FORM 2
THE PATENTS ACT, 1970
(39 OF 1970)
THE PATENTS RULES, 2003
Provisional/ Complete specification
[See section 10 and rule 13]
1. Title of invention:
"Quaternary Ammonium Surfactant Based Fracturing Fluids For Improving Oil Well Fracture Efficiency"
2. Applicant(s):
Name I Nationality I Address
Oil and Natural Gas India IOGPT, Phase -II, Panvel -
Corporation Ltd. 410221, Navi Mumbai,
Maharashtra, India.
2.Preamble to the description: The following specification particularly describes the invention and the manner in which it is to be performed.

QUATERNARY AMMONIUM SURFACTANT BASED FRACTURING FLUIDS FOR IMPROVING OIL WELL FRACTURE EFFICIENCY.
BACKGROUND OF THE INVENTION
1. Field of the Invention:
This innovation is aimed at developing and conducting basic research on surfactant based fracturing fluid (VES) that minimizes the formation damage of reservoir after the job. The components of Viscoelastic Surfactant based fracturing fluid formulation is selected from generic molecules that are cost effective and are commercially available locally. Quaternary ammonium compounds were chosen as basic surfactant that develops gel with an organic counter ion,
2. Description of the Prior Art:
Fracture fluid is a critical component of the hydraulic fracturing treatment. The function of the fracture fluid is to open the fracture and to transport propping agent along the length of the fracture, which is due to its viscous properties. In addition to exhibiting good viscosity in the fracture it should break and clean up rapidly after the treatment is complete, and should be compatible with fluid and formation, have good fluid loss control, exhibit low frictional pressure during pumping and at the same time it should be economical. In a hydraulic fracturing treatment, a high-viscosity fluid is injected into the well at treating pressures that are higher than the so-called formation breakdown pressure (practically speaking, the minimum horizontal stress.) These high pressures result in the propagation of a two-wing, vertically oriented fracture. Fluid injection continues for some time beyond this initial propagation, and when the created fracture is wide enough to accept the solid particles (sand or some other type of proppant material) that injected simultaneously with the carrying fluid. The proppant material

gradually fills up the fracture so that when the pumps are stopped, the fracture faces gradually close on the proppant creating a conductive flow path. Fracturing fluid plays a very important role in all the aspects of hydraulic fracturing treatment as creation of fracture by effectively transmitting the pressure applied, extension of the fracture by virtue of the sufficient viscosity, transportation of the proppant because of the elasticity and viscosity, clean up of fracture as the fluid loses viscosity with time and temperature.
History of Fracturing Fluids
Hydraulic fracturing as a well-stimulation method began in 1948, with crude oil as the fracturing fluid. Fracturing evolved rapidly and the use of surfactant-gelled hydrocarbons became common, in an effort to reduce loss of the fracturing fluid to the formation and generate larger dimension fractures, surfactant stabilized water/oil emulsion fluids were developed. The use of water-soluble polymers used to thicken these fluids began in the late 1950s. Polymer-thickened, water-based fluids were first used in the early 1960s, and by the late 1960s guar gum had become the polymer of choice because of its lower cost and viscoelastic behavior. The early 1970's saw significant growth in guar-based fracturing fluid technology. Controlled cross-linking reactions were evoked to provide the rheological properties required to provide low fluid loss to the formation and adequate elasticity to transport proppant into the fracture for these extensive fractures. While these fluids were robust and large fractures could be achieved, the economic performance did not justify the cost. It became generally recognized that cross-linked guar polymer also caused a dramatic loss in fracture conductivity. Laboratory measurements indicated that often less than 10% of the native fracture conductivity was achieved. Most of the remaining fracturing-fluid history centers on reducing the conductivity damage that guar-based polymers cause. Derivatized guar-based polymers were

