Patent Publication Number: US-2015083406-A1

Title: Force Monitoring Tractor

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of co-pending U.S. patent application Ser. No. 12/434,108, filed May 1, 2009, which is a continuation-in-part of prior co-pending U.S. patent application Ser. No. 12/396,936, filed on Mar. 3, 2009 and entitled “Self-Anchoring Device with Force Amplification”, which in turn is a continuation of U.S. patent application Ser. No. 11/610,143, file on Dec. 13, 2006, also entitled “Self-Anchoring Device with Force Amplification”, which in turn is entitled to the benefit of, and claims priority to, U.S. Provisional Patent Application Ser. No. 60/771,659 filed on Feb. 9, 2006 and entitled “Self-Anchoring Device for Borehole Applications”, the entire disclosures of each of which are incorporated herein by reference. 
    
    
     BACKGROUND 
     Downhole tractors are often employed to drive a downhole tool through a horizontal or highly deviated well at an oilfield. In this manner, the tool may be positioned at a well location of interest in spite of the non-vertical nature of such wells. Different configurations of downhole tractors may be employed for use in such a well. For example, a reciprocating or “passive” tractor may be utilized which employs separate adjacent sondes with actuatable anchors for interchangeably engaging the well wall. That is, the sondes may be alternatingly immobilized with the anchors against a borehole casing at the well wall and advanced in an inchworm-like fashion through the well. Alternatively, an “active” or continuous movement tractor employing tractor arms with driven traction elements thereon may be employed. Such driven traction elements may include wheels, cams, pads, tracks, wheels or chains. With this type of tractor, the driven traction elements may be in continuous movement at the borehole casing interface, thus driving the tractor through the well. 
     Regardless of the tractor configuration chosen, the tractor, along with several thousand pounds of equipment, may be driven thousands of feet into the well for performance of an operation at a downhole well location of interest. In order to achieve this degree of tractoring, forces are imparted from the tractor toward the well wall through the noted anchors and/or traction elements. In theory, the tractor may thus avoid slippage and achieve the noted advancement through the well. 
     Unfortunately, advancement of the tractor through a well may face particular challenges when the well is of an open-hole variety as opposed to the above-described cased well. That is, in certain operations, the well may be uncased and defined by the exposed formation alone. In such circumstances, the well is likely to be of a variable diameter throughout. For example, it would not be uncommon to see an 8 inch well expand to over 11 inches and taper back to about 8 inches intermittently over the course of a few thousand feet. Thus, without the reliability provided by a casing of uniform diameter, the tractor is left with the proposition of radial expansion to interface a changing diameter of the open hole well wall in order to maintain tractoring. 
     In order to ensure that the radial expansion is sufficient to maintain tractoring in an open hole, an excess of expansion forces may be employed. So, with reference to the well above for example, the amount of force imparted on the tractoring mechanisms (e.g. anchor or bowspring arms) may be pre-set at an amount sufficient to expand and drive the tractor through an 11 inch diameter section of the well. Thus, the tractor may be expected to avoid slippage when the well diameter begins to expand from 8 inches up to 11 inches. 
     Unfortunately, while excess expansion force may ensure tractoring through larger diameter sections of the open hole well, this technique may also lead to damaging of the tractor. For example, a conventional tractor may be equipped with anchor arms configured to withstand maximum forces of about 5,000 lbs. However, in a circumstance where the anchor arms are pre-set to operate at about 4,500 lbs. through an 11 inch diameter open hole well, forces well in excess of 5,000 lbs. may be imparted on the arms as the tractor traverses 8 inch well sections as noted above. Mechanical failure of the tractor is thus likely to ensue as a result of over-stressed anchor arms. 
     Furthermore, even in circumstances where the anchor arms or other expansive mechanisms are of sufficient strength and durability to withstand excess forces as noted, the exposed formation defining the well may not be. That is, in many circumstances the application of excess force may result in damage to the exposed well wall when its compressive strength is exceeded. Thus, where the formation is comparatively soft in nature, the utilization of forces adequate to drive the tractor through an 11 inch diameter well section may damage an 8 inch diameter section. Nevertheless, the utilization of excess force is often employed to help ensure tractoring through a variable diameter open hole well is achieved. As a result, the well wall often collapses or cracks in certain locations even where the tractor is left undamaged. In fact, even though technically undamaged, the tractor may be rendered inoperable with its expansion mechanism imbedded within a collapsed section of the well. In such circumstances, not only is tractoring halted, but a follow-on high cost fishing operation may be required. 
