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CROSS-REFERENCE TO RELATED APPLICATIONS 
   The present application is a division of application Ser. No. 10/270,424 filed Oct. 11, 2002 now U.S. Pat. No. 6,729,398, which was a continuation of application Ser. No. 09/971,205 filed Oct. 4, 2001, now U.S. Pat. No. 6,527,052, which was a division of application Ser. No. 09/378,124 filed Aug. 19, 1999, now U.S. Pat. No. 6,325,146, which claims the benefit of the Mar. 31, 1999 filing date of provisional application Ser. No. 60/127,106. The disclosure of each of these earlier applications is incorporated herein in its entirety by this reference. 

   BACKGROUND OF THE INVENTION 
   The present invention relates generally to operations performed in conjunction with subterranean wells and, in an embodiment described herein, more particularly provides a method of performing a downhole test of a subterranean formation. 
   In a typical well test known as a drill stem test, a drill string is installed in a well with specialized drill stem test equipment interconnected in the drill string. The purpose of the test is generally to evaluate the potential profitability of completing a particular formation or other zone of interest, and thereby producing hydrocarbons from the formation. Of course, if it is desired to inject fluid into the formation, then the purpose of the test may be to determine the feasibility of such an injection program. 
   In a typical drill stem test, fluids are flowed from the formation, through the drill string and to the earth&#39;s surface at various flow rates, and the drill string may be closed to flow therethrough at least once during the test. Unfortunately, the formation fluids have in the past been exhausted to the atmosphere during the test, or otherwise discharged to the environment, many times with hydrocarbons therein being burned off in a flare. It will be readily appreciated that this procedure presents not only environmental hazards, but safety hazards as well. 
   Therefore, it would be very advantageous to provide a method whereby a formation may be tested, without discharging hydrocarbons or other formation fluids to the environment, or without flowing the formation fluids to the earth&#39;s surface. It would also be advantageous to provide apparatus for use in performing the method. 
   SUMMARY OF THE INVENTION 
   In carrying out the principles of the present invention, in accordance with an embodiment thereof, a method is provided in which a formation test is performed downhole, without flowing formation fluids to the earth&#39;s surface, or without discharging the fluids to the environment. Also provided are associated apparatus for use in performing the method. 
   In one aspect of the present invention, a method includes steps wherein a formation is perforated, and fluids from the formation are flowed into a large surge chamber associated with a tubular string installed in the well. Of course, if the well is uncased, the perforation step is unnecessary. The surge chamber may be a portion of the tubular string. Valves are provided above and below the surge chamber, so that the formation fluids may be flowed, pumped or reinjected back into the formation after the test, or the fluids may be circulated (or reverse circulated) to the earth&#39;s surface for analysis. 
   In another aspect of the present invention, a method includes steps wherein fluids from a first formation are flowed into a tubular string installed in the well, and the fluids are then disposed of by injecting the fluids into a second formation. The disposal operation may be performed by alternately applying fluid pressure to the tubular string, by operating a pump in the tubular string, by taking advantage of a pressure differential between the formations, or by other means. A sample of the formation fluid may conveniently be brought to the earth&#39;s surface for analysis by utilizing apparatus provided by the present invention. 
   In yet another aspect of the present invention, a method includes steps wherein fluids are flowed from a first formation and into a second formation utilizing an apparatus which may be conveyed into a tubular string positioned in the well. The apparatus may include a pump which may be driven by fluid flow through a fluid conduit, such as coiled tubing, attached to the apparatus. The apparatus may also include sample chambers therein for retrieving samples of the formation fluids. 
   In each of the above methods, the apparatus associated therewith may include various fluid property sensors, fluid and solid identification sensors, flow control devices, instrumentation, data communication devices, samplers, etc., for use in analyzing the test progress, for analyzing the fluids and/or solid matter flowed from the formation, for retrieval of stored test data, for real time analysis and/or transmission of test data, etc. 
   These and other features, advantages, benefits and objects of the present invention will become apparent to one of ordinary skill in the art upon careful consideration of the detailed description of representative embodiments of the invention hereinbelow and the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic cross-sectional view of a well wherein a first method and apparatus embodying principles of the present invention are utilized for testing a formation; 
       FIG. 2  is a schematic cross-sectional view of a well wherein a second method and apparatus embodying principles of the present invention are utilized for testing a formation; 
       FIG. 3  is an enlarged scale schematic cross-sectional view of a device which may be used in the second method; 
       FIG. 4  is a schematic cross-sectional view of a well wherein a third method and apparatus embodying principles of the present invention are utilized for testing a formation; and 
       FIG. 5  is an enlarged scale schematic cross-sectional view of a device which may be used in the third method. 
       FIG. 6  is a schematic partially cross-sectional view of a fourth method and associated apparatus embodying principles of the present invention. 
