US2524933A - Interface locator - Google Patents

Description

Oct. 10, 1950 D. SILVERMAN 2,524,933 I INTERFACE LOCATOR Filtd larch 26, 1946 I 4 Shuts-Sheet 1 EMJW 1N VEN TOR.

Oct. 10, 1950 D. SILVERMAN 2,524,933

m'rsancz Locxron manna, 26, 1946 4 Sh eeit'a-Shoet' 2 ATWRNIY Filed larch 26,

SILVERMAN IMWME Locu INVENTOK Oct. 10, 1950 D. SILVERMAN 1mm: LQCATOR 4 Sheets-Shut 4 Filed lax-{2h 26, I946 INVENTOR.

MINE? Patented Oct. 10, 1950 manner LOCATOR Daniel Silverman, Tulsa, Okla., assignor to Stanolind Oil and Gas Company, Tulsa, Okla., a

corporation of Delaware Application March 26, 1946, Serial No. 657,293

1 12 Claims.

This invention pertains in general to a. method and apparatus for determining in a well the position of an interface between two fluids of dissimilar character. More particularly, it pertains to a method and apparatus adapted either to follow in an oil well the movement of an active, as distinguished from a quiescent or static, interface between two fluids of dissimilar characteror to hold such an interface at a given position in a well while fluid is being pumped into the well. As to common subject matter, this is a continuation-in-part of my copending patent applications, Serial Number 491,117, filed June 17, 1943, and Serial Number 580,659, filed March 2, 1945, which are both abandoned.

Numerous means have been suggested for detecting in a well the position of a static interface between two dissimilar fluids. For example, it has been proposed that a simple electrical-conductivity cell be employed to distinguish between a conducting fluid such as salt water and a nonconducting fluid such as oil. It has also been proposed that a density meter be employed to distinguish between two fluids of different density, as, for example, water and gas or water and oil. Other means for locating such interfaces consist in the employment of the difference in the light-, sound-, and heat-transmitting characteristics of the fluids in a well. These and other means for locating a static interface in a well are known in the art, but they have not received wide or extensive use due to the very limited field to which they may be applied. Actually, an interface between two fluidsin a well which is capable of production is rarely ever static, so theme of this type interface locator has been used only to determine the nature of a fluid in a well at a given point and at a. given time.

It has been proposed to hold an interface between two fluids at a given position in an oil well while the fluids are being pumped into the well. It has also been proposed to follow such an active interface in a well. Prior to my invention, however, the apparatus available for carrying out the proposed methods has in general been considered too complex to be of. practical value under the conditions encountered in an oil well. It is well established that for continuous dependable service any device lowered into an oil well must be the essence'of simplicity. The above-mentioned devices for detecting a static interface in a well,

particularly those depending upon mere qualitative determinations, have been found practical for this fundamental reason. On the other hand, the devices heretofore described for locating or following active interfaces are dependent upon a quantitative measurement or upon the simultaneous measurement of fluid character at a multiplicity of points. Quantitative measurements are impractical because any number of conditions or combinations of conditions may occur in a well to mask the surface indication; i. e., there may be emulsions either oil in water or water in oil or there may be a gas-water mixture. Any of these mixtures at the detector in the well will produce a confusing surface indication. In the other system, the measurement of a fluid character at a multiplicity of points as taught in U. S. Patent 2,248,982 issued to J. R. Gillbergh, the susceptibility to error in the apparatus is increased as the number of individual stations at which measurements are made increases. Furthermore, the accuracy of an interface locator of the latter .type is proportional to the number of detector units in the well. In order that the position of an interface may be determined at any instant with any degree of accuracy, the stations must be very close together and very numerous. If it is desired, for example, to follow the progress of an interface over a -foot section of a well with any degree of accuracy, from 25 to 100 units would be required. This multiple-unit system is thus not particularly adapted to following in a well the position of an active interface between two fluids of different character. By this invention I have overcome, by means not heretofore disclosed, these and other obstacles by employing the simplicity and dependability of a qualitative determination not heretofore employed in the location of an active interface in a well.

