Abstract:
An apparatus and method for determining permeability of a subterranean formation is provided. The apparatus and method comprise a work string, at least one selectively extendable member mounted on the work string to isolate a portion of the annular space between the work string and borehole. A predetermined distance proportional to the radius of a control port separates at least two ports in the work string. A sensor operatively associated with each port is mounted in the work string for measuring at least one characteristic such as pressure of the fluid in the isolated section.

Description:
RELATED APPLICATION  
       [0001]    This application is related to a U.S. provisional application titled “Formation Testing While Drilling Apparatus with Axially and Spirally Mounted Ports” filed on Aug. 15, 2000, Ser. No. 60/225,496, and from which priority is claimed for the present application. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    This invention relates to the testing of underground formations or reservoirs and more particularly relates to determining formation pressure and formation permeability.  
           [0004]    2. Description of the Related Art  
           [0005]    To obtain hydrocarbons such as oil and gas from a subterranean formation, well boreholes are drilled into the formation by rotating a drill bit attached at a drill string end. The borehole extends into the formation to traverse one or more reservoirs containing the hydrocarbons typically termed formation fluid.  
           [0006]    Commercial development of hydrocarbon fields requires significant amounts of capital. Before field development begins, operators desire to have as much data as possible in order to evaluate the reservoir for commercial viability. Various tests are performed on the formation and fluid, and the tests may be performed in situ. Surface tests may also be performed on formation and fluid samples retrieved from the well.  
           [0007]    One type of formation test involves producing fluid from the reservoir, collecting samples, shutting-in the well and allowing the pressure to build-up to a static level. This sequence may be repeated several times at several different reservoirs within a given borehole. This type of test is known as a Pressure Build-up Test or drawdown test. One of the important aspects of the data collected during such a test is the pressure build-up information gathered after drawing the pressure down, hence the name drawdown test. From this data, information can be derived as to permeability, and size of the reservoir.  
           [0008]    The permeability of an earth formation containing valuable resources such as liquid or gaseous hydrocarbons is a parameter of major significance to their economic production. These resources can be located by borehole logging to measure such parameters as the resistivity and porosity of the formation in the vicinity of a borehole traversing the formation. Such measurements enable porous zones to be identified and their water saturation (percentage of pore space occupied by water) to be estimated. A value of water saturation significantly less than one is taken as being indicative of the presence of hydrocarbons, and may also be used to estimate their quantity. However, this information alone is not necessarily adequate for a decision on whether the hydrocarbons are economically producible. The pore spaces containing the hydrocarbons may be isolated or only slightly interconnected, in which case the hydrocarbons will be unable to flow through the formation to the borehole. The ease with which fluids can flow through the formation, the permeability, should preferably exceed some threshold value to assure the economic feasibility of turning the borehole into a producing well. This threshold value may vary depending on such characteristics as the viscosity of the fluid. For example, a highly viscous oil will not flow easily in low permeability conditions and if water injection is to be used to promote production there may be a risk of premature water breakthrough at the producing well.  
           [0009]    The permeability of a formation is not necessarily isotropic. In particular, the permeability of sedimentary rock in a generally horizontal direction (parallel to bedding planes of the rock) may be different from, and typically greater than, the value for flow in a generally vertical direction. This frequently arises from alternating horizontal layers consisting of large and small size formation particles such as different sized sand grains or clay. Where the permeability is strongly anisotropic, determining the existence and degree of the anisotropy is important to economic production of hydrocarbons.  
           [0010]    A typical tool for measuring permeability includes a sealing element that is urged against the wall of a borehole to seal a portion of the wall or a section of annulus from the rest of the borehole annulus. In some tools a single port is exposed to the sealed wall or annulus and a drawdown test as described above is conducted. The tool is then moved to seal and test another location along the borehole path through the formation. In other tools, multiple ports exist on a single tool. The several ports are simultaneously used to test multiple points on the borehole wall or within one or more sealed annular sections.  
           [0011]    The relationship between the formation pressure and the response to a pressure disturbance such as a drawdown test is difficult to measure. Consequently, a drawback of tools such as those described above is the inability to accurately measure the effect on formation pressure caused by the drawdown test.  
