7/30/2019 FLC2000 and Wellbore Strengthening
1/10
FLC2000and Wellbore Strengthening 1
FLC2000
And
Wellbore Strengthening
Note : No warranty is given (including warranty as to fitness for a particular purpose or use or
application and any user of this report agrees to absolve and hold Impact Fluid Solutions harmless
against any consequences resulting or liabilities from the use thereof.
7/30/2019 FLC2000 and Wellbore Strengthening
2/10
FLC2000and Wellbore Strengthening 2
TABLE OF CONTENTS
Page
1. Introduction 3
1.1 Wellbore Strengthening 3
1.2 Technical Approaches 3
1.2.1 Chemical Consolidation of Weak Rocks 31.2.2 Stress Caging 4
1.2.3 Formation of an Ultra-Low Permeability Seal 4
2. Proof of Performance that FLC2000 Provides Wellbore Strengthening 5
3. The Effect of Shear on the Sealing Ability of FLC2000 versus Calcium Carbonate 6
4. How Does FLC2000 Work 7
4.1 Formation of Small Deformable Aggregates 7
4.2 Broad Particle Size Distribution 7
4.3 Formation of a Low Permeability Barrier 7
4.4 Preventing Fracture Propogation 8
5. FLC2000 Proof of Performance Case History Summary 10
7/30/2019 FLC2000 and Wellbore Strengthening
3/10
FLC2000and Wellbore Strengthening 3
1. Introduction
FLC2000
is Impact Fluid Solutions key additive to engineer ultra-low invasion drilling fluids,completion fluids and work-over fluids. To date, FLC2000 has been used successfully in over 1,000 wells
world-wide. FLC2000 greatly reduces fluid invasion into matrix permeability and micro-fractures. By
forming a very low permeability barrier over pores and micro-fractures, FLC2000 limits transmission of
the well-bore pressure to the pore fluid. This is instrumental in preventing formation fracturing by
preventing fracture propagation and effectively raises the fracture initiation pressure. For reservoir
applications, laboratory studies have shown that properly formulated FLC2000 fluids typically give
return permeabilitys in excess of 90% and show low flow initiation pressures. Excellent results have been
obtained for solids-free fluids as well as weighted systems.
1.1 Wellbore StrengtheningWellbore strengthening is currently of considerable interest to the drilling community. This is driven
mainly by the increasing challenges of drilling in environments such as deepwater and depleted zones
where the fracture gradient is low and the mud weight window is very narrow. The problem can become
even more extreme in deviated and high angle wells. Given that in most situations it is still very
desirable to keep the hydrostatic mud pressure higher than the pore pressure, this means that the ECD
will approach and frequently exceed the fracture initiation pressure. The result is induced lost circulation.
1.2 Technical Approaches
Several approaches have been considered with regard to well-bore strengthening. These include:
1.2.1 Chemical consolidation of weak rocks
In principle, the rock can be made stronger by using chemicals that form strong inter-granular
cements. However, in practice, most candidate treatments are difficult to apply successfully because of
one or more of the following problems:
The chemical reaction may be hard to control, leading to early setup in the pipe or well-bore The reaction may require unacceptably long soak times, particularly in low permeability rocks where
penetration of the treatment into the matrix will be slow
The chemicals may be incompatible with the drilling and completion fluids If used in the reservoir, the strengthening reaction may irreversibly damage the permeability and
hence well productivity
Many of the products considered carry health and safety concerns.In addition, while consolidation may significantly increase the compressive strength of some rocks,
any increase in tensile strength is usually very small. It is the tensile strength that needs to be increased if
the wellbore strengthening is to increase the fracture gradient.
7/30/2019 FLC2000 and Wellbore Strengthening
4/10
FLC2000and Wellbore Strengthening 4
1.2.2 Stress Caging
The concept of stress caging involves forming fractures around the well bore and propping these
open with a hard material such as a coarse marble. Propping open these fractures (resisting the fracture
closure stress) alters the hoop stress around the well-bore and, in theory, increases rock strength. An
additive such as graphite is also frequently added to reduce the permeability of the proppant and hence
reduce fluid and pressure transmission into the fracture. Several SPE papers have been published
describing the success of this technique and programs exist to calculate the amount and size of proppant
required for a particular rock type and stress regime. Information supplied by several users of this
technique indicates that it works best in permeable formations.
The stress cage method has been less successful in shales and it is difficult to see how it can be
effective in soft formations where the rock will deform around the propped fracture. The stress cage
mechanism is challenged by some groups who suggest that rather than creating fractures, invasion offluid into the pores is more likely to be a key factor. Solids added to the fluid form a protective filter cake
at the well-bore wall rather than act as a proppant in an induced fracture. Since the method, irrespective
of which of the above mechanisms might operate, generally uses coarse solid additives, it is difficult to
maintain the materials in the mud system. Hence it is often best suited to short sections of open hole or to
treating prior to, for example, casing running operations.
