Abstract:
In one embodiment an apparatus is disclosed that includes a tool in a wellbore. A probe is extendable from the tool to contact a wall of a formation surrounding the wellbore. A tube substantially surrounds the probe wherein the tube is extendable into the formation surrounding the wellbore. In another embodiment a method for reducing contamination of a sample of a formation fluid is disclosed that includes extending a probe to contact a wall of a formation. A barrier tube that substantially surrounds the probe is extended into the formation thereby restricting a flow of a contaminated reservoir fluid that would otherwise come from near-wellbore regions above and below the probe from going toward the probe.

Description:
BACKGROUND OF THE INVENTION  
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to the field of downhole formation testing. 
         [0003]    2. Background Information 
         [0004]    Oil and gas companies spend large sums of money to find hydrocarbon deposits. Oil companies drill exploration wells in their most promising prospects and use these exploration wells, not only to determine whether hydrocarbons are present but also to determine the properties of those hydrocarbons, which are present. 
         [0005]    To determine hydrocarbon properties, oil and gas companies often withdraw some hydrocarbons from the well. Wireline formation testers can be lowered into the well for this purpose. Initially, fluids that are withdrawn may be highly contaminated by filtrates of the fluids (“muds”) that were used during drilling. To obtain samples that are sufficiently clean (usually &lt;10% contamination) so that the sample will provide meaningful lab data concerning the formation, formation fluids are generally pumped from the wellbore for 30-90 minutes, while clean up is being monitored in real time. For some properties, samples can be analyzed downhole in real time. The present invention relates both to monitoring sample clean up and to performing downhole analysis of samples at reservoir conditions of temperature and pressure. A downhole environment is a difficult one in which to operate a sensor. Measuring instruments in the downhole environment must operate under extreme conditions and limited space within a tool&#39;s pressure housing, including elevated temperatures, extreme vibration, and shock. 
       SUMMARY OF THE INVENTION  
       [0006]    In a particular embodiment an apparatus is disclosed. The apparatus includes a tool positioned in a wellbore, a probe extendable from the tool to contact a wall of a formation surrounding the wellbore, and a tube substantially surrounding the probe wherein the tube is extendable into the formation surrounding the wellbore. 
         [0007]    In one aspect of the present invention, a tool is provided for traversing a wellbore. A probe is extendable from the tool to contact a wall of a wellbore drilled into a formation surrounding the wellbore. The tool further includes a tube which substantially surrounds the probe wherein the tube is extendable into the wall of the wellbore and into the formation surrounding the wellbore. 
         [0008]    In another aspect, a method for reducing contamination of a sample of a formation fluid is disclosed including extending a probe to contact a wall of a formation. A barrier tube that substantially surrounds the probe is extended into the formation thereby restricting a flow of a contaminated reservoir fluid toward the probe. 
         [0009]    In another particular embodiment the formation comprises an unconsolidated formation. In another particular embodiment the apparatus further includes a pump hydraulically coupled to the probe and in fluid communication with the formation. In another particular embodiment the apparatus further includes a drive system in mechanical communication with the tube. In another particular embodiment the apparatus wherein the drive system further comprises a linear drive system to push the tube into the formation. In another particular embodiment the drive system includes a rotary drive system acting cooperatively with a linear drive system to enhance extension of the tube into the formation. In another particular embodiment the apparatus wherein the tube has a shaped end to enhance penetration into the formation. 
         [0010]    In another particular embodiment the apparatus further includes a vibratory source coupled to the barrier tube to enhance penetration of the barrier tube into the formation. In another particular embodiment the tool is conveyed into the wellbore by a wireline, a coiled tubing, or a drill string. In another particular embodiment the apparatus further includes a sensor in the tool detecting fluid contamination. In another particular embodiment the apparatus wherein the sensor is chosen from the group consisting of: a fluid density sensor, an acoustic sensor, and an optical sensor spectrometer. In another particular embodiment the apparatus further includes a sensor in the tool detecting contamination of a fluid sample and a controller acting under programmed instructions to extend the barrier tube into the formation based on the detected contamination of the fluid sample. 
         [0011]    In a particular embodiment a method is disclosed for reducing contamination of a sample of a formation fluid. The method includes extending a probe to contact a wall of a formation and extending a barrier tube that substantially surrounds the probe into the formation thereby restricting a flow of a contaminated formation fluid toward the probe. In another particular embodiment the method further includes sensing a parameter of interest related to contamination of a sample fluid drawn into the tool. In another particular embodiment the method further includes controlling the extension of the tube into the formation in response to the sensed contamination. In another particular embodiment the method further includes vibrating the tube to enhance penetration into the formation. 
