The present invention relates generally to a process of preparing a loss
control composition. More particularly, the present invention relates to an improved
5 non-cementitious loss control composition and a process for preparing the noncementitious loss control composition for oil wells.
Background
10 [0002] Mud losses while drilling is a serious problem in onshore and offshore oil
fields that adversely affect drilling time and well productivity and increases drilling
cost. The oil fields are multilayered reservoirs comprising of fractured carbonate that
is highly porous having various dimensions of porosity i.e. micro, meso and macro.
Further, intensity of drilling fluid invasion in the oil field is very high due to pattern
15 and lithological characteristic of the oil well that is cavernous, vugular or fractured
formation. Typically, in the event lost-circulation zones are anticipated, preventive
measures are taken by treating the mud with cementitious lost-circulation materials
(LCMs). However, in the reservoir section of the oil well, the cementitious loss
control material chokes the reservoir section and it becomes difficult to take out
20 oil/gas from the reservoir.
[0003] Conventionally, in older oil fields, differential pressure depletion and loss
circulation takes place during drilling that becomes more severe with increased
directional drilling activity and reservoir depletion. Further, pressure in some of the
25 sub-hydrostatic reservoir layers are as low as 5 pounds per gallon (PPG) mud weight
equivalent (MWE) or less. Sub hydrostatic pressure and mud loss problem due to
lithological characteristics in the oil well causes wellbore instability, differential
stuck ups and sometimes blow out condition. Further, it has also been observed that
chances of mud loss is relatively high especially in slim-hole in the oil well where
30 lifting of cutting inside the well is not proper. Further, there are also number of
wellbore instability incidents like stuck-pipe, tight hole and cavings that occurs at
shale intervals inside the oil fields especially when there is a drop in hydrostatic head
of wellbore annulus due to mud losses in carbonate reservoirs. This problem further
3
escalates with depletion of reservoir pressures as well as increased directional drilling
activity.
[0004] In light of the above-mentioned drawbacks, there is a need for an improved
5 loss control composition and method of preparing the loss control composition.
Further, there is a need to provide a cost effective environment friendly and nondamaging loss control composition for drilling loss prone depleted reservoir having
fractured, cavernous and vuggy carbonate formation.
10 Summary of the Invention
[0005] In various embodiments of the present invention, a method for preparing a noncementitious loss control composition is provided. The method comprises adding
bentonite to water to form a gel slurry and adding a cross linking agent to the gel slurry.
15 Further, the method comprises adding a binding agent to the gel slurry and the cross
linking agent and adding a strengthening agent to the binding agent the gel slurry and
the cross linking agent. The method further comprises adding a bridging agent to the
strengthening agent, the binding agent, the gel slurry and the cross linking agent and
adding a retarder to the bridging agent, the strengthening agent, the binding agent to
20 the gel slurry and the cross linking agent. Further, the loss control composition is a
lightweight thixotropic composition that is prepared in a density range of 10 Pounds
Per Gallon (ppg) to 16 ppg.
[0006] In various embodiments of the present invention, a loss control composition is
25 provided. The loss control composition comprises a gel slurry comprising of bentonite
and water. Further, the loss control composition comprises cross linking agent, binding
agent, a strengthening agent, a bridging agent and a retarder. Further, the loss control
composition is a lightweight thixotropic composition that is prepared in the range of
10 Pounds per gallon (ppg) to 16 ppg.
30
Brief description of the accompanying drawings
[0007] The present invention is described by way of embodiments illustrated in
the accompanying drawings wherein:
4
[0008] Fig. 1A and Fig. 1B is a flow chart illustrating a process for preparation of
the improved loss control composition, in accordance with an embodiment of the
present invention;
5 [0009] FIG. 2 is a graph illustrating thickening time of the loss circulation
composition, in accordance with an embodiment of the present invention;
[0010] FIG. 3 illustrates thickening time graph of the loss control composition, in
accordance with an embodiment of the present invention;
10
[0011] FIG. 4 illustrates thickening time graph of the loss control composition, in
accordance with an embodiment of the present invention;
[0012] FIG. 5 is a graph illustrating thixotropic properties of the loss control
15 composition, in accordance with an embodiment of the present invention;
[0013] FIG. 6 is a graph illustrating compressive strength of the loss control
composition, in accordance with an embodiment of the present invention;
20 [0014] FIG. 7 illustrates thickening time graph of the loss control composition, in
accordance with an embodiment of the present invention;
[0015] Fig. 8 is a graph illustrating hesitation squeeze, in accordance with an
embodiment of the present invention;
25
[0016] FIG. 9 is a graph illustrating thixotropic effect of the loss control
composition, in accordance with an embodiment of the present invention; and
[0017] FIG. 10 is a graph illustrating static gel strength build up, in accordance
30 with an embodiment of the present invention.
Detailed description of the invention
[0018] The compositions, formulations and methods discussed herein are merely
35 illustrative of specific manners in which to make and use this invention and are not
to be interpreted as limiting in scope. While the compositions and methods have been
5
described with a certain degree of particularity, it is to be noted that many
modifications may be made in the details of the process without departing from the
scope of this disclosure. It is understood that the compositions and methods are not
limited to the embodiments set forth herein for purposes of exemplification.
5
[0019] In various embodiment of the present invention, an improved loss control
composition and process of preparing the loss control composition is provided.
[0020] FIG. 1A and 1B is a flow chart illustrating a process for preparation of loss
10 control composition, in accordance with an embodiment of the present invention.
