Description:Field of the invention

[0001] The present invention relates, generally, to the field of wellbore fluids used in hydrocarbon bearing subterranean formations. More particularly, the present invention relates to a hydraulic fracturing fluid composition for use in oil and gas exploration.

Background of the invention

[0002] Hydraulic fracturing or ‘fracking’ is a stimulation method used to enhance productivity in the oil and gas industry. Hydraulic fracturing is performed by pumping a hydraulic fracturing fluid at high pressure into a reservoir to fracture a hydrocarbon bearing formation. This increases permeability and creates additional passageways in the formation, allowing the hydrocarbons to flow more easily to the surface. Hydraulic fracturing fluids contain an aqueous phase and one or more additives. The additives generally comprise of biocide, viscosifier, clay stabilizer, cross linker etc.

[0003] Hydrocarbon bearing formations contain different types of minerals, formed in layers. Clay is one such naturally occurring mineral layer formed by weathering and decomposition of rocks. Under normal circumstances, clay is in a stable condition and therefore does not disrupt the flow of oil & gas through the formation. However, the clay becomes unstable upon contact with an aqueous fluid. When clay is exposed to any aqueous fluid such as well fluids, clay osmotically absorbs water from the well fluids, causing the clay to swell and disintegrate into fine particles. Such fine particles typically migrate through capillary flow channels of the formation causing clogging of the formation pore. This results in a reduction of permeability of formation, which in turn reduces productivity of the formation. The disintegrated fine clay particles also contaminate well fluids that are introduced into the well for various operations. Furthermore, clay swelling also poses a threat to stability of the formations.

[0004] Minimizing hydratable surface area of clay is crucial in inhibiting clay swelling. One of the components in a hydraulic fracturing fluid is a clay hydration suppressant (CHS), which inhibits swelling of clay. Traditionally, chemical additives such as potassium chloride, sodium chloride, calcium chloride, zinc chloride, magnesium chloride, or magnesium bromide are used as CHS. Among the chemical additives, potassium chloride (KCL) is commonly used in hydraulic fracturing fluids as a clay hydration suppressant component for inhibiting clay swelling. Potassium chloride, by ion exchange mechanism, converts the formation materials, including clay, from the sodium form to potassium form which is less vulnerable to swelling.

[0005] However, potassium chloride in hydraulic fracturing operations may be detrimental to a formation due to high concentration of chloride ions. Excessive concentration of chloride also pollutes underground water, which is a health hazard. Further, use of high concentrations of potassium salts also affects the underground osmotic balance. Moreover, potassium chloride corrodes tubing, casing and other equipment in a wellbore. Due to environmental concern chloride-based clay hydration suppressant is prohibited to be used in hydraulic fracturing fluids in many countries.
[0006] In light of the aforementioned drawbacks, there is a need for a clay hydration suppressant that is environmentally friendly and can function at low concentrations. There is a to need formulate a hydraulic fracturing fluid having a clay hydration suppressant to control clay swelling in subterranean formations.

Summary of the Invention

[0007] In various embodiments of the present invention, a composition of a hydraulic fracturing fluid is provided. The composition of the hydraulic fracturing fluid comprises a biocide in a range from 0.01-0.04% w/v, a thermo-stabilizer in a range from 0.08-0.20% w/v, a viscosifier in a range from 0.30 to 0.60% w/v. The composition further comprises of a buffering agent having a weak base and a strong base. In an embodiment of the present invention, the amount of weak base is in a range from 0.04–0.06% w/v and the amount of strong base is in a range from 0.04–0.06% w/v. The composition further comprises of a non-emulsifier in a range from 0.3–0.6% w/v, a cross-linker in a range from 0.02–0.04% w/v, a breaker in a range from 0.005-0.02% w/v, and a clay hydration suppressant in a range from 1.0 - 1.5% w/v. In an embodiment of the present invention, the clay hydration suppressant of the present invention is polyamine having at least 30 amines and a molecular weight having m/z range of 1500–2500.

[0008] In an embodiment of the present invention, the biocide is selected from a group comprising of glutaraldehyde, chlorophenate and isothiazoline.

[0009] In an embodiment of the present invention, the thermo-stabilizer is selected from a group comprising of sodium sulfite, sodium thiosulphate, sodium erythorborate, methanol, thiourea and mixtures thereof.

[0010] In an embodiment of the present invention, the viscosifier is selected from a group comprising of gelling agent, fast hydrating guar gum, hydroxypropyl guar (HPG), and carboxymethyl hydroxypropyl guar.

