Abstract:
A portable apparatus and method provide on-site permeability measurements of a core sample extracted from a subterranean reservoir. The portable apparatus is easily and conveniently transported to well locations for use on-site, thereby allowing the core sample to be tested in actual reservoir conditions. The apparatus can simultaneously test incoming liquids and liquids passing through the core sample, and can measure data in the forward and reverse flow directions. The apparatus requires only a single pump to pressurize and inject the liquid into the core sample.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to petrophysical reservoir characterization, and, in particular, to on-site permeability measurements obtained of core samples collected from formation rock adjacent well bores in subsurface reservoirs to determine formation areas of interest. 
     2. Description of the Related Art 
     In the petroleum extraction and production industry, ascertaining the subterranean characteristics of reservoirs is of vital economic importance. Characteristics such as formation rock permeability and porosity help to indicate subsurface areas of increased fluid movement. In order to locate these areas, the permeability and porosity of the reservoir rock must be determined. Permeability refers to the ability of the reservoir rock to transmit fluids through many large interconnected pore spaces. Porosity is a measure of the capacity of the reservoir rock which is able to store oil and gas, or in other words, the volume of the pore space in a porous medium. 
     In current reservoir analysis methods, so far as known, porosity and permeability measurements have been determined by removing core samples from a well drilled into a reservoir rock formation of interest. So far as known, once these samples had been removed, they were transported to a testing facility which was at a laboratory and not at the site of the well. Once the samples were transported to the laboratory, the technician or scientist could begin conducting various tests to determine the permeability of the reservoir samples. 
     There were many disadvantages to this type of reservoir analysis. First, preserving the fresh and original state of the core sample is highly important in ascertaining various data, such as water quality, biocide functioning, and microbial activity. However, during transportation to the experiment lab, maintaining the original state was very difficult. Also, the test fluids used in the lab tests might differ to an appreciable extent from the actual fluids at the reservoir or to be used at the reservoir. Further, in current analysis methods, the time it took to transport the samples to the laboratory resulted in lost time and higher production costs. Drilling companies spend vast amounts of money each day performing drilling operations; therefore, any way to reduce this time would be advantageous. Additionally, the present testing systems, so far as is known, are too large and cumbersome to be efficiently transported on-site to conduct testing. 
     SUMMARY 
     Briefly, the present invention provides a new and improved apparatus for permeability measurements of a core sample obtained from a subterranean reservoir. The apparatus of the present invention includes a core sample holder receiving a core sample obtained from the subterranean reservoir for permeability testing. The core sample holder has a test inlet port for receiving fluid for permeability testing of the core sample and also has an outlet port for exit of the fluid. An accumulator in the apparatus contains fluid for application to the core sample holder for permeability testing of the core sample, and a pump applies fluid from the accumulator to the core sample holder at selected controlled fluid pressure and flow rate. A pressure regulator is in fluid communication with the core sample holder to establish an inlet pressure for the fluid at the test inlet port of the core sample holder for the applied fluid. A pressure transducer section in the apparatus measures pressure differential of the fluid between the inlet and outlet ports of the core sample holder, and a data processor obtains a measure of the relative permeability of the core sample based on the pressure differential measurements and the fluid flow rates. 
     The present invention also provides a new and improved modular apparatus transportable to a well site for permeability measurements of a core sample obtained from a subterranean reservoir of the well. The modular apparatus includes a container module having a floor base, side walls and a partition between the side walls to form front and rear compartments. A core sample holder is mounted with the floor base of the module to receive a core sample obtained from the subterranean reservoir for permeability testing. The core sample holder has a test inlet port for receiving fluid for permeability testing of the core sample, and an outlet port for exit of the fluid. An accumulator is mounted with a side wall of the module and contains fluid for application to the core sample holder for permeability testing of the core sample. A pump is mounted with the floor of the module and applies fluid from the accumulator to the core sample holder at selected controlled fluid pressure and flow rate for sample testing. A pressure regulator in fluid communication with the core sample holder establishes an inlet pressure for the fluid at the test inlet port of the core sample holder. A pressure transducer section mounted with the partition of the module measures pressure differential of the fluid between the inlet and outlet ports of the core sample holder. A data processor mounted on an upper portion of the module for obtains measures of the relative permeability of core samples based on the pressure differential measurements and the fluid flow rates. 