[0021] At step 102, a gel slurry is prepared. In an exemplary embodiment of the
present invention, the gel slurry comprises bentonite and water. The bentonite is an
active ingredient of the gel slurry that is allowed to hydrate for a predefined time
15 duration. In an exemplary embodiment of the present invention, the hydrated
bentonite forms 4-6 parts of the gel slurry by weight. In an embodiment of the present
invention, the gel slurry is mixed in a waring blender in a predetermined amount. In
another exemplary embodiment of the present invention, the pre-defined time period
is a minimum time duration of 30 minutes. In another exemplary embodiment of the
20 present invention, the gel slurry comprises montmorillonite clay. In another
exemplary embodiment of the present invention, the bentonite comprises other
commercial clays. Advantageously, in an embodiment of the present invention, the
montmorillonite clay helps in reducing density of the gel slurry. In an embodiment
of the present invention, the loss control composition is a lightweight thixotropic
25 composition that is prepared in a density range of 10 Pounds Per Gallon (ppg) to 16
ppg.
[0022] At step 104, a cross linking agent is mixed with the gel slurry. In an
embodiment of the present invention, the cross linking agent is a cross linking
30 polymer which is added to the gel slurry and the solution comprising the cross linking
polymer and gel slurry is mixed thoroughly for a predefined time duration. In an
exemplary embodiment of the present invention, the pre-defined time duration is 5
minutes. In an exemplary embodiment of the present invention, the cross linking
6
polymer is produced by a bacteria viz. xanthomonas campestris that produces a gum
during its normal life cycle via an enzymatic process. In another exemplary
embodiment of the present invention, the cross linking polymer is diutan gum, welan
gum, guar gum or any other available biopolymer.
5
[0023] At step 106, a binding agent is added to the solution comprising cross
linking agent and gel slurry followed by adding a strengthening agent. In an
exemplary embodiment of the present invention, the binding agent used in the
solution is magnesium sulphate which is used in a ratio of 14-40 parts with respect to
10 the solution. In another exemplary embodiment of the present invention, the
strengthening agent is in form of a Dead Burnt Magnesite (DBM). DBM is in the
form of magnesium oxide which is calcined to high temperatures of upto 17000
C and
has a very low reactivity which provides sufficient time for pumping of the loss
composition solution in an offshore oil well. In an embodiment of the present
15 invention, the strengthening agent is added to the binding agent and the binding agent
reacts with the strengthening agent.
[0024] At step 108, a bridging agent is added to the solution comprising binding
agent, cross linking agent, gel slurry and strengthening agent. In an embodiment of
20 the present invention, a bridging agent in the form of Micronized Calcium Carbonate
(MCC) may be added depending on the loss circulation conditions in the offshore oil
well.
[0025] At step 110, a retarder may be added to the solution comprising bridging
25 agent, binding agent, cross linking agent, gel slurry and strengthening agent to obtain
the loss control composition. In an embodiment of the present invention, the retarder
may be added depending upon bottom hole circulating temperature. The retarder may
be used to slow down chemical reaction of the loss control composition inside an
offshore oil well. In an exemplary embodiment of the present invention, the
30 strengthening agent is in a ratio of 28-80 parts with respect to the loss control
composition.
7
[0026] At step 112, the loss control composition is mixed until the loss control
composition becomes homogenous. In an embodiment of the present invention, the
loss control composition is mixed at 4,000 rev/min until the loss control composition
becomes homogenous. After a 10-minute static period, the loss control composition
5 becomes unpumpable. After mixing with a spatula for a minute thoroughly and
briskly, the loss control composition reversibly becomes pumpable (fluid) that
exhibits thixotropic nature of the loss control composition. In various embodiments
of the present invention, the mixing may be carried out in a mixing device.
10 [0027] Table 1, Table 2, Table 3 below illustrates experimental data of various
quantities of gel slurry, binding agent, strengthening agent, bridging agent and cross
linking agent used at below mentioned temperature, pressure, and Raising Time (RT)
in various exemplary embodiments of the present invention. From the experimental
data it is observed that loss control composition provides cementitious property
15 without using cement and develops rapid static gel strength. The loss control
composition exhibits a low initial viscosity at surface of the oil well, and viscosity of
the loss control composition increases as the temperature increases inside the oil well.
Further, the loss control composition exhibits the thixotropic behavior because it is
viscous under static condition and once dynamic condition is attained, the material
20 viscosity of the loss control composition starts decreasing because of its shear
thinning property. The shear thinning property is represented by decreasing viscosity
with increasing shear rate, and such behavior provides many benefits such as placing
the loss control composition easily downhole, preventing gas migration, and reducing
flow of the loss control composition to thief zones before solidification of the loss
25 control composition.
[0028] The loss control composition also provides high resistance to
contaminations occurring due to water, gas and drilling fluid. The loss control
composition achieves enough compressive strength around 50 Pound Per Square Inch
30 (PSI) in 2hrs and 100 PSI in 5hrs that prevents washout in the oil well while resuming
operations after mud loss inside the oil well. Further, the loss control composition is
acid soluble in 15% Hydrochloric Acid (HCL) unlike conventional cementitious
8
compositions and therefore loss control composition causes no damage to reservoir
sections in the oil well. In an embodiment of the present invention, 94-96% of the
loss control composition is soluble in 15 percent hydrochloric acid (HCL).
