems, each has one or more chords structurally connected to each other forming one unit (a “leg”). Legs with one to four chords are now in use. Each chord has one or two (opposite to each other) racks. Each rack is driven by one or more pinions. The rig or platform is positioned at a desired site, and then raised to an operational height above the sea. Motorized displacement (“jacking”) of the rig along each of its legs raises the rig. Each a leg can be raised independently of the other legs to a certain extent, so that an operator can, for example, correct uneven penetration of the legs into the sea bed. 
         [0006]    The rig is raised or lowered in relation to each leg by the sets of racks-and-pinions driving each leg, the systems generally with three legs being arranged in each angle or corner of a triangular structure with three metal chords and struts (“chord” designating each “member” of each leg). The jacking system of this type includes at least one elongated rack which is mounted vertically on the exterior side surface of the upright legs and extends substantially through the entire length of the same, and a plurality of cooperating pinions engaged with each of the racks. Each of pinions is driven through a series of reduction gears by means of a respective motor. When the platform is supported by the upright legs on the sea floor, this support is effected by the engagement of the rack with the pinion of the jacking system. In this manner, during offshore operations the load which is composed of the self-weight of the platform and environmental forces such as wind, wave, current and others is placed on the jacking system in engagement of the rack with the pinion. 
         [0007]    When the position of a given leg is changed, the pinions relating to this leg are in operation simultaneously, in the same direction and with the same theoretical speed. The speed of linear displacement depends on the load on the leg. When a leg is inclined, the least-loaded chord is raised more quickly than the others by its motors, resulting in an additional increase in “Rack Path Difference” or rack phase differential (or “RPD”) on the leg concerned. The relative position of the rig (hull) and of the legs (geometry of the system) in relation to the sea bed is, in many prior systems, checked in relation to two series of fixed reference points, which are the bottom of the hull of the rig and the top of the “jacking structure” or “jacking house”. 
         [0008]    Correct positioning can be inhibited by many factors: e.g. incorrect positioning by an operator; the existence or appearance of major lateral stresses or loads, such as those due to currents, swell and/or wind; uneven embedding of the feet of the legs; heterogeneous or inclined ground; or to an operating fault on a lifting motor or brake. Often it is difficult to determine which factors are involved. Excessive stresses on the structure and particularly on the legs, with the risk of damage to the legs, can lead to rig down time and a significant reduction of the service life of the rig. 
         [0009]    “Rack Path Differential” (difference for a given rack path, i.e. geometrical difference in the structure for a given number of rack notches) is a horizontality defect. Normally, when the rig is on site, the legs are lowered until their tips are resting on the sea bed, then the rig is raised out of the water up to its operating position. This involves a certain penetration of the tips into the sea bed, according to the nature of the bed, but normally the legs remain vertical and the only forces acting on the unit remain within the strength limits selected when designing the rig. However, in certain cases, the sea bed may be inclined or uneven, etc., which can cause a horizontal deviation, a deviation of one or more legs in relation to the vertical, which creates a bending moment on the leg or legs concerned. These deviations, if they affect two or three legs, are not necessarily parallel to each other, which can complicate the problem. Such bending causes the load to become unequal on the three chords of the leg concerned, the leg being in a skewed position with respect to its guide. The imbalance can be such that it is no longer possible to move the rig. The rig then has to be lowered again to water level, to a floating state to eliminate the load, the supporting legs are withdrawn from the sea bed over a part of the penetration obtained, and then the jacking operation is recommended. This may possibly be combined, according to the seriousness of the situation, with a slight shift of position in order to avoid the first footprints, although such an operation is not generally recommended, and with a backward and forward movement of the legs such as reaming to correct the deviation. Such action is obviously time consuming and is not always successful. In certain severe situations, a decision has to be made to move the rig from the planned drilling point to another location 50 to 100 meters away, and to recommence the operation, with the same uncertainties. This latter solution is impossible to implement when the rig has to be located alongside a fixed production platform. In such a case, only a margin of a small distance is available for jacking up the rig. 
         [0010]    There has long been a need, recognized by the present inventors, for effective and efficient systems and methods for both monitoring loads on rig legs and for monitoring changes in position of the legs. 
       BRIEF SUMMARY OF THE INVENTION 
       [0011]    The present invention, in at least certain aspects, discloses systems and methods for simultaneously monitoring the rack path differential of chords of a platform&#39;s legs and for monitoring the load on each of the legs. In certain aspects, sudden changes in leg position are detected. 
         [0012]    In certain aspects, the present invention discloses a load monitoring system and a rack path differential monitoring system for jacking systems for, including floating jacking systems. 
