AMERICAS I S S T I T U T E OF BIISISG ASL) METALLURGICAL ESGISEERS Technical Publication No. 2301

Class G, Peeoleurn Technology, January 1948 DISCUSSIOS OF THIS PAPER IS ISVITED. Discussinn in writing ( z copies) may be scnt to the Sccre-

tary. American Institute of Mining and hIetallurpic?l Engineers, a9 Wcst.3qth Street. Sew,York, 18. S . Y. Unless special arrangement is made, d~scussion of t h ~ s paper a,ill close April 1 5 . 1948. Any dlscuss~on offered thereafter should preferably be in the fnrm of a new paper.

Diamond Coring in the Rangely Field, Coloraclo BY CARL J. CHRISTESSES' (Ilenver Meeting: October 19471

. ~ S T I W C T

THIS paper presents the development of diamond coring of the n'eber sand section in the Kangely Ficld, Colorado. The description and operation of the diamond-coring equip- ment is included as well as the economics and results obtained by its use. Diamond coring is cornparcd with the other methods used for drilling thc \Vebcr sand. Two types of diamond coring arc discussed. The first and the one used most extcnsively is the rcjiular 6'6 X A?$-in. diamond bit and bottom hole so-ft barrel. The sccond type, which has also been used success- fully by Stanolind, consists of a 41/3i6 X z l ! i z - in. cutting bit and reverse circulation coring quipmcnt. Thc first type ~vill be rcferred to as regular or conventional diamond coring while the latter type will be referred to as reverse circulation diamond coring.

the Kangely Engineering ('ommittre se- lected key wells tha t were to core the \Yeher section in it. entirety. These cores \\.tsrc t o be analyzed and various sections t r ~ t r ~ i t o gather sufficient information so that accu- rate reservoir stutiics coulri be made. The number of wells selcctetl \\.ere kcljt a t a minimum inasmuch as the protiuctive n ' r l ~ r r section. which is fouritl a t an a?)- proximatr tiepth of 6000 ft , is thick, 1)cing as much as 600 t o joo ft on top of the structure. 'The \\'et)cr section is also com- paratively hard t o tirill. For instancr, one well took 60 days t o core 400 ft of \\'c51>cr sand with conventional coring cqui~)mtmt . I t was noticrti, ho\vcver, tha t ('ore 1,nI)ora- torics' diamond plug cutter could quickly cut a plug from onc of thr.;c hart1 corrs. This fact let1 t o the scrious consic!eration of IXTRODUCTIOX diamond coring the \i'et)er sand.

Diamond coring has been uscd for many ,rhe first (1iamontl at ~~~~~l~ years in mines, quarries, surface coring a t performetl I ly Stanolintl in .Iugust Iq46 dam sites, laboratory work, a n d so on, but , anti , although \ve exl)cricnccstl some diffi- unti l recently, had never been used v W ' culties, t he results tlcfinitrly intlicatctl tha t extensively in coring oil sands and other diamond coring \,.Oultl t,r successful a t oil-bearing s t ra ta . I t was demonstrated Rangely far coring the san<l. .Is carly in its development t h a t hard forma- more \\.ells cOrt.(i anti thr equil,ment t ions coul(l be cut rapidly ant1 tha t core imI,rove(j diamontl I , ~ . recoveries far exceeded those obtained with less expensive than (irilljng thL> \vrher conventional hard rock hits ant1 quite often \\.ith bit , less 100 pct recovery \\-as otltained. Hot\-ever, than one (liamond coring has [lefi- the poorly constructe(l diamond-coring nitely provc(i its usefulness in ojl-field equipment anti resulting high costs of early drilling ol,crations in the ~ ~ ) ~ k ~ >lountain tliamontl coring slowed down its progress. area \\.here formations quite Often very

Early in t he ( l c v e l o ~ m e n t of t he Rangcly hartl. The practicc of spot coring in hard \Veber field, Kio Hlanco County , Colora(io, oil.t)caring formaticlrls ivith conventional

- .~ --

lan nu script rt.cuived at the office of thp coring equipmcnt is giving \yay to diamon(i Institutr, Aug. 2 1 , 1947. coring of the entirc section.;, thus giving an

*Stan,~l ind Oil and ( ; n s Co.. Frrt Wr~rth, Texas. operator the complete picture. -----p--p--p---p--.-- ~- - - - ~ ~~~p~

