US2160228A - Process and apparatus for cementing oil wells - Google Patents

Description

y 1939- I P. s. PUSTMUELLER 2,160,228

PROCESS AND APPARATUS FOR CEMENTING OIL WELLS Original Filed April 11, 1938 2 Sheets-Sheet l zil I V I W it Fig. l

1 Fig.3

lnvenior: Poul S. Pusi'mueller Fig. 2 by his A++ome m 2 Sheets-Sheet 2 Fig. 7

P. s. PUSTMUELLER Original Filed April 11, 1938 PROCESS AND APPARATUS FOR CEMENTING OIL WELLS May 30, 1939.

\nvenror: Paul S. Dusrmueller 5g his Afforneg: MW

Patented Ma 30, 1939 I v 2,160,228

UNITED STATES PATENT OFFICE PROCESS AND APPARATUS FOR CEMENT- ING OIL WELLS Paul s. Pustmueller, Bakersfield, Calif., assignor to Shell Development Company, San Francisco; Oalit; a corporation of Delaware 1 application April 11, 1938, Serial No.

201,346. Divided and this application December 19, 1938, Serial No. 246,617

' Claims- (Cl. 166-1) The present invention pertains to the art of mixture through suitable passagesinthe shoe into cementing oil and gas wells, and is more particuthe annular space 2 between the casing and the larly related to a process whereby the shoe or walls of the borehole, a certain amount of'cement lower end of a casing string may be cemented at 4 remaining also in the lowest section of the casan intermediate level of the well, that is, at ing. After the cement has 'set, a drill bit is a point relatively distant from the bottom of the lowered within the casing, and a hole 6 is drilled hole, and a bridging cement plug, necessary for through the hardened cement remaining in the testing the efliciency of water shut-off obtained by easing, through the casing shoe and through the cementing the casing, may be placed below the formation below the plug, usually to a distance i casing shoe in a single operation without moving not exceeding five feet of said formation. A 10 the casing. formation tester 3 such, for example, as the The present applicationis a division of my co- I-Ialliburton or the Johnston formation tester, is pending application Serial No. 201,346,1iled April then anchored in the hole drilled through the 11, 1938. cement plug, and the efllciency of the water shut- 5 The present invention will be understood from off is determined by observing the fluid passing the following description, taken with reference through said tester, an admixture to said iiuid of to the attached drawings, wherein: a brine due to leakage through or around the Fig. 1 diagrammatically illustrates a convencement plug from the water layer W indicating tional application of the water shut-oi! test to a in such cases an imperfect cementing of the cas- D casing string cemented near the bottom of the ing. a0

borehole. In some cases, however, it may be found desir- Fig. 2 diagrammatically illustrates a convenable to cement the casing shoe at a point contionalapplication of the water shut-ofl test to a siderably above the bottom of the hole. This is casing string cemented in an intermediate zone done, for example, when the whole, or at least a I of the well. portion of a producing sand has been penetrated, 5

Fig. 3 diagrammatically illustrates the applicaor the well has been drilled for coring or logging tion of the water shut-off test to a casing string purp se to its total pt before the most adcemented in an intermediate zone of the well 3.0- vantageous point f r cementing the shoe of the cording to the method of the present invention. casing is determined.

*0 Fig. 4 is an elevation view in cross section of a In such cases, as shown in Fig. 2, if .the casing preferred embodiment of the apparatus of the shoe I5 is lowered to the desired level A, and cepresent invention. ment is pumped down and out therethrough, the

Fig. 5 is a plan view of the open seat valve effect of the drilling fluid standing in the boreshown in Fig. 4. I r hole and having approximately the same coni5 Figs. 6 and? are elevation views in cross section sistency andspecitlc gravity as the cement will of other preferred embodiments of the tailpiece not permit the cement to settle for more than 1' is shown in Fig. 4. v or 2 feet below the shoe, the cement being there- Present 011 field practice requires that wells fore forced upwards around the casing. when,

