Abstract:
A coring apparatus is provided having an outer core barrel associated with a drill bit; an inner core barrel adapted to accept a core sample; and one or more sensors adapted to provide data relating to downhole conditions. The sensor may be selected from the group of: a strain sensor adapted to measure tension and/or compression experienced by the inner core barrel; a first pressure sensor adapted to measure pressure outwith the inner barrel and a second pressure sensor adapted to measure pressure within the inner barrel; a rotation sensor adapted to measure relative rotation between the inner core barrel and the outer core barrel; and a vibration sensor adapted to measure vibration experienced by the inner barrel. Methods of monitoring a coring operation and a method of gathering information about a coring operation are also provided.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application claims priority of United Kingdom Patent Application No. 0724972.5 filed on Dec. 21, 2007. 
       DESCRIPTION OF THE RELATED ART  
       [0002]    The present invention relates to apparatus and a method for obtaining a sample, such as a core sample, from a subterranean formation such as those found in an oil and/or gas reservoir. More particularly, it relates to a method of monitoring core barrel operations and a core barrel monitoring apparatus. 
         [0003]    Extracting core samples from subterranean formations is an important aspect of the drilling process in the oil and gas industry. The samples provide geological and geophysical data, enabling a reservoir model to be established. Core samples are typically retrieved using coring equipment, which is transported to a laboratory where tests can be conducted on the core sample. The coring equipment typically includes a core barrel provided with a drill bit on the lower end thereof. In use, the core barrel and drill bit are rotated such that the drill bit cuts into the formation and the sample to be retrieved enters into the inner bore of the core barrel within which it will be entrapped and brought to the surface of the well, at which point where it can be taken to a laboratory to be analysed. 
         [0004]    However, a major problem when coring is that the core sample can become jammed or can collapse in the barrel and so instead of obtaining for example a 30 metre core within a 30 metre core barrel, only a few metres of core may be obtained within the inner bore of the core barrel if it jams and accordingly that 30 metre potential core sample is lost forever. 
         [0005]    In recent years there have been some attempts to monitor the entry of a core into the barrel and one recent prior art system for doing so is disclosed in International PCT Patent Publication No. WO2006/058377 and which uses a core sample marker (32) (or “rabbit” as such equipment is known in the industry) located inside the inner core barrel 16 (see FIG. 4). As the core enters the inner barrel (16), the core pushes the rabbit (32) upwards and such upward movement is observed by using longitudinally spaced apart length markers (36, 38) and a location sensor (34). Accordingly, the distance travelled by the rabbit (32) can be transmitted in a signal to a signal receiver at the surface of the well. However, although there is some disclosure of providing a pressure sensor, a temperature sensor and possibly a rotational sensor, the information that can be sent to the operator at the surface is substantially limited to monitoring the entry of the core sample into the inner barrel and therefore it is not possible to foresee if a jam is likely to occur with the prior art system shown in PCT Publication No. WO2006/058377. Furthermore, the core barrel apparatus shown in International PCT Publication No. WO2006/058377 suffers from the disadvantage that the rabbit (32) will inherently to some extent inhibit the entry of the core sample into the inner core barrel. 
       SUMMARY OF THE INVENTION  
       [0006]    According to the present invention there is provided a coring apparatus comprising: 
         [0007]    an outer core barrel associated with a drill bit; 
         [0008]    an inner core barrel adapted to accept a core sample; and 
         [0009]    one or more sensors adapted to provide data relating to downhole conditions, the one or more sensors selected from the group of:
       a) a strain sensor adapted to measure tension and/or compression experienced by the inner core barrel;   b) a first pressure sensor adapted to measure pressure outwith the inner barrel and a second pressure sensor adapted to measure pressure within the inner barrel;   c) a rotation sensor adapted to measure relative rotation between the inner core barrel and the outer core barrel; and   d) a vibration sensor adapted to measure vibration experienced by the inner barrel.       
 
         [0014]    Optionally, the coring apparatus further comprises: 
         [0015]    e) a temperature sensor adapted to measure the downhole temperature. 
         [0016]    Optionally, the coring apparatus comprises two of sensors a) to d) and more preferably the coring apparatus comprises three of sensors a) to d) and most preferably the coring apparatus comprises all four sensors a) to d). 
