Abstract:
A downhole salinity measurement and logging sensor system has multiple cells, each to measure conductivity, temperature and pressure of fluids at depths of interest in a wellbore. The multiple cells protect against effects of non-homogeneous wellbore fluids. The system also determines salinity of the liquid in the wellbore from conductance measurements, and stores the salinity data along with the temperature and pressure readings from the well. The sensors of conductivity, temperature and pressure are made using micro-fabrication technologies, and the system is packaged to comply with harsh downhole environments. The system may be deployed in the well with coiled tubing (CT), wireline or vehicles with a robotic system. The system can be deployed with an onboard memory, or with wireline surface access for real time access to measurement data or programming the device.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to measurement and logging of salinity of fluids in well bores. 
     2. Description of the Related Art 
     Salinity measurement of fluid in a well borehole is important to evaluate the formation fluid. Salinity measurement can help in delineating oil and water and to estimate the moveable oil in a reservoir. Measurement of salinity as a function of well depth helps in differentiating between fresh and saline water and can help in identifying invasion of salt water into a producing borehole. 
     The downhole fluid environment is complex with presence of multiple non-homogenous phases with variable velocities. Measurement of a particular fluid characteristic performed at a single point in the wellbore might not represent an accurate representation of actual borehole fluid salinity. 
     So far as is known, downhole salinity measurement methods have in the past primarily been based on acoustic wave propagation through the formation fluid. Examples are U.S. Pat. No. 4,754,839 and U.S. Published Patent Application No. 2011/0114385. 
     U.S. Pat. No. 7,129,704 related to electromagnetic detection of progression of salt water fronts headed through formations to a water well. The increase of salt water in the formation before intrusion into the well water was measured with widely spaced electrodes since a significant portion of the induced electromagnetic field was required to pass through formation water outside the well bore. 
     SUMMARY OF THE INVENTION 
     Briefly, the present invention provides a new and improved apparatus for measuring salinity of fluid in a well bore. The apparatus includes a sonde for moving in the well bore to a depth of interest to receive well bore fluid. The sonde has a fluid sample chamber with fluid ports formed in it for entry of a well bore fluid sample volume. The apparatus includes at least one fluid conductivity sensor measuring conductivity parameters of the fluid sample volume in the sample chamber, and a data processor mounted in the sonde to determine salinity of the sample volume of well bore fluid at the depth of interest based on the measured conductivity parameters of the fluid in the sample chamber. 
     The present invention further provides a new and improved method of measuring salinity of fluid in a well bore at a depth of interest. A sonde is moved in the well bore to a depth of interest, and a sample volume of fluid from the well bore is admitted into a sample chamber in the sonde. A measure of the conductivity of the fluid sample in the sample chamber, and the salinity of the fluid sample is determined based on the formed measure of conductivity of the fluid sample in the sample chamber. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a view taken partly in cross-section of a borehole fluid salinity measurement tool according to the present invention deployed on coiled tubing in a wellbore. 
         FIG. 2  is an enlarged vertical cross-sectional view of structure of the borehole fluid salinity measurement tool according to the present invention. 
         FIG. 3  is a horizontal cross-sectional view taken along the lines  3 - 3  of  FIG. 2 . 
         FIG. 4  is a schematic electrical circuit diagram of the borehole fluid salinity measurement tool according to the present invention. 
         FIG. 5  is a schematic electrical circuit diagram of a conductivity measuring cell of the borehole fluid salinity measurement tool according to the present invention. 
         FIG. 6  is a functional block diagram of the procedure for measuring borehole fluid salinity according to the present invention. 
         FIG. 7  is a view taken partly in cross-section of a borehole fluid salinity measurement tool according to the present invention deployed on a wireline in a wellbore. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the drawings, a downhole salinity measuring tool or apparatus T is shown ( FIG. 1 ) deployed in a wellbore or borehole  10 . The downhole salinity measuring tool T includes a plurality of conductivity cells C ( FIGS. 2 and 5 ) deployed in a sonde S which is deployed in the well bore  10 , which may be a wet production hydrocarbon well or a water well. The borehole  10  may be either an uncased open hole or cased hole with well casing installed. The sonde S may be deployed on a lower end of coiled tubing  12  as shown in  FIG. 1  or on a signal conducting wireline or e-line  14  ( FIG. 7 ) as will be described. 