         [0013]    In certain particular aspects the present invention discloses a leg load monitoring system in which a shaft of a rack-and-pinion gear system has one or more strain sensors thereon, information from which is transmitted to a control system (e.g. any suitable computer system or programmable logic controller or “PLC”). 
         [0014]    In certain aspects, the present invention discloses load monitoring systems (“PLMS” means pinion load monitoring system) and rack path differential reading apparatus for jacking systems of the rack and pinion type. A pinion shaft, within a gear train, is provided with strain sensing components and a series of sensors are provided to measure the rotational amount and directional displacement of the same or another shaft arrangement. The information gathered from the strain measurements of a shaft, while static or in motion, is transmitted to a static connection in a junction box by means of a slip ring while the rotational measurement, being received on a static connection, is also directed to a junction box. All the information collected is fed into a computer (e.g. a PLC), optionally with displays located in or near the jacking system console. variations in the readings greater than specified, trigger a visual and/or sound alarm, requiring attention of the operator to effect corrections to the loadings and/or positioning of individual drives or a jack unit. 
         [0015]    In certain particular aspects, in the case of “floating jacking systems,” certain systems according to the present invention include an additional measurement of the vertical displacement of the jack unit in relation to the platform accomplished by means of a distance measurement device (see, e.g., devices D,  FIG. 10 ). The information collected from this measurement is combined with the information from the rotational readings and fed into a computer and processed. 
         [0016]    The present invention, in certain aspects, discloses a rack path differential monitoring system which includes the detection of the relative position of each chord with respect to the deck of the platform for identifying possible twisting or skewing of the legs due to imbalanced loading or effects due to the conditions of the seafloor as mentioned above, and/or uneven displacement of the chords and/or legs with respect to the deck. 
         [0017]    The present invention discloses, in certain aspects, methods for monitoring a load on a chord of a leg of an oilfield platform, the chord with a corresponding toothed rack, a rack-and-pinion leg jacking system for jacking the leg up or down, the rack-and-pinion leg jacking system with a motor, gear system with pinions, and a climbing pinion for meshing with the leg&#39;s toothed rack, the method including: providing for the selected chord at least one strain sensing apparatus on a selected pinion of the rack-and-pinion system associated with the selected chord; with the at least one strain sensing apparatus, sensing strain on the selected pinion, said strain indicative of load on the selected chord and on the selected chord&#39;s associated leg, and producing a signal indicative thereof; and transmitting said signal to a control system, and processing said signal producing a value of a load on the selected chord. 
         [0018]    The present invention discloses, in certain aspects, a method for monitoring load on legs of an oilfield platform, and, therefore, total platform load, the platform having a plurality of legs, each leg with a plurality of chords, each chord with a corresponding toothed rack, a rack-and-pinion leg jacking system for each chord for jacking the legs up and down, each rack-and-pinion leg jacking system with at least one drive unit, each of the at least one drive unit having a motor, a gear system with pinions, and a climbing pinion for meshing with a corresponding toothed rack, the method including: providing a load monitor of each chord with at least one strain sensing apparatus on a selected pinion of a rack-and-pinion system leg jacking system of each chord, including a selected pinion for each of the at least one drive unit of each rack-and-pinion leg jacking system; with each said load monitor&#39;s at least one strain sensing apparatus, sensing strain on all the selected pinions, said strains indicative of load on the associated chord, and producing a signal indicative thereof for each chord of the leg, the signals including signals for each drive unit; transmitting said signals to a control system, and processing said signals producing a value of load on each leg, summing load on each leg providing load on the platform; within the control system, comparing the value of leg loads to a specified leg load values, and/or the total platform load to a specified value for total platform load; if any specified value is exceeded, producing an alarm for a system operator. 
         [0019]    The present invention discloses, in certain aspects, system for monitoring load on a chord of a leg of an oilfield platform, the system including: a load monitor for each drive unit of the chord, with at least one strain sensing apparatus on a selected pinion of each drive unit for sensing strain on the selected pinion, said strain indicative of a load on the associated chord and producing signals indicative thereof; a control system; transmission apparatus for transmitting said signal to the control system; and the control system for processing said signals to produce a value of load on said chord. 