   

   DETAILED DESCRIPTION 
   Representatively illustrated in  FIG. 1  is a method  10  which embodies principles of the present invention. In the following description of the method  10  and other apparatus and methods described herein, directional terms, such as “above”, “below”, “upper”, “lower”, etc., are used for convenience in referring to the accompanying drawings. Additionally, it is to be understood that the various embodiments of the present invention described herein may be utilized in various orientations, such as inclined, inverted, horizontal, vertical, etc., without departing from the principles of the present invention. 
   In the method  10  as representatively depicted in  FIG. 1 , a wellbore  12  has been drilled intersecting a formation or zone of interest  14 , and the wellbore has been lined with casing  16  and cement  17 . In the further description of the method  10  below, the wellbore  12  is referred to as the interior of the casing  16 , but it is to be clearly understood that, with appropriate modification in a manner well understood by those skilled in the art, a method incorporating principles of the present invention may be performed in an uncased wellbore, and in that situation the wellbore would more appropriately refer to the uncased bore of the well. 
   A tubular string  18  is conveyed into the wellbore  12 . The string  18  may consist mainly of drill pipe, or other segmented tubular members, or it may be substantially unsegmented, such as coiled tubing. At a lower end of the string  18 , a formation test assembly  20  is interconnected in the string. 
   The assembly  20  includes the following items of equipment, in order beginning at the bottom of the assembly as representatively depicted in  FIG. 1 : one or more generally tubular waste chambers  22 , an optional packer  24 , one or more perforating guns  26 , a firing head  28 , a circulating valve  30 , a packer  32 , a circulating valve  34 , a gauge carrier  36  with associated gauges  38 , a tester valve  40 , a tubular surge chamber  42 , a tester valve  44 , a data access sub  46 , a safety circulation valve  48 , and a slip joint  50 . Note that several of these listed items of equipment are optional in the method  10 , other items of equipment may be substituted for some of the listed items of equipment, and/or additional items of equipment may be utilized in the method and, therefore, the assembly  20  depicted in  FIG. 1  is to be considered as merely representative of an assembly which may be used in a method incorporating principles of the present invention, and not as an assembly which must necessarily be used in such method. 
   The waste chambers  22  may be comprised of hollow tubular members, for example, empty perforating guns (i.e., with no perforating charges therein). The waste chambers  22  are used in the method  10  to collect waste from the wellbore  12  immediately after the perforating gun  26  is fired to perforate the formation  14 . This waste may include perforating debris, wellbore fluids, formation fluids, formation sand, etc. Additionally, the pressure reduction in the wellbore  12  created when the waste chambers  22  are opened to the wellbore may assist in cleaning perforations  52  created by the perforating gun  26 , thereby enhancing fluid flow from the formation  14  during the test. In general, the waste chambers  22  are utilized to collect waste from the wellbore  12  and perforations  52  prior to performing the actual formation test, but other purposes may be served by the waste chambers, such as drawing unwanted fluids out of the formation  14 , for example, fluids injected therein during the well drilling process. 
   The packer  24  may be used to straddle the formation  14  if another formation therebelow is open to the wellbore  12 , a large rathole exists below the formation, or if it is desired to inject fluids flowed from the formation  14  into another fluid disposal formation as described in more detail below. The packer  24  is shown unset in  FIG. 1  as an indication that its use is not necessary in the method  10 , but it could be included in the string  18 , if desired. 
   The perforating gun  26  and associated firing head  28  may be any conventional means of forming an opening from the wellbore  12  to the formation  14 . Of course, as described above, the well may be uncased at its intersection with the formation  14 . Alternatively, the formation  14  may be perforated before the assembly  20  is conveyed into the well, the formation may be perforated by conveying a perforating gun through the assembly after the assembly is conveyed into the well, etc. 
   The circulating valve  30  is used to selectively permit fluid communication between the wellbore  12  and the interior of the assembly  20  below the packer  32 , so that formation fluids may be drawn into the interior of the assembly above the packer. The circulating valve  30  may include openable ports  54  for permitting fluid flow therethrough after the perforating gun  26  has fired and waste has been collected in the waste chambers  22 . 
   The packer  32  isolates an annulus  56  above the packer formed between the string  18  and the wellbore  12  from the wellbore below the packer. As depicted in  FIG. 1 , the packer  32  is set in the wellbore  12  when the perforating gun  26  is positioned opposite the formation  14 , and before the gun is fired. The circulating valve  34  may be interconnected above the packer  32  to permit circulation of fluid through the assembly  20  above the packer, if desired. 
   The gauge carrier  36  and associated gauges  38  are used to collect test data, such as pressure, temperature, etc., during the formation test. It is to be clearly understood that the gauge carrier  36  is merely representative of a variety of means which may be used to collect such data. For example, pressure and/or temperature gauges may be included in the surge chamber  42  and/or the waste chambers  22 . Additionally, note that the gauges  38  may acquire data from the interior of the assembly  20  and/or from the annulus  56  above and/or below the packer  32 . Preferably, one or more of the gauges  38 , or otherwise positioned gauges, records fluid pressure and temperature in the annulus  56  below the packer  32 , and between the packers  24 ,  32  if the packer  24  is used, substantially continuously during the formation test. 