[0011] In an embodiment of the present invention, the weak base is selected from a group comprising of sodium carbonate, potassium carbonate, sodium bicarbonate and potassium bicarbonate.

[0012] In an embodiment of the present invention, the strong base is selected from a group comprising of potassium hydroxide and sodium hydroxide.

[0013] In an embodiment of the present invention, the non-emulsifier is selected from a group comprising of phenolic, esters, ethers, ether-esters based compounds, and a non-ionic phenolic base including nonyl phenol.

[0014] In an embodiment of the present invention, the cross-linker is selected from a group comprising of borax, titanium, zirconium, or aluminum complexes.

[0015] In an embodiment of the present invention, the breaker is selected from a group comprising of ammonium persulphate, sodium salts of peroxidisulphate, potassium salts of peroxidisulphate, sodium bromate and enzymes breaker.

Brief description of the drawings

[0016] The present invention is described by way of embodiments illustrated in the accompanying drawings herein:

[0017] Fig. 1 is a graph illustrating swell inhibition behavior of hydraulic fracturing fluid having 2% KCL as clay inhibitor, in accordance with an embodiment of the present invention;

[0018] Fig. 2 is a graph illustrating swell inhibition behavior of hydraulic fracturing fluid having 1% polyamine as clay inhibitor, in accordance with an embodiment of the present invention;

[0019] Fig. 3 is a graph illustrating swell inhibition behavior of hydraulic fracturing fluid having 2% polyamine as clay inhibitor, in accordance with an embodiment of the present invention;

[0020] Fig. 4 is a graph illustrating thermal stability of hydraulic fracturing fluid prepared with 2% KCl, in accordance with an embodiment of the present invention;

[0021] Fig. 5 is a graph illustrating thermal stability of hydraulic fracturing fluid prepared with 1.5% polyamine, in accordance with an embodiment of the present invention;

[0022] Fig. 6 is a graph of core flow study conducted with hydraulic fracturing fluid having 2% KCL as clay inhibitor, in accordance with an embodiment of the present invention;
[0023] Fig. 7 is a graph of core flow study conducted with hydraulic fracturing fluid having 1.5% polyamine as clay inhibitor, in accordance with an embodiment of the present invention; and

[0024] Fig. 8-10 are graphs of on-field implementation study conducted using the hydraulic fracturing fluid of the present invention in onshore fields.

Detailed description of the invention

[0025] In various embodiments of the present invention, a composition of a hydraulic fracturing fluid is provided. The composition of the hydraulic fracturing fluid comprises an aqueous base, a biocide, a thermo-stabilizer, a viscosifier, a buffering agent, a non-emulsifier, a cross-linker, a breaker and a clay hydration suppressant (CHS). In various embodiments of the present invention, the hydraulic fracturing fluid exhibits improved rheological properties and enhances the productivity of subterranean formations by maintaining the porosity & permeability of formations. The hydraulic fracturing fluid prevents reaction of aqueous base with clay in a formation, thereby preventing clay swelling and maintaining the formation stability.

[0026] The present invention discloses a hydraulic fracturing fluid composition for addressing the problems associated with clay swelling in a subterranean formation, in accordance with various embodiments of the present invention. The invention provides a hydraulic fracturing fluid composition that exhibits high density, high thermal stability, high viscosity, and low corrosion rate. Further, the hydraulic fracturing fluid is effective in inhibiting clay swelling with minimal dosage in accordance with various embodiments of the present invention. The hydraulic fracturing fluid of the present invention is environmentally friendly and compatible with various types of subterranean formations.

[0027] The disclosure is provided to enable a person having ordinary skill in the art to practice the invention. Exemplary embodiments herein are provided only for illustrative purposes and various modifications will be readily apparent to persons skilled in the art. The general principles defined herein may be applied to other embodiments and applications without departing from the spirit and scope of the invention. The terminology and phraseology used herein is for the purpose of describing exemplary embodiments and should not be considered limiting. Thus, the present invention is to be accorded the widest scope encompassing numerous alternatives, modifications, and equivalents consistent with the principles and features disclosed herein. For purposes of clarity, details relating to technical material that is known in the technical fields related to the invention have been briefly described or omitted so as not to unnecessarily obscure the present invention.

[0028] In various embodiments of the present invention, the hydraulic fracturing fluid composition of the present invention comprises an aqueous base and additives. In an embodiment of the present invention, the aqueous base is water. In an embodiment of the present invention, the additives comprise of a biocide, a thermo-stabilizer, a viscosifier, a buffering agent, a non-emulsifier, a cross-linker, a breaker, and a clay hydration suppressant (CHS). In various embodiments of the present invention, the hydraulic fracturing fluid of the present invention, by way of the composition exhibits superior properties to enhance the porosity and permeability of formations, thereby enhancing the productivity of an oil and gas reservoir.

