Abstract:
Apparatus and methods for downhole formation testing including use of a probe having inner and outer channels adapted to collect or inject injecting fluids from or to a formation accessed by a borehole. The probe straddles one or more layers in laminated or fractured formations and uses the inner channels to collect fluid.

Description:
FIELD 
       [0001]    The subject matter relates to underground formation investigation, and more particularly, apparatus and methods for formation testing and fluid sampling within a borehole. 
       BACKGROUND 
       [0002]    The oil and gas industry typically conducts comprehensive evaluation of underground hydrocarbon reservoirs prior to their development. Formation evaluation procedures generally involve collection of formation fluid samples for analysis of their hydrocarbon content, estimation of the formation permeability and directional uniformity, determination of the formation fluid pressure, and many others. Measurements of such parameters of the geological formation are typically performed using many devices including downhole formation testing tools. 
         [0003]    During drilling of a wellbore, a drilling fluid (“mud”) is used to facilitate the drilling process and to maintain a pressure in the wellbore greater than the fluid pressure in the formations surrounding the wellbore. This is particularly important when drilling into formations where the pressure is abnormally high: if the fluid pressure in the borehole drops below the formation pressure, there is a risk of blowout of the well. As a result of this pressure difference, the drilling fluid penetrates into or invades the formations for varying radial depths (referred to generally as invaded zones) depending upon the types of formation and drilling fluid used. The formation testing tools retrieve formation fluids from the desired formations or zones of interest, test the retrieved fluids to ensure that the retrieved fluid is substantially free of mud filtrates, and collect such fluids in one or more chambers associated with the tool. The collected fluids are brought to the surface and analyzed to determine properties of such fluids and to determine the condition of the zones or formations from where such fluids have been collected. 
         [0004]    One feature that all such testers have in common is a fluid sampling probe. This may consist of a durable rubber pad that is mechanically pressed against the rock formation adjacent the borehole, the pad being pressed hard enough to form a hydraulic seal. Through the pad is extended one end of a metal tube that also makes contact with the formation. This tube is connected to a sample chamber that, in turn, is connected to a pump that operates to lower the pressure at the attached probe. When the pressure in the probe is lowered below the pressure of the formation fluids, the formation fluids are drawn through the probe into the well bore to flush the invaded fluids prior to sampling. In some prior art devices, a fluid identification sensor determines when the fluid from the probe consists substantially of formation fluids; then a system of valves, tubes, sample chambers, and pumps makes it possible to recover one or more fluid samples that can be retrieved and analyzed when the sampling device is recovered from the borehole. 
         [0005]    It is important that only uncontaminated fluids are collected, in the same condition in which they exist in the formations. Often the retrieved fluids are contaminated by drilling fluids. This may happen as a result of a poor seal between the sampling pad and the borehole wall, allowing borehole fluid to seep into the probe. The mudcake formed by the drilling fluids may allow some mud filtrate to continue to invade and seep around the pad. Even when there is an effective seal, borehole fluid (or some components of the borehole fluid) may “invade” the formation, particularly if it is a porous formation, and be drawn into the sampling probe along with connate formation fluids. 
         [0006]    Additional problems arise in Drilling Early Evaluation Systems (EES) where fluid sampling is carried out very shortly after drilling the formation with a bit. Inflatable packers or pads cannot be used in such a system because they are easily damaged in the drilling environment. In addition, when the packers are extended to isolate the zone of interest, they completely fill the annulus between the drilling equipment and the wellbore and prevent circulation during testing. 
         [0007]    There is a need for an apparatus that reduces the leakage of borehole fluid into the sampling probe, and also reduces the amount of borehole fluid contaminating the fluid being withdrawn from the formation by the probe. Additionally, there is a need for an apparatus that reduces the time spent on sampling and flushing of contaminated samples. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  illustrates a system for testing and drilling operations as constructed in accordance with at least one embodiment. 
           [0009]      FIG. 2  illustrates a wireline system for drilling operations as constructed in accordance with at least one embodiment. 