   The tester valve  40  selectively permits fluid flow axially therethrough and/or laterally through a sidewall thereof. For example, the tester valve  40  may be an Omni™ valve, available from Halliburton Energy Services, Inc., in which case the valve may include a sliding sleeve valve  58  and closeable circulating ports  60 . The valve  58  selectively permits and prevents fluid flow axially through the assembly  20 , and the ports  60  selectively permit and prevent fluid communication between the interior of the surge chamber  42  and the annulus  56 . Other valves, and other types of valves, may be used in place of the representatively illustrated valve  40 , without departing from the principles of the present invention. 
   The surge chamber  42  comprises one or more generally hollow tubular members, and may consist mainly of sections of drill pipe, or other conventional tubular goods, or may be purpose-built for use in the method  10 . It is contemplated that the interior of the surge chamber  42  may have a relatively large volume, such as approximately 20 barrels, so that, during the formation test, a substantial volume of fluid may be flowed from the formation  14  into the chamber, a sufficiently low initial drawdown pressure may be achieved during the test, etc. When conveyed into the well, the interior of the surge chamber  42  may be at atmospheric pressure, or it may be at another pressure, if desired. 
   One or more sensors, such as sensor  62 , may be included with the chamber  42 , in order to acquire data, such as fluid property data (e.g., pressure, temperature, resistivity, viscosity, density, flow rate, etc.) and/or fluid identification data (e.g., by using nuclear magnetic resonance sensors available from Numar, Inc.). The sensor  62  may be in data communication with the data access sub  46 , or another remote location, by any data transmission means, for example, a line  64  extending external or internal relative to the assembly  20 , acoustic data transmission, electromagnetic data transmission, optical data transmission, etc. 
   The valve  44  may be similar to the valve  40  described above, or it may be another type of valve. As representatively depicted in  FIG. 1 , the valve  44  includes a ball valve  66  and closeable circulating ports  68 . The ball valve  66  selectively permits and prevents fluid flow axially through the assembly  20 , and the ports  68  selectively permit and prevent fluid communication between the interior of the assembly  20  above the surge chamber  42  and the annulus  56 . Other valves, and other types of valves, may be used in place of the representatively illustrated valve  44 , without departing from the principles of the present invention. 
   The data access sub  46  is representatively depicted as being of the type wherein such access is provided by conveying a wireline tool  70  therein in order to acquire the data transmitted from the sensor  62 . For example, the data access sub  46  may be a conventional wet connect sub. Such data access may be utilized to retrieve stored data and/or to provide real time access to data during the formation test. Note that a variety of other means may be utilized for accessing data acquired downhole in the method  10 , for example, the data may be transmitted directly to a remote location, other types of tools and data access subs may be utilized, etc. 
   The safety circulation valve  48  may be similar to the valves  40 ,  44  described above in that it may selectively permit and prevent fluid flow axially therethrough and through a sidewall thereof. However, preferably the valve  48  is of the type which is used only when a well control emergency occurs. In that instance, a ball valve  72  thereof (which is shown in its typical open position in  FIG. 1 ) would be closed to prevent any possibility of formation fluids flowing further to the earth&#39;s surface, and circulation ports  74  would be opened to permit kill weight fluid to be circulated through the string  18 . 
   The slip joint  50  is utilized in the method  10  to aid in positioning the assembly  20  in the well. For example, if the string  18  is to be landed in a subsea wellhead, the slip joint  50  may be useful in spacing out the assembly  20  relative to the formation  14  prior to setting the packer  32 . 
   In the method  10 , the perforating guns  26  are positioned opposite the formation  14  and the packer  32  is set. If it is desired to isolate the formation  14  from the wellbore  12  below the formation, the optional packer  24  may be included in the string  18  and set so that the packers  32 ,  24  straddle the formation. The formation  14  is perforated by firing the gun  26 , and the waste chambers  22  are immediately and automatically opened to the wellbore  12  upon such gun firing. For example, the waste chambers  22  may be in fluid communication with the interior of the perforating gun  26 , so that when the gun is fired, flow paths are provided by the detonated perforating charges through the gun sidewall. Of course, other means of providing such fluid communication may be provided, such as by a pressure operated device, a detonation operated device, etc., without departing from the principles of the present invention. 
   At this point, the ports  54  may or may not be open, as desired, but preferably the ports are open when the gun  26  is fired. If not previously opened, the ports  54  are opened after the gun  26  is fired. This permits flow of fluids from the formation  14  into the interior of the assembly  20  above the packer  32 . 
   When it is desired to perform the formation test, the tester valve  40  is opened by opening the valve  58 , thereby permitting the formation fluids to flow into the surge chamber  42  and achieving a drawdown on the formation  14 . The gauges  38  and sensor  62  acquire data indicative of the test, which, as described above, may be retrieved later or evaluated simultaneously with performance of the test. One or more conventional fluid samplers  76  may be positioned within, or otherwise in communication with, the chamber  42  for collection of one or more samples of the formation fluid. One or more of the fluid samplers  76  may also be positioned within, or otherwise in communication with, the waste chambers  22 . 