Copyright, 1948, by the American Institute of Mining and Metallurgical Engineers. Inc. Printed in USA

2 DIAMOND CORING IN THE RANGELY FIELD, COLORADO

REGULAR DIAMOND CORING stabilizing ribs welded approximately IS Description o j Equipm~nt Used in. above the bit. Another set of stabilizing

The regular cliamond-coring equipment ribs are welded on a sub which is screwed is used almost exclusively a t Rangely to into the top of the barrel. Construction of core the Weber section. Reverse circulation these stabilizing ribs can be seen in Fig 2

FIG I-LOIYER SECTION OF CORE B.\RREJ, T'IIITII DIAUOND C O R E HEAD IN P L A C L...

coring has been successfully used on a Stanolind well and \vill be discussed briefly later 011. The regular tliamond-coring

, . equipment cuts a 6?6-in. hole and removes a 394-in. core, thus being referred to as a 65S-in. ocl X g3i-in. id core head and core barrel. The lower section of the core barrel is shown in Fig I with the diamond core head in place, ready for coring. The core barrel consists of an outer and an inner barrel. This particular barrel is a as-it bar- rel but the standard barrel now being used will cut a so-ft core. The outer barrel of the jo-ft core barrel is a two-section, plain barrel, 59fs-in. od with a set of

FIG 2-CONSTRUCTIOK O F STABILIZlNG RIBS ON OUTER BARREL.

on the outer barrel. I n this case they were welded onto the barrel instead of a sub that fits on top of the barrel. These stabilizing sections are 6 ? f G in. in diameter and serve two purposes: ( I ) they keep the barrel from wobbling in the hole and force it to cut a straight core and, (2) they take all of the wear away from the outer barrel. The stabilizing sub tvas developed to eliminate \velding on the barrel. The sub can be exchanged without shopping the core bar- rel for building up the ribs.

From top to bottom in Fig 2 can be seen the top or head of the core barrel, the bear- ing on which the inner barrel is free to turn

CARL. J. CHRISTENSEN-TP 2301 3

independent of the outer barrel and head, individually and correctly for cutting. The the top of the inner barrel, ancl the top of matrix alloy, which is in a powdered form, the outer barrel. In the photograph the is poured into the mold. I t is then placed in head is unscrewed from the outer barrel and a furnace and sintered at proper tempera-

the inner barrel is pulled up out of the outer barrel. The circulating fluid passes down through drilled holes in the head and through the annulus between the inner and outer barrels. A small port with a ball and seat is providcd in the top of the inner barrel which keeps the circulating fluid from passing down inside the inner barrel but allows fluid to escape out of the top of the inner barrel as it fills with core.

Fig 3 shows two diamond core heads and a spring core catcher. The diamond cbre head on the left has fewer water courses than the other. The one on the right has 2 4

courses and was found to be most satis- factory in cooling the head and removing the cuttings.

The diamond core head is made up prin- cipally of two parts, the matrix in which the diamonds are set, and the blank upon which the matrix is fastened. The matrix is made of a hard special alloy while the blank is an ordinary tough alloy steel. Diamond setting is a highly skilled and highly developed process which has been developed over many years and it is this fact that maltes it possible for such a delicate bit to stand the abuse of oil-well coring. A mold is machined from hard carbon to the exact form of the matrix. I n this mold each diamond is set

ture to form the finished matrix. The dia- monds are set in a definite pattern on the matrix to produce most efficient cutting. The matrix is then fastened to the blank to form the finished head. One manufacturer of diamond bits screws the matrix lo the blank and then keys it'in place. Another manufacturer molds the matrix to the blank in the diamond-setting p.rocess. The dia- monds most commonly used are "Bortz" diamonds, which are hard commercial diamonds. ~ 6 4 6 X 35/4-in. head will con- tain approximately 200 carats. There are a number of other grades and sizes of diamonds used for oil-well diamond coring heads. One operator has obtained excellent results with large "Congo" gracle dia- monds, which are a softer grade of diamond than the "Bortz" and somewhat less expensive.