     SUMMARY 
     An example downhole tractor for positioning in an open hole well has an elongated body. The elongated body has a driving mechanism coupled thereto, the driving mechanism is configured for deploying relative to the elongated body for interfacing a wall of the well. A force monitoring mechanism is coupled to the driving mechanism for monitoring force thereon during the interfacing. 
     Another example downhole tractor for positioning in an open hole well includes a bowspring with a gripping saddle for interfacing a wall of the well, and an expandable arm coupled to said bowspring and deployable from an elongated body of the tractor to effectuate the interfacing. A force monitoring mechanism is coupled to the bowspring to monitor a force thereon during the interfacing. 
     An example method of tractoring in an open hole well includes positioning the tractor in the well, and interfacing a wall of the well with a driving mechanism of the tractor for the tractoring. The method also includes monitoring a force on the driving mechanism during said interfacing. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other features and advantages of the present disclosure will be better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings wherein: 
         FIG. 1  is a side cross-sectional view of an embodiment of a force monitoring tractor disposed in an open-hole well. 
         FIG. 2  is a perspective overview of an oilfield accommodating the open-hole well with force monitoring tractor of  FIG. 1 . 
         FIG. 3  is an enlarged cross-sectional view of a downhole sonde of the force monitoring tractor of  FIG. 1  in the open-hole well. 
         FIG. 4  is an enlarged view of a gripping saddle of the downhole sonde of the force monitoring tractor depicted in  FIG. 3 . 
         FIG. 5  is an enlarged cross-sectional view of the downhole sonde disposed adjacent a restriction of the open-hole well of  FIG. 1 . 
         FIG. 6  is a flow-chart summarizing an embodiment of employing a force monitoring tractor in an open-hole well. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Embodiments are described with reference to certain tools and techniques for employing an optical data transmission assembly joint in an oilfield environment. In particular, embodiments of deploying a well access line in the form of a wireline cable or intervention cable are described. Additionally, oilfield logging applications are described in some detail. However, a variety of other non-logging oilfield applications and alternate deployment lines may be run in a manner which takes advantage of embodiments detailed herein. Regardless, embodiments described herein include such a joint that allows for effective real-time optical data transfer from a movable line to a stationary housing for processing. In fact, such data may even be attained over the joint via multiple optical channels, simultaneously. 
     Referring now to  FIG. 1 , a side cross-sectional view of an embodiment of a force monitoring tractor  100  is depicted disposed within an open-hole well  180 . In the embodiment shown, the tractor  100  is of a multiple sonde variety with an uphole sonde  150  and a downhole sonde  175  to interface the well wall  185  and serve as the driving mechanism for the tractor  100 . However, in other embodiments other types of tractor configurations, such as those employing tracks, wheels, chains, or pads as the tractor driving mechanism may be employed. 
       FIG. 1  reveals a variability in well diameter which is not uncommon to open-hole wells. For example, an uphole portion  190  of the well  180  is of a greater diameter (D) than the diameter (D′) of a downhole portion  195  of the well  180 . Furthermore, in the case of an open-hole well  180 , the well wall  185  is no more than an exposed surface of the formation  194 . Together, the combination of exposed formation  194  and smaller diameter (D′) well portions leave the well  180  particularly susceptible to collapse and/or damage during intervention applications. However, as detailed below, the tractor  100  shown in  FIG. 1  is equipped with a force monitoring capacity to control forces applied to the well wall  185  during tractoring through smaller diameter (D′) well portions (e.g. at  195 ). Additionally, the tractor  100  may include gripping saddles  122 ,  124  configured to spread out the physical interfacing of the tractor  100  and well wall  185  over a greater area. In this manner, the likelihood of damage to the well wall  185  due to the forceful contact of the tractor  100  may be minimized 
     Continuing with reference to  FIG. 1 , the tractor  100  is made up of an elongated body  115  or shaft to accommodate each sonde  150 ,  175 . The sondes  150 ,  175  in turn are made up of bowsprings  142 ,  144  which are coupled to the body  115  via movable couplings  112 ,  114  as shown. Radially expandable arms  132 ,  134  are disposed between the couplings  112 ,  114  of each bowspring  142 ,  144  to forcibly engage the well wall  185  in an alternating fashion. As such, the tractor  100  may proceed downhole in an inchworm-like manner. Such is the nature of a reciprocating tractor  100  of multiple sonde configuration. 
