US2852936A - Apparatus for offshore well logging - Google Patents

Description

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APPARATUS FOR OFFSHORE WELL LOGGING Filed Feb. 15, 1956 2 Sheets-Sheet 1 INVENTOR FIG. I D. E. BROUSSARD His ATTORNEY 2852936 OR IN 73/152 Sept. 23, 1958 D. E. BROUSSARD 2,852,936

APPARATUS FOR OFFSHQRE WELL LOGGING Filed Feb. 15, 1956 2 Sheets-Sheet 2 INVENTOR FIG.2 D.E. BROUSSARD ms A-TTORNEY United States Patent APPARATUS FOR OFFSHORE WELL LOGGING Douglas E. Broussard, Bellaire, Tex., assignor to Shell Development Company, New York, N. Y., a corporation of Delaware Application February 13, 1956, Serial No. 564,910

Claims. (Cl. 73152) This invention relates to the logging of earth formations traversed by a borehole, and relates more particularly to apparatus for logging offshore earth formations from a floating vessel.

With the advent of offshore drilling in water having a depth requiring the use of a floating platform or vessel, there has arisen the problem of logging the formations traversed by these deepwater boreholes.

In the practice of those logging techniques which embody the use of a device moved through a borehole to identify the formations traversed thereby, it is essential to the obtaining of satisfactory data that precise depth and rate of running control be maintained over the device as it is moved through the borehole.

In logging formations from a stationary structure supported on dry land or built up from the floor of a body of relatively shallow water, the logging device is normally moved through the borehole by a lowering mechanism which can be readily supported in a stationary vertically stabilized position with respect to the borehole; and precise depth and rate of running control can be maintained over the logging device by controlling the speed of the lowering mechanism. Thus, measurements relating to properties of the formations such as spontaneous potentials, resistivities, acoustic characteristics, etc., can

be made at any desired depth intervals in the borehole to provide an accurate record indicating the character of the formations.

Heretofore, it has not been feasible to apply these logging techniques to the logging of deepwater boreholes since a lowering mechanism carried by a floating vessel affected by wave motion, Winds, etc., could not be fixed in a vertically stabilizing position with respect to the borehole. Due to the lack of sufficient control over the logging device as the result of the inability to compensate for the rise and fall of the vessel as the logging device is moved through the borehole, the records obtained would not be truly representative of the conditions in the borehole.

Accordingly, an object of the present invention is to provide a new and improved apparatus for logging an oilshore borehole, such particularly as an exploratory borehole, from a floating Vessel whereby precise depth and rate of running control may be maintained over a logging device as it is moved through a borehole regardless of the relative motion of the vessel.

Another object of the present invention is to provide a new and improved apparatus for vertically stabilizing the lowering mechanism of a logging device on a floating vessel at a selected distance above the floor of a body of water, whereby said mechanism may be operated to move the logging device through a borehole at any predetermined substantially constant rate of travel unaffected by the motion of the vessel.

These and other objects and advantages of this invention will be understood from the following description taken with reference to the drawings, wherein:

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Fig. 1 is a view looking at the stern of a floating vessel and illustrating the apparatus of the present invention in operation at a deep water borehole site, and

Fig. 2 is a view similar to Fig. 1, but illustrating another embodiment of the apparatus of the present invention.

The present invention is described, for illustrative purposes, with regard to the technique of seismic or acoustic logging. This technique is based upon the fact that rock formations of different character transmit seismic waves at different velocities. These velocities can be determined by moving a logging device, comprising a transmitter and a receiver, through a borehole while generating and receiving seismic waves or impulses. The logging device is moved through the borehole at a constant rate of travel with the seismic waves being generated at successive and predetermined intervals as a function of depth or time, or the logging device may be raised and lowered in a stepwise fashion, the seismic waves being generated as the device is momentarily maintained stationary at each depth.

In practicing this technique, the logging device is suspended from a lowering mechanism by a cable, which is electrically connected at the surface to suitable instruments capable of recording or indicating the desired data such as wave velocities, wave shapes, etc.

In addition to suitable controls for selectively controlling the speed of the lowering mechanism, a logging system preferably includes a cable measuring device which is operative in correlating data with the depths at which they were obtained. Additional details as to the construction and operation of acoustic logging systems may be had by reference to U. S. Letters Patent Nos. 2,651,021 and 2,708,485 issued to Vogel 2,137,485 to Salvatori, 2,233,420 to Wyckoff, etc.

