US2451520A - Method of completing wells - Google Patents

Description

Oct.v 19, 1948.

Filed 'May 29, 1945 A. J. TEPLITZ l METHOD OF COMPLETING WELLS 2 Sheets-Sheet 1 III wwf/ 15 Ll@ 15 21 '2O i. 26

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METHOD OF COMPLETIING WELLS Filed May 29, 1945 2 Sheets-Sheet 2 epo- X M M Z2 11.1 @s 16 -16 l l n 12 x 25 29 le) &\ 1'5 1 64 21.. g S5 2: .f 5 A 53 il? 'f .f/ 14j 1 55 17 l v17 19 K A l? ,l i 1 Afum-2f? f 2O 2O 1 15 j 15 16 5 16 3mm 'ABRAHAM J. :UQPLITZ my Patented Oct. 19, `1948 METHOD oF COMPLETING WELLS Abraham J. Teplitz, Oakmont,Pa., assignor to Gulf Research & Development Company, Pittsburgh, Pa., a corporation of Delaware Application May 29, 19475, Serial No. 59,511

This invention pertains to an improved'method of completing an oil well for satisfactory production by making use of a radioactive tracer material. It is particularly applicable in cases where pipe is set through the producing zone and then perforated for production.

In completing an oil well prior to placing it on production, it is highly desirable to guard against the possibility of producing undesirable components, particularly Water and sometimes gas. The early methods of completion consisted essentially of setting casing above the producing formation and allowing the oil to flow into the well from the open formation. 'I'his obviously permitted Water, gas and oil to enter the well more or less indiscriminately and the production of Water or gas was dini-cult to control.

In more modern completion practice the casing does not stop above the producing zone but is set through it. Cement is forced around the bottom of the casing and into the annular space between the casing and the formation. An attempt is made to force the cement into the annular space all along the producing zone. The casing (and cement) is then perforated by means of a gun perforator at the proper levels so as to permit production from only desirable oil formations. In this way the production of gas and water is to a large extent avoided. 'I'his technique is now being widely used.

In some parts of the United States, particularly along the Gulf Coast where many of the deeper sediments are relatively unconsolidated, some difficulties have been encountered in completing Wells by this latest technique. It is found in many cases that after the pipe is cemented and perforated for production, extraneous fluids such as water and gas still ow into the Well along with the oil. This usually results from channels or crevices in the cement behind the pipe, which permit communication with waterA or gas forma- `tions from which production is undesirable. The channels in the cement may be tortuous passages either between the casing and the cement or between cement and formation or through the body lof the cement itself. In any case, these channels form passages which permit unwanted movement of iiuid longitudinally along the hole behind the casing from one formation to another.

'I'he wide prevalence of such channels in casing cementations has only recently been recognized and no satisfactory method of combating the condition has previously been devised. In present practice when the initial production test yields water or an excess of gas along with oil, thus 2 Claims. (Cl. 166-2/2) revealing the existence of serious imperfections in the cementing, no attempt is made to determine the positions of the troublesome channels. The procedure heretofore used to correct this condition is to squeeze more cement into the perforations at high pressure, and then to re-perforate the pipe in the original interval hoping that channels have been closed by the squeeze job. An alternative procedure sometimes employed is to make a guess, aided by an electrical log or core .log of the well, as to the possible source of contamination that is whether it is above or below the producing formation, and then to perforate the pipe between thesesources and the original perforations, after which cement is squeezed into all perforations and the original zone is reperforated for production. Often as many as four or five squeeze cement operations are performed before the water and gas are successfully sealed off, and instances are known yWhere as many .as ten such squeezes have been necessary. In

addition to being costly in time and equipment, the practice of squeezing cement at high pressure directly against a producing formation sometimes damages the formation so that its productive capacity is reduced or even destroyed.

In this invention I provide a method of deiinitely determining the source of undesirable iluids so that any perforation and cement squeeze operations may be made intelligently and with utmost effectiveness. At the same time the method avoids contact of the cement with the producing formation, thus avoiding any chance of damaging the well.

It is an object of this invention to provide a positive method of determining which portion of the cement is defective in that it contain-s channels or crevices.

A further object of this invention is to provide a method of locating defective regions of cement in the annular space behind a well casing so that these regions may be recemented and sealed.

Another object of this invention is to provide a method of positively determining the source of undesirable fluid so that this source may be cemented and sealed olf.

