Patent Publication Number: US-8985200-B2

Title: Sensing shock during well perforating

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit under 35 USC §119 of the filing date of International Application Serial No. PCT/US10/61102, filed 17 Dec. 2010. The entire disclosure of this prior application is incorporated herein by this reference. 
     BACKGROUND 
     The present disclosure relates generally to equipment utilized and operations performed in conjunction with a subterranean well and, in an embodiment described herein, more particularly provides for sensing shock during well perforating. 
     Attempts have been made to determine the effects of shock due to perforating on components of a perforating string. It would be desirable, for example, to prevent unsetting a production packer, to prevent failure of a perforating gun body, and to otherwise prevent or at least reduce damage to the various components of a perforating string. 
     Unfortunately, past attempts have not satisfactorily measured the strains, pressures, and/or accelerations, etc., produced by perforating. This makes estimations of conditions to be experienced by current and future perforating string designs unreliable. 
     Therefore, it will be appreciated that improvements are needed in the art. These improvements can be used, for example, in designing new perforating string components which are properly configured for the conditions they will experience in actual perforating situations. 
     SUMMARY 
     In carrying out the principles of the present disclosure, a shock sensing tool is provided which brings improvements to the art of measuring shock during well perforating. One example is described below in which the shock sensing tool is used to prevent damage to a perforating string. Another example is described below in which sensor measurements recorded by the shock sensing tool can be used to predict the effects of shock due to perforating on components of a perforating string. 
     A shock sensing tool for use with well perforating is described below. In one example, the shock sensing tool can include a generally tubular structure which is fluid pressure balanced, at least one sensor which senses load in the structure, and a pressure sensor which senses pressure external to the structure. 
     Also described below is a well system which can include a perforating string including multiple perforating guns and at least one shock sensing tool. The shock sensing tool can be interconnected in the perforating string between one of the perforating guns and at least one of: a) another of the perforating guns, and b) a firing head. 
     These and other features, advantages and benefits will become apparent to one of ordinary skill in the art upon careful consideration of the detailed description of representative embodiments of the disclosure hereinbelow and the accompanying drawings, in which similar elements are indicated in the various figures using the same reference numbers. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic partial cross-sectional view of a well system and associated method which can embody principles of the present disclosure. 
         FIGS. 2-5  are schematic views of a shock sensing tool which may be used in the system and method of  FIG. 1 . 
         FIGS. 6-8  are schematic views of another configuration of the shock sensing tool. 
     
    
    
     DETAILED DESCRIPTION 
     Representatively illustrated in  FIG. 1  is a well system  10  and associated method which can embody principles of the present disclosure. In the well system  10 , a perforating string  12  is installed in a wellbore  14 . The depicted perforating string  12  includes a packer  16 , a firing head  18 , perforating guns  20  and shock sensing tools  22 . 
     In other examples, the perforating string  12  may include more or less of these components. For example, well screens and/or gravel packing equipment may be provided, any number (including one) of the perforating guns  20  and shock sensing tools  22  may be provided, etc. Thus, it should be clearly understood that the well system  10  as depicted in  FIG. 1  is merely one example of a wide variety of possible well systems which can embody the principles of this disclosure. 
     One advantage of interconnecting the shock sensing tools  22  below the packer  16  and in close proximity to the perforating guns  20  is that more accurate measurements of strain and acceleration at the perforating guns can be obtained. Pressure and temperature sensors of the shock sensing tools  22  can also sense conditions in the wellbore  14  in close proximity to perforations  24  immediately after the perforations are formed, thereby facilitating more accurate analysis of characteristics of an earth formation  26  penetrated by the perforations. 
     A shock sensing tool  22  interconnected between the packer  16  and the upper perforating gun  20  can record the effects of perforating on the perforating string  12  above the perforating guns. This information can be useful in preventing unsetting or other damage to the packer  16 , firing head  18 , etc., due to detonation of the perforating guns  20  in future designs. 
     A shock sensing tool  22  interconnected between perforating guns  20  can record the effects of perforating on the perforating guns themselves. This information can be useful in preventing damage to components of the perforating guns  20  in future designs. 