Referring now to Fig. 1 of the drawings, the embodiment of the present invention, there illustrated, includes a floating vessel or barge 10 shown anchored over a borehole 12 which extends downwardly through the floor 14 of a body of water.

The vessel may be anchored over the borehole by a plurality of lines 16 which may be attached at their lower ends to any suitable anchors (not shown). Suspended counterweights 18 hang from the lines and provide additional stability to the anchored vessel.

The apparatus for logging the borehole is diagrammatically shown as including a casing 20 of a logging device, which casing is suspended from the insulated conductor cable 22. The cable 22 is wound on or unwound from a lowering mechanism including a reel 24 which can be driven at a constant speed by a prime-mover 26 provided with a speed controller 28. The prime-mover is energized through a flexible, insulated cable 25 which may be electrically connected to any suitable power source 27 on the vessel. The upper end of the cable 22 is electrically connected by means such as slip rings 30 or equivalent devices well known in the art, a connector box 32 and a flexible cable 34, to the recording equipment 36, disposed on the working deck or in a cabin of the vessel. The reel 24 and preferably the prime-mover 26 are mounted on a support diagrammatically shown in the drawing as a suspended bracket or frame member 38.

In order to compensate for the rise and fall of the vessel as the logging device is moved through the borehole 12, the support 38 is fixed in a vertically stabilized position with respect to the sea bottom and the borehole by means which control the vertical reciprocating movement of the support 38 with respect to the vessel. The upper limit of the vertical position of the support 38 is fixed at a selected distance above the floor 14 of the body of water by the use of a non-resilient flexible cable or line 40. As illustrated in Fig. 1, the ends of the cable 40 are anchored to the floor 14 of the body of water by a pair of weights or anchors 42 which are preferably disposed on opposite sides of the borehole 12. The intermediate portion of the cable 40 is run through an eye 44 which depends from the support 38. The length of the cable is such that when it is tensioned, as shown, the support 38 is disposed above the working deck and outboard of the stern of the vessel 10. It is understood that a number of separately anchored cables may be used, or that a single weight and a cable having a length greater than the depth of the water and the freeboard of the vessel may be substituted for the arrangement as shown. I

The support 38 is maintained in the selected vertical position above the floor 14 of the body of water by the application of an upwardly directed force continuously acting on the support 38 to tension the flexible cable 40. More particularly, the vessel may be provided with an upstanding frame 46 having any suitable construction as i that of an A frame or a davit such as those commonly carried by a vessel for raising and lowering objects over the side. The frame 46 includes a pair of upwardly converging members 48, the lower ends of which are attached to the deck of the vessel 10, and the upper ends of which are connected by a cross brace 50, whereby a pulley 52 may be hung from the frame 46 outboard of the stern of the vessel and directly over the borehole 12. The yoke 54 of the pulley is rotatably mounted on a pin 56 carried by the frame 46, the axes of the pin and the pulley being disposed substantially transverse of the keel line of the vessel. Preferably, the stem 55 and collar 57 of the yoke 54 are connected by a ball and socket arrangement (not shown) whereby the pulley can swing substantially freely with respect to the cross brace 50.

The cable 40 is tensioned by means of a flexible line or cable 58 which is reeved over the pulley 52 and is attached at one end to the support 38, while its other end is attached to a weight 60, having a mass which is substantially greater than that of the lowering mechanism on support 38, but less than the combined mass of the lowering mechanism and the weight or weights 42 anchoring the cable 48. For example, the weights 42 may each have a mass of 250 lbs. The lowering mechanism and associated apparatus carried by the support 38 may have a mass of 320 lbs., and the weight 60 may have a mass of 600 lbs. Thus, as the vessel falls, the weight 60 will overcome the weight of the lowering mechanism on support 38 and will move downwardly to take up any slack in the cable 58 and to maintain the lowering mechanism in a vertically stabilized position. The cable 58 and weight 60, together with the pulley 52 (which is connected to frame 46), may be defined as the stabilizing means which apply an upward force to the lowering mechanism. These stabilizing means, in conjunction with weights 42 and cable 40, maintain the lowering mechanism in the aforesaid vertically stabilized position. As the vessel rises, the weight of the anchors 42 added to that of the lowering mechanism on support 38, will cause the weight 60 to move upwardly to maintain the cables 40 appropriately tensioned with the anchors 42 still resting on the bottom. Any suitable means may be provided for preventing the weight 60 from swinging during operation of the lowering mechanism.

