Investigation of drilling fluid loss and its affecting parameters in one of the Iranian gas fields

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Bulgarian Chemical Communications, Volume 48, Special Issue D (pp. 306 – 312) 2016
306
Investigation of drilling fluid loss and its affecting parameters in one of the Iranian
gas fields
M. Nasiri, I. Jafari*
Faculty of Chemical, Petroleum and Gas Engineering, Semnān University, Semnan, Iran
Received June 15, 2015; Revised October 13,2015
Received June 26, 2016; Revised September 10, 2016
Drilling fluid loss is one of the most important subjects in drilling industry causes the time waste and costs increase.
As a result of formation and drilling fluid pressure difference, fracture, formation properties and other factors this loss is
occurred. Different ways, such as mud weight loss, reducing the flow rate into formation, using the controller loss
materials and cement plug are used to avoid this problem. In order to access gas resources of Dahram group. During
drilling in the Asmari and Jahrum formation in section 24 " in field "A" we encounter the connected numerous sections
and fractures. Drilling mud loss is developed due to low fluid pressure of fluids within the pores in comparison with
drilling fluid. The mud loss occurs due to several reasons, some of them are geological and the others are drilling factors.
For this reason, the study tries to investigate the loss reasons, determination of the areas and given solutions using the
daily drilling reports, mud, geology and mud logging report to solve the problem. Drilling optimal parameters and drilling
fluid application program for cleaning section 24 are suggested through our aim of loss control.
Keywords: Formation, Drilling fluid, Drilling optimal parameters, Fracture, Fluid Loss.
INTRODUCTION
Drilling fluid loss problem has been evident since
the first time of being to drill oil and gas wells. This
issue becomes serious when drilling deeper or
drained wells were placed on the agenda. Oil
companies spent millions of dollars to solve the
problems such as stuck pipe, lost rig time, Blowout,
the loss of large volumes of drilling fluid and the
formation damage caused by loss. Stuck drill string
during loss, because of the pressure difference
between mud and formation the pipes stuck the in
the well. Fishing operation should be done costly to
solve this problem. Damage to the layers in many
cases, after the well tests indicates that as a result of
partial or total loss mud, especially in fractured
reservoir, intensity damage to high-permeability
production formations. Mud loss can transfer the
fine particles into the pores and reduce the
permeability of the formation near the well. In
addition, the filtration may cause a chemical reaction
between the mud and the reservoir fluid
compositions through sediment reduce the
permeability of the reservoir around the well. To
eliminate this problem formation acidizing and
stimulation operations have to be performed costly
[1,2].
Waste drilling fluid or cement grout in void
spaces during drilling operations is called loss. in the
industry loss is classified as leakage (less than bbl /
hr 10), mild (bbl / hr 10-100), intense (bbl / hr 100-
500) and complete (more than bbl / hr 500) [3 ]. It
should be noted that the mud volume reduction from
the total volume because of the extraction diminish
and filling the new well, is quite different from the
loss [4]. Loss is different in type, severity and
location of the well. Knowing the type and location
loss help to choice the control materials of loss. Loss
location is determined by using information from
previous drilling, formation changes and different
techniques of mud logging report [5]. A systematic
approach is known to control loss economically and
effectively. This includes both the prevention and
treatment [6].
Many parameters may affect the intensity of
drilling fluid loss. The fracture pressure gradient of
formation, drilling fluid properties, petrology and
the type of drilling formation, the existence of
fractures and caves in formation, drilling parameters
such as pressure and flow rate of the pump and the
known and unknown parameters made the
anticipation of the amount of fluid loss during
drilling of wells in a particular formation,
problematic [1,7].
In all of the drilling wells in field "A", loss
occurred and caused the waste time so that after the
waste time for waiting and remaining the most
wasted time dues to loss. And the waste time for the
improvement and further drilling some time is more
than the section time. During Asmari and Jahrom
drilling in section 24" of the field "A" in order to
achieve gas resources of Dehram group, we see
multiple fractures and joined cavities.
In comparison with the drilling fluid, as a result
of low fluid pressure of vein inside the sections,
drilling mud loss occurred in this formation. As a
section the mud loss occurs due to several reasons,
To whom all correspondence should be sent:
E-mail: jafari3760@gmail.com

307
some of them are geological and the others are
drilling causes. so this study investigates the drilling
causes and determination drilling areas and the ways
to solve this problem in section 24 at field "A".