         [0012]    In another particular embodiment the method further includes shaping an end of the tube to enhance penetration into the formation. In another particular embodiment the method further includes rotating the tube to enhance penetration into the formation. In another particular embodiment the method further includes conveying the tool into the wellbore using at least one of: a wireline, a coiled tubing, and a drill string. 
         [0013]    Examples of certain aspects of the invention have been summarized here rather broadly in order that the detailed description thereof that follows may be better understood and in order that the contributions they represent to the art may be appreciated. There are, of course, additional features of the invention that will be described hereinafter. 
     
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0014]    For a detailed understanding of the present invention, references should be made to the following detailed description of the exemplary embodiment, taken in conjunction with the accompanying drawings, in which like elements have been given like numerals, wherein: 
           [0015]      FIG. 1  shows an illustrative embodiment of a formation deployed in a downhole environment; 
           [0016]      FIG. 2  shows a non-limiting illustrative embodiment of a cross section of a formation test tool acquiring a sample and having a barrier tube penetrating a formation; 
           [0017]      FIGS. 3-5  show non-limiting examples of a penetrating end of a barrier tube; and 
           [0018]      FIG. 6  shows a non-limiting flow chart for collecting formation fluid samples according to in an illustrative embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0019]      FIG. 1  shows an illustrative embodiment of the present invention deployed in borehole  130  that passes through formation zone “A”. Formation zone “A” has a formation fluid  155  therein. Borehole  130  has working fluid  131  therein. Working fluid  131  may be a drilling fluid, a completion fluid, or any other suitable fluid as used in well drilling and completion. In one embodiment, formation zone “A” may comprise an unconsolidated formation having an invaded region  125  and an un-invaded region  135 . As used herein, an unconsolidated formation comprises sediment not cementitiously bonded together, and may consist of sand, silt, clay, and organic material. 
         [0020]    Working fluid  131  may invade the formation surrounding a wellbore, with the invasion depth being variable. Fluid  156  in invaded zone  125  may be a contaminated mixture of formation fluid  155  from un-invaded region  135  and working fluid  131 . As used herein, formation fluid means fluid that is substantially un-contaminated by fluid invasion from the wellbore. Formation fluid  155  may comprise water and/or hydrocarbon fluids. Formation hydrocarbon fluids may include hydrocarbon liquids and/or hydrocarbon gases of various compositions. Formation fluid  155  may be connate formation fluid. As used herein, connate formation fluid is formation fluid trapped in the formation at the time of the forming of the formation. 
         [0021]    As shown in  FIG. 1 , in one non-limiting embodiment, downhole tool  145  is deployed in borehole  130  on member  110 . Deployment member  110  may be a wireline, slick line, drill string, or coiled tubing. Downhole tool  145  may be a formation test tool for retrieving a sample of formation fluid  155  from formation “A”. Any suitable fluid sampling tool is intended to be encompassed by the present invention. Surface controller  202  is in data and/or power communication with downhole tool  145 . Surface controller  202  includes communication system  204  in communication with processor  206  and an input/output device  208 . The input/out device  208  may be a typical terminal for user inputs. A display such as a monitor or graphical user interface, not shown, may be included for real time user interface. When hard-copy reports are desired, a printer may be used. Storage media such as CD, DVD, tape, disk, or any other suitable storage media may be used to store data retrieved from downhole for future analyses. Processor  206  may be used for encoding commands to be transmitted downhole and for processing decoding data received from downhole via communication system  204 . In addition, processor  206  may be used for analyzing the data received from downhole. Surface communication system  204  may include a receiver for receiving data transmitted from downhole and transferring the data to processor  206  for evaluation, recording, and display. A transmitter may also be included with communication system  204  to send commands to the downhole components. Data may be transmitted between the surface and downhole tool using any suitable transmission scheme. The transmission scheme may be dependent on the type of deployment method used. Transmission schemes include, but are not limited to: hardwire telemetry, mud pulse telemetry, acoustic telemetry, and electromagnetic telemetry. 
         [0022]    As also shown in  FIG. 1 , downhole tool  145  has extendable probe  150  and opposing anchor arms  140 . Extendable probe  150  is extendable to contact wall  115  of borehole  130 . A sample of fluid is extracted from formation zone “A”. As shown in  FIG.1 , both formation fluid  155  and contaminated fluid  156  flow toward probe  150  possibly resulting in the extraction of a contaminated sample. 
