WO2003042496A1

WO2003042496A1 - Method for diverting treatment fluid into a low permeability zone of a formation

Info

Publication number: WO2003042496A1
Application number: PCT/GB2002/005117
Authority: WO
Inventors: Ian Ralph Collins; Philip Head
Original assignee: Bp Exploration Operating Company Limited; Xl Technology Limited
Priority date: 2001-11-15
Filing date: 2002-11-12
Publication date: 2003-05-22
Also published as: GB0127384D0

Abstract

A method of diverting treatment fluid into a low permeability zone of a hydrocarbon bearing formation wherein the formation is penetrated by a wellbore having a casing extending to below the low permeability zone and having at least one perforation (26) in the casing in fluid communication with the low permeability zone, the method comprising: (a) isolating (22, 23) a section of the wellbore having the perforation(s) in the casing in fluid communication with the low permeability zone of the formation; (b) pumping treatment fluid from a selected location in the wellbore into the isolated section of the wellbore by means of a downhole pumping (21) device at a rate sufficient to increase the pressure in the isolated section of wellbore to a value which is greater than the pressure at the selected location in the wellbore such that treatment fluid is diverted through the perforation(s) in the casing into the low permeability zone.

Description

METHOD FOR DIVERTING TREATMENT FLUID INTO A LOW PERMEABILITY

ZONE OF A FORMATION The present invention relates to a device and a method for controlling the injection of treatment fluid into a low permeability, high pressure zone of a subterranean hydrocarbon-bearing formation penetrated by a cased wellbore.

At various times during the life of a well, formed in a subterranean formation for the production of oil or gas, it is desirable to treat the well, for example, with an acid, a scale inhibitor, corrosion inhibitor, hydrate inhibitor, wax inhibitor, asphaltene inhibitor or a hydrogen sulphide scavenger. Where, the subterranean formation is penetrated by a cased wellbore, these treatments generally involve injection of a treatment fluid (liquid or gas) under pressure through the perforations in the casing into the formation. Although high fluid permeability is an important characteristic of a hydrocarbon- producing formation, these treatments may be adversely affectedjby the uncontrolled loss of treatment fluid into the highly permeable formation. For example, in an acidizing treatment where it is desired to treat the least permeable formation zone(s) to improve its permeability, the formation zone(s) having the higher permeability will most likely consume the major portion of the treatment fluid leaving the least permeable formation zone(s) virtually untreated. Similarly, during treatments to inhibit scale deposition, it is desirable to introduce a scale inhibitor into formation zone(s) that are producing scaling water. Where hydrocarbon-bearing zone(s) of the formation have a higher permeability or lower formation pressure than such water-producing zone(s), the major proportion of the treatment fluid will most likely enter the hydrocarbon-bearing zone(s) leaving the water-producing zone(s) virtually untreated. Therefore, it is desirable to control the injectivity of treatment fluids to the high permeability (or low pressure) formation zone(s) during such treatments.

It has now been found that a downhole pumping means, preferably, a remotely controlled electrically powered downhole pumping means may be used to pump treatment fluid from a selected location in a cased wellbore into an isolated section of the wellbore having at least one perforation, preferably, a plurality of perforations, in fluid communication with a low permeability (or high pressure) zone of the formation.

Thus, a first embodiment of the present invention provides a method of diverting treatment fluid into a low permeability zone of a hydrocarbon bearing formation wherein the formation is penetrated by a wellbore having a casing extending to below the low permeability zone and having at least one perforation in the casing in fluid communication with the low permeability zone, the method comprising: a) isolating a section of the wellbore having the perforation(s) in the casing in fluid communication with the low permeability zone of the formation; b) pumping treatment fluid from a selected location in the wellbore into the isolated section of the wellbore by means of a downhole pumping device at a rate sufficient to increase the pressure in the isolated section of wellbore to a value which is greater than the pressure at the selected location in the wellbore such that treatment fluid is diverted through the perforation(s) in the casing into the low permeability zone. Preferably, the isolated section of wellbore has a plurality of perforations in fluid communication with the low permeability zone of the formation.

