spe-1044-pa designing fast drilling fluid

8/10/2019 SPE-1044-PA Designing Fast Drilling Fluid

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ABSTRACT ,

The injluwcc of particle size and

concentration on the Aveiopntent of

chip ?told-down pressure CHDP) was

studied in an apparatus designed to

measure lh~ change of filtration rc tc

during the first second of the filtrutiou

process. CHDP is controlled h} tfw

Sht-i lgitfg particles i.e., particlcx in

Ihe .50 [0. 0,2 tnicron rcmgc>).wherea

filter Iosz is controlled by the col[oid

frartion. The results indiccded that a

fcist drillitw fhfid with a low filter 10ss

co[dd he ohtaiucd [f Ihc concentration

of bridging solids unfl the vi.rcwily

~tIt.Y t

k ept w


2/6

. . . . .

a ftne-bore capillary (0.032 cc/en])

resulted in precise measurements of

smrdl volumes, but the method was

tedious and time-consuming, Another

method was therefore developed in

which the filtrate displaced mercury

into the capillary tube. The tube was

wrapped with copper foil, and a cir- ~

cult was designed sothat the mercury

formed one plate of the variable con-

denser. The change in capacitance

as

the mercury advanced wasconverted

into a voltage signal which was re-

corded on ~a strip recorder with a

lineal chart speed of 100 mm/see.

[NFLUENCROF SC)LIf)S

CONCENTRATION

Figs..3 through 5 show the cumukt-

tive volume discharged vs time for

sevcrtd concentmtions of the same

lity u

medium-yield commercial

drilling clay).

Measurements were

made on three rocks with a wide range

of permeability. Curves for water,

also shown, were linear, With the

most permeable rock tested? Galhrp

sandstone (1,100 red), there was an

initial spurt tit a discharge rate &lose

to that of water. The rate then de- ,

creased rapidly asufilter.cake formed.

With the lCSSpermeable rocks; an ini-

tial spurt was obtained only with sus-

pensions having a low concentration

of

solids, .,

Tests with field muds covering a

concentration ranging from clear

brine to 10.4 ]b gal Iignosulforlatc

mud were made with the variable ca-

p~citance rectirder, and reprod~ctions

of the strip chart are shown in Fig.. 6.

CAIXULATIC)NOF CH;P

The CHDPY is determined by the

aniount, of I@r cake that can build

in the lifetim&~of mry surface element

below the bit, This time will depend

on the rate of tit rotation, the type

of the bk, the tooth. pattern, and the

areacleaned by each tooth strike. The

CHDP can be calculated for any par-

titular time interval, but to provide a

comparison between different muds it

is necessary to select a standard time.

For our calculations we chose a time

of 0.2 secbhd, which would be that ,

given by a tricone bit rotating at 100

rpm if each cone completely cleaned

the surface element along the radius

underneath it. To make the calcula-

tion we determined the average rate of

filtration over the first 0,2 second from

a graph such = those-shown in Figs. 3

through 6. ne pressure drop caused

by brine flowing at this rate t rrough

the coretrain was calculated by Dar-

cys law. The difference between thk

pressure drop ..and the-applied pres-. ...

sure, 500, psi, gave the pressure drop

5

ER

6E

R-k

.

,

I-f

1.. J

MOVIE CAMERA

F[c. 2loP

VIEW OF APPARATUS EWR hkAsuawc INITIAL FILHIATION RATES.

.

u

4

0,7 -

50 9/[ CLAY , 1100 md.-WATER, CA LCUL41TED

0.6 -

,00 ~/\

cLAY , Oo d ~

0.5

0.4

,,

0.3

/.,

0

1

zoo ~/1 CLAYS, 1100 md

._ .

0.2

.

0.1

.

4,

c

l...._

1

0.4 -o. s

1,2

1.6

2.0 2.4 2.6

3.2

SECONOS

Frc.

3INITIATION

OF FILTIWION, os GAI.LIY .%sIIw[)xI.,,

b

W,,:::i.

I I

I

[

0.4 0.s

1.2

I .s

2.0

2.4 2.8

3.2

. .. . .. . . .

SECON.DS . . . . . . . .. . .;

Fax 4--INITIATION OF

FILTRATION

ON BEREA SANDSTONE.

,,

.

..


3/6

s

resulting from cake formation on the

surface of the core. This value was

taken as a measure of CHDP. The

CHDPS, for the 0.2-second interval

for all the muds tested are shown in

Table 1. In addition, theCHDP was

calculated for two typical. muds

or

several. time ir?ervals (Fig. 7).

