Chilingarian G.V. et al. Surface Operations in Petroleum Production, II
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215
Port
collar
When run in the liner string, a port collar provides access to the annulus between
the liner and the open hole or casing. The port normally remains in the closed
position; however, it can be opened by rotating the inner sleeve with port collar
operating springs or dogs. Ths port allows for additional gravel to be placed in the
pack if insufficient amount of gravel was placed during the initial packing oper-
ation. Some operators attempt to repack the well after its first steam stimulation.
Port collars are also used when completing a well with two zones that are to be
gravel packed separately with a section of cemented casing between the two zones
(see Fig.
6-21).
Fig.
6-21.
Port collar.
(Courtesy
of
Solum
Oil
Tool
Corporation.)
216
Unipack
tool
The unipack is a gravel-packing tool that has been developed by researchers at
Union Oil Company (Maly and Robinson, 1972) for use in deviated wells. This tool
has a series of baffles that are attached to the washpipe. These baffles act to restrict
flow in the wash pipe-liner annulus and keep flow in the outer liner-open hole
annulus. This prevents dunes from growing to the point of occurrence of premature
screenout. Test results indicate that this tool tends to improve the gravel-packed
completions in deviated wells if the liners are not too long.
Liner
vibrator
The Solum Rotary Compactor is a tool that vibrates the liner during gravel-
packing operations. To operate the tool, the workmg string is rotated by the rotary
table of the drilling rig.
This
rotational energy is converted into a vibration at 60-ft
spacings along the liner. Laboratory and field tests indicate that vibration can result
in a
15-25%
denser or tighter pack (Solum, 1984). The tighter pack provides a better
sand control and considerably reduces the problem of after-pack settling.
Some operators reverse the flow
of
the carrier fluid in the case of occurrence of a
premature pack-off. This procedure is conducted in an attempt to breakdown any
bridges. This practice has been found to mix formation sand with the gravel and
fluff the pack into a looser arrangement (Shryock, 1979; Shryock et al., 1979; and
Solum, 1984). Vibration
of
the liner prevents bridges from occurring and eliminates
the need to reverse circulate.
EVALUATION
OF
GRAVEL
PACK
Several methods are currently available to evaluate the placement of a gravel
pack. The most widely used method involves comparing the actual volume
of
gravel
placed with the theoretical volume. In calculating the theoretical volume, it is
advisable to use a caliper log to account for changes in the wellbore radius. This
procedure can be deceptive, however, as sometimes washouts occur after the caliper
log
has been run or a washout can extend beyond the reach of the caliper arm.
Neal (1983) suggested using a compensated neutron log, nuclear fluid density log,
or a dual-spaced gamma-ray log to evaluate gravel placement. All of these logging
techniques involve running the log in the subject well after the gravel-pack hardware
has been placed in the wellbore, but before the gravel is pumped. A subsequent log
is
run after the well has been gravel packed and the two logs are then compared.
The comparison should indicate where gravel was actually placed. There are also
’
Trademark registered.
217
gravel-pack density logs available that are run after the gravel is placed. They
indicate gravel voids and the top of the gravel.
ADDITIONAL DESIGN CONSIDERATIONS
Borden et al. (1982, p. 100) has noted some additional considerations in desig-
ning an optimum gravel-packed completion. These considerations include the fol-
lowing:
(1) Blank pipe
is
eliminated between sections of gravel. Otherwise, the gravel
slurry would not be able to dehydrate properly and voids or after-pack settling may
occur.
(2) Rathole volume is kept to a minimum, because leakoff will not occur in the
rathole and voids may be created.
(3)
The gravel pack thickness should be at least two inches for openhole
completions and
3/4
in. for cased-hole completions.
(4)
Gravel pack-formation sand mixing must be avoided. If possible, crossover
ports must not be placed opposite open hole as they may cause erosion.
If
this can
not be avoided, then port exit velocities must be maintained below 4 ft/sec.
(5)
In wells that are deviated less than
60°,
a reserve of gravel must be provided
by running additional liner above the completed interval.
As
settling or dissolution
occurs, the gravel in this reserve will fill any created voids.
SUMMARY OF THE BASIC FACTORS THAT DETERMINE AN EFFECTIVE GRAVEL PACK
The basic factors that determine an effective gravel pack can be summarized as
(1) Selection of proper gravel size.
(2) Use of a packing fluid free of solids.