DESCRIPTION OF ISSUE
Field "A" placed in the northern part of the
Persian Gulf. This field is the largest known gas field
with estimated reserves of 14 trillion cubic meters
(8% of the world's proven reserves of natural gas)
and 17 billion barrels of natural gas liquids and 5
billion barrels of condensate, which is followed by
the line in Qatar, called North Field. Development of
field "A" is divided into several areas of
development or planed phases. A total of 24 phases,
between 1990 and 1992 a total of 4 exploratory and
descriptive wells were drilled in the main phase. This
field is geology placed on the bulging bow which is
always higher than the surrounding areas. Therefore
sediments residual speed on it is less than the
surrounding areas, so the sediment thickness of
various layers of the geological periods on the scale
with the surrounding is less.
The hydrocarbon field was formed in the Permian
and Triassic period and includes Dalan and Kangan
formation. The highest point of the reservoir is
approximately at a depth of 3,800 meters above sea
level. Reservoir thickness is approximately 400
meters.
The Fars group formation such as Asemary and
Jahrom exist in this section. Jahrom sediment
cycle,after upper certaceous series movements in
the early Tertiary, the Zagros was covered with a
progressive Sea. Sachun formation in coastal areas,
carbonate formation in shallow areas and pabdeh
shale formation in deep areas were deposited.
Asmari cycle in late Eocene-oligocene, northeast of
Lorestan and internal platform of Fars remained out
of the water but Fars and Khuzestan, deep
sedimentary Pabdeh formation continued. At the end
of the Oligocene as a result of slow and limited
progress of the sea, the small Asmari cycle, chatian
age, was formed.
In oligocene-miocene boundary, in the areas of
Ahwaz, sandstone was deposited as Ahvaz
sandstone from Asmari formation. The lower limit
of Jahrom formation in sample section is
harmonically placed on silt and dolomite of sachun
formation. Jahrom formation is placed above the
Ilam formation in the field "A" Existence of Glakonit
at the end of Jahrom formation shows this boundary.
According to the study [8] the formation's age in two
section around Shiraz related to Paleocene to Middle
Eocene. Upper boundary of Jahrom formation with
Asmari formation is erosive discontinuity so that in
the cutting sample of the boundary there are
limestone and conglomerate with irregular layered
iron compounds. But in the field, Asmari and Jahrom
are considered together but empirically the border is
placed at the change location of limestone to
dolomite and dolomitic [9].
METHODOLOGY
Development of field "A" is divided into several
areas of development areas or planned phase that
drilling wells in phases 13, 22 and 24 were studied.in
phase 13 there were 4 places and in total 48 wells
were drilled, in phase 22 there was and 11 drilling
wells and in phase 24 there were 2 places and 20
wells were drilled. In this study, the daily reports of
daily drilling, geological and mud logging of wells
in the section 24" , following the analysis of the loss
reasons, determination of the loss areas and provide
solution to prevent it. We aim to control loss, give
the optimal drilling parameters and the best drilling
program for section 24" to increase the speed for
drilling, give the best applied program of drilling
fluid and reduce costs.
Drilling in the section24"
After placing the casing 32" at the depth of 172
meters, the section 24" was drilled by insert bit size
24. Drilling the section was done by sea water and
pumping cells with high viscosity to clean the
section. Drilling in the Fars group is slow due to the
pre predominant lithology of the marl and marl
sticky. But drilling in Asmari formation has higher
speed because of the lithology of calcic - dolomite
and at Jahrom formation drilling is slow and done
with a special program, due to falling Dolomites and
the possibility of mud loss, the stuck pipe and the
closed well wall. These programs are used to control
the weight on bit, maximize the mud pump with Hi-
Vis pumping and lubricants with pumping loss
controller materials. after arrival in Ilam Formation
drilling was continued for about 30 meters and
casing shoe of5/8 18 " was placed in this formation
and cementing operations were done based on plan.
Loss in the section 24"
At first using the daily drilling reports, mud
drilling and geological drilling wells, all drilling
parameters and mud properties were extracted and
through the mud logging reports, affecting
parameters on the loss size were noted and they have
been set as table. The diagram related to the amount
of loss and the influencing loss factors to the depth
was plotted and the results were adapted with the
lithological data. Accordingly the Asmari-Jahrom
formation is created by two mainly parameter:
lithology and drilling parameters.
