US2433718A - Method and apparatus for determining the location of producing horizons in wells - Google Patents

Description

Dec. 30, 1947. I TEPUTZ 2,433,718

' METHOD AND APPARATUS FOR DETERMINING THE LOCATION OF PRODUCING HORIZONS IN WELLS Filed April 10, 1945 2 Sheets-Sheet l Mn *Mlzy/ 1 A? I W I v v a I z s a IIIIIIIIIIIIIIIIIlllllllllllllllllllllllll'lllll Dec. 30, 1947. n-z 2,433,718

METHOD AND APPARATUS FOR DETERMINING THE LOCATION OF PRODUCING HORIZONS IN WELLS Filed April 10, 1.945 2 Sheets-$heet 2 E EJMW i-"SBRf-XHJKM a TEPLITZ r Y fg. 6. 32

Patented Dec. 30, 1947 METHOD .AND. APPARATUS FOR' DETER- MINING THE LOCATI ON-OF PRODUCING HORIZONS IN WELLS- Abraham J. .Teplitz, Oakmont; Pa.,- assignor .to

:Gulf Research &;Development Compa ny,'Pittsburgh; Pa., a corporation of Delaware Application April '10, 1945'. Serial No.- 587,532

8 Claims. (01. 250--83) This invention pertains to a-methodbfand apparatus for determining the position-ofwater pr oil producing horizons in a well'by radiological means.

In the production of oil from wells, it is customary proceduretoset casing in-the well' and-.to place oppositethe producing formation ascreen or strainer through which fluid may pass into the casing or the tubing string 'Such-a-screen allows the formation fluids to pass into-the well but tends to restrain sand or other solid matter from doing so. If sufficient formation'pressure exists, the well fluids will flow through the screen and up the producing tubing to the-surface. If insufiicient formation pressure is available, a pump is usually installed in the tubing aboveithe screen.

Many oil producing formations do not' solely produce oil. The producing formation often is made up of a series of horizons, some of which are oil bearing and some of which are water bearing. If a screen is set opposite the; entire length of producing formation, a mixture of oil and water may be produced-and, moreover, this mixture may become emulsified so that separation is difficult. Moreover, the water is usually saline and highly corrosive, and in a pumping well represents an expensive and useless load. It is therefore important to determine the source horizons of the water andoil .so that steps maybe taken to shut off or seal the water producing. horizons and produce only oil.

The incursion of water into oil wellsrepresents one of the major sources of expense in the production of petroleum. The pumping of water, handling of emulsions, disposal of the .water, and the corrosion resulting from the water, are, all costly factors attending the operation of wells producingwater along with oil. Insome cases it has been possible to shut off the flow of water from the producing formation by mechanical and chemical methods, but a large number of such treatments have proved unsuccessful principally because of the inability to ascertain which portion of the formation was yieldingthe water.

The object of this inventionis to provide a method of locating the sources of water entering a well from the producing zone, thus making it possible to apply suitable tr atment in theparticular interval where it isneeded, with consequent opportunity for success in recovering water-free pipe line oil.

Another object of this invention'is toprovide a simple, apparatus for. locating the sources oftwater; or=oi1 entering a .well from theproducing zone.

A further object .of' this invention. is to;provide a method of determining-the points of entry of water in a well in such a manner7that treatment may beapplie d immediately without dismantling equipment in thewell.

The objects are accomplished .as set forth -.;in the following specification, which also includes anexampleof apparatus for carrying out the method -of.my invention. Referenceis made to the drawing in which:

Fig. llis a-section of the earth showing .onei -form of my apparatus in place in a producing well;

Fig. v2.is arecord obtainedfroma radiological examination .of the well .screenemployed in my invention;

. Fig, 3-shows details. ofconstruction of a'well screen which may be employed'in my invention;

Fig. 4;is a transverse sectionof awell screen which maybe employed in my, invention;

,Fig. 5 is a section through a form of-wirewhich retains the active material usedlin, myinvention; and

Fig; 6 is" a section through another form of wire which'maybe used to hold active material.

