Wells – Processes – With indicating – testing – measuring or locating
Reexamination Certificate
1999-04-15
2001-11-13
Bagnell, David (Department: 3672)
Wells
Processes
With indicating, testing, measuring or locating
C166S122000, C166S134000, C166S212000
Reexamination Certificate
active
06315041
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to the field of oil and gas well stimulation, and more particularly, to isolating segments of a subterranean cased or open hole well for stimulating and/or testing purposes. The invention is particularly well-suited for stimulating horizontal wellbores that extend through a naturally fractured reservoir.
2. Description of the Related Art
The field of oil and gas well stimulation sometimes involves wells with multiple horizontal laterals in a vertical well that are drilled to facilitate production from a formation. Some of the well laterals are substantially long, up to several thousand feet, and it is desirable to stimulate these horizontal well sections to increase their production. There are a number of stimulation methods, such as acidizing and fracturing. The typical way to stimulate the horizontal sections of a wellbore is to fill the entire horizontal wellbore with the desired stimulation fluid, increase the fluid pressure, and hope that the fluid encounters and enhances the formation's natural fractures. However, according to recent studies this method of stimulating a long horizontal section of a well only effectively treats the initial interval (e.g. the first one-thousand feet or so) of that section. It is desirable to enhance the natural fractures in the formation all the way to the end of the horizontal well, but current methods do not effectively provide for this. In order to effectively fracture a long horizontal well, the well needs to be isolated into sections which can each be independently stimulated.
One way to isolate horizontal sections of a well in anticipation of fracturing is to use inflatable packers. Inflatable packers can be maneuvered into a desired section of the horizontal well and set to isolate the section. However, inflatable packers have a limited pressure containing capacity, often not enough to facilitate fracture of a formation, and therefore they have a high tendency to fail and add significant downtime to the completion operation.
There is another tool, the Wizard Packer from Dresser, that allows isolation of a horizontal well into preset lengths to facilitate stimulation of the formation, but it requires sending darts into the sections to open sliding sleeves which allow the treating fluid to enter into the isolated section. Despite the isolation, there is sometimes still no stimulation within the preset segment if one or more of the interval sections does not contain a natural fracture to enhance. There is no way to adjust the isolated length and effectively stimulate a new length without removing and resetting the entire system. The Wizard Packer is often prohibitively expensive, and is not retrievable. The Wizard Packer is fairly long in length and rigid, such that it often cannot negotiate small radius turns in a wellbore. There is a need for a less expensive, more maneuverable tool to isolate sections of the horizontal lateral at any length without removing the tool from the wellbore since the time and expense for each entry and withdrawal of a tool from a well is significant. The location of the natural fractures within a wellbore may not be known, and presetting the isolated lengths allows no flexibility for moving and adjusting the sections to find natural fractures to enhance.
In addition, there is no effective method of testing the sections of a horizontal wellbore for their respective production levels following stimulation.
The present invention is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above.
SUMMARY OF INVENTION
In one aspect of the present invention, a FracShield assembly for isolating and stimulating single or multiple sections of a substantially horizontal or vertical wellbore in a single trip is provided. The assembly according to one embodiment comprises a mandrel with a topsub, a plurality of anchoring hydraulic buttons, a packing element, and a sealing cup. The sealing cup is housed within a removable protective sheath. The assembly is self-sealing upon the application of pressure within the isolated well segment and is designed primarily to facilitate fracturing a horizontal well when a pressurized fluid is introduced into the isolated section. The assembly is deployed by pumping a ball or dart through the work string and the mandrel of the assembly, which seats in the protective sheath until the pressure within the mandrel reaches a level necessary to shear the holding pins and jettison the sheath from the tool. Upon removal of the sheath, the sealing cup, which is radially outward biased, creates a seal with the inner circumference of the wellbore. The device may include a second seal that is also pressure activated to further contain significant pressure during the stimulation of the well. After stimulating a particular section of the wellbore, the assembly is pulled uphole and reset to stimulate another section of the wellbore. Thus, the assembly permits stimulating multiple zones of the wellbore in a single trip.
According to another embodiment, the assembly exhibits a plurality of slip-on-cone-type anchoring slips. The slips begin to traverse the cone when the pressure on the sealing cup reaches a predetermined level, and the slips continue to move longitudinally and radially along the cone until they anchor themselves in the wall of the wellbore. The slip assembly for gripping the wall of the wellbore in this embodiment can move relative to the mandrel in cases of contraction of the work string to which the mandrel is connected, or in other circumstances. The movement of the slip assembly is controlled by a control collet which includes several collet fingers initially engaged with a shoulder.
The device can be used for production testing of isolated well segments as well. When a well is completed, the tool can be used to isolate segments of the well to facilitate testing each interval for its respective production level.
One embodiment of the device is a single trip multiple-zone isolation tool for stimulating or testing a wellbore that includes a mandrel with a bore therethrough, multiple hydraulically actuated buttons that are arranged radially about the outer diameter of the mandrel for gripping the wall of the wellbore, and a sealing cup coaxially arranged about the mandrel wherein the the sealing cup is radially biased to extend to the diameter of the wall of the wellbore. The mandrel is adapted for connection to a jointed pipe or coiled tubing, the sealing cup is covered by a protective sheath during tool run-in, and the hydraulically actuated buttons are operable in response to hydraulic pressure to move radially outward to engage the wall of the wellbore. As the hydraulic pressure increases, the sealing force of the sealing cup against the wall of the wellbore also increases causing the portion of the wellbore adjacent to the tool to become isolated. The protective sheath is attached to the mandrel by multiple releasable means to ensure the sheath remains in place until it is desirable to jettison it from the end of the tool. These releasable means may include shear screws, collet fingers, or an interlock system. The interlock system may be unlocked by internal hydraulic pressure, allowing the sheath to be jettisoned from the tool.
In one embodiment the tool exhibits a secondary seal comprising a packing element that is predisposed to buckle under the application of longitudinal force and seal against the wall of the wellbore. This packing element returns to its pre-buckle condition upon the removal of longitudinal force. The hydraulically actuated buttons or slips return to their run-in positions when internal pressure is substantially equalized with annular pressure.
The present invention is directed to methods of stimulating a wellbore. The method for stimulating a subterranean well comprises: a) running an isolation tool on a jointed pipe or coiled tubing into the well and positioning the tool adjacent a first interval of interest; the isolation
Carlisle Stephen L.
Lehr Douglas J.
Bagnell David
Hawkins Jennifer M
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