be properly cased and cemented off in order however, ahole is drilled through the casing shoe to to prevent the dissipation of oil deposits into in orderto apply a water shut-off test as before, 4.0 non-productive strata or to protect said deposits it is obvious that such test will not be conclusive against contamination by aqueous liquids from as to the efficiency of the cement plug placed in adjacent formations. Some State laws prescribe the annular space behind the casing, since it it that the effectiveness of cementing operations innot known whether any brine flowing through the shutting off fluid flow behind the casing be in each formation tester 3 is {due to leakage from the case tested according to definite regulations. upper water layer W through or around the Whenever it is desired to cement a casing string cement plug surrounding the casing, or to a flow extending substantially to the bottom of the boreof brine from a lower water layer L; In such hole, the cementing operation and the water shutcases, therefore, it is customary to place, as a preoff test do not present especial difficulties. In liminary operation, a bridging plug 1 at some 5 Such cases as Shown in 1 h asin shoe point below the cementing level 8 to seal 01! the 5 is lowered at the end of a casing string i subportion of the'well extending below the casing stantially to the bottom'of the'hole, a desired shoe 5. quantity of a cementing mixture is lowered into The placement of the bridging plug 1 is usually the casing, and pressure is applied to force said carried out by one of the following methods:

1. A desired quantity of cement may be spotted to the level i. by means of bailers and left to set there, whereafter the casing shoe is lowered to the levelA and cemented there in the usual manner.

2. A string of tubing is lowered to the level I, and a desired quantity of cement is pumped down therethrough, whereafter the tubing string is withdrawn, the bridging plug I left to set, and the casing cemented at level A as before.

3. The casing string I is first lowered to level I, a desired quantity of cement is pumped therethrough to form the bridging plug 1, whereafter the casing string is raised to level A, the bridging plug at l is left to set, and the casing is finally cemented at level 6, the water shut-off test being then carried out as before.

In using method 1 or 2, great difiiculties are often experienced in placing an effective bridging plug due to admixture of the cement slurry with the drilling fluid in the borehole. Bridging operations must sometimes be repeated three or four times before a satisfactory bridging plug is placed,

. which entails a considerable loss of time and increases the cost of cementing operations. Moreover, even when the bridging operation has been successfully carried out, a loss of time is experienced since the bridging plug must be allowed to set before the main cementing operation, that is, the cementing of the casing shoe, may be performed.

The use of method 3 involves the additional danger of freezing the casing string at the level 1, that is, below the desired level A, due to a premature setting of the cement, and should not be attempted at any depth greater than 4000 feet.

All three of these methods have the additional drawback of badly damaging thedrilling fluid system by contamination with cementing slurry during the bridging operation. Since it is especially important to have the drilling fluid in good condition at the time, when the casing string is being set to prevent freezing due to the effect of settling cuttings or sloughing formations, a cementing method which eliminates the necessity of a separate bridging operation becomes of considerable value.

Furthermore, the circulation of a cement-contaminated drilling fluid in contact with the face of oil-bearing sands often causes a partial plugging of the latter and results in wells of reduced productivity.

It is therefore the object of the present in vention to provide a method and an apparatus for cementing a string of casing in an intermediate zone of the well and for placing a bridging cement plug below the casing shoe at the time and as a part of the regular casing cementing operation, whereby the time necessary for such operation is considerably reduced, and the danger of contaminating the drilling fluid during the bridging operation is eliminated.

Referring to Fig. 4, the apparatus of the present invention comprises a string of casing I, supporting a casing shoe 5, made of or comprising a drillable material such as cast iron, aluminum, bronze, cement, or any combination of these or similar materials. The casing shoe comprises a valve, such as a ball valve 15, or a non-return valve of any other desired type. The ball valve I5 is held within a housing l8, having an axial passage l2 forming an upper seat adapted to close the valve against any upward fluid flow, and with a downward axial passage I! provided with an open seat l6, shown in detail in Fig. 5,

which permits a downward flow of fluid through the valve. The housing i3 is also provided with ports and passages M, leading through the casing shoe upwards and at an angle designed to give the fluid passing therethrough a whirling motion on issuing out of the shoe. The cross-sectional area of the passages I4 is adjusted in such manner with regard to the cross-sectional area of the main downward passage N, that the liquid passing through the valve is automatically proportioned into streams having any desired capacity ratio, for example, 40 percent thereof passing through the whirler ports l4, and 60 percent through the main downward passage H.

