The document summarizes a laboratory study that investigated the effect of sand sorting on gravel pack permeability. Several experiments were conducted using sand samples with different grain size distributions and sorting. The results showed that permeability decreased with smaller grain sizes due to smaller pore throats, and decreased more significantly with poorer sand sorting and higher fluid flow rates. Permeability reduction was also greater with higher viscosity injection fluids. Under continuous flow, permeability was always higher than under discontinuous flow conditions.

1. THE EFFECT OF SAND SORTING ON GRAVEL PACK
CHAIRUL ABDI
SUPERVISOR: MR. ARIFF BIN OTHMAN
PETROLEUM ENGINEERING DEPARTMENT
FACULTY OF PETROLEUM AND RENEWABLE ENERGY ENGINEERING
UNIVERSITI TEKNOLOGI MALAYSIA
Abstract
A laboratory research study has been conducted to investigate the effect of sand sorting on gravel pack toward
permeability. Several experiments have been carried out by using a transparent cylinder shape Perspex material
sand holder with diameter 5cm and 25cm length. By using five samples of sand with different sorting and
median grain sizes, a model was designed to simulate a production zone. Fresh water and diesel with 3.57 cp of
viscosity were used as injection fluid at various flow rates and outlet pressure had been set at an atmospheric
pressure. The experimental result reveals that the permeability of sand greatly reduced when smaller size of the
sand present in formation because of smaller pore throat and greater resistance to flow. Permeability reduction
becomes more significant when the sand distribution is poorly sorted and the higher injection fluid flow rate
applied. In this study, it is also found that high viscosity of injection fluid will give higher permeability
reduction. In addition, injection fluid under the continuous flow conditions is always given the higher
permeability compare to discontinuous flow condition.
surface production facilities, then the problem of
Introduction sand production will cause new problems in the
next.
Sand problem is one of oldest and critical
In addition, the installation of gravel
problem in the production wells faced by most of
the oil and gas production companies due to packing is one of the ways to overcome sand
instability of formation sand is the inflow of production problem. There is much research was
formation sand with hydrocarbon, and it is one conducted due to this particular problem such as
issue that cannot be easily solved. sand control; gravel packing. Expected by
installing gravel packing sand problem can be
Reservoir can absorb and accommodate a
solved. Otherwise, by installing a gravel packing
large volume of hydrocarbon, and permeable sands
these other things are also very important, flow rate
permits oil and gas hydrocarbons to flow to
and pressure drop is often overlooked.
production wells easily. However, in addition to the
As a result, to optimize oil and gas
many things that are so beneficial, porous and
production in the oil or gas field, especially in a
permeable sand is not good enough in the knots
poorly consolidated formation, further studies are
(poorly cemented). Therefore, when the fluid has
required. This project was undertaken to study the
started to flow into producing wells, thus releasing
effect of sand sorting on gravel pack, which may
the reservoir began to crush the grains of sand into
cause the sand production problem.
the production wells. When oil and/or gas
produced, then the grains of sand are also
produced. Methodology
Besides reducing the volume of oil and The apparatus had been used in this
gas during production, resulting from sand project consist of sand holder with several piping,
production can also reduce the pressure. And if pump, and manometer tube. Before experiment
uncontrolled sand production could reach to the conducted, several preparations regarding to the