developed to provide cleaner fluids that have more control in cross linking reactions. The amount of polymer required to accomplish fracture stimulation was reduced. Foaming these fluids with nitrogen or carbon dioxide reduced the amount of polymer being used while providing the fluid rheology required for handling proppant. Computer-controlled blending equipment made it possible to make ultra-low polymer gels that provided "just enough" rheology. Despite these innovations, the typical fracture conductivity achieved was typically less than 30% of the expected conductivity with these fluids. Significant improvements in gel breaking and polymer degradation technology have recently emerged. These chemical improvements allow aggressive but delayed attack on the polymer after the completion of a fracturing treatment. These improvements resulted in fracture conductivity in the range of 50%. Significant efforts were directed toward developing cleaner fracturing fluids that are polymer-free. A review of fracturing fluid history leads to the following conclusions:
i) Improvements in fracturing fluid Theological properties led to
increased fracture conductivity damage. ii) Reduction in polymer concentration led to increased fracture
conductivity, but a loss of Theological properties.
The relationship between fracture conductivity damage and Theological properties required to accomplish fracture stimulation seem to be inversely related. This innovation is focused towards the state of art cleaner fluid systems and assesses the possibility of for development of these fluid systems for application of hydraulic fracturing treatments in future oil well stimulation.
3. DETAILED DESCRIPTION OF THE INVENTION:

This is a polymer free fracture fluid in which surfactant instead of polymer is used to achieve desired visco-elastic properties. The properties of the VES fluid are due to its unique chemistry. Viscoelastic surfactants are very small molecules with a size of the order of 5,000 times smaller than guar molecules. It consists of a hydrophilic head group and a long hydrophobic tail. In the presence of brine/ organic counter ion, they form elongated micellar aggregates. When the surfactant concentration in the VES fluid is above a certain critical concentration, the micellar structures entangle and form a mesh like structures. These structures are responsible for the extraordinary proppant transport characteristics at low viscosities.
Upon contact with oil or gas or dilution by formation water, the VES fluid reduces viscosity by breaking down the worm-like micelles to much smaller spherical micelles. The spherical micelles cannot entangle with each other and hence the resulting fluid has water-like viscosity, allowing the fracturing fluid to flow back to the surface along with the produced fluids, leaving a highly conductive proppant pack. Advantages and disadvantages of the fluid over conventional polymer based frac-fluid are as follows,
• Solid free and do not leave any residue in the proppant pack.
• Polymer base fluid does not build filter cake at the formation face of the fracture.
• Better fluid efficiency.
- Fluid leak off is much lower because of its unique Theological characteristics as the fluid moves through the reservoir matrix and not the filtrate as in case of guar.
• VES fluid eliminates need for breakers because it-breaks on contact with hydrocarbons or reservoir fluids.
• The result is retained conductivity in the proppant pack and increased well production.

• By minimizing the required viscosity VES treatments can result in contained fractures.
• Treatments can be more effectively placed and require smaller volumes
• VES fluid produces substantially lower friction pressure than polymer base fluids, so they can be pumped through coiled tubing.
• Better contained fractures,

- Low viscosity
- Better elasticity
- Better fluid efficiency.

• VES fluids are insensitive to pH. It can be used to gel the acids. It can also be used at higher pH.
• The VES fluids are water wetting and will not alter the formation
• VES fluid is economical and can be used at lower temperatures (up to 80 deg C)
• No breaker required.
• Reduced complexity of VES treatments simplifies onsite mixing and metering while increasing precision.
• It contains no metal ions and can also be prepared without chlorides, hence environmentally friendly.
• No additional expenses or disposal costs are incurred for unused fracturing fluids
3.1 Selection of Surfactant for Formulating VES fluid:
VES surfactants are quaternary ammonium salts derived from long chain fatty acids or dimethylamine oxides. In aqueous solutions these surfactants exist as misceles in spherical form and with very low viscosity. Addition of organic or inorganic counter ion to this solution transforms the miscellars into