     A shock sensing tool  22  can be connected below the lower perforating gun  20 , if desired, to record the effects of perforating at this location. In other examples, the perforating string  12  could be stabbed into a lower completion string, connected to a bridge plug or packer at the lower end of the perforating string, etc., in which case the information recorded by the lower shock sensing tool  22  could be useful in preventing damage to these components in future designs. 
     Viewed as a complete system, the placement of the shock sensing tools  22  longitudinally spaced apart along the perforating string  12  allows acquisition of data at various points in the system, which can be useful in validating a model of the system. Thus, collecting data above, between and below the guns, for example, can help in an understanding of the overall perforating event and its effects on the system as a whole. 
     The information obtained by the shock sensing tools  22  is not only useful for future designs, but can also be useful for current designs, for example, in post-job analysis, formation testing, etc. The applications for the information obtained by the shock sensing tools  22  are not limited at all to the specific examples described herein. 
     Referring additionally now to  FIGS. 2-5 , one example of the shock sensing tool  22  is representatively illustrated. As depicted in  FIG. 2 , the shock sensing tool  22  is provided with end connectors  28  (such as, perforating gun connectors, etc.) for interconnecting the tool in the perforating string  12  in the well system  10 . However, other types of connectors may be used, and the tool  22  may be used in other perforating strings and in other well systems, in keeping with the principles of this disclosure. 
     In  FIG. 3 , a cross-sectional view of the shock sensing tool  22  is representatively illustrated. In this view, it may be seen that the tool  22  includes a variety of sensors, and a detonation train  30  which extends through the interior of the tool. 
     The detonation train  30  can transfer detonation between perforating guns  20 , between a firing head (not shown) and a perforating gun, and/or between any other explosive components in the perforating string  12 . In the example of  FIGS. 2-5 , the detonation train  30  includes a detonating cord  32  and explosive boosters  34 , but other components may be used, if desired. 
     One or more pressure sensors  36  may be used to sense pressure in perforating guns, firing heads, etc., attached to the connectors  28 . Such pressure sensors  36  are preferably ruggedized (e.g., to withstand ˜20000 g acceleration) and capable of high bandwidth (e.g., &gt;20 kHz). The pressure sensors  36  are preferably capable of sensing up to ˜60 ksi (˜414 MPa) and withstanding ˜175 degrees C. Of course, pressure sensors having other specifications may be used, if desired. 
     Strain sensors  38  are attached to an inner surface of a generally tubular structure  40  interconnected between the connectors  28 . The structure  40  is preferably pressure balanced, i.e., with substantially no pressure differential being applied across the structure. 
     In particular, ports  42  are provided to equalize pressure between an interior and an exterior of the structure  40 . In the simplest embodiment, the ports  42  are open to allow filling of structure  40  with wellbore fluid. However, the ports  42  are preferably plugged with an elastomeric compound and the structure  40  is preferably pre-filled with a suitable substance (such as silicone oil, etc.) to isolate the sensitive strain sensors  38  from wellbore contaminants. By equalizing pressure across the structure  40 , the strain sensor  38  measurements are not influenced by any differential pressure across the structure before, during or after detonation of the perforating guns  20 . 
     The strain sensors  38  are preferably resistance wire-type strain gauges, although other types of strain sensors (e.g., piezoelectric, piezoresistive, fiber optic, etc.) may be used, if desired. In this example, the strain sensors  38  are mounted to a strip (such as a KAPTON™ strip) for precise alignment, and then are adhered to the interior of the structure  40 . 
     Preferably, four full Wheatstone bridges are used, with opposing 0 and 90 degree oriented strain sensors being used for sensing axial and bending strain, and +/−45 degree gauges being used for sensing torsional strain. 
     The strain sensors  38  can be made of a material (such as a KARMA™ alloy) which provides thermal compensation, and allows for operation up to ˜150 degrees C. Of course, any type or number of strain sensors may be used in keeping with the principles of this disclosure. 
     The strain sensors  38  are preferably used in a manner similar to that of a load cell or load sensor. A goal is to have all of the loads in the perforating string  12  passing through the structure  40  which is instrumented with the sensors  38 . 
     Having the structure  40  fluid pressure balanced enables the loads (e.g., axial, bending and torsional) to be measured by the sensors  38 , without influence of a pressure differential across the structure. In addition, the detonating cord  32  is housed in a tube  33  which is not rigidly secured at one or both of its ends, so that it does not share loads with, or impart any loading to, the structure  40 . 