         [0020]    The present invention discloses, in certain aspects, system for monitoring legs of an oilfield platform, the platform having a plurality of legs, each leg with a plurality of chords, each chord with a corresponding toothed rack, a rack-and-pinion leg jacking system for each chord for jacking the legs up and down, each rack-and-pinion leg jacking system with a plurality of drive units, each drive unit with a motor, gear system with pinions, and a climbing pinion for meshing with a toothed rack of a chord, the system including: a load monitor of each drive unit with at least one strain sensing apparatus on a selected pinion of the drive unit for sensing strain on the selected pinion, said strain indicative of load on the associated chord and producing signals indicative thereof; a control system; transmission apparatus for transmitting said signals to the control system; the control system for processing said signals to produce a value of leg load on each leg and platform load on the platform; and said control system for comparing said values to specified values for leg load and for platform load, and if said specified value is exceeded for either leg load or for platform load, the control system for producing an alarm for a system operator. 
         [0021]    Accordingly, the present invention includes features and advantages which are believed to enable it to advance offshore rig and platform jacking system technology. Characteristics and advantages of the present invention described above and additional features and benefits will be readily apparent to those skilled in the art upon consideration of the following detailed description of preferred embodiments and referring to the accompanying drawings. 
         [0022]    What follows are some of, but not all, the objects of this invention. In addition to the specific objects stated below for at least certain preferred embodiments of the invention, other objects and purposes will be readily apparent to one of skill in this art who has the benefit of this invention&#39;s teachings and disclosures. It is, therefore, an object of at least certain preferred embodiments of the present invention to provide the embodiments and aspects listed above and: 
         [0023]    New, useful, unique, efficient, nonobvious systems and methods for effectively raising an offshore platform or rig; and 
         [0024]    Such systems and methods which simultaneously provide monitoring of both leg rack path differential and leg loading. 
         [0025]    Certain embodiments of this invention are not limited to any particular individual feature disclosed here, but include combinations of them distinguished from the prior art in their structures, functions, and/or results achieved. Features of the invention have been broadly described so that the detailed descriptions that follow may be better understood, and in order that the contributions of this invention to the arts may be better appreciated. There are, of course, additional aspects of the invention described below and which are included in the subject matter of this invention. Those skilled in the art who have the benefit of this invention, its teachings, and suggestions will appreciate that the conceptions of this disclosure may be used as a creative basis for designing other structures, methods and systems for carrying out and practicing the present invention. This invention is to be understood to include any legally equivalent devices or methods which do not depart from the spirit and scope of the present invention. 
         [0026]    The present invention recognizes and addresses the problems and needs in this area and provides a solution to those problems and a satisfactory meeting of those needs in its various possible embodiments and equivalents thereof. To one of skill in this art who has the benefits of this invention&#39;s realizations, teachings, disclosures, and suggestions, other purposes and advantages will be appreciated from the following description of certain preferred embodiments, given for the purpose of disclosure, when taken in conjunction with the accompanying drawings. The detail in these descriptions is not intended to thwart this patent&#39;s object to cover this invention no matter how others may later attempt to disguise it by variations in form, changes, or additions of further improvements. 
         [0027]    The Abstract that is part hereof is to enable the U.S. Patent and Trademark Office and the public generally, and scientists, engineers, researchers, and practitioners in the art who are not familiar with patent terms or legal terms of phraseology to determine quickly from a cursory inspection or review the nature and general area of the disclosure of this invention. The Abstract is neither intended to define the invention nor is it intended to be limiting of the scope of the invention in any way. 
         [0028]    It will be understood that the various embodiments of the present invention may include one, some, or all of the disclosed, described, and/or enumerated improvements and/or technical advantages and/or elements in claims to this invention. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0029]    A more particular description of embodiments of the invention briefly summarized above may be had by references to the embodiments which are shown in the drawings which form a part of this specification. These drawings illustrate certain preferred embodiments and are not to be used to improperly limit the scope of the invention which may have other equally effective or legally equivalent embodiments. 
           [0030]      FIG. 1  is a side schematic view of a rig system according to the present invention. 
           [0031]      FIG. 2  is a top schematic view of the rig system of  FIG. 1 . 
           [0032]      FIG. 3  is a side view of part of the system of  FIG. 1 . 
           [0033]      FIG. 4  is a partial enlarged perspective view of part of a rig leg and jacking unit according to the present invention. 
           [0034]      FIG. 5  is a partial view of part of the gear train of the unit of  FIG. 4 . 
           [0035]      FIG. 6  is a schematic view of the unit of  FIG. 4 . 
           [0036]      FIG. 6A  is a partial perspective view of the system of  FIG. 6 . 
           [0037]      FIG. 6B  is an enlargement of part of the system of  FIG. 6A . 
           [0038]      FIG. 6C  is a perspective view of part of the system of  FIG. 6 . 
           [0039]      FIG. 6D  is a perspective view of part of the system of  FIG. 6 . 
           [0040]      FIG. 7  is a schematic view of a system according to the present invention. 