1.2.3 Formation of an ultra-low permeability seal
If an impermeable barrier can be formed on the wellbore wall such that the mud pressure (and
accompanying fluid) is not transmitted to the formation pore fluid then rock mechanics considerations
tell us that the rock will stay strong. If pressure invasion is allowed to take place, this will increase thepore pressure, which reduces the effective stress and thus reduces the rock fracture pressure.
While theoretically attractive, it is difficult to explain how a totally impermeable barrier can be set up
immediately fresh rock is exposed to the drilling fluid. All fluids in overbalance will invade to some
degree. In actual practice, there is emerging evidence that fluids that form an ultra-low permeability
barrier very quickly across matrix permeability or micro-fracture openings can restrict pressure and fluid
invasion enough to give an appreciable measure of wellbore strengthening. Impacts FLC2000 mud
additive falls into this category of material.
7/30/2019 FLC2000 and Wellbore Strengthening
5/10
FLC2000and Wellbore Strengthening 5
1. Proof of Performance For FLC2000 Providing Wellbore Strengthening?There are many examples where FLC2000 has increased the mud weight above that used in offset
wells without inducing lost circulation. One example (from SPE 101329), is taken from the Gulf of Mexico
and typifies the results obtained there and offshore Brazil, Middle East, North Africa and elsewhere:
An offset well had used oil mud to drill from 9,304 to 15,800 feet in 117 days. The upper part of the interval
was drilled with continuous partial losses and then an influx of formation water was detected. The drill string
showed snatches of high torque suggesting stuck pipe was imminent. As a result of these problems a cement plug
was set and the well sidetracked. While at 11,309 feet in the sidetrack, simultaneous losses and a water flow were
detected. An LCM pill was pumped but total losses were experienced and attempts to cure them were unsuccessful.
In all, some 25,000 barrels of oil mud were lost to the formation and it required 4 trips from shore by the supply boat
to make enough mud available to keep the well full.
On the subsequent well, FLC2000 was added at the start of the 12 section (8,425 feet) and was maintainedin the system until TD at 16,027 feet. A leak off test (LOT) was made at the 13 3/8 shoe with old water based mud
before switching to the FLC2000 oil mud: this LOT value was 15.7ppg. Drilling commenced with the FLC2000
mud at a density of 15.0ppg but this was increased to 15.3ppg when a pressure transition was encountered at 9,196
feet. In the next 6 days, drilling progressed to 10,157 feet, with the mud continuing to be weighted up as the well
went further into the high pressure zone. The static mud weight finally reached 16.6ppg. Even though this gave a
calculated ECD of 18.53ppg below the 13 3/8 shoe that had previously shown a LOT of 15.7ppg, no losses were
observed despite the high mud weight. Using the FLC2000, the operator had drilled more than 650 feet deeper
into the high pressure zone than on any previous well.
Unfortunately, having made a bit trip, the string was run back in the hole to just below the 13 3/8 shoe and
circulation was established by bringing the mud pumps up to speed rapidly, rather than by first rotating the pipeand then bringing the pumps in slowly. The resulting pressure surge broke down the 13 3/8 shoe and about 3,700
barrels of mud were lost before the loss zone was sealed with a dilatant LCM pill. Drilling recommenced once the
losses were controlled but the hole was unintentionally sidetracked. This sidetrack was drilled without problems to
9,678 feet using the FLC2000 fluid. 9 5/8 casing was set at 11,302 feet and, continuing with the same mud system,
the hole was deepened to 16,027 feet and 7 5/8 casing run and cemented without problems.
Despite the lost circulation incident and the unintentional sidetrack, this section was drilled in 69 days with the
FLC2000, compared with 117 days for the offset well using conventional invert OBM. Although there were induced
downhole losses totaling 5,700 barrels of mud, this volume was significantly lower than the 25,000 barrels lost in
the offset well. It is estimated that, compared with the offset well, around US$3.2 million was saved.
