Baker Hughes Incorporated (Houston, TX) earned U.S. 7,703,531 for multifunctional nanoparticles for downhole formation treatments to increase oil and gas production. The amount of nano-sized particles in the viscoelastic surfactant-gelled aqueous fluid may range from about 2.4 to about 60 kg/1000 liters of fluid.
The treatments are formed from an aqueous, viscoelastic fluid gelled with a viscoelastic surfactant (VES) is stabilized with an effective amount of an alkaline earth metal oxide alkaline earth metal hydroxide, alkali metal oxides, alkali metal hydroxides transition metal oxides, transition metal hydroxides, post-transition metal oxides, and post-transition metal hydroxides.
According to inventors Tianping Huang, James B. Crews and John Robert Willingham, these fluids are more stable and have a reduced or no tendency to precipitate, particularly at elevated temperatures, and may also help control fluid loss. When the particle size of the magnesium oxide or other particulate agent is a nanometer scale, for instance having a mean particle size of 100 nm or less, that scale may provide particle charges that use chemisorption, "crosslinking" and/or other chemistries to associate and stabilize the VES fluids, and also help trap or fixate formation fines when deposited into a proppant pack in a fracture.
Hydraulic fracturing is a method of using pump rate and 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 may 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.
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 also used as acid diverting, water and/or gas control fluids. VES fluids are non-cake-building fluids, and thus leave no potentially damaging polymer cake residue.
Baker Hughes provides a nanoparticle method for reducing fines migration in a subterranean formation, but which also gives improved properties to a fluid used in fracturing the formation. The method involves introducing into the subterranean formation an aqueous-based fluid. The fluid may include a viscoelastic surfactant in an amount effective to increase the viscosity of the fluid and proppants.
The fluid also includes a particulate additive in an amount effective to reduce fines migration and further in an amount effective to have an effect of (1) improved stability of the VES-gelled fluid viscosity, and/or (2) improved fluid loss of the VES-gelled fluid, as compared with an otherwise identical fluid absent the nano-particulate additive. The particulate additive has a mean particle size of 100 nm or less.
Suitable materials for the particulate additive include alkaline earth metal oxides, alkaline earth metal earth metal hydroxides, alkali metal oxides, alkali metal hydroxides, transition metal oxides, transition metal hydroxides, post-transition metal oxides, post-transition metal hydroxides, piezoelectric crystals, and/or pyroelectric crystals. The method further includes pumping the fluid against the subterranean formation with sufficient pressure to cause at least one fracture, and depositing the proppants and the particulate additive into the at least one fracture to form a proppant pack.
The nano-sized MgO particles are also suspected of having additional chemistry useful for VES thermal stability. Without being limited to any one particular theory, it is suspected that some nano-sized MgO particles have unique particle charges that use chemisorption, pseudo-crosslinking and/or other chemistries to associate and stabilize the VES micelles. This technical improvement is helpful in the field when applying the MgO stabilizer technology, to assure VES-gelled fluid stability when leaked-off into a reservoir during a frac-pack or other treatment.