US2249852A - Process for cementing oil wells - Google Patents

Description

y 1941- P. s. PUSTMUELLER 2,249,352

PROCESS FOR CEMENTING OIL WELLS Filed April 11, 1938 2 Sheets-Sheet 1 Fig. l.

.Invemor: Poul S. usirhueller B9 hi AHorneg July 22, 1941. P. s. PUSTMUELLER PROCESS FOR CEMENTING OIL WELLS 2 Sheet s-Sheet Filed April 11, 1938 6 $5 Q. 1 \U 4 i F I Q B M 555 W 8 m w l P ll Him m d Fig.4.

lnvenfor: Paul S. P sfmueller' 59 his Arforneg:

Patented July 22, 1941 2,249,852 raocsss ron CEMENTING om WELLS Paul S. Pustmueller,

by mesne assignmen 00., Inc., Whittier, Call! a corporation of California Bakersfield, Calif., assignor,

ts, to Security Engineering Application April 11, 1938,-Serial No. 201,34

8 Claims. (01. 166 -1) The present inventionpertains to the art of cementing oil and gas wells, and is more par-.

ticularly related to a process whereby the shoe or lower end of a' casing string may be cemented at an intermediate level of the well, that is at a point relatively distant from the bottom of the hole, and a bridging cement plug, necessary for testing the efiiclency of water shut-off obtained by cementing the casing, may be placed below the casing shoe in a single operation without moving the casing.

The present invention will be understood from the following description, taken with reference to the attached drawings, wherein:

Fig. tional application of the water shut-off test to a casing string cemented near the bottom of the borehole.

tional application of the water shut-ofi test. to a casing string cemented in an intermediate zone of the well.

Fig. 3 diagrammatically illustrates the application of the water shut-off test to a casing string cemented in an intermediate zone of the well according to the method of the present invention.

Fig. 4 is an elevation view in cross section of a preferred embodiment of the apparatus of the present invention.

.Fig. 5 is a plan shownin Fig.4.

Figs. 6 and 7 are elevation views in cross secview of the open seat valve 2 diagrammatically illustrates a conven- 1 diagrammatically illustrates a convenamount of cement 4 remaining also in the lowest section of the casing. After the cement has set, a drill bit is lowered within the casing, and a hole .6 is drilled through the hardened cement remaining in the casing, through the casing shoe and through the formation below the plug, usually to a distance not exceeding five feet of said formation. A formation tester 3 such, for example, as the Halliburton or the Johnston formation tester, is then anchored in the hole'drilled through the cement plug, and the efliciency of the water shutoff is determined by observing the fluid passing through said tester, an admixture to said fluid of a brine due to leakage through or around the cement plug from the water layer W indicating in such cases an imperfect cementing of the easing. s

In some cases, however, itmay be found desirable to cement the casing shoe at a point considerably above the bottom of the hole. This is done, for example, when the whole, or at least a portion of a producing sand has been penetrated, or the well has been drilled for coring or logging purposes to its total depth before the most advantageous point for cementing the shoe of the casing is determined.

tion of other preferred embodiments of the tail piece l9 shown in Fig. 4.

Present oil field practice requires that wells be properly cased and cemented off in order to prevent the dissipation of oil deposits into non-productive strata'or to protect said deposits against contamination. by aqueous liquids from adjacent formations. Some State laws prescribe that the effectiveness of cementing operations in shutting off fluid flowbehind the casing be in 'each case tested according to definite regulations.

Whenever it is desired. to cement a casing string extending substantially to the bottom of the borehole, the cementing operation and the watershut-oflf test do not present especial difliculties. In such cases as shown in Fig. 1 the casing .shoe 5- is lowered at the end of a casing string I substantially to the bottom of the hole, a. desired quantity of a cementing mixture is lowered into the casing, and pressure is applied to force ,said mixture through suitable passages in the 'shoe into the annular space {between the casing and the walls of the borehole',fa certain some point off the portion of the well extending below the v spotted to In such cases, as shown in Fig. 2, if the easing shoe 5 is lowered to the .desired level A, and cement is pumped down and out therethrough, the effect of the drilling fluid standing in the borehole and having approximately the same consistency and specific gravity as the cement will not permit the cement to settle for more than 1 or 2 feet below the shoe, the cement being therefore forced upwards around the casing. When, however, a hole is drilled through the casing shoe in order to apply a water shut-off test as before, it is obvious that such test will not be conclusive as to,the efiiciency of the cement plug placed in the annular space behind the casing, since it is not known whetherany brine flowing through the formation tester 3 is due to leakage from the upper water layer W through or around the cement plugsurrounding the casing, or to a flow of brine from a lower waterlayer L. In such cases, therefore, it is customary to place, as a preliminary operation, a bridging plug I at below the cementing level 6 to seal casing shoe 5.

The placement of the bridging plug I is usually carried out by one of the following methods:

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

2..A-string of tubing is lowered to the level-1, and a desired quantity of cement is pumped down therethrough, whereafter the tubing string is withdrawn, the bridging plug I left to set, and I the casing cemented at level A as before.

3. The casing string l is first lowered to level 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 lose 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 I, 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 the drilling fluid system by contamination with cementing slurry during the bridging operation. Since it is especially important to have the drilling fluid in 7 good condition at the time, when the casing string is being set tozprevent freezing" due toand passages l4, leading through thecasing shoe -upwards and at an angle designed to give the fluid passing therethrough a whirling motion onissuing 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 l1, that the liquid passing through the valve is automatically proportioned intostreams having. any desired capacity ratio, for example, 40 percent thereof passing through the whirler ports l4, andY60 percent through the main downward passage ll.

