Abstract:
An interface to provide coupling between a downhole sensor and wiring to other electrical equipment. The interface is configured to obtain voltage from a single power line and provide it to the downhole sensor while simultaneously converting sensor data to frequency form for transmission right back over the same power line. In this manner a substantial reduction in downhole wiring may be obtained. This may be particularly beneficial for sensors to be incorporated into downhole equipment where size and space issues are prevalent, particularly in the circumstance of equipment requiring a retrofit in order to accommodate the sensor capacity.

Description:
CROSS REFERENCE TO RELATED APPLICATION(S) 
       [0001]    This Patent Document 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. 
     
    
     FIELD 
       [0002]    Embodiments described herein relate to sensors for use in downhole applications in a well at an oilfield. In particular, embodiments of interfaces for electronic coupling to leads of such sensors are described in particular detail. 
       BACKGROUND 
       [0003]    In the oilfield industry, well applications often employ a variety of sensors coupled to downhole equipment to provide information relative to the well or equipment during a given application. For example, temperature, pressure, and other well conditions may be monitored as well as readings related to the equipment itself. These equipment readings may involve the monitoring of load and/or pressure imparted on the equipment during an application. 
         [0004]    Downhole equipment may include downhole tractors, for example, 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, 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. 
         [0005]    Regardless of the tractor configuration chosen, the tractor, along with several thousand pounds of equipment, may be pulled thousands of feet into the well for performance of an operation at a downhole well location of interest. It is over the course of such applications that monitoring conditions of the well and/or equipment with a sensor as noted above may be of particular benefit. For example, as the equipment is positioned deeper and deeper within the well, the load of the tractor assembly may approach a level that is beyond the load capacity of the tractor. Thus, monitoring load may play a significant role in carrying out such an operation. Therefore, a load sensor may be incorporated into the tractor assembly. 
         [0006]    Whether it be load, pressure or another condition being monitored, it is likely that the sensor is of a conventional strain gauge configuration. Generally, this includes the use of four leads that are run between the sensor and a microprocessor. These leads include two exitation leads, one for power, the other for ground. Two output leads are also provided to transmit data between the sensor and the microprocessor. 
         [0007]    Space available on the downhole tractor comes at a premium. That is, the well may offer less than about 12 inches in diameter to work with. Thus, the profile of the tractor may be minimal. As a result, features incorporated into the body of the tractor may be of limited sizing as well. The same may go for the overall amount of features employed in conjunction with the tractor. Indeed, the amount of wiring that is employed downhole may even be kept at a minimum. For example, where a downhole sensor is employed as described above, the downhole microprocessor may be positioned relatively near the sensor. In this manner, the amount of wiring may be kept at a minimum. This may be particularly beneficial in the case of a downhole sensor which is likely to make use of numerous wiring leads, generally about four, as also noted above. 
         [0008]    Unfortunately, even where a relatively short distance is utilized between the microprocessor and the sensor, a substantial amount of wiring may still be present over such a distance. For example, a separation of no more than about four inches between the sensor and the microprocessor still results in at least 16 inches of wiring due to the numerous leads employed by the sensor. As a result, many tractor assemblies fail to employ downhole sensors in order to preserve space. This may be particularly true for assemblies that would require retrofitting in order to accommodate such a sensor. 
       SUMMARY 
       [0009]    An electronic assembly is described for downhole use in a well. The assembly includes a processor with a power line running therefrom. A sensor for measuring a condition relative to the well is also provided. Thus, an interface is also provided that is coupled to the sensor and the power line in order to allow power and data communication over the power line and between the processor and sensor. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0010]      FIG. 1  is a side sectional view of a downhole assembly employing an embodiment of a downhole sensor interface. 
           [0011]      FIG. 2  is a perspective view of the downhole sensor interface of  FIG. 1  revealing power line and multi-line couplings. 
           [0012]      FIG. 3A  is a schematic representation of the downhole assembly of  FIG. 1  with focus on the electronic nature of the couplings of  FIG. 2 . 