Effect of the drilling parameters on the fluid loss
In this section, through study the daily drilling
reports and logging of well drilling parameters such

M. Nasiri, I. Jafari: Investigation of drilling fluid loss and its affecting parameters in one of the Iranian gas field
308
as WOB, ROP, RPM, Flow in and mud weight was
extracted and shown in Figure 1 and 2. These
parameters versus depth were plotted by Excel in
cross plots and the results were compared and
discussed. Many drilling factors can increase or
decrease the loss of drilling such as WOB, ROP,
RPM, Flow in. if the effect of these factors on loss is
known, it is easy to control and prevent the
occurrence of severe loss. Based on diagram some
of these parameters have direct relation with the mud
loss and some of them are inverse. For example, if
these parameters in A and B wells are compared
with the diagram, in both well there will be four loss
zones, each of these zones show different factors,
including lithological and digenetic factors and
drilling parameters. This means that in some of these
zones, lithological factors are determining factors
and the others intensify the loss degree or vice versa.
these four zones are
Zone A'A
This zone started from a depth of about 780
meters and continued to 620 meters, in this zone the
amount of loss is insignificant due to not very porous
lithology, and the drilling parameters determine the
loss degree. In this area lithology related to the
dolomitic limestone with anhydrite cement that
layers of anhydrite and limestone, argillite can be
found among them. As shown in the diagram, the
loss degree is below of 50 barrels and drilling
parameters such as WOB have an important effect
on this section. So the parameter of bit weight must
be controlled in this zone because if it is higher than
conventional degree, the formation will be broken
and cause the complete loss.
Zone B'B
This zone started at the depth of 780 meters and
continued to a depth of about 900 meters, the
diagrams show that the maximum loss occurred in
this depth, and the zones are known as loss zone.
Based on the obtained samples in this section and
analysis of their lithology we realized that this zone
includes some algae and coral reefs that are highly
porous. If drilling parameters especially the speed
and weight on the bit is not controlled and set out the
plan in this depth, enormous costs may be included
in addition to many hours of rig time is wasted.
Using Draw plots in this zone, it is indicated that the
drilling parameters are controlled For example, the
drilling rate, weight on bit , and rotation of the drill
pipe one minute decreased and flow in increased
due to the more mud pumps for cleaning wells. This
factor could slightly increase the loss degree.
Zone C'C
This zone started from a depth of about 900
meters and continued to a depth of 1060 meters. In
this zone the loss degree is less than 250 barrels. In
this zone the loss degree is variable and is a function
of lithology and drilling parameters. In areas where
the loss degree is high the section porosity figures,
fissure porosity and inter granular porosity due to the
conversion of calcite to dolomite can be seen.
However, in this zone increase the weight on the bit
and drill speed make the high loss degree.
Zone DˊD
This zone started at a depth of about 1060 meters
and continued to a depth of 1150 meters. In this zone
sometimes the loss degree reached 400 barrels per
hour. As a result of increased amount of anhydrite
cement, like the previous zone is not porous, but
sugar grained porous dolomite figures help to
increase porosity. In this zone More drilling
parameters have a significant role to intensify the
loss.
Proposed drilling fluid plan and well cleaning in
the section 24"
According to the definition 4 the loss area in
Asmari and Jahrom and the daily drilling reports of
the major oil companies in the other field "A" phases
to drill this section, drilling fluid and cleaning plan
as well as follows.
Sea water and well cleaning through cells with high
viscosity
The seawater is used as the main and cleaning
fluid through the cells with high viscosity
concerning the areas and the lithology according to
the following plan. Since the diameter of the section
was large, rubble evacuation and dug wells with high
speed combined mechanism and scanning with high
viscosity were occurred. Viscous scanning
composed of xanthan gum and a pre-hydrated gel
.analyze offset well indicates that the main problem
of loss is on the bottom of the section so the
hydrostatic pressure drop occurred within the well.
This hydrostatic pressure drop leads to break the
mouth of the well, poor well cleaning, stuck pipe and
the close well wall. in order to minimize these
problems ,the well should be cleaned at the depth of
780 to 172 meters in which the formation of the Fars
and A'A Asmari and Jahrom zone existed. In drilling
of 9 meters scan of cell 30 barrel with high viscosity
should be pumped to clean wells. At every 14 meters
of drilling scanning of pre-hydrated gel should be
pumped to clean the walls of the well. At the end

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Fig. 1. The effect of different parameters of the depth on drilling in wells A.
stand of the drill pipe with high viscosity was
pumped in 30 barrels and the mud was circulated for
5 minutes. Then 40 barrels of pre-hydrated gel were
pumped and mud was recirculated for 15 minutes.