Within recent years a new process has been introduced for use in logging the permeability of zones traversed by an oil well. This process in general consists of pumping two immisciblefluids of unequal density into an oil well in such a manher that an interface will be formed between them and then comparing the volumes of the fluids which will penetrate a unit length of the well above and below the interface. By making such a survey with the interface at a number of locations in the well a permeability log of the well may be made. This process, hereinafter referred to as permeability profiling," may be substantially improved by use of my invention as pointed out in detail below. Also, within recent years new methods have been employed for introducing a particular fluid into a selected section of an oil well. For example, where it is desired to acidize a particular formation or a particular group of formations in a well and where it is particularly desired that other formations in the same wells should not be acidized, a process hereinafter referred to as selective acidization" has been developed. Ithis process an upper formation may be selectively acidized while the lower zones are blanketed or covered with a fluid of specific gravity greater than that of acid. An interface locator is positioned at the lower limit to which acid will be permitted. Then the two immiscible fluids are separately pumped into the well, the acid above said lower limit and the denser fluid below said lower limit. The relative rates of injection of the two fluids is adjusted to hold the interface approximately at said lower limit to which acid will be permitted. This process is particularly desirable where a permeable zone containing salt water is located below the oil zone in which the acid is to be placed. Al ternatively, where it is desired to acidize an oilproducing formation without simultaneously acidizing a superjacent gas zone, the gas zone may be blanketed by a fluid immiscible with acid and having a specific gravity less than that of acid. Thus, it is possible by this process to acidize selectively a selected section in the producing zone of a well. Prior to my invention, however, there was no suitable instrument available for accurately controlling the position of the interfaces between the various fluids.

An application of the same principle may be found in the process hereinafter referred to as the oil squeeze process. This process consists of introducing oil into an oil well for the purpose of decreasing the water/oil or gas /oil ratios. The rate of injection is substantially above the common fluid production rate of the well. In this process oil may be pumped into all the exposed formations indiscriminately, but it is preferably introduced selectively into a particular formation which normally contains oil but which has been traversed near the well by a water or gas cone. By the use of my invention as hereinafter set out the upper or lower limit towhich oil will be permitted may be positively controlled as in the case of selective acidization. This selective oil-squeeze process, while obviously desirable in that it saves oil otherwise lost in water and gas formations, as well as the permeability profiling and selective acidization have not found widespread application, since active interfaces are involved and no suitable locator for such active intfirfaces has been available.

It is, therefore, an object of this invention to provide an improved method and apparatus for following an active interface in an oil or gas well. It is a further object of this invention to provide an apparatus of this character which will be reliable in the location of an active interface between two dissimilar fluids in an oil or gas well. It is a further object of this invention to provide an apparatus by which the movement of an active interface between two dissimilar fluids in a well can be followed. It is a still further object of this invention to provide an apparatus which will indicate at the surface the position of an interface between two dissimilar fluids in a well with greater accuracy than has heretofore been possible. A more specific object is to provide an apparatus by which with qualitative signals the position of an active interface between two dissimilar fluids in an oil or gas well can be determined. A still further specific object of this invention is to provide an apparatus by which the position of an active interface between two fluids of dissimilar character in a well can be controlled. Other objects and advantages of this invention will become apparent as a descriptlon thereof proceeds;

I accomplish these objects in general by introducing into a well an interface detector that will distinguish physically or chemically between two immiscible fluids in the well. The detector is located in the region of the interface and alternately submerged in each of the two fluids. By this means a positive intermittent signal is trans mitted to the surface which will accurately indicate the position of the interface in the well.

The accompanying drawings form a part of this specification and are to be read in conjunction therewith. In these drawings, the same reference numerals in the different figures refer to the same or similar parts. In these drawings:

Figure 1 is a sectional view of a well showing associated therewith in highly schematic form one embodiment of my invention in which an I interface between dissimilar fluids is periodically reciprocated in order to determine its position;

Figure 2 is a sectional view of the lower portion of the well tubing showing a detail of an electrode assembly which may be employed in certain embodiments of my invention;

Figure 3 is a sectional view of a well showing associated therewith in highly schematic form an embodiment of my invention in which an alternative means is provided for reciprocating an interface in a well;

Figures 4 and 5 are sectional views of a well showing associated therewith in highly schematic form alternative embodiments of this. invention by which the movement of an interface in a well may be accurately followed; I

Figures 6 and 7 are highly schematic forms of embodiments of my invention wherein the interface detector is periodically reciprocated;

Figures 8, 8a, and 8bare enlarged views of certain details of the apparatus shown diagrammatically in Figure 6; and

Figure 9 is an enlargedview of certain elements of the apparatus shown diagrammatically in Figure '7.

Referring now to Figure 1 of the drawings to illustrate and describe one embodiment of my invention, I have shown a well Ill drilled into the earth. An oil string ll encases a portion of the well. A tubing I2 is inserted into the well through the oil string I l and held in position by a tubinghead l3. This tubinghead further serves the purpose of sealing the annulus between oil string II and tubing l2 whereby a fluid from a suitable source It may be introduced under pressure by pump [5 into annulus I6. A metering device I1 is inserted in the flow line I8 so that the amount of fluid flowing into annulus I6 can be determined. As will be hereinafter shown, it is sometimes desirable to change the rate of fluid introduction into annulus IS, a valve l9 being provided for that purpose.