           [0012]    In the case of the single port tool, the time required to reposition the port takes longer than time is required for the formation to stabilize. Therefore, the test at one point has almost no effect on a test at another point making correlation of data between the two points of little value. Also, the distance between the test points is now known to be critical in accurate measurement of the permeability. When a tool is moved to reposition the port, it is difficult to manage the distance between test points with the precision required for a valid measurement.  
           [0013]    A multiple port tool is better than a single port tool in that the multiple ports help reduce the time required to test between two or more points. The continuing drawback of the above described multiple port tools is that the distance between ports is too large for accurate measurement.  
         SUMMARY OF THE INVENTION  
         [0014]    The present invention addresses the drawbacks described above by providing an apparatus and method capable of engaging a borehole traversing a fluid-bearing formation to measure parameters of the formation and fluids contained therein.  
           [0015]    An apparatus for determining a parameter of interest such as permeability of a subterranean formation is provided. The apparatus comprises a work string for conveying a tool into a well borehole, at least one selectively extendable member mounted on the work string. When extended, the at least one extendable member is in sealing engagement with the wall of the borehole and isolates a portion of the annular space between the work string and borehole. At least two ports in the work string are exposable to formation fluid in the isolated annular space. The distance between the ports is proportional to the radius of a control port to provide effective response measurement. A sensor operatively associated with each port is mounted in the work string for measuring at least one characteristic such as pressure of the fluid in the isolated section.  
           [0016]    In addition to the apparatus provided, a method is provided for determining a parameter of interest of a subterranean formation in situ by conveying a work string into a well borehole. The work string and borehole have an annular space extending between the borehole and a wall of the borehole. At least one selectively extendable member is disposed on the work string for isolating a portion of the annulus. At least two ports are exposed to a fluid in the isolated annulus, and the at least two ports are separated from each other by a predetermined distance proportional to the size of at least one of the ports. A measuring device is used to determine at least one characteristic of the fluid in the isolated section indicative of the parameter of interest.  
           [0017]    The novel features of this invention, as well as the invention itself, will be best understood from the attached drawings, taken along with the following description, in which similar reference characters refer to similar parts, and in which:  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]    [0018]FIG. 1 is an elevation view of an offshore drilling system according to one embodiment of the present invention.  
         [0019]    [0019]FIG. 2 is a schematic representation of an apparatus according to the present invention.  
         [0020]    [0020]FIG. 3A shows a knowledge-based plot of pressure ratio vs. radius ratio for a drawdown test at given parameters.  
         [0021]    [0021]FIG. 3B shows the effect of a disturbance to formation pressure such as the test of FIG. 3A.  
         [0022]    FIGS.  4 A- 4 C show three separate embodiments of the port section of a test string according to the present invention wherein each port of a plurality of ports is mounted on a corresponding selectively extendable pad member.  
         [0023]    FIGS.  5 A- 5 C show three alternative embodiments of the present invention wherein multiple ports are axially and spirally spaced and integral to an inflatable packer for conducting vertical and horizontal permeability tests.  
         [0024]    [0024]FIG. 6 shows another embodiment of a tool according to the present invention wherein the tool is conveyed on a wireline.  
         [0025]    [0025]FIG. 7 is an alternative wireline embodiment of the present invention wherein the multiple pad members are arranged such that the ports  216  disposed on the pad members are spaced substantially coplanar to one another around the circumference of the tool to allow for determining horizontal permeability of the formation.  
         [0026]    [0026]FIG. 8 is another wireline embodiment of the present invention wherein the multiple pad members are arranged spaced spirally around the circumference of the tool to allow for determining the composite of horizontal permeability and vertical permeability of the formation.  
         [0027]    [0027]FIG. 9 is another embodiment of the present invention wherein test ports  216  are integrated into a packer in an axial arrangement.  
         [0028]    [0028]FIG. 10 is another embodiment of the present invention wherein the multiple ports are arranged spaced substantially coplanar to one another around the circumference of the tool to allow for determining horizontal permeability of the formation.  