     The sonde S of  FIG. 1  is suitably attached to a lower end  12   a  of the coiled tubing  12  by clamping or other suitable connection arrangement. The coiled tubing  12  is injected into the borehole  10  from a storage reel  16  to lower the sonde S to selected depths of interest in the well bore  10  so that fluid salinity of fluid at those depths may be measured and recorded. The depth of the sonde in the well  10  is measured and recorded based on data readings of the length of coiled tubing  12  injected into the well. 
     As the sonde S is lowered in the well  10 , sample volumes of the well bore fluid at elected depths of interest are taken by the tool T in the conductivity cells C. As will be set forth, the salinity of the borehole fluid at a depth of interest is determined based on the conductivity measurements from the cells C, and the determined salinity value(s) of the borehole fluid at such depths measured and recorded or stored as data for analysis and evaluation. Measures of the temperature and pressure of the fluid samples are also obtained by instrumentation in the sonde S, as will be set forth. The fluid samples in the cells are then allowed to flow from the cells as the sonde S moves to a new well depth for another fluid sample. 
     By obtaining fluid samples and determining salinity, temperature and pressure at a number of selected depths of interest, a number of well fluid sampling and salinity measurements are obtained with a pre-programmed measurement schedule or plan over formations or depths of interest in the well  10 . Measured data obtained in the coiled tubing deployed sonde S of FIG.  1  is stored in on-system memory  18  of instrumentation components  20  contained in an instrumentation cartridge I ( FIGS. 1, 2 and 7 ) of the sonde S. Operating power for the instrumentation  20  of the sonde S is provided by an on-system battery  24  in the instrumentation cartridge I. The measured salinity, temperature and pressure data obtained at the various depths in the well  10  and stored in on-board memory  18  are transferred to a conventional computer for analysis, further processing and display after the tool T returns from the well  10 . 
     A salinity measurement performed based on a single measurement in a wellbore might not give an accurate value of fluid salinity because of the non-homogeneity of the wellbore fluid and the presence of multiphase flow regimes. Accordingly, with the present invention, to avoid the effect of possible wellbore fluid non-homogeneity and multiphase flow, as well as to improve accuracy of measurement, the tool T contains four conductivity cells C mounted at a common elevation on the instrumentation cartridge I within the sonde S as shown in  FIGS. 2 and 3 . A suitable number of fluid passage ports  26  are formed in the body of sonde S to allow well bore fluid presence and containment with the interior of the sonde S. 
     The well bore fluid sample in each conductivity cell C is received in a fluid sample chamber F ( FIGS. 2 and 5 ). The shape, size and volume of the chamber F defines the geometry of the conductivity cell C. The sonde S also preferably includes a fluid temperature sensor  30  measuring temperature of the sample volume of well bore fluid in the fluid sample chamber, and a fluid pressure sensor P measuring pressure of the sample volume of well bore fluid in the fluid sample chamber. 
       FIG. 5  is a cross-sectional view of a single conductivity cell C along with a schematic view of associated electronics. Each cell C includes fluid receiving channel or chamber F located between a fluid inlet port  32  ( FIG. 2 ) and a fluid outlet port  34  for wellbore liquids for passage of wellbore fluid from the interior of the sonde S. As shown schematically in  FIG. 5 , the chamber or channel F can be selectively opened and closed for entry and exit of well bore fluid by digitally controlled check valves  36  and  38  in inlet and outlet ports  32  and  34 , respectively to obtain sample volumes of the wellbore fluid. The valves  36  and  38  are preferably operated by solenoids or other suitable valve actuators. 
     Each conductivity cell C includes electrodes located within fluid chamber F. Two drive electrodes  40  and  42  apply alternating current (AC) to the wellbore fluid in the chamber F. Preferably a high frequency alternating current is applied between the drive electrodes  40  and  42  as indicated by the instrumentation  20 . The high frequency is used to avoid corrosion. In a preferred embodiment 10 KHz is used, although frequencies in a range of from 1 KHz to 100 KHz could be used. 
     Sense electrodes  44  and  46  form a measure of the voltage difference between spaced positions in the chamber F in response to the current between drive electrodes  40  and  42 . The electrodes  40 ,  42 ,  44  and  46  are preferably fabricated using platinum on a glass chip with an insulative plastic or synthetic resin used as the body of conductivity cell C housing the chamber F. 
     The conductivity of the wellbore fluid sample in the chamber F of each conductivity cell C is determined based on the product of the determined measure of liquid conductance (G) of the sample volume of well fluid in the cell, and cell constant (σ) which is a constant which is defined by the geometry and dimensions of the sample chamber. The conductance value G is the reciprocal of a measured fluid resistance (R) of the sample volume obtained based on the current and voltage measured with the drive electrodes  40  and  42  and the sense electrodes  44  and  46 . The fluid resistance R is determined using Ohm&#39;s law R=V/I relationship measured as indicated schematically at  45  of the voltage difference V between the sense electrodes  44  and  46  for an applied current level I applied by and flowing between the drive electrodes  40  and  42 . 