In Figure 1 I have also shown means for introducing a second fluid into tubing 12, said second fluid being of greater density than the abovementioned first fluid and immiscible therewith. This second fluid is pumped via the tubing directly to the bottom of well In from a suitable source M. The volume or rate of iniection of this second fluid may be controlled by valve 22 in the suction line of pump 23. The discharge to tubing l2 from pump 23 passes through a metering device 24 and a pulsator 25. This pulsator is adapted to introduce periodic oscillations in the dense fluid so that the interface 28 which is formed at some position in the well between the light and the dense fluid will intermittently and repeatedly rise and fall. The pulsator, which is shown in the second or densefluid flow line, may with equal facility be placed in light-fluid flow line l5. a cylinder 21, an associated piston 28, a connecting arm 29, a crank 3|, and a prime mover 32. The prime mover 32 is adapted to reciprocate piston 28 in cylinder 21 either by direct connection as shown or through a speed reducer. This prime mover may be, for example, a variablespeed electric motor by which the frequency of pulsations may be varied at will.

A detector 33 which is shown in greater detail It may consist of in Figure 2 is located at the lower end of tubing l2. It comprises a sleeve 34 of insulating material such as Bakelite. This sleeve is adapted to seat at the bottom of tubing l2 on tubing shoe 35 so that fluid entering the well through tubing i2 will be discharged at the lower end of sleeve 34 instead of at shoe 35. An insulated electrical conductor 35 is electrically connected to a ring electrode 31 surrounding the sleeve 34. A bail or handle 35 may be connected to the insulated conductor 35 whereby the detector 33 may be lifted and withdrawn through tubing l2. The surface end of electrical conductor 35 is connected to a slip ring 39 on a reel 4|. A brush 42, battery .43. and ammeter 44 connected between the slip ring 39 and the tubing or ground complete the electrical circuit as shown.

In operation under the embodiment of my invention described above a dense fluid may be introduced selectively into the formations 45 below interface and light fluid may be introduced selectively into the formations 45 above interface 25. For example, the formations 45 may be blanketed with oil pumped in through annulus l6 while formation 45 is acidized through tubing l2. Alternatively, oil may be introduced into formations 45 through pump [5 and annulus Hi to reduce a water or gas cone in these formations and at the same time formations 45 may be blanketed with water, for example, which is pumped in through pump 23, pulsator 25, and tubing l2 so that no oil will be lost in these latter formations. Furthermore, this embodiment of my invention may be employed to determine the relative permeabilities of the formations 45 below interface 25 and formations 45 above interface 25. The procedure followed in each of these processes will now be described in greater detail.

In selectively acidizing formations 45, i. acidizing these formations while blanketing formations 45, the acid is introduced into the well from source 2| through pump 23, metering device 24, pulsator 25, tubing I2, and detector 33. At the same time the lighter fluid, e. g., oil, is pumped into the annulus Hi from source [4 through pump l5 and metering device l1. These two fluids being immiscible will form an interface at some point in the annulus l5. Whether this interface is above or below electrode 31 will be indicated on ammeter 44. That is, if electrode 31 is submerged in acid, which is an electrical conductor of low resistance as compared to the resistance of oil, a current will flow in the circuit. That is, the gap in the circuit between electrode 31 and the tubing or ground return is closed by the acid. If the interface between the two fluids is below electrode 31, no current flow will be indicated on ammeter 44. Now, by proper adjustment of valves l9 and 22 the interface can be caused to move either up or down the annulus I5 or to remain substantially fixed at any given point. By this means the interface is brought into the region of the detector. As soon as it passes the detector a change in current flow through the electrical circuit will be indicated on ammeter 44. The valves l9 and 22 will then be adjusted to hold the interface in the region of electrode 31. Pulsator 25 induces surges in the flow of acid causing the interface to oscillate back and forth across the detector electrode 31.

The portion of the cycle in which acid covers electrode 31 will be indicated by passage of a current through ammeter 44. More particularly, as pulsator 25 is on the compression stroke the ratio of acid to oilintroduced into the well will be increased whereby the interface 26 will rise above electrode 31 and current flow will be indicated on ammeter 44. On the suction stroke of pulsator 25 the ratio of acid to oil introduced into the well will similarly be decreased whereby the interface 25 will be caused to fall below ring electrode 31 and current will cease to flow. Valves l9 and 22 can be so adjusted that the mean position of interface 25 will remain substantially constant at the electrode 31.