The drilled distance back reamed and reamed down
at the flow rate of 700 gallons per minute with the
drill pipe rotation rate of 30 rpm and at the bottom of
the well, 30 barrels of pre-hydrated gel were pumped
and when the it exited from bit the flow rate stopped
and the new stands were prepared and drilling
continued. At a depth of 780 meters the well
cleaning way should be changed. Based on the depth
of about 780 meters to a depth of about 900 meters
of B'B zone and according to the results, this zone is
made of some algae and coral reefs that are highly
porous that is the main reason of the loss. But based
on the current situation there are two methods to
control or minimize the loss. The controlled drilling
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M. Nasiri, I. Jafari: Investigation of drilling fluid loss and its affecting parameters in one of the Iranian gas field
310
Parameters are used according to the cleaning
following plan. Otherwise if the full loss is occurred
the cement plug will be placed and then the cement
and the formation is drilling. it leads to control the
loss. C'C zone started from a depth of about 900
meters and continued to a depth of 1060 meters. In
this zone the loss degree is variable and as a function
of geology and drilling parameters. The loss was
Fig. 2. The effect of different parameters of the depth on drilling in wells B.
prevented by controlling the drilling speed. D'D zone
started from a depth of about 1060 meters and
continued to a depth of 1150 meters. This zone like
the previous zone was not porous due to the
increased amount of anhydrite cement, but sugar
grained dolomite figures increased porosity. In this
zone, the drilling parameters intensify the loss
degree.it can be reduced by controlling the drilling
speed. From a depth of 780 to 1150 meters the
cleaning program was at every 5 meters of drilling
wells in which scanning of cell of 30 barrels with
high viscosity was pumped to clean wells.
In each 9 meters of drilling of the hydrated gel
scanning was pumped to clean the walls of the well
.At the end the stand drilling pipe of 40 barrels with
high viscosity was pumped. Then the mud circulated
for 10 minutes and then50 barrel of pre-hydrated gel
were pumped. The mud re-circulated for 20 minutes
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to of the flowers have become. The drilled distance
back reamed and reamed down at the flow rate of
800 gallons per minute with the drill pipe rotation
rate of 30 rpm and at the bottom of the well, 30
barrels of pre-hydrated gel were pumped and when
it exited from bit the flow rate stopped and the new
stands were prepared and drilling continued. The
maximum level of 2000 ppm hydrogen sulfide has
been recorded in offset wells. To protect the drill
pipes, CONQOR 202B should be used as a
protective element, which used as a Slough spray
while raising the pipes. The Table 1 shows the
optimal properties of section mud.
Yield point, of a pre-hydrated gel should be kept
between 25-18 to prevent the close of the wells that
can be caused by the additional accumulation of
particles around the BH.
Table 1: Properties of section mud.
Mud System
Depth TVD
(m)
Mud Wt. (ppg)
Funnel viscosity (sec/qt)
pH
Sea water
1150
8.6
26
7
PHG Sweeps
1150
8.6
<120
10-10.5
Polymer
Sweeps(Hi-Vis)
1150
8.6
<100
8-6
The use of bentonite based mud
This mud is an appropriate chance to prevent the
rise of hydrogen sulfide is a good option But due to
the fact that excessive weight gain goal, regardless
of lithology feature will be off Due to the large
volume of drilling sections in the mud weight
increased the loss. Because of the costly drilling
fluid and the complete loss at second zone is
generally this way is not used.
RESULTS
According to the above statement, section 24
started at the depth of 172 meters after cement
drilling of section 32 starts and continued to 1150
meters which is the Fars formation. This formation
was made of limestone, marl and clay limestone. The
loss did not occur in this formation and its drilling
rate was proper and the drilling can be occurred
with no problem at the rate of 25 -15 m. But it should
be noted that because of clay limestone and the use
of the seawater as a drilling fluid, the formation was
swollen, that makes the closed walls. So no time
should be given to wells and drilling was done as
soon as possible to prevent the walls tight hole.