The core catcher shown between the two diamond heads is used to break off and hold the Fore. The design is simple but very effective. I t is split in one place ancl slightly smaller in the unsprung position than the core to be cut. I t is made of a spring steel and the inside edge is covered with a hard metal coating to prevent it from wearing out quickly. The catcher is tapered and fits into the Lore head. While cutting the

4 DIAMOND CORING I N THE RANGELY FIELD, COLORADO

core the catcher rides up against the inner core about 4-ft long protrudes from the core barrel and does not rotate with the outer barrel and is broken off by use of a hammer barrel but remains stationary with the core or sledge. Long sections of continuous core and inner barrel. The outer barrel rotates are not uncommon. You will note from the

~ " I G ~ - R E ~ ~ ( ) v I N G THE CORE FRO11 TIIK B!iRREL.

with the drill pipe while coring. The core that is cut feeds through the core catcher up into the inner barrel. Circulating fluid passes down the drill pipe, through holes bored in the head, down the annulus be- tween the inner and outer barrels, through the holes shown in thc core catcher, through the water courses in the bit and then out the drill pipe and casing annulus. After the core is cut it is broken off by pulling up on the drill pipe. During this operation the outside taper on the core catcher causes it to squeeze down on the core harder and harder as more tension is placed in the drill pipe.

Fig 4 shows the procedure used in re- moving the core from the barrel. A piece of

picture that the downward motion of the core can be controlled by applying a fric- tion grip on it with the special tool shown.

Operalion of Diamond-coring Eqz~ipwze?zL

In operating any type of mechanical equipment care must be taken if failures are to be prevented. In the case of operating diamond-coring equipment this is ex- tremely important. The success and savings resulting from the use of diamond-coring equipment depend to a great extent on usjng proper technique. I t is impossible to set any hard and fast rules for the operation of the equipment under all conditions and in all types of formations. There are, how- ever, a number of general rules that will help to keep failures a t a minimum. Most of these rules have been developed through analyzing failures a t Rangely and else- where. They can be stated briefly as follows:

I . All metal junk must be removed from the well bore before commencing dia- mond coring.

.z. The core barrel should be checked thoroughly after cutting every core. The circulating ports in the head will plug with coarse material from the mud. Beafings on which the inner barrel rotates must be checked for wear.

3. Drill collars used above the core bar- rel should be straight to eliminate unnec- essary wear on the stabilizing ribs and to prevent undue stress in tool joints.

4. Before commencing diamond coring in a larger hole than the diamond head, it is advisable to drill a rat hole about 36 in. larger than the diamond core head for a few feet.

5 . Some float equipment used in ce- menting casing strings contains metal springs and other metal parts and should not be used. Extreme precaution should be taken to keep junk from entering the hole.

6. If the completion program can so be arranged, provision should be made for a casing string to the top of the sand that is to be diamond cored. Unsatisfactory results caused by damaged diamond heads were experienced in two wells in the Rocky Mountains where large sections of open hole containing shale formations provided shoulders where junk had accumulated and later fell into the hole while .diamond coring. The holes had been cleaned prior to coring.

7. Rock bits used for drilling the hole prior to coring should be 48 in. larger than the diamond head to be used for coring. A 6x411. hard rock bit should be used ahead of the 644-in. diamond bit.

8. Rotary table speed and fluid volume through the system should be set for coring when about 6 to 12 in. above the bottom of the hole. The bit should then be lowered gradually until it has cut a uniform seat over all of its face. In certain types of hard fractured formations a small piece of loose core might remain in the hole. If the bit is lowered rapidly with full weight on the bit from the start, the hard piece of loose core will roll around and damage the matrix on the inner periphery. The diamond head is actually damaged more under these condi- tions than in cutting an entire so-ft core.

9. When a core catcher fails and leaves several feet of core in the hole the core barrel should not be rotated while going down over the core unless a different head is being run. The weight indicator should he watched closely, however, and if there are any signs of the bit taking weight, the bit will have to be rotated. I n most cases the core remaining in the hole is not broken off and it is possible to go down over it. 10. After cutting a core it is broken off

by shutting down the rotary table and pull- ing up on the drill pipe. By watching the weight indicator it is possible to tell when the core breaks off. Usually a straight pull of 10,ooo lb will break a core off, this, of course, depending on the formation's phys-

ical characteristics. If a straight pull fails to break the core, the drill pipe can be rotated slightly to break off the core by twisting. Tension must be maintained during the twisting operation.

11. Use a sufficient number of drill col- lars so that all the weight to be used on the bit will be in the drill collars, thus leaving the drill pipe in tension.