     The present invention further provides a new and improved method of on-site permeability measurements of a core sample extracted from a subterranean reservoir adjacent a well. According to the method of the present invention, a modular test apparatus is transported to a well site for permeability measurements of a core sample obtained from a subterranean reservoir of the well. A core sample obtained from a subterranean reservoir is inserted into the core sample holder. A test fluid is pressurized and applied to the core sample holder at a test flow rate. Flow rate and pressure differential data measurements are acquired for the core sample being tested, and a measure of the relative permeability of the core sample at the well site is obtained based on the pressure differential measurements and the fluid flow rates. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The objects, advantages and features of the invention will become more apparent by reference to the drawings appended thereto, wherein like numerals indicate like parts and wherein an illustrated embodiment of the invention is shown, of which: 
         FIG. 1  is a front view of the portable testing apparatus according to an embodiment of the present invention. 
         FIG. 2  is a left side view of the portable testing apparatus of  FIG. 1 . 
         FIG. 3  is a right side view of the portable testing apparatus of  FIG. 1 . 
         FIG. 4  is a rear view of the portable testing apparatus of  FIG. 1 . 
         FIG. 5  is a schematic diagram of the interconnection and valving arrangement of the components of the portable testing apparatus of  FIG. 1 . 
         FIG. 6  is a flow chart illustrating a method sequence of steps according to the present invention. 
         FIGS. 7 ,  8  and  9  are data displays illustrating example measurements of permeability as a function of flow rate obtained according to the present invention. 
         FIGS. 10 ,  11  and  12  are data displays illustrating example measurements of differential pressure as a function of flow rate obtained according to the present invention. 
         FIGS. 13 and 14  are charts listing the data output of test results obtained according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In the drawings ( FIGS. 1-5 ), a portable, on-site core permeability testing apparatus A is shown according to the present invention. The permeability testing apparatus A of the present invention is modular and compact, as will be set forth, and thus is easily transportable, even to remote well sites. The permeability testing apparatus A accordingly measures fluid permeabilities, such as water or oil, on-site of reservoir samples at ambient pressure or at reservoir pressure conditions. The on-site permeability testing apparatus A enables scientists and technicians to determine the impact of injected brine or produced oil on reservoir core permeability in a minimal amount of time. Since data are obtained from freshly collected formation core samples, the quality of actual well injection water or brine can be assessed, and accurate measurements of biocide functioning and microbial activity in the reservoir are made available. Each of these advantages is significant. Further, since the apparatus A is capable of use at the well site with freshly collected formation samples, the results are more accurate than those obtained in an off-site lab due to changes in the field water quality during transport times. 
     The on-site permeability testing apparatus A includes a core holder section H, which includes a core sample container  20  which contains the formation core sample extracted from a subterranean reservoir. As will be set forth, the core sample container  20  is pressurized in the apparatus A during testing to desired pressures of either brine or oil at selected flow rates for permeability testing purposes. If desired, a heating tape  21  can be applied to core sample container  20  in order to heat the core sample to a desired ambient or reservoir temperature. During testing, fluids, such as water or oil, are pressurized and pumped across the core sample in core sample container  20  by a pump P. 
     The testing apparatus A includes the pump P ( FIGS. 4 and 5 ) which is capable of providing calibrated fluid pressure and volume for core sample permeability testing. The pump P is preferably of the type known as a high pressure liquid chromatography or HPLC pump of a suitable commercially available type. A suitable pump, for example, is a Model PU-2086 HPLC pump available from Jasco International Co., Ltd., of Tokyo, Japan. The pump P is connected to an accumulator bank B which can selectively furnish either water/brine or oil to the core holder H. With the present invention, the apparatus A is easily transportable to and usable at well locations on-site, even remote ones. Thus, the fluids used in testing a formation core sample can be those encountered in the same well from which the core sample was obtained. 
     Measurement instrumentation I in the form of a first or low differential pressure transducer section T and a second or high pressure differential transducer section S is connected to obtain pressure measurements in a manner to be set forth for permeability testing and measurement purposes. A data acquisition section D is connected to the measurement instrumentation I ( FIG. 5 ) for processing, recording, storage and display of data measurements obtained from tests performed on core samples in the core holder if The testing apparatus A also includes a filter, to be described further below, which is used to filter solids and other sediments from the testing fluids, thereby preventing clogging of the lines. 
