Patent Application
20050150661
1. Field of the Invention
The present invention relates generally to straddle packer tools for straddling and isolating a casing interval within which well treatment operations, such as production formation fracturing, are typically conducted. More particularly, the present invention concerns a straddle packer tool having spaced inflate packers for sealing within a well casing to define a sealed casing interval and having an inflate control system that is controllable from the surface for inflation of the packer elements, storing and releasing stored packer inflation pressure and for controlling differing modes of tool operation. The present invention also concerns a method, controllable from the surface, for flow responsive inflation of packer elements, storing inflation pressure within the packer elements, and selective mechanically actuated deflation of the packer elements to enable use of a straddle tool for interval treatment and to facilitate movement of the straddle packer tool to different subsurface locations and to facilitate retrieval of the tool.
2. Description of the Prior Art
The term “straddle stimulation tools”, as used herein, is intended to mean any well servicing tool having spaced packer elements and which is used within a well to isolate a particular subsurface zone or interval, typically having a casing with perforations, the tool having a fluid supply for various well treatment operations, such as acid injection, formation fracturing, with proppant injection into formation fractures that develop during fracturing, and any other well service operation where a fluid is injected into a casing interval for any character of treatment of the formation surrounding the casing interval. The term “element” as used herein is intended to mean a packer element, particularly an inflatable packer element, which is mounted on a well stimulation tool. Two or more packer elements are supported in spaced relation by a well stimulation tool and when sealed within the well casing, define a casing interval into which well stimulation fluid is pumped for treatment of a formation zone that is communicated with the well casing by perforations in the casing.
The production of an oil or gas well can often be improved by injecting treating or stimulation fluids directly into the formation(s) through perforations in the casing. Moreover, the benefits are often greater if, for a given well, multiple zones are isolated and treated separately. In order to isolate a particular zone, it must be effectively sealed off from the rest of the well. This can be done using elastomeric packer elements that seal with the well casing and block the annulus between the well casing and the downhole tool; the packer elements, when positioned in straddling position, are located above and below the casing perforations and thus straddle a given zone within the casing. Treatment fluid is then injected through a conveyance and fluid supply mechanism, such as coiled tubing, and the fluid is forced out of the tool, in between the packer elements, and into the formation via the casing perforations.
In many wells, the stimulation tool must pass through small diameter production tubing before reaching the larger diameter casing. This requires the use of inflatable sealing elements that, when deflated and thus contracted to a small dimension, will pass through production tubing and other restrictions and, after inflation, will have enough volume and mechanical integrity to fill and seal the large annulus that typically exists between the tool and the casing wall. Furthermore, the tool must be capable of directing fluid that is pumped from surface through different paths at the various stages of the tool operation. For example, at certain times the fluid must be directed into the packer elements for packer inflation, above the upper sealing element, and in between the elements for formation treatment.
Inflatable straddle stimulation tools in the market today require varying degrees of coiled tubing manipulation in order to accomplish packer deflation and to shift the tool from one position to another within the well casing and to direct the fluid pumped from surface. The inherent difficulties in accomplishing these features, particularly in deep or deviated wells, result in straddle tools that are often unreliable and difficult to operate.
It is a principal feature of the present invention to provide a novel inflatable stimulation or treatment tool for wells, with the tool having inflatable straddle packers for sealing at spaced locations within a well casing and thus defining an isolated casing interval for which stimulation or treatment is desired.
It is another feature of the present invention to provide a novel inflatable well stimulation or treatment tool having spaced inflatable packer elements and further having a control system for inflating the packer elements, storing and sealing the pressure in the packer elements and directing the pumped fluid between the inflatable packer elements and then deflating the packer elements to permit movement of the tool to another location within the well or to permit retrieval of the tool from the well.
It is also a feature of the present invention to provide a novel inflatable stimulation or treatment tool for wells, which establishes a flow path through an injection port and achieves packer inflation without any requirement for tool movement and achieves packer deflation by simple application of a pulling force of predetermined magnitude.
It is another feature of the present invention to provide a novel inflatable well stimulation or treatment tool that can be simply and efficiently operated from the surface to achieve the various operational modes of the tool and to switch between the operational modes.
Briefly, the various objects and features of the present invention are realized by a stimulation or treatment tool that is run into and retrieved from wells by a tubing string composed of coiled tubing or flexible jointed tubing, thus permitting the tool to be run into, moved within or retrieved from highly deviated or horizontal well sections as well as vertical well sections. Especially when coiled tubing is being employed for tool conveyance and treatment fluid delivery, it should be borne in mind that significant tensile force may be applied to the coiled tubing, such as for retrieval of the coiled tubing and straddle tool, but only limited compression or pushing force may be applied to the coiled tubing. When excessive pushing force is applied, the coiled tubing will readily become buckled and damaged. When the packer elements of a straddle tool are deflated and thus contracted, coiled tubing can easily be pushed at the surface without significant risk of buckling to enable downward movement of the straddle tool for tool positioning, even under circumstances where the wellbore has highly deviated or horizontal sections.