Another object of this invention is to provide a method of completing, or 1re-completing a well so as to eiectively exclude undesirable fluids.

A still further object of this invention is `to provide a method of locating behind the casing such channels which permit undesirable fluids to enter the well through peforations opposite desirable producing formations so as to ypermit the radioactive mud into nels,'but due to the nature of the drilling mud squeezing of cement into these to seal them.

Another object of this invention is to provide a method of determining defective portions of cement behind a well casing so as to permit squeezing fresh cement directly into the region where it is needed, thus avoiding injury to the producing "formation `.and expediting the completionvof the well.

These objects are accomplished by the method of this invention in the following manner. Its application is illustrated by way of example in the appended drawings of a well which is lproducing oil and excess gas and alittle -water from perforations in pipe which is'cemented through the active producing zone. Reference Ymay 'be made to the drawings in which:

Fig. 1 shows a cross section of a well'to which my invention may be applied;

Fig. 2 shows a cross section of a well after the applicationof .radioactive mud according to my invention Fig. 3 shows a graph of a preliminary well log taken in the practive of my invention;

Fig. 4 shows a cross section of the well of Fig. .2 after .o'wing fora brief period;

Figg shows afgraph of va well log taken after .the brief periodof flow,.and

Fig. 6 shows a Ycrossgsectionof a well complet- .ed according tomy invention.

YReferring :to Fig. A1, numeral I shows a bore ,hole in which the conventional final 'casing string vLI extendsto the bottom of Athe well, penetrating formations I2., I3, I4 and I5. The section extending through formation I2 to I5 is the producing zone .and the casing is .cemented at @I throughout `the length of this Aproducing section. Opposite the oil-bearing horizon le the channels in order v`casing and cement have been perforated vin conventional manner, suchperforations being shown at Il. The cementaround the casing is assumed to completely fill the space between the casing and the formation wall. However, imperfections I8 ,and i9 may be presentand are originally not known Yto exist. ,Following a production test, which for purposes of illustration in this well may show oil with .considerable undesirable excessgasand a small amount of undesirable water, it is deemednecessary to correct this faulty condition.

As a first step in the practice of Ymy invention, I locate opposite the producing section a quantity of drilling mud o1` bentonite suspension containing a suspended radioactive tracer material. Such radioactive tracer maybe nely ground carnotite, for instance, or any other insoluble natural or artificial radioactive compound. A 5% aqueous bentonite suspension containing about one pound of finely ground carnotite per .barrel may be used. Since-carnotite ores vary considerably in radioactive strength, it is desir- -able-to select for the purpose of vpracticing this invention, one of the-commercial carnotite ores Y.containing abouttento twenty-milligrams Vof ra- :dium per ton. Pressure is applied to this .mud in conventional manner, either `by use of a conventional packer or Vsqueezing tool,'and the mud isforced ,through the perforationsinto any space which may exist behind the casing.

Fig. 2 shows the radioactive mud 2U penetrat- Y ing theperforations Il and the channel defects -Iand I9. Sufficient pressure is applied to force these openings or chansuspension, the susp'nded'matter 'isnot forced -jinto the-formationi-tself. The pump ,pressure .aP-

type, being a graph 3i pushing plied at the surface is maintained at a value just sufficient to cause the suspension to move through the perforations and should not be permitted to rise to high values commonly used in squeezing operations. When the pressure begins to climb rapidly showing that the movement of the radioactive suspension has practically ceased, pressureis releasedand excess mud'isfcirculated out of the Well. Thus in VFig. 2, the well may be filled with non-radioactive mud or fluid, leaving radioactive mud 20 only in the openings Il, I8 and I9.

Upon removal of the excess mud, a radioactive logging instrument 2l is lowered into the well on -cable 22. Such instruments are Well known iin the art and do not form the subject matter of this invention. As the indicator 2I is loweredthrough the producing section, a radioactivity log is made, an example of which is illustrated in Fig. 3. This log is of a conventional showing depth markings 3E indicating 'the position of the detector .2| and a curve '2li which indicates the degree of radioactivity observed with reference to 4an arbitrary zero `line 23. Thus survey will reveal the position of the carnotite suspension which has entered any vpassages behind the pipe .by back into the formations any'fluid which was produced into these channels. .As .illustrated in Fig, 2, the radioactive mud has penetrated achannel defect I8 leading from producing formation M to formation I2 which forex- .ample may contain Ygas, andalso into channel defect i9 .leading .from producing formation I4 to formation i5 which for example may contain water. This radioactive Y.mud is shown on the curve by the two regions of high intensity at 26 and 21 opposite the defects. The vdepth at which perforations l'I were made is known and may be marked on the graph at the properpoints l33'for purposes of reference.