12. I t is very noticeable when a diamond bit ceases to cut inasmuch as diamond cor- ing time is low, sometimes as low as 3 min per foot. Also, a diamond bit will cut as fast just before failing as it did when first run in the hole. Therefore, when cutting ceases, either the diamond bit has failed or the core barrel is plugging, and it is advisable to come out of the hole and check the equip- ment. If this is done, larger salvage values are obtained on the bits.

13. While diamond coring, uniform and constant weight should be maintained on the bit a t all times. Allowing the bit to drill off not only doubles the drill time but is harder on the bit.

14. Even though the diamond-setting process has been highly developed, there is usually a small variation in the size of dia- mond heads. A variation in outsicie diam- eter of a few thousands of an inch will make it necessary to ream down a larger head being run behind a smaller head. If the section to be cored will require two or three heads, the largest head should be used first, and so on. A ring gauge can be used to check the outside diameter of the bits so that reaming can be eliminated.

15. After running a junk sub to ensure a clean hole, stripper rubbers should be used on all trips going in and coming out of the hole. Tong dies and other metal parts are always getting in the hole and the above precaution should be taken.

The amount of weight to carry on the bit, rotary table speed and amount of fluid to be circulated through the system while coring, are variable, depending on the formation being cut and the size of bit being used.

6 DIAMOND CORING IN THE RANGELY FIELD, COLORADO

This must be established in each field for quickly wears around the face of the bit and each size head and for the kind of fluid or sh~ts :~of f circulation, which, in turn, in- mud being used. General practice is to creases the pump pressure. By watching start out with the lowest weight, table the pump pressure it is possible to detect a -4

5800

5900

6000

+ a 6100 +.

f a

0" 6200

6300

6400

6 5 0 0 J I I I I I I I I I I I I I I I I I I I 2 4 6 8 10 12 14 16 I8 20

Time,days

FIG 5-DRILLING VS. DIAMOND CORING. Depth-time log of Stanolind's Well No. 5 , Weber sand section, Rangely, Colo.

speed, and the like, as found for similar conditions elsewhere and increase these factors until the most desirable operating conditions are determined. Approximately IOO gpm of oil-base mud should be circu- lated or 80 gpm of water-base mud. Water- base mud has much greater erosive action on the bit than oil-base or emulsion mud. The pressure and volume of water-base mud should be kept just high enough t o carry away the cuttings and cool the head. On the other hand, oil-base mud has a tendency to plug the water courses if a sufficient volume is not circulated. There- fore, it is usually necessary to circulate a larger volume of oil-base mud than water- base mud. Once the proper volume of fluid has been checked the particular pump pres- sure while circulating this volume can be used by the driller to detect any change of conditions. When a bit fails, a groove

bit failure, providing nothing else is restrict- ing the flow of fluid through the system.

For the Rangely Weber sand section we have found a rotary table speed of 125 to 150 rpm and a weight of 3000 to 5000 lb on the bit t o be most satisfactory. Coring time under these conditions' varies from 3 to 4 min per foot in porous sand t o 30 min per foot in shale, average time being g to 10 min per foot.

Discussion

During August 1946, diamond coring was initiated by Stanolind a t Rangely. A 25-ft core 'barrel with a 634-in. od by 3%-in. id cutting head was used. The first diamond bit cut 70 f t before failing. The failure re- sulted from the loss of a couple of the sec- tions or lugs from the bit. The second bit failed immediately when the matrix in which the diamonds were set broke away

from the steel body of the bit. While wait- ing for additional diamond bits we con- tinued coring with a conventional core barrel and bits. A total of six diamond bits were used in this well to core 353 ft of sand giving an average life per bit of 58.8 ft. We received IOO pct recovery for the 353 ft cored and the average cutting time per foot was 9.6 min. In the same well we cored 119 ft with conventional rock bit coring, recovering 97 ft for a recovery of 80.8 pct. The average coring time for the 119 ft was 42.9 min per foot. Diamond coring proved to be far superior and much more economi- cal than conventional coring on this well even with all the difficulties and bit failures experienced. The causes for the bit failures in this well have been corrected. The 634-in. diamond matrices on the bits used in this well were molded in half sections and keyed to the steel blank. The bits now being used' have matrices that are molded in one piece, making a more uniform and much stronger diamond bit. Failures resulting from the matrix pulling loose in the hole are now few.