   After the test, the valve  66  is opened and the ports  60  are opened, and the formation fluids in the surge chamber  42  are reverse circulated out of the chamber. Other circulation paths, such as the circulating valve  34 , may also be used. Alternatively, fluid pressure may be applied to the string  18  at the earth&#39;s surface before unsetting the packer  32 , and with valves  58 ,  66  open, to flow the formation fluids back into the formation  14 . As another alternative, the assembly  20  may be repositioned in the well, so that the packers  24 ,  32  straddle another formation intersected by the well, and the formation fluids may be flowed into this other formation. Thus, it is not necessary in the method  10  for formation fluids to be conveyed to the earth&#39;s surface unless desired, such as in the sampler  76 , or by reverse circulating the formation fluids to the earth&#39;s surface. 
   Referring additionally now to  FIG. 2 , another method  80  embodying principles of the present invention is representatively depicted. In the method  80 , formation fluids are transferred from a formation  82  from which they originate, into another formation  84  for disposal, without it being necessary to flow the fluids to the earth&#39;s surface during a formation test, although the fluids may be conveyed to the earth&#39;s surface if desired. As depicted in  FIG. 2 , the disposal formation  84  is located uphole from the tested formation  82 , but it is to be clearly understood that these relative positionings could be reversed with appropriate changes to the apparatus and method described below, without departing from the principles of the present invention. 
   A formation test assembly  86  is conveyed into the well interconnected in a tubular string  87  at a lower end thereof. The assembly  86  includes the following, listed beginning at the bottom of the assembly: the waste chambers  22 , the packer  24 , the gun  26 , the firing head  28 , the circulating valve  30 , the packer  32 , the circulating valve  34 , the gauge carrier  36 , a variable or fixed choke  88 , a check valve  90 , the tester valve  40 , a packer  92 , an optional pump  94 , a disposal sub  96 , a packer  98 , a circulating valve  100 , the data access sub  46 , and the tester valve  44 . Note that several of these listed items of equipment are optional in the method  80 , other items of equipment may be substituted for some of the listed items of equipment, and/or additional items of equipment may be utilized in the method and, therefore, the assembly  86  depicted in  FIG. 2  is to be considered as merely representative of an assembly which may be used in a method incorporating principles of the present invention, and not as an assembly which must necessarily be used in such method. For example, the valve  40 , check valve  90  and choke  88  are shown as examples of flow control devices which may be installed in the assembly  86  between the formations  82 ,  84 , and other flow control devices, or other types of flow control devices, may be utilized in the method  80 , in keeping with the principles of the present invention. As another example, the pump  94  may be used, if desired, to pump fluid from the test formation  82 , through the assembly  86  and into the disposal formation  84 , but use of the pump  94  is not necessary in the method  80 . Additionally, many of the items of equipment in the assembly  86  are shown as being the same as respective items of equipment used in the method  10  described above, but this is not necessarily the case. 
   When the assembly  86  is conveyed into the well, the disposal formation  84  may have already been perforated, or the formation may be perforated by providing one or more additional perforating guns in the assembly, if desired. For example, additional perforating guns could be provided below the waste chambers  22  in the assembly  86 . 
   The assembly  86  is positioned in the well with the gun  26  opposite the test formation  82 , the packers  24 ,  32 ,  92 ,  98  are set, the circulating valve  30  is opened, if desired, if not already open, and the gun  26  is fired to perforate the formation. At this point, with the test formation  82  perforated, waste is immediately received into the waste chambers  22  as described above for the method  10 . The circulating valve  30  is opened, if not done previously, and the test formation is thereby placed in fluid communication with the interior of the assembly  86 . 
   Preferably, when the assembly  86  is positioned in the well as shown in  FIG. 2 , a relatively low density fluid (liquid, gas (including air, at atmospheric or greater or lower pressure) and/or combinations of liquids and gases, etc.) is contained in the string  87  above the upper valve  44 . This creates a low hydrostatic pressure in the string  87  relative to fluid pressure in the test formation  82 , which pressure differential is used to draw fluids from the test formation into the assembly  86  as described more fully below. Note that the fluid preferably has a density which will create a pressure differential from the formation  82  to the interior of the assembly at the ports  54  when the valves  58 ,  66  are open. However, it is to be clearly understood that other methods and means of drawing formation fluids into the assembly  86  may be utilized, without departing from the principles of the present invention. For example, the low density fluid could be circulated into the string  87  after positioning it in the well by opening the ports  68 , nitrogen could be used to displace fluid out of the string, a pump  94  could be used to pump fluid from the test formation  82  into the string, a difference in formation pressure between the two formations  82 ,  84  could be used to induce flow from the higher pressure formation to the lower pressure formation, etc. 