Laboratory tests have shown that an FLC2000 filter cake built on 100 Darcy 20/40 frac sand will
maintain its integrity to at least 3500psi overbalance in both WBM and OBM. The laboratory tests have
also shown that an FLC2000 mud will seal the mouth of a 0.25mm wide fracture in Ohio Sandstone
(
7/30/2019 FLC2000 and Wellbore Strengthening
6/10
FLC2000and Wellbore Strengthening 6
3. The Effect of Shear on the Sealing Ability of FLC2000 versus Calcium Carbonate
Calcium carbonate is often used as a bridging agent to protect permeable formations from theexcessive invasion that can contribute to formation damage and differential sticking. To be most effective,
it should be sized for the specific pore throat sizes of the rocks being drilled. However, these pore sizes
are not always known and, even when they are, pore sizes commonly vary both horizontally and
vertically in a formation. Even if the particle size distribution (PSD) of the carbonate can be optimized at
the start of drilling, the particles are ground down as drilling proceeds, so the size distribution shifts from
the ideal case and increased formation invasion can result. An alternative is to replace the calcium
carbonate with particles that are much more resistant to grinding. The flexible particles formed by
FLC2000 meet this requirement.
Laboratory tests were carried out to compare how sized calcium carbonate and FLC2000 fluids
respond to shear. The carbonate chosen for the study was a commercially available material commonlyused in drilling fluids. The carbonate had a PSD with a d90 of about 120 microns, a d50 of about 50 microns
and a d10 of about 10 microns. The materials were mixed into a 20 ppb bentonite mud and sheared at two
different shear rates on a Silverson mixer for varying lengths of time. The depth of penetration of each
fluid into a bed of 20/40 frac sand in the Impact sand bed test (SBT) was measured.
The figure below shows that the base bentonite mud cannot seal the sand and the fluid
completely penetrates the 15 cm bed. Addition of 20 ppb CaCO3 or 10 ppb FLC2000 into a 20 ppb
bentonite mud produces a good seal in the SBT with penetrations of less than 3 cm. However after only 5
minutes of shearing on the Silverson mixer at 6000 rpm, the CaCO3 mud completely penetrates the sand
bed. 10 minutes of shearing at the slower mixer speed of 3000 rpm also produces a CaCO3 fluid that
cannot seal the sand bed. In comparison, after 30 minutes of shear at 6000 rpm, the fluid containing
FLC2000 still seals with fluid penetration still less than 3 cm.
Figure 3.1 Sand Bed Test Results
7/30/2019 FLC2000 and Wellbore Strengthening
7/10
FLC2000and Wellbore Strengthening 7
4. How Does FLC2000 Work?
FLC2000 is a blend of modified cellulosic polymers and surface functionalized organic solids. Themolecular weights of the polymer components are low, which allows easy mixing and does not
contribute significantly to fluid viscosity. The technology has been presented in several SPE papers and
other acknowledged industry publications, including SPE 77189, SPE 85304, SPE 85326, SPE101329,
AADE HO-DF-04-33 and AADE 06-DF-HO15.
4.1 Formation of Small Deformable Aggregates
The high-grade polymers and organic solids in FLC2000 have been modified to exhibit a range of
water and oil solubilitys and wettabilitys, covering a wide range of HLB values. In water-based fluids,
some components dissolve and disperse to provide fluid loss control similar to many conventional
additives, while other components only partially solvate because of their oil-loving properties. Theseother components assemble into small deformable aggregates that give an FLC2000 fluid its ultra-low
invasion, low damage characteristics. A similar mechanism operates in oil-based fluids except that here it
is the more water-loving components now produce the aggregates.
Particle analysis shows the aggregates are present in the fluid in a very wide range of sizes, from a
few microns to several hundred microns in diameter. The d50 is around 60m, d10 9m and the d90 340m.
These aggregates provide the excellent invasion control seen with FLC2000. As well-bore fluid tries to
enter rock pores or micro-fractures because of the overbalance pressure, an ultra-low permeability layer
of aggregates quickly forms and greatly reduces any further invasion of solids or fluid. The aggregates
making up the layer are deformable so, as the pressure is raised, they are increasingly compressed and
the barrier permeability is reduced even further. In laboratory tests and field measurements FLC2000
gives much lower fluid invasion than conventional fluids, including sized calcium carbonate muds.
4.2 Broad Particle Size Distribution
The broad size distribution and compressibility of the aggregates means that the one grade additive
can seal a wide range of pore sizes and micro-fractures. There is no need to change the size distribution of
the product as drilling moves from formations of one permeability to another, as is the case with calcium
carbonate. In some respects, the aggregates in an FLC2000 fluid act like the water droplets in invert
emulsion oil muds. The water droplets in OBM are known to concentrate in the filter cake where they
make a major contribution to the good fluid loss control seen with oil muds. The major difference, and
benefit, of the FLC2000 aggregates is that they are more deformable and cover a much wider size range.
Hence they are better sealing agents and work over a much wider range of pore sizes and permeabilities.