     The apparatus A is mounted in a container module M ( FIGS. 1-4 ) which is modularized for ease of transport to remote well sites. The container module is easily lifted and moved by two people onto a vehicle for transport to a well site. The container module M has a base or floor  24 , two upright side walls  26  and  28 , and a central partition or wall  30  which separates the module M into a front compartment  31  ( FIG. 1 ) and a rear compartment  32  ( FIG. 4 ). An upper ledge or wall  33  is mounted above the walls  26 ,  28  and  30 . 
     As will be set forth, the fluid permeability testing components, valving and interconnection fluid tubing and pipes of the apparatus A are mounted in the module M for ease of transport and storage. Typical dimensions of the container module M are twenty-four inches high, twenty-five inches deep and thirty inches wide. The side walls  26  and  28  both have one or more hand grip portals or slots formed therein as indicated at  36  and  38 , respectively, for ease of lifting and loading the apparatus A into a vehicle for transport. 
     The pump P is connected through a fluid tube or pipe  40  to a three way connector  42  which is in turn connected through a fluid tube  44  and a two stem, three way control valve  46  to the fluid accumulator bank B. The pump P is also connected by a check or bypass control valve  47  and a fluid tube or pipe  48  to a centrally located inlet port  50  of the core sample container  20 . 
     The control valve  46  is connected by fluid tubes  52  and  54 , respectively, to a brine accumulator  56  and an oil accumulator  58  of the accumulator bank B. Each of the accumulators  56  and  58  is preferably of the floating piston type and stores a volume of fluid under regulated and controlled pressures and flow rates for the purpose of permeability testing of core sample specimens with the apparatus, as will be described. The filter may be located within the accumulator  56 , or at an outlet port of the accumulator  56 , or as shown at  36   a  in the line to valve  46  ( FIG. 2 ). 
     The accumulators  56  and  58  are each connected as indicated at fluid tubes  60  and  62  to a two stem, three way control valve  64  at the outlet of the accumulator bank B. The three way control valve  64  in a first of its three positions blocks flow of fluid from the accumulator bank B, and in its second and third positions allows either the brine in accumulator  56  or the oil in oil accumulator  58 , as the case may be, to pass from the accumulator bank B to a control valve  66 . The control valve  66  is connected by a fluid tube  68  to a four way connector manifold  70 . Control valve  66  when opened allows fluid flow from the accumulator bank B to the core sample container  20  for testing purposes. 
     The valves  42 ,  46 ,  64  and  66 , the brine accumulator  56 , the oil accumulator  58  and their associated connection fluid tubes or piping are mounted on an outer surface  26   a  ( FIG. 2 ) of the side wall  26  of the module M. The pump P is located in the rear compartment  32  ( FIG. 4 ) on a stand or platform as shown at  33  on the floor  24  of the module M behind the central wall or partition  30  for the purposes of weight distribution. The fluid tube  40  which connects the pump P to the valve  42  extends through the side wall  26  of the module M to the connector  42 . The core sample container  20  is mounted on the floor  24  of the module M. 
     The pump P is provided with a control or instrumentation panel  71  ( FIG. 3 ) which is accessible through an opening  28   a  ( FIG. 4 ) formed in the side wall  28  of the module M. One or more fluid containers  72  of test fluids such as brine or oil are, as shown in  FIG. 4 , located in the rear compartment  32  such as by being mounted on the pump P. Fluids in the containers  72  are furnished to the pump P and provided therefrom as test fluids for permeability testing in the apparatus A. 
     A pressure gauge  73  is connected through a fluid tube  74  to the four way manifold  70  through a control valve  76  to an inlet pressure regulator  80 . The pressure regulator  80  is connected to the manifold  70  by a control valve  70   a . Pressure regulator  80  controls the inlet pressure to the core sample holder section H according to the desired test conditions. The pressure regulator  80  is connected to a fluid outlet and vent tube  82  to convey excess outlet brine or oil to a suitable waste or recycling vessel or container  84  located on the floor  24  of the module M. Container  84  can be marked or otherwise calibrated to indicate its volumetric contents. The pressure gauge  73  is connected to the inlet pressure regulator  80  when the control valve  76  is open so that pressure at the inlet to the sample holder section H may be observed by operators of the apparatus A. 
