Patent Grant
7875574
The present invention relates generally to proppants for fracturing operations for subterranean formations. More particularly, the present invention relates to deformable proppants.
In oil and gas operations, stimulation or treatment of the subterranean formations using a fluid containing suspended particles, referred to as hydraulic fracturing, may be used to improve production. That is, a fluid, referred to in the art as a fracturing fluid, is pumped or injected through a well bore into a subterranean formation to be stimulated at a rate and pressure such that existing fractures are opened and/or new fractures are formed and extended into the subterranean formation. The fracturing fluid carries particles, referred to in the art as proppant particles, into the fractures. The particles are deposited in the fractures and the fracturing fluid dissipates into the subterranean formation and/or is returned to the surface. The particles function to “prop” open or prevent the fractures from closing whereby conductive channels remain through which produced fluids can flow to the well bore.
The paper “Propping Fractures with Aluminum Particles”, Kern L. R. in (Petroleum Technology, June 1961 p. 583) teaches the use of malleable aluminum particles for producing high-conductivity fractures. Kern also teaches that flow capacity may be increased several fold with a sparse distribution of particles, but such flow capacity is limited by both crushing of the propping particles and by embedment of the propping particles in the walls of the formation. Kern teaches that as high loads are applied to the malleable aluminum particles, they deform slightly but do not shatter resulting in an increased bearing area against the formation wall, reducing stress on the malleable aluminum particle and reducing penetration of the malleable aluminum particle into the formation. Kern assesses the performance of nearly spherical aluminum particles which are deformed to produce nearly uniform disks (deformed thickness less than or equal to 0.5 times the original nearly spherical diameter). Kern suggests that malleable aluminum could be used in combination with sand to lower costs (compared to aluminum alone) and to provide a safety net in the event the aluminum does not perform as expected.
Disadvantages of propping with aluminum include limitations associated with the specific gravity of aluminum which restricts the fluids which may be used to place aluminum proppant particles, and the fluid may require special treatment such as viscosification or emulsification, etc., and in addition, as suggested by Kern, the high cost of aluminum is a factor. In addition, formations typically fractured today are very susceptible to damage produced by the fracturing fluid itself. This requires the use of less viscous fluids and physically less liquid (or foam) or gas (nitrogen, carbon dioxide etc.). Less viscous fluids and less volume of liquid or foam or gas means less carrying capacity for proppants, which may mean that proppants may not always enter the fracture or many not be distributed along the full length of the fracture.
U.S. Pat. No. 3,933,205 (Kiel) teaches a method for increasing well productivity by multiple hydraulic fracturing cycles using no proppant (self propping) or using sand as a proppant. The initial cycles are designed to form spalls of the formation material in the fracture and subsequent cycles displace the spalls into the fracture, thus propping the fracture open or creating extensions or branches and propping open the extensions or branches.
However, this method relies on causing formation damage to create the desired spalls and teaches only the use of no proppant or sand as a proppant.
U.S. Pat. No. 5,531,274 (Bienvenu) teaches a high strength, lightweight proppant for use in hydraulic fracturing, having a specific gravity approximately equal to the specific gravity of water. Bienvenu teaches that such a proppant, such as a styrene-divinyl-benzene copolymer bead, set in a formation as a packed mass of particles adjacent to a fracture, will prop open the fracture.
However, when closure stress exceeds the deformation limits of the proppant in the packed mass, the effective permeability of the packed mass (and the related conductivity of the formation) decreases as the proppant is deformed, thus reducing or eliminating the flow channels that normally exist between the particles forming the packed mass.
U.S. Pat. No. 6,059,034 (Rickards et al.) teaches a formation treatment method using deformable particles, the deformable particles formed of a blend of fracture proppant material and deformable particulate. As examples, the fracture proppant material may be a material such as sand, and the deformable particulate may be a material such as polystyrene, as divinylbenzene beads.
However, this blend requires that both materials be blended and sufficiently mixed, and may result in the usual problems with sand type fracturing, such as fines.
It is, therefore, desirable to provide a deformable proppant that avoids the problems of metallic proppants, that is not formed into a deformed packed mass, and can be used on its own without additional proppants to improve stimulation and increase productivity in the fracturing operations of subterranean formations.
It is an object of the present invention to obviate or mitigate at least one disadvantage of previous proppants.
In a first aspect, the present invention provides a non-metallic, substantially deformable, proppant particle that is “elastically flexible” or “plastically compressible” adapted for use alone as a propping agent in subsurface formation fracturing operations at concentrations which will substantially create a partial monolayer. The proppant may be an organic, inorganic, or combination polymer. The proppant may be manmade or naturally occurring. The proppant may be a single polymer or a mixture of polymers to form the particles. The proppant may include a single polymer or a combination of polymers that are layered or coated to create a particle. The proppant may include a solid outer shell or layers of polymer that encase an inner fluid.
