CA2318297A1

CA2318297A1 - Fracturing fluid

Info

Publication number: CA2318297A1
Application number: CA002318297A
Authority: CA
Inventors: Kewei Zhang
Original assignee: Trican Well Service Ltd
Current assignee: Trican Well Service Ltd
Priority date: 2000-09-01
Filing date: 2000-09-01
Publication date: 2002-03-01
Also published as: AU2001287435A1; WO2002018745A3; WO2002018745A2

Abstract

A subterranean fracturing fluid includes a surfactant, specifically a cationic surfactant and an organic salt in an aqueous medium. The fluid can be foamed for fracturing applications without employing an additional foaming surfactant.

Description

SEP-01-00 05;44PM FROM-STIKEMAN, ELLIOTT +6132308877 T-657 P.04/20 F-972 BACXCG>(tOUND of THE INVENTION
FIELD OF THlE INVENTION
This invention relates to a fracturing fluid and to a method of using the fluid tQ
fracture a subterranean formation to increase the permeability of the formation.
More specifically, the invention provides a viscoelastic surfactant-based fracturing fluid and foam, and, the use of the fluid or foam to fracture a subterranean formatioxt and transport proppant into thus created fractures.
BACKGROUND OF THE INVENTION
I-Iydraulic fracturing has begirt used for many years to stimulate the production of petroleum from s~tbterrarrear< formations. In hydraulic fracturing, a fracturing fluid is injected through a wellbore into the formation at a pxessure and flow rate sufficient to overcome the overburden stress and to initiate a fracture in the formation.
Frequently, a pra~partt, the function of which is to prevent the created fracture from closing when the pressure is released, is suspended in the fracturing fluid for transport into a fracture. Proppants in use include, for example 20-~U mesh sine sand and ceramics, the mast common proppant being sand. '1'he prappant filled fractures provide permeable channels allowing petroleum to seep through the fractuxes into the wellbore from whence it iu pumprd tn the surface. Accordingly, good fracturing fluid should have the following properties: (a} compatibility with the reservoir rock and reservoir fluids, (b) sufficient viscosity and fluid structure to suspet'td proppants and transport them deep into the formation, (c) enough stability to retain sufficient viscosity and Quid SEP-01-00 05:45PM FROM-STIKEMAN, ELLIOTT +6132306677 T-657 P.05/20 F-972 structure throughout proppant placement, (d) lQw fluid loss properties and.
law fluid flow friction pressures, (e) easily removable from the formation with little residues, (f) easily made under field conditions and (g) relatively inexpensive. Production of petroleum can be enhanced significantly by the use of speeiali2ed fracturing fluids, which exhibit high levels o~ rheplogical performance.
Fracturing fluids in common use include various aqueous and hydrocarbon gels.
The gels are formed by introducing cross-Iinkable pplymers or surfactants into an aqueous or hydroce~rban fluid, followed by cross-linking of the polymer or surfactant molecules. '~'he cross-linking give the fluid high viscoelastic properties that are necessary to transport and place proppants into the ~ractures.
Viscaelasac suxfactarrts have long been used far well stimulation. A
surfactant is a type of substance, which contains bt~th hydrophobic and hydrophilic groups in the same molecule. The hydrophobic group is usually one of a vaxiety A~ alkyl groups and the hydrophilic group can be ionic, i.e. positive (cationic), negative (anionic) or contain both positive and negative moieties (amphoteric), ar nonionic - often consisting of a neutral polyoxyalkylene group. When dissolved in an aqueous medium, surfactants generally farm various aggregates called micelles if the surfactant concentration is above a critical micelle concentration (cme). At low concentration of surfactant, the micelles usually are smal3 and spherical. Under certain conditions and sux~actant concenxrations, the spherical micelles grow in size and/or change their shape resulting in the formation of long flexible micelles. Above a certain concentration, the long SEP-O1-00 05:45PM FROM-STIKEMAN, ELLIOTT +6132308877 T-657 P.06/20 F-972 flexible micelles can become entangled and exhibit strong viscoelastic behavior. 1~ven though this feature has been observed in a number of systems containing nonionic and anionic surfactants, the effect is more pronounced in cationic surfactants, especially those containixtg an amixte or quaternary amrnoruum group, in the presence of certain argar~ic counterions such as, for example salicylate, betuonate and alkyl sulfonate.
ViscQelastic surfactant fluids have been studied extensively in recent years and have found a wide variety of uses.
LT.S. Patent No. 4,061,580, issued to R.W. )ahnke on December 6,1977 discloses surfactant gelled fracturing and aczdizing fluids suitable far well stimulation. The gelled fluids are prepared by addixig certain amine salts to agueous acid ox salt solutions. The amine salts used as thickeners are prepared by merely mixing one equivalent of amine per equivalent of acid or, in the case of polybasic acids such as sulfuric and phosphoric acids, as little as one-half equivalent of amine per equivalent of acid may be used resulting in the formation of art acidic salt. The aqueous acid ox salt solution can be gelled by the addition of the above-described salts- pot example,159~
by weight of HCI can be gelled by the addition of a small amount, usual 3-l~~
by weight and typically about 5~ by weight of an antir<e or amirve salt as described above.
Fox fracturing fluids, aqueous solutions containing some inorganic salts can be gelled by the addition of 3-~0~. by weight, preferably about 5% by weight, of an amine salt described above.