     The pressure regulator  80  is capable of obtaining samples of the fluid while maintaining pore pressure on the core sample holder section H. Although severable types of such pressure regulators may be used, in a preferred embodiment a suitable example pressure regulator may be a Model MBPR-3 back pressure regulator available from Coretest Systems, Inc. of Morgan Hills, Calif. The apparatus A can thus sample any fluid used in the inlet or the outlet without disturbing permeability testing measurements and without removing or reducing pore pressure. 
     The pressure regulator  80  is mounted as indicated by a bracket or comparable structure  80   a  on inside surface  26   b  ( FIG. 1 ) of the side wall  26  of module M. The pressure gauge  73  is mounted in a comparable manner to the same inside surface  26   b.    
     A two stem, three way control valve  86  connected at the inlet of each of a low pressure differential transducer section  90  and a high pressure differential transducer section  92  of the measurement instrumentation I receives fluid through a tube  94  from the four way manifold  70 . Control valve  86  in a first of its three positions blocks flow of fluid from manifold  70 , and in its second and third positions allows fluid to pass to the low pressure differential transducer section  90  and the high pressure differential transducer section  92  of the measurement instrumentation I, as the case may be, for obtaining pressure data readings in the data acquisition section D regarding fluids in the accumulator bank B. The components of the transducer sections  90  and  92  are mounted on a front surface  30   a  ( FIG. 1 ) of the central wall  30  of the module M. 
     A two stem, three way control valve  96  in the sample holder section H of the apparatus A is connected to the manifold  70  by a fluid tube  98 . The valve  96  controls application of test fluids from the accumulator bank B through a manifold  99  to a test fluid inlet port  100  of the core sample container  20 . The manifold  70  is also connected to the instrumentation section I by the fluid tube  94 , where either the low differential pressure transducer  90  or the high pressure differential transducer  92  may be selectively connected to sense pressure conditions. Pressure conditions at inlet port  100  of the core sample container  22  are sensed and converted in the transducers of instrumentation section I into electrical signals and transferred to the data acquisition section D. The electrical connections for transferring the signals for this purpose are not shown in the drawings so that other structure may be more clearly seen. 
     With the present invention, the differential pressure transducer sets include preferably at least two differential transducers  90  and  92  which can be selectively used to sense pressure differentials in different pressure sensing ratings or ranges. This is done so that flexibility is provided to measure low and high core permeabilities. For example, for core samples with expected very high permeability, differential pressure transducer section  90  with a relatively low range may be used to obtain more accurate results. Conversely, for core samples with expected low permeability, differential pressure transducer section  92  with a relatively high pressure differential range may be used. 
     The manifold  99  is also connected through a fluid tube  102  and a control valve  104  to a second four way distribution manifold  106  for application of reverse flow and pressure conditions to a test inlet port  110  at an end portion  112  of the core sample container  20 . A two stem, three way control valve  116  is connected through a fluid tube  118  to the manifold  106 . The control valve  116  allows application of fluid from the accumulator bank B to the core sample container  20  at test inlet port  110  as testing procedures require. 
     The manifold  106  is also connected by a fluid tube  120  to a two stem, three way control valve  122  at an inlet side of the high pressure differential transducer section  92  of the measurement instrumentation I. The control valve  116  is also connected by a fluid tube  124  to control valve  96  for fluid routing purposes as testing procedures require. Manifold  106  additionally is connected to an outlet or fluid outlet section O of the apparatus A, as will be described. 
     A three way connector  126  is connected by a fluid tube  128  to a central outlet port  130  in the core sample container  22 . A pressure gauge  132  is in fluid communication through connector  126  with the central outlet port  130  so that pressure at the outlet of the core holder section H may be observed by operators of the apparatus A. A two stem, three way control valve  136  in fluid communication with the connector  126  and central outlet port  130  is connected (not shown) to the fluid pressure transducer sections  90  and  92 . The gauge  132 , transducer sections  90 ,  92  and valve  136  are mounted with the surface  30   a  of the central wall  30  of the module M. 