After making a study of the coring in this frrst well, it was decided to try a 50-ft core barrel, thus cutting the number of trips in half. Longer wear could also be expected from the diamond bits because most of the wear and tear on the bits was received while making trips and commencing the next core. The results obtained with a 50-ft core barrel on overall cutting time is de- picted on Fig 5. Approximately the first 75 ft of Weber section in this well was drilled with conventional hard rock bits and took seven bits and'a total of 4.7 days. The next 398 ft were diamond cored which took a total of 5.6 days with one bit. The next few feet were cut with reverse circulation coring without success. The well was then completed after cutting two more 50-ft cores. Fig 5 can be taken as typical of dia- mond coring a t Rangely with the 50-ft core barrel.

The first four wells cored with the 50-ft core barrel gave excellent results and the

equipment worked perfectly. However, on the following three wells we experienced considerable trouble in operating the equip- ment. This time the difficulty was not the bits but the core barrel. Up to this time we were using only one stabilizing point on the barrel, which was at the top. The core that was being cut by the barrel was grooved, the groove forming a spiral around the core. After cutting several feet of this crooked core, the barrel became plugged solid and the equipment ceased to operate. This plugging condition of the barrel threw all of the weight being carried on the bit onto the inner core-barrel bearing. Failure of the bearing was frequent and quite dis- astrous. Broken parts of the bearing were pumped down between the inner and outer barrels, and in a few instances the core barrel had to be shopped to remove the inner barrel. We overcame this diiculty by welding stabilizing ribs on the 50-ft core barrel approximately 18 in. above the bit. This gave the outer barrel stabilization a t the top and a t the bottom and the difficulty was eliminated. These stabilization ribs are approximately ?i6 in. less in diameter than the bit. Before correcting the trouble, we noticed that these crooked cores were al- ways obtained while cutting the hard, dense dolomite in the Weber section.

The bearing on which the inner barrel floats while in operation is a critical point in the barrel. Although the bearing gives comparatively long service in oil-base mud, it should be checked on every trip and re- placed periodically to eliminate failure while coring. A recess is now being cut in the inner barrel cap which will serve to catch and retain broken bearing parts. Another barrel is now being manufactured in the Rocky Mountain area.which uses a completely sealed bearing. Although the writer has not had any experience with this barrel, this feature appears to have con- siderable merit.

The Rangely Weber sand is made up of hard, dense, dry dolomite and dolomitic

8 DIAXOSD CORIXG IS TIIE RANGELY FIELD, COLORADO

GORING T'ML - M ' N / ~ . I0 PO 30 40

TOTAL DEPTH 6 ~ 0 2 '

l D P O F W E E R SAND 5192.' 0 I A N 3 7 " U S I N G 5 ' ' A T 5808' CORED WlTn OIL BLISE MUD n S H A L E USE0 54' CORE BARREL. 100 PER C E N T R-ERI. D O L O M ~ T L

FIG ~ C O X P O S I T E LOG SEOWISG CORISG TIYE ASTI FORXATIOS CORED.

\Yeber sand, Stanolind Well S o . 5, Rangely, Colo.

sand, gray hard shale, red shale, h e and medium grain sand, and sandy shale, con- taining some limey blotches, quartzitic sand and pyrites. Fig 6 shows the rate a t which these various strata are cored with dia- mond bits. Generally the porous true sands core a t a rate of five or less minutes per foot; sandy-dolomite with some porosity, a t a rate of 5 to 10 min per foot; sandy shales with some porosity, a t a rate of 10 to 15 min per foot; hard, dense dolomite, a t a rate of approximately I 5 min per foot; and true hard shales a t a rate of 20 to 30 min per foot.

At the present time three major oper- ators in the Rangely field are diamond cor- ing the R'eber sand section in practically every well and having the cores analyzed. This program has been developed as a result of the economics of diamond coring the Rangely \Veber section. The section can be cored with diamonds a t less cost than it can be drilled with conventional hard rock bits. Fig 7 presents a comparison of four methods that have been used to drill the Weber sand section. Reverse circu- lation drilling with hard rock bits has been used and proven very economical and satis- factory in the north and west portions of the field where the section drills much faster. IIo\vever, crude oil must be used with reverse circulation to prevent loss of fluid to the formation. If oil-base or water- base mud is used, the circulating pressure in reverse circulation against the formation causes loss of fluid. Whenever crude oil is used around a conventional drilling rig, the danger of explosion and fire is always present. Therefore, this method has not been used extensively.