rod / thread like misceles thereby imparting visco-elastic character to the fluid. Dilution of the solution or addition of hydrocarbons causes disentanglement or formation of spherical miscelles,
Surfactants for this type of application are Cetyl Tri-Methyl Ammonium Bromide (CTAB), Cetylpyridinium Chloride, Stearyl Tri-Methyl Ammonium Chloride etc. Out of the three, first one, Cetyl Tri-Methyl Ammonium Bromide (CTAB), a VES surfactant with Mol. Formula [CH3 (CH2)15] (CH3)3 NBr, CTAB is selected as the base , Sodium Salicylate (SAL), and Potassium. Chloride as counter ion. All the three chemicals are in dry powder form.
3.2 Laboratory Studies:
Surfactant solutions of graded concentration, ranging from 2% to 6% (w/V) were prepared by dissolving CTAB in KCI brine. De-mineralized water was used for the preparation of all the solutions. Surfactant solutions were stirred for 10 minutes in batch mixer for proper dissolution. CTAB is completely soluble in water; hence observed no fish eye formation. SAL solution is prepared separately, and added to surfactant solution slowly by stirring at low rpm until the vertex is closed. Concentration of the SAL is varied from 0.5% to 3.6% depending on surfactant and SAL/CTAB ratio (Z).
The viscosity and degree of visco elasticity obtained is dependent upon the conditions employed (surfactant concentration, brine or electrolyte concentration and temperature) and will range from 500 to 1000 cp. The gel will break upon contact with isopropanol or other hydrocarbon fluid. The gel is shear dependent. Under high shear the solution has a low viscosity, but a high viscosity gel forms rapidly under low shear conditions. The gel also has a high yield strength which provides the fluids a good solid carrying capability, even under high shear/low viscosity conditions.

Visual inspection:
■ Lip Formation at room temperature and elevated temperatures.
■ Temperature stability up to 80 deg C in static condition CTAB/ SAL system.
3.3 Chemical Formulation Optimization:
Objective: Determine surfactant concentration (CTAB) to achieve desired viscosity (>75 cp) at temp of 80 deg C.
Procedure: Fracture fluid samples with varying concentrations of surfactant as shown in the legend box of above two plots were prepared. These samples were then placed in the Haake viscomter and effect varying shear and temperature was observed.
Equipment: Haake Rotary viscometer using profiled rotor bob and cup with MV DIN sensor to minimize the slip.
Observations: As is clear from Figures FIG1A and FIG 1B,
• At lower surfactant concentrations the fluid is behaving more Newtonian type, i.e., shear thinning is not significant. However initial viscosities are also very low. Any higher concentrations of VES thinning as a function of shear rate are appreciable.
• Power law behavior is prominent at surfactant concentrations above 4%.
Inference: Surfactant concentration 4 - 6% was found to retain desired apparent viscosity in the range of 300 to 1000 cp at 60-80 degree Celsius.
3.3.1 Counter ion Concentration
Objective: Determine counter ion concentration for a given surfactant
concentration (4%) to achieve desired viscosity (>75cp) at temp of 80 0C

Procedure: Fracture fluid samples with varying concentrations of surfactant as shown in the legend box of above two plots were prepared. These samples were then placed in the Haake viscomter and effect varying shear and temperature was observed.
Equipment: Haake Rotary viscometer using profiled rotor bob and cup with MV DIN sensor to minimize the slip.
Observations: As is clear from Figures FIG2A and FIG 2B,
• For counter ion concentration in the range of 0.25 - 0.4% the visco-
elastic behavior is predominant.
• At higher counter ion concentrations the fluid is more Newtonian with
very iow initial viscosities.
Inference: Counter ion concentration in the range of 0.25 - 0.4 is seen to provide desired visco-elastic behavior.
3.3.2 EFFECT OF KCL SALT CONCENTRATION: Rheological Behavior:
Objective: Study rheological behavior of 4% surfactant VES frac fluid at different temperatures and KCL concentration at 170 S'1 shear rate.
Procedure: Fracture fluid samples with different concentration of KCL and SAL / CTAB ratio at 0.25 counter ion concentration were prepared. These samples were then placed in the Haake viscomter and effect of varying temperature at shear rate 170 S'1 was observed.
Equipment: Haake Rotary viscometer using profiled rotor bob and cup with MV DIN sensor to minimize the slip