     The high frequency alternating current wave signal between drive electrodes is generated under control from microprocessor  50  ( FIG. 4 ) of the instrumentation  20 . The signal so generated is converted to a current signal in an operational amplifier  52  ( FIG. 5 ), and a resistor  54 . The amplitude of sine wave voltage signal from operational amplifier  52  is preferably limited to an acceptable low level such as 1V to avoid electrolysis and metal corrosion, as the borehole fluid sample could be brine with high saturation of salts. It should be understood that low voltage levels in the range of less than 2 volts may be used. 
     Based on the resistance R obtained from the conductance and the cell constant σ based on the physical geometry of cell C, resistivity of the borehole fluid sample is thus determined. The determined wellbore fluid sample resistivity is representative of the salinity of the borehole fluid sample in the each conductivity cell C. The conductivity measurements are obtained in each of the cells C and an average of these values is determined and stored as the representative salinity of the wellbore fluid at the sample depth of interest. 
     The temperature sensor  30  is usually a thermal resistive device with a linear resistance-to-temperature relationship for temperature measurement. Resistance (R) of a thermal resistive device depends on the material&#39;s resistivity (ρ), the structure&#39;s length (L) and cross section area (A):
 
 R=ρL/A  
 
     The change in temperature can be calculated by measuring the change in resistance by the following formula using initial values of resistance and temperature, R o  and T o  and the temperature coefficient (α):
 
 R=R   o (1+α( T−T   o ))
 
     A platinum resistance thermometer (PRT) is preferably used as the temperature sensor  30 . Platinum has a higher temperature range, good stability and low tendency to react with surrounding material as required for downhole conditions. These unique properties of platinum enable PRT to operate in temperature range of −272.5° C. to 961.78° C. The platinum resistor of temperature sensor  30  is typically fabricated on a glass substrate. 
     The pressure sensor P which determines fluid pressure in the well is preferably a piezoresistive pressure sensor made using micro electro-mechanical systems (MEMS) fabrication techniques. The pressure sensor P thus preferably takes the form of a membrane over a cavity. In such a pressure sensor, the magnitude of membrane movement corresponds to the pressure level imposed by the wellbore fluid on the membrane. Changes in pressure on the membrane change the stress in membrane which can be measured by a change in resistance. 
     The conductivity cells C, the temperature sensor  30 , and the pressure sensor P each form analog signal measures indicative of the value of the boreholes fluid parameter measures sensed. The analog signals from the borehole sensors are converted in analog-to-digital converters  60 ,  62  and  64 , respectively, into suitable digital format for data acquisition and storage in on-system memory  18  and for processing by the microprocessor  50 . 
     The salinity of the well bore fluid sample is determined in the on-board microprocessor  50  of the instrumentation  20  based on liquid conductivity, as described above, and stored in on-board memory  18 , along with measured temperature and pressure of the wellbore fluid. From the measured salinity, conductance, temperature and pressure obtained wit the tool T, other borehole fluid parameters can also be computed including resistivity, density, acoustic velocity, freezing point, specific heat and potential density. 
     The microprocessor  50  serves as the main processing unit in on-board instrumentation of the sonde S. The microprocessor  50  includes a main controller  70 , a power management unit  72 , a digital signal processer  74 , a timer  76  and the on-board memory  18 . The memory  18  serves as internal memory for the tool T. The amount of memory provided depends upon the wellbore fluid measurement interval, total measurement time and number of parameters to be stored for each measurement. If the measurement is to be done over a larger range of depths of interest or with small measurement intervals, an external random access memory can be included and interfaced with microprocessor  50 . 
     The digital signal processor  74  performs signal processing tasks including generation of signals for conductivity testing and computation of liquid conductance, resistivity and salinity in the manner described above. The timer  76  determines the time of occurrence of and the time interval between obtaining borehole fluid measurements, and thus defines the measurement frequency. The controller  70  controls the other subsystems of the microprocessor  50  and performs the required synchronization. An USB interface  78  is provided for connection of the controller  70  to an external computer at the surface for programming of operations in the wellbore and for transfer of data from the memory  18 . 