In general, my inventionjconsists of'settingppposite the producing formation, a special'screen orstrainer' coated, with or" impregnated with a water-soluble radioactive substance or mixture. Afterallowing the well to produce for a suff cient lengthgf time, the screen maybe 'examined'either in 'place in the well-or upon beingbrought to the surface. Examination is madeby-meansofairinstrument sensitiveto emanations from the radioactive substance; It is evidentthat the lowest radioactivity will be found at'the point'or points where themost radioactivematerial has been dissolved away.

In one way of employing my invention, a .well is completedby setting a strainer oppositethe producing-zone in the conventional manner. This is showndiagrammatically. in 'Fig. 1 in. which is indicated a well penetrating earth formations l, 2, 3-, 4, 5, 6, I, 8 and 9. Formations .4, .5, 6', land 8 are in the producing zone, but some of' these either initially or subsequently will produce water and somewill-produce oil. A casing I 0' is cemented at H. Equipment at the top of the well is not indicated since this is conventional. At the lower end of the casing I0 is suspended the strainer I4 with a conventional packer [5 which may beeither an expansion'type or a permanent seal. Inside the casing andprojectinginto the strainer is suspended the production tubing-l3. The strainer I4 is provided-with the usual-openingsthrough-its wall and along its length; these openings 'being indicated by numeral l1. strainer is further provided with grooves I 8 cut in the outer face of the solid portion, said grooves being filled with a mixture consisting of a radioactive substance dissolved or suspended in a cement or plastic material which is soluble in water.

A simplified sketch showing the details of a strainer which may be employed is shown in Figs. 3 and l. The pipe 23 containing perforations 24 and provided with separators 25, is wrapped with wire of the cross-section shown in Fig. 6 by 21, this wire having spacing lugs 23 which form the openings 3| which permit fluid to enter the inside of the strainer while restraining the entrance of sand and other solid particles. The upper part of the screen assembly is equipped with threads 29 for attachment with a suitable packing device and to the lower portion is fastened the set-shoe 30 containing a back pressure valve assembly which permits washing around the outside of strainer while preventing the entrance of formation cavings into the inside of the screen.

The radioactive material is contained in grooves 32 in the wire wrapping. Wire wrapping of suitable type is conveniently formed by running wire, which may be stainless steel or bronze, of the cross-section 26 shown in Fig. through rollers designed to produce the spacing lug 28 (Fig. 6) and at the same time press in the outer edge making the groove 32 of a dove-tail shape which provides better retention for the radioactive material.

A suitable mixture for filling these grooves may be made by mixing plaster of Paris with about per cent of its weight of finely ground carnotite and then adding suflicient water to make a pasty mass. This mass can then be thoroughly spread over the surface of a screen having wire of the cross-section indicated. After allowing sufiicient time for the mixture to partially set, the opening at the bottom of the screen may be plugged and water pressure applied to the inside at the upper end thus washing the excess plaster out of the screen openings 3| and leaving the grooves 32 full of the radioactive material. The set plaster of Paris has a slight solubility in water (about 0.1 gram in 100 ml.) and will gradually be removed in the well by water moving past it.

Another method of forming the screen could be accomplished by incorporating a radioactive substance in a plastic, such as the polyvinyl alcohol resins which are manufactured with varying degrees of solubility in water depending upon the method of preparation. Such a mixture having considerable flexibility could be filled into the groove in the wire before the latter is wrapped around the pipe.

A considerable variety of straining devices are known to those familiar with oil-field practice but any of these may either be provided with recesses for retaining the radioactive material or be coated with radioactive material incorporated in a suitable binder or cement. It is desirable in some cases to incorporate a radioactive element into the screen wire itself, in which case the wire could be made of a magnesium alloy or other alloy having a slight solubility in water. Also instead of plaster of Paris, or plastic material, low solubility salts such as magnesium phosphate, lithium triphosphate, calomel, and thallium iodide may be used by first fusing the salt and dispersing the carnotite or other radioactive substance in the molten mass.

If the annular space between the strainer and the well bore is large so that there exists the possibility that some of the fluid entering the well may pass vertically up or down the annulus before entering the strainer, this condition may be remedied by afiixing barriers of metal, leather or other material to the outside of the strainer, causing the fluids to travel horizontally from the formation through the strainer.