           [0041]      FIG. 8  is a schematic view of a system according to the present invention. 
           [0042]      FIG. 9  is a schematic view of a system according to the present invention. 
           [0043]      FIG. 10  is a schematic view of a system according to the present invention. 
       
    
    
       [0044]    Presently preferred embodiments of the invention are shown in the above-identified figures and described in detail below. Various aspects and features of embodiments of the invention are described below. Any combination of aspects and/or features described below can be used except where such aspects and/or features are mutually exclusive. It should be understood that the appended drawings and description herein are of preferred embodiments and are not intended to limit the invention. On the contrary, the intention is to cover all modifications, equivalents and alternatives falling within the spirit and scope of the invention. In showing and describing the preferred embodiments, like or identical reference numerals are used to identify common or similar elements. The figures are not necessarily to scale and certain features and certain views of the figures may be shown exaggerated in scale or in schematic in the interest of clarity and conciseness. 
         [0045]    As used herein and throughout all the various portions (and headings) of this patent, the terms “invention”, “present invention” and variations thereof mean one or more embodiment, and are not intended to mean the claimed invention of any particular embodiment. Accordingly, the subject or topic of each such reference is not automatically or necessarily part of, or required by, any particular embodiment merely because of such reference. So long as they are not mutually exclusive or contradictory any aspect or feature or combination of aspects or features of any embodiment disclosed herein may be used in any other embodiment disclosed herein. 
       DETAILED DESCRIPTION OF THE INVENTION  
       [0046]      FIGS. 1 and 2  show a jackup rig  10  according to the present invention which includes a barge type hull  12  having at least one leg  14 , here shown as three, which movably extend through the hull  12  within spud wells  16  with at least one set of rack teeth  18  attached to each of the legs  14 . The hull  12  supports the legs  14  in an upright position. When the rig  10  arrives at its intended location, the legs  14  are lowered down until firmly engaged with the ocean floor. Continued jacking on the legs  14  lifts the hull  12  to a nominal height above the body of water  13  for preload operations. Upon the completion of preloading, jacking resumes until the bottom of the hull  12  reaches an elevation above the sea, e.g. greater than the highest wave height anticipated during a severe ocean storm. The main deck of the hull  12  may be outfitted with the necessary equipment to conduct operations, e.g. drilling, production or workover operations, such as a derrick  20 , a cantilever beam and elevated pipe rack  22 , pilot house  27 , heliport  28 , crew quarters  29 , as well as general purpose cranes  30 . 
         [0047]    Elevation of the hull  12  of the jackup rig  10  is achieved by a number of different techniques which are well known to the industry. One form of elevation system according to the present invention is useful with a rack and pinion elevating system according to the present invention. Elevating pinions  32  are housed in a jacking frame  34 , on and within which is drive apparatus (electric or hydraulic) with a drive mechanism and a gear train (see  FIGS. 3 ,  4 ) to drive the elevating pinions  32 . The elevating pinions  32  engage the rack teeth  18  on a leg chord  36 . Rotation of the pinions  32  in one direction moves the legs  14  upwardly relative to the hull  12 , while rotation of the pinions  32  in the opposite direction lowers the legs  14  relative to the hull  12 . An upper guide structure  38  is mounted above the jacking frame  34  and is used as an upper guide/support structure to control the position of the legs  14 . The upper guide structure  38  is laterally supported back to the hull or deck  12  with brace beams  39 . Each of the legs  14  have one or more generally vertically extending leg chords  36  which are structurally tied together by suitable bracing. For the embodiment shown, rack teeth  18  are provided on both sides of four chords of each leg  14 . For smaller platforms, the leg members may consist of a single leg or leg chord with one or more tooth rack  18  thereon. Locking apparatuses  40  selectively lock the legs in position. 
         [0048]    One pinion in the system, e.g. a drive pinion  32 , has at least one (one shown) strain gauge  50  thereon for measuring load on the pinions  32  under static or dynamic conditions. The strain on a pinion shaft which is indicative of load jacking unit which is indicative of load on the corresponding leg which is indicative of load on the platform. A control system  54  which includes a control system  54   a  for each leg is in communication with each strain gauge  50 , in one aspect via a slip ring assembly. The strain gauge(s) may be directly connected to the systems  54   a  with the systems including the devices etc. for communication with the strain gauge(s); optimally, each strain gauge can be connected to a junction box  58  which is in communication with the systems  54   a . The control system  54  is also in communication with a jacking system console  56  with display  59  showing the load (in one aspect, in real time) on each pinion, e.g. a drive pinion  32 . 