           [0013]      FIG. 3B  is a block diagram revealing an embodiment of an electronic application series performed by the downhole sensor interface of  FIG. 1 . 
           [0014]      FIG. 4  is a perspective overview of the downhole assembly of  FIG. 1  employed in a well at an oilfield. 
           [0015]      FIG. 5  is a flow-chart summarizing an embodiment of employing a downhole sensor interface. 
       
    
    
     DETAILED DESCRIPTION  
       [0016]    Embodiments of a downhole sensor interface are described with reference to certain downhole equipment. Indeed, focus is drawn to a downhole tractor assembly employing an embodiment of a sensor interface. In particular, a reciprocating downhole tractor assembly is depicted in many figures of the present Application. However, a variety of downhole equipment types may employ a sensor that is coupled to an embodiment of a sensor interface as detailed herein. Embodiments of the downhole sensor interface are configured to for simultaneously coupling to a conventional multi-line portion of a downhole sensor and a single power line of a microprocessor. Thus, data and power transmission may simultaneously be transmitted over the power line, thereby reducing the overall amount of wiring employed in the assembly. As a result, any number of downhole equipment types may be equipped with a sensor in a manner taking advantage of the reduced wiring requirements afforded by embodiments described herein. In particular, active and/or interventional equipment such as tractors, sleeve shifting devices and others which are often devoid of sensor features may be more readily fitted or retrofitted with sensor capacity afforded by embodiments of interfaces detailed herein. 
         [0017]    Referring now to  FIG. 1 , an embodiment of a downhole sensor interface  100  is internally incorporated into the shaft  115  of a reciprocating tractor  400  near it&#39;s downhole sonde  175  (see  FIG. 4 ). The sensor interface  100  is coupled at one end to multi-wire leads  102  of a sensor  103  which is described in greater detail below. The other end of the interface  100  is coupled to a power line  101  of a downhole microprocessor  104  configured to direct and interpret signals from the sensor  103 . Thus, the downhole sensor interface  100  serves to allow for the interfacing of a single unitary power line  101  to multi-wire leads  102  in a manner that allows for effective power and data communication between the microprocessor  104  and the sensor  103 . 
         [0018]    Employing the downhole sensor interface  100  as indicated allows for the overall amount of wiring between the sensor  103  and the microprocessor  104  to be kept to a minimum. That is, all of the multi-wire leads  102 , which may number about four wires, need not run the entire length between the sensor  103  and the microprocessor  104 . As detailed below, this is achieved through techniques that result in a conversion of voltage to frequency signals that may be passed along the power line  101  to the microprocessor  104  simultaneous with power delivery to the sensor  103  along the same line  101 . 
         [0019]    As shown, in  FIG. 1 , the microprocessor  104  is incorporated into the shaft  115  at the opposite side of the sonde  175  relative to the sensor  103 , perhaps a couple of feet away. Thus, given the mechanical workings of the sonde  175  as described below and the limited amount of spacing available, the use of a single power line  101  for electrical coupling between the sensor and microprocessor  104  is particularly advantageous. However, as described below, even in other embodiments where the microprocessor  104  is positioned closer to the sensor  103 , the reduction in wiring may still be of substantial value. 
         [0020]    In another embodiment, the microprocessor  104  and sensor  103  may be positioned closer to one another, perhaps initially less than 3 inches apart, but configured to allow for changing positions relative to one another. This may be beneficial, for example, where the downhole assembly is prone to a degree of deformation. Similarly, this may be beneficial where the sensor  103  is a pressure sensor that is physically responsive to pressure changes to a degree. Regardless, in such an embodiment, the power line  101  between the sensor  103  and microprocessor  104  may be of an expandable coiled configuration to allow for the change in position of the features ( 103 ,  104 ) relative to one another. This type of coupling may be seen in U.S. Pat. No. 6,396,414, incorporated herein by reference in its entirety. Even though positioned close to one another, the utilization of multiple wires to provide such communication may present a significant challenge for a coiled configuration as described. Thus, the use of a the single power line  101  between the sensor  103  and microprocessor  104  as detailed herein may more easily allow for an effective coiled configuration to be employed. 