With the present program of diamond coring a t Rangely, the writer feels that more coring data \)-ill be obtained in this reservoir than has ever been obtained else- where. Correlation of the \I'eber sand sec- tion a t Rangely is practically impossible because of the varied sand conditions from one well to another. However, with the large amount of core data being obtained,

reservoir studies will be more accurate and Trained drilling crews are essential if valuable. The data will also be very valu- maximum benefit from diamond coring is able for future shooting of the section, to be obtained. Diamond coring requires

TOTAL COST OVERALL CUT- N O . OF BITS PER FOOT. TlNG TIME PER 5 0 0 '

MIN/FT. FEET CUT.

CONVENTIONAL CORING STANOLIND - W E L L NO. I @ .

CONVENTIONAL DRILL1 NC

3TANOLlND - WELL N O . 2 0 .

DIAMOND CORING - 5 0 BBL - 6 $ " x 3 3/4"

srANoLIND - WELL N o . 4 .

REVERSE DIA. CORING - WASINC CORES TO SURFACE - 4 X 2 . STANOLINC - WELL NO. 2 1 .

FIG '/--COMPARISON OF METHODS USED FOR DRILLING, RANGELY WEBER SAND, RANGELY, COLO.

water shut-off jobs, selective production to constant attention from the driller. Most control gas-oil ratios, and so on. Data on crews a t Rangely are now familiar with diamond coring of the Rangely Weber sand diamond coring. The total footage drilled is given in Table I. by a single bit is steadily increasing. Maxi-

I0 DIAMOND CORING IN T H E RANGELY FIELD, COLORADO

TABLE I-Diamo?zd-coring Data in the Rangely JVeber Sand

I 2 3 4 5 3 4 5 6 7 8 9

I 0 I I I2 I 3 I 4 I5 16 I7 18

Total. -

Well Total Sum- Footage

b e Cored

I I I I

a Includes cost of core barrel equipment.

Zumber Average Total Diamond F t Cored Cost of Rvg~tt. Total Cost Remarks

Bits per Day 1 .Its 1 1 1 p Z $ t ~ 25-ft core barrel 25-ft core barrel 50-ft core barrel 50-ft core barrel 50-ft core barrel 25-ft core barrel 25-ft core barrel 50-ft core barrel 50-ft core barrel 50-ft core barrel 50-ft core barrel 50-ft core barrel 50-ft core barrel 50-ft core barrel 50-ft core barrel 50-ft core barrel qo-ft core barrel 50-ft core barrel 50-ft core barrel 50-ft core barrel 2s-ft core barrel

TABLE a-Diamond Bit Record (Complete Data)

' Bit

A B C D E P G H I J K

L

M

N

0

P

Q R

S T

U

V

. Total. . . . Average..

g~fp,";~ ---

179.99

:%:$: 169.29 197.39 198.80 194.60 194.87 194.35 183. 11 z o o . 8 ~

183. 11

190.03

197.14

200.48

186.55

202.06

201 .70

zz bits

S e t Bit Cost per

F t

$ 7 .60 9 .59 9 .63 9.21 4 .10 2.06

449.92 8 .32

17.83 9 .71 3 .50

3 .28

18.81

26.07

3 .99

2 .43

2 .86

4.49

7 .32 2.32

27.28

7. I I

8 5.14

F 5 i i i e

68 .0

: 125.0 223.5 599.4

2.0 125.0 50.0 93.7

239.0

258.0

44.0

49.0

279.5

431.5

400. o

399. o

202.0 612.0

49.0

197.5

-- 4.613. I

209.7

Remarks

Normal bit failure. qormal bit failure. hormal b i t failure. Normal bit failure. Normal b i t failure. Normal bit failure. Bit failure because of junk in hole. Normal bit failure. Piece of hard core damaged matrix. Piece of hard core damaged matrix. Some wear still remained in bit when

salvaged. Some wear still remained in b i t when

salvaged. Lost key out of bit-returned for full

credit. Junk from float equipment in hole--

ruined head. Bit wore out on inner periphery because of settlng down on hard pieces of core.

Head became loose. Returned t o factory and then continued t o use.