           [0010]      FIG. 3  illustrates a probe as constructed in accordance with at least one embodiment. 
           [0011]      FIG. 4  illustrates a probe as constructed in accordance with at least one embodiment. 
           [0012]      FIG. 5  illustrates a probe as constructed in accordance with at least one embodiment. 
           [0013]      FIG. 6  illustrates a side view of a probe as constructed in accordance with at least one embodiment. 
           [0014]      FIG. 7  illustrates a side view of a probe as constructed in accordance with at least one embodiment. 
           [0015]      FIG. 8  illustrates a side view of a probe as constructed in accordance with at least one embodiment. 
           [0016]      FIGS. 9-16  illustrates an example of a retractable wiper for a probe as constructed in accordance with at least one embodiment. 
       
    
    
     DESCRIPTION 
       [0017]    In the following description of some embodiments of the present invention, reference is made to the accompanying drawings which form a part hereof, and in which are shown, by way of illustration, specific embodiments of the present invention which may be practiced. In the drawings, like numerals describe substantially similar components throughout the several views. These embodiments are described in sufficient detail to enable those skilled in the art to practice the present invention. Other embodiments may be utilized and structural, logical, and electrical changes may be made without departing from the scope of the present invention. The following detailed description is not to be taken in a limiting sense, and the scope of the present invention is defined only by the appended claims, along with the full scope of equivalents to which such claims are entitled. 
         [0018]      FIG. 1  illustrates a system  100  for drilling operations. It should be noted that the system  100  can also include a system for pumping operations, or other operations. The system  100  includes a drilling rig  102  located at a surface  104  of a well. The drilling rig  102  provides support for a down hole apparatus, including a drill string  108 . The drill string  108  penetrates a rotary table  110  for drilling a borehole  112  through subsurface formations  114 . The drill string  108  includes a Kelly  116  (in the upper portion), a drill pipe  118  and a bottom hole assembly  120  (located at the lower portion of the drill pipe  118 ). The bottom hole assembly  120  may include drill collars  122 , a′ downhole tool  124  and a drill bit  126 . The downhole tool  124  may be any of a number of different types of tools including measurement-while-drilling (MWD) tools, logging-while-drilling (LWD) tools, etc. 
         [0019]    During drilling operations, the drill string  108  (including the Kelly  116 , the drill pipe  118  and the bottom hole assembly  120 ) may be rotated by the rotary table  110 . In addition or alternative to such rotation, the bottom hole assembly  120  may also be rotated by a motor that is downhole. The drill collars  122  may be used to add weight to the drill bit  126 . The drill collars  122  also optionally stiffen the bottom hole assembly  120  allowing the bottom hole assembly  120  to transfer the weight to the drill bit  126 . The weight provided by the drill collars  122  also assists the drill bit  126  in the penetration of the surface  104  and the subsurface formations  114 . 
         [0020]    During drilling operations, a mud pump  132  optionally pumps drilling fluid, for example, drilling mud, from a mud pit  134  through a hose  136  into the drill pipe  118  down to the drill bit  126 . The drilling fluid can flow out from the drill bit  126  and return back to the surface through an annular area  140  between the drill pipe  118  and the sides of the borehole  112 . The drilling fluid may then be returned to the mud pit  134 , for example via pipe  137 , and the fluid is filtered. 
         [0021]    The downhole tool  124  may include one to a number of different sensors  145 , which monitor different downhole parameters and generate data that is stored within one or more different storage mediums within the downhole tool  124 . The type of downhole tool  124  and the type of sensors  145  thereon may be dependent on the type of downhole parameters being measured. Such parameters may include the downhole temperature and pressure, the various characteristics of the subsurface formations (such as resistivity, radiation, density, porosity, etc.), the characteristics of the borehole (e.g., size, shape, etc.), etc. 