When used as part of an inflatable straddle stimulation tool, a well stimulation tool embodying the principles of the present invention will allow the operator at surface to inflate the packer elements, store and seal the pressure within the inflated packer elements to maintain effective sealing within the well casing, direct the flow path of the fluid supply through the inject port between the packer elements, and then deflate the packer elements when stimulation tool movement or retrieval is desired. The only coiled tubing manipulation that is typically necessary will be required at the end of the well or formation stimulation procedure to deflate and thus unseal the packer elements. The apparatus will also automatically reset to its starting position after deflation so that the tool can be moved downwardly or upwardly to additional zones during the same trip in the well.
So that the manner in which the above recited features, advantages and objects of the present invention are attained and can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to the preferred embodiment thereof which is illustrated in the appended drawings, which drawings are incorporated as a part hereof.
It is to be noted however, that the appended drawings illustrate only a typical embodiment of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.
In the Drawings:
This invention consists of an inflation control system (ICS) that is used as part of an inflatable straddle stimulation tool (inflate tool) for coiled tubing. The ICS does not control the entire operation of the inflate tool, only the process of inflating the elements, storing and releasing the stored pressure, and directing the pumped fluid into the annulus between the packer elements. Additional components are required upstream of the ICS to switch between a “circulate” mode, where fluid exits the tool into the annulus between the tool and casing before reaching the ICS and is returned to surface, and an “inflate/inject” mode, where all flow is forced into the ICS and is used to either inflate the packer elements or stimulate the formation. The ICS is operated with a minimal amount of coiled tubing manipulation and shifts into most of its positions automatically if the appropriate pump schedule is followed.
Referring now to the drawings and first to
At its upper end, the inflation control system 10 is provided with a tubing connector 30 by which a string 32 of tubing, such as coiled tubing or flexible jointed tubing, is connected to the inflation control system 10. The tubing string 32 extends through the wellbore to tubing handling equipment at the surface, by which the tubing string is manipulated for running the tool to a desired location within the well, for repositioning the tool within the well after stimulation or treatment of a zone or interval or for deflating and releasing the inflatable straddle packers to enable movement or retrieval of the straddle stimulation tool. It is envisioned that during a single trip into the well, any desired number of formations or zones may be treated. It is simply appropriate to deflate and de-energize the inflatable packer elements after each stimulation treatment has been completed and to use the coiled tubing to selectively position the tool at another perforated zone or interval of the well casing, where the stimulation treatment process is repeated.
The inflation control system 10 of the straddle stimulation tool defines a tool housing 34 having an internal chamber 36. A deflate shifter member 38 to which the tubing connector 30 and tubing 32 are assembled or to which a tool section is assembled, serves to connect the ICS to the rest of the flow control section of the inflate straddle well stimulation tool 12. The deflate shifter member 38 is connected to the ICS through a very stiff spring 42 which will yield significantly only when a tensile force of predetermined magnitude is applied to the deflate shifter by the tubing string 32. The deflate spring 42 connects the deflate shifter member 38 to the ICS. Therefore, if the ICS is restrained from moving (as when the inflate tool is anchored by the inflated packer elements) and tension is applied to the deflate shifter member 38, the spring 42 will be compressed by the upwardly directed force and the deflate shifter member 38 will move upwardly. If the deflate shifter member 38 moves upwardly and the element pressure piston 50 is in the down position, then the deflate shifter member 38 will engage the element pressure piston 50 and move it to the “up” position. Otherwise, however, the deflate shifter member 38 and element pressure piston 50 will not engage.
The deflate shifter member 38 defines a depending actuating section 40 that extends into the internal chamber 36 and is sealed with respect to the tool housing 34 by an O-ring seal 41. The deflate spring 42 is located within the internal chamber 36 and is positioned with its upper end positioned in force transmitting engagement with a downwardly facing shoulder 44 within the tool housing and its lower end in force transmitting engagement with an upwardly facing shoulder 46 of an annular enlargement or flange 48 of the depending actuating section 40 of the deflate shifter member 38. The deflate spring 42 has a very high spring constant and therefore requires application of a large tensile force to the deflate shifter member 38 in order to compress the deflate spring sufficiently to permit upward travel of the deflate shifter member 38 relative to the tool housing 34.