5 [0029] Table 1: Temperature: 50-70° C, Pressure: 3000 psi, Raising Time (RT):
30 Min, Specific Gravity (SG) (1.37)
SG Gel
Slurry
Binding
Agent
Strengthening
Agent
Bridging
Agent
Crosslinking
Agent
Initial
Consistency
(BC)
Thickening
Time
(Min)
1.37 100 20 40 07 0.6 34 392 @50°c
1.37 100 20 40 07 0.4 11 170 @60°c
1.37 100 20 40 07 0.4 27 126 @70°c
[0030] Table 2: Temperature: 80°C, Pressure: 3000-8000 psi, RT: 40 Min,
10 Specific Gravity (SG) 1.20-1.40
SG Gel
Slurry
Binding
Agent
Strengthening
Agent
Bridging
Agent
Crosslinking
agent
Initial
Consistency
BHP
(PSI)
Thickening
Time
(Mins)
1.20 100 14 28 - 0.4 5 3000 110
1.27 150 20 40 - 0.5 22 5000 220
1.33 125 20 40 07 0.5 22 5000 151
[0031] In the Table 2 as shown above, the thickening time for loss control
composition increased from 110 minutes to 220 minutes by increasing proportion of
15 gel slurry to 150 parts by weight, binding agent to 20 parts by weight, strengthening
agent to 40 parts by weight, cross linking agent to 0.5 parts by weight of the loss
control composition at a pressure of 5000 psi. The increase in thickening time results
in the thixotropic property. In another embodiment of the present invention, the loss
control composition may be prepared from a range of 10 ppg to 16 ppg. Further, the
20 loss control composition may operate at Bottom Hole Circulating Temperature
(BHCT)of 500C to 1500C and at Bottom Hole Pressure (BHP) of 3000-10000 PSI.
In an embodiment of the present invention, the 10ppg lightweight loss control
9
composition is easier to pump that prevents further formation breakdown due to
excessive hydrostatic head. In an exemplary embodiment of the present invention, a
12 ppg formulation controlled dynamic losses from 150 bbl/hr to NIL.
5
[0032] Table 3: Temperature: 90° C, Pressure: 5000 Psi, RT: 40 Min
SG Gel
Slurry
Binding
Agent
Strengthening
Agent
Bridging
Agent
Crosslinking
agent
Initial
Consistency
Thickening
TIME
(Min)
1.29 150 20 40 05 0.4 18 165
Test results Obtained prior to field implementation of slurry
10 [0033] Table 4 below illustrates experimental data of the test results obtained prior
to field implementation of the loss control composition.
Table 4: Temperature: 75° C, Pressure: 3000 Psi, RT: 30 Min, Motor Break of 45mins
after 60mins to simulate actual field operations
15
SG Gel
Slurry
Binding
Agent
Strengthening
Agent
Retarder Crosslinking
agent
Initial
Consistency
Thickening
TIME (Min)
1.30 100 20 40 0.4 0.4 18 227
[0034] The compressive strength is obtained in 24hrs @1000
C, 244psi and the
Gel0/Gel10 is 25/41. Table 5 below illustrates the average dial reading at different
values of RPM at BHCT.
20 Table 5
RPM 3 6 30 60 100 200 300
Average Dial Reading 24 28 37 41 49 61 71
Test results if Hesitation Squeeze method is followed
25 [0035] Hesitation squeeze method involves intermittent application of pressure—
by pumping at a rate of 1/4 to 1/2 bbl/min—separated by an interval of 10 to 20 min
10
for pressure falloff caused by filtrate loss to the formation inside the oil well. In the
hesitation squeeze method, pause interval and pumping schedule depends on loss rate
and thixotropy of the loss control composition. During the pause interval, the loss
control composition gains gel strength that helps in curing of the losses inside the oil
5 well. Further, the subsequent pumping of small volume of the loss control
composition and pause interval helps in curing the losses. Furthermore, the hesitation
squeeze method illustrates the thixotropic properties of the loss control composition.
Test results in terms of Thickening Time of the Loss Control Composition
10
[0036] Table 5.1, Table 6, Table 7 and Table 7.1 and the below mentioned tables
illustrate test results in terms of thickening time of the loss control composition.
[0037] Table 5.1: Temperature 850
C, Pressure: 2500psi, RT: 35 mins, SG 1.60
15
SG Gel
Slurry
Binding
Agent
Strengthening
Agent
Retarder Initial
Consistency
Thickening
Time (Min)
1.60 100 40 80 10 18 227

[0038] Table 6: Temperature 1200
C, Pressure: 8000psi, RT: 60 mins SG 1.23

SG Gel
Slurry
Binding
Agent
Strengthening
Agent
Crosslinking
Agent
Retarder Initial
Consistency
Thickening
TIME (Min)
1.23 150 20 40 0.5 10 14 278
[0039] Table 7: Temperature 1500 20 C, Pressure: 10000psi, RT: 60 mins SG 1.23

SG Gel
Slurry
Binding
Agent
Strengthening
Agent
Crosslinking
agent
Retarder Initial
Consistency
Thickening
TIME
(Min)
1.23 150 20 40 0.5 10 13 153
[0040] The test conditions for testing the loss control composition is provided below:
25 Temperature : BHCT-85°C
11
Pressure : 3100 PSI
Raising Time : 62 Minute
Break Schedule : As per Table 8 as shown below
5 [0041] Further, composition in grams of the loss control composition is illustrated in
the below table:
Table 7.1
Water Bentonite Crosslinking
Agent
Binding Agent Strengthening Agent
100 5 0.4 20 40
10 [0042] Table 8 and Table 9 illustrate displacement, pumping and break timing
required for the loss control composition.
Table 8
Schedule Time in minute
Displacement 62
Pump 62-72
Break 72-82
Pump 82-87
Break 87-97
Pump 97-102
Break 102-112
Pump 112-117
Schedule Time in minute
Break 117-127
Pump 127-132
Break 132-142
Pump 142-147
Break 147-167
Pump 167-173
Break 173-203
WOP -------
15
Table 9
Schedule Time in
minute
Results
in BC
Displacement 62
Pump 62-72
1st
Break 72-82 Hump
upto 41
Schedule Time in
minute
Results in BC
Pump 127-132 26
5th
Break 132-142 Hump upto 41
BC
12
BC
Pump 82-87 22
2nd
Break 87-97 Hump
upto 32
BC
Pump 97-102 23
3rd
Break 102-112 Hump
upto 41
BC
Pump 112-117 23
4th
Break
(Safety Pull
out)
117-127 Hump
upto 42
BC
Pump 142-147 29
6th
Break 147-167 Hump upto 42
BC
Pump 167-173 29
7th
Break 173-203 Hump upto 46
BC and
thereafter set
Thickening
time
203
[0043] In an embodiment of the present invention, the loss control composition is
prepared at an oil well rig by the following steps:
5 Step 1: Cleaning the slug tanks/pit/batch mixer and mixing lines flushing with drill
water. Ensuring agitator rotation as per preparation requirement.