     As noted above, the well  180  is of an open-hole variety. As such, the emergence of a step  192  or change in well morphology and/or diameter (e.g. (D) vs. (D′)) may be a common occurrence. With this in mind, the tractor  100  is also equipped with force monitoring mechanisms  102 ,  104  associated with each sonde  150 ,  175 . As detailed further below, these mechanisms  102 ,  104  may be employed to help ensure that the forcible engagement directed by the expandable arms  132 ,  134  does not exceed a predetermined amount, irrespective of the well diameter at any given location. As such, the structural integrity of the open-hole well  180  may be largely left intact, in spite of the noted tractoring. 
     Referring now to  FIG. 2 , a larger overview of the tractoring is depicted. In this depiction it is apparent that the open hole well  180  runs through the formation  194  well below other formation layers  294  at an oilfield  275 . In the embodiment shown, the tractor  100  is deployed from the surface of the oilfield  275  via a conventional wireline  220 . However, other forms of well access line may be employed. As shown in  FIG. 2 , several thousand feet of wireline  220  may be run from wireline equipment  210  through a wellhead  230  at the oilfield  275  and to the tractor  100  as shown. The equipment may include a conventional wireline truck  215  configured to accommodate a drum  217  from which the wireline  220  may be drawn. In the embodiment shown, control equipment  219  is also provided by way of the truck  215  to direct the deployment of the wireline  220  and associated tractoring. 
     A reciprocating tractor  100  may be particularly adept at delivering a downhole tool  250  to a location as shown in  FIG. 2 . For example, the location may be of relatively challenging access such as a horizontal well section several thousand feet below surface as depicted. In such circumstances, the amount of load pulled by the tractor  100  may exceed several thousand pounds and continually increase as the tractor  100  advances deeper and deeper into the well  180 . However, the tractor  100  may be adequately powered by the wireline  220  and secured thereto through a conventional logging head  240 . Thus, tractoring may proceed with the uphole sonde  150  and downhole sonde  175  interchangeably grabbing and gliding relative to the well wall so as to pull the entire assembly further and further downhole. So, for example, logging of the well  180  may proceed in an embodiment where the downhole tool  250  is a logging tool. Once more, due to the force monitoring mechanisms  102 ,  104  associated with the sondes  150 ,  175 , the logging application may take place without substantial damage to the open hole well  180  as a result of the tractoring. 
     Referring now to  FIG. 3 , an enlarged cross-sectional view of the downhole sonde  175  is depicted within the smaller diameter (D′) downhole portion  195  of the well  180 . The force monitoring mechanism  104  of the sonde  175  may play a significant role in regulating the physical interaction of the sonde  175  and the well wall  185 . That is, consider that the bowsprings  144  of the sonde  175  may be set to expand for gripping the wall  185 . However, the diameter (D′) of the well  180  is reduced in the downhole portion  195 . Thus, the force monitoring mechanism  104  may be employed to ensure that the force of this expansion does not exceed a predetermined amount. In this manner, damage to the exposed well wall  185  may be avoided as the gripping saddles  124  of the bowsprings  144  grab hold of the wall  185  for pulling the assembly downhole. 
     Continuing with reference to  FIG. 3 , the force monitoring mechanism  104  includes a pressure sensor  303  such as a transducer for monitoring the pressure and/or force translated through the bowsprings  144  during operation. More specifically, the pressure sensor  303  may be coupled to a hydraulic chamber  302  that is in communication with a piston  301 . While the depicted force monitoring mechanism  104  is pressure-based, alternate embodiments may be strain gauge based or include other suitable detection mechanisms. 
     As shown, the piston  301  may be directly coupled to the radially expandable arms  134  that forcibly control the interfacing of the bowsprings  144  and the wall  185 . Thus, as the diameter (D′) of the well  180  decreases and the force on the bowsprings  144  increases, the piston  301  may be forced toward the chamber  302 . As such, hydraulic pressure in the chamber  302  may be driven up in a manner detectable by the pressure sensor  303 . In one embodiment, the pressure in the chamber may be in the neighborhood of 7,500-12,500 psi. Such pressure may be recorded and interpolated by a downhole processor  304  as described below to determine roughly the amount of force translating through the bowsprings  144 . 