It will be of interest to note here that the gradual movement of the mean position of interface 25 can be detected at the surface by the current flow in the circuit as indicated by ammeter 44. More specifically, when the mean position of interface 25 is substantially below electrode 31, current will flow only a relatively short period of time in each cycle of the pulsator 25. As the mean position of interface 26 rises, the ratio of current-on to current-off time as indicated by ammeter 44 will likewise increase. By this means an operator will anticipate the movement of the mean position of interface 25 and will accordingly adjust valves 19 and/or 22 whereby said interface is maintained in the proper position to a high degree of accuracy. It will be apparent that the movement of interface 25 during a cycle of pulsator 25 will depend somewhat upon the frequency of the pulsations. I have found that this frequency may be maintained in the region of from about 1% to about 20 cycles per minute, preferably in the region of l to 5 cycles per minute, depending upon the depth of the interface 25. Lower frequencies are in general used for greater depths. At the higher frequencies it is sometimes desirable to substitute a galvanometer for ammeter 44.

While I have shown electrode 31 associated with detector 33 which is removably mounted at the lower end of tubing 12 and which has accompanying means for being withdrawn to the surface, it will be apparent that electrode 31 could be mounted on and insulated from tubing l2 at any convenient location. Connection to the surface could then be made, for example, by means disclosed in U. S. Patent 2,247,417. Alternatively, in this embodiment insulated electrical conductor means may be mounted on the tubing as is well known in the art.

The procedure outlined above for selectively acidizing formations 45 is adaptable to reducing a water or gas cone in formations 46 while at the same time blanketing formations 45 with a heavy fluid. In this process heavy fluid, for example salt water from source 2i, is pumped into the well through tubing l2, and light fluid, for example oil from source I4. is pumped into the well through annulus IS. The procedure followed in maintaining interface 25 between the salt water and the oil is identical to the procedure described above for selective acidization and therefore will not be described here in detail. In general, I have found it highly desirable that oil be pumped into formations 46 at a very rapid rate for the most economical reduction of a water or gas cone in an oil well. By this procedure the oil can be placed selectively in the proper section of the well at a much greater rate per unit length of well penetrating formations 46 than was heretofore possible, since oil is not indiscriminately pumped into water formations 46.

In the application of the embodiment of my invention shown in Figure 1 to the determination of permeabilities of strata traversed by well ill the procedure is substantially as outlined above, except that in this case the relative rates of injectlon of the light and dense fluids must be determined. For this reason metering devices l1 and 24 are installed in the lightand dense-fluid flow lines respectively. Salt water is generally used as the heavy fluid and oil as the light fluid, since they are generally available and since their other properties meet the requirements. As described' above, the mean elevation of interface 26 between the light and dense fluids is maintained contiguous to electrode 31 by proper adjustment ofvalves l and 22. After the interface has been properly located at electrode 31, the relative volumes of the twofluids as indicated by metering devices I! and 24 is an indication of the relative total permeabllities of the two formations 46 and 45. By locating electrode 31 at other points in well it below casing II and by determining the relative permeabilities of the formations-above and below electrode 31 at each of these points a relafive-permeability log of the well may be made.

In the embodiment of my invention described above the position of interface 26 has been controlled by manipulation of valves l9 and. I have found it convenient to produce a pulsating interface at any given point in a well between two dissimilar fluids by automatic means as shown in Figure 3. In this case the light-fluid pump I is adapted to introduce light fluid from source H into the annulus 16 at a constant rate. Heavy-fluid pump 23, which pumps heavy fluid from source 2| to the bottom of well I6 via tubin i2, is controlled by a relay 41. Through this relay, which is actuated in accordance with the position of interface 26, the mean elevation of interface 26 is maintained at the elevation of electrode 31 a hereinafter explained. When insulated electrode 31 is submerged in a conducting fluid such as salt water, current from battery 43 flows in the control circuit comprising insulated conductor 36, tubing [2, and solenoid 46. When this solenoid is energized, contacts 43 in relay 41 are opened and pump 23 becomes idle. With heavy-fluid pump 23 idle and light-fluid pump l5 pumping a non-conducting light fluid into annulus l6 at a constant rate, the interface 26 will fall. As the heavy conducting fluid surface at interface 26 descends below electrode 31, the flow of current through the control circuit and solenoid 48 will be terminated, and contacts 49 will be closed by spring 5|. Thus, dense-fluid pump 23 is again started and interface 26 is caused to rise by the addition of dense fluid below interface 26 until electrode 31 is again submerged in the heavy electrical conducting fluid. At this point pump 23 is again automatically stopped. The cycle is thus repeated at a frequency which can be controlled at will by the relative sizes an speeds of pumps 16 and 23. It

will be apparent that this embodiment of my invention can be utilized in the same type of operations and for the some purposes as the embodiment shown in Figure 1. The simplicity of apparatus and the quantitative measurements are retained. While I have shown electrical prime movers on pumps I5 and 23, it will be obvious to those skilled in the art that other types can be adapted.