Bit wore out on inner periphery because of setting down on hard pieces of core.

Matrix became loosened but reran after tightening.

Normal bit failure. Bit failed. M a t r ~ x unscrewed-left in hole.

Bearings failed in barrel and dropped in hole ruinin bit.

Had large gamonds se t around inside diameter. Failed on face of bit.

Total Cost

8 1.169.70 1.050.04

954.98 1,631.57 1,828.22 1.823.95 1,794.44 1,791.92 1.787.86 1,791.24 1,837.02

1,709.64

1,777.21

1,828.30

1,746.42

1,734.44

2.599.76

2,767.47

2,935.68 1,719.95

1,612.89

1.855.57

839.748.27 8 1,806.74

Net Cost

8 516.67 685.83 910.03

1,151.57 915.77

1,237.49 899.84

1,039.70 891.37 909.38 837.28

847.31

827.80

1.277.45

1,116.35

1,046.90

1.145.26

1,793. zz

1,479.00 1.419.95

1,336.53

1,404.90

$23,689.60 8 1,076.80

mum footage drilled with one bit has now reached 721 ft, and 400 to 500 ft per bit is not uncommon. However, the failures of a few bits because of unsuspected junk, hard pieces of core, and the like, lower the aver- age footage drilled per bit. From Table 2

and 3 it can be noted that the average footage cut is over zoo f t per bit. A few failures are still to be expected but if they are kept a t a minimum, satisfactory results are possible.

TABLE 3-Diamond Bit Record (Cost Data Not Available)

Several operators in the Rocky Mountain area outside of the Rangely field are now using diamond coring successfully. The Tensleep sand in Wyoming has been dia- mond cored successfully. A formation that is well cemented should diamond core with success. However, highly fractured, hard formations crumble and plug the core bar- rel. West Texas has experienced difficulty in coring hard cherty formations for this reason.

Diamond coring was a big success in the Rangely Weber sand right from the start.

Bit

--

AA

BB CC DD CC DD EE FF GG HH

11

JKJK LL

MM N N 00

PP

Total . . . . Average. .

However, trip time was high and if it could be eliminated or reduced, a large saving would result. Diamond bits would cut zoo to 600 ft and therefore, it was not necessary to come out of the hole to change bits. In- creasing the length of the core barrel to 50 ft reduced trip time by 50 pct. The use of reverse circulation diamond coring by which cores are washed to the surface as they are cut, eliminates all trip-time delays. This method of diamond coring was at- tempted several times but only on the most recent attempt did we obtain successful results.

On our first attempt, the equipment con- sisted of the following, starting from the bottom of the string to the surface: , I . A 413i6-in. od X zll.S2-in. id dia- mond head.

2. A special core barrel approximately 12 ft in length, designed with an outer and inner barrel and resembling the standard 50-ft core barrel. The inner barrel, of course, had a flush opening to allow cores to pass on through and into the tubing string. I t was designed so that the circulating fluid would not pass through the inner barrel, but up between the inner and outer barrel to a port in the top of the inner barrel.

3 . Five 4)/4-in. od drill collars having the same inside diameter as 2%-in. EUE tubing.

4. Adapter sub from drill collars to 2%-in. EUE tubing.

5. z?/z-in. EUE tubing used as drill pipe. 6. A joint of 3-in. EUE tubing imme-

diately under the Kelly which was called . . the receiving core barrel. In the bottom of this barrel was installed a flapper-type core catcher. A pin was placed near the top of the barrel to prevent cores from being washed out of the core receiver.

7. Regular. Kelly. This equipment proved to be unsatis-

factory for two reasons. The bottom core barrel became plugged after filling up with core because no circulation was maintained in the inner barrel. Cuttings and broken ,

Total Footage

Cut

rzo. o

50. o 107. o 345.8 zoo. o 439. o 521. o a15. o 488. o

4 1 . 4

a91. 0 184. o 46. o

176. o

107. o a w . o roo. o

4 2 . 0 -- 3,772.2

209.6

Num- ber of Carats

158.55

177.04 164.29

18 bits

Remarks

--- -- Bearings failed in barrel damaging bit.

Junk in hole ruined head. Junk in hole ruined head. Sormal bit failure. Sormal bit failure. Still some wear in bit. Still some wear in bit. Pr'ormal bit failure. Pr'ormal bit failure. Bit failed because of junk in hole.