The selected location in the wellbore may have a pressure, Pi, less than the pressure, P₂, of the low permeability zone of the formation with treatment fluid being pumped into the isolated section of the wellbore to increase the pressure, P₃, in the isolated section of the wellbore to above the pressure, P₂, of the low permeability zone thereby diverting treatment fluid, through the perforation(s), into the low permeability zone (i.e. P₃ > P₂ > Pi). However, it is also envisaged that the selected location may have a pressure, Pi, greater than the pressure of the low permeability zone, P₂, with the downhole pumping device being used to increase the pressure differential, P -P₂, between the pressure in the isolated section of wellbore, P₃, and the pressure of the low permeability zone, P₂, thereby increasing the amount of treatment fluid which is diverted, through the perforation(s) into the low permeability zone (i.e. P₃ > P₂ and Pi > Preferably, the casing may be run into the wellbore from the surface to the bottom of the wellbore. Alternatively, the casing may be run from the surface into an upper section of the wellbore with the lower section of the wellbore comprising a barefoot or open-hole completion. Where the lower section of the wellbore comprises a barefoot completion, the casing must run to below the section of the wellbore having the perforation(s) in fluid communication with the low permeability (high pressure) zone into which the treatment fluid is to be diverted.

Suitably, the treatment fluid is pumped from the surface to the selected location in the wellbore. Preferably, a production conduit is arranged in the wellbore in sealing relationship with the walls of the casing with the treatment fluid introduced from the surface into the production conduit. The selected location in the wellbore from which the treatment fluid is pumped into the isolated section of wellbore may be in the production conduit or in a section of the wellbore extending from the production conduit to the isolated section of wellbore. This section of wellbore may penetrate a zone of the formation having a higher permeability (and lower pressure) than the low permeability zone into which the treatment fluid is to be diverted. Where the casing has at least one perforation, preferably, a plurality of perforations, in communication with the high permeability zone, the pressure in the wellbore in the vicinity of these perforation(s), P₄, must at least balance the pressure of the high permeability zone, P₅, in order to prevent fluids, for example, hydrocarbon fluids and/or water from being produced from this zone into the wellbore. Suitably, the pressure, P₄, in the wellbore in the vicinity of the high permeability zone and the pressure, P₃, in the isolated section of wellbore may be controlled by adjusting the rate at which the treatment fluid is introduced from the surface into the wellbore and the rate at which the treatment fluid is pumped from the selected location in the wellbore into the isolated section of wellbore such that P₄ > P₅ and P₃ > P₄ (where P₃ and P₄ are as defined above). Where, it is desired to divert the majority of the treatment fluid into the low permeability zone, the pressure differential, P₃ - P₂, should be substantially higher than the pressure differential P₄-P₅. Where it is desired to balance the amount of treatment fluid injected into the low and high permeability zones, the pressure differential, P₃ - P₂, should be substantially equal to the pressure differential P₄-P₅.

Preferably, the pumping device is introduced into the wellbore prior to pumping the treatment fluid from the surface to the selected location in the wellbore. Suitably, the pumping device may be introduced into the wellbore, for example, through the production conduit, suspended on a cable. Preferably, the cable is formed from reinforced steel. The cable may be connected to the pumping device by means of a connector, preferably, a releasable connector. Preferably, the cable encases one or more wires for transmitting electricity or electrical signals from the surface, for example, a multicore wire. Alternatively, the pumping device may be provided with a separate electric cable comprising one or more wires for transmitting electricity or electrical signals. Suitably, the electric wire(s) are isolated from the wellbore fluids, for example, by encasing the wire(s) in a protective material that is resistant to the wellbore fluids. Suitably, the pumping device comprises an elongate housing, preferably a cylindrical housing, having a passage in fluid communication with an inlet and outlet of the housing. The housing is provided with an electrically powered pumping means for pumping the treatment fluid through the passage in the housing. Suitably, the housing is provided with an electric motor for the pumping means with the motor being operated from the surface. Preferably, the motor is a brushless direct current (DC) motor. The electrically powered pumping means may be of any conventional design, for example, a suction pump, a progressive cavity pump or a centrifugal pump. Suitably, the inlet and outlet of the housing are longitudinally spaced apart with a radially expandable packer arranged on the housing between the inlet and the outlet. Preferably, the packer is controlled from the surface via a signal transmitted along the electric wire(s).

Where the casing is run to the bottom of the wellbore and the low permeability zone is the lowest zone in the formation, the pumping device may be passed from the surface through the production conduit until the packer on the housing is located immediately above the perforation(s) which are in fluid communication with the low permeability zone. The packer is then expanded radially outwards to seal the annular space formed between the casing and the housing thereby isolating the section of wellbore below the packer. Treatment fluid is then drawn through the inlet of the housing and is pumped through the passage to the outlet and into the lower isolated section of the wellbore.