   After perforating the test formation  82 , fluids are flowed into the assembly  86  via the circulation valve  30  as described above, by opening the valves  58 ,  66 . Preferably, a sufficiently large volume of fluid is initially flowed out of the test formation  82 , so that undesired fluids, such as drilling fluid, etc., in the formation are withdrawn from the formation. When one or more sensors, such as a resistivity or other fluid property or fluid identification sensor  102 , indicates that representative desired formation fluid is flowing into the assembly  86 , the lower valve  58  is closed. Note that the sensor  102  may be of the type which is utilized to indicate the presence and/or identity of solid matter in the formation fluid flowed into the assembly  86 . 
   Pressure may then be applied to the string  87  at the earth&#39;s surface to flow the undesired fluid out through check valves  104  and into the disposal formation  84 . The lower valve  58  may then be opened again to flow further fluid from the test formation  82  into the assembly  86 . This process may be repeated as many times as desired to flow substantially any volume of fluid from the formation  82  into the assembly  86 , and then into the disposal formation  84 . 
   Data acquired by the gauges  38  and/or sensors  102  while fluid is flowing from the formation  82  through the assembly  86  (when the valves  58 ,  66  are open), and while the formation  82  is shut in (when the valve  58  is closed) may be analyzed after or during the test to determine characteristics of the formation  82 . Of course, gauges and sensors of any type may be positioned in other portions of the assembly  86 , such as in the waste chambers  22 , between the valves  58 ,  66 , etc. For example, pressure and-temperature sensors and/or gauges may be positioned between the valves  58 ,  66 , which would enable the acquisition of data useful for injection testing of the disposal zone  84 , during the time the lower valve  58  is closed and fluid is flowed from the assembly  86  outward into the formation  84 . 
   It will be readily appreciated that, in this fluid flowing process as described above, the valve  58  is used to permit flow upwardly therethrough, and then the valve is closed when pressure is applied to the string  87  to dispose of the fluid. Thus, the valve  58  could be replaced by the check valve  90 , or the check valve may be supplied in addition to the valve as depicted in  FIG. 2 . 
   If a difference in formation pressure between the formations  82 ,  84  is used to flow fluid from the formation  82  into the assembly  86 , then a variable choke  88  may be used to regulate this fluid flow. Of course, the variable choke  88  could be provided in addition to other flow control devices, such as the valve  58  and check valve  90 , without departing from the principles of the present invention. 
   If a pump  94  is used to draw fluid into the assembly  86 , no flow control devices may be needed between the disposal formation  84  and the test formation  82 , the same or similar flow control devices depicted in  FIG. 2  may be used, or other flow control devices may be used. Note that, to dispose of fluid drawn into the assembly  86 , the pump  94  is operated with the valve  66  closed. 
   In a similar manner, the check valves  104  of the disposal sub  96  may be replaced with other flow control devices, other types of flow control devices, etc. 
   To provide separation between the low density fluid in the string  87  and the fluid drawn into the assembly  86  from the test formation  82 , a fluid separation device or plug  106  which may be reciprocated within the assembly  86  may be used. The plug  106  would also aid in preventing any gas in the fluid drawn into the assembly  86  from being transmitted to the earth&#39;s surface. An acceptable plug for this application is the Omega™ plug available from Halliburton Energy Services, Inc. Additionally, the plug  106  may have a fluid sampler  108  attached thereto, which may be activated to take a sample of the formation fluid drawn into the assembly  86  when desired. For example, when the sensor  102  indicates that the desired representative formation fluid has been flowed into the assembly  86 , the plug  106  may be deployed with the sampler  108  attached thereto in order to obtain a sample of the formation fluid. The plug  106  may then be reverse circulated to the earth&#39;s surface by opening the circulation valve  100 . Of course, in that situation, the plug  106  should be retained uphole from the valve  100 . 
   A nipple, no-go  110 , or other engagement device may be provided to prevent the plug  106  from displacing downhole past the disposal sub  96 . When applying pressure to the string  87  to flow the fluid in the assembly  86  outward into the disposal formation  84 , such engagement between the plug  106  and the device  110  may be used to provide a positive indication at the earth&#39;s surface that the pumping operation is completed. Additionally, a no-go or other displacement limiting device could be used to prevent the plug  106  from circulating above the upper valve  44  to thereby provide a type of downhole safety valve, if desired. 
   The sampler  108  could be configured to take a sample of the fluid in the assembly  86  when the plug  106  engages the device  110 . Note, also, that use of the device  110  is not necessary, since it may be desired to take a sample with the sampler  108  of fluid in the assembly  86  below the disposal sub  96 , etc. The sampler could alternatively be configured to take a sample after a predetermined time period, in response to pressure applied thereto (such as hydrostatic pressure), etc. 
   An additional one of the plug  106  may be deployed in order to capture a sample of the fluid in the assembly  86  between the plugs, and then convey this sample to the surface, with the sample still retained between the plugs. This may be accomplished by use of a plug deployment sub, such as that representatively depicted in  FIG. 3 . Thus, after fluid from the formation  82  is drawn into the assembly  86 , the second plug  106  is deployed, thereby capturing a sample of the fluid between the two plugs. The sample may then be circulated to the earth&#39;s surface between the two plugs  106  by, for example, opening the circulating valve  100  and reverse circulating the sample and plugs uphole through the string  87 . 