[0029] The aqueous base of the hydraulic fracturing fluid and residual water within a subterranean formation may contain various types of microorganisms. Control of microorganisms is essential in hydraulic fracturing operations to prevent biofilm formation (biofouling) that may lead to clogging of the formation pores and consequently inhibiting productivity. The presence of microorganisms in a subterranean formation also causes corrosion of equipment used for oil and gas extraction. Biocide is a critical component of the hydraulic fracturing fluid composition to eliminate the growth of deleterious microorganisms that causes biofouling and corrosion. In an exemplary embodiment of the present invention, the biocide is selected from a group comprising of glutaraldehyde, chlorophenate and isothiazoline. In an exemplary embodiment of the present invention, the amount of biocide in the hydraulic fracturing fluid composition is in a range from 0.01 - 0.04% w/v, preferably 0.03% w/v.

[0030] The aqueous base of the hydraulic fracturing fluid also contains dissolved oxygen which may react with other components of the hydraulic fracturing fluid and generate reactive free radicals. The reactive free radicals may react with wellbore equipment thereby contributing to corrosion of the equipment. In an embodiment of the present invention, the hydraulic fracturing fluid composition comprises a thermo-stabilizer that performs as an oxygen scavenger to remove oxygen from the aqueous base and prevent generation of free radicals. In an exemplary embodiment of the present invention, the amount of thermo-stabilizer in the hydraulic fracturing fluid composition is in a range from 0.08 - 0.20% w/v, preferably 0.1% w/v. In an exemplary embodiment of the present invention, the thermos-stabilizer is selected from a group comprising of sodium sulfite, sodium thiosulphate, sodium erythorborate, methanol, thiourea and mixtures thereof.

[0031] In an embodiment of the present invention, the hydraulic fracturing fluid comprises a viscosifier to increase the carrying capacity of the hydraulic fracturing fluid and to maintain the necessary pressure during hydraulic fracturing operation. Viscosifiers also improve lubricity of the hydraulic fracturing fluid for suspending solids and enhance wellbore stability at high pressure high temperature conditions. In an exemplary embodiment of the present invention, the amount of viscosifier in the hydraulic fracturing fluid is in a range from 0.3 – 0.6% w/v, preferably 0.5% w/v. In an exemplary embodiment of the present invention, the viscosifier is selected from a group comprising of gelling agent, fast hydrating guar gum (FHGG), hydroxypropyl guar (HPG), and carboxymethyl hydroxypropyl guar (CMHPG).

[0032] pH of the hydraulic fracturing fluid considerably influences the performance during hydraulic fracturing operations. Any change in pH results in an increase or decrease of H+ ions in the hydraulic fracturing fluid that may impact its viscosity. Buffering agent is a critical component to maintain the pH of the hydraulic fracturing fluid. The buffering agent also facilitates the delay in crosslinking reaction and as a result maintains the hydraulic fracturing fluid at a stable viscosity. In an embodiment of the present invention, the buffering agent is a blend of salts of a weak base and a strong base. In an exemplary embodiment of the present invention, the weak base is selected from a group comprising of sodium carbonate, potassium carbonate, sodium bicarbonate and potassium bicarbonate. In an exemplary embodiment of the present invention, the amount of weak base is in a range from 0.04–0.06% w/v. In an exemplary embodiment of the present invention, the strong base is selected from a group comprising potassium hydroxide and sodium hydroxide. In an exemplary embodiment of the present invention, the amount of strong base is in a range from 0.04 – 0.06% w/v. In an exemplary embodiment of the present invention, the pH of the hydraulic fracturing fluid is in a range from pH 11–12.

[0033] The aqueous base of the hydraulic fracturing fluid may form emulsions with the oil in the formation which may clog the subterranean formations. In an embodiment of the present invention, the hydraulic fracturing fluid comprises a non-emulsifier to break such an emulsion in-situ. In an exemplary embodiment of the present invention, the amount of non-emulsifier is in a range from 0.3 – 0.6% w/v, preferably 0.5% w/v. In an exemplary embodiment of the present invention, the non-emulsifier is selected from a group comprising of phenolic, esters, ethers and ether-esters based compounds, and non-ionic phenolic base such as nonyl phenol. The non-emulsifier also improves recovery of hydraulic fracturing fluid after the hydraulic fracturing operation.