         [0049]      FIG. 4  shows an enlarged view of part of a rig according to the present invention which includes a leg  102  (shown partially; e.g. like the legs  14 ,  FIG. 1 ) with chords  104  each with a corresponding toothed rack  106 . A jacking unit  100  (one for each chord) has spaced-apart climbing pinions  108  which mesh with a rack  106 . Motors  120 , via couplings  121 , turn pinions  122  which turn additional mechanism (gears, pinions, etc; not shown in  FIG. 4 ) in a gear train  124 . Brakes  126  provide selective braking for the motors  120 . Each pinion  122  has at least one strain gauge  130  thereon (like the strain gauges  50 ,  FIG. 3 ) which is in communication with suitable junction box(es) and/or control system(s). (Two, three, four or more strain gauges may be used as is true for any pinion or shaft of any embodiment according to the present invention.) 
         [0050]      FIG. 5  shows an exploded view of some parts of one embodiment of a jacking unit  100  and of a gear train  124 . The motor  120  drives the pinion  122  whose gear  122   a  on a shaft  122   s  meshes with a gear of an adjacent pinion assembly  132 , and so on for additional pinion assemblies  133 ,  134  and  135  each with corresponding gears. 
         [0051]    Each pinion assembly  132 - 135  has gears for meshing with adjacent assemblies and a shaft ( 132   s - 135   s , respectively) on which the gears are mounted. Any and all shafts of any and all pinion assemblies may have one, two, three, four or more strain gauges thereon (like the strain gauges  50  or  130 ) in communication with a suitable junction box and/or control system. As an example, and not by way of limitation, a strain gauge  134   g  is shown on the shaft  134   s  and strain gauges  135   g  are shown on the shaft  135   s . It is within the scope of the present invention to use any suitable motor and any suitable gear train to drive the climbing pinions  108 . The gears and shafts of the gear train are under load unless the rig or platform has separate structures for holding the legs fixed in position. 
         [0052]      FIG. 6  shows schematically parts of the system as shown in  FIGS. 4 and 5 . The strain gauges  130  are connected to a slip ring  142  sending the signal to signal conditioner/transmitters  145  within a junction box  144  (see  FIG. 6A ). The signal transmitters  145  convert the signal coming from the slip ring  142  into an output that travels through the junction box  58  to a programmable logic controller (“PLC”) the output of which may include numerical, graphical and/or alarm signals that may be directed to display devices on the rig and/or to a main console of the platform. A system (e.g. the system  150  with one or more programmable logic controllers  154 ) receives signals from the signal conditioner/transmitters  145  which receive signals from the strain gauges  130  (in one aspect, sixteen strain gauges are used spaced apart around the shaft). A rotation sensor apparatus (e.g.  140  or  210 ,  FIG. 8 ) detects marks, ridges, or indentations  141  on the shaft providing an indication of rotation direction and the number of rotations of the shaft  122   s . This rotation, being part of the gear train, is directly proportional to the rotation on the pinion  108  (see  FIG. 5 ) which translates into the linear displacement of the rack  106  with respect to the platform  12  ( FIG. 1 ) and, therefore, the signal, translated into a linear dimension, is sent to the display  152  (or display  59 ,  FIG. 3 ) as is compared against other similar readings from the other jack units on the rig, which may give indication of any rack path differential among all chords on the rig. The slip ring assembly  142  sends signals, via the junction box  144 , to the control system  150 . Results based on strain gauge output and/or rotation sensor output are displayed on an optional display  152 . 
         [0053]    A jacking unit  100  can move slightly with respect to its corresponding rack (and leg), both up and down and at an angle away from horizontal (e.g. two degrees). In one aspect, the jacking units  100  are mounted between shock pads  162  and  164  in a housing  161  to provide a small “float” distance between the jacking units and the rig deck  170 . To measure this movement (the float distances), one, two, or more position transducer assemblies  165  (which can measure the distance between two points) are placed between the deck  170  and the jack unit  100 . The assembly  165  has, in one aspect, a spring loaded, cable-actuated, digital, displacement transducer that is attached to the deck or the jack unit while the cable end is attached to the opposite part (the deck  170  or the jack unit  100 ); and as the cable  166  attached at point  163  is pulled out or retrieved into the transducer (see  FIG. 6B ), the distance is measured and a signal representative of the measurement is transmitted combined with that of the rotation sensor apparatus  140 , described above, resulting in the measurement of the actual displacement between the platform and the leg chords. Cables  166  are connected to position transducer assemblies  167  which provides signals indicative of jacking unit position (and, therefore, over time of any jacking unit movement), to the control system (e.g. system  150  or  54 ) either directly or via a junction box. The position transducer assemblies  167  have an input/output connection  169  (e.g. for cables  303 , see  FIG. 10 ). The amount of extension of a cable  166  indicates the relative position of the jacking unit with respect to the frame. 