It is understood that the pulley 52, cable 58 and weight 60 may be replaced by a tensioned resilient member such as a helical spring (not shown) connected between the cross brace 50 and the support 38. Such a spring should have a construction whereby the variations in the spring tension within the expected rise and fall of the vessel would be sufficient appropriately to tension the cable 40 without lifting the weights 42 from the bottom 14. Thus, this tensioned resilient member acts in the same manner as the stabilizing means disclosed above in connection with the description of Figure l Preferably, the resilient member may be of the type which is maintained in a substantially constant degree of tension over a considerable range of displacement. Such a device is shown in the embodiment of the invention as illustrated in Fig. 2 of the drawings. In this embodiment, the cable 40 has been replaced by a pair of non-resilient cables 62 which are attached between the weights 42 and the opposite ends of the support 38. The cables are appropriately tensioned by a balancer 64 which is hooked to a clevis 66 carried by the cross brace 50. The balancer may be of any suitable type, and is illustrated as including a spring powered tapered drum 68 on which is wound a cable 70, the lower end of which is attached to the top of the support 38. The taper of the drum 68 is such that the variation in drum diameter compensates for the variation in spring tension as the drum rotates to take up and pay out the cable 70 to compensate for the rise and fall of the vessel, and the capacity of the balancer is such that it operates to maintain the cables 62 and 70 in a substantially constant degree of tension without lifting the weights 42 from the bottom 14.

From the foregoing description, it is apparent that the rise and fall of the vessel occurring as a result of wave action, etc., is compensated for by the apparatus of the present invention whereby the lowering mechanism on support 38 is free to reciprocate vertically with respect to the vessel, and is maintained in a vertically stabilized position with respect to the borehole 12, thereby permitting precise depth and rate of running control.

While the present invention has been disclosed, for illustrative purposes, in accordance with the technique of seismic or acoustic logging, it is understood that it may be employed advantageously with substantially any of the logging techniques embodying the use of a device which is moved through a borehole at a constant speed to identify the earth formations traversed thereby, such in particular as the electrical logging technique.

I claim as my invention:

1. An apparatus for logging an offshore borehole from a vessel, said apparatus comprising: a logging device adapted to be lowered and moved on a cable from said vessel into and through the borehole, reel means for said cable, prime mover means coupled to said reel means for selectively raising and lowering said logging device at a predetermined rate of travel, anchoring means, including connecting means, attached to said reel means and extending downwardly therefrom for anchoring the reel means to the floor of a body of Water, said anchoring and connecting means fixing the limit of the upward movement of the reel means with respect to the floor of the water body, and stabilizing means carried by said vessel and connected to the reel means for continuously applying an upwardly directed force to the reel means, thereby tensioning said connecting means to stabilize said reel means in a substantially fixed position above the floor of the body of water.

2. The apparatus of claim 1 wherein said anchoring means includes a flexible cable having its ends anchored in a spaced relation on opposite sides of the borehole and its intermediate portion attached to said reel means.

3. The apparatus of claim 1 wherein said anchoring means includes a flexible cable having its ends anchored in a spaced relation on opposite sides of the'borehole and its intermediate portion attached to said reel means, and wherein said stabilizing means includes a sheave carried by said vessel and a line reeved over said sheave and attached at one end to said mechanism and at the other to a weight for tensioning said cable.

4. The apparatus of claim 1 wherein said anchoring means includes a flexible cable having an upper end attached to said reel means and a lower end adapted to be anchored to the floor of the body of water, and wherein said stabilizing means includes a resilient tensioned member opcratively connected between said reel means and the vessel to apply a constant upwardly acting force to said reel means.

5. An apparatus for vertically stabilizing the lowering mechanism of a logging device with respect to the floor of a body of Water to compensate for the movement of a floating vessel supporting the mechanism above a borehole comprising: a substantially non-resilient flexible member having a length greater than the depth of the water above the borehole and the freeboard of the vessel, anchoring means on one end of said member, means for attaching the other end of said member to the mechanism, and a tensioning member adapted to be attached between the vessel and the mechanism, said tensioning member being adapted to apply an upward force to said lowering mechanism, and thus tensioning the flexible member when said member is attached to the mechanism and anchored to 5 the floor of the body of water.

References Cited in the file of this patent UNITED STATES PATENTS 10 2,236,489 Rose Mar. 25, 1944 2,358,096 Peterson Sept. 12, 1944 2,606,003 McNeill Aug. 5, 1952

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