   Referring additionally now to  FIG. 3 , a fluid separation device or plug deployment sub  112  embodying principles of the present invention is representatively depicted. A plug  106  is releasably secured in a housing  114  of the sub  112  by positioning it between two radially reduced restrictions  116 . If the plug  106  is an Omega™ plug, it is somewhat flexible and can be made to squeeze through either of the restrictions  116  if a sufficient pressure differential is applied across the plug. Of course, either of the restrictions could be made sufficiently small to prevent passage of the plug  106  therethrough, if desired. For example, if it is desired to permit the plug  106  to displace upwardly through the assembly  86  above the sub  112 , but not to displace downwardly past the sub  112 , then the lower restriction  116  may be made sufficiently small, or otherwise configured, to prevent passage of the plug therethrough. 
   A bypass passage  118  formed in a sidewall of the housing  114  permits fluid flow therethrough from above, to below, the plug  106 , when a valve  120  is open. Thus, when fluid is being drawn into the assembly  86  in the method  80 , the sub  112 , even though the plug  106  may remain stationary with respect to the housing  114 , does not effectively prevent fluid flow through the assembly. However, when the valve  120  is closed, a pressure differential may be created across the plug  106 , permitting the plug to be deployed for reciprocal movement in the string  87 . The sub  112  may be interconnected in the assembly  86 , for example, below the upper valve  66  and below the plug  106  shown in  FIG. 2 . 
   If a pump, such as pump  94  is used to draw fluid from the formation  82  into the assembly  86 , then use of the low density fluid in the string  87  is unnecessary. With the upper valve  66  closed and the lower valve  58  open, the pump  94  may be operated to flow fluid from the formation  82  into the assembly  86 , and outward through the disposal sub  96  into the disposal formation  84 . The pump  94  may be any conventional pump, such as an electrically operated pump, a fluid operated pump, etc. 
   Referring additionally now to  FIG. 4 , another method  130  of performing a formation test embodying principles of the present invention is representatively depicted. The method  130  is described herein as being used in a “rigless” scenario, i.e., in which a drilling rig is not present at the time the actual test is performed, but it is to be clearly understood that such is not necessary in keeping with the principles of the present invention. Note that the method  80  could also be performed rigless, if a downhole pump is utilized in that method. Additionally, although the method  130  is depicted as being performed in a subsea well, a method incorporating principles of the present invention may be performed on land as well. 
   In the method  130 , a tubular string  132  is positioned in the well, preferably after a test formation  134  and a disposal formation  136  have been perforated. However, it is to be understood that the formations  134 ,  136  could be perforated when or after the string  132  is conveyed into the well. For example, the string  132  could include perforating guns, etc., to perforate one or both of the formations  134 ,  136  when the string is conveyed into the well. 
   The string  132  is preferably constructed mainly of a composite material, or another easily milled/drilled material. In this manner, the string  132  may be milled/drilled away after completion of the test, if desired, without the need of using a drilling or workover rig to pull the string. For example, a coiled tubing rig could be utilized, equipped with a drill motor, for disposing of the string  132 . 
   When initially run into the well, the string  132  may be conveyed therein using a rig, but the rig could then be moved away, thereby providing substantial cost savings to the well operator. In any event, the string  132  is positioned in the well and, for example, landed in a subsea wellhead  138 . 
   The string  132  includes packers  140 ,  142 ,  144 . Another packer may be provided if it is desired to straddle the test formation  134 , as the test formation  82  is straddled by the packers  24 ,  32  shown in  FIG. 2 . The string  132  further includes ports  146 ,  148 ,  150  spaced as shown in  FIG. 4 , i.e., ports  146  positioned below the packer  140 , ports  148  between the packers  142 ,  144 , and ports  150  above the packer  144 . Additionally the string  132  includes seal bores  152 ,  154 ,  156 ,  158  and a latching profile  160  therein for engagement with a tester tool  162  as described more fully below. 
   The tester tool  162  is preferably conveyed into the string  132  via coiled tubing  164  of the type which has an electrical conductor  165  therein, or another line associated therewith, which may be used for delivery of electrical power, data transmission, etc., between the tool  162  and a remote location, such as a service vessel  166 . The tester tool  162  could alternatively be conveyed on wireline or electric line. Note that other methods of data transmission, such as acoustic, electromagnetic, fiber optic etc. may be utilized in the method  130 , without departing from the principles of the present invention. 
   A return flow line  168  is interconnected between the vessel  166  and an annulus  170  formed between the string  132  and the wellbore  12  above the upper packer  144 . This annulus  170  is in fluid communication with the ports  150  and permits return circulation of fluid flowed to the tool  162  via the coiled tubing  164  for purposes described more fully below. 
   The ports  146  are in fluid communication with the test formation  134  and, via the interior of the string  132 , with the lower end of the tool  162 . As described below, the tool  162  is used to pump fluid from the formation  134 , via the ports  146 , and out into the disposal formation  136  via the ports  148 . 