(3)
Proper relationship between the size of perforations and gravel size.
(4)
The cleanliness of the face of producing formation.
(5)
Gravel/fluid ratio.
(6)
Compaction of the gravel.
follows:
SAMPLE PROBLEMS AND QUESTIONS
(1)
Using the following sand sieve analysis data, plot cumulative weight per-
centage versus the log
of
opening size. Determine the optimum gravel size using
both the Saucier and the Schwartz methods:
218
Opening Sample weight
(in.) (g)
0.065
0.046
0.0328
0.0232
0.0164
0.0116
0.0082
0.0058
0.0041
0.0029
0.0000
0.1
0.1
0.1
0.5
3.2
7.5
7.7
5
.O
1.9
1.3
2.2
(2) If a gravel with a median grain diameter of
0.025
in. is required to achieve
adequate sand control in a well with a cubic packing, what median gravel diameter
would give the same degree of sand control if packing is rhombohedral?
(3) Describe common gravel pack design criteria for sand control.
(4) What
is
the age of formations which are usually associated with sand
production?
(5)
Distinguish between the pore size distribution resulting from the cubic
packing and the rhombohedral (hexagonal) packing. Which one is ideal for sand
control?
(6) Formation sieve analysis showed the uniformity coefficient to be 3.48 and the
flow velocity is 0.006 ft/sec. Using work by Schwartz (1969), determine the average
size
of
gravel required for this formation. The 10-percentile sand size is 0.011 in. and
the 40-percentile sand size is 0.003 in.
(7)
If average gravel diameter is
0.55
in., what is the average pore throat diameter
of
the gravel pack in (1) cubic packing and (2) in rhombohedral packing (hexagonal)?
(8)
What additive has been found to reduce silica dissolution by approximately
94%?
(9) Describe the most desirable type of gravel packing fluid. What
is
the
minimum size of solids that should be filtered out?
(10) While steaming a well, the bottomhole temperature is
495
OF
and the pH is
11.
If resin-coated sand
is
used, what would be the approximate weight percent loss
of sand using 20/40
U.S.
mesh gravel?
(11) If the smallest gravel grain used in gravel packing of the well is 0.045 in. in
size, what is the size of liner slots that should be used?
(12) In an openhole gravel pack, what should the average thickness of the pack
be and how should the liner be positioned?
(13) What type of surface gravel packing equipment should one use in order to
achieve (1) good control of the gravel/fluid ratios and
(2)
the minimum breakup of
the placed gravel?
219
(14) With a single-stage gravel packing method, what technique is available to
reduce formation damage due to the leak-off into the formation?
(15) What should viscosity (give range)
of
fluid be in order to achieve the best
compaction of the gravel grains, and what is the compaction percentage propor-
tional to?
(16) What type
of
carrier fluid should be used in a well having a lost-circulation
problem?
(17) How can after-pack settling be prevented when gravel packing?
(18) With liner vibrations spaced every
60
ft inside the slotted or wire-wrapped
(19) What basic gauges are used to control the surface handling of the gravel?
(20) What type of system has been developed to reduce gravel breakup in the
gravel crossover tool? What percentage reduction in crushing can be achieved for
gravel striking the steel?
(21) What is the best method to evaluate gravel placement after gravel packing?
liner, how much denser would the pack be?
REFERENCES
Allen, J.R.L.,
1969.
Notes towards a theory of concentration of solids in natural sands.
Geol. Mag.,
106:
Allen, T.O. and Roberts, A.P.,
1982.
Production Operations,
Vol.
2.
Oil and
Gas
Consultants Int., Tulsa,
Borden, T.F., Elson, T.D. and Millhone, R.S.,
1982.
State-of-the-Art Gravel Packing for
1982.
Proc. Am.
Boulet, D.P.,
1979.
Gravel for sand control: A study of quality control.
J.
Per. Technol.,
31(2): 164-168.
Carborundum Company,
1983.
Sintered Bauxite for Sand Control Applications.
Carborundum, Dallas,
Cheung,
S.K.,
1985.
Effect
of
Acids
on
Gravels and Proppants.
Proc. SOC. Pet. Eng., 55th Annu. Calif. Reg.
Chilingarian, G.V. and Wolf, K.H.,
1976.
Compaction of Coarse-Grained Sediments,
11.
Elsevier, Amster-
Coberly, C.J.,
1937.
Selection of screen openings for unconsolidated sands.
API Drill. Prod. Pract.