DISCUSSION

These results indicate that at nor-

mal rotary speeds the CHDP would

be virtually equal to the full differ-

ential between the mud column and

formation pressures with all except

very low solids drilling fluids. It must

be remembered, however, that the

above calculation Of CHDP rests on

broad assumptions, For example, we

assumed that the bottom of the hole

was cleaned perfectly by each pass of

a bit cone, which in practice is not

so: Thus, in some model drilling ex-

periments we found that the filtrate

rate beneath the micmbit was about

one fourth that calculated from fN-

trate rates for the sante mud over the

appropriate time interval in the filter

tes~r. This would suggest that the ac-

tual CHDP in a well would be higher

than that obtained from the filter

tester, On the other hand, the very

high eros@nrd forces arising from the

jetting -,aiition a;ound the &t would

tend to give lower CHDPS. In view of

these uncertainties, the CHDPS ob-

tained in the above experiments can-

not be regarded as the numerical

equivalent of the CHDPS that would

be given by the same muds in a well.

The results do, however, illustrate the

principles @volved, and then provide

a convenient means of rating drilling

tluids with respect to. their intluence

on rate of penetration;

PRINCIPLES OF LOW-CHDP

DRILLING, FLUIDS

INFLUENCEOF PARTICLE-

SIZE DK3TRIBUTION

In the last section it was shown that

initial filtration rates, and hence

CHDPS, depended on the concentra-.

tion of solids in the mud. The fact

that particle-size distribution was an

equally important factor was shown

by the following experiments, Four

muds of diflererkt particle-size distribu-

tion were prepared by centrifuging

Wyoming bentonite and by adding

different size fractions of quartz flour

to the bentonite base. The muds were

filtred against Berea sandstone cores

in the dynamic cell, and their initial

filtration rates were measured. The

rates and the particle size distfbution

of the muds are shown in Fig. 7.

High -initial- filtration.. rates were oh-.

cles because they could not enter the

- -- --

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. . ,. . .. . . . . . . , .,. . . . .. . . . . . . .

. . . . . ..

... .. . . . . . . . . .. . . . . .

. . . . . . . . . .

4.... . . . ...+.-- . . . . . . . . . . . . . . . . . . . .

,., . . -- . . , :

-.-:- . . . . . ...462..

. . . . . . . . . . . . . .. .

.. .. . ... . . . . . .

,. ... ... ,. . . . . . .. ..... . ----- . . . . . . . . ..

. ... .. .

,.- . . . ..,

:

-... . .. .

. . . .. . . . .,

.

tained with Muds 1 and 2, which con-

tained no particles larger than 2 mi-

crons, and with Mud 4, which was

composed of particles either smaller

than 0.2 or larger than 10 microns

and few particles between these sizes.

Low initial filtration rates were ob-

tained only when a substantial con-

centration of solids in the 2- to 10-

micron range were present. Evidently

this size range was critical for bridg-

ing in the surface pdres of Berea sand-

stone. Larger or smaller particles did

not cause bridgingthe larger parti-

SECONDS

1.. -

=~RN,,n

.....-

.3

0.2

cc

BEREA, 105 md

0, I

.,

0

_-

1

. . .

0.1 0,2

0.5

1.0

sECONDS

.

J

. .

..

o.:

1/

.

0.2

OIL-EMULSION MuD, 3.2A SOLIDS ,

cc ,

BEREA, 106 md

o

0.1 0.2

0.5

1.0

sECONDS

c20

BErEX Saridstone

Swea Sandstone

Serea Sand$tone

Arkrma Sanditorle

A:iz8ena Sandstone

Arizona Sandstone

Arizona Sandstone

Berea Sond tone

Serea Sandctone

Serea Sandstorm

sew Sandstone

---

200 sm/llter clay

485

100 sm/llter day

470

50 9m/litw clay

2A0

200 Om/lltw clay .

50 smifl lter clay

25 gmf ll tmr clay

12 gm/lVe r clay

5.$Q~ Brine (no

Oi l Emulsion, S,4

Oi l Emulsion Salt , 9 .4

l isnowlfenate, 10.4

- .-

460

460

;::

:ol lds] -20

lb/sml 90

Ibfoa

300

Ib(kml 490

..,..

.L

. --.. - .+ . .-, _.. _ -.