     The force information obtained by the pressure sensor  303  may be employed in a variety of manners. For example, the sensor  303  may be coupled to a downhole processor  304  as indicated. Thus, the information may be recorded and relayed uphole (e.g. over the wireline  220  of  FIG. 2 ). In this manner, well diameter and/or sonde and tractor location information may be retrieved and utilized. That is, by having a predetermined map of the well  180  geometry knowing the well diameter may be used to determine the tractor location. Additionally, as indicated above, the information may be employed to control the amount of force translated through the bowsprings  144  so as to minimize damage to the well wall  185  during tractoring. For example, upon acquiring information indicative of forces exceeding a predetermined amount, the processor  304  may be employed to direct release of fluid from the chamber  302  via conventional means. In this manner, the pressure on the piston  301 , and ultimately the forces translated through the bowsprings  144 , may be reduced. 
     With added reference to  FIGS. 1 and 2 , the tractor  100  may be configured to pull a load of several thousand pounds to deep within the well  180 . Thus, sufficient forces necessary for tractoring are to be employed. However, given the exposed, open-hole nature of the well  180 , the tractor  100  may also be configured to avoid excessive translation of forces through any of the bowsprings  142 ,  144  to the well wall  185 . With reference to controlling forces through these bowprings  142 ,  144 , a more specific illustration is described below. 
     In one embodiment, a predetermined target of about 5,000 psi of pressure may be set to ensure a sufficient, but not damaging, amount of pressure be translated through anchored bowsprings  142 ,  144  during a power stroke of the respective sonde  150 ,  175 . For example, the ultimate compressive strength of the formation  194  may be about 5,250 psi. In such an embodiment, the downhole processor  304  may effectuate a deflation or release of fluid from the chamber  302  once pressure greater than a predetermined value of about 5,000 psi are detected by the pressure sensor  303 . For example, as the dowhole sonde  175  moves from a 10 inch uphole portion  190  of a well  180  and into an 8 inch portion  195 , pressure translated through the bowsprings  144  may initially increase. However, the release of fluid from the chamber  302  will allow pressure to return to the targeted 5,000 psi. Similarly, the processor  304  may direct inflating or filling of the chamber  302  as described below, once pressure less than about 5,000 psi are detected. All in all, a window of between about 4,800 psi and about 5,200 psi of pressure through the bowsprings  144  may be maintained throughout a powerstroke of a given sonde  175 . 
     In the example provided above, a powerstroke is noted as the period of time in which a given sonde  150 ,  175  is anchored to the well wall  185  by the forces translated through the bowsprings  142 ,  144 . It is this anchoring force that is monitored by the noted mechanisms  102 ,  104 . At other times during reciprocation of the tractor  100 , however, a given sonde  150 ,  175  may be intentionally allowed to glide in relation to the well wall  185 . Indeed, at any given point, one sonde  150 ,  175  may be anchored as the other glides, thereby leading to the inchworm-like advancement of the tractor  100  downhole as alluded to earlier. 
     It is worth noting that during the glide of a sonde  150 ,  175  (e.g. it&#39;s ‘return stroke’), the amount of forces translated between the bowsprings  142 ,  144  and the wall  185  drops to well below the window of between about 4,800 psi and about 5,200 psi, for example. Further, regulation of such forces during the return stroke may be controlled by features outside of the force monitoring mechanisms  102 ,  104 . In another embodiment however, these mechanisms  102 ,  104  may be employed to initiate the glide of the sonde  150 ,  175  for the return stroke. Additionally, upon returning to the power stroke a brief amount of inflating of the chamber  302  may take place to allow for sufficient anchoring forces to build up therein. Such inflating may take place in conjunction with the natural reciprocation of the tractor  100 . 