Step 2: Taking required quantity of technical water (Salinity<500ppm) and adding
required quantity of bentonite through hopper. After preparation, stopping agitator for
10 hydration time of at least 30mins.
Step 3: Adding mixed metal oxide through hopper and mixing it thoroughly.
Step 4: Adding XCP through hopper slowly, mixing it thoroughly and leaving
15 solution idle for 10 – 15 minutes.
Step 5: Adding Magnesium Sulphate (MgSO4) through hopper, mixing it thoroughly
followed by adding DBM.
20 [0044] FIG. 2 illustrates thickening time graph of the loss control composition at a
temperature of 800
Celsius and a pressure of 5000 psi. FIG. 3 illustrates thickening
13
time graph of the loss control composition at a temperature of 1200 Celsius and a
pressure of 8000 PSI. FIG. 4 illustrates thickening time graph of the loss control
composition at a temperature of 1500 Celsius and a pressure of 10000 PSI. FIG. 5
illustrates thixotropic properties of the loss control composition at a temperature of
1500 5 Celsius and a pressure of 10000 PSI. FIG. 6 illustrates compressive strength
graph of the loss control composition at a pressure of 100 psi in 5hrs and 50 psi in
2hrs at a bottom hole temperature of 10000
C and a bottom hole pressure of 3000 psi
raised in 4hrs. FIG. 7 illustrates thickening time graph of the loss control composition
at a temperature of 900 Celsius and a pressure of 5000 psi. FIG. 8 illustrates hesitation
squeeze at BHCT-850 10 C, BHP-3000 psi and RT-60 mins. FIG. 9 illustrates thixotropy
effect of the loss control composition at a temperature of 850 Celsius and a pressure
of 3000 psi. FIG. 10 illustrates Static Gel Strength (SGS) build up from 100 SGS to
500 SGS in 12 minutes, reflecting rapid build-up of static gel strength.
15 [0045] In an exemplary embodiment of the present invention, the graph as illustrated
in FIG. 2 is generated by a HPHT consistometer machine. The thickening time is time
elapsed from initial application of temperature and pressure to the time required for
the loss control composition to reach a consistency of 100 Bc. Conventionally, the
thickening time graph provides an idea of placement time that is controlled by a
20 cementing engineer and the graph provides an exact estimate of time as of how long
the cement remains pumpable. Advantageously, in an embodiment of the present
invention, the thickening time graph provides an estimated time when the loss control
composition becomes unpumpable and also provides an estimated time by when the
loss circulation has been completely cured inside the oil well. Advantageously, in an
25 embodiment of the present invention, the loss control composition is easily pumpable
through drill bit and when pumping is stopped it gives thixotropic properties which
is helpful in controlling losses. Further, the loss control composition provides a
predictable and controllable pumping time, ranging from a few minutes to several
hours at a given temperature. This is an important advantage of the loss control
30 composition as it allows the formulation of the loss control composition to remain
pumpable for sufficient time for placement that helps in developing a network
structure that leads to gelation over a predictable period of time.
14
[0046] In an embodiment of the present invention, the loss control composition is
acid soluble in 15% acid which provides quick, reliable control of loss circulation in
offshore oil well. In an embodiment of the present invention, the following procedure
5 is used for measuring acid solubility.
1. Curing loss control composition specimen in HPHT curing Chamber
2. Place it on beaker on the atmospheric consistometer of the specimen at designed
BHCT;
3. Removing the specimen from the water, blot drying, weighing and placing it on
10 the support stand.
4. Preparing 15% HCl acid solution for testing; pouring it into the beaker where
cured loss control composition is placed.
5. Note down the timing as soon as the acid solution is poured over the lcc and
additionally heat the composition at designed BHCT.
15 6. After a particular lapse of time in hours the loss control composition becomes
completely acid soluble, filter it and note the amount till insoluble.
7. Calculating the solubility with the following equation:
20
where S% is solubility in percent, Wt is sample weight at time, and Wi is initial
specimen weight.
[0047] Advantageously, in various embodiments of the present invention, the loss
25 control composition has a low initial viscosity that allows the loss control
composition to flow easily, and, further the loss control composition becomes gelled
near wellbore to form a permanent sealant. In another embodiment of the present
invention, the loss control composition develops a nominal compressive strength that
helps it to adhere to the formation of the offshore oil well and also prevents it from
30 getting displaced in subsequent well operations. Consequently, severe circulation
losses that result from large fractures or vugular spaces are controlled.
[0048] Further, advantageously, in various embodiments of the present invention,
the loss control composition has a very low viscosity under applied shear and hence it flows
15
easily into loss zones inside the oil well. Further, a decreasing shear rate is
encountered when the loss control composition flows inside the loss zone, causing a
rapid development of gel strength. The rapid buildup of static gel strength along with
marginal compressive strength development of 200psi of the loss control composition
5 helps plug loss zones and mitigate loss circulation. Marginal compressive strength
development helps the loss control composition to adhere to the formation of the
offshore oil well by forming a weak bond that helps in preventing displacement
during subsequent well operations. Yet further, the loss control composition takes a
liquid form for a few cycles after shear force is applied and therefore becomes less
10 viscous during mixing and displacement. Subsequently, viscosity of the loss control
composition increases as the shear rate is reduced that helps to avoid recurrent losses
when the drilling process restarts in the offshore oil well.