A drillable swage I8 is attached to the lower portion of the shoe 5, and serves to support the tail piece or tubing section l9, which has preferably an outside diameter smaller than the inside diameter of the casing string, and is made of an easily drillable material such as aluminum, Bakelite, hard rubber, brass, cast iron, etc. The tail piece 19 is usually from 10-to 20 feet long, being closed at the bottom by a screw plug 2!, made of the same material, and provided in its lower portion with perforations 20 to permit a fluid flow therethrough.

As shown in Fig. 6, a drillable float shoe 5A, provided with a valve similar in construction to that of the casing shoe 5, may be used if desired instead of the screw plug 2| at the lower end of the tail piece 19, or said lower end may be left open, as shown in Fig. '7. It may likewise be desirable to provide the tail piece I9 with inside or outside rifling, or both, as shown at 22 and 23 in Fig. '7. This rifling may be grooved on or attached to the tail piece in a manner well known to the art, and serves to give the cement slurry descending through the tail piece or ascending around it a whirling motion.

In placing a bridging plug and cementing a casing string in an intermediate well zone, that is, at a point considerably above the bottom of the borehole, the following procedure may be followed according to the present invention.

Referring to Fig. 3, the casing shoe 5, provided with the tail piece I9, is lowered into the borehole at the end of a casing string and placed at the exact level A where it is to be cemented, the tail piece l9 extending to approximately from 10 to 20 feet below said level. A desired amount of cement, such, for example, as three to five hundred sacks, or more, is then made into a slurry of any desired water content, and is pumped down the casing, followed by a solid wooden or rubber plug to which fluid pressure is applied from the top. The cement slurry is thereby forced out of the casing, a certain proportion thereof issuingthrough the whirler ports l4 into the space around the casing shoe, and another portion issuing through the perforations 2! in the lower portion of the tail piece I9 into the space around said tail piece. The borehole being filled with a drilling fluidgwhose consistency and specific gravity do not greatly differ from that of the cement slurry, the latter has no tendency to settle down to a greater distance than 1 or 2 feet below the plug 2|, and is forced upwards to a point considerably higher than the casing shoe 5, completely filling the annular space between the casing, casing shoe and tail piece, and the walls of the borehole. When the wooden or rubber plug following the cement charge within the casing string strikes the casing shoe 5, or a special stop for said plug provided .within the casing string at some distance, such as one casing stand damage #1 above the casing shoe, the fluid flow is stopped, and a rise of pressure indicates to the operator that the whole of the cement slurry has been forced into the borehole, excepting a small portion within the casing and tail piece below said wooden plug. The cement slurry is then allowed to set, a considerable saving of time being effected due to the fact that the bridging plug, that is, the cement within and around the tail piece Hi, can be allowed to set at the same time with the cement used for the main cementing operation, that is, with the cement in the annular space around the casing string I. In view of the fact that the bridging plug is placed within and around the tail piece l9, which serves as a metallic member reinforcing the cement, the cement slurry has no appreciable tendency to mix and be diluted or absorbed by the drilling fluid within the borehole and the formation of the bridging plug is thereby positively insured.

After the cement slurry has set, a drill bit is lowered within the casing string, and the hardened cement within the lowest casing joint, the friable casing shoe, as well as the upper portion of the tail piece l9, together with the cement in which it is embedded, is drilled out to a distance not exceeding about 5 feet below the casing shoe, that is, to a distance equal to approximately from one-fifth to one-half of the tail piece l9, as shown at 6 in Fig. 3. A formation tester 3 is then anchored within the hole thus drilled, and a water shut-off test is run in the usual manner 7 It will be noted that, although the space 6 is not actually in contact with the formation through which the well has been drilled, the annularbody of cement 9 separating said space from the walls of the borehole has a relatively small thickness, such as about 2 inches, and is, moreover, considerably cracked and damaged during the drilling of the space 6, being therefore quite pervious to fluid flow. Suitable and well known means may furthermore be used to break and/or remove said annular body of cement. If, therefore, the cement plug around the casing string, or the bridging plug around the tail piece l9, have been imperfectly placed, and leakage through or around said plug takes place from any upper water layer, the leaking fluid will easily penetrate into space 6, and can be detected by means of the formation tester.