Normal bit failure. Normal bit failure. Still in good condition. Matrix tw~sted off in hole.

Inner peripher failed. Normal bit faiLre. Matrix cracked and dia- monds chipped out.

Still in good condition.

I 2 DIAMOND CORING I N T H E I W N G E L Y F I E L D , COLORADO

core could not be forced out of it. The core was washed to the surface and re- tubing with recessed collars causer1 small covered. At first, it was not known how pieces of core to hang up in the tubing often the core should be broken off, but string. after experimenting i t was found that the

~ . + + ~ - - ~ *

T ime, days I:lc 8 KEVERSP: CIR(:ULATIOS D I X Y ~ S V CORING.

Cutting-time Iog of Stanolind Tell No. 21, U'eber sand section, Rangely, Colo.

After changing the equipment somewhat, core should be broken off every 3 f t cut. well No. 2 1 was successfully cored. The The longest piece of core recovered was equipment was changed as follows: the approximately 6 f t in length. This was bottom core barrel was removed and the di- recovered while the core was broken off a t amond bit was reduced in inside diameter less frequent intervals. to ~ l f $ ~ - i n . to allow greater core clearance Crude oil was used on this job as the in the tubing. In place of the bottom-hole circulating medium. Oil-base mud had barrel, a special core breaker and catcher been tried on another well but i t r a s lost to sub was designed which fitted immediately the IVeber sand whenever a piece of core above the bit. Steel balls in tapered grooves hung up in the tubing and the pump pres-

. clamped on the core upon pulling up on the sure exceeded 300 psi. By using crude oil, tubing string. The tubing was made inter- greater pump pressures could be used to nal flush by placing ferrules in the tubing start stuck pieces of core without losing couplings. With these changes the equip- fluid to the formation. The surface equip- ment worked satisfactorily. ment was connected up so tha t circulation

On Fig 8 are shown the results of reverse could be reversed easily. This method was - circulation diamond-coring equipment a t used to release stuck pieces of core in the well S o . 21. A 4%-in. rock bit was used to tubing. drill a rat hole before the reverse diamond After cutting approximately half of the coring was started. A total of 399 f t of \Veber section, the crude oil became loaded Weber sand was then cored without making with h e sand cuttings. Only a small cir- a trip with the tubing. A total of 392 ft of culating pit was used and the small sand

cuttings did not have time to settle out. On subsequent jobs using this equipment, larger pits aTe to be used. A desander would be helpful in keeping the sand out of the crude oil.

Reverse circulation diamond coring of a second well will soon be commenced. The economics of this method over the others used at Rangely are shown on Fig 7. The results indicate reverse circulation diamond coring has considerable merit. There is the disadvantage of the reduced hole but this is not considered too serious. The produc- tivity of well No. 21 has not been noticeably affected by its smaller bore hole.

I. Regular diamond coring with a so-ft core barrel and a 646 X 33.4 in. diamond bit in the Rangely Weber section has proved more economical than conventional hard rock bit drilling or coring.

2. The drilling rate with regular dia- mond-coring equipment has proved twice as fast as with conventional hard rock drill- ing at Rangely .

3. Diamond coring equipment has now been developed to a point where it is very sturdy and can be expected to give excel- lent service if operated properly.

4. Diamond coring will give approxi- mately IOO pct recovery.

5. To obtain best results with diamond coring, personnel operating the equipment should be experienced.

6. Providing the diamond bits are all the same outside diameter the hole is always cut to gauge and no reaming down is necessary.

7. Water-base mud causes much more cutting action on the diamond bit than oil- base mud and also causes the bearings to wear out much more rapidly.

8. Reverse circulation diamond coring a t Stanolind's well No. 21 proved to be less expensive than the regular diamond coring in the Rangely field.

9. Diamond coring in oil wells in the Rocky Mountain area is now commonplace.

This paper was made possible only be- cause of data taken from Stanolind Oil and Gas Company's operations at Rangely. I wish to express my appreciation to Stano- lind Oil and Gas Company for the permis- sion to prepare and present this paper.

The assistance of Mr. C. Deely, with Drilling and Service, Ltd., is herewith acknowledged.

Acknowledgment is made to the engi- neers and production men at Rangely who have advanced valuable ideas toward mak- ing diamond coring a success at Rangely.