In Figures 4 and 5 I have shown alternative embodiments of my invention which are particu larly adapted to following an active interface.

' Whereas the embodiments shown in Figures 1 and nected to electrode 31.

3 are better adapted to locating and maintaining an active interface at a relatively fixed position, these embodiments of my invention may be employed in following an active interface of which the mean elevation may move to any point between the bottom and top of a well. This embodiment may, for example, be applied to the making of a log of permeabilities of the various strata traversed by well ill. When thus employed, tubing in the well is unnecessary as shown from the following description. Detector 33 having mounted thereon an electrode 31 which is exposed to the well fluids is suspended in well In by an insulated conductor 36 which is electrically con- The other end of conductor 36 is wound on reel 4| and is electrically connected through a slip ring 39, brush 42, ammeter 44, and battery 43 to the tubing l2 or to ground. Conductor 36 runs over a measuring wheel 52 which has associated therewith a depth indicator 53. By this means the position of detector 33 in the well with reference to the surface can be determined at any time.

Well I0 is first fllled through pump 23 to a point above the section of the well to be surveyed with a dense fluid which may be an electrolyte, e. g., salt water. Detector 33 is then introduced into the well and located at the surface of the dense fluid. A light fluid which is immiscible with the dense fluid and which may be a nonelectrolyte, e. g., oil, is then pumped into well In from source 2| through pump 23 and forms an interface with the dense fluid previously pumped into the well. This light fluid will also tend to displace the heavy fluid into the permeable formations at the bottom of the well and the interface will fall. Referring now to Figure 4, if detector 33 is lowered in well III at a relatively uniform rate by unreeling insulated conductor 36 and light fluid is introduced into the well at a uniform rate so that the detector is in the region of the active interface 26, pulsator 25 will cause detector 33 to be intermittently submerged in the dense conducting fluid below interface 26 and the light non-conducting fluid above interface 26. As previously explained in the description of my invention with reference to Figures 1 and 3, the ammeter or other current-sensitive device 44 will indicate a current flow when detector 33 is submerged in the dense conducting fluid; when submerged in the light non-conducting fluid above the interface, no current will flow and ammeter 44 will so indicate. Thus, by observing the ammeter 44 the operator will be able to unreel insulated electrical conductor 36 at the same rate that interface 26 is being depressed. Alternatively, by means of a servomotor or otherwise the detector can be made to follow automatically the movement of this interface. As in the case of the stationary detector, the operator will be able to determine very accurately the position of the interface, since by the ratio of time current is flowing to the time current is 9 not flowing in the signal circuit as indicated by ammeter 46 he is able to determine the percentage of time that detector 33 is below or above interface 26. Furthermore, by observing depth indicator 52 and recording this depth against time either manually or automatically a permeability proflle will be made. Thus, if the formations penetrated by well l6 or of uniform permeability, interface 26 will be depressed at a constant rate, and if the formations are not of uniform permeability the rate of change of depth of interface 26 with respect to time is not uniform. The relative permeabilities of the various formations may be calculated as shown, for example, by Kelley and Fitzgerald in Petroleum Technology, Technical Publication 1604.

Turning now more particularly to a description of the embodiment of my invention shown in Fig. 5, it will be noted that, as with the embodiment shown in Figure 4. with this embodiment an active interface may be followed in the well to any point between the bottom and top thereof. Detector 33 having an insulated electrode 31 mounted thereon is, as in Figure 4, suspended in well l6 by an insulated conductor 36. One end of this conductor is connected to electrode 31. The conductor passes over a measuring wheel 52, through a pulsator 25, and is wound on reel 6|. The surface end of conductor 36 is then connected through slip ring 33, brush 62, ammeter 66, and battery 43 to the tubing l2. While an earth return is thus shown, it will be apparent that in many cases a second conductor such as the metallic sheath is preferred. In operation detector 33 is intermittently raised and lowered at a frequency of from about 1 6 to about cycles per minute. preferably 1 to 5 cycles per minute, depending upon the depth of the detector. Lower frequencies are in general used for greater depths. In order that detector 33 may be vertically reciprocated. crank 3| 0n pulsator is connected directly or by linkage to conductor 36. Pin 54 on crank 3| slidably contacts conductor 36 in such a manner that when crank 3| is rotated conductor 36 will be displaced laterally. This lateral displacement in turn raises and lowers detector 33. Thus, when crank 3| is rotated at a substantially uniform rate, detector 33 reciprocates vertically in the well.