An element pressure piston 50 is moveable within the internal chamber 36 and defines a stimulation fluid flow passage 51 therethrough. The sole purpose of the element pressure piston 50 is to store and release pressure in the inflatable packer elements. The element pressure piston 50 is comprised in part of a collet 64 that has two positions, an “up” collet position and a “down” collet position. In the up collet position, the packer elements 14 and 16 can be inflated through an inflate equalization port 100, but since the element pressure piston 50 is not sealed within the tool housing at this position, the packer inflation pressure cannot be stored and will always equalize with the coiled tubing pressure. In the down collet position, the inflate equalization port is blocked by the sealed lower end of the element pressure piston 50 and high-pressure fluid will not be allowed to leave the inflated packer elements even after the coiled tubing pressure drops. The element pressure piston 50 is shifted to the “down” collet position by a slider ring 72 and to the “up” collet position by the deflate shifter member 38 and has a lost motion connector housing 52 establishing a connector receptacle 54 within which a connector extension 56 of the depending actuator section 40 of the deflate shifter member 38 is moveable. An enlargement or flange 58 at the lower end of the connector extension 56 defines an upwardly facing shoulder 60 that comes into force transmitting engagement with a downwardly facing internal shoulder 62 when the deflate shifter member 38 is moved upwardly against the force of the deflate spring 42. In absence of this tension force, which is applied via the tubing string 32, the element pressure piston 50 is essentially mechanically isolated from the deflate shifter 38.
The connector housing 52 of the element pressure piston 50 is provided with a collet member 64 that is normally positioned within an upper collet recess 66 of the tool housing as shown in
At the lower end of the generally cylindrical section 70 of the packer element pressure piston 50 there is provided an annular sealing member 96 that establishes sealing within a lower cylindrical section 98 of the internal tool chamber 94. An inflate equalization port 100 is in communication with the inflation flow passage 22 and, with the packer element pressure piston 50 in the upward position shown in
An inflation orifice 106 is provided in the wall structure of the tool housing 34 and communicates the casing annulus 90 with a piston chamber 108 that is defined within the tool housing 34. The inflation orifice 106 makes it possible to inflate the packer elements to a desired pressure differential without actually knowing the well pressure at the tool. This is because a given flow rate across the inflation orifice 106 results in a known pressure drop. This pressure drop is effectively independent of the absolute values of pressure on each side of the orifice. Furthermore, by changing orifice properties, the operator can achieve different pressure drops with the same flow rate; this may be necessary depending on the capabilities of the pump used.
An inflate/inject piston 110 is moveable within the piston chamber 108 and is urged downwardly by a compression spring member 112, referred to as an inject spring, and is sealed within the piston chamber 108 by a piston seal member 113. The inflate/inject piston 110 directs pumped fluid either across the inflate orifice 106 and out of the ICS, or it blocks this path and directs the fluid down the ICS and ultimately in between the inflated packer elements and into the formation. If the element pressure piston is in the up position, then the inflate/inject piston 110 is pressure-balanced and is forced down by the inject spring 112. Once the element pressure piston 50 shifts to the down position as shown in
An inflation poppet valve 114 is located within a valve chamber 116 and is urged to a position closing a valve passage 118 by a valve spring 120. The inflation poppet is essentially a check valve that will allow fluid to flow from inside the coiled tubing, into the internal chamber 101 and to the inflation port, but not from the spaced inflatable packers through the passage 22 and to the internal chamber 101. This feature causes the spaced inflatable packer elements to remain inflated and sealing the straddle stimulation tool to the casing, until packer element pressure is subsequently equalized with tubing pressure. During inflation, fluid flows into the inflatable packer elements through the inflate equalization port until the element pressure piston 50 shifts to the down position of
The piston chamber below the inflate/inject piston 110 is in communication with the inflation flow passage 22 via a port 122 so that, under low fluid flow conditions packer inflation as shown in
The tool housing 34 defines an equalizing piston chamber 124 having a cylindrical wall surface 126. An equalizing piston member 128 is moveable with the equalizing piston chamber 124 and is sealed with respect to the cylindrical wall surface 126 by annular piston seals 130. An equalizing passage 132 is defined by the tool housing 34 and communicates the casing annulus 92 with the equalizing piston chamber 124 below the equalizing piston when the equalizing piston is at its upper position. A piston spring 134 is located within the tool housing 34 below the equalizing piston and imparts upwardly directed spring force to the equalizing piston and normally maintains the position of the equalization piston above the communication port 132 as is evident from
Operation of the Inflation Control System
As mentioned above, the ICS must be used in conjunction with components that, when assembled upstream of the ICS, direct pumped fluid either 1) out of the tool before reaching the ICS or 2) through the ICS. It is important to keep the ICS isolated from flow until the operator is ready to inflate the packer elements. Alternatively, the pressure differential stored in the packer elements by the ICS is directly related to the flow rate. Therefore, it is equally important that, when the ICS is operated, all of the pumped fluid is directed through the ICS before exiting the tool. The following description of the operation of the ICS assumes that all pumped fluid is being directed through the ICS and that the operator has located the proper depth for straddling the casing perforations and is ready to begin packer element inflation. The operation of the ICS will be broken down into three major categories, each of which is described below. Also, as explained above,
1. Inflate
Once the tool is located at the proper depth in the well and the spaced inflatable packer elements are straddling the zone of interest, the operator begins inflating the spaced inflatable packer elements. Inflation fluid is pumped through the ICS at a low flow rate as indicated by schematic block 140 of
After the inflatable packer elements have had adequate time to adjust to the pressure differential (this time varies with the magnitude of the differential) the flow rate is increased by some fixed amount, ΔQ, which results in a corresponding packer element pressure differential increase. Again, the operator must wait for the inflatable packer elements to adjust to the change in pressure before proceeding.