         [0023]      FIG. 2  shows another illustrative embodiment of a downhole tool  245  that may comprise a formation tester. As shown in  FIG. 2 , downhole tool  245  comprises communication and power unit  212  and includes a transmitter and receiver for two-way communication with the surface controller  202  using transmission schemes similar to those previously described. Connected to the communication and power unit  212  is downhole controller  214 . In one embodiment, downhole controller  214  comprises processor  126  and memory  127 . Downhole controller  214  may use commands stored in downhole controller  214 , surface-initiated commands, or a combination of the two to control the downhole components. 
         [0024]    As shown in  FIG. 2 , probe  255  extends to wall  115  of borehole  130  that has working fluid  131  therein. Probe  255  has flow passage  260  for extracting a sample of formation fluid  155  from formation zone “A”. A sample of formation fluid is drawn through flow passage  260  and through flow line  236  by pump  338 . Pump  338  discharges fluid samples to valve assembly  239 . Valve assembly  239  may be actuated by controller  214  to direct the fluid sample to sample chamber  242 . Sample chamber  242  may comprise multiple sample chambers for taking multiple samples in one downhole deployment. Samples may also be taken at multiple depths in other formation zones of interest. Contaminated fluid samples may be diverted to borehole  130 . 
         [0025]    A sensor  261  in line  236  may detect a parameter of interest of the fluid sample related to the level of contamination in the fluid sample. Such a parameter of interest may include, but is not limited to: sample fluid density; sample fluid resistivity; sample fluid acoustic velocity; sample fluid optical emission spectra; and sample fluid optical transmission spectra. Examples of sensor  261  include, but are not limited to: a fluid density sensor, an acoustic sensor, and an optical sensor and optical spectrometer. Sensor  261  may comprise a suite of sensors measuring several of the indicated parameters of interest. Signals from sensor  261  may be used by downhole controller  214  to determine when a fluid sample is sufficiently un-contaminated for collection and/or further downhole analysis. In one embodiment, downhole controller  214  acts according to programmed instructions and cooperatively with sensor  261  to determine when a fluid sample is suitable for collection, and actuates valve assembly  239  to divert the fluid sample to sample chamber  242 . Alternatively, signals from sensor  261  may be transmitted to surface controller  202  which then analyzes the fluid sample and directs the collection of fluid samples downhole. 
         [0026]    As further shown in  FIG. 2 , barrier tube  250  substantially surrounds probe  255 . Barrier tube  250  is extendable into formation zone “A”. In one non-limiting embodiment, barrier tube  250  and probe  255  are arranged in a substantially concentric arrangement, as shown in  FIG. 2 . Barrier tube  250  may be extended by any drive system suited for providing a force sufficient for extending barrier tube  250  into formation zone “A”. Drive systems suitable for such a task include, but are not limited to, a hydraulic system, a mechanical gear driven system, an electro-mechanical system, and an electromagnetic system. In one example, as shown in  FIG. 2 , hydraulic drive system  241  comprises a hydraulic pump  242  which may be controlled by controller  214 . Hydraulic pump  242  provides hydraulic fluid to the appropriate channels in cylinder housing  237  to extend probe  255  and/or barrier tube  250  to their operable positions for taking a fluid sample. The hydraulic pressure from hydraulic pump  242  may be controlled to control the force exerted on probe  255  and barrier tube  250 . The end  251  of barrier tube  250  may be shaped to provide more effective penetration of formation zone “A”, as discussed below. Alternatively, other drive systems may be used, such as, for example, a ball-screw actuator. Other examples of drive systems include, but are not limited to: a linear motor drive power system, and a solenoid driven power system. Barrier tube  250  may also be rotated during extension using a rotary drive system (not shown) to facilitate penetration into the formation through the borehole wall. 
         [0027]    The extension of barrier tube  250  into formation zone “A” restricts flow of contaminated fluid  156  from invaded region  125  into extended probe  255 . As one skilled in the art will appreciate, the thickness of contaminated region  125  is dependent on formation properties and working fluid properties. In some cases, barrier tube  250  may extend entirely through contaminated region  125 , as shown in  FIG. 2 . In this case, substantially all of the flow of contaminated fluid  156  from invaded region  125  may be precluded from entering probe  255  with formation fluid  155 . In other cases, the invaded region may extend to a depth deeper than barrier tube  250  can reach. However, even when barrier tube  250  does not extend completely through contaminated region  125 , at least a portion of contaminated fluid  156  is restricted from entering probe  255  and contaminating a formation fluid sample. 