Where the low permeability zone is an upper or an intermediate zone in the formation, prior to deploying the pumping device, a radially expandable plug may be lowered into the wellbore, through the production conduit, suspended on a cable via a releasable latch means, until the plug is positioned immediately below the perforation(s) in fluid communication with the low permeability zone. The plug is then expanded radially outwards to plug the wellbore. The cable is subsequently released from the latch means and is pulled from the wellbore. The pumping device is then lowered into the wellbore and operated as described above. Alternatively, the housing may be provided with a first and a second radially expandable packer separated by a section of housing having a length corresponding to the length of the section of wellbore that it is desired to isolate. The inlet to the housing lies above the first packer while the outlet is located in the section of housing between the first and second packers. In use, the pumping device is lowered into the wellbore, for example, through the production conduit, until the first and second packers lie respectively immediately above and below the section of wellbore that it is desired to isolate. The packers are then expanded radially outwards, as described above, to seal the annulus formed between the housing and the casing thereby isolating the section of wellbore having perforation(s) in fluid communication with the low permeability zone. Treatment fluid is then drawn through the inlet in the housing, via the pumping means, and is passed through the passage in the housing to the outlet and into the isolated section of wellbore.

The housing of the pumping device may be provided with an electrically powered traction means which, following radial contraction of the packers, is used to advance the pumping device through the wellbore thereby allowing further low permeability zone(s) of the formation to be treated. Suitably, the traction means comprises wheels or tracks which engage with and move over the walls of the casing. Preferably, the inlet of the housing of the pumping device is in fluid communication with the interior of a length of tubing (hereinafter referred to as

"extension tubing"). The extension tubing may be steel tubing or plastic tubing, for example, drill tubing. Alternatively, the extension tubing may be an electric drill string. A suitable electric drill string for use in the method of the present invention is described in UK patent application number 0115524.1 which is herein incorporated by reference. Preferably, the extension tubing may be up to 1000 feet in length, more preferably 500 feet in length, for example, 100 to 300 feet in length, thereby allowing the selected location in the wellbore, from which the treatment fluid is pumped, to be remote from the isolated section of wellbore.

Where the wellbore has a production conduit in sealing arrangement with the casing, the extension tubing has an outer diameter smaller than the inner diameter of the production conduit thereby allowing the extension tubing to pass through the production conduit. Preferably, the production conduit has an inner diameter of 2.5 to 8 inches, more preferable 3.5 to 6 inches. Preferably the extension tubing has an outer diameter of 2 to 5 inches. Preferably, the housing of the pumping device is substantially cylindrical and has a diameter smaller than the inner diameter of the production conduit. Preferably, the extension tubing extends from the inlet of the housing into the production conduit.

Suitably, the upper end of the length of tubing (extension tubing) may be open- ended. Suitably, a radially expandable seal is provided at or near the upper end of the extension tubing to seal the annulus formed between the tubing and the production conduit. Where the extension tubing does not extend into a production conduit, a radially expandable packer may be provided at or near the upper end of the tubing to seal the annulus formed between the casing and the tubing. Suitably the radially expandable seal or packer is operated from the surface via a signal transmitted along the electric wire(s). Where the extension tubing is steel tubing or plastic tubing, it is preferred that the housing is releasably connected to a cable that passes through the interior of the extension tubing to the housing. Where the extension tubing is an electric drill string, the housing may be connected either directly or indirectly to the electric drill string which in turn may be suspended from a cable. Once the pumping device is in position in the wellbore, the packer(s) on the housing is radially expanded to isolate the section of wellbore, as described above. The electrically powered pumping means is then remotely operated and draws the treatment fluid through the interior of the extension tubing to the inlet of the housing. The treatment fluid is then pumped through the passage in the housing to the outlet and into the isolated section of the wellbore.