[0049] Furthermore, advantageously, in various embodiments of the present
15 invention, the loss control composition has a low initial viscosity at surface of the
offshore oil well. The viscosity of the loss control composition increases as the
temperature increases inside the offshore oil well. Further, the low initial viscosity of
the loss control composition aids in pumping loss control composition easily. Further,
the loss control composition exhibits a thixotropic behavior as it is viscous under
20 static condition and once dynamic condition is attained, the viscosity of the loss
control composition starts decreasing because of shear thinning property. The shear
thinning property is represented by decreasing viscosity with increasing shear rate,
and this property provides advantages such as placing the loss control composition
downhole easily, preventing gas migration, and reducing flow of loss control
25 composition to loss zones inside the offshore oil well before solidification of the loss
control composition. Further, the loss control composition provides a predictable and
controllable pumping time, ranging from a few minutes to several hours at a given
temperature that allows the loss control composition to remain pumpable for
sufficient time for placement that also develops the network structure that leads to
30 gelation, over a predictable period of time.
16
[0050] Yet further, advantageously, in accordance with various embodiments of
the present invention, the loss control composition is self-supporting and is used for
plugging loss circulation zone. The loss control composition takes a liquid form for
a few cycles after shear is applied providing less viscosity during mixing and
5 displacement in the offshore oil field. Subsequently, viscosity of the loss control
composition increases as the shear rate is reduced helping avoid recurrent losses when
drilling process restarts in the offshore drilling well. In an exemplary embodiment of
the present invention, the loss control composition develops a compressive strength
of 100 Psi in 5hrs and 50Psi in 2hrs as illustrated in Fig. 3 which is sufficient to stop
10 lost circulation. In an exemplary embodiment of the present invention, a static gel
analyzer test conducted on the loss control composition shows rapid buildup of the
static gel strength of the loss control composition.
[0051] In an embodiment of the present invention, Static Gel Strength Analyzer
15 (SGSA) test shows build up from 100SGS to 500SGS in 12 minutes, reflecting rapid
build-up of static gel strength of the loss control composition. SGSA is measured
using MACS II device that performs static gel strength tests on loss control
composition slurry samples to analyze the gas-tight property of loss control
composition slurry during transition phase. MACS II conducts these tests under
20 simulated down-hole pressure and temperature conditions to determine the transition
time of the loss control composition. The loss control composition slurry being tested
is maintained in a static condition in a pressure chamber at a controlled temperature
and pressure. The SGS is calculated from the torque required to rotate a paddle of
known geometry intermittently at very low speed. Transition time is defined as time
25 required for the loss control composition slurry to transition from 100 SGS to 500
SGS. Conventionally, a cement slurry at a SGS of 100 lbf/100 ft2
loses its ability to
fully transmit hydrostatic pressure due to gel strength development. Further, during
this gelling stage, gas migration can occur. However, at 500 lbf/100 ft2
, the
hydrostatic pressure is still decreased but the loss control composition slurry is solid
30 enough to hold its weight and gas migration through the oil well ceases. Further, for
gas migration prevention in the oil well, transition time may be as short as possible
17
and should be less than 30mins. In an exemplary embodiment of the present
invention, a good transition time is considered to be 30 minutes or less.
[0052] In various embodiments of the present invention, advantageously, the loss
5 control composition controls partial and total losses both under static and dynamic
conditions and may be used in vertical, deviated as well as in horizontal offshore oil
wells. Further, the loss control composition does not have any detrimental effect on
producing formation and on productivity and life of the offshore oil well and thereby
it is economically viable. Further, the loss control composition is simple, easily
10 applicable, and without any major modification in the offshore oil field. In an
embodiment of the present invention, the gel slurry is applicable to the offshore oil
fields up to a depth of 4000 m where the reservoir temperature ranges between 600
C
to 1500
C. The loss control composition has a low initial viscosity at the surface when
shearing force is applied, and the viscosity increases as the temperature increases.
15
[0053] Table 10 illustrates experimental data associated with constituents of the
loss control composition for measuring shear rate and shear stress of the loss control
composition as shown in Table 11 below, in accordance with an embodiment of the
present invention.
20
Table 10
Specific
Gravity
(SG)/PPG
Gel
Slurry
Binding
Agent
Strengthening
Agent
Bridging
Agent
Crosslinking
Agent
Initial
Consistency
1.33/11.1 100 20 40 05 0.25 18
Table 11
25
S. No. Shear Rate (RPM) Shear Stress(lbs/100ft2
)
1. 3 36
2. 6 39
3. 30 52
4. 60 65
18
5. 100 79
6. 200 106
7. 300 126
8. 600 175
[0054] Further, the Gel0/Gel10 is 41/64 lbs/100ft2
, Plastic Viscosity/ Yield Point
(PV/YP) is 82cps/48.01 lbs/100ft2
and n’/k’ is 0.61/1.1 of the loss control
composition. Plastic viscosity (PV) is a measure of flow resistance that is caused by
5 mechanical friction. In an example, lower value of PV signifies lower concentration
of solids used for preparation of thixolite. Further, the Yield Point (YP) signifies
electrochemical or attractive forces present in the loss control composition. These
forces are as a result of negative and positive charges located on or near the particle
surface of the loss control composition, that on turn depends on quantity and
10 concentration of chemicals added to prepare the loss control composition.