         [0029]    [0029]FIG. 11 is an alternative wireline embodiment of the present invention wherein the multiple ports are arranged spaced spirally around the circumference of the tool to allow for determining the composite of horizontal permeability and vertical permeability of the formation. 
     
    
     DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0030]    [0030]FIG. 1 is a typical drilling rig  102  with a well borehole  104  being drilled into subterranean formations  118 , as is well understood by those of ordinary skill in the art. The drilling rig  102  has a work string  106 , which in the embodiment shown is a drill string. The drill string  106  has a bottom hole assembly (BHA)  107 , and attached thereto is a drill bit  108  for drilling the borehole  104 . The present invention is also useful in other drill strings, and it is useful with jointed pipe as well as coiled tubing or other small diameter drill string such as snubbing pipe. The drilling rig  102  is shown positioned on a drilling ship  122  with a riser  124  extending from the drilling ship  122  to the sea floor  120 . The present invention may also be adapted for use with land-based drilling rigs.  
         [0031]    If applicable, the drill string  106  can have a downhole drill motor  110  for rotating the drill bit  108 . Incorporated in the drill string  106  above the drill bit  108  is a typical testing unit, which can have at least one sensor  114  to sense downhole characteristics of the borehole, the bit, and the reservoir. Typical sensors sense characteristics such as temperature, pressure, bit speed, depth, gravity, orientation, azimuth, fluid density, dielectric etc. The BHA  107  also contains the formation test apparatus  116  of the present invention, which will be described in greater detail hereinafter. A telemetry system  112  is located in a suitable location on the drill string  106  such as above the test apparatus  116 . The telemetry system  112  is used for command and data communication between the surface and the test apparatus  116 .  
         [0032]    [0032]FIG. 2 is a schematic representation of an apparatus according to the present invention. The system includes surface components and downhole components to carry out formation testing while drilling (FTWD) operations. A borehole  104  is shown drilled into a formation  118  containing a formation fluid  216 . Disposed in the borehole  104  is a drill string  106 . The downhole components are conveyed on the drill string  106 , and the surface components are located in suitable locations on the surface. A typical surface controller  202  includes a communication system  204 , a processor  206  and an input/output device  208 . The input/output device  208  may be any known user interface device such as a personal computer, computer terminal, touch screen, keyboard or stylus. A display such as a monitor may be included for real time monitoring by the user. A printer may be used when hard-copy reports are desired, and with a storage media such as CD, tape or disk, data retrieved from downhole may be stored for delivery to a client or for future analyses. The processor  206  is used for processing commands to be transmitted downhole and for processing data received from downhole via the communication system  204 . The surface communication system  204  includes a receiver for receiving data transmitted from downhole and transferring the data to the surface processor for evaluation and display. A transmitter is also included with the communication system  204  to send commands to the downhole components. Telemetry is typically mud pulse telemetry well known in the art. However, any telemetry system suitable for a particular application may be used. For example, wireline applications would preferably use cable telemetry.  
         [0033]    A downhole two-way communication unit  212  and power supply  213  known in the art are disposed in the drill string  106 . The two-way communication unit  212  includes a transmitter and receiver for two-way communication with the surface controller  202 . The power supply  213 , typically a mud turbine generator, provides electrical power to run the downhole components. The power supply may also be a battery or any other suitable device.  
         [0034]    A controller  214  is shown mounted on the drill string  106  below the two-way communication unit  212  and power supply  213 . A downhole processor (not separately shown) is preferred when using mud-pulse telemetry or whenever processing commands and data downhole is desired. The processor is typically integral to the controller  214  but may also be located in other suitable locations. The controller  214  uses preprogrammed methods, surface-initiated commands or a combination to control the downhole components. The controller controls extendable anchoring, stabilizing and sealing elements such as selectively extendable grippers  210  and pad members  220 A-C.  