Usually at a depth of 620 meters we entered into
Asmari and Jahrom formations which most
problems of drilling occurred in this part of field "A"
gas. Most oil companies drill the Fars and Jahrom
formation without using engine to avoid waste and
saving the possible cost. Accordingly, four zones of
loss were defined. Each of them was affected by one
of the loss factors such as Lithological and digenetic
and drilling parameters. Many factors increased or
decreased the loss which can be defined as
dependent or independent parameters. The weight
on the bit, flow in and the pipe rotation in minute are
the dependent parameters and the rate of drilling and
the output pressure pump were defined as
independent parameters. It should be noted that the
dependent parameters were the function of the
weight on the drill and the flow. So zone A'A started
at a depth of 620 meters and continued about 780
meters .In this zone, the loss degree was
insignificant due to the lithology and more drilling
parameters determined the loss degree. So the
drilling rate was at 8-6 meters per hour and weight
on bit should be corresponding to the drilling rate,
flow in was 800 gallons per minute and drilling pipe
rotation in a minute was determined based on BHA.
If the engine was used in well the rotation would be
rpm 40 and otherwise 110-90 rpm. B'B zone started
at a depth of 780 meters and continued to 900 meters,
the maximum loss degree was occurred in this depth
so this zone is known as the loss zone. This zone
includes some algae and coral reefs that are highly
porous the drilling speed was 6.4 meters per hour.
The corresponding weight on bit with the speed
drilling should be controlled. If this action was done
out of the determined depth, there would be the
enormous costs. It should be noted that the rate of
flow in about 800 gallons per minute was suitable. If
the flow rate became low, the well cleaning was not
done properly that could stick pipe. C'C zone started
from a depth of about 900 meters and continued to a
depth of 1060 meters. The loss degree was variable
and as a function of geology and drilling parameters
in this zone. In areas where the loss degree is high,
the section porosity figures, fissure porosity and
inter granular porosity due to the conversion of
calcite to dolomite can be seen. However, in this
zone the increase weight on the bit and the high
drilling speed increased the loss degree. The drilling
must be controlled at the drilling rate of 7-5 meters
per hour and the weight on the bit was corresponding
with the drilling speed and flow in of 850 gallons
per minute that would be the ideal. Zone D'D started
at a depth of about 1060 meters and continued to
1150 meters. Sugar grained Dolomite figures
increase the porosity. The drilling parameters in the

M. Nasiri, I. Jafari: Investigation of drilling fluid loss and its affecting parameters in one of the Iranian gas field
312
zone intensified the loss degree. The most loss was
occurred due to lithology type.
Two proposed programs are given for the main
drilling fluid and cleaning wells. The justifiable use
of sea water as the main fluid and cleaning programs
are offered which is the best choice to reduce the cost
and increase the drilling speed.
CONCLUSION
According to the division of the loss areas and its
selection and optimization of drilling parameters in
each section and the application of the proposed mud
plan and cleaning wells can be expressed as the
following results:
1. Comparison the affected drilling parameters at
wells A and B with the related diagram of the loss
degree in section "24, show that there are four zones,
each zone indicates the factors such as lithological
and digenetic factors and drilling parameters. This
means that in some of these zones, lithological factor
and other factors are determining factors and the
others intensified the loss degree or vice versa.
2. Many factors can increase or decrease the loss
that the most important include the weight on bit,
drilling speed, drill pipe rotation in one minute, flow
in and the mud weight. Through study the effect of
these factors on the loss can be easily to control the
loss due to the influence of various parameters or
even prevent the occurrence of acute loss.
3. Drilling parameters can reduce or increase the
loss which is defined as the dependent and
independent parameter. The drill pipe rotation in one
minute as independent parameters and the rate of
drilling and output pump pressure are defined as the
independent parameters. Note that the dependent
parameters are the function of the weight of the drill
and the flow in.
4. The optimal method to fluid loss control is the
application of controlled drilling parameters of
weight on bit, flow in and drilling speed.
5. The loss control indicates the logical
consequence with the pump pressure. So based on
the specific areas the increased and decreased flow
in should be controlled. The cleaning wells should
be considered to prevent the possible problems.
6. According to two proposed drilling fluid plan,
using sea water as the main fluid and cleaning wells
in different geological zones the best choice to
manage the loss and drilling speed is proper.
7. Since increasing the mud weight is one of the
reasons to occur the loss, the use of the Betonite
based mud due to the higher weight than the sea
water and increased weigh during drilling due to
high volume of cuttings and its high cost, this type
of fluid is not recommended.
8. The pre-hydrated gel with high viscosity is
used to clean the well it is the best choice to clean
wells.
9. There is an inverse relation between the loss
degree and fracture pressure. If the pressure of the
fracture is low the loss degree will be high.
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