[0034] Cross-linking of the viscosifier component of the hydraulic fracturing fluid increases the viscosity and high temperature stability of the hydraulic fracturing fluid. During fracking operations, the hydraulic fracturing fluid is expected to remain in a viscous state inside a formation. Therefore, delayed crosslinking is desirable in hydraulic fracturing fluid to maintain the fluid at pumpable viscosity for extended duration. The control of the delayed crosslinking is achieved by optimizing the pH and viscosifier of the hydraulic fracturing fluid. The buffering agent dissolves slowly in the hydraulic fracturing fluid allowing the cross-linker to react slowly, thereby delaying the cross-linking. In an exemplary embodiment of the present invention, the amount of cross-linker in the hydraulic fracturing fluid is in range from 0.02 – 0.04% w/v, preferably 0.03% w/v. In an exemplary embodiment of the present invention, the cross linker is selected from a group consisting of boron, titanium, zirconium, or aluminum complexes, preferably boron complexes. Boron based cross-linkers impart desirable viscosity to the hydraulic fracturing fluid under conditions of low shear. In an embodiment of the present invention, the hydraulic fracturing fluid composition of the present invention comprising cross-linkers surprisingly exhibits excellent rheological profile, and fracture conductivity properties even at elevated temperatures up to 100?C. In an embodiment of the present invention, the cross-linker enables increase in viscosity of the composition and renders the composition stable for more than 2 hours at a temperature of 90? temperature which shows excellent rheology (Fig.5).

[0035] In an embodiment of the present invention, the hydraulic fracturing fluid comprises of a breaker. The breaker facilitates breakdown of the molecular backbone of the cross-linker to reduce its molecular weight. This results in reduction of the viscosity of the crosslinked hydraulic fracturing fluid so that the fluid is more easily recovered from the subterranean formation. In an exemplary embodiment of the present invention, the amount of breaker in the hydraulic fracturing fluid composition is in a range from 0.005 to 0.02% w/v, preferably 0.01% w/v. In an exemplary embodiment of the present invention, the breaker is selected from a group comprising of ammonium persulphate, sodium salts of peroxidisulphate, potassium salts of peroxidisulphate, sodium bromate and enzymes breaker. The breaker acts as oxidizing agent to break the cross-linked hydraulic fracturing fluid of the present invention.

[0036] Clay layers, such as shale layers, form a substantial portion of subterranean formations, which get hydrated upon contact with water during hydraulic fracturing operations. Hydration induces the clay to undergo osmotic swelling resulting in disintegration of clay into fine particles. The dispersed fine clay particles may disperse in the surroundings and migrate into the formations and reduce the permeability of a formation, resulting in decrease of productivity. Clay hydration may also lead to the collapse of the formation. In an embodiment of the present invention, the hydraulic fracturing fluid composition comprises of a clay hydration suppressant to inhibit clay swelling. In an exemplary embodiment of the present invention, the amount of clay hydration suppressant is in a range from 1.0 - 1.5% w/v. In an exemplary embodiment of the present invention, the clay hydration suppressant is a polyamine. Advantageously, the clay hydration suppressant has a low molecular weight amine that facilitates suppression of clay hydration and minimizes disintegration of clay into fines particles. In an embodiment of the present invention the polyamine has at least 30 amine content and a molecular weight having m/z range of 1500–2500, to impart significant inhibition of clays hydration in the reservoir. The combination of higher amine content and molecular weight enables the polyamine to adsorb strongly on the silicate with many points of attachment, thereby inhibiting clay swelling.

[0037] Advantageously, the hydraulic fracturing fluid composition of the present invention does not employ KCL as clay hydration suppressant and therefore is less corrosive to the wellbore equipment. The hydraulic fracturing fluid composition of the present invention is free of chloride and therefore has no adverse impact on the environment and the reservoir. Furthermore, the clay hydration suppressant in the hydraulic fracturing fluid surprisingly exhibits higher compatibility with other additives added to the fluid.

[0038] Advantageously, the hydraulic fracturing fluid in accordance with an embodiment of the present invention exhibits surprising clay swelling inhibition. The hydraulic fracturing fluid composition of the present invention efficiently ceases disintegration of clay and prevents clogging of formations. The hydraulic fracturing fluid of the present invention exhibits thermal stability up to 90-100oC. Therefore, the hydraulic fracturing fluid composition of the present invention is capable of being applied in high pressure high temperature conditions for inhibiting clay swelling in formations.

[0039] pH of hydraulic fracturing fluid composition plays a critical role in improving its cross-linking ability and stability. In an embodiment of the present invention, the pH of hydraulic fracturing fluid composition is in a range from pH 11 to 12.