         [0035]    The grippers  210  are shown mounted on the drill string  106  generally opposite the pad members  220 A-C. The grippers may also be located in other orientations relative to the pad members. Each gripper  210  has a roughened end surface  211  for engaging the borehole wall to anchor the drill string  106 . Anchoring the drill string serves to protect soft components such as an elastomeric or other suitable sealing material disposed on the end of the pad members  220 A-C from damage due to movement of the drill string. The grippers  210  would be especially desirable in offshore systems such as the one shown in FIG. 1, because movement caused by heave can cause premature wear out of sealing components.  
         [0036]    Mounted on the drill string  106  generally opposite the grippers  210  are at least two and preferably at least three pad members  220 A-C for engaging the borehole wall. A pad piston  222 A-C is used to extend each pad  220 A-C to the borehole wall, and each pad  220 A-C seals a portion of the annulus  228  from the rest of the annulus. Not-shown conduits may be used to direct pressurized fluid to extend pistons  222 A-C hydraulically, or the pistons  222 A-C may be extended using a motor. A port  224 A-C located on each pad  220 A-C has a substantially circular cross-section with a port radius R P . Fluid  216  tends to enter a sealed annulus when the pressure at a corresponding port  224 A-C drops below the pressure of the surrounding formation  118 . A drawdown pump  238  mounted in the drill string  106  is connected to one or more of the ports  224 A-C. The pump  238  must be capable of controlling independently a drawdown pressure in each port to which the pump is connected.  
         [0037]    The pump  238  may be a single pump capable of controlling drawdown pressure at a selected port. The pump  238  may in the alternative be a plurality of pumps with each pump controlling pressure at a selected corresponding port. The preferred pump is a typical positive displacement pump such as a piston pump. The pump  238  includes a power source such as a mud turbine or electric motor used to operate the pump. A controller  214  is mounted in the drill string and is connected to the pump  238 . The controller controls operations of the pump  238  including selecting a port for drawdown and controlling drawdown parameters.  
         [0038]    For testing operations, the controller  214  activates the pump  238  to reduce the pressure in at least one of the ports  224 A-C, which for the purposes of this application will be termed the control port  224 A. The reduced pressure causes a pressure disturbance in the formation that will be described in greater detail hereinafter. A pressure sensor  226 A is in fluid communication with the control port  224 A measures the pressure at the control port  224 A. Pressure sensors  226 B and  226 C in fluid communication with the other ports  224 B and  224 C (hereinafter sensing ports) are used to measure the pressure at each of the sensing ports  224 B and  224 C. The sensing ports  224 B and  224 C are axially, vertically or spirally spaced apart from the control port  224 A, and pressure measurements at the sensing ports  224 B and  224 C are indicative of the permeability of the formation being tested when compared to the pressure of the control port  224 A. For reliable and accurate determination of formation permeability, the ports  224 A-C must be spaced relative to the size of each port. This size-spacing relationship will be discussed with reference to FIGS. 3A and 3B.  
         [0039]    [0039]FIG. 3A shows a knowledge-based plot of pressure ratio vs. radius ratio for a drawdown test at given parameters. The parameters affecting the plot and their associated units are formation permeability (k) measured in milli-darcys (md), test flow rate (q) measured in cubic centimeters per second (cc/s) and drawdown time (t d ) measured in seconds (s). For the plot of FIG. 3A, the values selected are k=1 md, q=2 cc/s and t d =600 s. In the graph, P D  is a dimensionless ratio of pressures associated with a typical drawdown test. Equation 1 can describe this ratio as follows. 
           P   D =( P   f   −P )/( P   f   −P   min )  Eq. 1 
         [0040]    In Equation 1, P f =Formation Pressure, P min =minimum pressure at the port during the drawdown test, and P=pressure at the port at any given time. R D  is a dimensionless ratio of radii associated with a well borehole and test apparatus such as the apparatus in FIG. 2. Equation 2 describes R D . 
           R   D =( R−R   w )/ R   p   Eq. 2 
         [0041]    In Equation 2, R=radius from the center of the borehole to any given point into the formation. R w =the borehole radius, and R p =the effective radius of the tool probe port. Any distance dimension for distance is suitable, and in this case centimeters are used.  