         [0054]      FIG. 7  illustrates schematically a monitoring system  171  according to the present invention for monitoring loads on pinion shafts of a gear train of a jacking unit of a rig and for monitoring rack path differential according to the present invention. Since the load (strain) on the platform, its legs, and the legs&#39; jacking units is transferred to the jacking unit&#39;s gear train (the pinions of the gear train are always under the load), measuring the load on a shaft of a pinion of the gear train provides an indication of the load on the legs and on the platform. The strain gauges on a pinion shaft provide a signal indicative of load in both static and dynamic conditions. The signals from the strain gauges, transmitted to the control system, can, after processing by the control system, result in a warning or an alarm. 
         [0055]    As shown in  FIG. 7 , for the load monitoring function  172 , each jacking unit J for chords C has a corresponding junction box JB in communication with a corresponding programmable logic controller (PLC)  172  (or multiple PLC&#39;s are used). Three jacking units J are shown for a three chord leg. (There are, e.g., four units per leg in other systems according to the present invention.) Since the driving pinions of the gear train are always engaged with corresponding racks, displacement (movement) of the racks, and therefore of the legs, can be detected by monitoring rotation of a pinion shaft of the gear train. The amount of rotation, and its direction, can be measured by using a system  174  with a set  178  of proximity sensors adjacent a shaft for detecting ridges and/or depressions on the rotating shaft (or placed near the gears&#39; teeth, and protected from oil or other lubricants). Each system  178  is in communication with a programmable logic controller  177  via a junction box JX. Numeral  171 ,  FIG. 7 , indicate the load monitoring system. 
         [0056]    A real-time display of load measurements and leg displacement measurements is provided on a display  184 . By maintaining in the PLC&#39;s, or in other storage devices, or in a control system  180  with a jacking system console  181 , a log of the measurements over time, previous measurements can be accessed and displayed. Warnings and/or alarms are provided via alarm apparatus  182  (e.g. audio, visual or both). 
         [0057]      FIGS. 8 and 9  illustrate schematically different methods and structures according to the present invention for measuring strain on a rotating shaft and for measuring rotation of the shaft. As shown in  FIG. 8  a shaft  200  (e.g. any shaft of a jacking unit&#39;s gear train) has two spaced-apart gears  201 ,  202  secured thereto. Strain gauges  204  are spaced-apart around the entire circumference of the shaft  200  between the gears  201 ,  202  (in an area which is a torque affected area, i.e. an area in which the torque produces a twisting on the shaft and the resulting strain is read by the strain gauges  204 ). Wires  206  from the strain gauges  204  are secured to the exterior of the shaft  200  (e.g. with an adhesive, e.g. epoxy) and are connected to an input of a slip ring  214  and then to output wires  208  which are then connected to a junction box (or boxes), not shown (e.g. like that of  FIG. 3 ). A rotation sensor device  210  senses notches  212  in the shaft  200  (or, optionally, senses the spacing of gear teeth of any gear on the shaft) and transmits signals indicative of shaft rotation based on such sensing via a wire  209  to a signal transducer  213  in a junction box. The wires connected to the slip ring connect the slip ring  214  to a control system (e.g. via a junction box). Optionally, notches, indentations, depressions or ridges on a gear are sensed by the rotation sensor. A holding bracket  222  holds the slip ring in place. 
         [0058]    As shown in  FIG. 9  a shaft  250  of a motor M (like the motor  120 ,  FIG. 4 ) has a gear  252  secured thereto with a series of spaced-apart strain gauges  254  around the shaft  250 . Wires  256  from the strain gauges  254  go through holes  258  to a slip ring  260 . Notches  262  on the shaft  250  are sensed by a rotation sensor device  264 . Output wires from the rotation sensor device  264  are connected to a junction box  270  which is in communication with a control system S (any described herein). A holding bracket  274  holds a static end of the slip ring  260  in place. The torque affected area for the shaft  250  is the area between a coupling  251  and the gear  252 . The motor M has a brake B (like the brake  126 ,  FIG. 4 ). 
         [0059]      FIG. 10  shows a system  300  according to the present invention for a Leg A of a platform that has three legs, Legs A, B, C. The system  300  includes parts, devices and components identified with numerals indicating the same parts, etc. described above and identified with these same numerals. Legs B and C each have a system like the system  300 -system  302  (Leg B) and system  304  (Leg C). 