     In other examples, the structure  40  may not be pressure balanced. A clean oil containment sleeve could be used with a pressure balancing piston. Alternatively, post-processing of data from an uncompensated strain measurement could be used in order to approximate the strain due to structural loads. This estimation would utilize internal and external pressure measurements to subtract the effect of the pressure loads on the strain gauges, as described for another configuration of the tool  22  below. 
     A temperature sensor  44  (such as a thermistor, thermocouple, etc.) can be used to monitor temperature external to the tool. Temperature measurements can be useful in evaluating characteristics of the formation  26 , and any fluid produced from the formation, immediately following detonation of the perforating guns  20 . Preferably, the temperature sensor  44  is capable of accurate high resolution measurements of temperatures up to ˜170 degrees C. 
     Another temperature sensor (not shown) may be included with an electronics package  46  positioned in an isolated chamber  48  of the tool  22 . In this manner, temperature within the tool  22  can be monitored, e.g., for diagnostic purposes or for thermal compensation of other sensors (for example, to correct for errors in sensor performance related to temperature change). Such a temperature sensor in the chamber  48  would not necessarily need the high resolution, responsiveness or ability to track changes in temperature quickly in wellbore fluid of the other temperature sensor  44 . 
     The electronics package  46  is connected to at least the strain sensors  38  via pressure isolating feed-throughs or bulkhead connectors  50 . Similar connectors may also be used for connecting other sensors to the electronics package  46 . Batteries  52  and/or another power source may be used to provide electrical power to the electronics package  46 . 
     The electronics package  46  and batteries  52  are preferably ruggedized and shock mounted in a manner enabling them to withstand shock loads with up to ˜10000 g acceleration. For example, the electronics package  46  and batteries  52  could be potted after assembly, etc. 
     In  FIG. 4  it may be seen that four of the connectors  50  are installed in a bulkhead  54  at one end of the structure  40 . In addition, a pressure sensor  56 , a temperature sensor  58  and an accelerometer  60  are preferably mounted to the bulkhead  54 . 
     The pressure sensor  56  is used to monitor pressure external to the tool  22 , for example, in an annulus  62  formed radially between the perforating string  12  and the wellbore  14  (see  FIG. 1 ). The pressure sensor  56  may be similar to the pressure sensors  36  described above. A suitable pressure transducer is the Kulite model HKM-15-500. 
     The temperature sensor  58  may be used for monitoring temperature within the tool  22 . This temperature sensor  58  may be used in place of, or in addition to, the temperature sensor described above as being included with the electronics package  46 . 
     The accelerometer  60  is preferably a piezoresistive type accelerometer, although other types of accelerometers may be used, if desired. Suitable accelerometers are available from Endevco and PCB (such as the PCB  3501 A series, which is available in single axis or triaxial packages, capable of sensing up to ˜60000 g acceleration). 
     In  FIG. 5 , another cross-sectional view of the tool  22  is representatively illustrated. In this view, the manner in which the pressure transducer  56  is ported to the exterior of the tool  22  can be clearly seen. Preferably, the pressure transducer  56  is close to an outer surface of the tool, so that distortion of measured pressure resulting from transmission of pressure waves through a long narrow passage is prevented. 
     Also visible in  FIG. 5  is a side port connector  64  which can be used for communication with the electronics package  46  after assembly. For example, a computer can be connected to the connector  64  for powering the electronics package  46 , extracting recorded sensor measurements from the electronics package, programming the electronics package to respond to a particular signal or to “wake up” after a selected time, otherwise communicating with or exchanging data with the electronics package, etc. 
     Note that it can be many hours or even days between assembly of the tool  22  and detonation of the perforating guns  20 . In order to preserve battery power, the electronics package  46  is preferably programmed to “sleep” (i.e., maintain a low power usage state), until a particular signal is received, or until a particular time period has elapsed. 