SEP-O1-DO 05:45PM FROM-STIKEMAN, ELLIOTT +6132308877 T-651 P.07/20 F-972 1J.S. Patent No. 4,163,727, issued to C.G. Inks an August 7, 1979 discloses an acidizing-gel composition which consists essentially of, for example, approximately 15%
by weight of HCI, approximately 2D~o by weight of a suitable nonionic gel-farmiztg surfactant containing oxyethylene and oxyprapylene units, a corrosion inhibitor to the extent needed, and the balance water.
U.S. Patents Nos. 5,551,516, issued to W.D. Norman et al on September 3,1996 and 5,964,295, issued to J.F. Brown et al on October 12, 1999 disclose a fracturing fluid composition comprising a quaternary ammonium salt, erucyl bis (2-hydraxyethyl) methyl ammonium chloride, an organic salt such as radium salicylake, inorganic salts such as amtxtonium chloride and potassium chloride and water. The patents state that the fluid has good viscoelastic properties and is easily formulated and handled.
Furthermore, very little if any residue is left in a formation after the completion of the fracturing process.
Anpther widely used fracturing fluid is a foamed, water-based fracturing fluid.
Foams are defined as dispersions of gas in a liquid. Typically, foamed fluids contain sufficient amount of surfactants in an aqueous liquid. The composition of the foamed fluid is such that the quality of the foam at the bottom of the well is in the range of from about 53°~6 to 90~. The pressure at which the foamed fluid is pumped into the well is high enough to initiate and extend a fracture in the hydracarbanwbearing formakion.
Foamed fracturing fluids, which contain a significant quantity of gas, have several advantages over cunvenkional fracturing fluids. Firstly the gas aids in cleanup after the SEP-01-OO 05:46PM FROM-STIKEMAN, ELLIOTT +613230888 T-657 P.06/20 F-9T2 completion of the hydr2~uli~c fratfi~.ring process. The gas "energizes" the fluid, and when the pressure is decreased, such as by producing fluids from the well, the gas expands and drives much of the liquid component of the fracturing fluid out of the farrnatian.
9ecoridly, foams have a lower liquid content compared to conventional fracturing fluids and therefore are less likely to cause formation damage. As aqueous fluids invade a formation, they can sometimes cause formation damage by interacting undesirably with the formation ur by interfering with gas and/ or oil flow into the wellbore causing a decrease in the relative permeability-A water based foamed fracturing fluid is described, for example in U.S. Patent No. 3,980,136, issued to R.A. Plummet et aI on September 14, 3976. Briefly, the foamed fracturing process described iri the patent involves generation of foams with a desired quality and stability which are pumped through a wellbore into a #ormation.
US Patent No. ~ ?58,137 issued to Bonekamp et al ors November 2,1993 discloses a viscoelastic surfactant-based foamed fracturing-fluid. The fluid includes a catiori.ic surfactant, namely an alkyltrimethyl ammonium chloride, whexein the alkyl gxoup is a long chain alkyl having 12-2? carbon atoms which may be saturated or contain one or more double bonds, with an organic salt such as sodium salicylate to associate with the cationic surfactant to form a viscoelastic surfactant iz~ an aqueous fluid, and a foaming surfactant irt order to have sufficient foam quality. ~'he viscoelastic suxfactant-based foamed fluids are said to have high foam quality and stability and therefore good SEP-01-00 05:46PM FROM-STIKEMAN, ELLIOTT +6132308877 T-657 P.09/20 F-972 leak-off properties.
As disclosed, fox example, in US Patent No. 5,575,335 issued to King on November 19,1996 and in US Patent No. 5,711,376 issued to Sydansk on ]anuary 27, 1998, it has become a common practice to incorporate various polymexs into the foamed fracturing fluids in order to increase the viscosity of the fluid and the foam stability to transport a high concentration of pxoppant and provide more favourable leakoff properties. Natural polymers such as guar gums and them derivatives are commonly used. Typically a polymer has to be hydrated above ground before being pumped into the formation. The process of polymer hydration is time consuming and often requires bulky equipment at the well site. Moreover, the viscosity of such compositions can change substantially with variations in terr~perature, and the compositions are shear degradable, can have short shelf lives, and can leave a significant amount of polymer residue is in the formation having r<egative impact on formation permeability.
Moreover, the fluid is formation benign in the sense that very little, if any residue is left in the formation upon cornpletian of the fracturing process. However, the fluid disclosed in $oneka~np (supra) requires the introduction of an additional foaming surfactant into the viscoelastic surfactant base get in order to have sufficient foam quality and stability.
SUMMARY of THh INVhI~ITION
An object of the present invention is to overevme the disadvantages itinerant to existing palyrner-based fracturing fluids by providing a surfactant-based fracturing B