         [0060]    The present invention, therefore, provides in at least certain embodiments, a method for monitoring legs of an oilfield platform, the platform having a plurality of legs, each leg with a plurality of chords, each chord with a corresponding rack, the platform including a rack-and-pinion leg jacking system with a motor and gear system with pinions for each leg for jacking the legs up, the method including providing a load monitor of each leg with a strain sensing apparatus on a selected pinion of the rack-and-pinion system, said selected pinion associated with a particular leg of the platform, and providing a rack path differential monitoring system for monitoring rotation of each selected pinion to provide an indication of a linear displacement of the selected pinions and the legs associated therewith for comparison to indicate rack path differential for racks of the legs of the platform. 
         [0061]    The present invention discloses in some, but not necessarily all, embodiments a method for monitoring a load on a chord of a leg of an oilfield platform, the leg with a plurality of chords, each chord with a corresponding toothed rack, each leg having a rack-and-pinion leg jacking system for jacking the leg up or down, each rack-and-pinion leg jacking system with a motor, gear system with pinions, and a climbing pinion for meshing with a leg&#39;s toothed rack, the method including: providing for a selected chord at least one strain sensing apparatus on a selected pinion of the rack-and-pinion system associated with the selected chord; with the at least one strain sensing apparatus, sensing strain on the selected pinion, said strain indicative of load on the selected chord and on the selected chord&#39;s associated leg, and producing a signal indicative thereof; and transmitting said signal to a control system, and processing said signal producing a value of a load on the selected chord. Such a method may have one or some of the following in any possible combination: wherein the at least one strain sensing apparatus is a plurality of strain gauges; measuring load on multiple pinions of the rack-and-pinion leg jacking system; displaying on a display a load measurement for the selected chord; wherein load measurement is displayed in real time. 
         [0062]    The present invention discloses in some, but not necessarily all, embodiments a method for monitoring load on legs of an oilfield platform, the platform having a plurality of legs, each leg with a plurality of chords, each chord with a corresponding toothed rack, a rack-and-pinion leg jacking system for each chord for jacking the legs up and down, each rack-and-pinion leg jacking system with at least one drive unit, each of the at least one drive unit having a motor, gear system with pinions, and a climbing pinion for meshing with a corresponding toothed rack, the method including: providing a load monitor of each chord with at least one strain sensing apparatus on a selected pinion of a rack-and-pinion system leg jacking system of each chord, including a selected pinion for each of the at least one drive unit of each rack-and-pinion leg jacking system; with each said load monitor&#39;s at least one strain sensing apparatus, sensing strain on all the selected pinions, said strains indicative of load on the associated chord, and producing a signal indicative thereof for each chord of the leg; transmitting said signals to a control system, and processing said signals producing a value of load on each leg; within the control system, comparing said value to a specified value; and if said specified value is exceeded, producing an alarm for a system operator; wherein the at least one strain sensing apparatus is a plurality of strain gauges; wherein the alarm is one of visual alarm and sound alarm; displaying on a display load measurements for each drive and/or for each leg; wherein load measurements for each leg are displayed in real time; maintaining an historical record of load measurements for each leg; and with the control system, providing access to the historical load measurements; wherein the control system includes, for each leg, a programmable logic controller for processing signals indicative of load; each programmable logic controller of a particular leg in wired communication with the at least one strain sensing apparatus of each chord of said leg, processing the signals indicative of load with the programmable logic controllers; maintaining an historical record of all signals and/or load measurements for each chord and/or leg; and with the control system, providing access to the historical load measurements; measuring vertical displacement of each leg jacking system in relation to the oilfield platform using a distance measuring device; providing a rack path differential monitoring system for monitoring rotation of each selected pinion to provide an indication of a linear displacement of each selected pinion of each chord and the leg associated therewith for comparison to indicate rack path differential for the legs of the platform; wherein the oilfield platform has a deck, the method further including detecting relative position of each chord with respect to the deck to thereby identify possible twisting of each leg; wherein each rack has associated therewith a measurement apparatus for measuring actual displacement between each chord and the platform, the method further including providing a signal from each measurement apparatus to an associated programmable logic controller of the control system for determining the displacement between each chord and the platform; providing a display in real time of displacement between each chord and the platform; maintaining in the control system a second historical record of said displacements; and/or with the control system, providing access to the second historical record. 