The operator will be able to follow the movement of the interface by unreeling cable 36 as indicated by ammeter U. More particularly, where the interface 26 is between a lower conducting fluid and an upper non-conducting fluid, current will flow in the detector circuit and a qualitative measurement thereof will be indicated on ammeter 46 when electrode 31 is in contact with the conducting fluid: or, alternatively, in the embodiment where the return circuit is through the conductor sheath, when the ball 38 and electrode 31 are both submerged in the conducting fluid. When electrode 31 is intermittently raised out of co tact with the conducting fluid so that it is totally submerged in the nonconducting fluid, no current will flow in the det ctor circuit, and ammeter 44 will so indicate.

The pos tion of the int rface with respect to the extrem ties of the vert cal oscillations of electrode 31 can be accurately detected, and the direction of movement can be readily and accurately determined by this invention, inasmuch as the submergence of electrode 31 into the conducting fluid is ecual to the total vertical travel of the electrode multipled by the ratio of the time current is flowing in the circuit to time A form of apparatus which is particularly adapted to the movement of a detector cyclically in a well is shown in alternative embodiments in Figures 6 and 7. In this form of the invention the cyclic movement of the detector originates in the well, preferably near the lower end of tubing l2 instead of at the surface as shown in previously described embodiments. Essentially in this form of the apparatus the sensitive element or detector is reciprocated periodically through a given portion of the well, and an indication of a character of the fluid in the well at all points along the path of the detector is transmitted to the surface. A detector such as a pair of electrodes 55 may be mounted respectively on a pair of continuous belts 51. These belts are preferably made of insulating mater al, such as fabric, plastic or the like. They carry on their outer surfaces bare-wire conductors 53 (Figures 8, 8a, and 8b). These conductors are preferably small so that their surface areas are small compared to the surface areas of electrodes 55, thus having a substantially higher contact resistance than the electrodes and tending to cause the greater portion of current to flow between the electrodes. The electrodes 55 are each connected electrically to one of the bare-wire conductors 53, the two electrodes preferably being disposed adjacent one another as shown in the drawings. These belts 51 may be of any convenient length, for example from about 5 to about 50 feet, and the pulleys 6| and 62 which are mounted on the tubing l2 and over which the belts pass may be spaced accordingly. Brushes 63 are provided near the upper pulleys 6|, each being in contact with one of the bare-wire conductors 59. Leads 64 connect brushes 63 to battery 43 and ammeter which are in series. A short-circuit bar 65 having brushes 66 adapted to contact electrodes 55 simultaneously is provided for reasons hereinafter described. The pulleys 6| may be driven by a motor 61, which is preferably located in the well. Details of the belt assembly and the electrical connection between electrodes 55 and the brushes are shown in Figures 8 and 8a. The brushes 63 are shown in the position of contact with the wire conductors 53 while the brushes 66 are out of contactwith these conductors but are in a position to contact electrodes 55 as these electrodes pass once each cycle. An enlarged view of electrodes 55 showing their relationship to the belts 51 and the connection to the bare-wire conductors is given in Figure 8b.

With reference to Figure 7 I have illustrated a modification of the apparatus shown in Figure 6. The principle of operation in the two embodiments is substantially identical. However, the latter has the advantage of simplicity inasmuch as only one belt 6'! is employed. Single pulleys 68 and 69 are provided on the tubing whereby this single belt may be rotated. Rotation of the belt causes spaced electrodes ii to move up and down cyclically in the well and contact the fluid at different elevations therein. An electrical conductor 13, preferably insulated, is connected 'between electrodes II as shown in detail in Figure 9. Electrical conductor 13 preferably contains several turns of insulated wire wrapped longitudinally around belt 61, the ends being attached to the electrodes H as shown. A pair of shortcircuiting brushes 14 is provided for shorting the electrodes when they pass said brushes, thus caus ng an impulse of maximum strength to be recorded at the surface as described hereinbefore. The pulley 68 is driven by a motor 61, which may be located at the surface or adjacent the electrodes as shown. Electrical conductor 13 passes through and forms a part of toroidal transformer 15. The primary coil 15 of this transformer is connected by leads 64 to a battery and ammeter in series at the surface as indicated in Figure 6. In accordance with the principles of induced currents the electrical energy passing through the leads 64 and the primary coil I6 will be affected by the resistance to flow of induced currents in the secondary winding of the transformer, conductor 13. For example, when the electrodes II are passing through a conducting fluid so that little or no resistance is offered to the induced current in the conductor 13, there will be little or no eflect on the current passing through the primary coil 16 of the transformer. If, on the other hand, the electrodes pass through a fluid having high electrical-resistance characteristics, the flow of induced current in conductor 13 will be reduced, thereby causing a reduced flow of current through the primary coil. The variations in flow of current in the primary coil and the leads 64 will be recorded at the surface, thereby giving an instantaneous indication as to when the electrodes H are passing through a conducting fluid such as brine or a relatively non-conducting fluid such as oil.