[0055] Gel strength is a measure of attractive forces between particles in a fluid
under static conditions. Gel0/Gel10 values indicate the degree of gelation of the loss
control composition. Further, the Gel0 value indicates how quickly without shear the
15 loss control composition is converted into gel and further stops losses from occurring
within 10 seconds. In an embodiment of the present invention, for measuring Gel0, a
viscometer is used that is turned off for 10 sec after which the rotational speed is set
to be equivalent to 5.1 sec–1 (3 rpm) and the highest dial reading is measured.
Similarly, Gel10 values indicates degree of gelation after 10mins when the LCC is
20 kept idle for 10 minutes. Further, ‘n’ indicates degree of thixotropic or degree of shear
thinning, lower the value of ‘n’, better the shear thinning property, it is a
dimensionless number. Whereas ‘k’ indicates an apparent viscosity of the lost control
composition.
25 [0056] In another embodiment of the present invention, compatibility of loss
control composition with different types of Water Based Mud (wbm) and NonDamaging Drilling Fluid (NDDF) is measured. Tables 12 and 13 below illustrate that
the loss control composition has a positive R-index value that indicates compatibility
19
of the loss control composition with NDDF & similarly with other water based muds.
The R-index value indicates rheological compatibility of fluids (cement: spacer and
mud: spacer) where the R-index value is calculated as below:
5 R index (R) = [Highest 100 RPM reading from a mixture - Highest 100 RPM reading
from an individual fluid]. Table 12 below illustrates compatibility of fluids with
different range of R values.

Table 12
10
If R < 0 Fluids are compatible.
R is more than zero & less
than 40
Fluids are compatible, but friction pressures
should be verified to avoid fracturing the
formation.
R is more than 41 & less than
70
Fluids are slightly incompatible. Additional
testing is required.
R >70 Definitely Incompatible. An alternative
formulation must be re-designed.
[0057] R-Index as illustrated in the tables 13, 14 and 15 provides quantification
on degree of compatibility between loss control composition and spacer and
compatibility between loss control composition and mud. In most of the cases while
15 drilling we encounter losses, that results in loss of drilling fluid. During this stage
only we need to pump loss control solutions, while pumping this loss control
formulation it will come in contact with drilling fluid that may be NDDF/SOBM or
any other Water base mud (WBM)/Low Toxic Synthetic Oil Based Mud (LTSOBM)
that is used in the well and it may form an unpumpable mass i.e. show signs of
20 incompatibility. It is now pertinent that the mixture of lost control solution when
comes in contact with spacer which acts as a buffer fluid doesn’t form a viscous mass,
or shows phase separation or settling or flocculation etc.
25
20
Table 13
Loss circulation
composition (LCC)
mixture
Rheometer dial readings @ 800
C RIndex
Value
Remarks
300 200 100 60 30 6 3
100% LCC 11 PPG 126 106 79 65 52 39 36 Compatible
100% NDDF 9.6
PPG
36 30 20 16 12 5 3
95% LCC : 5%
NDDF
119 99 74 68 45 31 29
+10 Compatible
75% LCC : 25%
NDDF
128 109 89 75 66 51 48
50% LCC : 50%
NDDF
97 79 61 53 46 32 29
25% Lcc : 75%
NDDF
57 48 36 30 24 14 11
5% Lcc :9 5%
NDDF
38 32 24 19 16 8 6
Table 14
5
LCC Mixture
Rheometer dial readings @ 800
C RIndex
Value
Remarks
300 200 100 60 30 6 3
100% LCC 11
PPG
126 106 79 65 52 39 36 -
100% NDDF 9.6
PPG
45 37 25 21 17 12 9 -
95% LCC : 5%
NDDF
119 99 74 68 45 31 29
+29
Compatible
No viscous
mass
observed
75% LCC : 25%
NDDF
180 149 108 86 70 49 43
50% LCC : 50%
NDDF
125 102 75 61 49 34 30
21
25% LCC : 75%
NDDF
66 53 39 31 25 17 15
5% LCC :9 5%
NDDF
51 433 31 27 19 15 11
[0058] In another embodiment of the present invention, compatibility of loss
control composition with spacer is measured. The spacer is used such that there is no
contamination or compatibility issues between mud and the loss control composition.
5 Table 14 below illustrates that the loss control composition has a positive R-index
value within the limit specified that indicates compatibility of the loss control
composition with the spacer. Further, compatibility studies of the loss control
composition are carried out with various available spacers and drilling fluid that are
used to drill oil and gas wells.
10
[0059] Table 15 below illustrates rheological compatibility studies of loss control
composition of 10 ppg with B250 spacer at 800
C
Table 15
15
LCC Mixture
Rheometer dial readings @ 800
C RIndex
Value
Remarks
300 200 100 60 30 6 3
100%Spacer (3%
B250)
Sp.gr-1.15
58 52 43 39 34 26 23 -
100% LCC, sp.gr10 PPG
126 106 79 65 52 39 36 -
95% Spacer : 5%
LCC
61 54 46 41 36 28 25
+0 Compatible
75% Spacer : 25%
LCC
74 65 55 50 39 31 28
50% Spacer : 50%
LCC
94 78 65 62 43 33 30
25% Spacer : 75% 111 96 79 84 51 39 35
22
LCC
5% Spacer : 95%
LCC
121 102 76 81 48 37 34
[0060] Table 16 below illustrates rheological compatibility studies of the loss
control composition with D182 spacer at 800
C.
5 Table 16
Fluid Mixture
Rheometer dial readings @ 800
C RIndex
Value
Remarks
300 200 100 60 30 6 3
100%Spacer (3%
D182)
Sp.gr-1.30
55 49 40 35 29 21 16 -
100% LCC, sp.gr11.1 PPG
126 106 79 65 52 39 36 -
95% Spacer : 5%
LCC
59 52 43 38 31 24 18
+1 Compatible
75% Spacer : 25%
LCC
70 61 51 45 36 27 23
50% Spacer : 50%
LCC
81 78 60 51 41 31 27
25% Spacer : 75%
LCC
102 91 80 56 45 34 30
5% Spacer : 95%
LCC
121 101 74 62 49 36 34
[0061] While the exemplary embodiments of the present invention are described
and illustrated herein, it will be appreciated that they are merely illustrative. It will
10 be understood by those skilled in the art that various modifications in form and detail
may be made therein without departing from or offending the scope of the invention.