         [0021]    Continuing with reference to  FIG. 1 , the mechanics of the tractor sonde  175  and the relationship to the sensor  103  are described in detail. That is, as shown, the sensor  103  is configured to monitor pressure in a chamber  122  as directed by a piston  110 . Together, these features ( 103 ,  110 ,  122 ) serve as a force monitoring mechanism which may be employed to regulate the physical interaction of the sonde  175  and the wall  185  of the well  180 . That is, as shown, the sonde  175  is equipped with bowsprings  144  that include gripping saddles  124  to grip the wall  185  during actuation by arms  134  that are coupled to the piston  110 . However, the diameter of the well  180  at any given location may affect the amount of force imparted at the interface of the gripping saddles  124  and the wall  185 . Thus, as described below, the sensor  103 , piston  110  and chamber  122  may be employed to monitor this force to help reduce the possibility of under-expansion of the bowsprings  144  and slippage of the sonde  175 . Similarly, these features  103 ,  110 ,  122  may be employed to help reduce the possibility of over-expansion of the bowsprings  144  in a manner damaging the bowsprings  144  or the wall  185  (and including avoidance of immobilizing of the bowsprings  144  by sinking into the wall  185 ). 
         [0022]    Continuing with reference to  FIG. 1 , the sensor  103  is a pressure sensor such as a conventional solenoid or transducer. As indicated, the sensor  103  is configured to monitor pressure changes in the chamber  122 . For example, where the diameter of the well  180  decreases as the tractor  400  moves through the well, the force on the bowsprings  144  increases (see  FIG. 4 ). As such, the piston  110  is forced toward the chamber  122  increasing hydraulic pressure therein. As noted, this occurs in a manner detectable by the sensor  103 . For example, the pressure in the chamber may be in the neighborhood of 20,000-40,000 psi. Information relative to this pressure may ultimately be recorded and interpolated by the microprocessor  104  so as to determine roughly the amount of force translating through the bowsprings  144 . Thus, where applicable, corrective action may be taken when the detected force is above or below predetermined values of acceptability. 
         [0023]    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  104  may be employed to direct release of fluid from the chamber  122  via conventional means. In this manner, the pressure on the piston  110 , and ultimately the forces translated through the bowsprings  144 , may be reduced. 
         [0024]    With added reference to  FIG. 4 , the downhole sonde  175  is part of a larger reciprocating tractor assembly  400  that also includes an uphole sonde  475 . Together these sondes  175 ,  475  interchangeably engage the wall  185  of the well  180  as it drives through a formation  195  pulling several thousand pounds of an equipment load. When one of the sondes  175 ,  475  is engaged with the wall  185  for this inchworm-like advancement, a predetermined amount of force may be employed, for example, about 5,000 psi. In this manner, a sufficient, but not damaging, amount of force may be translated through anchored bowsprings  144  during a power stroke of the sonde  175 ,  475 . 
         [0025]    In an embodiment as described above, the microprocessor  104  may effectuate a deflation or release of fluid from the chamber  122  once forces greater than a predetermined value of about 5,000 psi are detected by the sensor  103 . Similarly, the microprocessor  104  may direct inflating or filling of the chamber  122  once forces 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 force through the bowsprings  144  may be maintained throughout the powerstroke or engagement of a given sonde  175 ,  475 . 
         [0026]    In the above example, a powerstroke is noted as the period of time in which a given sonde  175 ,  475  is anchored to the well wall  185  by the forces translated through the bowsprings  144 . This anchoring force is ultimately monitored by the noted microprocessor  104  via the sensor  103  and through the interface  100 . At other times during reciprocation of the tractor  100 , however, a given sonde  175 ,  475  may be intentionally allowed to glide in relation to the well wall  185 . During this “return” stroke, the acceptable pressure threshold may be different. However, pressure may still be monitored by the microprocessor  104  via the sensor  103  and interface  100  at this time. 
