Fluid loss control agents for viscoelastic surfactant fluids

This application is a divisional patent application of U.S. patent application Ser. No. 11/755,581 filed May 30, 2007 which claims the benefit of U.S. Provisional Application No. 60/815,693 filed Jun. 22, 2006; and is a Continuation-in-Part of U.S. patent application Ser. No. 11/125,465 filed May 10, 2005, which in turn claims the benefit of U.S. Provisional Application No. 60/570,601 filed May 13, 2004.

The present invention relates to aqueous, viscoelastic fluids used during hydrocarbon recovery operations, and more particularly relates, in one non-limiting embodiment, to methods and additives for controlling the fluid losses thereof.

Hydraulic fracturing is a method of using sufficient pump rate and effective hydraulic pressure to fracture or crack a subterranean formation. Once the crack or cracks are made, high permeability proppant, relative to the formation permeability, is pumped into the fracture to prop open the crack. When the applied pump rates and pressures are reduced or removed from the formation, the crack or fracture cannot close or heal completely because the high permeability proppant keeps the crack open. The propped crack or fracture provides a high permeability path connecting the producing wellbore to a larger formation area to enhance the production of hydrocarbons.

The development of suitable fracturing fluids is a complex art because the fluids must simultaneously meet a number of conditions. For example, they must be stable at high temperatures and/or high pump rates and shear rates which can cause the fluids to degrade and prematurely settle out the proppant before the fracturing operation is complete. Various fluids have been developed, but most commercially used fracturing fluids are aqueous based liquids which have either been gelled or foamed. When the fluids are gelled, typically a polymeric gelling agent, such as a solvatable polysaccharide is used, which may or may not be crosslinked. The thickened or gelled fluid helps keep the proppants within the fluid during the fracturing operation.

While polymers have been used in the past as gelling agents in fracturing fluids to carry or suspend solid particles in the brine, such polymers require separate breaker compositions to be injected to reduce the viscosity. Further, the polymers tend to leave a coating on the proppant even after the gelled fluid is broken, which coating may interfere with the functioning of the proppant. Studies have also shown that “fish-eyes” and/or “microgels” present in some polymer gelled carrier fluids will plug pore throats, leading to impaired leakoff and causing formation damage. Conventional polymers are also either cationic or anionic which present the disadvantage of likely damage to the producing formations.

Aqueous fluids gelled with viscoelastic surfactants (VESs) are also known in the art. VES-gelled fluids have been widely used as gravel-packing, frac-packing and fracturing fluids because they exhibit excellent rheological properties and are less damaging to producing formations than crosslinked polymer fluids. VES fluids are non-cake-building fluids, and thus leave no potentially damaging polymer cake residue. However, the same property that makes VES fluids less damaging tends to result in significantly higher fluid leakage into the reservoir matrix, which reduces the efficiency of the fluid especially during VES fracturing treatments. It would thus be very desirable and important to discover and use fluid loss agents for VES fracturing treatments in high permeability formations (SPE 31114).

T. Ito et al. in “Adsorption of Methane on Magnesium Oxide Studied by Temperature-Programmed Desorption and ab Initio Molecular Orbital Methods”, The Journal of Physical Chemistry, 1991, Vol. 95, page 4476, examined chemisorption of methane on magnesium oxide clusters by means of ab initio molecular orbital methods. In this study it was shown that methane heterolytically dissociates on the nearest pair of three-coordinated surface magnesium and oxygen atoms which were the most active sites. I. Onal, et al. in “Quantum Chemical Study of the Catalytic Oxidative Coupling of Methane”, Industrial & Engineering Chemistry Research, 1997, Vol. 36, pages 4028-4032, studied that the surface of MgO catalyst was modeled by a Mg₉O₉ molecular cluster containing structural defects such as edges and corners.

There is provided, in one form, a method for treating a subterranean formation that involves an aqueous viscoelastic treating fluid. The fluid includes an aqueous base fluid, a viscoelastic surfactant (VES) gelling agent in an amount effective to increase the viscosity of the aqueous base fluid, and an amount of a fluid loss control agent effective to improve the fluid loss of the aqueous viscoelastic treating fluid as compared with an identical fluid absent the agent. The agent may be an alkaline earth metal oxide, an alkaline earth metal hydroxide, a transition metal oxide, a transition hydroxide, or a mixture thereof. The method involves injecting the aqueous viscoelastic surfactant treating fluid through a wellbore and to the subterranean formation; and treating the subterranean formation.