     Battery  24  which provides power for the microprocessor  50  and other electronics of the sonde S preferably is a rechargeable lithium ion battery. The power management unit  72  is implemented in the microprocessor  50  to efficiently manage the operating electrical power usage. A power optimized system architecture is utilized in the power management unit  72  in order to maximize the system service life. The functionality of the system is divided into different working states. The power management unit  72  activates modules required for the current working state and switches off the rest. Power saving strategies at both sensor level and system level are implemented to minimize power consumption of the system. 
     Detailed analysis and further measurements based on the borehole fluid data obtained S can be performed after the sonde S is moved out of the well bore to the surface. The contents of memory  18  are transferred by connecting the microprocessor  50  with a computer at the surface and retrieving the data. 
       FIG. 6  illustrates the operating sequence of measuring salinity of borehole fluid according to the present invention. The sonde S is deployed in the well bore with coiled tubing  12 . At a pre-programmed time to allow the sonde to reach a depth of interest, the valves of the conductivity cells C are activated to sample the wellbore fluid as indicated at step  100 . The sensors of the conductivity cells C are activated by the microprocessor  50  as indicated at step  102  so that borehole fluid salinity can be determined at the depth of interest. 
     During step  104 , the alternating current signal is applied to the borehole fluid samples in the conductivity cells C by current flow between the drive electrodes  40  and  42 . The resultant voltage is concurrently sensed by the sense electrodes  44  and  46  as indicated by step  106 . Pressure and temperature measures of the wellbore fluid are also obtained from pressure sensor P and temperature sensor  30  in step  106 . The measured borehole fluid data after collection is then collected and processed by the microprocessor  50  to determine borehole fluid salinity, as indicated by step  108 . 
     The computed salinity and other measurements of borehole fluid data are stored in the memory  18  during step  110 , along with a time stamp or record of the time the sample was taken. The sensors in the sonde S are then disabled during step  112 . Movement of the sonde S in the well bore continues and at the next pre-programmed time indicated by the timer  76 , the foregoing sequence is repeated. 
     The well bore fluid parameter sensors of the sonde S are preferably fabricated with micro electro-mechanical fabricated or MEMS microfabrication technologies which offer miniaturization as well as accurate measurement. The analog-to-digital converters  60 ,  62  and  64 , the microprocessor  50  and other electronic components used as instrumentation  20  in the sonde S may be commercial, off the shelf harsh environment electronic components. A harsh environment commercial electronics component line is provided by Texas Instruments which can operate in the temperature range of −55° C. to 210° C. 
     Alternatively, a custom made application specific integrated chip or ASIC may be utilized, with multilayer thick film fabrication or silicon-on-insulator techniques and ceramic packaging. The board for the electronics of the sonde S is preferably a high temperature printed circuit board with an inorganic ceramic substrate. The board and electronics have ceramic packaging and are hermetically sealed to protect the circuits from well fluids. 
     As described above, the sonde S can also be deployed using the e-line or signal conducting wireline  14  ( FIG. 7 ). In this case, the wireline  14  is connected to a computer system  120  at the surface. The components of the sonde S in  FIG. 7  to obtain measures of borehole fluid salinity, temperature and pressure are of like structure and functionality to those described for the coiled tubing deployed sonde S of  FIG. 1 . 
     Borehole fluid data from the sonde S are received and recorded as functions of borehole depth in memory of uphole telemetry and preprocessing circuitry  122 . A surface processor computer  124  receives and processes the borehole fluid data of interest under control of stored program instructions stored as indicated at  126 . The results from processing by the processor computer  124  are available in real time during salinity measurement operations for analysis on a suitable display or plotter, such as display  128 . A depth measurement system (not shown) also is present as a component of the wireline  14  to also correlate or indicate downhole wellbore fluid sensor measurements and parameters of interest to their respective depths or true locations within the borehole  10  at which such measurements are made. 
     The surface computer  124  can be a mainframe server or computer of any conventional type of suitable processing capacity such as those available from any of several sources. Other digital computers or processors may also be used, such as a laptop or notebook computer, or any other suitable processing apparatus both at the well site and a central office or facility. 
     A power cable or conductor in the wireline  14  is used to charge the battery  24  and borehole fluid parameters of interest measured by the tool T can be accessed at the surface by computer system  120  in real-time. Conventional wireline telemetry and control circuitry are included in the tool T of  FIG. 7  for transfer of data over the wireline  14  to the surface for processing by processor computer  124  and to receive control signals for the tool T from the computer system  120 . The controller  70  in the tool T can also be programmed while in the well by instruction signals sent by wireline to change the acquisition parameters including measurement frequency of sensors, total measurement time and other required parameters. 
     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.