Preferably, the proppant has a sphericity of 0.9 to 0.3, tested in accordance with API RP 56. Preferably, the proppant has a roundness of 0.1 to 0.90, tested in accordance with API RP 56.
Preferably, the proppant is shatter resistant under a closure stress. Preferably, the expected closure stress to be resisted is between about 10 MPa and about 80 MPa. More preferably, that closure stress is between about 20 MPa and about 50 MPa.
Preferably, the proppant is resistant to chemical reaction. Preferably, the proppant is adapted to be substantially non-soluble in a formation fluid, and vice versa. Preferably, the proppant is substantially non-permeable. Preferably, the proppant is a material selected from the group of high density polyethylene (HDPE), polyethylene terephthalate (PET), polypropylene (PP), or styrene-divinyl-benzene copolymer.
Preferably, the proppant includes particles having a specific gravity of between about 0.1 and about 2.5. More preferably, the particles have a specific gravity of between about 0.5 and about 2.2. Most preferably, the particles have a specific gravity of between about 0.9 and about 2.0.
Preferably, the proppant has a crush resistance of more than substantially 50 MPa. More preferably, the proppant has a crush resistance of more than substantially 80 MPa.
Preferably, the proppant has an undeformed maximum cross sectional measurement of about 5.0 mm. Preferably, the proppant is formed to have a pre-deformed initial shape, the initial shape comprising a disk, rice-shape, cubeoid, spheroid, or toroid (donut).
In further aspect, the present invention provides a method of treating a subterranean formation with a non-metallic deformable proppant, including the steps of injecting a carrier fluid into the formation, the carrier fluid carrying an amount of the deformable proppant, wherein the carrier fluid is injected at a pressure and a flow rate sufficient to open a fracture (creating a new fracture or opening an existing fracture) in the formation, placing at least a portion of the deformable proppant in the fracture, the deformable proppant forming substantially a partial monolayer in the fracture, and reducing the pressure and/or the flow rate sufficient to allow the fracture in the formation to at least partially close, wherein at least a portion of the deformable proppant remains in the fracture to prop open at least a portion of the fracture.
Preferably, the amount is selected such that the proppant is placed in the fracture in a monolayer about 1.0 layer thick. Preferably, the amount is between about 10 and 40 kg/m3 of carrier fluid. More preferably, the amount is between about 25 and 100 kg/m3 of carrier fluid. Most preferably, the amount is less than about 200 kg/m3 of carrier fluid.
Preferably, the portion of the proppant that remains in the fracture to prop open at least a portion of the fracture is distributed at a proppant concentration, the proppant concentration in kg/m2 being less than 1.088 (r)(SG), wherein r is the equivalent radius of the proppant in millimeters and SG is the specific gravity of the proppant.
Preferably, the fracture is a single or multiple fracture with both generally vertical components and generally horizontal components. The fracture may include a portion that is a generally horizontal fracture.
Preferably, the carrier fluid is a gas (for example CO2, N2), a liquid (for example Water, HC), a foam (for example liquid, gas, and surfactant) or a combination thereof (for example N2+CO2+Water).
Preferably, the proppant is elastically deformed under a closure stress. Preferably, the proppant is plastically deformed under a closure stress. Preferably, the proppant is elastically and plastically deformed under a closure stress. Preferably, the closure stress is between about 20 MPa and about 80 MPa.
Preferably, the proppant has an elastic deformation resistance and a plastic deformation resistance, and the closure stress is greater than the elastic deformation resistance and the closure stress is less than the plastic deformation resistance.
Preferably, the proppant is deformed when a closure stress is applied.
In a further aspect, the present invention provides a method of treating a formation with a non-metallic deformable proppant, comprising the steps of applying a treatment cycle comprising the steps of i) injecting a carrier fluid into the formation, the carrier fluid carrying an amount of the deformable proppant, wherein the carrier fluid is injected at a pressure and a flow rate sufficient to open a fracture in the formation, ii) placing at least a portion of the deformable proppant in the fracture, the deformable proppant forming substantially a partial monolayer in the fracture, and iii) reducing the pressure and/or the flow rate sufficient to allow the fracture in the formation to at least partially close, wherein at least a portion of the deformable proppant remains in the fracture to prop open at least a portion of the fracture, and then repeating the treatment cycle at least one time.
Other aspects and features of the present invention will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments of the invention in conjunction with the accompanying figures.
