Patent Application
20150218924
The present invention relates to a method for fracturing the earth from a wellbore by over pressuring a fluid(s) and/or gases inside a wellbore under conditions of resonance.
Fracturing the earth from a wellbore is a known technique for enhancing oil production and recovery from an oil bearing bed. A variety of methods have been proposed to create both short and long fractures near a wellbore. One of method is described and claimed in U.S. Pat. No. 5,617,921 by Schmidt et al. wherein a method for initiating and/or extending a fracture in an earth's formation from a well penetrating the formation utilizing a source of high pressure fracturing fluid disposed on the earth's surface which is released to flow into and through the well at a predetermined time to initiate and/or extend the fracture. However, this method requires a significant amount of energy and to have a relatively large diameter tubing string in which to hold a sufficient charge of pressured gas to provide an adequate fracture fluid pressure and flow characteristics.
The use of high pressured gas or other pressured fluid(s) in a wellbore to clean perforations and /or create fractures has been described in U.S. Pat. Nos. 5,669,448 and 5,131,472. These references disclose a method of stimulating a well by suddenly applying pressure to the formation in excess of the fracture gradient pressure and thereafter pumping fluid into the well before the pressure declines below the fracture gradient pressure. In addition, there are other more expensive means of injecting treatment liquids that have been proposed. One such type of approach is to place the treatment liquid in the well and ignite a gas generating propellant in the production string, as shown in U.S. Pat. Nos. 6,138,753; 5,443,123; 5,145,013; 5,101,900; 4,936,385 and 2,740,478. Of more general interest is the disclosure in U.S. Pat. No. 3,029,732 and the principles of how a crack in the earth's formation appears under cyclic loading as described in “Erdogan F. “Crack Propagation Theories”. Fracture, N.-Y., London, Academic Press, 1968, p. 70-77”.
While there have been a variety of methods proposed for creating hydraulic fractures around the wellbore, there remains a need for an effective, high-pressure method which creates a pattern of fractures extending from all perforations into the formation in particular with the required parameters of fractures.
Accordingly, a primary object of the present invention is to provide a method for enhancing of the formation fracturing around a wellbore in the regime of resonance by means of applying a vibrations to the formation surrounding wellbore which is undergoing pressures exceeding the fracture gradient pressure of the formation as a result of pumping of fracturing fluid into a wellbore. In accordance with the invention, the method includes the steps of arranging a device attached to the end of tubing inside the wellbore in the vicinity of perforations, providing a fracturing fluid via tubing into the device for generating vibrations on a resonant frequency fr in accordance with following expression:
where fr is the frequency of resonance, c is a speed of sound in fracturing fluid, π equals 3.1415, r is the required width of fracture, H is a combined thickness of a casing and a cement bond surrounding the casing, W is a distance on a casing arch between an adjacent perforations, L is the required length of fracture.
It is another object of the present invention to provide an apparatus for enhancing of the formation fracturing around a wellbore in the regime of resonance which includes a flow line at the surface supplying a fracturing fluid from a tank via a pump into the wellbore and a flow line having a check valve preventing flow of fracturing fluid from the wellbore back into the flow line, a tubing string connected to the flow line and extending downwardly into the wellbore, an elongated cylinder connected to the bottom of tubing string at the upper end and having an opening to wellbore, a plunger movably arranged within an elongated cylinder to move within the elongated cylinder and having a taper on a lower end of said plunger, the pumping means, accommodated inside a lubricator to prevent the leakage of the fracturing fluid from the tubing and the flow line at the surface, and connected with plunger for moving of said plunger within the elongated cylinder and compressing the fracturing fluid contained between check valve inside the flow line and plunger inside the elongated cylinder and discharging said fracturing fluid into the wellbore via an opening when said plunger exits out of the elongated cylinder on every upstroke of pumping means to generate a vibrations on resonant frequency, and an angle θ of taper on lower end of said plunger is determined by the following expression:
where θ is the angle of taper on lower end of the plunger, φ is a slippage of fracturing fluid between the elongated cylinder and plunger, Sh is Strouhal number, Ls is the length of stroke of the pumping means, D1 is the diameter of plunger, dr is the diameter of pumping means, fr is the resonant frequency, Δt is the discharging time of compressed liquid.
It is another object of the present invention to provide an apparatus for enhancing of the formation fracturing around a wellbore in the regime of resonance in which the length l of said taper on the lower end of plunger is determined by the following expression:
where l is length of taper on the lower end of plunger, D1 is the diameter of plunger, θ is the angle of taper on lower end of the plunger.
Referring to
where fr is the frequency of resonance, c is a speed of sound in the fracturing fluid, π equals 3.1415, r is the required width of fracture, H is the combined thickness of the casing and the cement bond surrounding the casing, L is the required length of fracture, W is a distance on the casing arch between the adjacent perforations. In particularly, for fracturing event shown on
To generate the vibrations on resonant frequency the device for generation of vibrations in accordance with present invention has to have the corresponding angle θ of taper 16 on the lower end of said device determined in accordance with the following formulae:
where θ is the angle of taper on lower end of the plunger, φ is a slippage of the fracturing fluid between the elongated cylinder and plunger (no dimensional), Sh is Strouhal number, Ls is the length of stroke of the pumping means, D1 is the diameter of plunger, dr is the diameter of pumping means, fr is the resonant frequency, Δt is the discharging time of compressed liquid.
For instance for the following parameters: D1=0.08255 m, φ=0.1, Sh=0.21, dr=0.0254 m, Ls=2.8 m, Δt=0.25 sec and resonant frequency fr=38 Hz the corresponding angle θ of taper 16 equals 36°, meanwhile the length l of taper 16 on the lower end of plunger 4 is determined by the following expression:
where l is length of taper on the lower end of plunger, D1 is the diameter of plunger, θ is the angle of taper on lower end of the plunger.
Thus for above noted parameters (D1=0.08255 m and θ=36°) the length l of taper 16 can vary in the range of 0.008255 m to 0.05681 m depending on particular design of elongated cylinder 3.
As an alternative source of the said vortices generating the vibrations on resonant frequency, for instance, can be used the devices described in U.S. Pat. No. 6,015,010 and No. 6,899,175.
While in accordance with the provisions of the Patent Statutes the preferred forms and the embodiments of the invention have been illustrated and described, it will be apparent to those of ordinary skill in the art various changes and modifications may be made without deviating from the inventive concepts set forth above.