:
Elson, T.D. and Anderson, G.W.,
1982.
Foam Gravel Packing.
Proc. SOC. Pet. Eng.,
53rd
Annu. Calif.
Reg. Meet., Ventura, Calif., Mar.
23-25,
SOC. Pet. Eng.,
11013: 33-42.
Elson, T.D., Darlington, R.H. and Mantooth, M.A.,
1984.
High-angle gravel-pack completion studies.
J.
Pet. Technol.
36(1): 69-78.
Graham, J.W., Monaghan, P.H. and Osoba,
J.S.,
1959.
Influence of propping sand wettability
or
productivity of hydraulically fractured
oil
wells.
Trans. AIME,
216: 324.
Gruesbeck, C., Salathiel, W.M. and Echols, E.E.,
1979.
Design of gravel packs in deviated wellbores.
J.
Pet. Technol.,
27(1): 109-115.
Gulati, M.S. and Maly, G.P.,
1975.
Thin-section and permeability studies call for smaller gravels in gravel
packing.
J.
Pet. Technol.,
27(1): 107.
Hails, J.R.,
1976.
Compaction and diagenesis of very coarse-grained sediments, pp.
445-473.
In: G.V.
Chilingarian and
K.H.
Wolf (Editors),
Compaction of Coarse-Grained Sediments,
ZZ
(Developments in
Sedimentology, 18B).
Elsener, Amsterdam, pp.
445-473.
Hill, K.E.,
1941.
Factors affecting the use
of
gravel in oil wells.
APZ Drill. Prod. Pract.,
pp.
134-143.
Krumbein, W.C. and Sloss,
L.L.,
1951.
Stratigraphy and Sedimentation.
W.H. Freeman and Co., San
309-321.
Okla., pp.
35-62.
Pet. Inst., Pac. Joint Chapter Meet., Ventura, Calif., Oct.
12-14,
pp.
95-116.
Tex.,
2
pp.
Meet., Bakersfield, Calif., Mar.
27-29,
SOC. Pet. Eng. Pap.,
13842: 863-870.
dam,
808
pp.
189-201.
Francisco, Calif.,
497
pp.
220
Krumbein, W.C. and Sloss, L.L.,
1963. Stratigraphy and Sedimentation.
Freeman, San Francisco, Calif.,
Landreth, T.C.,
1969.
Gravel packing for sand control.
Can. Pet.,
Sept.:
8-13.
Maly, G.P. and Robinson, J.P.,
1972. Apparattu for Gravel Packing Inclined Wells.
U.S.
Patent
No.
Maly, G.P., Robinson, J.P. and Laurie, A.M.,
1974.
New gravel pack tool for improving pack placement.
Neal, M.R.,
1983.
Gravel pack evaluation.
J.
Pet. Technol., 35(10): 1611-1616.
Patton, D.L. and Abbott, W.A.,
1982. Well Completions and Workouers: The Systems Approach.
Energy
Reed, M.G.,
1980.
Gravel pack and formation sandstone dissolution during steam injection.
J.
Pet.
Saucier, R.J.,
1974.
Considerations in gravel pack design.
J.
Pet. Technol., 26(2): 205-212.
Schwartz, D.H.,
1969.
Successful sand control design for
high
rate oil and water wells.
J.
Pet. Technol.,
Shryock, S.G.,
1979.
Tests show methods for improved gravel packing.
World Oil, 1,
Aug.:
55-58.
Shryock, S.G.,
1980. Gravel Packing Studies
in
a
Fullscale Deviated Model Wellbore.
In:
55th
Annu. Meet.
SPE-AIME, Dallas, Tex., Sept.
21-24,
SPE Reprint
9421.
Shryock, S.G., Dunlap, R.G. and Millhone, R.S.,
1979.
Preliminary results from full-scale gravel-packing
studies.
J.
Pet. Technol., 31(6): 669-675.
Solum, J.R.,
1984. A
New
Technique in Sand Control Using Liner Vibration with Gravel Packing.
In:
Formation Damage Control Symp., Bakersfield, Calif., Feb.
13-14,
SPE Pap.
12479,
pp.
79-90.
Solum Oil Tool
Corp.,
1983. Completion Methodology for Peak Production.
Signal Hill, Calif.
Suman Jr., G.O.,
1975. World Oil's Sand Control Handbook.
Gulf, Houston, Tex.,
57
pp.