         [0042]    An important observation should be made in the plot of FIG. 3A. The plot shows P D  at observation intervals of t=0.1 s through t=344 s. P D  becomes essentially invariant after R D  exceeds 6.5 for t =0.l  s and also when R D  exceeds approximately 12 for t&gt;=5.0 s. This means that changes in the formation pressure based on a disturbance such as a drawdown test at a port location are almost nonexistent in the formation beyond about 12×the radius of the port (R p ) creating the disturbance.  
         [0043]    [0043]FIG. 3B shows the effect of a disturbance to formation pressure such as the test of FIG. 3A. FIG. 3B shows a control port  224 A at a given time where the port pressure has been reduced thereby disturbing the formation pressure P f . Each semicircular pressure gradient line is a cross section of the actual effect, which is a hemispherical propagation of disturbance originating at the center of the control port  224 A. Each line represents the ratio of pressure related to the initial formation pressure P f  to the pressure disturbance at a distance R f  from the control port  224 A. The distance of each line is a multiple of the port radius R p  into the formation. At R f =5×R p , the pressure ratio P D =0.85. Meaning the pressure of the formation is 0.85×the initial pressure P f  at a distance of R f =5×R p  away from the center of the control port  224 A. At 12×R p  the formation pressure is virtually unaffected by the initial disturbance P p  at the control port  224 A.  
         [0044]    As stated above, the disturbance pattern is substantially spherical and originating at the center of the control port  224 A, thus the distances of 5×R p  and 12×R p  also define locations along a drill string  106  and about the circumference of the drill string  106  housing the control port  224 A relative to the control port  224 A. Therefore, referring back to FIG. 2, the distance D between the control port  216 A and any of the sensing ports  224 B and  224 C must be selected based on the size of the port and borehole such that P D  is maximized. The preferred distance between ports for the present invention is a range of between 1 and 12 times the radius of the control port  224 A.  
         [0045]    Permeability of a formation has vertical and horizontal components. Vertical permeability is the permeability of a formation in a direction substantially perpendicular to the surface of the earth, and horizontal permeability is the permeability of a formation in a direction substantially parallel to the surface and perpendicular to the vertical permeability direction. The embodiment shown FIG. 2 is one way of measuring vertical permeability. The embodiments following are different configurations according to the present invention for measuring vertical permeability, horizontal permeability and combined vertical and horizontal permeability.  
         [0046]    FIGS.  4 A- 4 C show three separate embodiments of the port section of a test string according to the present invention wherein each port of a plurality of ports is mounted on a corresponding selectively extendable pad member. FIG. 4A shows selectively extendable pad members  220 A-C mounted in the configuration shown in FIG. 2. Grippers  210  are mounted generally opposite the pad members to anchor the drill string and provide an opposing force to the extended pad elements  220 A-C. The straight-line distance D between the control port  224 A and either sensing port  224 B or  224 C must conform to the distance calculations described above.  
         [0047]    [0047]FIG. 4B shows a plurality of selectively extendable pad members disposed about the circumference of the drill string  106 . The circumferential distance D between each sensing port  224 B and  224 C and the control port  224 A is selected based the criteria defined above. In this configuration horizontal permeability can be measured in a vertically oriented borehole.  
         [0048]    [0048]FIG. 4C is a set of selectively extendable pad members  220 A-C spirally disposed about the circumference of a drill string  106 . In this configuration a determination can be made of the composite horizontal permeability and vertical permeability of a formation. The helical distance D between the control port  224 A and either sensing port  224 B or  224 C must be selected as discussed above.  
         [0049]    Another well-known component associated with formation testing tools is a packer. A packer is typically an inflatable component disposed on a drill string and used to seal (or shut in) a well borehole. The packer is typically inflated by pumping drilling mud from the drill string into the packer. FIGS.  5 A- 5 C show three alternative embodiments of the present invention wherein multiple ports are axially and spirally spaced and integral to an inflatable packer for conducting vertical and horizontal permeability tests.  