SEP-Oi-OD 05:46PM FROM-STIKEMAN, ELLIOTT +6132306877 T-657 P.10/20 F-972 fluid, which leaves no sigtuficant residue in a subterranean formation upon completion of the fracturing process.
Another abject of the pxesent inverttian is to overcome the disadvantages iriherertt to existing fracturing fluids by providing a surfactant-based fracturing fluid having relatively good foamir4g capa>aility arid foam stability over a wide range of temperatures without employing additional foaming surfactants.
According to one aspect, the invention relates to a fracturing fluid comprising an aqueous medium, at least one cationic surfactant and at least one oxganic salt havit'tg the general formula.
W-M
wherein W is ors Qrganic anion and M is a canon.
According to a second aspect, the invention relates to a method of fracturing a subterranean formatior< comprising the step of injecting a fracturing fluid into the formation at a pressure sufficient to ir<itiate fracturing, said fluid including an aqueous medium, at least one cationic sur#actant arid at Ieast one organic salt having the general formula Rl-M
wherein R~ is an organic anion, and M is a catiort. The composition may also be formed intp a gei of desired viscosity for a particular application by selecting an appropriate SEP-O1-00 05:47PM FROM-STIKEMAN, ELLIOTT +6132308877 T-657 P.11/20 F-972 combination of cationic surfactant and an arganic salt.
DESCRII'TiON QF THE PR~FERR~~ >l=1Vi>3ppI11~ENT
The cationic surfactant has a saturated ar ur~aturated alkyl group containix~g 22 carbon atoms- The general formula of the cationic surfactant is ~3 I
R-N-CHsX
I
CHs where R is an hydrophobic group and X is an anionic group. The group R can be aliphatic, straight or branched, saturated or unsaturated containing 14-22 carban atoms.
The group P can suitably be tetradecyl, hexadecyl, octadecyl, oleyl and tallow.
The composition of the invention includes an acjueous medium, at least one cationic surfactant and an organic salt. The fluid may also contain a gas, for example N2 or CO~
and thus be in the farm of a foam. The composition also has excellent foaming capability and foam stability within wide temperature ranges without employing additional foaming surfactants.
The organic salt has the general formula where ~l is an organic anion selected from the group consisting of 3-hydraxy-2-naphchalenecarboxylate, cumene sulphonate, salirylate and toluene sulphonate, and M