     The transducer sections  90  and  92  sense pressure conditions at the outlet port  130  of the core sample container  20  and convert these measurements into electrical signals for transfer via suitable electrical or signal connection to the data acquisition section D. Electrical power for the components of apparatus A needing such power is typically provided by suitable connections to the well site power, although generators, batteries or other power sources may be used, if desired. 
     The control valve  122  is connected to both the low pressure differential transducer section  90  and the high pressure differential transducer section  92  of the measurement instrumentation I. Control valve  122 , in a comparable manner to valve  86 , in a first of its three positions blocks flow of fluid from its associated manifold  106 , and in its second and third positions allows fluid to pass to the low pressure differential transducer section  90  and the high pressure differential transducer section  92  of the measurement instrumentation I, as the case may be, for obtaining data readings in the data acquisition section D regarding fluids in the accumulator bank B. The control valves  86  and  136  are each operable independently of each other and are connected to provide the apparatus A with multichannel data acquisition capability. Differential pressures at different locations in the apparatus A can thus be sensed and recorded while tests are in progress, without need to affect the test operations then under way. 
     The low pressure differential transducer section  90  of measurement instrumentation I includes a three way fluid connector  140  connected to an outlet of the control valve  86  by fluid tube  142  and a three way fluid connector  144  connected to an outlet of the control valve  122  by fluid tube  146 . A bypass control valve  148  and a low differential pressure transducer  150  are connected in alternate flow paths between the connectors  140  and  144 . Depending on the setting of the bypass control valve  148 , fluid pressure conditions in low ranges in the core sample holder  20  can be sensed by the low differential pressure transducer  150  and converted to electrical signals which are furnished to the data acquisition section D. 
     Similarly, the high pressure differential transducer section  92  of measurement instrumentation I includes a three way fluid connector  151  connected to an outlet of the control valve  122  by fluid tube  152  and a three fluid connector  154  connected to an outlet of the control valve  86  by a fluid tube  156 . A bypass control valve  158  and a high differential pressure transducer  160  are connected in alternate flow paths between the connectors  151  and  154 . Depending on setting of the bypass control valve  158 , fluid pressure conditions in high ranges in the sample holder chamber  20  can be sensed by the differential pressure transducer  160  and converted to electrical signals which are furnished by suitable communication to the data acquisition section D. 
     The data acquisition unit D includes a data acquisition processor/computer  170  of any suitable commercially available type. The measurements obtained by the pressure transducers described above in the apparatus A are received by the data acquisition computer  170  for processing, storing and storage according to the present invention in order to determine permeability of the core sample currently being tested in the core sample chamber or container  20 . 
     The computer  170  can be a portable or PC compatible computer of any conventional type of suitable processing capacity such as those available from any of several sources. The computer  170  may be a laptop computer, notebook computer or any other suitable data processing apparatus. It should also be understood that other types of digital signal processors or other forms of data processors may also be used, as well. 
     In any case, the processor of the computer  170  accesses the data measurements provided from the measurement instrumentation I through a data input/output unit  172  to undertake the pressure reading signal processing and analysis logic of the present invention, which may be executed by a processor as a series of computer-executable instructions in the computer  170 . The processed results from computer  170  are then available for analysis on an output display or printer of suitable display or plotter of the data input/output unit  172 . The data input/output unit  172  also includes an input and control portion  174  such as a keyboard, touchpad, mouse or other suitable data and instruction entry mechanism. 
     The computer  170  is mounted on a shelf  176  located in the rear compartment  32  ( FIG. 4 ) adjacent an opening  30   b  ( FIG. 1 ) formed at an upper central portion of the partition or wall  30  below the upper ledge or wall  33 . The data input/output unit  174  is preferably mounted on the upper ledge or shelf  33 . The rear compartment  32  of the module M is preferably enclosed, having doors  177  and  178  which may be opened for access to the computer  170 , the pump P and the fluid containers  72 . Locks may be provided for the doors  177  and  178 , if desired, for security or safety purposes. 
     In the fluid outlet section O ( FIG. 5 ) of the apparatus A, a three-way or T connector  180  is connected to the manifold  106  by a fluid tube  182 . The connector  180  is connected to the instrumentation section I, which senses outlet fluid pressure conditions of the core sample holder section H in the manner set forth above, converting the sensed pressure conditions into electrical signals. The signals from the pressure differential transducers  150  or  160 , as the case may be, are furnished to computer  170  in the data processing section D for processing. 