1

I

I

APPLIED PRESSURE

509

P

1

9.3 lb/qol

I

/ ~~~~

*\$

. .

v.

CLAY MUD 200/o SOL IO S AND OIL

EMULSION 3.2 osOLIDs B Eff EA

SANDSTONE

o

0.2

SECONDS

I .

F]~. 7- \A11[AT1 {1\ (JF ( ;[11[ , [IOL])-])()\\:i II{IZ S. [{ .: ~.III ~1 NC.

-

,.

.

~The Iower limit of the JASt?inrr size ranBc -

cwmot bs

precise ly determined. because with

.

- low-pefiiimbitity rocks, h~idsdrrfr-of fractures ---

,0. 10 4. MICRONSAND

hrduced by the bit b?rn,obrddy more significant

. . . .. . .

than brhking tbe rock POY% .

FIG. 8IXFLUEXCE

OF P.wwtcL~Stzs

lhnrowmo~ cm

I~ITIAL FILTRATION RATES.

000s

t

10 27. STARC H 5USPEN 510N

I /41 NCti MICROS (1, 20001b wEIGHT.

~

+

60 ,pm, 8qPm

: 60 -

0004

.

.

0

%

70 -

0003

s

a

.

2

*

Iu OQ

Z 80 ,

+

- 0002

&

:

0

90

0

0001

0

.,

100

[_ .-.-J.. 1.4------ 1--.-

0

2

4 6

8 10 12

14 16

18

PER CENT B RIDGING SOL IDS

. . . . .

.-

. . . . . .

. . . . . . . . . .

llG,

9INFLUENCE;OF

Bamctrm

SOLIDS ON

DRILL;hCRAT;

ASD CIlf)p.


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.

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. . ,. .._.

.

treatments it was necessary only to

add more concentmte.

CONCLUSIONS

The development of the fast drill-

ing fltt~d~described h this paper was

based on the con~ept ,of lessening. the

tendency of the mud to form a filter

cake on the bottom pf the hole. One

would therefore expect faster drilling

rates only when driI1ing the more

permeab[e formations. However, im-

proved drilling rates have been ob-

tained in all types of formations, in-

cluding shales, whose permeability is

several o~ders of magnitude less than

that ot mud filter cakes. It is clear,

therefore, that more complex mechan-

isms than that of static chip hold-

down are ittvolved. We believe that

the fast drilling characteristic of this

fluid is due, fundamentally, to faster

pressure equalization around the

chips. In the more permeable rocks

this is achieved hy penetration of N-

trate through the pores of the rock,

and in the less permeable rocks by

permitting easier access of fluid to the

fractures created ahead of the bit, and

by Iowering dynamic chip holddown.

Asphalt colloid emulsions have ef-

fected considerable savings in drilling

hard, stable formations. Although fast

drilling rates can also .be .obttiined in

other types of formation, the emul- ,

sion generally cannot be used because

of economic or technical limitations.

Some of these might be overcome in

the future by modifying the formula-

tion or by developing other types of

fluid which will also enable a low vis-

cosity and low solids content to be

maintained. Other limitations are in-

herent in any fluid with such a low

viscosity and low solids content, and

these must be overcome by mechan-

ical means or by the development of

new engineering techniques.

REFERENCES

L Gamier+A. J. and van L&en, N, H,:

Phenomena Atlecting Drilling Rates at

Depth,

1ran.s.,

AIME (Sept., 1959)

216, 232.

2. Cunningham, R, A, and Eenink, J. G.:

Lnbor~tory Study of Effect of O\er.

burden, Formation, and Mud Column

Pressures on Drilling Rate of Permeable

Formations, Zrans. ,AIME (Jan,, 1959)

216.9.

3 .van L1ngen, N. EL: ~130ttom Scavenging,

a Major Factor Governing Penetration

Rates at Ilepd), jour. pet. ~qch. (Feb,,

(1962) 187.

4. Prokop, C. L.:

Radial Filtradon of

l&ll~{ Mud,

Trrms.,

AIME (1952)

,.

5. Chal]lUan, C, W, (SlleU Development

Co.) Personal communicat ion.

6. Maurer, W. C.:

The Perfect Cleaning

Theory of Rotary Drilling, Jour . Pet ,

Tech. (Nov,, 1 2) 1,270.

7. Godfrey, W. K.: (Shel l Development

Co. ) Personal communication. **

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spe-1044-pa designing fast drilling fluid

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