[0040] A linear gel is prepared with the fast hydrating guar gum [FHGG] in the technical water to determine desired viscosity. Average viscosity of hydraulic fracturing fluid of the present invention is 700 cPs at 100s-1 at 90oC temperature (measured with HPHT viscometer). Viscosity of the linear gel prepared with 0.5 wt% fast hydrating guar gum [FHGG] is 36 cP at 511s-1 (measured with Fan 35 SA make viscometer). The viscosity increases with multiple folds up to 700 cPs after cross linking in suitable alkali medium. In an embodiment of the present invention, the addition of buffering agent and cross-linker increases the viscosity of linear gel and remains stable to carry proppant concentration during hydraulic fracturing operation. In an embodiment of the present invention, maintaining this viscosity is necessary to create fractures into the reservoir and to carry desired concentration of proppant into fractured reservoir. In an embodiment of the present invention, the viscous nature of hydraulic fracturing fluid enhances the stability of the hydraulic fracturing fluid in high pressure high temperature conditions.

[0041] In an embodiment of the present invention, the hydraulic fracturing fluid has a density in a range from 1.01 to 1.03 g/m3.

[0042] In an embodiment of the present invention, the hydraulic fracturing fluid exhibits significant clay hydration inhibition with minimum dosage. In an embodiment of the present invention, the amount of clay hydration suppressant added to the hydraulic fracturing fluid is approximately 25% less than conventionally used potassium chloride. The hydraulic fracturing fluid, by way of selection of additives in the specified amount in accordance with various embodiments of the present invention attains superior properties to satisfy the requirements of high pressure and high temperature well applications.

[0043] Advantageously, the hydraulic fracturing fluid is devoid of KCL and yet exhibits an inhibition of clay swelling by 36% higher than conventionally used potassium chloride. Additionally, the components of the hydraulic fracturing fluid are in a dissolved state, thereby rendering the fluid solid free. Further, advantageously, the hydraulic fracturing fluid of the present invention exhibits a low corrosion rate by controlling biofouling within the reservoirs.

[0044] The properties of the hydraulic fracturing fluid are provided in table 1, in accordance with an embodiment of the present invention.

Hydraulic fracturing fluid Composition Density (g/cm3) Viscosity Thermal Stability Corrosion Rate
Biocide 1.01-1.03

36 Cps (Linear Gel)

90-100oC

Negligible
Thermo-stabilizer
Viscosifier
Buffering agents
Non-emulsifiers
Cross-linker
Breaker
Clay hydration
suppressant
Table 1

[0045] In an embodiment of the present invention, a process for preparation of hydraulic fracturing fluid is provided. In an embodiment of the present invention, the process of preparing hydraulic fracturing fluid comprises the steps of adding 0.03% (w/v) of biocide and 0.1% (w/v) of thermo-stabilizer. The process further comprises adding 0.5% (w/v) of viscosifier into the above mixture to obtain a hydrated base gel having a viscosity in a range of 35-40 cPs. The process further comprises adding 0.05% (w/v) of buffering agent to increase the pH in a range of 10-12. The process further comprises of adding 1.5% (w/v) clay hydration suppressant, 0.5% (w/v) non-emulsifier, 0.01% (w/v) breaker and 0.03% (w/v) X-linker solution to obtain the hydraulic fracturing fluid of present invention. In an embodiment of the present invention, the process optionally comprises of adding a proppant.

[0046] The disclosure herein provides for examples illustrating the process for preparing the hydraulic fracturing fluid in accordance with an embodiment of the present invention. The examples used herein for such illustration are intended merely to facilitate an understanding of ways in which the embodiments may be practiced and to fu1ther enable those of skill in the art to practice the embodiments. Accordingly, the following examples should not be construed as limiting the scope of the embodiments herein.

Working Examples

[0047] The hydraulic fracturing fluid composition in accordance with an embodiment of the present invention is provided in table 2 below.

Composition of Hydraulic Fracturing Fluid
Biocide 0.03 % w/v
Thermo-stabilizer 0.10 % w/v
Viscosifier 0.5 % w/v
Buffering agents
a) Weak Base
b) Strong Base
a) 0.05 % w/v
b) 0.05 % w/v
Non-emulsifiers 0.5 % w/v
Cross-linker 0.03 % w/v
Breaker 0.01 % w/v
Clay hydration suppressant 1.5 % w/v
Table 2
[0048] The hydraulic fracturing fluid of table 2 was subjected to various studies as follows:

Swelling Studies

[0049] Control of clay swelling, and migration of fine clay particles is an important property of hydraulic fracturing fluid to minimize formation damage. Bentonite was used for studying the swelling inhibition properties of hydraulic fracturing fluid of table 2. The swelling tendency of bentonite in hydraulic fracturing fluid of present invention having different concentrations of CHS was compared with that of hydraulic fracturing fluid having 2% KCl.