After setting th strainer, the well is put on production in the usual manner. Later, when the well begins to produce appreciable quantities of water along with the oil, any suitable detector of radioactivity is lowered into the well. Such a detector, indicated by numeral it in Fig. 1, may be a Geiger counter or ionization chamber commonly used in making gamma ray well surveys. The instrument is suspended by cable l2, over which indications of the radioactivity are obtained electrically and recorded in any known manner. Cable [2 may pass through a lubricator at the top of tubing [3 so measurements may be made while the well is producing. Known devices are used to determine the depth of unit It. Measurements of the radioactive intensity are made over the entire length of the strainer, and the results of the examination are customarily obtained in the form of a graph, such as is indicated in Fig. 2.

In Fig. 2, numeral [9 represents a chart or record as obtained by a conventional recording means such as is used for gamma ray well logging. Along one side a scale 20 shows the depth of the detecting instrument IS. A curve 2| whose arbitrary zero line is indicated by dotted line 22 shows the measured intensity of radioactivity produced by the material in strainer grooves l8 (Fig. 1). The curve 2 I shows a high value where the radioactive material in the grooves has not been disturbed, while the points of lowest intensity will be found opposite the water producing zone or zones. As illustrated in Fig.2, the curve 2| shows high radioactive intensity opposite formations 4 and 5, indicating that these are oil producing horizons, while opposite the formation 6 a low value of radioactivity is observed, indicating that this formation produced water which removed the radioactive material from the adjacent section of the strainer. In some cases a formation may produce both oil and water. Thus opposite the top of formation 8, for example, the curve shows an intermediate intensity 23 thereby indicating only a partial removal of the water-soluble radioactive material. This means that the upper part of this formation produces a relatively smaller amount of water. The gradual decrease in radioactive material observed on the screen progressing toward the bottom of formation 8 indicates that there is a gradual increase in the amount of waterproduced. Thus one may determine that formation 8 produces a small amount of water at its top and a large amount of water at the bottom.

Once the water sources have been located by the method of this invention, any known suitable steps may be taken to stop the flow of water. The water producing horizons may be cemented off, or selective plugging operations may be performed on horizons which are indicated as producing mixtures of oil and water. One of the particular advantages of this process is that the water producing formation may be located and in many cases treated without removing the strainer, an operation which is often rather costly.

In the case of oil wells which are producing water, similar information may be obtained by lowering into the well opposite the producing have accumulated in the bottom of the well dur-= in; previous production, it .would be desirable to ,fdisplacethe fluid in. the well. with dry oil just ..before. makinga test. a p

The method and apparatus of .my invention may alternatively bev used for detecting the point.

of entry of oil into a well by using an oil-soluble" radioactive material on the strainer. For holding the radioactive material in this case a matrix -may beused-which has suitable solubility characteristics in oil. Suitable oil soluble materialsv are naphthalene, anthracene, orelemental sul-" phur. The radioactive substance may also be embedded in oil resistant rubber such as Neoprene andjDup rene which"are onlyslightly .soluble in oil.

My invention may be further used to detect both the points of entry of water and the points of entry of oil by means of a single strainer in one production test. This is done by filling alternate grooves I8 on the strainer with watersoluble and with oil-soluble radioactive material, the radioactive materials being so chosen that their emanations are distinctive in order that they may be distinguished by the instrument l6. This may b done by using for one material a radioactive compound which gives off relatively soft gamma rays, while for the other material a radioactive compound which gives off hard gamma rays may be used. After the production test a gamma ray log is first run using an ordinary ionization chamber in unit l6, and then repeated with a shield around the unit IS. The first curve then indicates the presence of both materials and the second indicates presence of only the hard ray producing material. By comparing these curves with the known initial distribution of the radioactive materials one may easily deduce where oil is produced and where water is produced. Obviously also where neither of the two materials are removed the formation is either barren or produces gas.

The radioactive matrix material chosen should have a solubility depending on the duration of the production test made while the screen or strainer is in the well. Furthermore, artificially radioactivated materials may be used provided only that their lifetime be sufiiciently long to permit of making the necessary production and inspection tests.