4.3 Formation of a Low Permeability Barrier
A key benefit is that, by forming a very low permeability barrier, the FLC2000 additive also has the
ability to protect weak formations against pressure transmission and fracturing. The very low
permeability barrier formed by the FLC2000 additive is much more effective at preventing fluid invasion
7/30/2019 FLC2000 and Wellbore Strengthening
8/10
FLC2000and Wellbore Strengthening 8
than conventional mud additives and as such greatly reduces formation damage, the risk of differential
sticking and (by controlling leak-off into micro-fractures in shales) certain types of wellbore instability.
The barrier also effectively increases the fracture initiation pressure and widens the safe drilling window
by allowing the wellbore fluid density to be raised without inducing losses.
Effective concentrations of FLC2000 in a drilling, completion or work-over fluid range between 3 and
8ppb. This concentration is much lower than more conventional additives such as sized calcium
carbonates where 30 to 40ppb may be required and, even then, sealing is not as efficient as with FLC2000.
The optimum FLC2000 concentration within the above range will depend on the base fluid properties
determined both in the laboratory and in the field by using a simple sand bed invasion test. The
effectiveness of FLC2000 in giving wellbore strengthening in permeable formations is undoubtedly due to
the very low permeability of the filter cake formed. It is too soft a material and is present in too low a
concentration to work by a stress cage mechanism (see discussion of the stress cage method in Section 3).
4.4 Preventing Fracture Propagation
While it is feasible that the product can form a very low permeability seal that is complete enough,
and formed quickly enough, to prevent the initial pressure penetration into a permeable formation, and
hence stop a fracture initiating, it is more likely that the additive mainly functions by plugging a fracture
with a very low permeability membrane once it starts to grow. The formation of this seal will stop the
fracture propagating, much in the way a tip screen-out will stop a hydraulic fracture from growing. In
low permeability formations such as shales, FLC2000 works by one of 2 mechanisms:
In fracture blocking experiments on Ohio Sandstone, the product can seal the mouth of a 250 micronfracture. Since in the timescale of the experiment the Ohio Sandstone can be treated as an
impermeable rock, we can envision a similar seal will form on a low permeability shale. While a base
mud without FLC2000could not seal the fracture, mud with FLC2000 sealed and held a differential
pressure of almost 1600psi before failing.
7/30/2019 FLC2000 and Wellbore Strengthening
9/10
FLC2000and Wellbore Strengthening 9
There is growing support for the concept that, when shale breaks down, the failure is at an interfacebetween the low permeability shale and a higher permeability streak of sand, silt or marl.
Alternatively the failure can occur within a thin streak of more permeable rock enclosed in the shale.
If this is the case, then the invading fluid can leak off and a filter cake forms to stop fracture
propagation in the same way as in a more massive permeable rock.
7/30/2019 FLC2000 and Wellbore Strengthening
10/10
FLC2000and Wellbore Strengthening 11
Main Office
Offi ce Researc h/Support laboratory
Product Sales
Sales Office
No warranty is given (including warranty as to fitness for a particular purpose or use or application) and any user of this
report agrees to absolve and hold Impact Fluid Solutions harmless against any consequences resulting or liabilities fromthe use thereof.
Impact Fluid Solutions LLC is a technology driven company supplying specialty chemicals to the drilling fluids,completion fluids and cementing applications market and has a worldwide distribution network as well as a world-class
R&D and Field Support laboratory in Cornwall, England.
Contact Addresses
United States: 2800 Post Oak Blvd., United Kingdom: Unit 8,
Suite 2000, Wheal Kitty,Houston, TX 77056. St. Agnes, TR5 0RD
USA. Cornwall, UK.
Tel: 1 713 964 7736 Tel: 44(0)1872 553655
Regional Contacts:
North America: Douglas Byrne Europe/CIS/Africa: Scott ChesneyTel: 1 713 964 7736 Cell: 44(0)7825 289056
Dir: 1 713 551 4611 Email: [email protected]
Cell: 1 713 484 9205
Email: [email protected]
South America: Jay Haas Middle East: Peter Robottom
Tel: 1 713 964 7736 Impact Solutions Oilfield Services Co. (ISOS)Dir: 1 713 551 4613 Tel: +9712 6454 117
Cell: 1 713 204 4617 Cell: +97150 4567 301Email: [email protected] Email:[email protected]
(Exclusive distributor for the Middle East)Asia/Pacific: Mike Wilder
Cell: +6012 393 1062
Email: [email protected]
Information: [email protected] Website: www.impactfluids.net
Infotrac Emergency Response: USA 800-535-5053; International 352-323-3500
mailto:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]://[email protected]/http://[email protected]/http://[email protected]/mailto:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]Top Related