[0050] Swelling behavior was calculated (by taking the reference value (Zero) of the samples observed in diesel) using conventional method. The results are tabulated in table 3.

S. No Solutions used Volume occupied by Bentonite (ml) % Swelling of Bentonite
1 Diesel 3 0
2 D/w 7 40
3 1.0 % KCl 5.8 28
4 2.0 % KCl 5.2 22
5 1.0 % CHS 5.0 20
6 1.5 % CHS 4.8 18
7 2.0 % CHS 4.8 18
Table 3
[0051] Another study on swelling behavior of bentonite was also carried out on a linear swell meter. The swelling tendency of bentonite in hydraulic fracturing fluid of the present invention having different concentrations of CHS was compared with that of hydraulic fracturing fluid having 2% KCl. The results are tabulated in table 4 and figs. 1-3 which indicates a good swelling inhibition obtained with hydraulic fracturing fluid of present invention having 1.5% CHS.

Sl. No. Clay Stabilizer Used Initial Height
(mm) Final Height (mm) % Swelling
1 2 % KCl 14.51 16.73 15.3
2 1 % CHS 14.65 16.80 14.7
3 2 % CHS 14.70 16.87 14.8
Table 4
Compatibility

[0052] The test of compatibility of the clay hydration suppressant of present invention with various additives of the hydraulic fracturing fluid was carried out as per standard procedures and found compatible with all additives. The results are tabulated in table 5.

Sl. No. Frac fluid additives with conc. (%) Formation of precipitate in 1.5% solution of clay hydration suppressant (Polyamine)
1 Biocide
(0.03%) No Precipitation
2 Non-Emulsifier
(0.5%) No Precipitation
3 Sodium Thiosulphate
(0.1 wt%) No Precipitation
4 Soda Ash
(0.05 wt%) No Precipitation
5 Caustic Soda
(0.05 wt%) No Precipitation
6 Borax (0.03 wt%) No Precipitation
7 Ammonium Per Sulphate (0.1 wt%) No Precipitation
Table 5
Gelation and Hydration Tendency

[0053] Stability of the hydraulic fracturing fluid plays a vital role in fracturing operation. Optimization of gelation and hydration time was performed to achieve required viscosity. Viscosity of linear gel prepared with 0.5% FHGG in solutions with 1.5% clay hydration suppressant was measured with Fann 35 SA make viscometer and the results are tabulated in table 6.

Gellant Used Viscosity measured at 511 s-1 (cP)
2% KCl 1.5 % CHS
FHGG (0.5%) 35 36
Table 6
Gel Stability Test

[0054] The stability of a linear gel prepared with hydraulic fracturing fluid of the present invention was carried out in water bath at static temperature of 40±20C. The gel stability was observed in presence of 0.03vol% biocide for 48 hours. The results are tabulated in table 7.
Formulation Used Viscosity measured at 511 s-1 (cP)
2% KCl 1.5 % CHS
FHGG (0.5%)+ 0.03%
Bactericide Aldehyde Initial After 48 hours Initial After 48 hours
35 32 36 33
Table 7
Cross-linking Behavior

[0055] Studies were carried out to optimize the dosage of cross-linker at ambient temperature. Cross-linker dosage was optimized to ensure the sufficient rheological strength of the fracturing fluid to carry the proppant deep into the targeted formation zone. The results are tabulated below in table 8. From table 8 it is evident that 0.03% of cross linker is sufficient for getting stable very good cross linked gel.

Cross Linker (%) Quality of Cross Linked gel prepared
Initial After 4 Hrs. without breaker at room temperature
0.02 Loose Loose
0.025 Good Good
0.03 Very good Very good
0.04 Syneresis occurs Syneresis occurs
Table 8

[0056] A linear gel prepared in different clay stabilizers were cross linked at elevated pH system (0.05% Soda Ash and 0.05% Caustic Soda) adding 0.03% Borax. 0.1% Sodium thiosulphate was also added to improve thermal stability. The cross-linking behavior was checked after keeping in water bath at 90±20C for 3 hours as tabulated in table 9.
Formulation Crosslinking behavior at 90±20C
0.5% FHGG+0.05% Soda Ash+ 0.05% Caustic
Soda+0.1% Sod. Thio+0.03% Borax 2% KCl 1.5% CHS
1hr 2hrs 3hrs 1hr 2hrs 3hrs
Good
X-
Linked Good
X-
Linked Good
X-
Linked Good
X-
Linked Good
X-
Linked Good
X-
Linked
Table 9
Thermal Stability

[0057] Thermal stability of the hydraulic fracturing fluid of the present invention was compared to conventionally known hydraulic fracturing fluid prepared using 2%KCL as clay hydration suppressant. Thermal stability was observed on HPHT Rheometer at constant shear rate of 100 s-1 at a temperature of 90oC. The results are shown in table 10 and figs. 4 and 5.