   Referring additionally now to  FIG. 5 , the tester tool  162  is schematically and representatively depicted engaged within the string  132 , but apart from the remainder of the well as shown in  FIG. 4  for illustrative clarity. Seals  172 ,  174 ,  176 ,  178  sealingly engage bores  152 ,  154 ,  156 ,  158 , respectively. In this manner, a flow passage  180  near the lower end of the tool  162  is in fluid communication with the interior of the string  132  below the ports  148 , but the passage is isolated from the ports  148  and the remainder of the string above the seal bore  152 ; a passage  182  is placed in fluid communication with the ports  148  between the seal bores  152 ,  154  and, thereby, with the disposal formation  136 ; and a passage  184  is placed in fluid communication with the ports  150  between the seal bores  156 ,  158  and, thereby, with the annulus  170 . 
   An upper passage  186  is in fluid communication with the interior of the coiled tubing  164 . Fluid is pumped down the coiled tubing  164  and into the tool  162  via the passage  186 , where it enters a fluid motor or mud motor  188 . The motor  188  is used to drive a pump  190 . However, the pump  190  could be an electrically-operated pump, in which case the coiled tubing  164  could be a wireline and the passages  186 ,  184 , seals  176 ,  178 , seal bores  156 ,  158 , and ports  150  would be unnecessary. The pump  190  draws fluid into the tool  162  via the passage  180 , and discharges it from the tool via the passage  182 . The fluid used to drive the motor  188  is discharged via the passage  184 , enters the annulus, and is returned via the line  168 . 
   Interconnected in the passage  180  are a valve  192 , a fluid property sensor  194 , a variable choke  196 , a valve  198 , and a fluid identification sensor  200 . The fluid property sensor  194  may be a pressure, temperature, resistivity, density, flow rate, etc. sensor, or any other type of sensor, or combination of sensors, and may be similar to any of the sensors described above. The fluid identification sensor  200  may be a nuclear magnetic resonance sensor, an acoustic sand probe, or any other type of sensor, or combination of sensors. Preferably, the sensor  194  is used to obtain data regarding physical properties of the fluid entering the tool  162 , and the sensor  200  is used to identify the fluid itself, or any solids, such as sand, carried therewith. For example, if the pump  190  is operated to produce a high rate of flow from the formation  134 , and the sensor  200  indicates that this high rate of flow results in an undesirably large amount of sand production from the formation, the operator will know to produce the formation at a lower flow rate. By pumping at different rates, the operator can determine at what fluid velocity sand is produced, etc. The sensor  200  may also enable the operator to tailor a gravel pack completion to the grain size of the sand identified by the sensor during the test. 
   The flow controls  192 ,  196 ,  198  are merely representative of flow controls which may be provided with the tool  162 . These are preferably electrically operated by means of the electrical line  165  associated with the coiled tubing  164  as described above, although they may be otherwise operated, without departing from the principles of the present invention. 
   After exiting the pump  190 , fluid from the formation  134  is discharged into the passage  182 . The passage  182  has valves  202 ,  204 ,  206 , sensor  208 , and sample chambers  210 ,  212  associated therewith. The sensor  208  may be of the same type as the sensor  194 , and is used to monitor the properties, such as pressure, of the fluid being injected into the disposal formation  136 . Each sample chamber has a valve  214 ,  216  for interconnecting the chamber to the passage  182  and thereby receiving a sample therein. Each sample chamber may also have another valve  218 ,  220  (shown in dashed lines in  FIG. 5 ) for discharge of fluid from the sample chamber into the passage  182 . Each of the valves  202 ,  204 ,  206 ,  214 ,  216 ,  218 ,  220  may be electrically operated via the coiled tubing  164  electrical line as described above. 
   The sensors  194 ,  200 ,  208  may be interconnected to the line  165  for transmission of data to a remote location. Of course, other means of transmitting this data, such as acoustic, electromagnetic, etc., may be used in addition, or in the alternative. Data may also be stored in the tool  162  for later retrieval with the tool. 
   To perform a test, the valves  192 ,  198 ,  204 ,  206  are opened and the pump  190  is operated by flowing fluid through the passages  184 ,  186  via the coiled tubing  164 . Fluid from the formation  134  is, thus, drawn into the passage  180  and discharged through the passage  182  into the disposal formation  136  as described above. 
   When one or more of the sensors  194 ,  200  indicate that desired representative formation fluid is flowing through the tool  162 , one or both of the samplers  210 ,  212  is opened via one or more of the valves  214 ,  216 ,  218 ,  220  to collect a sample of the formation fluid. The valve  206  may then be closed, so that the fluid sample may be pressurized to the formation  134  pressure in the samplers  210 ,  212  before closing the valves  214 ,  216 ,  218 ,  220 . One or more electrical heaters  222  may be used to keep a collected sample at a desired reservoir temperature as the tool  162  is retrieved from the well after the test. 