         [0050]    [0050]FIG. 5A shows a selectively expandable packer  502  disposed on a drill string  106 . Integral to the packer  502  are axially spaced ports  224 A- 224 C. When the packer is inflated, the packer seals against the wall of a borehole. The axially spaced ports are thus urged against the wall. The straight-line distance D between control port  224 A and either port  224 B or  224 C is selected in compliance with the requirements discussed above.  
         [0051]    [0051]FIG. 5B shows a selectively expandable packer  502  disposed on a drill string  106 . Ports  224 A-C are disposed about the circumference of the packer  502 . For this configuration, a plane intersecting the center of the ports  224 A-C should be substantially perpendicular to the drill string axis  504 . The circumferential distance D between the control port  224 A and either sensing ports  224 B or  224 C is selected based the criteria defined above. In this configuration horizontal permeability can be measured in a vertically oriented borehole.  
         [0052]    [0052]FIG. 5C shows a selectively expandable packer  502  disposed on a drill string  106 . Ports  224 A-C are integral to and spirally disposed about the circumference of the expandable packer  502 . In this configuration a determination can be made of the composite horizontal permeability and vertical permeability of a formation. For a spiral configuration, ports  224 A-C are displaced horizontally and axially from each other about the circumference of the packer  502 . The helical distance D between the control port  224 A and either sensing port  224 B or  224 C is as described above.  
         [0053]    [0053]FIG. 6 shows another embodiment of a tool according to the present invention wherein the tool is conveyed on a wireline. A well  602  is shown traversing a formation  604  containing formation fluid  606 . The well  602  has a casing  608  disposed on a borehole wall  610  from the surface  612  to a point  614  above the well bottom  616 . A wireline tool  618  supported by an armored cable  620  is disposed in the well  602  adjacent the fluid-bearing formation  604 . Extending from the tool  618  are grippers  622  and pad members  624 A-C. The grippers and pad members are as described in the embodiment shown in FIG. 2. Each pad member  624  has a port  628 A-C, and the ports  628 A-C are vertically spaced in accordance with the spacing requirements described with respect to FIGS. 3A and 3B. A surface control unit  626  controls the downhole tool  618  via the armored cable  620 , which is also a conductor for conducting power to and signals to and from the tool  618 . A cable sheave  627  is used to guide the armored cable  620  into the well  602 .  
         [0054]    The downhole tool  618  includes a pump, a plurality of sensors, control unit, and two-way communication system as described above for the embodiment shown in FIG. 2. Therefore these components are not shown separately in FIG. 6.  
         [0055]    [0055]FIG. 7 is an alternative wireline embodiment of the present invention. In this embodiment, with the exception of the grippers  622  (FIG. 6) all components of a wireline apparatus as described above with respect to FIG. 6 are present in the embodiment of FIG. 7. The difference between the embodiment of FIG. 7 and the embodiment of FIG. 6 is that the multiple pad members in FIG. 7 are arranged such that the ports  628 A-C disposed on the pad members  624 A-C are spaced substantially coplanar to one another around the circumference of the tool  618  to allow for determining horizontal permeability of the formation  604 .  
         [0056]    [0056]FIG. 8 is another wireline embodiment of the present invention. In this embodiment, all components of a wireline apparatus as described above with respect to FIG. 6 are present. The difference between the embodiment of FIG. 8 and the embodiment of FIG. 6 is that the multiple pad members  624 A-C in FIG. 8 are arranged spaced spirally around the circumference of the tool  618  to allow for determining the composite of horizontal permeability and vertical permeability of the formation  604 .  
         [0057]    [0057]FIG. 9 is yet another alternate wireline embodiment of the present invention wherein test ports  628 A-C are integrated into a packer  502  in an axial arrangement as described above with respect to FIG. 5A. In this embodiment, a wireline apparatus is as described with respect to FIG. 6 with the exception of the pad members  624 A-C and grippers  622 . Instead of extendable pad members  624 A-C, an inflatable packer  502  such as the packer described with respect to FIGS.  5 A-C includes at least two and preferably at least three test ports  628 A-C. One test port is the control port  628 A and the other ports are the sensor ports  628 B and  628 C for sensing the effect on the formation pressure at the test port locations caused by reducing the pressure at the control port  628 A. The ports in FIG. 9 are shown spaced axially, as in FIG. 5A, for determining vertical permeability of the formation  604  when the well  602  is essentially vertical.  