The Iwell is now-permitted to vproduce fora lshort time so as vto permit it to lclean out the radioactive mud which hasbeen forced intojfiowing channels.

Fig. 4 illustrates the condition vof -the well after such a period of flushing. The well is produced Vfor a time sufficient to allow the undesirable constituent to enter the casing thus cleaning the mud out of the channel through which it flows. Thus Fig. 4 illustrates the radioactive mud ushed out of defect I8 iby the .gas vcoming 'from formation I 2. Partial removal of radioactivemud from defect I9 by a flowof oilfrom formation-i4 and possiblya slight flow of .waterfrom forma- Vtion I5 .is also illustrated.Y These facts dare .dertermined vfrom a subsequent radioactivity log `-as Fig. 5. It will be noted that the high intensity indication of `point 26 (Fig. 3) -does not appear -on the second log, Fig. 5; whereas, the high intensity `indicationat 2l (Fig. ,3) ,has decreased only slightly. This indicates that the foreign iiuid has been produced from the formation 'I2 Y and, in fact, one may conclude that its source is opposite the point of farthest extremity 28 from the producing perforations .II` where., previously .indicated radioactive mud .has been removed Aby the flowing process.

The well is now perforated opposite the point 28 indicated to be the source of the undesirable fluid. Su-ch new perforations are shown at 29 in Figure 6. A packer 32 is inserted between this point and the original perforations I1 and cement squeezed into the perforations 29. This cement, shown in Fig. 6 at 34, will eifectively seal the source of undesirable fluid without in any way damaging the face of the producing formation I4. The lower portion of channel I9, indicated by the region of high radioactivity at 21, Figs. 3 and 5, is not contributing to the output of the well, since the radioactive logs show that the mud is not completely ushed out. If, at a later date, water production becomes excessive, its source may be determined by repeating the method of this invention.

Although the channel I8 communicates with the producing formation, the pressure developed against the producing formation during the squeeze will be relatively small since in most cases the cement will bridge somewhere in the channel. If it is felt necessary, a small amount of cement may be squeezed in and allowed to harden before squeezing the main portion of the cement. This precaution will entirely eliminate any danger of damaging the producing sand. Subsequently the packer 32 may be removed, either by collapsing it if a removable type, or by drilling it if it is a drillable type.

My invention may also be applied to a pumping well in a similar way asy applied to a flowing well. In this case the step of flushing radioactive mud from channels producing undesirable nuid must be accomplished by pumping or bailing.

In some instances it may be desirable to use an oil base fluid instead of the aqueous radioactive fluid. A suspension of carnotite in oil containing a thickening agent may be employed in such cases.

While I have described my invention in the case of a well producing oil with considerable undesirable excess gas and a small amount of undesirable water, this is for purposes of illustration and not a limitation. My method may be used with equal effectiveness on any type of well in which it is desired to ascertain the source of undesirable components and avoid their production.

What I claim as my invention is:

1. A method of completing a well which is cased and cemented throughout the producing section said casing and cement being perforated in the zone of desirable production, comprising forcing drilling mud containing radioactive material in suspension into the producing perforations, removing excess drilling mud, running a radioactivity log of the producing section, allowing the well to produce for a short interval, running a second radioactivity log to determine the presence of channels permitting entrance of undesirable components, and perforating and re-cementing opposite the indicated source of such undesirable iluids.

2. A method of completing a Well whi-ch is cased and cemented throughout the producing section said casing and cement being perforated in the zone of desirable production comprising forcing a suspension of radioactive material into the producing perforations and cement channels, removing the suspension from inside the casing, running a lradioactivity log of the producing section, allowing the well to produce for a short interval, running a second radioactivity log to determine the presence of channels which permit entrance of undesirable components, perforating and re-cementing opposite the indicated source of said undesirable fluids and erecting a barrier inside the casing between said perfora tions and the original perforations whereby the zone of production and original perforations are protected from contact with the cement during such re-cementing operation.

ABRAHAM J. TEPLITZ.

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

NITED STATES PATENTS

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