Alternatively, the upper end of the length of tubing (extension tubing) may be connected to a further housing, preferably a cylindrical housing. The housings connected to the lower and upper ends of the extension tubing are hereinafter referred to as "first" and "second" housings respectively. The second housing is provided with a passage in fluid communication with an inlet of the second housing and with the interior of the extension tubing thereby allowing the treatment fluid to flow through the passage in the second housing, the interior of the extension tubing and into the passage in the first housing. The second housing is also provided with a radially expandable seal or packer that is operable from the surface, as described above. Preferably, the pumping device is lowered into the wellbore, through the production conduit, suspended on a cable that is releasably attached to the second housing. Once in position in the wellbore, the seal (or packer) on the second housing is radially expanded to seal the annulus formed between the second housing and the walls of the production conduit (or casing). The packer(s) on the first housing is also radially expanded to isolate the section of wellbore having perforation(s) in fluid communication with the low permeability zone, as described above. An electrically powered pumping means in the first housing is then remotely operated to draw the treatment fluid through the passage in the second housing and the interior of the extension tubing to the inlet of the first housing. The fluid then passes through the passage in the first housing to the outlet and into the isolated section of wellbore. Alternatively or additionally, the treatment fluid may be pumped into the isolated section of wellbore via a remotely controlled electrically operated pumping means located in the second housing. Preferably the inlet of the second housing and the outlet of the first housing are provided with valves such that the inlet and outlet may be closed during deployment of the pumping device thereby preventing any produced fluids from entering the housings and the extension tubing. For example, the inlet and outlet may each comprise a plurality of slots or perforations which are closed via a sleeve moveable relative to the slots or perforations. When the valve is in its closed position the sleeve will cover the slots or perforations. When the valve is in its open position the plurality of slots or perforations are uncovered so that the treatment fluid may pass into the isolated section of wellbore. As discussed above, the first housing of the pumping device may be provided with tractions means that may be used to advance the pumping device through the wellbore. Alternatively, where the extension tubing is steel tubing or an electric drill string, the second housing may be provided with traction means. Preferably, where the extension tubing is steel tubing or an electric drill string, both the first and second housings are provided with traction means.

Preferably, the pumping device is retrieved from the wellbore following diversion of the treatment fluid into the low permeability (high pressure) zone(s). However, it is also envisaged that the pumping device may be left in place in the wellbore. Suitably, the radially expandable seal or packer(s) on the device may be radially contracted prior to producing hydrocarbon fluid from the wellbore thereby providing a fluid by-pass. Suitably, the pumping means of the device may be operated in the reverse direction to aid production of the hydrocarbon fluid.

It is also envisaged that a first and a second pumping device according to the present invention may be deployed in series in the wellbore to treat a first (for example, an upper) and a second (for example, ajower) low permeability zone of the formation respectively. Suitably, the housing of the first pumping device is provided with a passage in fluid communication with an inlet, a first outlet and second outlet of the housing. Suitably, the housing of the second pumping device has a passage in fluid communication with an inlet and an outlet of the housing. The second outlet of the first pumping device is in fluid communication with the inlet of the second pumping device via tubing having a length corresponding to the interval between the first and second low permeability zones of the formation. The tubing that connects the first and second pumping devices (hereinafter "connection tubing") may be steel or plastic tubing, for example, drill tubing. Suitably, an electric cable passes through the interior of the connection tubing to the second pumping device to provide an electric power supply for the pumping means of the second pumping device. Alternatively, the connection tubing may be an electric drill string, as described above. First and second radially expandable packers on the housing of the first pumping device may be used to isolate a first section of the wellbore having perforation(s) in fluid communication with the first low permeability zone, as described above. For avoidance of doubt, the first outlet of the housing of the first pumping device lies between the first and second packers while the inlet lies above the first packers. Similarly, first and second radially expandable packers on the housing of the second pumping device may be used to isolate a second section of wellbore having perforation(s) in fluid communication with the second low permeability zone. The passage in the first pumping device may comprise a main passage and a branch passage with the main passage being in fluid communication with the inlet and first outlet of the housing and the branch passage being in fluid communication with the main passage (and hence the inlet) and the second outlet of the housing. Suitably, treatment fluid is drawn through the inlet of the housing of the first pumping device and into the main passage via a pumping means provided in the housing. The treatment fluid is then divided into a first stream and a second stream with the first stream passing through the main passage to the first outlet and into the first isolated section of the wellbore and the second stream passing through the branch passage to the second outlet and into the interior of the connection tubing. Alternatively, the housing of the first pumping device may be provided with a first passage and a second passage. The first passage is in fluid communication with a first inlet and the first outlet of the housing. The second passage in fluid communication with a second inlet of the housing and the . second outlet. For avoidance of doubt, the first and second inlets of the housing of the first pumping device lie above the first packer. Suitably, a first stream of treatment fluid is pumped through the first passage in the housing of the first pumping device to the first outlet and out into the first isolated section of the wellbore while a second stream of treatment fluid is pumped through the second passage of the first pumping device to the second outlet and into the interior of the connection tubing. The second stream of treatment fluid passes through the interior of the connection tubing to the inlet of the housing of the second pumping device. The second stream is then pumped through the passage in the housing of the second pumping device to the outlet and into the second isolated section of the wellbore. It is envisaged that a pumping means may be omitted from the second pumping device in which case, the pumping means of the first pumping device is used to pump the second stream through the interior of the connection tubing, through the passage in the housing of the second pumping device and into the second isolated section of wellbore. Where the second isolated section of wellbore is the lowest section of the wellbore, it is envisaged that the housing of the second pumping device may be provided with a single radially expandable packer with the second pumping device being positioned in the wellbore with the packer arranged immediately above the perforation(s) of the second section of wellbore. It is envisaged that 3 or more, preferably, 3 or 4 pumping devices may be employed in series with the devices separated by lengths of tubing ("connection" tubing) corresponding to the intervals between the low permeability zones that are to be treated.