         [0058]    [0058]FIG. 10 is an alternative wireline embodiment of the present invention. In this embodiment, all components of a wireline apparatus as described above with respect to FIG. 9 are present. The difference between the embodiment of FIG. 10 and the embodiment of FIG. 9 is that the multiple ports  628 A-C in FIG. 10 are arranged spaced substantially coplanar to one another around the circumference of the tool  618  as in FIG. 5B to allow for determining horizontal permeability of the formation  604 .  
         [0059]    The tool of FIG. 10 may be used while drilling a horizonital borehole. In this case, an orientation sensing device such as an accelerometer may be used to determine the orientation of each of the ports  628 A-C. The controller (See FIG. 2 at  214 ) may then be used to select a port on the top side of the tool for making the measurements as described above.  
         [0060]    [0060]FIG. 11 is an alternative wireline embodiment of the present invention. In this embodiment, all components of a wireline apparatus as described above with respect to FIG. 9 are present. The difference between the embodiment of FIG. 11 and the embodiment of FIG. 9 is that the multiple ports  628 A-C in FIG. 11 are arranged spaced spirally around the circumference of the tool  618  as in FIG. 5C to allow for determining the composite of horizontal permeability and vertical permeability of the formation  604 .  
         [0061]    Other embodiments and minor variations are considered within the scope of this invention. For example, the ports  216 A- 216 C may be shaped other than with a substantially circular cross-section area. The ports may be elongated, square, or any other suitable shape. Whatever shape is used, R p  must be the distance from the center of the port to an edge nearest the center of the control port. The control port edge and an adjacent sensor port must be spaced as discussed above with respect to FIGS. 3A and 3B.  
         [0062]    Now that system embodiments of the invention have been described, a method of testing formation permeability using the apparatus of FIGS. 1 and 2 will be described. Referring first to FIGS. 1 and 2, a tool according to the present invention is conveyed into a well  104  on a drill string  106 , the well  104  traversing a formation  118  containing formation fluid. The drill string  106  is anchored to the well wall by extending a plurality of grippers  210 . At least two and preferably three pad members  220 A-C are extended until each is brought into sealing contact with the borehole wall  244 . A control port  224 A is exposed to the sealed section such that the control port is in fluid communication with formation fluid in the formation  118 . Using a pump  238 , fluid pressure at the control port  224 A is reduced to disturb formation pressure in the formation  118 . The level to which the pressure at the control port  224 A is reduced is sensed using a sensor  226 A. The pressure disturbance is propagated through the formation, and the effect of the disturbance is attenuated based on the permeability of the formation. The attenuated pressure disturbance is sensed at the sensor ports by sensors  226 B and  226 C disposed in fluid communication with the sensor ports  224 B and  224 C. At least one parameter of interest such as formation pressure, temperature, fluid dielectric constant or resistivity is sensed with the sensors  224 A-C, and a downhole controller/processor  214  is used to determine formation pressure and permeability or any other desired parameter of the fluid or formation.  
         [0063]    Processed data is then transmitted to the surface using a two-way communications unit  212  disposed downhole on the drill string  106 . Using a surface communications unit  204 , the processed data is received and forwarded to a surface processor  206 . The method further comprises processing the data at the surface for output to a display unit, printer, or storage device  208 .  
         [0064]    Alternative methods are not limited to the method described above. The tool may be conveyed on a wireline. Also, whether conveyed on a wireline or drill string, the ports  224 A-C may be configured axially, horizontally or spirally with respect to a center axis of the tool. The ports  224 A-C may also be extended using extendable pad members as discussed or by using an expandable packer.  
         [0065]    While the particular invention as herein shown and disclosed in detail is fully capable of obtaining the objects and providing the advantages hereinbefore stated, it is to be understood that this disclosure is merely illustrative of the presently preferred embodiments of the invention and that no limitations are intended other than as described in the appended claims.