         [0063]    The present invention discloses in some, but not necessarily all, embodiments a method for monitoring load on legs of an oilfield platform, the platform having a plurality of legs, each leg with a plurality of chords, each chord with a corresponding toothed rack, a rack-and-pinion leg jacking system for each chord jacking the legs up and down, each rack-and-pinion leg jacking system a plurality of drive units, each drive unit with a motor, gear system with pinions, and a climbing pinion for meshing with a corresponding toothed rack, the method including providing a load monitor of each drive unit of each chord with at least one strain sensing apparatus on a selected pinion of each drive unit of each rack-and-pinion leg jacking system of each chord; with each strain sensing apparatus, sensing strain on the selected pinion, said strain indicative of a load on the associated leg and producing a signal indicative thereof related to each drive unit of each chord; transmitting said signals to a control system, and processing said signals to produce a value of load on each leg and a total load value for a platform load comprising total load on the platform; displaying in real time on a display any sensed load and/or the platform load and/or measurements for each leg; within the control system, comparing said values to specified values for each leg and for the platform, if said specified valve is exceeded for any individual leg or for total platform load, producing an alarm for a system operator; wherein the at least one strain sensing apparatus is a plurality of strain gauges, maintaining a first historical record of load measurements for each leg and for platform load, with the control system, providing access to the first historical load record, the control system including, for each leg, a programmable logic controller for processing signals indicative of load, each programmable logic controller in wired communication with the at least one strain sensing apparatus, processing the signals indicative of load with the programmable logic controllers, providing a rack path differential monitoring system for indicating rack path differential for the toothed racks of the legs of the platform, wherein the oilfield platform has a deck, detecting relative position of each chord with respect to the deck to thereby identify possible twisting of each leg, providing a display in real time of displacement between each chord and the platform, maintaining in the control system a second historical record of displacements between each chord and the platform, and with the control system, providing access to the second historical record. 
         [0064]    The present invention discloses in some, but not necessarily all, embodiments a system for monitoring load on a chord of a leg of an oilfield platform, the chord with a corresponding toothed rack, a rack-and-pinion leg jacking system for the chord for jacking the leg up and down, the rack-and-pinion leg jacking system with a plurality of drive units, each drive unit having a motor, a gear system with pinions, and a climbing pinion for meshing with the toothed rack, the system including: a load monitor for each drive unit with at least one strain sensing apparatus on a selected pinion of each drive unit, for sensing strain on the selected pinion, said strain indicative of load on the associated chord and producing a signal indicative thereof; a control system; transmission apparatus for transmitting said signal to the control system; and the control system for processing said signal to produce a value of load on said chord. 
         [0065]    The present invention discloses in some, but not necessarily all, embodiments a system for monitoring legs of an oilfield platform, the platform having a plurality of legs, each leg with a plurality of chords, each chord with a corresponding toothed rack, a rack-and-pinion leg jacking system for each chord for jacking the legs up and down, each rack-and-pinion leg jacking system with a plurality of drive units, each drive unit with a motor, gear system with pinions, and a climbing pinion for meshing with a toothed rack of a chord, the system including: a load monitor of each drive unit with at least one strain sensing apparatus on a selected pinion of the drive unit for sensing strain on the selected pinion, said strain indicative of load on the associated chord and producing signals indicative thereof; a control system; transmission apparatus for transmitting said signals to the control system; the control system for processing said signals to produce a value of leg load on each leg and platform load on the platform; and said control system for comparing said values to specified values for leg load and for platform load, and if any specified value is exceeded for either leg load or for platform load, the control system for producing an alarm for a system operator. Such a system may have one or some any possible combination of the following: the at least one strain sensing apparatus is a plurality of strain gauges; the control system includes, for each leg, a programmable logic controller for processing signals indicative of load, each programmable logic controller in wired communication with all strain sensing apparatus for a corresponding leg, and the programmable logic controllers for processing the signals indicative of load; rack path differential monitoring apparatus for detecting relative position of each chord within respect to a deck of the oilfield platform to thereby identify possible twisting of each leg, and for providing a signal from each measurement apparatus to an associated programmable logic controller of the control system for determining the displacement between each chord and the platform; and/or maintaining in the control system an historical record of displacements between each chord and the platform, and the control system for providing access to the historical record. 
         [0066]    In conclusion, therefore, it is seen that the present invention and the embodiments disclosed herein and those covered herein are well adapted to carry out the objectives and obtain the ends set forth. Certain changes can be made in the subject matter without departing from the spirit and the scope of this invention. It is realized that changes are possible within the scope of this invention and it is further intended that each element or step recited herein is to be understood as referring to the step literally and/or to all equivalent elements or steps. It is intended to cover the invention as broadly as legally possible in whatever form it may be utilized. The inventors may rely on the Doctrine of Equivalents to determine and assess the scope of their invention as it may pertain to apparatus not materially departing from, but outside of, the literal scope of the invention. All patents and applications identified herein are incorporated fully herein for all purposes.