         [0017]    Optionally, sensor a) is located on or embedded within a side wall of the inner core barrel. 
         [0018]    In one embodiment, the coring apparatus comprises sensor b) and further includes an electronics housing with a lower end, wherein the inner core barrel includes a side wall and wherein the first pressure sensor is provided on the lower end of the electronics housing in fluid communication with the interior of the inner core barrel and the second pressure sensor is provided on or embedded within a side wall of the inner core barrel and is in fluid communication with the exterior of the inner core barrel. 
         [0019]    Optionally, the coring apparatus comprises sensor c) wherein the coring apparatus includes an electronics housing and sensor c) is provided in the electronics housing. 
         [0020]    In one embodiment, sensor d) is mounted on the inner core barrel. 
         [0021]    In another embodiment, the coring apparatus further comprises a data transmission means to transmit the data received from the one or more sensors to an operator at the surface. In an alternative embodiment, the apparatus comprises a data memory device capable of collecting and storing data output from the one or more sensors such that the data can be analysed back at the surface when the coring apparatus and core sample are retrieved back to surface in order to provide information on the downhole conditions experienced when the core sample was obtained. 
         [0022]    In a further embodiment, the coring apparatus comprises sensor b) and further includes a pressure release mechanism operable to release pressure from within the inner core barrel if the pressure differential between the inner and outer core barrels exceeds a pre-determined level. 
         [0023]    According to a first aspect of the present invention there is provided a method of monitoring a coring operation comprising: 
         [0024]    providing a coring apparatus having one or more sensors associated therewith; 
         [0025]    inserting the coring apparatus into a downhole borehole; and 
         [0026]    collecting data output from the one or more sensors and transmitting it to the surface, said data being indicative of downhole conditions, such that the operator is provided with real time data of the coring operation. 
         [0027]    According to a second aspect of the present invention there is provided a method of gathering information about a coring operation comprising: 
         [0028]    providing a coring apparatus having one or more sensors associated therewith and a data memory device; 
         [0029]    inserting the coring apparatus into a downhole borehole, and collecting data output from the one or more sensors and storing it in the data memory device; and 
         [0030]    retrieving the coring apparatus and a core sample back to surface and analysing the data stored in the data memory device to provide information on the downhole conditions experienced when the core sample was obtained. 
         [0031]    In one embodiment, the coring apparatus used in the methods of the invention comprises one or more sensors selected from the group consisting of: 
         [0032]    a) a strain sensor adapted to measure tension and/or compression experienced by the inner core barrel; 
         [0033]    b) a first pressure sensor adapted to measure pressure outwith the inner barrel and a second pressure sensor adapted to measure pressure within the inner barrel; 
         [0034]    c) a rotation sensor adapted to measure relative rotation between the inner core barrel and the outer core barrel; and 
         [0035]    d) a vibration sensor adapted to measure vibration experienced by the inner barrel. 
         [0036]    Typically, the apparatus further comprises a first fluid pathway therethrough, wherein the first fluid pathway is typically located in between the inner and outer core barrel. Typically, the apparatus further comprises a second fluid pathway therethrough where the second fluid pathway is typically selectively obturable, such as by means of an object dropped from the surface of the well, where the object may be a drop ball or the like. The second fluid pathway may connect the interior of the inner core barrel with the exterior of the apparatus. The first fluid pathway typically provides a pathway for fluid, such as drilling mud pumped from the surface, to carry drill debris away from the apparatus and the second fluid pathway typically provides a pathway to clear drill debris from the interior of the inner barrel. Typically, the second fluid pathway is formed through the length of the electronics housing. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0037]    Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: 
           [0038]      FIG. 1  is a cross-sectional schematic view of a coring apparatus in accordance with the present invention; 
           [0039]      FIG. 2  is a perspective cross-sectional view of an electronics housing which forms part of the coring apparatus of  FIG. 1 ; and 
           [0040]      FIG. 3  is an exploded perspective view of the electronics housing, electronics board and electronics head which together make up part of the coring apparatus of  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION  
       [0041]      FIG. 1  is a schematic view of a core barrel apparatus  10  in accordance with the present invention. The core barrel  10  comprises an outer core barrel  12  and an inner core barrel  14  which is rotatable with respect to the outer core barrel  12  via a rotatable bearing  13 . The core barrel  10  comprises a threaded pin connection  16  at its uppermost end for connection to the lower end of a drillstring such that the core barrel  10  can be run into a downhole borehole on the lower end of the drillstring (not shown). The core barrel  10  further comprises a drill bit  18  located at its lowermost end for cutting into a hydrocarbon reservoir and associated surrounding formation when a core sample is desired. 