   Note that the pump  190  could be operated in reverse to perform an injection test on the formation  134 . A microfracture test could also be performed in this manner to collect data regarding hydraulic fracturing pressures, etc. Another formation test could be performed after the microfracture test to evaluate the results of the microfracture operation. As another alternative, a chamber of stimulation fluid, such as acid, could be carried with the tool  162  and pumped into the formation  134  by the pump  190 . Then, another formation test could be performed to evaluate the results of the stimulation operation. Note that fluid could also be pumped directly from the passage  186  to the passage  180  using a suitable bypass passage  224  and valve  226  to directly pump stimulation fluids into the formation  134 , if desired. 
   The valve  202  is used to flush the passage  182  with fluid from the passage  186 , if desired. To do this, the valves  202 ,  204 ,  206  are opened and fluid is circulated from the passage  186 , through the passage  182 , and out into the wellbore  12  via the port  148 . 
   Referring additionally now to  FIG. 6 , another method  240  embodying principles of the present invention is representatively illustrated. The method  240  is similar in many respects to the method  130  described above, and elements shown in  FIG. 6  which are similar to those previously described are indicated using the same reference numbers. 
   In the method  240 , a tester tool  242  is conveyed into the wellbore  12  on coiled tubing  164  after the formations  134 ,  136  have been perforated, if necessary. Of course, other means of conveying the tool  242  into the well may be used, and the formations  134 ,  136  may be perforated after conveyance of the tool into the well, without departing from the principles of the present invention. 
   The tool  242  differs from the tool  162  described above and shown in  FIGS. 4 &amp; 5  in part in that the tool  242  carries packers  244 ,  246 ,  248  thereon, and so there is no need to separately install the tubing string  132  in the well as in the method  130 . Thus, the method  240  may be performed without the need of a rig to install the tubing string  132 . However, it is to be clearly understood that a rig may be used in a method incorporating principles of the present invention. 
   As shown in  FIG. 6 , the tool  242  has been conveyed into the well, positioned opposite the formations  134 ,  136 , and the packers  244 ,  246 ,  248  have been set. The upper packers  244 ,  246  are set straddling the disposal formation  136 . The passage  182  exits the tool  242  between the upper packers  244 ,  246 , and so the passage is in fluid communication with the formation  136 . The packer  248  is set above the test formation  134 . The passage  180  exits the tool  242  below the packer  248 , and the passage is in fluid communication with the formation  134 . A sump packer  250  is shown set in the well below the formation  134 , so that the packers  248 ,  250  straddle the formation  134  and isolate it from the remainder of the well, but it is to be clearly understood that use of the packer  250  is not necessary in the method  240 . 
   Operation of the tool  242  is similar to the operation of the tool  162  as described above. Fluid is circulated through the coiled tubing string  164  to cause the motor  188  to drive the pump  190 . In this manner, fluid from the formation  134  is drawn into the tool  242  via the passage  180  and discharged into the disposal formation  136  via the passage  182 . Of course, fluid may also be injected into the formation  134  as described above for the method  130 , the pump  190  may be electrically operated (e.g., using the line  165  or a wireline on which the tool is conveyed), etc. 
   Since a rig is not required in the method  240 , the method may be performed without a rig present, or while a rig is being otherwise utilized. For example, in  FIG. 6 , the method  240  is shown being performed from a drill ship  252  which has a drilling rig  254  mounted thereon. The rig  254  is being utilized to drill another wellbore via a riser  256  interconnected to a template  258  on the seabed, while the testing operation of the method  240  is being performed in the adjacent wellbore  12 . In this manner, the well operator realizes significant cost and time benefits, since the testing and drilling operations may be performed simultaneously from the same vessel  252 . 
   Data generated by the sensors  194 ,  200 ,  208  may be stored in the tool  242  for later retrieval with the tool, or the data may be transmitted to a remote location, such as the earth&#39;s surface, via the line  165  or other data transmission means. For example, electromagnetic, acoustic, or other data communication technology may be utilized to transmit the sensor  194 ,  200 ,  208  data in real time. 
   Of course, a person skilled in the art would, upon a careful reading of the above description of representative embodiments of the present invention, readily appreciate that modifications, additions, substitutions, deletions and other changes may be made to these embodiments, and such changes are contemplated by the principles of the present invention. For example, although the methods  10 ,  80 ,  130 ,  240  are described above as being performed in cased wellbores, they may also be performed in uncased wellbores, or uncased portions of wellbores, by exchanging the described packers, tester valves, etc. for their open hole equivalents. The foregoing detailed description is to be clearly understood as being given by way of illustration and example only.

Summary:
Methods and apparatus are provided which permit well testing operations to be performed downhole in a subterranean well. In various described methods, fluids flowed from a formation during a test may be disposed of downhole by injecting the fluids into the formation from which they were produced, or by injecting the fluids into another formation. In several of the embodiments of the invention, apparatus utilized in the methods permit convenient retrieval of samples of the formation fluids and provide enhanced data acquisition for monitoring of the test and for evaluation of the formation fluids.