It is important to realize that, if the pump stops for any reason before inflation is completed, the inflate/inject piston will unseat and move up some amount. This property makes it impossible to simply start pumping to continue inflating, since some of the pumped fluid will not be directed across the inflate orifice but will instead travel down the inject path below the inflate/inject piston. However, the ICS is robust to situations where the pumping stops inadvertently for any reason. The slider ring will not shift the element pressure piston until a minimum pressure differential has been achieved (See
The operator continues the process of increasing the pump rate incrementally and allowing the elements to respond until the target pressure differential is reached. Note that the target pressure differential must always be larger than the minimum pressure stored by the element pressure piston; otherwise the elements will simply deflate after pumping stops. Once the desired pressure differential is achieved, the operator stops pumping. As soon as pumping stops, the pressure differential across the inflate/inject piston causes it to move upward, closing off the exit path across the inflate orifice and opening the path through the rest of the ICS. From this point on, all fluid pumped through the ICS will flow through the bottom of the inflate/inject piston and out the inject port.
2. Inject
Once the elements are inflated to the desired pressure differential, the stimulation fluid is pumped from surface, through the ICS, and into the formation. In order for the stimulation fluid (often acid) to reach the tool, the operator must first displace whatever fluid is in the coil. The operator will do this by pumping the stimulation fluid to force the undesired fluid out of the tool above the ICS and up to surface. Once the stimulation fluid reaches the tool, the operator stops circulating to surface, closes off the circulate path, and opens the inject path that directs the fluid through the ICS.
Because the inflate/inject piston is in the up position, the stimulation fluid cannot exit the ICS across the inflate orifice and will instead travel through the lower portion of the ICS. At some low flow rate (approximately 0.25 bpm to 0.5 bpm), the stimulation fluid generates a pressure drop across the equalize piston that is sufficient to close the piston and shut off the inject equalization port (See
As an alternative to the orifice in the equalize piston, a unidirectional valve such as a check valve may be used instead. The check valve allows flow from surface to pass through after a nominal pressure differential has been achieved, but the valve does not allow fluid to pass through from below. The shifting pressure differential of the check valve for pumped fluid is sized such that the equalize piston shifts down to block the inject equalization port before the check valve opens. For example, if it requires 50 psi of pressure differential to shift the equalize piston, the check valve might be designed to open with 100 psi of differential. This characteristic ensures that all the pumped fluid will travel out the inject port and not the inject equalization port.
When pumping stops, the equalization piston returns to its original position and open the inject equalization port (See
This invention relates to the flow control portion of a straddle tool and not the tool in its entirety. Consequently, for clarity in
3. Deflate
The process of circulating fluid to the tool and then injecting it into the formation can continue indefinitely without deflating the packer elements. When the operator has finished treating a particular zone and wishes to deflate the packer elements, the operator must simply wait a sufficient period of time for the pressure across the packer elements to equalize through the inject equalization port 132. The amount of time required for this will vary depending on the characteristics of each zone.
Once the pressure across the packer elements is equalized with casing pressure, the operator will apply tension to the tool through the coiled tubing to achieve packer deflation. Since the deflate shifter member 38 is only connected to the ICS through the deflate spring 42 and the packer elements are anchored to casing by inflation pressure, the deflate spring will compress when tension is applied. When the deflate spring 42 is compressed by the tension force of the tubing, the deflate shifter member 38 engages the element pressure piston 50, moving it to the up position (See
Once enough time has elapsed for the elements to become equalized, the inflate/inject piston member 110 will become pressure balanced and will be returned to its down (starting) position by the force of the spring 112. At this point, the ICS is completely reset and may be moved to another zone. The above process is repeated as needed for each zone in the well.
In view of the foregoing it is evident that the present invention is one well adapted to attain all of the objects and features hereinabove set forth, together with other objects and features which are inherent in the apparatus disclosed herein.
As will be readily apparent to those skilled in the art, the present invention may easily be produced in other specific forms without departing from its spirit or essential characteristics. The present embodiment is, therefore, to be considered as merely illustrative and not restrictive, the scope of the invention being indicated by the claims rather than the foregoing description, and all changes which come within the meaning and range of equivalence of the claims are therefore intended to be embraced therein.