Underdown, D.R. and Das Kamalendu,
1983. Stability of Gravel Packing Materials for Thermal Wells.
In: Proc. Int. Symp.
Oil
Field Geothermal Chem., Denver, Colo., June
1-3,
pp.
199-204.
Watkins, D.R., Kalfayan, L.J., Watanabe, D.J. and Holm, J.A.,
1985. Preventing Gravel Pack and
Formation Dissolution During Steam Injection.
Proc. SPE
55th
Annu. Calif. Reg. Meet., Bakersfield,
Calif., Mar.
27-29,
SPE Pap.
13660,
pp.
665-674.
Wright, K.A. and Solum, J.R.,
1967. Principles of Gravel Compaction
for
Oil and Water Well Sand
Exclusions.
In: Lone
Star
Water Well Drill. Assoc. Annu. Conv., Austin, Tex.
2nd ed.
3,637,010;
Jan.
25.
J.
Pet. Technol., 26(1): 19-24.
Publications, Dallas, Tex., pp.
84-91.
Technol., 32(6): 941-949.
21(9): 1193-1198.
221
Chapter
7
STEAM
ENHANCED
OIL
RECOVERY
J.P.
FANARITIS and GEORGE V. CHILINGARIAN (EDITOR)
INTRODUCTION
Two third
of
al[
the petroleum discovered worldwide to date is still in the ground,
and much of this in-place oil cannot be recovered by conventional primary produc-
tion methods. It is particularly difficult to achieve
high
recovery efficiencies in
heavy oil reservoirs, and even more
so
in tar sand deposits which are presently
receiving increasing attention as potential major sources
of
liquid hydrocarbons. As
a result
of
the relatively low primary production recovery efficiency in many large
heavy oil reservoirs, enhanced oil recovery techniques which have the potential
of
significantly improving oil yields from proven reservoirs are assuming increasing
importance.
Of
the various enhanced oil recovery techniques currently being employed in
heavy oil reservoirs and tar sand deposits, steam injection is the most widely used,
the most efficient process available today. The steam injection process presently
accounts for the production
of
well over
500,000
bbl/D
of
heavy oil worldwide, and
this production rate can be anticipated to increase markedly in the future with
expanded utilization
of
the process in the United States, Canada, Venezuela,
Indonesia, the Soviet Union, and the People’s Republic
of
China. Steam injection
presently accounts for the production
of
approximately
300,000
bbl/D in the
United States,
15,000
bbl/D in Western Canada, and
250,000
bbl/D in Venezuela.
There is also developing interest in applying the steam injection technique to light
oil reservoirs to improve oil recovery efficiency, particularly reservoirs containing
highly parafhic crude oils.
It
is
the objective
of
this section to provide some general data related to the
steam injection process, more specific information on the two types
of
steam
injection techniques which are in current use, and a brief coverage
of
some ancillary
factors related to the steam injection process. The reader should consider this
section as an introduction to the steam injection process, and utilize the references
for more detailed information on specific aspects
of
steam injection technology.
GENERAL DATA PERTAINING
TO
STEAM INJECTION
General data pertaining to the steam injection process is presented here in order
to provide the reader with an overview
of
the potential applications
of
the technol-
ogy, and a working knowledge
of
the mechanics
of
steam injection.
222
Enhanced oil recovery classification
Most enhanced oil recovery techniques can be classified as secondary or tertiary,
depending at whch stage of the producing life
of
a heavy oil reservoir they are
applied. Steam injection is unique among enhanced oil recovery techniques in that it
can qualify as a primary, secondary, or tertiary enhanced oil recovery process,
depending on the particular application in which it is being used. This will become
apparent when the following varying conditions under which steam injection has
been successfully applied are considered:
(1)
Primary production technique
The hydrocarbons found in tar sand deposits have a gravity around minus
2"
API and have viscosities ranging from
100,000
to 2,000,000 CP (Britton et al., 1982).
In addition, tar sands have essentially no formation pressure.
As
a result, the
hydrocarbons cannot be recovered by conventional primary production methods. A
number of projects are currently in operation in which steam injection is being used
to produce hydrocarbon liquids from tar sand deposits. In this application, steam
injection becomes a primary production technique.