         [0028]    In another non-limiting embodiment, downhole controller  214  acts cooperatively with sensor  261  to extend barrier tube  250  into formation zone “A” until an acceptably uncontaminated sample is detected by sensor  261 , or until barrier tube  250  reaches maximum extension. 
         [0029]    In one illustrative embodiment, still referring to  FIG. 2 , a piezoelectric element  264  is coupled to barrier tube  250 . Piezoelectric element  264  couples vibratory motion into barrier tube  250  which may enhance the movement of barrier tube  250  through formation zone “A”. Piezoelectric element  264  is connected through conductor  262  to downhole controller  214 . Downhole controller  214  may control the activation of piezoelectric element  262  in a feedback loop based on the amount of power required to extend barrier tube  250  into formation zone “A”. 
         [0030]    Penetration of formation zone “A” is enhanced by shaping end  251  of barrier tube  250  as shown in the non-limiting examples of  FIGS. 3-5 .  FIG. 3  shows end  251  of barrier tube  250  having a contoured end with both an internally beveled surface  276  having an angle, α, and an externally beveled surface having an angle, β. Each of angles α and β may have a different value in the range of about 0° to about 45°. The thickness “t” of the wall of barrier tube  255  may be in the range from about 0.13 mm (0.005 in) to about 6.35 mm (0.25 in). The beveled surfaces  276  and  277  may have a hard coating to improve abrasion resistance. Such coating may include, but is not limited: tungsten carbide coating and diamond coating. 
         [0031]      FIG. 4  shows another embodiment of end  251 ′ of barrier tube  250 . End  251 ′ has a single internal bevel with an angle, θ. Angle θ has a value in the range from about 0° to about 45°.  FIG. 5  shows yet another embodiment of end  251 ″ of barrier tube  250 . End  251 ″ has a single external bevel with an angle, θ′. Angle θ has a value in the range from about 0° to about 45°. While the ends  251 ,  251 ′, and  251 ″ of barrier tube are shown in  FIGS. 3-5  as solid ends, it is contemplated that the present invention also encompass a serrated configuration around the periphery of ends  251 ,  251 ′, and  251 ″. 
         [0032]    Computer simulations were done of the barrier tube concept based on round sand grains having sizes of 0.020 inch to 0.035 inch that were held together by 500 psi of differential pressure. A friction coefficient of 0.3 between the barrier tube wall and the grains was assumed. In this simulation, the grains were not cemented to each other so as to represent an unconsolidated sand. The edge of the barrier tube was beveled like a razor blade. Entry force plots were prepared for barrier tubes having tube wall thickness of 0.010 inch, 0.040 inch and 0.160 inch. 
         [0033]    The peak forces for penetration for the different thickness of tube wall were not very different. These peak forces were associated with the tip of the tube edge running into a grain and having to push it out of the way to the side and the force required to do that does not change much with tube wall thickness. Once a blocking grain was out of the way, there was a “background” force for continuing to push the barrier tube into the formation. This background force changes significantly with barrier tube wall thickness. For a 0.010-inch thick tube wall, the background force was around 15 pounds per inch of tube wall edge. For a 0.040-inch thick tube wall, the background force reached about 50 to 70 pounds per inch of tube wall edge. For a 0.160-inch thick tube wall, it was on the order of 400 pounds per inch tube wall edge. The background force increases with tube wall thickness because: (1) friction on the side walls increases because the lateral forces are higher as the wall thickness increases and (2) the thicker walls have to displace a larger volume of grains. 
         [0034]    In principle, the thinner the barrier tube wall, the easier the penetration of the formation. However, in practice, a 0.010 inch wall may buckle under load depending on the material of which it is constructed. To reduce the likelihood of buckling, the wall of the tube could be corrugated. A wall thickness in the range of 0.030″ to 0.050″ range would be stronger without increasing the penetration force too much. The thicker wall barrier tube could also be corrugated for added strength. The barrier tube could optionally be a disposable item that is left in place and not retrieved from the formation. 
         [0035]    Turning now to  FIG. 7 , a flow chart  700  is shown wherein an illustrative embodiment probe is extended to contact a formation at block  715 . A barrier tube is extended into the formation at block  720 . Fluid is withdrawn from the formation at block  725 . Uncontaminated formation fluid is detected at block  730 . A formation fluid sample is collected at block  740  and the process ends. 
         [0036]    While the foregoing disclosure is directed to the exemplary embodiments of the invention, various modifications will be apparent to those skilled in the art. It is intended that all variations within the scope of the appended claims be embraced by the foregoing disclosure.