Embodiments of the present invention will now be described, by way of example only, with reference to the attached Figures, wherein:
a-e are representative simplified drawings of a portion of a fracture propped with a partial monolayer placement of proppant using the substance and method of the present invention;
Generally, the present invention provides a method and substance for propping a fracture in a subterranean formation, such as in hydraulic fracturing operations in the oil and gas production industry used to fracture underground reservoirs bearing oil and gas, to provide or enhance flow channels to improve the fluid conductivity of the formation to provide increased oil and gas production rates.
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The deformable proppant of the present invention may be of a unitary material or may include a core surrounded by a shell. The core may be a fluid (liquid), such as water, hydrocarbon, or other fluid known in the industry. This composite (liquid with shell) design provides a less compressible base and increases the elastic limit while allowing the shell to deform, reducing embedment into the formation. The core may be a gas. This composite (gas with shell) design provides reduced specific gravity.
The proppant and method of the present invention can be used with equipment typically used for fracturing operations known to one skilled in the art, using conventional carrier fluids.
The art has been developing with very high concentrations of proppants and very viscous carriers to substantially create a multilayer proppant pack. The state of the art requires a large amount of proppant to maximize the propping open of the cracks formed in the formation, such as 1,000 kg/m3 of proppant (or more).
Placing that much proppant that is a deformable proppant leads to a “pack” that is deformed into a low conductivity mass by closure stresses in the formation. This leads to the practical necessity that the proppant be spherical and very rigid to allow the spaces in-between individual proppant particle when closely packed act as flow channels (i.e. remaining open even under the closure stress of the formation). However, the rigid particles may then become embedded into the formation when closure stress is applied, leading to lower conductivity or formation damage.
In the present invention, a partial monolayer is formed to prop open fractures. The partial monolayer arrangement allows improved conductivity and the deformable proppant reduces embedment of proppant particles into the formation. In order to obtain the partial monolayer placement of the proppant, the proppant is introduced into the carrier fluid at a relatively low concentration to substantially create a partial proppant monolayer rather than a closely packed multilayer.
The deformable proppant may be any shape, including but not limited to: spherical, disk shaped, rice-shaped, or cubical.
“Proppant concentration” refers to the amount of proppant per unit area of fracture wall (measured on one side only). In US customary units, it is expressed in pounds of proppant per square foot of one wall of fracture. In SI units it is expressed in kilograms per square meter of one wall of fracture face. In SI units, the Deformable Proppant Concentration in kg/m2<1.088 (r) (SG) where r is the equivalent radius of the proppant in millimeters and SG is the specific gravity of the proppant. In US customary units, the Deformable Proppant Concentration in lbm/ft2<5.647 (r) (SG) where r is the radius of the proppant in millimeters and SG is the specific gravity of the proppant.
Two example applications are outlined below:
Case #1
A sandstone formation in Alberta, Canada was treated with conventional fracturing techniques with initial flow rates being too small to measure (TSTM). A similar treatment on the same formation utilizing 2270 kg of light weight polystyrene divinyl benzene deformable proppant (CBM-LWP) with a specific gravity of 1.05 was placed in stages. Each stage was engineered to place proppant within the fracture at a concentration of 0.0825 kg/m2. Proppant was pumped at a concentration between 25 and 150 kg/m3 of carrier fluid. After initial flow back, the well produced measurable gas and the subsequent pressure build up and analysis showed a stimulated well.
Case #2
A dry coal (Horse Shoe Canyon Formation) in Alberta, Canada is normally treated with high rate nitrogen fracturing. A well from the field was fractured using 330 kg of light weight polystyrene divinyl benzene deformable proppant (CBM-LWP) in each of two coal seams. Each stage was engineered to place proppant within the fracture at a concentration of 0.0825 kg/m2. Proppant was pumped at a concentration of approximately 13 kg/m3 of carrier fluid. After initial 300 hour flowback, gas rates were higher than surrounding wells.
As used herein, “crush” means catastrophic failure of the proppant and “deformation” means any change in shape of the proppant.
The above-described embodiments of the present invention are intended to be examples only. Alterations, modifications and variations may be effected to the particular embodiments by those of skill in the art without departing from the scope of the invention, which is defined solely by the claims appended hereto.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2536957 | Feb 2006 | CA | national |
This application is a continuation of U.S. application Ser. No. 11/360,140 filed on Feb. 22, 2006, now abandoned, and claims the benefit of and priority to Canadian Application No. 2536957 filed on Feb. 17, 2006 and issued on Jan. 22, 2008, the entireties of which are herein incorporated by reference.
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| Number | Date | Country | |
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| Parent | 11360140 | Feb 2006 | US |
| Child | 12258810 | US |