In practice either of the devices shown in Figures 6 and 7 is lowered into a well, and the upper pulleys are driven at a. substantially constant speed, so that the electrodes will move cyclically downwardly around the bottom pulleys and up the opposite side through a fixed path. Whenever the electrodes pass through a conducting fluid so that current passes from one electrode to another, an indication is given at the surface on ammeter 44. When the electrodes 55 or H reach the short-circuit brushes 66 or H, re-

spectively, a current impulse of maximum strength will be indicated at the surface. This strong current impulse may be used for callbrating the data obtained, since it will always be known that the electrodes are at a particular point in their cycle when this impulse is recorded. Thus the position relative to the short-circuit brushes of an interface between two fluids having different characteristics may be readily determined. The invention is not, however, limited to the specific apparatus shown, since other forms of apparatus adapted to reciprocate the electrodes cyclically in a well will be apparent to those skilled in the art.

While I have described my invention by reference to the preferred embodiments, in which fluids have been distinguished by their differences in conductivity, and have used certain speciflc terms, it is to be understood that changes and modifications, such as the use of other fluid characteristics to distinguish the various fluids used in my invention, may be resorted to without departing from the spirit or the scope of the claims appended hereto.

I claim:

1. A method of indicating the position of anactive interface between a conducting fluid and a non-conducting fluid in a well comprising introducing said conducting fluid into said well, introducing said non-conducting fluid into said well, said conducting and said non-conducting fluids being immiscible and of different densities, whereby an interface is formed in said we l, 19-

12 eating a detector in the region of said interface, said detector being adapted to distinguish between said conducting and said non-conducting fluids, indicating at the surface in which fluid said detector is submerged, and cyclically submerging said detector alternately in said conducting and said non-conducting fluids, the frequency of said submersions being between about and about 20 cycles per minute, whereby a positive qualitative signal will be repeatedly and intermittently produced at the surface when said detector is in the region of said interface and the ratio of signal-on to signal-oil. time indicates the mean level of said interface relative to said detector.

2. A method of indicating the position of an active interface between a dense fluid and a light fluid in a well comprising introducing said dense fluid into said well, introducing said light fluid into said well on top of said dense fluid, said dense and said light fluids being immiscible, whereby an interface between said dense fluid and said light fluid is formed in said well, locating a detector in the region of said interface, said detector being adapted to distinguish between said dense and said light fluids, indicating at the surface in which fluid said detector is submerged, and pulsating said detector alternately in said dense and said light fluids at a frequency of from about 1 6 to about 20 cycles per minute, whereby a positive qualitative signal will be repeatedly and intermittently produced at the surface whenever said detector is within the region of said interface and the ratio of signal-on to signal-off time indicates the mean level of said interface relative to said detector.

3. A method of indicating the position of an active interface between a dense fluid and a light fluid in a well comprising introducing said dense fluid into said well, introducing said light fluid into saidwell,said dense and said light fluids being immisible, whereby an interface between said dense fluid and said light fluid is cause to be depressed, locating a detector in the region of said interface, said detector being adapted to distinguish between said dense and said light fluids, indicating at the surface in which fluid said detector is submerged, and continuously and cyclically varying the velocity of one of said fluids at a frequency of from about to about 20 cycles per minute, whereby a positive qualitative signal will be repeatedly and intermittently produced at the surface whenever said detector is within the region of said interface.

4. An apparatus for indicating the position of an active interface between two distinguishable and immiscible fluids in a well comprising means for introducing a light and a dense fluid into said well, a detector adapted to distinguish between said two fluids, means at the surface connected to said detector for indicating the fluid in which said detector is submerged, and a pulsator for continuously and cyclically varying the velocity of one of said fluids in said well. whereby said detector is alternately submerged in each of said fluids.