         [0042]    The core barrel  10  furthermore comprises a number of sensors as follows: 
         [0043]    a) Strain (Tension/Compression) Sensors 
         [0044]    One or more strain meters  22  are located on or are preferably embedded or otherwise formed or provided in the side wall of the inner barrel  14  such that the strain meters  22  act to provide a measurement of the tension or compression experienced by the inner barrel  14 . Because the inner barrel  14  is hung from the rest of the core barrel  10  by means of the rotational bearing  13 , the strain meters  22  will normally be in tension. However, once the core sample (not shown) starts to enter the inner core barrel  14 , the strain meters  22  will experience less tension and may even experience compression because of the friction created between the core sample and the inner surface of the inner core barrel  14 ; in this regard, the inner diameter of the inner core barrel is intentionally chosen to be around the same as the inner diameter of the throughbore of the drill bit  18 . Accordingly, in use, the output of the strain meters  22  is indicative of entry of a core sample into the inner core barrel  14 . 
         [0045]    b) Pressure Sensors 
         [0046]    Two or more pressure sensors  24 L,  24 U are provided with two being shown in  FIGS. 1 ,  2  and  3 . The first pressure sensor  24 L is provided on the lower end of the electronics housing  20  such that the lower pressure sensor  24 L senses the pressure within the inner core barrel  14 . An upper pressure sensor  24 U is also provided on or embedded within the sidewall of the inner core barrel  14  but is in fluid communication with the exterior of the inner core barrel  14  and senses the pressure within the outer barrel  12  but outwith the inner core barrel  14 ; in other words, the upper pressure sensor  24 U senses the pressure in the annulus between the outer surface of the inner core barrel  14  and the inner surface of the outer core barrel  12 . Accordingly, the pair of pressure sensors  24 L,  24 U can be used to sense any difference in pressure between the interior of the inner core barrel  14  and outside of the inner barrel  14 . Consequently, when a core sample enters the inner core barrel  14 , the pressure within the rest of the inner core barrel  14  will start to increase because the fluid located therein will have to be squeezed out. The pressure on the outside of the inner barrel  14  is always higher than the pressure on the inside of the inner barrel  14 . As the core enters the interior  15  of the inner core barrel  14 , the pressure on the inside  15  of the inner barrel  14  increases and the monitoring of the pressure fluctuation on the inside of the inner barrel  14  will provide information on the coring process. For example, if hydraulic jamming occurs (i.e. the core acting as a sealed piston on the inside of the inner barrel  14 ), the pressure will increase until it is able to lift the ball  25  seated at the top of the inner barrel  14 . When this happens, the pressure seen by sensors  24 L and  24 U will be equal. As explained below, ball  25  seals off the fluid pathway via conduit  34  used to clean debris from the apparatus  10  prior to initiation of a coring operation. 
         [0047]    Ordinarily, with no sample located in the inner core barrel  14 , the pressure at sensor  24 U will likely be greater than the pressure sensed by sensor  24 L because of the downhole fluid pressure; as a result of the pressure drop created by the mud flow,  24 U is always higher than  24 L. However, if a hydraulic jam occurs in the inner core barrel  14 , then the pressure sensed by the sensor  24 L will increase and may become equal to the pressure sensed by the sensor  24 U. 
         [0048]    c) Rotatable Bearing Sensor 
         [0049]    The rotatable bearing  13  is also provided with a sensor  26 , the output of which is indicative of rotational movement occurring between the inner core barrel  14  and the outer core barrel  12 . In other words, the rotatable bearing sensor  26  measures relative rotation occurring between the inner core barrel  14  and the outer core barrel  12 . Ordinarily, when there is no core sample located within the inner barrel  14 , the inner core barrel  14  will usually rotate with the outer core barrel  12  due to the presence of some level of friction in the bearing  13 . However, when a core sample starts to enter the inner core barrel  14 , the friction generated between the core sample and the inner surface of the inner core barrel  14  will tend to prevent rotation of the inner core barrel  14  relative to the core sample and can even stop any rotation occurring at all. Consequently, the rotatable bearing sensor  26  will see high levels of relative rotation occurring between the inner core barrel  14  and the outer core barrel  12  and therefore such high relative rotation is indicative of a core sample entering or being located within the inner core barrel  14 . 