Chemical Formulation Avg. viscosity (cP) at 100 s-1 at 90oC
2% KCl+0.5% FHGG +0.05% Soda Ash+ 0.05% Caustic Soda+0.1% Sod. Thio+0.03 % Borax 650
1.5 % CHS+0.5 % FHGG+0.05 % Soda Ash+ 0.05 % Caustic Soda+0.1 % Sod. Thio+0.03% Borax 700
Table 10

[0058] It is observed from table 10 that the cross-linked fluids prepared with 2% KCl or 1.5% polyamine are stable at 90oC for more than 02 hours in absence of APS.

Breaking Tendency

[0059] Optimization of breaker dosage was carried out for smooth flow back. The breaking tendency of the cross-linked fluid in presence of APS was evaluated at elevated temperature and the data are tabulated in table 11.

Formulation Breaking tendency at 90±20C after (minutes)
30 60 90 120 150 180
0.5% FHGG + 0.1%Sod. Thiosulphate + 0.05% Soda Ash + 0.05% Caustic Soda +1.5% CHS +0.03% Borax + 0.015% APS Loose
X-linked Broken Gel Broken Gel Broken Gel Broken Gel Broken Gel
0.5% FHGG +0.1%Sod. Thiosulphate + 0.05% Soda
Ash + 1.5% CHS + 0.05% Caustic Soda
+0.03% Borax +0.0125% APS Good
X-linked Loose
X-linked Very loose
X-linked Very loose
X-linked Broken Gel Broken Gel
0.5% FHGG +0.1%Sod. Thiosulphate + 0.05% Soda
Ash +1.5% CHS + 0.05% Caustic Soda
+0.03% Borax + 0.01% APS Good
X-linked Good
X-linked Loose
X-linked Loose
X-linked Very loose
X-linked Broken Gel
Table 11

[0060] The results indicate that the hydraulic fracturing fluid prepared with 1.5% CHS and 0.01% APS is stable up to 150 minutes.

Core Flow Study

[0061] Core flow experiment was carried out to study the ability of polyamine and KCL to inhibit clay swelling and migration of fines into reservoir. Core flow study was carried out using Matrix Acidization Tester 700 equipment by passing innovated product solution through Berea core. The decrease/increase in permeability was observed with respect to pore volumes. The change in instant permeability was recorded. The details of the core samples and result are given in table 12 below.

Mineralogy of NGM Field Core sample
Mineral Concentration, wt.%
Quartz 57.9
Muscovite 1.4
Ilmenite 1
Siderite 8.4
Pyrrhotite 0.9
Kaolinite 17.9
Chlorite 6.1
Illite 2.5
Illite-montmorillonite 0.8
Calcite 1.1
Barite 2.0
Table 12

[0062] As shown in fig. 6, in the core flow studies performed with KCl, a permeability decrease of up to 36% was observed due to fine generation of particles as observed in the outlet sample. The decrease in permeability indicates that the fine particles penetrate into reservoir and affect the porosity and permeability. This restricts the flow movement of reservoir fluid and hampers the productivity.

[0063] As shown in fig. 7, in the core flow studies performed with polyamine, the permeability remains unchanged as no fine generation of particles observed in the outlet sample. The permeability remaining unchanged shows that a high degree of inhibition and minimization of fine generation of clay particles.

Corrosion Test

[0064] Corrosion study was carried out to compare the corrosion reduction ability of clay hydration suppressant added to the hydraulic fracturing fluid vis-à-vis conventionally used potassium chloride. The corrosion test was carried out with N/80 steel coupon at 120°C temperature & 1000 psi pressure.

Sl. No Formulation Corrosion Rate (mpy) Surface Morphology of Coupon after experiment
1 2% Potassium chloride 3.144 The coupon became blackish in colour and very little pit was observed
2 1.5% Polyamine 0.022 The coupon became brown in colour and no pit was observed

Field Implementation

[0065] The hydraulic fracturing fluid of the present invention was implemented in a hydraulic fracturing operation in western onshore fields of India. The results are shown in table 13 and figs. 8-10.