We claim:
1. A method for preparing a non-cementitious loss control composition, the
method comprising
5 adding bentonite to water to form a gel slurry;
adding a cross linking agent to the gel slurry;
adding a binding agent to the gel slurry and the cross linking agent;
adding a strengthening agent to the binding agent, the gel slurry and the cross
linking agent;
10 adding a bridging agent to the strengthening agent, the binding agent, the gel
slurry and the cross linking agent; and
adding a retarder to the bridging agent, the strengthening agent, the binding
agent, the gel slurry and the cross linking agent;
wherein the loss control composition is a lightweight thixotropic composition that
15 is prepared in a density range of 10 Pounds Per Gallon (ppg) to 16 ppg.
2. The method as claimed in claim 1, wherein the hydrated bentonite solution
forms 4-6 parts of the gel slurry by weight.
20 3. The method as claimed in claim 1, wherein the bentonite solution is hydrated
for 30 minutes.
4. The method as claimed in claim 1, wherein the gel slurry comprises
montmorillonite clay.
25
5. The method as claimed in claim 1, wherein 94-96% of the loss control
composition is soluble in 15% hydrochloric acid.
6. The method as claimed in claim 1, wherein the cross linking agent is a cross
30 linking polymer that is mixed for a duration of 5 minutes.
7. The method as claimed in claim 6, wherein the cross linking polymer is diutan
gum.
24
8. The method as claimed in claim 6, wherein the cross linking polymer is welan
gum.
9. The method as claimed in claim 6, wherein the cross linking polymer is guar
5 gum.
10. The method as claimed in claim 1, wherein the binding agent is magnesium
sulphate used in a ratio of 14-40 parts with respect to the loss control composition.
10 11. The method as claimed in claim 1, wherein the strengthening agent is dead
burnt magnesite.
12. The method as claimed in claim 11, wherein the dead burnt magnesite is in the
form of magnesium oxide that is calcined to a temperature of 17000
C and has low
15 reactivity that provides sufficient time for pumping of the loss control composition.
13. The method as claimed in claim 1, wherein the strengthening agent is in a ratio
of 28-80 parts with respect loss control composition.
20 14. The method as claimed in claim 1, wherein the bridging agent is in the form of
micronized calcium carbonate that is added to the loss control composition depending
on the loss circulation conditions.
15. The method as claimed in claim 1, wherein the retarder is added to the loss
25 control composition depending upon Bottom Hole Circulating Temperature (BHCT)
of the oil well.
16. The method as claimed in claim 1, wherein the loss control composition is
mixed until the loss control composition becomes homogeneous.
30 17. The method as claimed in claim 1, wherein the loss control composition is
mixed at 4000 revolutions per minute.
18. The method as claimed in claim 1, wherein the loss control composition is
mixed with spatula that makes the loss control composition a pumpable fluid providing
35 thixotropic properties.
25
19. The method as claimed in claim 1, wherein the loss control composition
exhibits a low initial viscosity at surface of the oil well and viscosity of the loss control
composition increases as the temperature increases inside the oil well.
5
20. The method as claimed in claim 1, wherein the loss control composition
achieves compressive strength of around 50 pounds per square inch (psi) in 2 hours at
100 psi in 5 hours that prevents washout in the oil well while resuming operations after
mud loss inside the oil well.
10
21. The method as claimed in claim 1, wherein the loss control composition
operates between bottom hole circulating temperature of 500
C to 1500
C and at a
bottom hole pressure of 3000-10000 psi.
15 22. The method as claimed in claim 1, wherein a 12 ppg loss control composition
controls dynamic losses from 150 Barrel per Hour (bbl/hr) to nil.
23. The method as claimed in claim 1, wherein the gel slurry is 150 parts by weight
of the loss control composition, the binding agent is 20 parts by weight of the loss
20 control composition, and the cross linking agent is 0.5 parts by weight of the loss
control composition at a pressure of 5000 psi at specific gravity of 1.27 that increases
thickening time of the loss control composition to 220 minutes.
24. The method as claimed in claim 1, wherein the gel slurry is 100 parts by weight
25 of the loss control composition, binding agent is 20 parts by weight of the loss control
composition, a strengthening agent is 40 parts by weight of the loss control
composition, a retarder is 0.4 parts by weight of the loss control composition, and a
cross linking agent is 0.4 parts by weight of the loss control composition with a specific
gravity of 1.30, the said composition of gel slurry achieves an initial consistency of 18
30 and a thickening time of 227 minutes.
25. The method as claimed in claim 1, wherein the gel slurry is 150 parts by weight
of the loss control composition, the binding agent is 20 parts by weight of the loss
control composition, the strengthening agent is 40 parts by weight of the loss control
26
composition, the retarder is 10 parts by weight of the loss control composition, and the
cross linking agent is 0.5 parts by weight of the loss control composition, the said
composition of gel slurry achieves an initial consistency of 14 at a specific gravity of
1.23 and a thickening time of 278 minutes.
5
26. The method as claimed in claim 1, wherein the compressive strength is
obtained in 24hrs at 1000
C, at a pressure of 244psi, and value of Gel0/Gel10 of the loss
control composition is 25/41, wherein the Gel0/Gel10 value indicates a degree of
gelation of the loss control composition.