SEP-O1-00 05:47PM FROM-STIKEMAN, ELLIOTT +6132308877 T-657 P.12/20 F-972 is a canon preferably a mortovalent canon such a5 sodium.
Apart from the cationic surfactants and organic electrolyte salts, the aqueous-medium may contain a number of conventional components such as clay stabilizers, anti-freeze agents arid bactericides. In addition, a foam of desired stability far a particular practical application can be created by selecting a proper cornbiriation of cationic surfactant and organic salt The preferred cationic surfactant is a tallow trimethyl ammonium salt pr halide.
Dther cationic surfactants which may be employed either alone or in combination include octadecyl trimethyl ammonium salts or halides, cetyl trixnethyl amntoruum salts or halides, tetradecyl trirnethyl ammonium salts or halides and nurtures thereof.
By "aqueous-medium" is meant that at least 50°~° by weight, preferably at least 9Q96 by weight, of the water-based liquid system consists of water. The combination of the specific cationic surfactants and the organic salts provides an excellent #oaming capability and foaming stability within a wide temperature range. ~'he carbon numbers of the hydrophobic groups lZ will usually determine the useful temperature range for the mixture, high carbon numbers usually yielding products suitable for high temperatures.
Tlte present invention is described below in greater detail by means of the following examples.

SEP-O1-00 05:4TPM FROM-STIKEMAN, ELLIOTT +613230888 T-65T P.13/2D F-912 E7CAMI'LE~
Foaming properties of the compositions according to the preser~t ixwention were tested by a simple method involving the measuring foam volume and of foam half-life.
Fxumpl~ 1 0.5 g of octadecyl trimethyl ammonium chloride (hereinafter referred to as OTAC) with the Str~.acture eH3(cHr)~~ N(CH3)3c1 (hereinafter referred to as OTAC) and 0.5b g of sodium toluene sulphonate, CHs~aH9503Na (hereirtaftex referred to as STS) were mixed with 2~m1 of tap water.
A clear viscoelastic gel was formed. The resulting gel was poured into a 1 litre blaring blender jar and mixed at maximum blender speed for 30 secr~xlds. The resulting foam was poured into a 1000 ml graduated cylinder, and a tuner was started. The foam volume and foam half life were measured. (the foam volume is the maximum volume occupied by the foam, and cart be used to calculate foam quality, and the foam half-life is the time required fox 100 ml of solution to accumulate on the bottorrt a~f the graduated cylindex). The results axe listed in Table 1.
Example 2 0.5 g of OTAC and 0.~ g of sodium salicylate (hereinafter referred to as SS) were mixed in 200 ml of tap water A clear viscoelastic gel was formed. The gel was tested in the same manner as described in ~x.ample 1. The results are listed in Table 1.

SEP-O1-00 05:41PM FROM-STIKEMAN, ELLIOTT +6132308811 T-651 P.14/20 F-912 ExRmpIe 3 p_5 g of tallow trimethyl ammonium chloride (hereinafter called TTAC) and A.1.7 g of the sodium salt of 2-hydraxy-3-naphthoic acid, W ol~ib (~f~) ~~Na (hereinafter referred to as Na-BON) in aqueous NaOH salutiort were mixed in ?00 ml of tap water.
A clear viscoelastic gel formed. The gel was tested in the same manner as in >Eacample 1. The results are listed in Table I.
Example 4 0.5 g of '~'AC and U.18 g of the sodium salt of cumene sulphanate (hereinafter called SCS) were mixed in 200 ml of tap water. A clear viscoelastic gel formed. The gel was tested in the same maruier as in example 1 and the results are listed in Table I

SEP-D1-00 05:48PM FROM-STIKEMAN, ELLIOTT +6132308877 T-657 P.15/2D F-972 Table I
Composuron Foam Volume Foam Half life '1 CTAC O.2S% 450 ml 27 min.

STS 0.28%

2 OTAC 0.25% 450 ml b5 min.

S S 0.20%

3 TTAC 4.25% S40 ml 62 min.

Na-BQN 0.0$"/0 NaOH 1.0%

4 TTAC U.25% 500 ml 2U min SCS 4.09%

Example 5 3.0 g of OTAC was first dissralved in 300 ml of tap water. The resulting solutipn was mixed with 2.2g o~ STS. A clear gel was formed. The viscosity of the gel was measured using a BrQolcfield viscometer (Model LVT, Spindle 2) at room temperature.
The results are listed in Table II
Example 6 3.0 g of TTAC was dissolved in 300 ml of tap water. The resulting solution was mixed with 2.2 g of STS. A clear gel formed. The gel was tested in the same manner as in Example 5. The results axe shown in Table II.
~'xample 7 3.0 g of aTAC was dissolved in 300 ml of tap water. The resulting solution was SEP-O1-00 05:4BPM FROM-STIKEMAN, ELLIOTT +6132306877 T-657 P.16/20 F-972 mixed with 0.72 g active substance of ~'aS). A clear gel formed. The gel was tested in the same manner as in Example 5. The results are shown in Table II.
Example 8 4.5 g of TTAC and 1.26 g of of Na-BON in aqueous NaOH solution were mined in 300 ml of tap water. A clear gel was formed_ 'f'he gel was tested in the same manner as in Example 5_ T ~e results are listed in Table lt.
Table II
Corn os~t~dnS 1RSCOsIt1 P els oTAC 1.0 ~