The pumping device of the present invention may be deployed in deviated wells, in addition to vertical wells. If necessary, traction means on the pumping device may be used to move the pumping device to the desired location in the deviated well. The present invention will now be illustrated by reference to Figures 1 to 5.

Referring to Figure 1, a wellbore 1 penetrates through a hydrocarbon bearing subterranean formation comprising a high permeability (low pressure) zone 2 and a low permeability (high pressure) zone 3 located below the low pressure zone 2. A casing 4 is arranged in the wellbore 1 and is fixed to the wellbore wall by a layer of cement 5. The casing and cement is then perforated to allow fluid communication between the low and high pressures zones and the wellbore. A hydrocarbon fluid production conduit 6 is positioned within the wellbore 1 and a packer 7 is provided at the lower end thereof to seal- the annular space formed between the production conduit 6 and the casing 4. An expandable plug 8 is passed through the production conduit 6 suspended on a cable via a releasable connector (latch means) until the plug is positioned in the wellbore below the high pressure zone 3. The plug 8 is then expanded radially outwards such that it engages with the casing 4 of the wellbore thereby plugging the wellbore. Once expanded in the wellbore, the plug 8 is released from the cable which is then pulled from the wellbore. An electrically powered pumping device 9 is passed into the wellbore through the hydrocarbon fluid production conduit 6 suspended on a reinforced steel cable 10 comprising at least one electric conductor wire (not shown). The pumping device comprises a cylindrical housing 10 having a passage (not shown) in fluid communication with an inlet 12a and outlet 12b of the housing 10. The pumping device is provided with a radially expandable packer 13 and an electrically operated pumping means 14, controlled from the surface. The inlet 12a and outlet 12b of the housing 10 are located above and below the packer 13 respectively.

The pumping device 9 is lowered from the surface into the wellbore, suspended on the cable 10, until the packer 13 on the pumping device is located immediately above the perforations 15 of the low permeability (high pressure) zone 3. The packer 13 is then expanded radially outwards until it engages with the casing 4 of the wellbore 1 thereby sealing the annular space between the housing 10 of the pumping device 9 and the casing 4. A treatment fluid is then pumped from the surface down the production conduit 6 and into the wellbore 1. The pumping means 14 is then operated to draw treatment fluid through the inlet 12a, and the passage in the housing 10. The treatment fluid exits the passage through the outlet 12b and passes into the isolated section 16 of the wellbore (between the packer and the plug). Perforations 15 in the isolated section 16 of the wellbore are in fluid communication with the high pressure zone 3. Once the pressure of the treatment fluid in the isolated section 16 of wellbore is greater than that of the high pressure zone 3, the treatment fluid will pass through the perforations 15 and into the high pressure zone 3. The rate at which the treatment fluid is pumped into the isolated section of wellbore must therefore be sufficient to maintain the pressure in the isolated section of wellbore above the pressure of the high pressure zone, preferably, substantially above this pressure. The pressure of the treatment fluid in the section of the wellbore 17 communicating with the low pressure zone 2 via perforations 18 must be at least equal to the pressure of the low pressure zone in order to prevent produced fluids from entering the wellbore 1. Preferably, the pressure of the treatment fluid in wellbore section 17 is greater than the pressure of the low pressure zone thereby allowing simultaneous treatment of the low pressure zone 2 and high pressure zone 3.