         [0022]    The downhole tool  124  further includes a power source  149 , such as a battery or generator. A generator could be powered either hydraulically or by the rotary power of the drill string. The downhole tool  124  includes a formation testing tool  150 , which can be powered by power source  149 . In an embodiment, the formation testing tool  150  is mounted on a drill collar  122 . The formation testing tool  150  includes a probe that engages the wall of the borehole  112  and extracts a sample of the fluid in the adjacent formation via a flow line. The probe includes one or more inner channels and one or more outer channels, where the one or more outer channels captures more contaminated fluid than the one or more inner channels. As will be described later in greater detail, the probe samples the formation and, in an option, inserts a fluid sample in a container  155 . In an option, the tool  150  injects the carrier  155  into the return mud stream that is flowing intermediate the borehole wall  112  and the drill string  108 , shown as drill collars  122  in  FIG. 1 . The container(s)  155  flow in the return mud stream to the surface and to mud pit or reservoir  134 . A carrier extraction unit  160  is provided in the reservoir  134 , in an embodiment. The carrier extraction unit  160  removes the carrier(s)  155  from the drilling mud. 
         [0023]      FIG. 1  further illustrates an embodiment of a wireline system  170  that includes a downhole tool body  171  coupled to a base  176  by a logging cable  174 . The logging cable  174  may include, but is not limited to, a wireline (multiple power and communication lines), a mono-cable (a single conductor), and a slick-line (no conductors for power or communications). The base  176  is positioned above ground and optionally includes support devices, communication devices, and computing devices. The tool body  171  houses a formation testing tool  150  that acquires samples from the formation. In an embodiment, the power source  149  is positioned in the tool body  171  to provide power to the formation testing tool  150 . The tool body  171  may further include additional testing equipment  172 . In operation, a wireline system  170  is typically sent downhole after the completion of a portion of the drilling. More specifically, the drill string  108  creates a borehole  112 . The drill string is removed and the wireline system  170  is inserted into the borehole  112 . 
         [0024]      FIG. 2  illustrates the formation testing tool  150  in greater detail. As mentioned above, the formation testing tool  150  can be included on the wireline system  170  or a drilling system, for example. It should be noted the formation testing tool  150  can be included on other tools, including, but not limited to tools that lower themselves into the borehole. In  FIG. 2 , an example of the wireline system is shown with formation testing tool  150 . 
         [0025]    A portion of a borehole  201  is shown in a subterranean formation  207 . The borehole wall is covered by a mudcake  205 . The formation tester body  171  is connected to a wireline system  170  leading from a rig at the surface ( FIG. 1 ). The formation tester body  171  is provided with a mechanism, denoted by  210 , to clamp the tester body at a fixed position in the borehole. In an option, the clamping mechanism  210  is at the same depth as a probe  152 . Other mechanisms for engaging the probe  152  with the borehole include, but are not limited to inflatable packers. 
         [0026]    In an example, a clamping mechanism  210  and a fluid sampling pad  213  are extended and mechanically pressed against the borehole wall. The fluid sampling pad  213  includes a probe  152  that has one or more outer channel  156 , and one or more inner channel  154 . The inner channel(s)  15  is disposed within at least a portion of the outer channel(s)  156 . In an option, the inner channel(s)  154  is extended from the center of the pad, through the mud cake  205 , and pressed into contact with the formation. For instance, the inner channel(s)  156  is connected by a hydraulic flow line  223   a  to an inner channel sample chamber  227   a . In another option, the fluid sample pad  213  is extended via extendable members  211  ( FIGS. 6 and 7 ), and the inner and outer channels  154 ,  156  can contact the formation. In an option, flow lines  223   a ,  223   b  for the inner and/or outer channels  154 ,  156  extend through the extendable members  211 , and to their respective channels. In a further option, the probe  152  is an articulating probe, where the probe can hinge at one or more locations  184  ( FIG. 8 ) to contact the surface of a formation and borehole more readily. 