     The signal which “wakes” the electronics package  46  could be any type of pressure, temperature, acoustic, electromagnetic or other signal which can be detected by one or more of the sensors  36 ,  38 ,  44 ,  56 ,  58 ,  60 . For example, the pressure sensor  56  could detect when a certain pressure level has been achieved or applied external to the tool  22 , or when a particular series of pressure levels has been applied, etc. In response to the signal, the electronics package  46  can be activated to a higher measurement recording frequency, measurements from additional sensors can be recorded, etc. 
     As another example, the temperature sensor  58  could sense an elevated temperature resulting from installation of the tool  22  in the wellbore  14 . In response to this detection of elevated temperature, the electronics package  46  could “wake” to record measurements from more sensors and/or higher frequency sensor measurements. 
     As yet another example, the strain sensors  38  could detect a predetermined pattern of manipulations of the perforating string  12  (such as particular manipulations used to set the packer  16 ). In response to this detection of pipe manipulations, the electronics package  46  could “wake” to record measurements from more sensors and/or higher frequency sensor measurements. 
     The electronics package  46  depicted in  FIG. 3  preferably includes a non-volatile memory  66  so that, even if electrical power is no longer available (e.g., the batteries  52  are discharged), the previously recorded sensor measurements can still be downloaded when the tool  22  is later retrieved from the well. The non-volatile memory  66  may be any type of memory which retains stored information when powered off. This memory  66  could be electrically erasable programmable read only memory, flash memory, or any other type of non-volatile memory. The electronics package  46  is preferably able to collect and store data in the memory  66  at &gt;100 kHz sampling rate. 
     Referring additionally now to  FIGS. 6-8 , another configuration of the shock sensing tool  22  is representatively illustrated. In this configuration, a flow passage  68  (see  FIG. 7 ) extends longitudinally through the tool  22 . Thus, the tool  22  may be especially useful for interconnection between the packer  16  and the upper perforating gun  20 , although the tool  22  could be used in other positions and in other well systems in keeping with the principles of this disclosure. 
     In  FIG. 6  it may be seen that a removable cover  70  is used to house the electronics package  46 , batteries  52 , etc. In  FIG. 8 , the cover  70  is removed, and it may be seen that the temperature sensor  58  is included with the electronics package  46  in this example. The accelerometer  60  could also be part of the electronics package  46 , or could otherwise be located in the chamber  48  under the cover  70 . 
     A relatively thin protective sleeve  72  is used to prevent damage to the strain sensors  38 , which are attached to an exterior of the structure  40  (see  FIG. 8 , in which the sleeve is removed, so that the strain sensors are visible). Although in this example the structure  40  is not pressure balanced, another pressure sensor  74  (see  FIG. 7 ) can be used to monitor pressure in the passage  68 , so that any contribution of the pressure differential across the structure  40  to the strain sensed by the strain sensors  38  can be readily determined (e.g., the effective strain due to the pressure differential across the structure  40  is subtracted from the measured strain, to yield the strain due to structural loading alone). 
     Note that there is preferably no pressure differential across the sleeve  72 , and a suitable substance (such as silicone oil, etc.) is preferably used to fill the annular space between the sleeve and the structure  40 . The sleeve  72  is not rigidly secured at one or both of its ends, so that it does not share loads with, or impart loads to, the structure  40 . 
     Any of the sensors described above for use with the tool  22  configuration of  FIGS. 2-5  may also be used with the tool configuration of  FIGS. 6-8 . 
     In general, it is preferable for the structure  40  (in which loading is measured by the strain sensors  38 ) to experience dynamic loading due only to structural shock by way of being pressure balanced, as in the configuration of  FIGS. 2-5 . However, other configurations are possible in which this condition can be satisfied. For example, a pair of pressure isolating sleeves could be used, one external to, and the other internal to, the load bearing structure  40  of the  FIGS. 6-8  configuration. The sleeves could encapsulate air at atmospheric pressure on both sides of the structure  40 , effectively isolating the structure  40  from the loading effects of differential pressure. The sleeves should be strong enough to withstand the pressure in the well, and may be sealed with o-rings or other seals on both ends. The sleeves may be structurally connected to the tool at no more than one end, so that a secondary load path around the strain sensors  38  is prevented. 
     Although the perforating string  12  described above is of the type used in tubing-conveyed perforating, it should be clearly understood that the principles of this disclosure are not limited to tubing-conveyed perforating. Other types of perforating (such as, perforating via coiled tubing, wireline or slickline, etc.) may incorporate the principles described herein. Note that the packer  16  is not necessarily a part of the perforating string  12 . 