There is further provided in another non-limiting embodiment an aqueous viscoelastic treating fluid that includes an aqueous base fluid, a VES gelling agent, and an amount of fluid loss control agent effective to improve the fluid loss as compared with an identical fluid absent the agent. Again, the additive may be an alkaline earth metal oxide, an alkaline earth metal hydroxide, a transition metal oxide or transition metal hydroxide, or a mixture thereof. Again, the amount of the VES gelling agent is that effective to increase the viscosity of the aqueous base fluid, typically water or brine.

The fluid loss control agents (e.g. MgO and/or MgOH₂, and the like) appear to help develop a pseudo-filter cake of VES micelles by associating with them as well as ions and particles (in one non-restrictive explanation) to produce a novel and unusual viscous fluid layer of pseudo-crosslinked elongated micelles on the reservoir face that limits further VES fluid leak-off. Additionally, the art may be further advanced by use of nanometer-sized fluid loss control agents that also form a similar viscous fluid layer of pseudo-crosslinked micelles on the formation face that are equivalent to micron-sized fluid loss control agents herein in controlling rate of VES fluid loss, yet can be non-pore plugging and physically easier to produce back with the VES fluid after a VES treatment. That is, the effectiveness of the method is largely independent of the size of the fluid loss control agents. The use of MgO for fluid loss control also has utility over a broad range of temperature of about 70° F. to about 400° F. (about 21° C. to about 204° C.).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph of leakoff as a function of time for tests with 400 md ceramic discs at 250° F. (121° C.) and 300 psi (2.1 MPa) for different fluid loss control agents, where the base fluid was 13.0 ppg (1.6 kg/liter) brine, 4% VES, 6 pptg (0.7 kg/m³) stabilizer and 1 gptg internal breaker (SI units of gallons per thousand gallons have the same value for any convenient SI unit; e.g. liters per thousand liters or m³/1000 m³, etc.);

FIG. 2 is a graph of leakoff as a function of time for tests with 2000 md ceramic discs at 250° F. (121° C.) and 300 psi (2.1 MPa) for different fluid loss control agents, where the base fluid was 13.0 ppg brine (1.6 kg/liter), 4% VES, 6 pptg (0.7 kg/m³) stabilizer and 1 gptg internal breaker;

FIG. 3 is a graph of leakoff as a function of time for tests with 400 md ceramic discs at 150° F. (66° C.) and 300 psi (2.1 MPa) for different fluid loss control agents, where the base fluid included 3% brine, 4% VES and 2 gptg internal breaker;

Continue reading about Fluid loss control agents for viscoelastic surfactant fluids...
Full patent description for Fluid loss control agents for viscoelastic surfactant fluids

Brief Patent Description - Full Patent Description - Patent Application Claims

Click on the above for other options relating to this Fluid loss control agents for viscoelastic surfactant fluids patent application.
###


How KEYWORD MONITOR works... a FREE service from FreshPatents
1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored.
3. Each week you receive an email with patent applications related to your keywords.  
Start now! - Receive info on patent apps like Fluid loss control agents for viscoelastic surfactant fluids or other areas of interest.
###


Previous Patent Application:
Surfactants for hydrocarbon recovery
Next Patent Application:
Lubricant composition with improved varnish deposit resistance
Industry Class:
Earth boring, well treating, and oil field chemistry

###

Design/code © 2009 FreshContext LLC/Freshpatents.com. Website Terms and Conditions - Also read: About this Page
Patent data source: patents published by the United States Patent and Trademark Office (USPTO)
Information published here is for research/educational purposes only (and in conjunction with our Keyword Monitor) and is not meant to be used in place of the full USPTO patent document/images or a comprehensive patent archive search. Complete official applications are on file at the USPTO and often contain additional data/images (Freshpatents is currently text-only). FreshPatents.com is not affiliated with or endorsed by the USPTO or firms/individuals or products/designs/ideas related to listed patents.

FreshPatents.com Support
Thank you for viewing the Fluid loss control agents for viscoelastic surfactant fluids patent info.
IP-related news and info


Results in 3.3155 seconds


Other interesting Feshpatents.com categories:
Novartis , Pfizer , Philips , Polaroid , Procter & Gamble , paws