         [0027]    The outer channel(s)  156  has one or more openings  158  ( FIG. 3 ) therealong, the openings being hydraulic connected with the formation thru the channel. Optionally the outer channel(s) can be directly contacting the formation. All of the openings can be connected to one or more hydraulic lines with in the body of the tool. In an option, the outer channel(s)  154  is connected by its own hydraulic flow line,  223   b , to an outer channel sample chamber,  227   b . Because the flow line  223   a  of the inner channel(s)  154  and the flow line  223   b  of the outer channel(s)  156  are separate, the fluid flowing into the outer channel(s)  156  does not mix with the fluid flowing into the inner channel(s)  154 . The outer channel(s) can  156  isolate the flow into the inner channel(s)  154  from the borehole beyond the pad  213 . In a further option, the inner channel flow line  223   a  and/or the outer channel flow line  223   b  extend through extendable members  204  ( FIGS. 6 and 7 ). 
         [0028]    The hydraulic flow lines  223   a  and  223   b  are optionally provided with pressure transducers  211   a  and  211   b . In an option, the pressure maintained in the outer channel flowline  223   b  is the same as, or slightly less than, the pressure in the inner channel flowline  223   a . In another option, the pressure ratio maintained in the inner channel flowline  223   a  to the outer channel flowline  223   b  is about 2:1 to 1:2. In another option, the flow rates of the inner channel(s)  154  and the outer channel(s)  156  are regulated. For example, the flow rate ration of the inner channel(s)  154  to the outer channel(s)  156  is about 2:1 to 1:2. With the configuration of the pad  213  and the outer channel(s)  156 , contaminated borehole fluid that flows around the edges of the pad  213  is drawn into the outer channel(s)  156 , and diverted from entry into the inner channel(s)  154 . 
         [0029]    The flow lines  223   a  and  223   b  are optionally provided with pumps  221   a  and  221   b , or other devices for flowing fluid within the flow lines. The pumps  221   a  and  221   b  are operated long enough to substantially deplete the invaded zone in the vicinity of the pad  213  and to establish an equilibrium condition in which the fluid flowing into the inner channel(s)  154  is substantially free of contaminating borehole filtrate. 
         [0030]    The flow lines  223   a  and  223   b  are also provided with fluid identification sensors,  219   a  and  219   b . This makes it possible to compare the composition of the fluid in the inner channel flowline  223   a  with the fluid in the outer channel flowline  223   b . During initial phases of operation, the composition of the two fluid samples will be the same; typically, both will be contaminated by the borehole fluid. These initial samples are discarded. As sampling proceeds, if the borehole fluid continues to flow from the borehole towards the inner channel(s)  154 , the contaminated fluid is drawn into the outer channel(s)  156 . Pumps  221   a  and  221   b  discharge the sampled fluid into the borehole. At some time, an equilibrium condition is reached in which contaminated fluid is drawn into the outer channel(s)  156  and uncontaminated fluid is drawn into the inner channel(s)  154 . The fluid identification sensors  219   a  and  219   b  are used to determine when this equilibrium condition has been reached. At this point, the fluid in the inner channel flowline is free or nearly free of contamination by borehole fluids. Valve  225   a  is opened, allowing the fluid in the inner channel flowline  223   a  to be collected in the inner channel sample chamber  227   a . Similarly, by opening valve  225   b , the fluid in the outer channel flowline  223   b  is collected in the outer channel sample chamber  227   b . Alternatively, the fluid gathered in the outer channel(s) can be pumped to the borehole while the fluid in the inner channel flow line  223   a  is directed to the inner channel sample chamber  227   a . Sensors that identify the composition of fluid in a flowline can also be provided, in an option. 
         [0031]      FIGS. 3-5  illustrate additional variations for the probe  152 . The probe  152  is defined by a height  180  and a width  182 . In an option, the probe has an elongate shape and the height  180  is greater than the width  182 . This allows for the probe  152  to contact a greater number of laminates. In another option, the probe  152  has an overall oval shape. 