2. 2
experimental apparatus had been prepared as pack permeability for zone 1 of which
follows: measurement starts from P0 to P1. K1 and K2 are
the measurement from zone 2 and zone 3
1. Design and fabricate a sand holder. respectively. However, the primary concern of this
2. Calibrate flow rate of pump. study is with the permeability measurement for
3. Design and prepare formation sand. zone 2 and 3, which are K1 and K2. The result
4. Prepare injection fluid. presented in this report is collected from
5. Conduct the main experiments. permeability K1 and also K2 respectively.
The experiments were conducted with
Figure 1 shows the schematic diagram of water as injection fluid with 1.0 cp of viscosity and
the experimental apparatus; Figure 2 reveals the three experiments were used more viscous fluid,
sand holder design configuration and for Figure 3 which was diesel as injection fluid with 3.57 cp of
to 5 exposes the photographic view of experimental viscosity. The objective was to determine the
flow system, sand holder and also U-tube relationship between the sand pack permeability
manometer. with the experiments flow time in certain
conditions.
In the experiment, the permeability was
Result and Discussion determined by using Darcy’s equation. This
equation had been used since it is applicable in
Several experiments were conducted to laminar flow with the porous media is 100 percent
investigate the effect of sand sorting on gravel homogeneous with the following fluid and the fluid
pack. The experiment was done on unconsolidated is not reacted with the particles (glass beads).
sand under continuous and discontinues flow
condition. The outcomes of concern in this
investigation are: Formation Sand Grain Size Distribution
i. The effect of particle size The grain size of the unconsolidated sand
distribution on unconsolidated used in this study was measured using dried sieving
sand technique. Five types of sample with different grain
ii. The effect of flow rate change
size distribution were labelled as sand A, B, C, D
due to time
iii. The effect of injection fluid and E were used to demonstrate that different size
viscosity distribution that may cause different permeability.
iv. The effect of sand sorting In Figure 6. shows that the formation sand
v. The effect of permeability distribution that had been used in this experiment.
responds to flow condition. The graph on figure 7. shows the pattern
of particle size distribution for these five samples.
From this graph, the median particle size, which is
Flow rate changes under continuous flow
D50 for each sample was measured and uniformity
condition mean that the flow rate will be started at
coefficient, C; which is D40/D90 can be calculated
20 cc/s for 60 minutes before being increased to 30
for each sample. From this graph shows all five
cc/s for 60 minutes and finally increased to 50 cc/s
samples have significantly differ in its sorting.
also for 60 minutes. Under the discontinuous flow
Sorting sample was a measure of deviation
conditions, the flow rate will be started with 20 cc/s
both from the median diameter to given a normal
for 60 minutes before switching off the pump for
distribution of grain sizes, both larger and smaller
20 minutes and then increased the flow rate to 30
are present in the total population of sand pack. The
cc/s also for 60 minutes. And finally, flow rate 50
sand size distribution graph in Figure 4.2 indicates
cc/s will be applied after the pump switch off for 20
that sorting, D40/D90 for all samples varies from
minutes.
1.3 to 10.6. The median sand size for Sand A, D50
is 130 μm and D40/D90 is 1.6. San A, B, and C
Figure 2. shows that the schematic
consider as uniform regarding to the Uniformity
diagram of the sand holder. This sand holder is
coefficient; C is less than three (C < 3). But, sand
divided into three phase zone for the pressure and
size for Sand D is consider as non-uniform and
permeability measurement. K0 represents the sand
sand E is consider as very non-uniform / very non-

3. 3
sorting this is due to the value of D40/D90 both pressure drop toward permeability, which was
sample was very large. Which was uniformity converted to permeability data with varying flow
coefficient for Sand D are 7.6 and 10.6 sand E. rates. In each test, the injection fluid was injected
under continuous and discontinuously circulated
Permeability is the ease with which fluids
for about 60 minutes at each constant flow rate.
flow through a rock or sediment. A rock is The permeability was measured periodically, and
permeable if fluids pass through it, and the circulation was continued until the flow rate is
impermeable if fluid flow through the rock is stable.
negligible. Normally, permeability depends on;
Grain size (Coarser-grained sediments are more In this research study, three different flow
rates were set for these experimental studies, which
permeable than fine-grained sediments because the
are 20 cc/s, 30 cc/s and 50 cc/s. Fresh water with
pores between the grains are larger), sorting, grain 1.0 cp was used as injection fluid for all five
shape, and packing (controls pore size). samples. A comparison was made for the results of
the permeability against flow time with three
different flow rates. There were some fluctuation
Response of the Sand Pack to the Effect of Flow profiles in the graph. This is due to the
Rate rearrangement of the particles in the sand pack.
Flow rate plays an important aspect to
Permeability is the ease with which fluids determine the movement of sands particles process.
flow through a rock or sediment. A rock is Basically, when the flow rate is become higher, the
permeable if fluids pass through it, and potential of the sand particles to move is higher as
impermeable if fluid flow through the rock is well. These movements occur when the fluids flow
negligible. Normally, permeability depends on; rate is unsteady until it reaches a level where the
Grain size (Coarser-grained sediments are more progress of the particles stopped after it achieves a
permeable than fine-grained sediments because the steady state of the flow rate.
pores between the grains are larger), sorting, grain
shape, and packing (controls pore size). Effect of Flow Rate on Sand A Permeability
According to Darcy’s law, the fluid flow is Figure 8. shows the effect of flow rate on
proportionally to the pressure differential between Sand A permeability as measured at K1 and K2.
inlet pressure and outlet pressure at constant The results show that with increasing flow rate of
permeability of the formation. This is only true for the injection fluid it will reduce the permeability of
the solid-cemented particles (normal sand) such as the sand pack until it became constant after 10
core samples but not in a loose pack or minutes of flow time. The reduction was
unconsolidated sands such as gravel packing significantly evident by the different between the
completion. permeability at flow rate 20 cc/s and 30 cc/s and 50
cc/s for both zones.
Generally, the overall behaviour of the
sand particulates migration process is critical; this As the permeability for the sample A is
is due to the magnitude of the flow rate, since it determined, an analytical study has been conducted
affects the gravel permeability and may cause to discover the relationship between the particle
serious plugging problem during high flow rate of grain sizes and permeability over time. From figure
fluid. If the flow is too low, no migration of sand 4.3, the lowest injection flow rate gives the highest
will occur, as the fluid flow is not strong enough to permeability. The permeability is estimated about
carry particulates, then the permeability is obeying 1200mD for flow rate 20 cc/s, 970 mD for 30 cc/s,
the Darcy’s law. Moreover, at high flow rate, a and 820 mD for injection 50 cc/s. Mostly, after 10
large amount of particulates is moving quickly, and minutes. The curve shows constant. These are
possibly causing the sand pack to self filtrate after where the flow is reach stabilized and stabilized
sometimes. The self filtration is due to the particles permeability is reached. A huge reduction for flow
build up within the pores and pores throats, thus, rate 30 cc/s and 50 cc/s curve is due to the
causing the pores to block and the porosity of this instability of the flow. Ironically, for this samples
element is reducing. The possibility for particles to the tame taken for flow rate to reach its stability is
migrate depends on the compaction forces caused relatively short. This had happened because of the
by the flowing liquid. Therefore, the permeability particles in the sample reaching its packing
in this layer will decrease, causing a large increase rearrangement in short time and smaller grain
in the pressure drop. particle migrate faster to the pore space between
bigger grain size particles.
A study on the effect of sand sorting on
gravel pack was conducted by measuring its