I claim as my invention:

1, In a process for cementing a well casing, the steps of attaching thereto a shoe supporting a drillable tubing section of substantial length, said shoe having transverse passages communicating with the outside of the casing and a downward passage coaxial with said tubing section, lowering said shoe to the desired level within the borehole, lowering a cement slurry into said casing and tubing, applying downward pressure thereto within the casing, forcing said slurry out of the casing shoe passages and out of the lower end of the tubing, and causing said slurry to fill the annular space between said casing and tubing and the walls of the borehole to a point above the casing shoe.

2. In a process for cementing a casing string at an intermediate level of a borehole filled with a drilling fluid, the steps of attaching to said casing a drillable shoe supporting a drillable tubing section of a smaller diameter than said casing, said shoe having transverse fluid passages communicating with the outside of the casing,

ing section, lowering said shoe to the desired level within the borehole, lowering a cement slurry into said casing and tubing, applying downward pressure thereto within the casing, forcing a portion of said slurry out of the casing through the transverse passages of the shoe, forcing another portion of said slurry out of the lower end of the tubing, causing said slurry to fill the annular space between said tubing and casing and the walls of the borehole to a point above the casing shoe, discontinuing the pressure when substantially all the slurry has been driven out of the casing, allowing the tubing to remain filled with the, slurry, allowing the slurry within the borehole to set, lowering a drill bit within the casing, drilling out the casing shoe, and not more than five feet of the\ upper portion of the tubing, and testing the space thus drilled out for the leakage of fluids l through the cement plugs formed above the casing shoe.

3. In an apparatus for simultaneously cementing a casing in a borehole filled with a drilling fluid and placing a bridging plug below the shoe of said casing, a casing strip, a shoe attached to the end of said casing,transversepassagesthrough said shoe in communication with the outside of the casing, an axial passage through said shoe, and a drillable tubing section supported by the shoe and coaxial with said last passage, said tubing section having an outside diameter smaller than the inside diameter of the casing.

4. In the apparatus of claim 3, a spiral rifling on the outside wall of the tubing section.

5. In the apparatus of claim 3, a spiral rifling on the inside wall of the tubing section.

6. In the apparatus of claim 3, a spiral rifling on the inside and outside walls of the tubing section.

7. In an apparatus for simultaneously cementing a casing in a borehole filled with a drilling fluid and placing a bridging plug below the shoe of said casing, a casing string, a drillable shoe attached to the end of said casing, transverse passages through said shoe in communication with the outside of the casing, an axial passage through said shoe, a drillable tubing section supported by the shoe and coaxial with said last passage, said tubing section having an outside diameter smaller than the inside diameter of the casing, a plug closing the lower end of said tubing section, and a plurality of perforations in the lower portion of said tubing section above said plug.

8. In an apparatus for simultaneously cementing a casing in a borehole filled with a drilling fluid and placing a bridging plug below the shoe of said casing, a casing string, a drillable shoe attached to said casing, a vertical passage through said shoe, a non-return valve allowing a downward fluid flow within said passage, means compr sing a plurality of fluid passages in communication between said valve and the outside of the shoe for causing a predetermined proportion of the fluid passing downwardly through the valve to issue through said passages transversely of the shoe, and a drillable tubing section supported by the shoe and coaxial with the vertical passage through the shoe, said tubing section having an outside diameter smaller than the inside diameter of the casing.

9. In the apparatus of claim 8, a drillable shoe attached to the end of said tubing section, a vertical passage through said shoe, a non-return valve allowing a downward flow through said passage, and a plurality of transverse fluid passages in communication between said valve and the outside of said shoe.

10. In an apparatus for simultaneously cementing a well casing in a borehole filled with a drilling fluid and placing a bridging plug below the shoe of said casing, a casing, a shoe attached to the end of said casing, transverse passages through said shoe in communication with the outside of the casing, an axial passage through said shoe, and a drillable tubing section supported by the shoe and coaxial with said last passage, the lower outlet of said tubing section being at a 5 substantial distance below the casing.

PAUL S. PUSTMUELLER.

Images