(2)
Secondary production technique
Heavy crude oils in the range
of
10-25" API can be partially extracted by
conventional primary production techniques; however, the oil recovery efficiency is
generally relatively low. Experience in California,
U.S.A.,
indicates that roughly
10-15% of the oil in-place is the maximum which can be recovered from heavy oil
reservoirs by primary production methods. When steam injection follows the
primary production cycle in this application, it is classified as a secondary produc-
tion technique.
(3)
Tertiary production technique
In certain reservoirs, particularly with the lighter grades of crude oil, a secondary
enhanced oil recovery technique such as waterflooding is employed when the rate of
oil recovery by primary production has dropped off. After improved oil recovery by
the secondary technique drops off, in certain instances, steam injection has been
used to further stimulate the rate of crude oil recovery. In this instance, steam
injection would properly be classified as a tertiary production technique because it
follows the preceding two production methods.
As previously described, steam injection is a versatile tool for improving the
recovery effectiveness from heavy oil reservoirs and tar sand deposits. It can be
applied at various stages in the producing cycle of a reservoir, depending on the
gravity of the oil and the structure of the formation.
Steam injection mechanisms
Steam injection is unique among enhanced oil recovery techniques in that it
functions through several mechanisms to improve the oil recovery efficiency. This
223
TEMPERATURE,
'C
TEMPERATURE,
OF
Fig.
7-1.
Typical relationship between heavy oil viscosity and temperature. (After
Buckles,
1979; courtesy
of
the Society
of
Petroleum Engineers
of
AIME.)
ability of steam injection to enhance the recovery efficiency of heavy crude oil
through multiple mechanisms significantly increases the range
of
crude oil proper-
ties and types of formations in which ths enhanced oil recovery technique can be
applied efficiently.
A
study of how steam injection performs in improving the recovery efficiency
of
heavy crude oil in-place shows the following basic factors as being influential:
(1)
The heat released to the formation by the high-pressure injected steam
sharply reduces the viscosity of the heavy crude oil.
As
a result, the improved
flowing characteristics
of
the crude oil allow it to flow more readily to the producing
wells from whxh it is pumped to the surface. Figures
7-1
and
7-2
show the effect
of
temperature on the viscosity of typical heavy crude oils.
(2)
The steam
is
injected into the formation at the maximum possible pressure,
commensurate with the depth of the injection well, in order to provide the
maximum temperature at the bottom
of
the hole. Thus the high-pressure steam
serves as a driving force to push the crude oil to the production wellbore.
(3)
The condensate, which is formed as the injected steam releases its latent heat
of vaporization to the strata, serves to act as a hot waterflood to displace crude oil
in the direction of the production wellbore.
(4)
The heat provided by the high-pressure injected steam vaporizes light ends
from the heavy crude oil, and the vaporized light ends have the effect
of
building up
a pressure in the formation as a result of the volume increase which results from the
formation
of
the vapor. This pressure buildup in the formation also acts as a driving
force to push crude oil toward the production wellbore.
In
addition, the vaporized
224
TEMPERATURE,
OF
Fig. 7-2. Interrelationship among viscosity, temperature, and gravity
of
heavy oils. (After Buckles, 1979;
courtesy
of
the Society
of
Petroleum Engineers of
AIME.)
light ends mix with the heavy crude oil and tend to exert a viscosity-lowering effect.
Unquestionably, the crude oil viscosity reduction resulting from the heat pro-
vided by the high-pressure injection steam is the major factor contributing to the
success of steam injection as an enhanced oil recovery technique. The other listed
factors, however,
are influential in various degrees in improving oil recovery
efficiency, and combine with the crude oil viscosity reduction to make steam
injection the leading enhanced oil recovery process in use throughout the world.
Steam injection performance data
Typical strata and performance data for a number of typical operating steam
injection projects is presented in Table 7-1. This data has been assembled from
personal discussions with the field operators and fragmentary published data. The
table is
of
interest in that it shows a number of elements essential in the evaluation
of
reservoirs for the application
of
thermal enhanced oil recovery through steam
injection. The pertinent elements are discussed individually in order to give the
reader a better insight into the requirements for a successful steam injection project.
(1)
Well depth
Most heavy oil reservoirs are at relatively shallow depths of less than
2500
ft,
although well depths of over
5500
ft are being subjected to steam injection in the
Far East. Heat losses through the casing become excessive for well depths of over
2500
ft, and insulated downhole tubing must be used to maintain reasonable
economics in deeper wells. Heat loss is covered in more detail in a later section.
(2)
Permeability
Permeability is the measure of tightness of a formation, and the units of measure