4. 4
Effect of Flow Rate on Sand B Permeability no effect on the graph line, it will be at the constant
rate. Because at that moment all the particles in the
Figure 9. below shows the result for sand pack had reached a dynamic rearrangements.
sample B. from the curve below mention that the
permeability at flow rate 20 cc/s is about 1160 mD,
followed by 970 mD for injection 30 cc/s and end
up with 960 mD for 50 cc/s. From this result it Effect of Flow Rate on Sand E Permeability
proves that the permeability of each sample, mainly
decrease through the time of different flow rates. Figure 12. The effect of injection flowing
Generally, drop of the value of permeability is fluid rate toward permeability on the sample E. The
happened in the beginning of the experiment of curve below shows that the permeability is varied
each starting injection applied until the minutes of and very unstable in sometime at the starting point,
5th. From the 5th minutes until 10th to 15th this is regarding to rearrangement of particle grain
minute, the permeability seems to vary / unstable size due to hydrodynamic force.
for a short period, and it seem stable afterwards.
This phenomenon is not always occurred at the The Effect of Injection Fluid Viscosity
highest flow rate used where the permeability is
decreasing for a long period but the reducing
permeability is higher when the higher flow rate In Figure 13 through 15 it shows that the
was applied. effect of injection fluid viscosity. There were three
samples used in this experiment, which is “Sample
C” where represent of uniformity sample. Sample
Effect of Flow Rate on Sand C Permeability
D represented the non-uniformity and sample E is
represented of very non-uniformity.
Figure 10. is shown the relationship of the
permeability ratio aver time for sample C. As In all cases, declining of permeability rate
bigger particle grain size is being tested, a higher is more significant with 1.0 cp viscosity of water as
permeability is obtained. For this sample, the injection fluid. When diesel is injected into the
porosity is 29 percent. It can be seen that the sand pack with 3.57 cp of viscosity it shows that,
highest permeability is shown about 1920 mD for the permeability reduction significantly achieved
injection rate 20 cc/s, 1460 mD for 30 cc/s and higher. This is due to the higher lifting power for
1452 mD 50 cc/s fluid injection rate. This had more viscous injection fluid, thereby more grains
happened because of particle are stable in slow and particles are invaded and plugged the pore
flow rate. The rearrangement of packing are spaces. The increase in viscosity also affects the
difficult to occur and the small particles are not mobility ratio.
migrating to the pore space of bigger particle grain
size. In contrast, the force induced in high flow The increasing in permeability of the sand
fluid injection are enough to migrate a small pack is due to the increasing in injection fluid
particle and rearranged the packing of particles viscosity. With high viscosity was injected in the
hence reduced the existing porosity. sand pack, the grater the permeability reduction
was achieved. These phenomena occurred due to
Effect of Flow Rate on Sand D Permeability the increase of flowing fluid viscosity will increase
the pressure differential too. The increase of
flowing fluid viscosity will increase the drag forces
Figure 11. shows the experimental result
as well. The increase of drag force will cause more
for sample D with 600 µm of Median Grain Size
severe plugging on pores spaces and reduces the
Distribution. The result shows that the effect of
flow path respectively. Because of higher drag
flow rate on the Sand D permeability as measured
forces have the higher capability to carry particles
at K1 and K2 respectively by using the sand holder.
and will increase the pore plugging and minimize
Same as the previous trend, any increasing in the
the pore space simultaneously.
flow rate will result in the decreasing of the
permeability. The differential value of permeability
is as follows 820 mD for 20 cc/s, 670 mD for 30 The Effect of Sand Sorting
cc/s and 528 mD for injection fluid 50 cc/s. The
collected data show that a relatively higher The experiment has been conducted to
reduction of permeability curve trend than the other identify the effect of sand sorting on gravel pack
flow rate, which may be due to the rearrangement toward permeability. This experiment only used
of the particle in the sand pack. water at 1.0 cp as injection fluid and at three
different flow rates as well as under both
Hence, if we continue injecting fluid with conditions; continuous and discontinuously flow
the same flow rate after 60 minutes, there will be condition. The experiments were conducted with