         [0050]    Accordingly, particularly by measuring the relative rotation between the inner core barrel  14  and the outer core barrel  12 , the operator will be able to tell when a jam is likely to occur because in such a situation the inner core barrel  14  will likely stop rotating completely. Accordingly, the operator will then have the opportunity to manage the coring operation in a much better way compared to conventional systems in that he will be able to change how the coring operation is conducted. For example, he could take the decision to reduce the weight on bit (WOB) or increase WOB or increase or decrease the flow rate of drilling muds that are used etc. 
         [0051]    It is known that high rotation of the inner barrel  14  is detrimental to the core entry as it can induce jamming and also damage the core. Accordingly, being able to monitor the relative rotation will allow the operator to adapt the parameters to minimise the risk of damage to the core. 
         [0052]    d) Vibration Sensors 
         [0053]    One or more vibration sensors  28  are mounted on the inner core barrel  14 , the output of which is indicative of any vibration being sensed in the inner core barrel  14 . Vibrations are very detrimental to the coring process and to the quality of the core sample because they can damage the core sample and therefore could induce a jam occurring between the core sample and the inner core barrel  14 . Furthermore, a high level of vibration might be induced by resonance and might be dampened by a change of parameters. 
         [0054]    e) Temperature Sensor 
         [0055]    A temperature sensor is also provided in the electronics housing  20  and is particularly included to permit the operator to calibrate the rest of the sensor readings because, for example, the pressure sensor outputs  24 L,  24 U will vary depending on the ambient temperature. Furthermore, it is useful for the operator to know what the downhole temperature is. 
         [0056]    Suitable connections/wiring (not shown) is provided to connect all the aforementioned sensors to the electronics board  32 . 
         [0057]    As shown in  FIG. 1 , an electronics board  32  is provided to process all the data received from the sensors a) to e) described above and to transmit it using conventional data transmitting means (such as a radio transmitter (not shown)) back to the surface so that the operator can see the output from the various sensors a) to e) in real time. This provides a great advantage over the prior art systems in that the operator then has the opportunity to change the coring operation depending upon the downhole conditions as sensed by the various sensors a) to e). 
         [0058]    Alternatively, the data transmitting means (not shown) could be omitted and instead all data could be stored on inboard memory provided on the electronics board  32  (in the same way that an aeroplane black box recorder operates to store data for later analysis). 
         [0059]      FIG. 2  also shows that the electronics housing  20  is provided with a conduit  34  formed all the way longitudinally through it where the conduit  34  provides a flow path for drilling mud such that the drilling mud that is required for the cleaning of the inner barrel  14  (prior to the start of the coring operations) can pass through the electronics housing  20  without coming into contact with the electronics board  32 . 
         [0060]    Prior to the start of a coring apparatus, such as when the apparatus  10  is being run into the well, ball  25  is not in place. As a consequence, two fluid flow paths are provided in the apparatus  10  both primarily for use in a running in configuration: conduit  34  and annulus  36 . Annulus  36 , as shown in  FIG. 1 , is provided between the inner and the outer core barrel. 
         [0061]    In the absence of ball  25 , drilling mud and fluid is able to flow through annulus  36  and through conduit  34 . The portion of the fluid flowing through conduit  34  can enter inside the inner core barrel  24  to clean away any debris which may have accumulated. Once cleaning of the inner core barrel is complete, ball  25  is dropped from the surface and when in position as shown in  FIG. 1 , closes fluid flow through conduit  34 . Thus, when ball  25  is in place, as shown in  FIG. 1 , i.e. when cleaning is complete or during a coring operation, any mud being pumped from the surface through the coring apparatus  10 , flows through the annulus  36  provided between the inner, and outer, core barrel. 
         [0062]    Modifications and improvements may be made to the embodiments described herein without departing from the scope of the invention.