         [0027]    Continuing now with reference to  FIG. 2 , with added reference to  FIG. 1 , a perspective view of the downhole sensor interface  100  is depicted. The interface package may be less than about 2 inches in length by less than about half an inch in height. Thus, the sensor interface  100  is sufficiently small enough to be incorporated into the shaft  115  near the sonde 157 of a tractor  400  (see also  FIG. 4 ). Additionally, given the downhole environment, the interface  100  may be rated for temperatures in excess of about 150° C. 
         [0028]    The sensor interface  100  is equipped with a lead connector  275  as shown. Given that the sensor  103  may include multi-wire leads  102  as is common with a conventional strain gauge sensor, the lead connector  275  may be equipped for such multi-coupling. As shown in  FIG. 2 , the multi-wire leads  102  may include two input leads  205 , one for power and the other for ground. Additionally, two output leads  207  may be provided for transmission of date acquired by the sensor  103  back uphole. The lead connector is configured to accommodate all such leads  102 . 
         [0029]    The sensor interface also includes a central housing  250  for accommodating downhole circuitry  200 . This circuitry  200  is configured to effectively translate the nature of the multi-wire leads  102  described above to a single wire solution (i.e. over the power line  101 ). As such, the amount of wiring employed may be reduced as indicated above. The manner in which the circuitry  200  achieves this translation is described in detail with reference to  FIGS. 3A and 3B  below. In the embodiment shown, the circuitry  200  may be configured to accommodate up to about 20 volts from the power line  101 . Additionally, a frequency signal of up to about 1.5 MHz may be transmitted back uphole over the power line  101  as directed by the circuitry  200 . 
         [0030]    Continuing with reference to  FIG. 2 , the sensor interface includes a power line coupling  225  which receives the power line  101  therein. The coupling  225  allows for electronic interfacing of the power line  101  and the circuitry  200  noted above. Thus, the power from the power line  101  may be transmitted downhole beyond the circuitry  200 , across the input leads  205  and eventually to the sensor  103  of  FIG. 1 . Similarly, data obtained from the sensor  103  may eventually be transmitted back uphole across the power line  101 . 
         [0031]    Referring now to  FIG. 3A , a schematic representation of the assembly of  FIG. 1  is shown. In particular, the electronic couplings of the sensor interface  100  are described. That is, as noted above, voltage (see arrow  325 ) is supplied over the power line  101  and directed toward the sensor  101 . Depending on the amount of voltage supplied, the interface  100  may serve to modulate down the voltage supplied over the multi-wire leads  102  and to the sensor  103  (see arrow  350 ). 
         [0032]    The powered sensor  103  may be utilized in a downhole environment as depicted in  FIG. 1 , for example, to monitor pressure. Depending on the sensor information obtained by the sensor  103  at this time, a voltage may then be transmitted back over the multi-wire leads  102  and processed by the interface  100 . At this point, the sensor interface  100  may serve to convert this information signal from a voltage-based signal to frequency (i.e. Hz at arrow  300 ). Thus, the information relative to downhole conditions detected by the sensor  103  may be transmitted back over the power line  101  even though voltage is simultaneously incoming over the same line  101  (see arrow  325 ). As such, the amount of wiring required to utilize the assembly is reduced. 
         [0033]    Continuing now with reference to  FIG. 3B , a block diagram revealing electronic applications of the downhole sensor interface  100  of  FIG. 3B  is depicted. For example, starting with the “Sensor”, power thereto is regulated as indicated in the block labeled “Power Regulation”. More specifically, in one embodiment voltage in excess of about 10 volts is regulated down to no more than about 5 volts (to the sensor). The powered sensor may then obtain readings, for example of pressure. For example, in a conventional strain gauge sensor setup, 20,000-40,000 PSI may be read as 200-400 mV. With this information detected, a conversion may take place to a smaller voltage scale as indicated by the block labeled “Op-amp Variable Gain”. 