Figure 2 illustrates a modification of the device of Figure 1 in which the housing 20 of the pumping device 21 is provided with upper 22 and lower 23 radially expandable packers. The distance between the upper 22 and lower 23 packers corresponds to the length of the section 24 of the wellbore 25 which is in fluid communication with the high pressure zone 25 via perforations 26. The inlet 27 of the housing 20 is located above the upper packer 22 while outlet 28 of the housing is located below the upper expandable packer 22 and above the lower expandable packer 23. The pumping device 21 is lowered into the wellbore, suspended on a cable 29, until the lower packer 23 lies below the perforations 26 communicating with the high pressure zone 25 and the upper packer 22 is located above said perforations. Once the pressure in the isolated section of the wellbore is greater than the pressure in the high pressure zone 25 of the formation, the treatment fluid will pass through the perforations 26 into the high pressure zone. As discussed above, treatment fluid is pumped from the surface into the wellbore such that the pressure in the section of wellbore 30 which communicates with low pressure zone 31 is at least equal to the pressure of the low pressure zone 31. A pumping means 32 in the pumping device is then operated and treatment fluid is drawn from the wellbore 30 through the inlet 27 of the housing into a fluid passage (not shown). The treatment fluid then passes into the isolated section of wellbore 24 via the outlet 28 in the housing 20. Suitably, the housing 20 of the pumping device 21 is provided with a traction means (not shown), for example, traction wheels or tracks. Following radial confraction of the upper and lower packers 22, 23, the traction means can be operated to advance the pumping device 21 through the wellbore to treat further low permeability (high pressure) zones of the formation. Figure 3 illustrates a preferred embodiment of the pumping device of the present invention. In this embodiment, the pumping device 40 is provided with a length of steel tubing 41 ("extension" tubing), having an open end 42 which extends into the production conduit 43 located in the wellbore 44 with the cylindrical housing 45 of the pumping device 40 arranged at the lower end of the length of steel tubing 41. The housing 45 has a fluid passage (not shown) in fluid communication with the interior of the steel tubing 41 and with an outlet 46 of the housing 45. The housing 45 is also provided with a remotely controlled electrically operated pumping means 47 and with a first and second radially expandable packer 48 and 49 respectively. The outlet 46 of the housing is located below the first packer 48 and above the second packer 49. A radially expandable seal 50 is provided at or near the open end of the steel tubing 41.

In use, the pumping device 40 is lowered into the wellbore 44, suspended on a reinforced steel cable 51 comprising at least one electric conductor wire (not shown) until the first packer 48 and second packer 49 on the housing are located respectively immediately above and below the perforations 52 which communicate with the high pressure zone 53 of the formation. The first and second packers 48, 49 are then expanded radially outwards so as to engage with the walls of the casing 54 thereby sealing the annular space between the housing 45 and the casing 54. The expandable seal 50 on the length of steel tubing 41 is also expanded radially outwards to seal the annular space between the steel tubing 41 and the production conduit 43. Treatment fluid is then pumped from the surface down the production conduit 43 and into the open end 42 of the steel tubing 41. The freatment fluid is then drawn through the interior of the steel tubing 41, via the pumping means 47, and then passes through the passage in the housing 45 to the outlet 46. The fluid then enters the section 55 of the wellbore isolated by the first and second packers 48, 49. Once the pressure in the isolated section of the wellbore is greater than the pressure in the high pressure zone 53 of the formation, the treatment fluid will pass through the perforations 52 into the high pressure zone.

Figure 4 illustrates a modification of the pumping device of Figure 3 in which the lower end of the steel tubing 60 is connected to the inlet of a first housing 61 of the pumping device and the upper end of the steel tubing is connected to an outlet of a second housing 62. The first housing 61 has the same features as the housing of Figure 3. The second housing 62 has a passage (not shown) in fluid communication with an inlet 63 of the housing and with the interior of the steel tubing 60. The second housing 62 is also provided with a radially expandable seal 64 located below the inlet 63 to the housing and optionally with an electric pumping means (not shown), operated from the surface. Where the second housing 62 has a pumping means, the pumping means may be omitted from the first housing 61 of the pumping device.

In use, the pumping device is lowered into the wellbore through the production conduit 65 suspended on a reinforced steel cable 66 comprising at least one electric conductor wire (not shown). The first housing 61 is located in the wellbore in an identical manner to the housing of Figure 3. The length of the steel tubing 60 is selected such that the steel tubing extends into the production conduit 65. The second housing 62 is therefore located in the production conduit 65. The radially expandable seal 64 of the second housing 62 is then expanded thereby sealing the annular space between the second housing 62 and the production conduit 65. Treatment fluid is then pumped into the production conduit 65 and is drawn through the inlet 63 of the second housing 62, into the steel tubing. The treatment fluid flows to the outlet 67 of the housing 61 and into the isolated section 68 of the wellbore. As the pressure in the isolated section 68 of the wellbore increases to above the pressure of the high pressure zone 69, the treatment fluid passes through the perforations 70 into the high pressure zone 69.

Preferably, the inlet 63 of the second housing 62 and the outlet 67 of the first housing 61 are provided with valves, e.g. the inlet and outlet are slotted sleeve valves thereby allowing the inlet and outlet to be closed when the pumping device is being lowered into position in the wellbore. This is advantageous since produced fluids will be prevented from entering the length of steel tubing 60. The valves are opened once the device has been positioned in the wellbore and treatment fluid has been pumped from the surface into the wellbore.