     It may now be fully appreciated that the above disclosure provides several advancements to the art. In the example of the shock sensing tool  22  described above, the effects of perforating can be conveniently measured in close proximity to the perforating guns  20 . 
     In particular, the above disclosure provides to the art a well system  10  which can comprise a perforating string  12  including multiple perforating guns  20  and at least one shock sensing tool  22 . The shock sensing tool  22  can be interconnected in the perforating string  12  between one of the perforating guns  20  and at least one of: a) another of the perforating guns  20 , and b) a firing head  18 . 
     The shock sensing tool  22  may be interconnected in the perforating string  12  between the firing head  18  and the perforating guns  20 . 
     The shock sensing tool  22  may be interconnected in the perforating string  12  between two of the perforating guns  20 . 
     Multiple shock sensing tools  22  can be longitudinally distributed along the perforating string  12 . 
     At least one of the perforating guns  20  may be interconnected in the perforating string  12  between two of the shock sensing tools  22 . 
     A detonation train  30  may extend through the shock sensing tool  22 . 
     The shock sensing tool  22  can include a strain sensor  38  which senses strain in a structure  40 . The structure  40  may be fluid pressure balanced. 
     The shock sensing tool  22  can include a sensor  38  which senses load in a structure  40 . The structure  40  may transmit all structural loading between the one of the perforating guns  20  and at least one of: a) the other of the perforating guns  20 , and b) the firing head  18 . 
     Both an interior and an exterior of the structure  40  may be exposed to pressure in an annulus  62  between the perforating string  12  and a wellbore  14 . The structure  40  may be isolated from pressure in the wellbore  14 . 
     The shock sensing tool  22  can include a pressure sensor  56  which senses pressure in an annulus  62  formed between the shock sensing tool  22  and a wellbore  14 . 
     The shock sensing tool  22  can include a pressure sensor  36  which senses pressure in one of the perforating guns  20 . 
     The shock sensing tool  22  may begin increased recording of sensor measurements in response to sensing a predetermined event. 
     Also described by the above disclosure is a shock sensing tool  22  for use with well perforating. The shock sensing tool  22  can include a generally tubular structure  40  which is fluid pressure balanced, at least one sensor  38  which senses load in the structure  40  and a pressure sensor  56  which senses pressure external to the structure  40 . 
     The at least one sensor  38  may comprise a combination of strain sensors which sense axial, bending and torsional strain in the structure  40 . 
     The shock sensing tool  22  can also include another pressure sensor  36  which senses pressure in a perforating gun  20  attached to the shock sensing tool  22 . 
     The shock sensing tool  22  can include an accelerometer  60  and/or a temperature sensor  44 ,  58 . 
     A detonation train  30  may extend through the structure  40 . 
     A flow passage  68  may extend through the structure  40 . 
     The shock sensing tool  22  may include a perforating gun connector  28  at an end of the shock sensing tool  22 . 
     The shock sensing tool  22  may include a non-volatile memory  66  which stores sensor measurements. 
     It is to be understood that the various embodiments described herein may be utilized in various orientations, such as inclined, inverted, horizontal, vertical, etc., and in various configurations, without departing from the principles of the present disclosure. The embodiments are described merely as examples of useful applications of the principles of the disclosure, which is not limited to any specific details of these embodiments. 
     In the above description of the representative embodiments, directional terms, such as “above,” “below,” “upper,” “lower,” etc., are used for convenience in referring to the accompanying drawings. In general, “above,” “upper,” “upward” and similar terms refer to a direction toward the earth&#39;s surface along a wellbore, and “below,” “lower,” “downward” and similar terms refer to a direction away from the earth&#39;s surface along the wellbore. 
     Of course, a person skilled in the art would, upon a careful consideration of the above description of representative embodiments of the disclosure, readily appreciate that many modifications, additions, substitutions, deletions, and other changes may be made to the specific embodiments, and such changes are contemplated by the principles of the present disclosure. Accordingly, the foregoing detailed description is to be clearly understood as being given by way of illustration and example only, the spirit and scope of the present invention being limited solely by the appended claims and their equivalents.