         [0034]    In one embodiment, the application of “Op-amp Variable Gain” converts the large mV readings to a scale that is from 0-2.5 volts. Subsequently, an application of frequency modulation may be applied as indicated by the block labeled “Frequency Modulation”. For example, the voltage reading may be converted to frequency. In one embodiment, the frequency range employed following the modulation application ranges from about 50 KHz to about 1.5 MHz. Regardless, once modulated, the frequency information may be transmitted back over the power line (as indicated by the block labeled “DC Coupling”). Thus, these frequency readings may be obtained and processed by the microprocessor detailed above. 
         [0035]    Referring now to  FIG. 4 , a perspective overview of the downhole assembly of  FIG. 1  is shown employed in the well  180  at an oilfield  490 . As shown, the well  180  runs through various formation layers  195 ,  495 . A tractor  400  which employs the assembly of  FIG. 1 , is deployed from the surface of the oilfield  490  via a conventional wireline  450 . However, other forms of well access line may be employed. As shown in  FIG. 4 , several thousand feet of this wireline  450  may be run from wireline equipment  425  through a wellhead  430  and to the tractor  400  as shown. The equipment may include a conventional wireline truck  415  configured to accommodate a drum  417  from which the wireline  450  may be drawn. In the embodiment shown, control equipment  419  is also provided by way of the truck  415  to direct the deployment of the wireline  450  and associated tractoring. 
         [0036]    The reciprocating tractor  100 , which employs the downhole sonde  175  with sensor and interface as detailed herein, may be particularly adept at delivering a downhole tool  460 , such as a logging tool, to a location as shown. For example, the location may be one 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  400  may exceed several thousand pounds and continually increase as the tractor  400  advances deeper and deeper into the well  180 . Thus, monitoring of tension and/or pressure via the assembly as detailed hereinabove may be of significant benefit to the well  180  and the tractor  400 . Thus, the advantage of reduced wiring in order to accommodate the sensor and interface as detailed above may translate to significant benefit to continued downhole operations. This may be particularly the case where retrofitting of the tractor or other equipment is to be undertaken in order to accommodate the sensor and interface. 
         [0037]    Referring now to  FIG. 5 , a flow-chart summarizing an embodiment of employing a downhole sensor interface is described. Namely, the sensor may be provided as part of a larger assembly that is deployed downhole as indicated at  515  and described with reference to  FIG. 4  above. As indicated at  530 , power may be supplied in one direction over a unitary power line, for example, running from a downhole microprocessor and toward the sensor interface. This power may be modulated to a predetermined level and the sensor then employed to monitor a condition of the well or the assembly itself as indicated at  545  and  560 . 
         [0038]    As noted, the sensor may be employed to monitor a condition of the assembly as shown at  560 . This is described in greater detail hereinabove where the sensor is employed to monitor pressure imparted through bowsprings of a tractor during downhole advancement thereof. However, the sensor may also be provided to monitor conditions of the well itself. For example, in another embodiment, the sensor may be provided as part of a logging tool. 
         [0039]    Continuing now with reference to  FIG. 5 , the information obtained by the sensor may be converted to frequency information as indicated at  575 . Thus, this information may be sent back over the same power line in the opposite direction of the above noted power input as indicated at  590 . Thus, the amount of wiring running to and from the sensor interface may be kept to a minimum. 
         [0040]    Embodiments described hereinabove allow for the incorporation of a sensor on downhole assemblies where space available is at a minimum. This is achieved through the use of a sensor interface which minimizes the amount of wiring that is required in order to utilize strain gauge based sensors. Such embodiments may be particularly beneficial for utilization with tractors and other assemblies which traditionally fail to leave space for sensor capacity thereat and thus, may require retrofitting. 
         [0041]    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. For example, strain gauge sensors other than pressure sensors, such as tension monitors may employ a sensor interface as detailed herein. Regardless, 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.