5. An apparatus for indicating the position of an active interface between two distinguishable and immiscible fluids in a well comprising means for introducing a light and a dense fluid into said well, a detector adapted to distinguish between said two fluids, means at the surface connected to said detector for indicating the fluid in which said detector is submerged, a pulsator for continuously and cyclically varying the veloc- 13 ity of one of said fluids in said well, whereby said detector is alternately submerged in each of said fluids, and means for indicating the position of said detector in said well.

6. An apparatus for indicating the position of an active interface between two dissimilar fluids in a well comprising at least one pump for introducing said two dissimilar fluids into said well, a chamber in the flow line from a pump to said well, a detector in said well adapted to distinguish between said two dissimilar fluids, means at the surface connected with said detector for producing a signal indicative of the fluid inwhich said detector is submerged, and means for cyclically varying the volume of said chamber to vary the velocity of one of said fluids entering said well, whereby said detector is alternately submerged in each of said two fluids and the ratio of signal-on to signal-01f time indicates the mean level of said interface relative to said detector.

7. An apparatus for indicating the position of an active interface between two distinguishable and immiscible fluids in a well comprising at least one pump for introducing said two dissimilar fluids into said well, means to vary the rate of fluid flow into said well, a detector adapted to distinguish between said two fluids, means at the surface connected to said detector for indicating the fluid in which said detector is submerged, and a continuously driven pulsator means in the flow line of said pump to superim'pose upon said fluid flow a periodic variation in rate, whereby said detector is alternately submerged in each of said two fluids and the ratio of signal-on to signal-olT time indicates the mean level of said interface relative to said detector.

8. An apparatus for selectively acidizing a well having a string of tubing therein comprising means for introducing an acid into said well, means for introducing a non-conducting fluid of different specific gravity from said acid into said well, said acid being introduced through said tubing into said well near the bottom thereof. and said non-conducting fluid being introduced into the well near the top thereof, whereby an interface between said acid and said non-conducting fluid will be formed at a'point in said well above the lower end of the tubing, detector means in said well adapted to distinguish between said acid and said non-conducting fluid, means at the surface connected to detector for indicating in which of said acid or said non-conducting fluid said detector is submerged, a pulsator in the flow line of one of said non-conducting fluid or acid for submerging said detector intermittently in said acid and said non-conducting fluid when said detector is in the region of said interface.

9. Apparatus for logging wells electrically comprising an elongated support adapted to be lowered to any desired depth in a well, a pair of spaced electrodes movably mounted on said support, means for moving said pair of spaced electrodes relative to said support cyclically and con- 14 tinuously around an endless elongated path extending along the elongated support, a source of electric energy for creating a potential between said electrodes, and means associated with said electrodes and said source of electric energy for indicating at least one characteristic of the electric energy passing between said electrodes, whereby the nature of the fluid between the electrodes may be determined.

10. Apparatus for logging wells electrically as claimed in claim 9 and further comprising means for periodically short-circuiting said electrodes, whereby the indicating means may be calibrated.

11. Apparatus for logging a well electrically comprising an elongated support adapted to be lowered to any desired depth in a well, at least one endless belt movably mounted on said support and extending substantially parallel to the length of said support, a pair of spaced electrodes supported on said at least one belt,means for moving said belt so that said electrodes will move cyclically and continuously around the endless elongated path of movement of said belt, a source of electric energy for creating a potential between said electrodes, and means associated with said electrodes and said source of electric energy for indicating at least one characteristic of the electric energy passing between said electrodes, whereby the nature of the fluid between the electrodes may be determined.

12. Apparatus for logging wells electrically comprising at least one endless belt, a pair of spaced electrodes supported thereon, means adapted to be lowered into a well for supporting said belt in a substantially elongated form and for moving said belt so the electrodes will move together cyclically up and down the well through a fixed path, a toroidal transformer having a primary winding, a source of electric energy connected to the primary winding of said transformer, insulated conducting means connecting said electrodes and constituting the secondary winding of said transformer, whereby a potential is induced between said electrodes, means associated with said electrodes and said source of electric energy for indicating at least one char-: acteristic of the electric energy passing between 'said electrodes, whereby the nature of the fluid between the electrodes may be determined.

DANIEL SILVERMAN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 402,229 Buschmann Apr. 30, 1889 2,347,589 Barstow Apr. 25, 1944 2,347,615 Shelley Apr. 25, 1944 2,376,878 Lehnhard, Jr. May 29, 1945 2,394,220 Wagner Feb. 5, 1946 2,413,435 Courter Dec. 31, 1946

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