Wells – Packers or plugs – Spaced sealing portions
Reexamination Certificate
2002-11-12
2004-08-31
Bagnell, David (Department: 3672)
Wells
Packers or plugs
Spaced sealing portions
C166S400000, C166S306000, C166S250170
Reexamination Certificate
active
06782946
ABSTRACT:
TECHNICAL FIELD
A method and apparatus for injecting one or more fluids into a borehole.
BACKGROUND OF THE INVENTION
Boreholes such as producing wellbores may periodically require treatment in order to maximize the efficiency of the recovery of fluids from the borehole. Such treatments often involve the injection of treatment fluids into the borehole and thus into the formation surrounding the borehole.
The treatment fluids may serve a variety of purposes. For example, fluids may be injected into a borehole in order to “clean” a clogged formation or may be injected into a borehole in order to seal off a portion of the formation which has become fractured or which is excessively permeable. Sometimes the fluid treatment of boreholes requires the injection of several fluids either simultaneously or in sequence.
One option for performing fluid treatment of boreholes is merely to inject treatment fluids into the borehole from the ground on the assumption that an adequate amount of the fluids will be delivered to their desired location. This option is potentially very expensive, since considerable waste of treatment fluids may result. In addition, where a long section of the borehole must be treated, it may be difficult to deliver adequate amounts of treatment fluids to the desired section of the borehole.
A second option for performing fluid treatment of boreholes is to first isolate the section of the borehole that must be treated with packers or other sealing devices and then inject the treatment fluids only into the isolated section. This option is also potentially very expensive, since the apparatus for isolating the treatment section must be installed in the borehole before the fluid treatment occurs and must be removed from the borehole after the fluid treatment is finished. In addition, if multiple sections or a long continuous section of the borehole must be treated, the isolation apparatus must be moved through the borehole between treatments.
Exemplary apparatus and methods for isolating borehole sections for injection of fluids therein include those described in U.S. Pat. No. 2,764,244 (Page), U.S. Pat. No. 2,869,645 (Chamberlain et al), U.S. Pat. No. 3,319,717 (Chenoweth), U.S. Pat. No. 3,398,796 (Fisher et al), U.S. Pat. No. 3,454,085 (Bostock), U.S. Pat. No. 3,527,302 (Broussard), U.S. Pat. No. 3,945,436 (Nebolsine), U.S. Pat. No. 4,030,545 (Nebolsine), U.S. Pat. No. 4,424,859 (Sims), U.S. Pat. No. 5,002,127 (Dalrymple et al), U.S. Pat. No. 5,018,578 (El Rabaa et al) and U.S. Pat. No. 5,350,018 (Sorem et al).
The apparatus described in the above patents constitute relatively fixed and permanent installations in the borehole which typically require the setting of the sealing devices before fluid injection takes place and the unsetting of the sealing devices after fluid injection is finished in order to facilitate the injection apparatus being removed from or moved within the borehole.
It would be desirable to be able to move the injection apparatus through the borehole without first setting and unsetting the sealing devices since this would undoubtedly result in a saving of time and cost associated with fluid treatment. Unfortunately, none of the patents referred to above appear to contemplate simultaneous fluid injection and movement of the injection apparatus through the borehole.
One explanation for this is that it is difficult to achieve the objective of isolating the section of the borehole into which injection is performed without the use of sealing devices which exert a relatively high sealing force against the interior surface of the borehole, which sealing force is an impediment to movement of the injection apparatus through the borehole.
One attempt to provide an injection apparatus which offers simultaneous fluid injection and movement of the apparatus through the borehole is found in PCT International Publication No. WO 99/34092 (Blok et al), which was published on Jul. 8, 1999.
The Blok apparatus includes a tool which comprises at least three axially spaced swab assemblies which define at least two annular spaces between the tool body and a wellbore. In use the tool is moved through the wellbore while a first treatment fluid is pumped via a first annular space into the wellbore and the formation and a second treatment fluid is pumped via a second annular space into the wellbore and the formation.
The combined effect in Blok of the movement of the tool and the injection of the two treatment fluids is that the first treatment fluid enters the formation before the second treatment fluid so that the two treatment fluids together provide a complete fluid treatment without the need for wellbore cycling to deliver different fluids to the treatment zone separately.
The swab assemblies in Blok are required to satisfy two somewhat incompatible design criteria since they must minimize the amount of sealing force between themselves and the wellbore in order to facilitate movement of the tool through the wellbore and also must provide an “effective seal” between the annular spaces in order to maintain segregation of the treatment fluids in the wellbore before they enter the formation.
In some circumstances, it may be desirable to maintain segregation of fluids after they have entered the formation in addition to maintaining their segregation within the borehole. Blok does not appear to contemplate or address this issue.
One mechanism for maintaining segregation of different fluids in the formation surrounding the borehole is to create an interface between them which restricts their movement in the borehole.
U.S. Pat. No. 4,842,068 (Vercaemer et al) contemplates containing a fluid treatment zone between two protection zones in a wellbore and a formation by simultaneously injecting a treatment fluid into the treatment zone and injecting protection fluids into the protection zones. The interface between the treatment fluid and the protection fluids is created by providing that the protection fluids are immiscible with the treatment fluid. There is no discussion in Vercaemer concerning the pressures or relative pressures at which the treatment fluid and the protection fluids are injected into the wellbore and the formation. There is also no indication in Vercaemer that the method can be performed while moving the injection apparatus through the wellbore.
U.S. Pat. No. 5,002,127 (Dalrymple et al) describes a method for controlling the permeability of an underground well formation by creating a chemical barrier in the formation as an interface between fluids. This chemical barrier is created by simultaneously injecting a first treatment fluid and a second sealant fluid into the formation via a wellbore which is fitted with a packer for maintaining separation of the first fluid and the second fluid in the wellbore. Migration of the second fluid into the portion of the formation occupied by the first fluid is inhibited by substantially balancing the injection pressures of the first fluid and the second fluid. Dalrymple does not contemplate moving the injection apparatus (including the packer) through the wellbore while injection of the first fluid and the second fluid is ongoing.
U.S. Pat. No. 5,018,578 (El Rabaa et al) contemplates the delivery of two separate fluids into two separate zones in a borehole, which zones are separated within the borehole by sealing means such as a packer. The two fluids are chemically reactive with each other such that they form a precipitate which acts as a barrier and interface between the two zones in the formation surrounding the borehole.
Although El Rabaa indicates that the two fluids should be injected into the borehole and the formation sufficient to achieve the stated goal of fracturing the formation in a controlled manner, there is no discussion in El Rabaa concerning the relative pressures at which the two fluids should be injected in order to control the location of the chemical barrier between the two injection zones. Furthermore, El Rabaa does not suggest that the injection apparatus (including the sealing means) can be moved throu
Lillico Douglas A.
Perkins Ernest H.
Rispler Kevin
Alberta Research Council Inc.
Bagnell David
Dougherty Jennifer R.
Kuharchuk Terrence N.
Rodman & Rodman
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