A drillable swage I8 is attached to the lower portion of' the shoe 5, and serves to support the Bakelite, hard rubber, brass cast iron, etc.. The

tail piece I!) is usually from 10 to feet long, being closed at the bottom by a screw plug 2|,

- made of the same'material, and provided in its the effect of settling cuttings or shoughing 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 pluggln'g of the latter and results in wells-of reduced productivity.

It is therefore the object of the 'present invention to provide a method and an apparatus for cementing a string of casing in a r 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 casin'g cementing. operation, whereby the time necessary for such operation is considerably reduced, and the danger of contaminatin 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 sup porting a casing shoe 5, made of or'comprising a drillablematerial 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 l5, or a non-return valve of any other desired type. The ball valve I5 is .held within a housing' l3, having an axial I passage I2 forming an upper seat adapted to close the valve against. any upward fluid flow, and with adow'nwazd axial passage .ll. provided with an open'seat l5, shown in detail in Fig. 5, which permits a downward flowof fluid through the pumped down the casing; followed by a solidlower portion with perforations 20 to permit a fluid flow therethrough.'

As shown in Fig.- 6, a drillable float shoe 5A,

open, as shown in Fig. '7. It may likewise be desirable to provide the tail piece 19 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 flve hundredsacks; or-more, is then made into a slurry of any desired water content, and is wooden or rubber plug. to which fluid pressure isapplied from the top. The cement slurry-is thereby forced out of the casing, a certain proportion thereof issuing through the whirler portsl4 into the space around the casing shoe, and another portion issuing through the perforations 2| in the lower portion of the tail piece Iii into the space around said tail piece. The borehole beingfilled with .a drilling fluid whose consistency and specific gravity do not greatly differ from'that of the cement slurry, the latter I has no tendency to settle down to a greater discharge within the casing string strikes the casing shoe 5, or a special stopfor said plug provided within the casing string-at some distance, such as one casing standfabove the casing shoe, the fluid flow is stopped, and a rise of pressure ining of time cement slurry has been forced into the borehole. excepting a smalL-portlon within the casing and tail piece below said wooden plug. The cement slurry is then 'allowed to set, a considerable savbeing effected due to the fact that 2,249,852 dicates to the operator thatthe whole 'of the the bridging plug, that is the cement within and around the tail piece H, can be allowed to set .,at the same time with the cement used for the ciable tendency to mix and be diluted or absorbed by the drilling fluid within the borehole and the formation of the bridging plug is thereby'posltively 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 thetail piece 19, together with the cement in which it is embedded, is drilled out to a distance not exceeding about 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 8 in Fig. 3. A formation tester 3 is then anchored within the hole thus drilled, and

a water shut-of! test is run in the usual manner.

It will be noted that although the space 8 is' not actually in, contact with the formation through which the well has been drilled, the

annular body 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 8, being. there- ,fore quite pervious to fluid flow. Suitable and well known mean may furthermore b'e used to break and/or remove said annular body of cements 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 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 diameterthan said casing, lowering said shoe to the desired level within the borehole, lowering a cement slurry into said casingand tubing, applying downward pressure thereto within the casing, forcing said slurry out 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 the upper portion of the tubing, and testing the space thus drilled out for the leakage of fluidsthrough the cement plugs formed 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 outsideof the casing,

and a downward passage coaxial with the 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 a por- 'tion of said slurry out of the casing-through the transverse passages of the shoe,- forcing another portion or said slurry out of the lower end of the tubing, causing said slurry to flll 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 substan tially' 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,

2 drilling out the casing shoe, and not more than tubing a short distance five feet of the upper portion of the tubing, and testing the space thus drilled out for the leakage offluids through the cement plugs formed above the casing shoe.

3. In a process for cementing a casing string in a well, the steps of attaching to said casing. a shoe capable of being drilled through, supporting a drillable tubing section of smaller diameter than thecasing by the drfllable shoe, lowering said shoe and tubing into the well, lowering a.

cement slurry into said casing and tubing, forcing the slurry to be expelled outof the tubing and to rise thereabout to fill the annular space between said tubing and casing and the walls of.

the well to a point above the casing shoe, allowing the slurry to set and drilling through the casing shoe and the upper portion oi the tubing, allowing the remainder of the tubing and the slurry thereabout to remain intact, and testing the casing for leakage through the'cement plug around the casing above the casing shoe while the lower portion of the tubing and the slurry thereabout remains intact.

4. An apparatus attachable to a casing for cementing a casing in a well comprising a shoe capable of being drilled through adapted to be attached to the casing, a section of readily drillable tubing of smaller diameter than the casing,-

means for attaching said tubing tothe casing shoe, a drillable plug closing the bottom of the tubing, there being outlet ports formed in the above the plug.

5. An apparatus attachable to a casing for cementinga casing in a well comprising a shogcapable of being drilled through adapted to be attached to the casing, a section of readily drillable tubing of smaller diameter than the casing, means for atta'ching'sa'id tubing to the casing shoe, the interior of the tubing being rifled tending to produce swirling of cement slurry forced downwardly therethrough.

6. An apparatus attachable to a casing for cementing a casing in a well comprising a shoe means for attaching said tubing to the casing shoe, the exterior of the tubing beingrifled so as,

to tend to produce swirling of cement slurry as it ascends thereabout.

7. An apparatus attachable to a casing for cementing a casing in awell comprising. a shoe capable of being drilled through adapted to be attached to the casing, a section of readily drillas it isable tubing of smaller diameter thanthe casing,

means for attaching said tubing to the casing shoe, the exterior and the interior of said tubing being rifled as and for the purposede scribed.

V 8. An apparatus attachable to a casing for 5 cementing a casing in a well comprising a. shoe capable of being drilled through adapted to be attached to'the casing, a section of readily dri1l.

drillable tubing, said plug being equipped with a'

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