STS 0.796 10,'00 cp 2. OTAC 1.0r6 STS 0.73~ g,~0 cp 3. OTAC 1.0~

SS 0.24% 6.~~'p 4. TTAC 1.5~

Na-BOI~i 0.~2% 19,500 cp NaOH 1.0 ~

From the results, it is evident that combinations of the cationic surfactant and an organic salt in an aqueous medium form clear gels with good theological properties.
These gels can be used for hydraulic fracturing application.. Furthermore, the gels cart also be used as foamed fracturing fluids having high foam quality anti stability withaut employing additional foaming surfactant. For applications requiring higher viscosity, higher surfactant lauding is generally required.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A fracturing fluid comprising an aqueous medium, at least one cationic surfactant of the general formula wherein R is a hydrophobic group and X is an anionic group and at least one organic salt of the general formula wherein R, is an organic anion and M is a cation.

2. The fracturing fluid of claim 1, wherein the hydrophobic group R
is a saturated or unsaturated alkyl group containing 14-22 carbon atoms.

3. The fracturing fluid of claim 1, wherein said organic anion R1 is selected from the group consisting of 3-hydroxy-2-naphthalenecarboxylate; cumene sulphonate;
salicylate and toluene sulphonate.

4. The fracturing fluid of claim 1, wherein said cation M is a monovalent cation.

5. The fracturing fluid of claim 2 wherein said hydrophobic group R is selected from the group consisting of tetradecyl, hexadecyl; octadecyl; oleyl;
and tallow.

6. The fracturing fluid of claim 2 or 5, wherein said anionic group X is a monovalent group.

7. The fracturing fluid of any of claims 1 to 6, wherein said cationic surfactant is a tallow trimethyl ammonium halide.

8. The fracturing fluid of any of claims 1 to 6, wherein said cationic surfactant is a tallow trimethyl ammonium salt.

9. The fracturing fluid of any of claims 1 to 6, wherein said cationic surfactant is selected from the group consisting of octadecyl trimethyl ammonium, cetyl trimethyl ammonium and tetradecyl trimethyl ammonium salts and mixtures thereof.

10. The fracturing fluid of any of claims 1 to 6, wherein said cationic surfactant is selected from the group consisting of octadecyl trimethyl ammonium, cetyl trimethyl ammonium and tetradecyl trimethyl ammonium halides.

11. The fracturing fluid of claim 1, wherein said aqueous medium is water, said cationic surfactant is octadecyl trimethyl ammonium chloride and said organic electrolyte is sodium toluene sulphonate.

12. The fracturing fluid of claim 1, wherein said aqueous medium is water, said cationic surfactant is octadecyl trimethyl ammonium chloride and said organic electrolyte is sodium salicylate.

13. The fracturing fluid according to claim 1, wherein said aqueous medium is a solution of NaOH in water, said cationic surfactant is tallow trimethyl ammonium chloride and said organic electrolyte is the sodium salt of 2-hydroxy-3-naphtoic acid.

14. The fracturing fluid according to claim 1, wherein said aqueous medium is water, said cationic surfactant is trimethyl ammonium chloride and said organic electrolyte is the sodium salt of cumene sulphonate.

15. The fracturing fluid according to claim 1, wherein said aqueous medium is water, said cationic surfactant is tallow trimethyl ammonium chloride and said organic electrolyte is sodium toluene sulfonate.

16. A fracturing fluid according any one of claims 1 to 15 including a gas.

17. A fracturing fluid according to claim 16, wherein said gas is N2 or CO2.

18. A method of fracturing subterranean formation comprising the step of injecting the fracturing fluid of any of claims 1 to 17 into the formation at a pressure sufficient to initiate fracturing.