10
27. The method as claimed in claim 1, wherein the method comprises:
adding a pre-determined quantity of bentonite in water through a hopper;
adding mixed metal oxide through hopper and mixing it thoroughly;
adding cross linking polymer through a hopper and leaving the solution idle for 10-
15 15 minutes; and
adding magnesium sulphate through a hopper followed by adding a dead burnt
magnesite.
28. A loss control composition comprising:
20 a gel slurry comprising of bentonite and water;
a cross linking agent;
a binding agent;
a strengthening agent;
a bridging agent; and
25 a retarder
wherein the loss control composition is lightweight thixotropic composition that
is prepared in the range of 10 Pounds per gallon (ppg) to 16 ppg.
29. The loss control composition as claimed in claim 28, wherein the bentonite
30 forms 4-6 parts of the gel slurry by weight.
30. The loss control composition as claimed in claim 28, wherein the bentonite is
hydrated for 30 minutes.
27
31. The loss control composition as claimed in claim 28, wherein the gel slurry
comprises montmorillonite clay.
5 32. The loss control composition as claimed in claim 28, wherein 94-96% of the
loss control composition is soluble in 15% hydrochloric acid.
33. The loss control composition as claimed in claim 28, wherein the cross linking
agent is a cross linking polymer that is mixed for a duration of 5 minutes.
10
34. The loss control composition as claimed in claim 28, wherein the cross linking
polymer is diutan gum.
35. The loss control composition as claimed in claim 28, wherein the cross linking
15 polymer is welan gum.
36. The loss control composition as claimed in claim 28, wherein the cross linking
polymer is guar gum.
20 37. The loss control composition as claimed in claim 28, wherein the binding agent
is magnesium sulphate used in a ratio of 14-40 parts with respect to the loss control
composition.
38. The loss control composition as claimed in claim 28, wherein the strengthening
agent is dead burnt magnesite.
25
39. The loss control composition as claimed in claim 28, wherein the dead burnt
magnesite is in the form of magnesium oxide that is calcined to a temperature of 17000
C and has a very low reactivity that provides sufficient time for pumping of the loss
control composition.
30
40. The loss control composition as claimed in claim 28, wherein the strengthening
agent is in a ratio of 28-80 parts with respect to the loss control composition.
28
41. The loss control composition as claimed in claim 28, wherein the bridging
agent is in the form of micronized calcium carbonate that is added to the loss control
composition depending on the loss circulation conditions.
5 42. The loss control composition as claimed in claim 28, wherein the retarder is
added to the loss control composition depending upon Bottom Hole Circulating
Temperature (BHCT) of the oil well.
43. The loss control composition as claimed in claim 28, wherein the loss control
10 composition is mixed until the loss control composition becomes homogeneous.
44. The loss control composition as claimed in claim 28, wherein the loss control
composition is mixed at 4000 revolutions per minute.
15 45. The loss control composition as claimed in claim 28, wherein the loss control
composition is mixed with a spatula or in any other mixing device that makes it
pumpable fluid providing thixotropic properties.
46. The loss control composition as claimed in claim 28, wherein the loss control
20 composition exhibits a low initial viscosity at surface of the oil well and viscosity of
the loss control composition increases as the temperature increases inside the oil well.
47. The loss control composition as claimed in claim 28, wherein the loss control
composition achieves compressive strength of around 50 pounds per square inch (psi)
25 in 2 hours at 100 psi in 5 hours that prevents washout in the oil well while resuming
operations after mud loss inside the oil well.
48. The loss control composition as claimed in claim 28, wherein the loss control
composition operates between bottom hole static temperature of 500
C to 1500
C and
30 at a bottom hole pressure of 3000-10000 psi.
49. The loss control composition as claimed in claim 28, wherein a 12 ppg
formulation controls dynamic losses from 150 Barrel per hour (bbl/hr) to nil.
29
50. The loss control composition as claimed in claim 28, wherein the gel slurry is
150 parts by weight of the loss control composition, the binding agent is 20 parts by
weight of the loss control composition, the cross linking agent is 0.5 parts by weight
of the loss control composition at a pressure of 5000 psi at specific gravity of 1.27 that
5 increases thickening time of the loss control composition to 220 minutes.
51. The loss control composition as claimed in claim 28, wherein the gel slurry is
100 parts by weight of the loss control composition, the binding agent is 20 parts by
weight of the loss control composition, the strengthening agent is 40 parts by weight
10 of the loss control composition, the retarder is 0.4 parts by weight of the loss control
composition, and the cross linking agent is 0.4 parts by weight of the loss control
composition with a specific gravity of 1.30, the said composition of gel slurry achieves
an initial consistency of 18 and a thickening time of 227 minutes.
15 52. The loss control composition as claimed in claim 28, wherein the gel slurry is
150 parts by weight of the loss control composition, the binding agent is 20 parts by
weight of the loss control composition, the strengthening agent is 40 parts by weight
of the loss control composition, the retarder is 10 parts by weight of the loss control
composition, and the cross linking agent is 0.5 parts by weight of the loss control
20 composition, the said composition of gel slurry achieves an initial consistency of 14 at
a specific gravity of 1.23 and a thickening time of 278 minutes.
53. The loss control composition as claimed in claim 28, wherein the loss control
composition achieves compressive strength of around 50 pounds per square inch (psi)
25 in 2 hours at 100 psi in 5 hrs that prevents washout in the oil well while resuming
operations after mud loss inside the oil well.
54. The loss control composition as claimed in claim 28, wherein Gel0/Gel10 value
of the loss control composition is 25/41, wherein the Gel0/Gel10 value indicates a
30 degree of gelation of the loss control composition.
30
55. The loss control composition as claimed in claim 28, wherein the loss control
composition is compatible with spacer, water based mud and non-damaging drilling
fluid.