5. 5
flow rate at 20 cc/s, and then followed by 30 cc/s yet. Therefore, the increasing hydrodynamic force
and finally end up with 50 cc/s. All five samples will increase permeability reduction respectively.
(Sand A, B, C, D and E) had done the same
procedure. In Figure 16. it shows that, by Field Application of Experimental Results
increasing the median grain size it will increase the
permeability value. Base on the experimental result, it shows
that good sorting will perform the good
In addition, on Non-Uniformity sample permeability. Meaning, in field application, gravel
with 7.6 of Uniformity Coefficient; C and on Very pack needed good sorting. We cannot control the
Non-Uniformity sample with 10.6 Coefficient; C in sorting on the formation. But, for gravel packing
sample E, presented the very high permeability placement, we can control the sorting. However, if
reduction. This is happened because of non-sorting formation particles (has smaller size particles)
particle grain size. The small grain size particles manage to invaded (not penetrate), there is no way
are migrating to the pore space of bigger particle to control them (permeability impairment). If
grain size. Thereafter, the force induced in high smaller particles were invaded, the fine grain
flow fluid injection are enough to migrate the small particle will plugged the pore throat and it will
particle and rearranged the packing of particles reduce the existing porosity as well. The bottom
hence reduced the existing porosity. line here is that we need to control the movement
of formation particles at the sand face.
At the beginning of the flow time Figure
16. shows that all the graph line has fluctuated,
these occur at 0 to 30 minutes of flow time. At
these moments, assumed that all the particles in the
sand pack are rearranging each other because of the Conclusions
velocity of the flow rate. Nevertheless, after 30
minutes of flow time due to injection, the Figure The following conclusions can be made based on
16. shows that all line at a relatively constant rate. the experiments conducted:
So, it is predicted that the particle had reached the
dynamic rearrangements. From this plateau region, 1. Higher injection fluid flow rate gave
it shows that the uniform sand distribution which is higher permeability reduction.
Sand A, B and C have the highest value of
permeability compare with non-uniformity and 2. Large median grain size particles with
very non-uniform sand distribution, which is sand the uniformity coefficients; C, less
D and E that had slightly lower value of than three gave better permeability
permeability. compared to smaller grain size
particles with C value less than three.
The Effect of Permeability responds to Flow
3. The sand pack permeability reduction
Condition. is more severe when more viscous
injection fluid was used.
From Figure 16. Generally, permeability
under continuous flow conditions is always slightly 4. Good sorting with the uniformity
better than permeability under the discontinuous coefficients less than three performed
flow conditions. These phenomena occurred due to better permeability compare to poor
the packing already reach their stability while sorting with the uniformity
flowing fluid flow at 20 cc/s. The particles only coefficients greater than 5.
face a small increase of hydrodynamics force
compare to unstable gravel packing, which had to 5. Gravel packing under the continuous
face a higher increment of hydrodynamic force at flow conditions is always rewarded
the beginning of particles movement and the better permeability compared to
rearrangement before it reached their packing permeability under a discontinuous
stability. Therefore, it minimized the pore space flow conditions.
sizes and ability of the fluid to flow through the
gravel pack besides reduces the permeability
respectively. Whereas, for discontinuous flow References
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6. 6
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7. 7
Figure 1: Schematic of experimental apparatus
Figure 2: Sand holder design configuration.

8. 8
Figure 3: Photograph of experimental flow system.
Figure 4: Photograph of sand holder. Figure 5: Photograph of monometer U.

9. 9
Figure 6: Pressure and permeability measurement zone
Figure 7: Formation sand size distribution

10. 10
Figure 8: Effect of flow rate on Sand A permeability with 1.0cp
Figure 9: Effect of flow rate on Sand B permeability with 1.0 cp.

11. 11
Figure 10: Effect of flow rate on Sand C permeability with 1.0 cp.
Figure 11: Effect of flow rate on Sand D permeability with 1.0 cp.

12. 12
Figure 12: Effect of flow rate on Sand E permeability with 1.0 cp.
Figure 13: Effect of injection fluid viscosity on Sand C permeability.

13. 13
Figure 14: Effect of injection fluid viscosity on Sand D permeability.
Figure 15: Effect of injection fluid viscosity on Sand E permeability.

14. 14
Figure 16: Effect of sand sorting on sand permeability with 1.0 cp.