My invention may also be used when it is desired to locate highly permeable horizons which by-pass or short circuit the input fluid used in water flooding operations. Such horizons, sometimes called thief sands are encountered in input wells and may be located by setting a special strainer similar to that shown in Fig. 1. Fluid, usually water in this case, is pumped down the well and flows out through the strainer into the producing formations. The water-soluble radioactive material used in grooves I8 should for this purpose be only slightly soluble, so that it is not completely removed by the water flowing out into the formation. The degree of removal of radioactive material may be ascertained from the radioactive intensity observed on examination awith..:.i.ns trument l 6.; as indicated on; curve 2 I :1Fig.2 ;;A;.sl igh t decrease in observedcradioactive ;;intensity--; results from only a slight removal of .-,material indicating thatthe. adjacentformation istaking onlya small flow of water, whilealarge decrease results from a larger'removal of zradioactive material indicating that: this formation is takingalarge flow ofwater. Any fthief formations'taking excessive water may thenbe. plugged or sealed by known methods.

Other well known variations of the equipment .in the'well may be made withoutafiecting my invention.- The casing I0,-Fig. 1, may for, example extend all the way to the-bottom of the. hole and may have perforationsalong-its length oppo- ,sitethe-producing formations. -As another; ex-

ample the, strainer may be eliminated and the outsideofe the perforated casing may contain, the

radioactive material that indicates the nature: of the produced fluids. ..--While Ihave shown the radioactive. material .placed in external grooves on thestrainer; such material may ,be otherwise disposed ;on the strainer. Theessential feature is that its;,position may be detected and that it come in contact with the fluid being produced from the adjacent formation. The distribution of radioactive material is advantageously made uniform along the length of the strainer, but any known distribution may be used as well. If the operator suspects loss of material while running the strainer into the hole, an initial test with'the gamma ray instrument may be made after the strainer is in place and before production is begun.

Other radioactive materials may be substituted for those mentioned, e. g. inorganic or organic derivatives of radioactive elements mixed with a suitable binder may be employed as the indicating substance.

What I claim is:

1. A method of determining the source of fluid entering a well which comprises placing in the well opposite the producing formation a known configuration of solid radioactive material removable by the produced fluid, allowing the well to produce for a period suiflcient to remove a portion of said radioactive material and subsequently determining the distribution of radioactive material remaining in the Well. I

2. A method of determining the source of fluid entering or leaving a well which comprises placing in the well a known configuration of solid radioactive material removable by the fluid flow, permitting the well fluid to flow for a suflicient time to remove a portion of said radioactive material and subsequently measuring the distribution of radioactive material remaining in the well.

3. A method of determining the source of fluid entering a well which comprises placing in the well opposite the producing formation a known configuration of solid radioactive material removable by the produced fluid, allowing the well to produce for a period sufficient to remove a portion of said radioactive material and examining the well with an instrument sensitive to emanations from the radioactive material to determine the regions in which said radioactive material has been removed by the fluid.

4. An apparatus for determining the source of any fluid being produced in a well comprising a strainer having associated therewith a known distribution of radioactive material soluble in said fluid, means for producing the well and means for examining the strainer for radioactive emanations to determine the regions in which said ra- 7 dioactive material has been removed by the fluid. 5. An apparatus for producing a well and determining the source of water being produced comprising a strainer having on its outer surface a substantially uniform distribution of watersoluble radioactive material, means for producing the well and means for examining the strainer for radioactive emanations to determine the regions in which said radioactive material has been removed.

6. An apparatus for simultaneously producing a well and determining the source of water being produced comprising a strainer initially having a substantially uniform distribution of water-soluble radioactive material thereon, means for restricting external axial flow of fluid, means for producing the well and means for examining the strainer for radioactive emanations to determine the regions in which said radioactive material has been removed.

7. An apparatus for simultaneously producing a well and determinin the source of oil being produced comprising a strainer initially having a substantially uniform distribution of oil-soluble radioactive material thereon, means for producing the well and means for examining the strainer REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,352,993 Albertson July 4, 1944 2,358,945 Teichman Sept. 26, 1944

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