The first and/or second housings of the pumping device may be provided with traction wheels or tracks (not shown). Following radial contraction of the seal 64 and packers 71, 72, the traction wheels or tracks may be used to advance the pumping device through the wellbore thereby allowing further high pressure zone(s) of the formation to be treated.

Figure 5 illustrates the use of a first and second pumping device to treat a first high pressure zone 80 and a second high pressure zone 81 respectively of a formation. In this embodiment of the present invention, the first pumping device comprises a first housing 82, a length of steel "extension" tubing 83 and a second housing 84. The second pumping device comprises a housing 85. A length of steel "connection" tubing 86 links the first and second pumping devices. Turning, to the first pumping device, the first housing 82 has a branch passage (not shown) leading to an outlet 87 of the housing and a main passage (not shown) which is in fluid communication with the interior of the length of steel "connection" tubing 86. The pumping means 88 in the first housing 82 is a two-way pump thereby allowing treatment fluid to pass through both the branch and main passages in the housing. The length of the steel "connection" tubing 86, linking the first and second pumping devices, is selected to correspond to the interval between the first and second high pressure zones 80, 81.

In use, the first and second pumping devices are lowered into the wellbore suspended on a reinforced steel cable 89 comprising at least one electric conductor wire (not shown) until the first housing 82 of the first pumping device and the housing 85 of the second pumping device are arranged in the sections of the wellbore communicating with the first and second high pressure zones 80, 81 respectively. Radially expandable packers 90 and 91 located on the first housing 82 of the first pumping device are then expanded radially outwards so as to isolate section 92 of the wellbore that is in fluid communication with the first high pressure zone 80 via perforations 93. Similarly, radially expandable packers 94 and 95 located on the housing 85 of the second pumping device are expanded radially outwards so as to isolate section 96 of the wellbore that is in fluid communication with the second high pressure zone 81 via perforations 97. A radially expandable seal 98 on the second housing 84 is also expanded radially outwards thereby sealing the annular space between the second housing 84 and the production conduit 99. Treatment fluid is then pumped from the surface into the production conduit 99. The treatment fluid passes through an inlet 100 of the second housing 84 of the first pumping device, through the length of steel "extension" tubing 83 and into a passage in the first housing 82 of the pumping device to the two-way pump 88. A first sfream of treatment fluid is then passed through the main passage (not shown) in the first housing 82 and through the outlet 87 into the first isolated section 92 of the wellbore and a second stream of treatment fluid passes through the branch passage (not shown) in the first housing 82 and into the interior of the length of steel "connection" tubing 86 linking the first and second pumping devices. This second stream of treatment fluid flows through a passage (not shown) in the housing 85 of the second pumping device and through an outlet 101 into the second isolated section 96 of the wellbore. A pump 102 is provided in the housing 85 of the second pumping device to assist in pumping the second stream of treatment fluid into the second isolated section 96 of the wellbore. As discussed above, once the pressure in the first isolated section 92 of the wellbore exceeds the pressure of the first high pressure zone 80, treatment fluid will pass through the perforations 93 into the first high pressure zone 80. Similar, once the pressure in the second isolated section 96 of wellbore exceeds the pressure of the second high pressure zone 81 , the treatment fluid will pass through perforations 97 into the second high pressure zone 81.

Claims

1. A remotely controlled pumping device for use in a wellbore comprising:

(a) an elongate housing having a passage in fluid communication with an inlet and outlet of the housing;

(b) an electrically powered pumping means located within the housing for pumping fluid through the passage; and

(c) a radially expandable packer for sealing the annular space formed between the housing and the walls of the wellbore, wherein the inlet and outlet are spaced apart along the longitudinal axis of the housing and the packer is arranged on the housing between the inlet and the outlet.

2. A device as claimed in claim 1 wherein the housing is provided with an electric motor for operating the pumping means.

3. A device as claimed in claims 1 or 2 wherein the device is suspended from a reinforced cable that encases one or more wires for transmitting electricity or electrical signals from the surface.

4. A device as claimed in any one of claims 1 to 3 wherein the device is provided with an electrically powered traction means.

5. A device as claimed in any one of claims 1 to 4 wherein a first and a second radially expandable packer are arranged on the housing with the first and second packers spaced apart by an elongate section of housing and the inlet to the housing lies above the first packer and the outlet of the housing lies between the first and second packers.