     An outlet fluid pressure regulator  186  is in fluid communication with the connector  180  through fluid tube  188  and serves to establish the required outlet pressure in the required testing outlet pressure in the core sample holder section H for the various tests and data measurements. A pressure gauge  190  is connected by a control valve  192  through fluid tube  194  so that pressure at the outlet of core sample holder section H may be observed by the operator or technician. An outlet drain tube  196  connects the pressure regulator  186  to a fluid drainage or disposal container  198  at the outlet of the apparatus A. The container  198  is located on the floor  30  of the module M and is calibrated or otherwise marked or indexed to provide indications of its volumetric content. 
     As was the case with pressure regulator  80  at the inlet, the pressure regulator  186  is capable of obtaining samples of the fluid while maintaining pore pressure on the core sample holder section H. Although severable types of such pressure regulators may be used, in a preferred embodiment a suitable example pressure regulator may be a Model MBPR-3 of the type available from Coretest Systems, Inc. of the type used as pressure regulator  80 . The apparatus A can thus sample any fluid used in the inlet or the outlet without disturbing permeability testing measurements and without removing or reducing pore pressure. 
     The pressure regulator  186  is mounted as indicated by a bracket or comparable structure  186   a  on inside surface  28   b  ( FIG. 1 ) of the side wall  28  of module M. The pressure gauge  190  is mounted in a comparable manner to the same inside surface  28   b.    
     Permeability testing according to the present invention is performed in the manner indicated schematically in the process flow chart of  FIG. 6 . With the apparatus A on-site, an operator or technician sets or establishes the desired testing parameters at step  201 . For example, these parameters can include setting the overburden pressure, pore pressure, and the flow rate of the fluids. Once the parameters have been set, the technician then measures the diameter and length of the sample in step  203 . In the preferred embodiment, core sample holder  20  can accommodate a 3 inch long core sample with a diameter of 1.5 inches. However, those skilled in the art realize the core holder can be designed to accommodate other sizes. 
     At step  205 , the technician vacuums and saturates the sample with a brine or NaCl solution. At step  207 , the technician then measures the viscosity of the brine solution at room temperature. Once viscosity measuring is complete, the technician then loads the sample into core holder  20 . Pump P is then used to pressurize to simulate the formation overburden with distilled water up to a suitable pressure, such as 1500 psi, as indicated at step  209 . At step  211 , the technician then calibrates inlet pressure transducer  102 , inlet pressure regulator  80 , as well as outlet pressure transducer  184  and pressure regulator  186 . Thereafter, the technician fills piston accumulator  56  with filtered brine solution, preferably that used in the well from which the core sample was obtained. The operator then connects all system lines, and sets the valves of the apparatus A in a forward flow direction of the fluid from the accumulator bank B into the port  100  of the core sample holder  20 . 
     At step  213 , the technician sets the pump rate of the pump P to a first desired flow rate. At step  215 , the technician starts the pump P and opens the by-pass valve  47  to the core holder  20  in order to flush the fluid tubes or lines. After the fluid lines are clear, the technician then checks to be certain the pressure differential or dP readings are zero. Once checked, the by-pass valve  47  is then closed, and differential transducers in instrumentation section I begin to monitor the differential pressure across core sample holder  20  until a stabilized pressure drop at the desired rate is achieved. 
     The fluid permeability of the sample in the core sample holder  20  then proceeds over the specified range of pressures and flow rates. The testing procedure can be performed for a number of desired flow rates and pressure differentials. The data acquisition section D receiving data measurements for the desired flow rates and pressure differentials and computes, stores and displays the permeability testing results. For forward flow, valve  96  is set so that flow is permitted at  96   b  and blocked at  96   a , while valve  116  is set so that flow is permitted at  116   b  and blocked at  116   a . For reverse flow, valve  96  is set to opposite flow conditions, permitting flow at  96   a  and blocking flow at  96   b . Similarly, valve  116  is set for reverse flow so that flow is permitted at  116   a  and blocked at  116   b.    