Sl. No JOB DETAILS
Well No NGM#329 AMD#259 AMD#248
1 Pad (bbls) 380 380 380
2 With Proppant (bbls) 750 710 760
3 Flush (bbls) 27.8 29.5 29.0
4 Under flush (bbls) 0 0 6
5 Average Treating Pressure (psi) 3883 3414 3791
6 Max Treating pressure (psi) 4243 3700 7073
7 Average Annulus Pressure(psi) 2355 1800 1200
8 Max Annulus Pressure (psi) 3003 2300 NA
9 Break down Pressure (psi) - - -
10 BH ISIP (psi) 2471 1792 1298
11 Max Pumping rate (bpm) 17 16.9 16.6
12 Max Proppant Conc. (ppg) 7 7.1 7
13 Proppant quantity used (MT) 60 MT 50 MT 50 MT
Table 13
Production Details after hydraulic fracturing

[0066] A significant improvement was observed in the onshore fields in terms of cumulative production which indicates that the hydraulic fracturing fluid of the present invention imparts high degree of inhibition and able to arrest deeper penetration of fines particle to keep the porosity and permeability of reservoir healthy. The production details of onshore fields after hydraulic fracturing are tabulated in table 14.

Well No. Tonnage Proppant Pre-Job
Production
(m3/d) Post-Job
Production
(m3/d)
NG-329 60 LSP 20/40 0 2.2
AM-259 50 LSP 20/40 5.0 25.0
AM-248 50 LSP 20/40 0 2.0
WSBN-16 50 ISP 20/40 0 11.0
JTN-267_Z 60 LSP 20/40 0 8.0
Table 14
[0067] While the exemplary embodiments of the present invention are described and illustrated herein, it will be appreciated that they are merely illustrative. It will be understood by those skilled in the art that various modifications in form and detail may be made therein without departing from the scope of the invention.

, Claims:We Claim:

1) A hydraulic fracturing fluid composition, comprising:
a biocide in an amount ranging from 0.01-0.04% w/v;
a thermo-stabilizer in an amount ranging from 0.08-0.20% w/v;
a viscosifier in an amount ranging from 0.30 to 0.60% w/v;
a buffering agent having a weak base and a strong base, wherein the amount of weak base is in a range from 0.04–0.06% w/v and the amount of strong base is in a range from
0.04–0.06% w/v;
a non-emulsifier in an amount ranging from 0.3–0.6% w/v;
a cross-linker in an amount ranging from 0.02–0.04% w/v;
a breaker in an amount ranging from 0.005-0.02% w/v; and
a clay hydration suppressant in an amount ranging from 1.0 - 1.5% w/v,
wherein the clay hydration suppressant is a polyamine having at least 30 amines and a molecular weight having m/z range of 1500–2500.

2) The composition as claimed in claim 1, wherein the biocide is selected from a group comprising of glutaraldehyde, chlorophenate and isothiazoline.

3) The composition as claimed in claim 1, wherein the thermo-stabilizer is selected from a group comprising of sodium sulfite, sodium thiosulphate, sodium erythorborate, methanol, thiourea and mixtures thereof.

4) The composition as claimed in claim 1, wherein the viscosifier is selected from a group comprising of gelling agent, fast hydrating guar gum, hydroxypropyl guar (HPG), and carboxymethyl hydroxypropyl guar.

5) The composition as claimed in claim 1, wherein the weak base is selected from a group comprising of sodium carbonate, potassium carbonate, sodium bicarbonate and potassium bicarbonate.

6) The composition as claimed in claim 1, wherein the strong base is selected from a group comprising of potassium hydroxide and sodium hydroxide.

7) The composition as claimed in claim 1, wherein the non-emulsifier is selected from a group comprising of phenolic, esters, ethers, ether-esters based compounds, and a non-ionic phenolic base including nonyl phenol.

8) The composition as claimed in claim 1, wherein the cross-linker is selected from a group comprising of borax, titanium, zirconium, or aluminum complexes.

9) The composition as claimed in claim 1, wherein the breaker is selected from a group comprising of ammonium persulphate, sodium salts of peroxidisulphate, potassium salts of peroxidisulphate, sodium bromate and enzymes breaker.

10) The composition as claimed in claim 1, wherein pH of the hydraulic fracturing fluid is in a range from pH 11–12.

11) The composition as claimed in claim 1, wherein viscosity of the hydraulic fracturing fluid is 700 Cps at 90oC.

12) The composition as claimed in claim 1, wherein density of the hydraulic fracturing fluid is in a range from 1.01 to 1.03 g/m3.

13) The composition as claimed in claim 1, wherein the hydraulic fracture fluid composition exhibits a reduction in clay swelling of 36%.