6. A first device as claimed in claim 5 connected in series with a second device as claimed in any one of claims 1 to 5 wherein:

(a) the housing of the first device is provided with a passage in fluid communication with an inlet, a first outlet and a second outlet of the housing and wherein the first outlet is located between the first and second packers; and (b) the second outlet of the housing of the first device and the inlet of the housing of the second device are in fluid communication with the interior of a length of tubing connecting the first and second devices (hereinafter "connection tubing") with the longitudinal axis of the connection tubing aligned with the longitudinal axes of the housings of the first and second devices.

7. A device as claimed in any one of claims 1 to 5 wherein the inlet of the housing is connected either directly or indirectly to the lower end of a length of tubing (hereinafter "extension tubing") and the longitudinal axis of the extension tubing is aligned with the longitudinal axis of the housing.

8. A device as claimed in claim 6 wherein the inlet of the housing of the first device is connected either directly or indirectly to the lower end of a length of tubing (hereinafter "extension tubing") and the longitudinal axis of the extension tubing is aligned with the longitudinal axes of the housings of the first and second devices.

9. A device as claimed in claims 7 or 8 wherein the extension tubing has a length of up to 500 feet.

10. A device as claimed in any one of claims 7 to 9 wherein an expandable seal or packer is provided at or near the upper end of the extension tubing.

11. A device as claimed in any one of claims 7 to 9 wherein a further housing is provided at the upper end of the extension tubing with the further housing having a passage in fluid communication with an inlet and an outlet and wherein the outlet of the further housing is connected either directly or indirectly to the upper end of the extension tubing.

12. A device as claimed in claim 11 wherein the further housing is provided with a radially expandable seal or packer.

13. A device as claimed in claims 11 or 12 wherein the further housing is provided with an electrically powered pumping means for pumping fluid through the passage therein and into the interior of the extension tubing.

14. A device as claimed in any one of claims 6 to 13 wherein the tubing is selected from steel tubing, plastic tubing, and an electric drill string.

15. A method of diverting treatment fluid into a low permeability zone of a hydrocarbon bearing formation wherein the formation is penetrated by a wellbore having a casing extending to below the low permeability zone and having at least one perforation in the casing in fluid communication with the low permeability zone, the method comprising: a) isolating a section of the wellbore having the perforation(s) in the casing in fluid communication with the low permeability zone of the formation; b) pumping treatment fluid from a selected location in the wellbore into the isolated section of the wellbore by means of a downhole pumping device at a rate sufficient to increase the pressure in the isolated section of wellbore to a value which is greater than the pressure at the selected location in the wellbore such that treatment fluid is diverted through the perforation(s) in the casing into the low permeability zone.

16. A method as claimed in claim 15 wherein the selected location in the wellbore has a pressure, Pi, less than the pressure, P₂, of the low permeability zone of the formation and the treatment fluid is pumped into the isolated section of the wellbore by means of the downhole pumping device to increase the pressure, P₃, in the isolated section of the wellbore to above the pressure, P₂, of the low permeability zone.

17. A method as claimed in Claim 15 wherein the selected location has a pressure, Pi, greater than the pressure of the low permeability zone, P₂, and the treatment fluid is pumped into the isolated section of the wellbore by means of the downhole pumping device to increase the pressure differential, P₃-P₂, between the pressure in the isolated section of wellbore, P₃, and the pressure of the low permeability zone, P₂.

18. A method as claimed in any one of claims 15 to 17 wherein the treatment fluid is infroduced from the surface into the wellbore through a production conduit that is arranged in the wellbore in sealing relationship with the walls of the casing.

19. A method as claimed in any one of claims 15 to 18 wherein the pumping device is introduced into the wellbore suspended on a cable encasing one or more wires for transmitting electricity or electrical signals to the pumping device.

20. A method as claimed in claim 19 wherein the pumping device is connected to an electric drill string and is introduced into the wellbore suspended from the electric drill string which in turn is suspended from the cable.

21. A method as claimed in any one of claims 15 to 20 wherein the section of the wellbore is isolated by means of at least one radially expandable packer located on the downhole pumping device.

22. A method as claimed in claim 21 wherein prior to introducing the downhole pumping device into the wellbore, a radially expandable plug is arranged in the wellbore in sealing relationship with the wellbore at a location immediately below the perforation(s) in the casing that are in fluid communication with the low permeability zone of the formation.

23. A method as claimed in any one of claims 15 to 22 wherein two or more sections of the wellbore are isolated and treatment fluid is simultaneously pumped into the isolated sections of the wellbore by means of two or more downhole pumping devices connected in series.

24. Use of a downhole pumping device as claimed in any one of claims 1 to 14 to divert a treatment fluid into a low permeability zone(s) of a hydrocarbon bearing formation.