Observation: As is shown in Fig 3 KCI concentration at 4% appears to be
optimum.
3.3.3 EVALUATION FLOW BEHAVIOUR INDEX (N) AND CONSISTANCY
FACTOR (k):
Objective: Study Theological behavior of 4% surfactant VES frac fluid at different temperatures and shear rates.
Procedure: Frac fluid samples with different concentration of surfactant and counter ion concentration were prepared. These samples were then placed in the Haake viscomter and effect varying shear and temperature was observed.
Equipment: Haake Rotary viscometer using profiled rotor bob and cup with MV DIN sensor to minimize the slip
Observations: As is shown, in. Figs 4A., 4B, 4C, At Low Counter ion. concentrations VES gel behaves like Newtonian fluid ( z=0 to 0.20); with increasing SAL concentration they form worm/thread like micelles (z=0.25 to 0.4) and acquire viscoelastic character by random orientation of entangled thread like micelles. At higher Counter ion concentrations, Elastic component overweighs the viscous component, so initial low viscosities observed at moderate temperatures. Decrease in viscous component is attributed to structural evolution from entangled to multi connected network. Viscoelastic gels do not exhibit permanent loss of viscosity on exposure to high shear or temperature.
Inference: Counter ion concentration in the range of 0.25 - 0.4% is seen to provide desired visco-elastic behavior.
3.3.4 PROPPANT SUSPENSION TEST:
Proppant slurry of 60 g / 100ml of the VES gels was prepared. The slurry was placed in graduated cylinder after heating it to the desired temperature. The temperature was maintained through out the test. The settling time was

determined at the Proppant / fluid interface of the 100ml volume of slurry in 100ml graduated cylinder. Proppant carrying capacities of different formulations were evaluated in static conditions at elevated temperatures. Percentage of Settling was recorded watching the proppant and gel interface, holding the temperature for 30 minutes.
3.3.5 BREAKING TEST:
Breaking characteristics were evaluated using kerosene and isopropyl alcohol. Less than 1% of kerosene is sufficient to break the VES gel. Time taken for complete breaking is 2 to 3 minutes. Viscosity of the broken fluid is less than 10 cp,
SUMMARY OF THE INVENTION:
A Viscoelastic Surfactant derived from Quaternary ammonium salts of fatty acid, namely CTAB with SAL counter ion in KCI brine is found to generate desired viscoelastic behavior, quite analogous to polymer based fracture fluid systems. The formulation is found suitable for application in reservoirs up to 80°C. The innovation carries detailed lab studies to optimize concentrations of surfactant, counter ion and salt. Concentration of VES varied from 2-6% and the ratio of SAL /CTAB varied from 0.25 to 0.6 and evaluated rheological behavior. Optimum concentration of VES and the ratio of SAL/CTAB observed to be 3-4% and 0.25 respectively. This composition of VES is efficiently keeps the sand in suspension and 'n', and 'k' values favor effective transportation of sand in to fracture during hydraulic fracturing.

BRIEF DESCRIPTION OF DRAWINGS
The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:
1) Fig-1A is a table illustrating the Effect of VES Concentration on Viscosity with 4% KCI and 0.25 SAL /CTAB ratio at 170 S'2) Fig -1B is a table illustrating the Variation of VES viscosity with shear at 600C.
3) Fig.- 2A is a table illustrating the Effect of Counter Ion on 4% VES at 170 S-1 Shear.
4) Fig. - 2B is a table illustrating the Shear Thinning Behavior of 4% VES at 600c and different Z.
5) Fig.3 is a table illustrating the Effect of KCI concentration on 4% VES, Z=0.25at170S"1 Shear.
6) Fig.- 4A is a table illustrating the Variation of n' with Surfactant Concentration at 60°C.
7) Fig -4B is a table illustrating the Variation of K' with VES Concentration at 60°C.
8) Fig - 4C is a table illustrating the Variation of n' of 4%VES with varied Z at 600C.
9) Fig-.4D is a table illustrating the Variation, of k' of 4% VES with Z at 600C.
10) Fig.5 is a table illustrating the Sand settling rate at varied temperatures and VES %.

We claim:
1) The Viscoelastic Surfactant (VES) based formulation consisting of 4%-Cetyl-trimethyl Ammonium Bromide (CTAB) and 1%-Sodium Salysilate in 4%-KCI brine solution can generate a viscous gel that is suitable for hydraulic fracturing operations for reservoir temperatures up to 80°C.
2) The 4%-Cetyl-trimethyl Ammonium Bromide (CTAB) with 1%-Sodium Salysilate in 4%-KCI brine based VES formulation can suspend and transport the sand effectively in to the fracture.
3) The innovated VES formulation does not require breaker. It breakes on contact with hydrocarbon natural gas.
4) The innovated formulation can be used as hydraulic fracturing fluid for the temperature range 25 deg C to 80 deg C.