     Continuing now with added reference to  FIG. 4 , one of the gripping saddles  124  of the downhole sonde  175  is described in greater detail. That is, in addition to employing the force monitoring mechanism  104 , a specially configured gripping saddle  124  may be utilized to help minimize damage to the wall  185  of the well  180  during anchoring. In particular, the gripping saddle  124  includes a surface  400  that is configured to interface the well wall  185  across a wide area. That is, rather than provide a toothed cam or other conventional interfacing feature, the surface  400  spreads out interfacing contact between the radially forced bowspring  144  and the wall  185 . Thus, a potentially damaging and forcibly induced line or point of contact between the bowspring  144  and wall  185  is avoided. Stated another way, the saddle  124  is configured to contact the wall  185  in a non-point and line manner for protection thereof. In one embodiment, the surface  400  is even of a comparatively harder material such as tungsten carbide. 
     With added reference to  FIG. 3 , the gripping saddle  124  is coupled to the sonde  175  via a linkage wheel  375  of the radially expandable arms  134 . As shown, the linkage wheel  375  extends from the arms  134  and through a recess  350  of the saddle  124 . The recess  350  of the embodiment shown is of an inclined orientation such that downhole movement of the wheel  375  takes place in conjunction with outward radial forces of expansion on the bowspring  144 . This may enhance stable anchoring during a power stroke relative to the sonde  175 . 
     Continuing with reference to  FIGS. 3 and 4 , the sonde  175  is shown for interfacing, and during a power stroke, anchoring relative to the well wall  185 . However, both a force monitoring mechanism  104  and a gripping saddle  124  are provided. Alone, each of these features  104 ,  124  may substantially avoid the collapse of the formation  194  as a result of tractoring. However, when employed in conjunction with one another, the mechanism  104  and saddle  124  may substantially eliminate all reasonable likelihood of well damage at the wall  185  due to forces imparted by the sonde  175  during tractoring. 
     Referring now to  FIG. 5 , the downhole sonde  175  is shown advanced further into the well  180  reaching a restriction  550 . As described here, the term “restriction” is meant to refer to the presence of a feature that carries with it a sudden reduction in well diameter (D″). For example, given the open-hole nature of the well  180  depicted in  FIG. 5 , the restriction  550  may be a natural build-up of stable formation debris. However, in other circumstances, valves or other hydrocarbon well features may be pre-positioned downhole. Regardless, the well diameter (D″) may shrink in a sudden manner as indicated such that the bowsprings  144  make contact with the restriction  550 , such as at midpoint  575 , in absence of the gripping sadles  124 . That is, there may be a sudden emergence of force translated through the bowsprings  144  from a non-axial location (e.g. outside of the gripping saddles  124 ). Nevertheless, biasing toward such a location may be effectively achieved. 
     Referring now to  FIG. 6 , a flow-chart is depicted summarizing an embodiment of employing a force monitoring tractor in an open-hole well. The tractor may be advanced in the well as indicated at  615  while forces that are translated through the tractor relative to the wall of the well are continuously monitored as indicated at  630 . This monitoring may provide a host of information relative to the well, tractor positioning therein, etc. 
     Monitoring of forces relative to the interface may also involve the tracking of truly radial forces that are translated directly through expansive arms that extend from a central elongated body of the tractor as noted at  645 . This is detailed herein with reference to  FIG. 3  and the tracking of forces that are translated through radially expansive arms (e.g.  134 ). 
     Alternatively, monitored forces at the interface may involve the tracking of forces that are imparted through the tractor without primarily being directed through the radially expansive arms (e.g. non-radial forces) as noted at  660 . An example of monitoring of such forces is detailed herein with respect to  FIG. 5 . 
     Regardless of the particular type or combination of monitoring employed, the information obtained may be employed to adjust expansive pressure on the arms as indicated at  675 . In this manner, the forces present at the interface of the tractor and the exposed surface of the open hole well may be regulated in a manner that optimizes tractoring while preserving the structural integrity of the formation as much as possible. 
     Embodiments detailed hereinabove provide techniques and assemblies that allow for tractoring in an open hole well in a manner that address concern over forces present at the interface of the tractor and the wall of the well. Such forces may be monitored and controlled in a manner that promotes the life of the tractor as well as the structural integrity of the exposed well wall surface. 
     The preceding description has been presented with reference to presently preferred embodiments of the invention. Persons skilled in the art and technology to which this invention pertains will appreciate that alterations and changes in the described structures and methods of operation can be practiced without meaningfully departing from the principle, and scope of this invention. As such, the foregoing description should not be read as pertaining only to the precise structures described and shown in the accompanying drawings, but rather should be read as consistent with and as support for the following claims, which are to have their fullest and fairest scope.