     The relative permeability of a core sample is determined in the data acquisition system computer  170 , typically using Darcy&#39;s Law of Relative Permeability. Code for the computer  170  is conventional and can be using any well known programming language, such as C, C++, or Java. Darcy&#39;s Law is a known relation used in permeability testing, expressed as a derived equation that describes the flow of a fluid through a porous medium. The relation of the permeability coefficient for a formation core sample of a particular volume based on fluid flow therethrough may be expressed as: 
     
       
         
           
             K 
             = 
             
               
                 245 
                 · 
                 dV 
                 · 
                 U 
                 · 
                 L 
               
               
                 dT 
                 · 
                 A 
                 · 
                 dP 
               
             
           
         
       
     
     In the foregoing expression of Darcy&#39;s law: 
     K=permeability coefficient, measured in Darcy units 
     dV=throughput volume, in cc 
     U=viscosity, in centipoise or cP (liquid) 
     L=length of the sample (cm) 
     A=cross-sectional area of sample (diameter 2×3.1416 ) (4)=area, cm 2 , 
     dP=pressure differential in psi, and 
     dT=time. 
     After data acquisition system D has determined the permeability coefficient during a test of a sample for a particular throughput volume and pressure differential, the calculated data can be transferred to a workable file program, such as EXCEL, contained in memory associated with the computer  170 , and plotted or displayed, or both, with input/output unit  172 . 
     Examples of permeability testing according to the present invention are illustrated in  FIGS. 7 through 14 . Conventional sandstone sample plugs of the known Berea core type with a 3% brine or NaCl solution were used, and  FIG. 13  is a replicated chart of example data readings for permeability coefficients obtained over a range of flow rates per unit area with an apparatus according to the present invention.  FIG. 7  is a plot of those portions of the data from  FIG. 13  for forward flow of the solution through the sample, and  FIG. 8  is a plot of those portions of the data from  FIG. 13  for reverse flow of the solution through the sample.  FIG. 9  is a composite plot of the data displayed in  FIGS. 7 and 8 . The results are used to compare the results between forward and reverse flow rates. Data from reverse flow allows a determination of whether damage to a core sample from pressure and fluid passage has occurred. If the damage is only on the face of the inlet side of the core sample, and not internal, the pressure differential readings do not differ to any appreciable extent. Based on the pressure differential data from both the forward and reverse flow rates, damage to the formation indicated by the sample can be assessed. 
       FIG. 14  is a replicated chart of example data readings for differential pressures obtained over a range of flow rates with an apparatus according to the present invention.  FIG. 10  is a plot of those portions of the data from  FIG. 14  for forward flow of the solution through the sample, and  FIG. 11  is a plot of those portions of the data from  FIG. 14  for reverse flow of the solution through the sample.  FIG. 12  is a composite plot of the data displayed in  FIGS. 10 and 11 . The data of  FIGS. 10 through 12  illustrate the linearity between measurements obtained of pressure differential as a function of flow rate. 
     From the foregoing, it can be seen that the permeability testing apparatus A of the present invention measures fluid permeabilities, such as water or oil, on-site of reservoir samples at ambient pressure or at reservoir pressure conditions. The on-site permeability testing apparatus A enables rapid measurement of the impact of injected brine or produced oil on reservoir core permeability in a minimal amount of time. The pressure regulators  80  and  186  assist in maintaining the pore flowing pressure without disturbing testing. Further, since the apparatus A is capable of use at the well site with freshly collected formation samples, the results are more accurate than those obtained in an off-site lab due to changes in the field water quality during transport times. The apparatus A of the present invention is thus capable of performing tests at field conditions rather than having to scale down or to simulate field conditions in a lab offsite from the well. 
     The apparatus A can monitor damage in reservoir core samples and also can sample fluids used either in the inlet or outlet lines without disturbing testing or pore pressure. The apparatus A can also be used for testing or monitoring quality of injected or disposed fluid into a reservoir. It can also assist in studying the impact of water quality on injectivity decline in wells or formations of interest. 
     The invention has been sufficiently described so that a person with average knowledge in the matter may reproduce and obtain the results mentioned in the invention herein. Nonetheless, any skilled person in the field of technique, subject of the invention herein, may carry out modifications not described in the request herein, to apply these modifications to a determined structure, or in the manufacturing process of the same, requires the claimed matter in the following Claims; such structures shall be covered within the scope of the invention. 
     It should be noted and understood that there can be improvements and modifications made of the present invention described in detail above without departing from the spirit or scope of the invention as set forth in the accompanying claims.