         [0032]    As discussed above, the probe  152  includes inner and outer channels  154 ,  156 , and the inner and outer channels  145 ,  156  include a number of openings  158  or ports therein, where fluid flows through the openings  158 . The number of flow ports, in an option, in the outer channel(s)  156  is different than in the inner channel(s)  154 . In an option, the outer channels  156  have an overall oval, elongate shape and/or encircle with inner channel(s)  154 . While an elongate or oval shape are discussed, it should be noted other shapes for the probe or outer channels can be used. Furthermore, the area of the outer channel(s)  156  relative to the area of the inner channel(s)  154  can be varied, for example, as seen in  FIGS. 3 and 4 . In another option, the outer channel(s)  156  do not completely encircle the inner channel(s)  154 , as shown in  FIG. 5 . For example, the outer channel(s)  156  are disposed on one or more sides of the inner channel(s)  154 . 
         [0033]    In a further option, the probe  152  includes an outer sealing member such as a seal  162  that encircles the outer channel(s)  156 , as shown in  FIG. 3 . In further option, the probe  152  includes a seal  164  disposed between the outer channel(s)  156  and the inner channel(s)  154 , where the seal  164  is optionally retractable within the probe  152 . The seals  162 ,  164  seal against the bore hole wall to enclose a contact surface therein. The seals can be made of elastomeric material, such as rubber, compatible with the well fluids and the physical and chemical conditions expected to be encountered in an underground formation. 
         [0034]    The probe  152  can be operated, cleansed, or kept cleansed in a number of manners. For example, the probe  152  includes one or more screens  166  over the openings  158 . In an option, the one or more screens  166  are retractable to promote flow. Although only one screen  166  is shown in  FIG. 3 , the screens  166  can be disposed over one or more of the openings  158  for the inner channel(s)  154  and/or the outer channel(s)  156 . In another option, the probe further includes at least one wiper that excludes or assists in excluding mud entry into the inner or outer channels. 
         [0035]    In another example, fluid can be pumped through the probe  152  in various manners, such as out of the inner and/or outer channels  154 ,  156  or into the inner and/or outer channels  145 ,  156 . For instance, fluid is pumped through the probe  152  clearing the inner channel(s)  154  including pumping fluid out of the inner channel(s)  154  while optionally pumping into the outer channel(s)  156 . In a further option, fluid is pumped through the probe  152  clearing the outer channel(s)  156  including pumping fluid out of the outer channels)  156  while optionally pumping into the inner channel(s)  154 . In another option, fluid pump through the probe  152  is a selected fluid, such as a fluid that is capable of dissolving material that can clog formation pores near the probe. The fluid can be stored in a collection chamber that can be prefilled, or empty. 
         [0036]    In yet another option, mud cake can be displaced, including removed, adjacent the seals, the inner channel member, or the outer channel member. For example, a wiper assembly as shown in  FIG. 9-16  can be included with the above-discussed probe  152 . The wiper assembly includes a retractable wiper. The wiper can be used to remove or exclude mud cake from the probe as the pad sets. 
         [0037]    Advantageously, the formation samples with low levels of contamination can be collected more quickly using the formation tester. Furthermore, the probe can be self cleaning without having to remove the probe from the borehole. This can increase the efficiency of the pumping or drilling operations. Furthermore, the probe allows for a thin layer or fracture to be identified because the probe can capture a layer or fracture by spanning vertically along the well bore. 
         [0038]    Reference in the specification to “an option,” “an embodiment,” “one embodiment,” “some embodiments,” or “other embodiments” means that a particular feature, structure, or characteristic described in connection with the options or embodiments is included in at least some embodiments, but not necessarily all embodiments, of the invention. The various appearances of “an embodiment,” “one embodiment,” or “some embodiments” are not necessarily all referring to the same embodiments. 
         [0039]    Although specific embodiments have been described and illustrated herein, it will be appreciated by those skilled in the art, having the benefit of the present disclosure, that any arrangement which is intended to achieve the same purpose may be substituted for a specific embodiment shown. This application is intended to cover any adaptations or variations of the present invention. Therefore, it is intended that this invention be limited only by the claims and the equivalents thereof.